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The Ordovician litho- and biostratigraphic framework of Alborz, Kopet-Dagh and the East-Central Iranian blocks is outlined and significantly updated, and a broad summary of the current state of knowledge of the Ordovician deposits and faunas across Iran is documented. Four tectono-stratigraphical units (including the Alestan, Damghan, Saluk and Talesh domains) are distinguished in northern Iran. They differ considerably from one another in their lithology, facies, fossil record and completeness of their sedimentary record. A comprehensive revision of the Ordovician stratigraphy in the eastern Alborz and the Kopet-Dagh regions leads to the definition of the (i) Simeh-Kuh Formation (new), (ii) the Qumes Formation (new) and its subdivision into the Gerd-Kuh (new) and Raziabad (new) members, (iii) the Lashkarak Formation and its subdivision into the Cheshmeh-Ali (new) and Hajiabad (new) members, (iv) the Abarsaj Formation (formalised) in the Alestan Domain, (v) the Qyzlar (new) and Pelmis formations in the Saluk Domain, and (vi) the Tatavrud Formation (new) in the Talesh Domain. The Ordovician strata of the eastern Alborz and Kopet-Dagh Mountains comprise a rifting volcanism emplaced within an active horst-and-graben palaeotopography. Despite the strong Ordovician biogeographical affinities with South China and, to a lesser extent, with Mediterranean peri- Gondwana, zircon populations analysed from Cambro-Ordovician sandstones in the area point to the Arabian-Nubian Shield of the western Arabian Peninsula and northeastern Africa as the principal continental sources. Consequently, an open oceanic communication between the Mediterranean and the northern (Alborz) margins of Gondwana and the southern margin of South China favoured the establishment of strong biogeographical affinities between these mid-latitude basins.

The Rinconada Formation is a mélange that crops out in the eastern margin of the Argentine Precordillera, an exotic terrane accreted to Gondwana in Ordovician times. Its gravity-driven deposits have been studied by means of conodont and graptolite biostratigraphy, and complemented with stratigraphic analyses. 46 rock samples (85 kg total weight) were obtained from blocks of limestones and of carbonate-cemented quartz-arenites, and from limestone clasts included in conglomerate blocks and debrites. 16 of these samples were productive after standard laboratory acid procedures, yielding 561 conodont elements. The specimens occur in variable number per sample and are frequently fragmented, but they reveal the occurrence of phantom stratigraphic units in the Darriwilian of the Precordillera. Lithological and fossil evidence from the Rinconada Formation provide new constraints on the biostratigraphy, palaebiogeography and tectonostratigraphic history of the southwestern margin of Gondwana during the Ordovician to Lower Devonian times. La Formación Rinconada es una mélange que aflora en el margen oriental de la precordillera Argentina, parte de un terreno exótico acrecionado a Gondwana durante el Ordovícico. Los depósitos gravitacionales de la mélange se han estudiado mediante bioestratigrafía de conodontes y graptolitos, complementados con análisis estratigráficos. Con este fin se obtuvieron 46 muestras de roca (85 kg peso total) de bloques de caliza, de bloques de cuarzoarenitas con cemento carbonático, y de clastos de calizas incorporados en bloques de conglomerados y debritas. Luego del tratamiento estándar de laboratorio, 16 muestras fueron productivas, brindando 561 elementos de conodontes. Los especímenes se encuentran en número variable por muestra y frecuentemente fragmentados; aun así, permiten revelar la existencia de unidades estratigráficas fantasma en el Darriwiliano de la precordillera. La evidencia paleontológica y litológica de la Formación Rinconada brinda nuevos ajustes para el Ordovícico a Devónico Temprano en relación con la bioestratigrafía, paleobiogeografía e historia tectonoestratigráfica del margen sudoccidental de Gondwana. Fil: Voldman, Gustavo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Alonso, Juan Luis. Universidad de Oviedo; España Fil: Fernández, Luis P.. Universidad de Oviedo; España Fil: Ortega, Gladys del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas, CIGEA and Museo de Paleontología, Universidad Nacional de Córdoba; Argentina Fil: Albanesi, Guillermo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Banchig, Aldo Lui. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentina Fil: Cardó, Raúl. Servicio Geológico y Minero Argentino, San Juan, Argentina; Argentina

The continental protomargin of Western Gondwana in South America records an important Early-Middle Ordovician magmatic activity associated with the development of the Famatinian orogen. Almost the entire margin has evidence of a magmatic arc preserved as orthogneisses in the high grade metamorphic domains up to volcanic rocks of the same age interfingered with sedimentary facies. These subduction related calcalkaline rocks have new UPb zircon dates that show striking similar ages bracketed between 490 and 460 Ma. The different domains along the continental margin are compared taking the western Sierras Pampeanas as the type locality, showing an alternation among high grade metamorphic – greenschist facies – sedimentary facies. There are three deeply-exhumed segments preserved as orthogneisses in high grade amphibolite facies, the Sierras Pampeanas, the Marañón and the Santander-Mérida domains. These domains are flanked by greenschist facies such as the Quetame in Colombia, the Vilcabamba in Perú, and the Puna Eruptive Belt in northern Argentina. Some segments are characterized by sedimentary facies as the Altiplano domain of Bolivia and the Olmos-Loja domain between Perú and Ecuador. The location and metamorphic grade are controlled by the amount of shortening and uplift, responsible for the different crustal levels exposed, as a consequence of the characteristics of the distinct terranes that collided against the continental margin. As a final remark, the time span of the Famatinian episode when globally compared has a widespread development in Laurentia, Baltica, and Australia, as a consequence of a period of high mobility of the plates during Early-Middle Ordovician times. Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

The Lower Ordovician Shirgesht Formation in central Iran is composed of siliciclastic and carbonate rocks deposited in diverse coastal and marine shelfal environments (tidal flat, lagoon, shoreface, offshore-shelf and carbonate ramp). Five facies associations contain diverse ichnofossil assemblages that show distinct proximal to distal trends formed in a wide range of physical-chemical conditions. The ethological groups of trace fossils in the Shirgesht Formation reflect a gradient of depositional stress conditions across a wave-influenced shoreline and shelf. Deposits of wave-influenced environments make up a significant component of the geological record of shallow marine settings, and the ability to determine paleoenvironments in detail in such successions is critical for reconstruction of depositional histories and sequence-stratigraphic interpretation. The Cruziana ichnofacies of the study shows highly diverse suites that record the establishment of a benthic community under stable conditions and a long-term colonization window. The Skolithos ichnofacies recognized is a low diversity opportunistic ichnocommunity suite that resulted from colonization after tempestite deposition in a stressed environment. The strata record an onshore to offshore replacement of the Cruziana ichnofacies (with abundant feeding traces of deposit-feeders) by the Skolithos ichnofacies (dominated by suspension-feeders and predators). A transitional zone between the two ichnofacies coincides with the offshore-transition/distal lower-surface deposits. The distribution of ichnofacies, the diversity and range of ethological characteristics reflected by the ichnogenera, and the wide range of wave-dominated coastal facies demonstrate the potential to use individual trace fossils and ichnofacies for significantly refined palaeoenvironmental analysis of wave-dominated coastal settings, particularly in Ordovician successions. Fil: Bayet Goll, Aram. Institute for Advanced Studies in Basic Sciences. Department of Earth Sciences; Irán. Ferdowsi University of Mashhad; Irán Fil: Myrow, Paul M.. Colorado College. Department of Geology; Estados Unidos Fil: Aceñolaza, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Moussavi, Harami, Rez. Ferdowsi University of Mashhad; Irán Fil: Mahboubi, Asadollah. Ferdowsi University of Mashhad; Irán

This study is focused on the analyses of a Chaschuil section (27° 49′ S–68° 04′ W), north of the Argentina Famatina Belt, where Ordovician explosive-effusive arc volcanism took place under subaerial to subaqueous marine conditions. In analyzing the profile, we have recognized an Arenigian succession composed by dominant volcaniclastic lithofacies represented by volcaniclastic debris flow, turbidity current and minor resedimented syn-eruptive pyroclastic depositsand lavas. The upper portions of succession are represented by volcanogenic sedimentary lithofacies with fossiliferous levels. Great volumes of the volcaniclastic deposits are strongly controlled in their transport by mass flow processes. These representative deposits provide significant data in relation to the coeval volcanic events for recognizing a continuous explosive volcanism together a minor effusive activity and the degradation of volcanic edifices. Likewise mass flow deposits give indications of the high rate of sedimentation, strong slope control and instability episodes in the basin, typical of those volcanic environments. That substantial information was the key to understand the features and evolution of the Arenigian basin in the north of the Famatina System. Fil: Cisterna, Clara Eugenia. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Coira, Beatriz Lidia Luisa. Universidad Nacional de Jujuy; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The Caucete Group and structurally overlying Pie de Palo Complex in western Argentina are characterised by two generations of west-verging folds and thrust-related shear zones, which formed under amphibolite facies conditions. The Caucete Group is separated from the Pie de Palo Complex by the Pirquitas thrust. These structures are interpreted to have formed as a result of a progressive deformation, generated during Middle Ordovician, underthrusting of the Laurentian-derived Cuyania microcontinent beneath the active Famatina margin. Geometrical relationships are most simply explained if the Pie de Palo Complex was basement to the Caucete Group prior to Ordovician orogenesis. We propose that this basement-cover relationship was established during Cambrian rifting of the Cuyania microcontinent from Laurentia. The Pirquitas fault may have been initiated during this extension prior to its long-lived remobilization as a thrust. We cannot rule out the possibility that the Pie de Palo Complex was exotic with respect to the Caucete Group, but for this to be possible we have to introduce an extra generation of structures, for which no evidence is preserved. The deformation was characterised by early strain localization followed by a more homogeneously distributed non-coaxial flow during F2. Thermal softening probably dominated over fabric softening during this stage. Fil: van Staal, C. R.. Canadian Geological Survey; Canadá Fil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Currie, K. L.. Canadian Geological Survey; Canadá Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

The Pavón Formation crops out in the central-east region of the San Rafael block; it is composed of massive green-reddish-grey sandstones, wackes, quartz sandstones, siltstones and shales. The sand-dominated facies show tabular bedding with sharp contacts and scarce syndepositional deformational structures, and were deposited in a turbidite sand-rich ramp. The graptolite fauna, in particular the presence of Climacograptus bicornis Biozone indicates a Sandbian age (Upper Ordovician ). Sandstone petrography records a stable craton or a faulted continental basement as probable source areas. Illite crystallinity index suggest anchimetamorphic conditions underwent by the sequence. Relatively high CIA values and K/Cs ratios indicate intermediate to advanced weathering. Geochemical provenance proxies display detrital compositions derived from an average upper continental crust, but relatively high abundances of compatible elements (Cr, Ni, V, Ti and Sc) along with low Th/Sc ratios suggest mixing with a less fractionated component. The Zr/Sc ratios indicate that recycling was not important. An ophiolitic source can be neglected based on Y/Ni and Cr/V ratios. Chemical analyses of detrital chromian spinels indicate that they were formed within mid-ocean ridge basalts and continental flood basalts. Nd model ages of Pavón sandstones scatter around 1.4 Ga, ε Nd(t) (t = 455 Ma) values range from −0.4 to −4.1 and ƒSm/Nd is of −0.40 ± 0.06 on average, indicating an affinity to Grenvillian-age crust. Detrital zircon grains dated confirmed a main Mesoproterozoic source (with peaks at 1.1 and 1.4 Ga), with subordinated inputs from Neoproterozoic and Paleoproterozoic crystalline rocks. The complete provenance dataset suggest the basement of the San Rafael block (Cerro La Ventana Formation) as the main source of detritus, but derivation from the Western Pampeanas Ranges was also probable. The siliciclastic sequence was deposited in a foreland basin at latitude of around 26°S, and linked to the accretion of the Cuyania terrane towards west of Gondwana; this accretion caused uplift by thrusting of the Mesoproterozoic crust to the east at ca. 460 Ma. Fil: Abre, Paulina. Universidad de la República; Uruguay Fil: Cingolani, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División geología; Argentina Fil: Manassero, Marcelo Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División geología; Argentina

We studied the petrogenesis of mafic igneous rocks in the Famatinian arc in the western Sierra Famatina (NW Argentina), an Early Ordovician middle-crustal section in the proto-Andean margin of Gondwana. Mafic rock types consist of amphibolite, metagabbro, and gabbro, as well as pod- and dike-like bodies of gabbro to diorite composition. Field relations together with geochemical and isotopic data for the mafic rocks of the western Sierra de Famatina (at 29°S) define two contrasting suites, which can be correlated with similar assemblages noted in other parts of the orogen. Amphibolite, metagabbro, and gabbro bodies are mostly the oldest intrusive rocks (older than 480 Ma), with the host tonalite and post-tonalite mafic dikes being slightly younger. The older mafic suite is tholeiitic to calc-alkaline and isotopically evolved, except for most of the amphibolite samples. The younger suite is calc-alkaline, typically displaying subduction-related geochemical signatures, and it is isotopically more juvenile. Whole-rock chemical composition and isotopic analyses are compatible with a progressive mixing of different isotopic reservoirs. Pyroxenite (±garnet) was likely the dominant source of the older gabbroic magmas, whereas peridotite dominated in the source of the younger suite, implying that the mafic magma experienced a progressive shift toward more juvenile compositions though time (over 20 m.y.). Pyroxenite-derived melts could have been generated by lithospheric foundering followed by upwelling of primitive melts by adiabatic decompression of mantle wedge peridotite., Funds were provided by an Argentinean grant PICT-2013 0472 and by Spanish grants CGL2009- 07984 and GR58/08 Universidad Complutense de Madrid–Santander.

The Macon granitoids are part of a tonalite/diorite granodiorite suit. Their trace elements place these rocks in the volcanic arc field. They have distribution patterns similar to those observed for rocks from Choschas, Taca Taca, Chuculaqui, and Quebrada de Batin. Macon rocks show strong enrichment of elements such as K, Rb, Th, and light REEs, which suggests crustal participation associated with the arc source. 87Sr/86Sri and (143Nd/144Nd)i isotopic ratios of two samples are compatible with arc-related rocks. Their calculated age of 482.7 Ma is consistent with other ages determined for the Ordovician western Puna eruptive belt (Faja Eruptiva de la Puna Occidental). This belt is made up of a set of granitoids, characteristic of the northern part of the Puna of Catamarca that, together with similar exposures of Salta and the Chilean region near the border with Argentina, suggests a meridian strike. The Ordovician ages and arc characteristics of the Sierra de Macon rocks, at the eastern extreme of the belt, incorporate them into this igneous province. This significantly increases the width of the Sierra de Macon igneous province to as much as 150 km at this latitude. Fil: Poma, Stella Maris. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Quenardelle, Sonia Monica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Litvak, Vanesa Dafne. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Maisonnave, Emma Beatriz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina Fil: Koukharsky, Magdalena Maria L.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

En la presente contribución se realiza la descripción e interpretación de las microfacies carbonáticas de laFormación San Juan (Ordovícico) en la sección de Niquivil, considerando el intervalo estratigráfico comprendidoentre las zonas de conodontos Oepikodus evae y Oepikodus intermedius. El análisis de las microfaciesy los conodontos asociados permiten el reconocimiento de diferentes subambientes carbonáticos dentrode la rampa carbonática desarrollada durante el Floiense tardío de la Precordillera Central. Se reconocieroncinco microfacies que, de base a techo, son: M1 Mudstone-Wackestone bioclástico; M2 Wackestone bioclástico-peloidal; M3 Wackestone intra-bioclástico; M4 Packstone intra-bioclástico; M5 Grainstone peloidal. Lainterpretación vertical de estas microfacies indica una tendencia hacia la somerización de la rampa carbonáticaen la sección de Niquivil para el lapso temporal estudiado. El que se correspondería con un ambientede rampa media de baja energía sin efecto de acción de olas que evoluciona hacia a un ambiente de rampamedia-interna, con mayor energía por acción de oleaje y desarrollo de tempestitas. This contribution presents the description and interpretation of carbonate microfacies of the San Juan Formation (Ordovician) at the Niquivil section, considering the stratigraphical interval between the Oepikodus evae and Oepikodus intermedius conodont zones. The distribution of the microfacies and the conodonts assemblages allow us to identify different sub-environments within the late Floian carbonate ramp of the Central Precordillera. Five microfacies were recognized from the base to the top: M1 Bioclastic mudstone-wackestone; M2 Bioclastic-peloidal wackestone; M3 Intra-bioclastic wackestone; M4 Intra-bioclastic packstone; M5 Peloidal grainstone. The vertical distribution of these microfacies indicates a shallowing trend of the carbonate ramp in the Niquivil section for this temporal interval, which suggests a middle ramp environment with low energy, without wave action, and that evolved towards the middle-inner ramp environment with more energy by wave action and development of tempestites. Fil: Soria Pures, Tatiana Belen. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Beresi, Matilde Sylvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Mestre García, Ana Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Investigaciones Mineras; Argentina Fil: Heredia, Susana Emma. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Investigaciones Mineras; Argentina Fil: Rodriguez, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

Ordovician deposits from the Central Andean Basin cover a vast region with thick exposed sequences in several areas, including the Sierras Subandinas, Cordillera Oriental and Puna geological provinces of northwestern Argentina. This basin was situated along the active margin of a Paleozoic foreland basin in western Gondwana. Continuous sedimentation occurred in different paleoenvironments from east to west: marginal marine settings with estuarine and deltaic deposits (Sierras Subandinas), shallow marine shelf environments with large clastic deposits in the central part (Cordillera Oriental–eastern Puna), and deep marine deposits with volcaniclastic supplies (western Puna). Limited biostratigraphic and chronostratigraphic data from these sequences are known from graptolites, conodonts and trilobites, and more recently also from palynomorphs. An analysis of Ordovician sections from the different sedimentological settings of northwestern Argentina produced 60 chitinozoan-bearing samples from which 19 genera and 45 species have been recorded. Four chitinozoan assemblages were observed in the Lower Ordovician from northwestern Argentina. Correlations with other fossil groups provide independent biostratigraphic control. A stratigraphic range chart of selected acritarch taxa throughout the Ordovician of the Central Andean Basin is developed and biostratigrapic or potential biostratigraphic markers for the basin are proposed. In northwestern Argentina, Late Ordovician chitinozoan assemblages display affinities with Polar to Subpolar faunas. Fil: de la Puente, Graciela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Rubinstein, Claudia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

The study of a magmatic series composed of Qtz-diorites to granites of the south part of the Sierra de Velasco batholith (Famatinian arc) in Argentina reveals that most rocks follow a coherent cotectic trend, which is comparable to a (CLL) traced from experimental liquid compositions of calc-alkaline (andesitic) systems. The identification of cotectic relationships is crucial to interpret the meaning of geochemical variation trends in terms of phase equilibria. We show the contrast between typical CLL trends defined by rocks of the Palanche pluton and rocks departing from CLL array, which are interpreted as resulting from local processes of bulk assimilation of a pelitic host. Zircon U-Pb age determinations with SHRIMP support a coeval zircon crystallization record from of about 480 to 450Ma of samples plotting on the CLL. The absence of intrusive contacts between these coeval cotectic granites implies that they were fractionated in situ at the level of emplacement. Other younger pulses (442 ±5 Ma), also fall on the CLL, denoting that uniform processes of melting and fractionation were operative for at least 40Ma at the same locus at the active continental margin of Gondwana. During this protracted magmatic activity, sporadic pulses of mafic magma were injected (e.g. at 456 ±7 Ma), revealing a complex process of pulse amalgamation in the building up of the batholith. These mafic magma pulses may have contributed to basification of the host granitoid by enclave dissolution at the low pressure of emplacement. The reported geochemical trends, as true CLL, together with observed textures and crystallization sequences, point to a parental intermediate system of andesite composition (SiO2>55 wt%) with a water content of about 2.5 wt% H2O, similar to those formed by sediment-basalt subducted mélanges. A sublithospheric origin for the mafic precursor is proposed in agreement with prediction by recently published thermo-mechanical modeling and experimental phase equilibria. Fil: Bellos, Laura Iudith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucuman. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucuman. Facultad de Cs.naturales E Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geologica; Argentina Fil: Castro, Antonio. Universidad de Huelva. Facultad de Ciencias Experimentales. Departamento de Geologia; España Fil: Díaz Alvarado, Juan. Universidad de Atacama. Departamento de Geología; Chile Fil: Toselli, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucuman. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucuman. Facultad de Cs.naturales E Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geologica; Argentina

Biostratigraphic data from the Precordillera Basin have traditionally been analyzed to contribute to the understanding of its biogeographic evolution as an allochthonous microcontinent accreted to the western Gondwanan margin in the Middle-Late Ordovician. The first palynological data from Late Ordovician units of the eastern Precordillera are incorporated in an attempt to better constrain the timing of the collision. The Las Vacas Formation has previously been assigned to the Sandbian (gracilis–bicornis zones). Chitinozoans from the Las Vacas Formation are poorly diversified. The basal part of this unit contains Lagenochitina sp. cf. baltica, previously recorded in the late Darriwilian of Precordillera and the late Darriwilian-early Sandbian of eastern Canada. The assemblages from its upper part contain primarily Spinachitina bulmani, Cyathochitina sp. cf. kuckersiana, Cyathochitina sp. aff. macastyensis, and Desmochitina minor form typica. The lower-upper part of this formation also yields Kalochitina multispinata. Acritarchs are poorly preserved and the few recognized genera are not biostratigraphically significant. Cryptospore findings contribute to the record of evidences for land plants in the Ordovician of Argentina and suggest that the upper part of the unit was deposited proximal to the shoreline. The lower part of the Trapiche Formation contains a few poorly preserved chitinozoans, acritarchs and algae (cf. Gloeocapsomorpha sp.), probably due to reworking of the material. The basal chitinozoan assemblage could indicate that the deposition of the Las Vacas Formation started during the Middle-Late Ordovician (late Darriwillian-basal Sandbian). Typical Katian chitinozoans from the uppermost part of the Las Vacas Formation indicate that these deposits would have reached the middle Late Ordovician. Palynological studies seem to be a useful tool to contribute to the biostratigraphic knowledge of controversial terrains, such as the Precordillera. Fil: de la Puente, Graciela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Rubinstein, Claudia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina

Along the proto-Pacific margin of Gondwana, from Venezuela to northeastern Patagonia, the Early–Middle Ordovician Famatinian orogeny was the first orogenic event following assembly of the supercontinent. Previous isotope studies of the igneous and (meta-)sedimentary rocks of southwestern Gondwana yield ambiguous implications for the role of juvenile mantle addition during the early crustal growth at the supercontinental margin. To interpret the geological and tectonic evolution of the orogen and the magma sources in different episodes we look at evidence from a large area of southern South America, including the 700 × 600 km type sector of the orogen in the Sierras Pampeanas (27°–33°S), the Precordillera, and northeastern Patagonia. Previous geological, geochemical and geochronological results are reviewed together with new U—Pb SHRIMP crystallization ages, 177Hf/176Hf and 18O/16O data for dated zircon, and whole-rock Sr and Nd isotope compositions., Four geological domains are recognized in the Sierras Pampeanas (Western, Central, Eastern and Foreland Famatinian domains). Magmatism is mostly restricted to the interval 463 ± 4 to 486 ± 7 Ma, with the most intense period of emplacement between 468 and 472 Ma constituting a magmatic flare-up. Granitoid emplacement in both northeastern Patagonia and the Cordon de Lila (Puna Altiplano, Chile) was effectively synchronous with that in the Sierras Pampeanas, defining a continuous belt. Combined geochemical and isotopic data (whole-rock Sr, Nd; Hf, O in zircon) indicate that the source of calcic metaluminous suites is the subcontinental lithosphere – both mantle and mafic lower crust – with variable contamination by the Early Paleozoic metasedimentary country rocks. The lithospheric mantle involved is assumed to underlie the outcropping 1330–1030 Ma age basement of the Western Domain, which exhibits tectonic characteristics of active continental margin in the north and oceanic arc-back arc in the south. The latter sector is the potential source of some minor Famatinian igneous rocks with less evolved isotopic compositions, although a restricted asthenospheric addition cannot be discarded in this case. Minor peraluminous granites are spatially associated with the metaluminous sequence, but major highly-peraluminous batholiths occur on the eastern flank of the Central Domain. Field relations and geochemical/isotopic evidence indicate that the most obvious source of these crustal melts was the very thick post-early Cambrian metasedimentary sequence comprising the host country rocks., Episodic tectono-magmatic evolution of the Famatinian magmatic belt in two overlapping stages is invoked to explain different characteristics in the four recognized domains in the type sector: • ca. 474–486? Ma, roll-back stage. This is a mainly extensional interval involving asthenospheric upwelling and thinning of the subcontinental mantle; full development of the marine ensialic basins and early emplacement of both metaluminous granites and highly-peraluminous batholiths in the Central and Eastern Famatinian domains. Trondhjemite plutons with an adakitic signature were emplaced in the Foreland Domain • ca. 468–472 Ma, slab break-off stage. Steepening of the oceanic slab and arc migration to the southwest ended with slab break-off due to subduction of continental crust during continental collision with the Precordillera terrane. This stage produced voluminous metaluminous magmatism at the western edge of the Central Domain (the flare-up episode), K-bentonites in the Precordillera, leucogranites in the Western Domain and scattered metaluminous and peraluminous plutons in all Famatinian domains. Both slab roll-back and break-off stages developed during a high-T regime typical of hot orogens. Although asthenospheric mantle was a necessary heat source for lithospheric melting, its material contribution to the growth of Early Paleozoic crust was apparently very minor. Recycling of Mesoproterozoic lithosphere, including the subcontinental mantle, coupled with crustal melting of Early Paleozoic metasedimentary sequences, accounts for most Famatinian magmatism. Comparable results from the Central Andes and East Antarctica confirm that the early stages of the Terra Australis orogen in SW Gondwana were dominated by lithospheric reworking processes., Financial support for this paper was provided by Argentine public grants CONICET PIP0229, FONCYT PICT 2013-0472 and Spanish grants CGL2009-07984, GR58/08 UCM-Santander and CGL2016-76439-P.

Conodonts recovered from the Devendeus Formation at the Angosto de La Quesera locality (Cordillera Oriental of Salta) in northwestern Argentina include Nogamiconus sp., Problematoconites perforatus, Drepanoistodus sp., Oneotodus sp., Scolopodus filosus, Teridontus nakamurai and Variabiloconus sp., as a part of an association that defines a pre-Paltodus deltifer Zone. The material most likely represents the Cordylodus angulatus and/or the lower part of the Rossodus manitouensis Zone. These microfossils support the dating of the Devendeus Formation as Tremadocian (Early Ordovician). Fil: Carlorosi, Josefina María Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Heredia, S.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina Fil: Aceñolaza, Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina

In the Tafí del Valle region, in northwestern Argentina, several intrusive bodies of lower Paleozoic age wereemplaced in the metasedimentary Puncoviscana Formation, belonging to the Sierras Pampeanas. Four intrusivebodies outcrop in the study area: La Ovejería, El Infiernillo, Loma Pelada and Los Cuartos. La Ovejería and ElInfiernillo intrusive bodies represent the I-type magmatism according to their major element contents and showcotectic evolutions similar to those described by Famatinian I-type batholiths. These moderately peraluminousadakitic trondhjemites have characteristic high Sr/Y ratios and low Fe2O3+MgO+MnO+TiO2 contents. They arerelated to high-pressure conditions at the source, where dehydration melting of basaltic rocks may be involvedand garnet is retained in the residue leading to generation of HREE depleted melts. The Loma Pelada granitesshow characteristics of S-type magmatism (low CaO and MgO, and high SiO2 and K2O contents) typical ofgranites segregated in the last stages of magmatic differentiation, or anatectic granites. They show an increasingperaluminosity due to garnet entrainment and they are related to the anatectic melts generated in the PuncoviscanaFm. Both the Loma Pelada and Los Cuartos granitoids include samples with intermediate geochemicalcharacteristics that range between those of the El Infiernillo and La Ovejería and the regional metasedimentaryrocks. These characteristics could be explained by assimilation processes involving the I-type intrusive magmasand the metasedimentary host rocks or by hybridization processes between trondhjemitic I-type magmas as LaOvejería and El Infiernillo and anatectic S-type melts. Fil: López, J.P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Bellos, Laura Iudith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Díaz Alvarado, J.. Universidad de Atacama; Chile Fil: Castro, A.. Universidad de Huelva. Facultad de Ciencias Experimentales. Departamento de Geología; España

The paper describes ubiquitous extensional structures developed in a passive margin of Ordovician age in the Argentine Precordillera. These extensional structures include normal faults and boudinaged sequences. In some places the boudinage reaches very high extension values, giving rise to block-in-matrix formations. Most of these extensional structures developed when sediments were not well lithified, as recorded by hydroplastic fractures, slump folds and pinch-and-swell structures. The presence of slump folds coeval with the extensional deformation, the variable extension directions obtained from the kinematic analysis and a weak cleavage recording layer-perpendicular shortening support the interpretation that gravitational collapse related to submarine sliding was the cause for extensional deformation. Well-consolidated rocks, located at the lower part of the stratigraphic sequence, also display scarce extensional faults. These extensional faults predate folding because they were breached by flexural-slip faults and, as a result of their passive rotation in fold limbs, these initial normal faults may now appear as reverse faults, particularly in steep and overturned limbs. The truncation of extensional faults by flexural-slip faults produces typical bed thickness changes across the extensional faults, giving rise to apparent synsedimentary faults. These normal faults can be attributed to the crustal extension that generated the passive continental margin or may represent deep parts of faults related to gravitational collapse. Fil: Alonso, J.L.. Universidad de Oviedo; España Fil: Gallastegui, J.. Universidad de Oviedo; España Fil: García-Sansegundo, J.. Universidad de Oviedo; España Fil: Farias, P.. Universidad de Oviedo; España Fil: Fernández, L.R. Rodríguez. Instituto Geológico y Minero de España; España Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

The taxonomy, biostratigraphical and palaeogeographical distribution of the Lower Ordovician graptolite genus Bryograptus is evaluated. Bryograptus is recognized as a distinct triradiate anisograptid with a multiramous, pendent rhabdosome. The species of the genus Bryograptus can be interpreted as shallow water faunal elements with a strongly limited biogeographical distribution to the Atlantic Faunal Realm. Bryograptus is restricted to a narrow interval in the Upper Tremadocian, the Bryograptus Biozone of Scandinavia and South America (Argentina), making it a taxon with a high potential for precise biostratigraphical correlations. The proximal end development can be used to differentiate the genus Bryograptus from other pendent multiramous graptoloid genera with a homoplastic rhabdosome development. Characteristics of the proximal end development and structure easily differentiate these genera in relief specimens, but not in flattened material. Fil: Maletz, Jörg. Saint Francis Xavier University; Canadá Fil: Egenhoff, Sven. State University Of Colorado - Fort Collins; Estados Unidos Fil: Alonso, Ricardo Narciso. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

In recent years, contradictory reports about whether or not an unconformity exists at the base of the Upper Ordovician succession of the Pyrenees have been made. In the Cerdanya area (Central Pyrenees), good outcrop evidence for this unconformity is displayed at the base of the Rabassa conglomerates. In this area, the Upper Ordovician rocks overlie a tilted Cambro-Ordovician sequence, displaying an angular unconformity and indicating a break in the stratigraphic series. Moreover, the existence of such an unconformity is supported by the distribution of Variscan minor structures, suggesting that the Cambro-Ordovician and the Upper Ordovician strata initially had different orientations before the main Variscan folding.

Field relationships and structural studies combined with in situ U-Th-Pb dating of monazite from Las Chacritas pluton (LCP), Sierra de Humaya, provide insight into the emplacement of peraluminous magmas triggered by lateral shortening of the host rock and magmatic stoping at a mid-crustal level of a retro-arc zone in a convergent orogen. Modal and chemical compositions indicate that the LCP is composed of two main igneous units of peraluminous granitoids. The predominant two-mica granitoids were generated by interaction of crustal rocks with mafic or mafic-derived magmas and/or crystal-rich magmas that entrained residual phases, whereas less abundant leucocratic granitoids may have been originated by partial melting of metasedimentary rocks. The calculated crystallization age of 474 ± 4 Ma is consistent with Ordovician ages (477-470 Ma) of the high grade metamorphic rocks, indicating concomitant magmatism and metamorphism during the Famatinian orogeny. The LCP was emplaced in the middle crust at a maximum depth of ~ 14.5 km, where attendant fracturing and ductile deformation were active. Field evidence shows strong temporal and spatial relationships between host rock ductile deformation and the emplacement of the pluton such as folding and strike deflection of the host rock layering and folded concordant leucocratic sheets with magmatic fabrics. This suggests that material transfer processes like lateral wall rock displacement (lateral shortening) was a viable mechanisms for the emplacement of the LCP. However, cross section restoration and field evidence such as wall-rock xenoliths and intrusive truncations of the host rock foliation and fold traces suggest that magmatic stoping was a complementary mechanism to create the necessary space for the emplacement of the LCP. This work supports previous studies showing that participation of multiple material transfer processes are the rule rather than the exception in the emplacement of plutons. Fil: Larrovere, Mariano Alexis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina. Universidad Nacional de la Rioja; Argentina Fil: Alasino, Pablo Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina. Universidad Nacional de la Rioja; Argentina Fil: de Los Hoyos, Camilo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Willner, Arne P.. Ruhr-universität Bochum; Alemania

The Lower Palaeozoic sedimentary cover of the Tandilia (Balcarce Formation) is made up of thick quartz arenite beds together with kaolinitic claystones and thin fine-grained conglomerates. The Balcarce Formation was formed in the nearshore and inner shelf environments of a tide-dominated and storm influenced open platform. It shows many features suggesting tidal sedimentation. Coarse-grained facies were formed by sand bar migration and accretion. Heterolithic packages are interpreted as interbar (swale) deposits. Subordinated HCS sandstones indicate storm events. The recognition of thick progradational clinoforms allows to confirm that the Balcarce sea was open to the south, as suggested years ago through palaeocurrent interpretation. The great abundance and variety of trace fossils is among the most outstanding characteristics of this unit. The ichnotaxa that have been recognised so far are: Ancorichnus ancorichnus, Arthrophycus alleghaniensis, Arthrophycus isp., Bergaueria isp., Cochlichnus isp., Conostichus isp., Cruziana furcifera, Cruziana isp., Daedalus labeckei, Didymaulichnus lyelli, Didymaulichnus isp., Diplichnites isp., Diplocraterion isp., Herradurichnus scagliai, ?Monocraterion isp., Monomorphichnus isp., Palaeophycus alternatus, Palaeophycus tubularis, Palaeophycus isp., Phycodes aff. pedum, Phycodes isp., Plagiogmus isp., Planolites isp., Rusophycus isp., Scolicia isp. and Teichichnus isp. Trace fossils have traditionally been used to assign the Balcarce Formation to the Lower Ordovician, due to the presence of Cruziana furcifera. However, Plagiogmus is typical of Cambrian successions world-wide., Facultad de Ciencias Naturales y Museo

Se discute el marco conceptual en el que fue definida la “Fase Oclóyica” en el norte argentino, marco que se modificó no sólo por la introducción de nuevos conceptos aportados por la tectónica de placas y la estratigrafía de secuencias, sino por la creciente información radiométrica y bioestratigráfica, que permitió ajustar la edad de los principales eventos geológicos ocurridos durante el Paleozoico inferior en esta región. La discusión se inicia con el análisis de la discordancia que marca el techo del Grupo Santa Victoria (Furongiano superior - Ordovícico Superior), cuya génesis fue atribuida al tectonismo de la “Fase Oclóyica”, evento tradicionalmente considerado como el responsable del plegamiento de los depósitos ordovícicos en el norte argentino. Se muestran evidencias que se contraponen con tal interpretación y se brindan hipótesis alternativas respecto de los tiempos de deformación de las secuencias ordovícicas de la región. The conceptual framework in which was defined the “Ocloyic Phase” in the Argentine Northwestern is discussed. This conceptual framework was modified not only by the introduction of new concepts contributed by plate tectonics and sequence stratigraphy, but by the increasing radiometric and biostratigraphic information, which allowed to adjust the age of the major geological events that occurred during the lower Paleozoic in this region. The discussion begins with an analysis of the unconformity that marks the top of the Santa Victoria Group (Upper Furongian - Upper Ordovician), whose genesis was attributed to the “Ocloyic Phase” tectonism, event that was traditionally considered responsible for the folding of the Ordovician deposits in northern Argentina. Evidences that contradict this interpretation are shown and alternative hypotheses are provided about the deformation times of the Ordovician sequences in the region. Fil: Moya, Maria Cristina. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

En este trabajo se estudia la sección ubicada en el tramo de Las Angosturas (27°42´10,2´´ - 27°42´10,4´´ S y 67°57´20,5´´- 67°56´54,8´´ O), sierra de Narváez, norte del Sistema de Famatina. En esta zona aflora una sucesión volcánica - sedimentaria asignable al Tremadociano temprano, la que reúne niveles de lavas ácidas y básicas, intercaladas con areniscas y pelitas macizas y laminadas, con graptolitos. En esta sucesión se han reconocido, además de un bandeado primario S0 y de un clivaje por soterramiento S1, dos episodios deformacionales que generan los plegamientos superpuestos P1 y P2. La estructura compleja, con indicadores de deformación polifásica de estos depósitos, contrasta con la estructura simple de la sucesión volcánica - sedimentaria arenigiana que aflora en la misma región. El análisis de estas estructuras permite sostener la existencia de más de un episodio tecto - magmático durante el Ordovícico inferior en el Sistema de Famatina. This study is focused on the analysis of the Las Angosturas section (27°42´10.2´´ - 27°42´10.4´´ S and 67°57´20.5´´ - 67°56´54.8´´ W), sierra de Narváez, northern Famatina System, where a volcanic - sedimentary sequence of early Tremadocian age crops out. Basic and felsic lavas, intercalated with massive and laminated sandstones and siltstones, locally hosting graptolitic levels. In the sedimentary rocks were recognized S0 primary layering and other S1 discontinuous cleavage, but the better developed structures are the superimposed folds P1 and P2. This complex structure, including polyphasic deformation of beds, contrasts with the simple structure of the Arenigian successions. The detailed study of these structures suggests the presence of more than one tecto - magmatic event during the Lower Ordovician in the Famatina System. Fil: Cisterna, Clara Eugenia. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentina Fil: Mon, Ricardo. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán; Argentina

The first late-Cambrian aged palynomorph assemblage of Bolivia is presented. The sampled material comes from the Cambro-Ordovician Iscayachi Formation cropping out in the Antenna of the Sierra de Sama, Tarija department, southern Bolivia. The palynomorph assemblage occurs in levels correlated to the Parabolina (Neoparabolina) frequens argentina trilobite biozone. It is comprised of Acanthodiacrodium spp., Cristallinium cambriense, Cy- matiogalea cf. C. aspergillum, C. velifera, C. virgulta, Dasydiacrodium spp., Eliasum llaniscum, Impluviculus multiangularis, Ladogella rommelaerei, Ladogella sp., Leiofusa sp., Leiosphaeridia sp., Lophosphaeridium sp., Lusatia? sp., Micrhystridium sp., Poikilofusa squama, Poikilofusa sp., Polygonium dentatum, Retisphaeridium brayense, Saharidia fragilis, Solisphaeridium akrochordum, S. lucidum, Timofeevia phosphoritica, Timofeevia microretis, Vulcanisphaera africana and V. turbata. The assemblage provides elements of comparison with pre- viously reported palynofloras in northern Argentina, eastern Newfoundland, southwestern Sardinia, Algeria, nor- thern Spain, Baltica and Avalonia (Arctic Russia, East-European Platform). All microphytoplancton are indicative of cold water affinities as expected from the western margin of Gondwana, showing some Baltic affinities as well. Fil: Vergel, Maria del Milagro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET- Tucumán. Instituto Superior de Correlación Geológica; Argentina; Fil: Aceñolaza, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET- Tucumán. Instituto Superior de Correlación Geológica; Argentina; Fil: Araoz, Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET- Tucumán. Instituto Superior de Correlación Geológica; Argentina

Phylogenetic relationships among species of the family Olenidae (Trilobita, Ptychopariida) were traditionally established by the direct comparison of morphological features and the evaluation of stratigraphic placement. In this study, a cladistic analysis of Parabolinella Brøgger is conducted in order to test the supposed monophyly of the genus and to determine the relationships of its species. Twenty-one taxa (sixteen of this genus) from the late Cambrian and Tremadocian of Baltica, Avalonia, Laurentia, South China and the western margin of Gondwana were revised. Forty non-ordered characters were considered in the analysis, 34 belonging to the cephalon, four to the pygidium, and two to the thorax. Some of these characters were specially defined for this study. The phylogenetic analysis was performed under unweighted parsimony. The obtained tree is partially consistent with the stratigraphic record of the studied species and shows correspondence with global late Cambrian and early Ordovician palaeogeography. Parabolinella may have originated in deep water sites of the Oaxaca region, Mexico and then migrated to other regions. The genus diversified in outer shelf facies of the Baltica Province during the late Cambrian and Tremadocian, whereas it would have dispersed to the South China Province in early Tremadocian times. Fil: Monti, Daniela Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Confalonieri, Viviana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

New SHRIMP U-Pb zircon ages are reported for igneous and sedimentary rocks of the Famatina Complex, constraining the age of the magmatism and the ensialic basins. Together with whole-rock and isotope geochemistry for the igneous rocks from the complex, these ages indicate that the voluminous parental magmas of metaluminous composition were derived by partial melting of an older lithosphere without significant asthenospheric contribution. This magmatism was initiated in the Early Ordovician (481 Ma). During the Mid-Late Ordovician, the magmatism ceased (463 Ma), resulting in a short-lived (no more than ~20 Ma) and relatively narrow (~100–150 km) magmatic belt, in contrast to the long-lived cordilleran magmatism of the Andes. The exhumation rate of the Famatina Complex was considerably high and the erosional stripping and deposition of Ordovician sediments occurred soon after of the emplacement of the igneous source rocks during the Early to mid-Ordovician. During the upper Mid Ordovician the clastic contribution was mainly derived from plutonic rocks. Magmatism was completely extinguished in the Mid Ordovician and the sedimentary basins closed in the early Late Ordovician., Centro de Investigaciones Geológicas

The Sistema de Famatina is located in the northwestern sector of Argentina, sharing territories with La Rioja and Catamarca provinces. The Sistema de Famatina display N-S orientation being represented by metamorphites (Negro Peinado/La Aguadita Formations) of the Pampean Cycle. The marine clastic and volcaniclastic sedimentary rocks, the volcanic-subvolcanic bodies of basic and acid composition and the widespread outcrops of granitoids belong to the posterior Famatinian Cycle. The Sierra de Velasco is located eastwards of the Sistema de Famatina in La Rioja province. This is the largest orographic unit of the Sierras Pampeanas, nearly totaly represented by Famatinian granitoids with porfiric and equigranular textures. Epigenic mineralizations (Cu, Mo, W, Be) are recorded in the region, related to the different magmatic units. These igneous manifestations are formed by a volcano-sedimentary secuences of El Chuschin Formation and the Ñuñorco and Paimán Granites in the Sistema de Famatina, and the Huaco Granite in the Sierra de Velasco. Fil: Sardi, Fernando Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Toselli, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina

The basement of the Central Andes located in central-western Argentina (31º20′S - 69º22′W) is composed by the Cuyania and Chilenia terranes which were amalgamated to Gondwana in the Early-Mid Paleozoic. Between the Precordillera (Cuyania) and Frontal Cordillera (Chilenia) there are exposures of marine metasedimentary rocks associated with mafic rocks with an E-MORB chemical signature that represent the remnants of an extensional basin developed between both terranes. The stratigraphic features and the distribution of the Early-Mid Paleozoic units along the Western Precordillera were constrained by remote sensing techniques. This allowed us to identify two stages in the evolution of the sedimentary in-fill of the marine basin: an initial stage (Mid-Late Ordovician) marked by widespread extensional tectonics and a finning-upwards sequence interbedded with volcanic-plutonic mafic rocks; and a Late Ordovician?-Devonian where the sedimentation was characterized by the development of coarsening-upwards sequences with low participation of mafic rocks. Flattened parallel folds associated with pre-Andean thrusts have locally a top-to-the SW vergence. These pre-Andean (Late Devonian) structures are the relics of the Chanic orogen whose double vergence is the result of the control exerted by previous structures related to the ordovician rifting. This is constrained by the residual and regional magnetic anomalies which reflect an important correlation between deep and surface structures. We propose the inception of a subduction zone with an eastward polarity on the proto-Pacific margin of Gondwana as the responsible for the compressive geotectonic framework that led to the closure of the Western Precordillera basin during the Late Devonian and the development of the Chanic thick-skinned-dominated orogen. Fil: Ariza, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina Fil: Boedo, Florencia Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Sanchez, Marcos Ariel. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina Fil: Christiansen, Rodolfo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina Fil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina Fil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Martínez, Myriam Patricia. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina

In the Famatina range, Sierras Pampeanas of Argentina (SW Gondwana), subvertical calc-alkaline lamprophyric dike swarms crop out through >300 km. The dikes cut Ordovician units with a prominent NW-SE trending and are covered by continental sedimentary successions of Pennsylvanian to Permian age. The dikes show a strong structural control associated with Riedel fault systems. Detailed field analysis suggested a ∼N-S opening direction oblique to the attitude of dike walls and a left-lateral transtensional tectonics during the emplacement. 40Ar/39Ar geochronology of a lamprophyric sample defined a crystallization age (plateau; whole rock) of 357.1 ± 7.1 Ma (MSWD = 2.3). Coetaneous ductile zones with dominant strike-slip motion, documented along western Argentina for >600 km, suggest a regional event in SW Gondwana during the Mississippian. We propose that this deformation was the result of the counterclockwise fast rotation of Gondwana between 365 and 345 Ma, when the Famatina range and western Argentina occupied a sub-polar position. A transform margin along SW Gondwana better explains our (and others) data rather than a subduction margin. This scenario is also consistent with the occurrence of A-type granites and normal-fault basins within the foreland as well as bimodal volcanics. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Canelo, Horacio Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Davila, Federico Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: de Hollanda, María Helena M.. Universidade de Sao Paulo; Brasil Fil: Teixeira, Wilson. Universidade de Sao Paulo; Brasil

The Paleozoic-Triassic Patagonian basins, at present comprising the Andean hinterland and structural basement of active basins, document a pre-Jurassic evolution associated with accretionary processes at the paleo-Pacific convergent margin. The Early Cambrian basins constitute the earliest record for the emplacement of the Terra Australis Orogen in northern Patagonia and preserve metavolcanic strata derived from an extensional magmatic arc. Together, pre-Jurassic basins document the Early Cambrian to Late Triassic oceanward migration of the trench-forearc system, evidencing that slab retreat was the common subduction setup. Tectonostratigraphy of these basins can be divided into three major sequences, from east to west: (i) early-middle Cambrian, (ii) Silurian-Carboniferous and (iii) Late Permian-late Triassic, which are separated by angular unconformities, evidencing large deformational pulses (advancing stages?) at Early Ordovician, early-middle Permian, and Late Triassic-Early Jurassic times. The Early Cambrian basins are mainly represented in the North Patagonian Massif by the Nahuel Niyeu forearc basin and the El Jagüelito backarc basin, which were closed and metamorphosed during the Early Ordovician. The Silurian-Devonian clastic sequences of the Atlantic region and Malvinas Islands evolved in an intracontinental rift setting and were deformed in the Permian when thrust tectonics took place at the continental scale, while the contemporaneous trench-forearc system represented in western Patagonia was governed by slab dynamics and accretion of oceanic material. During the final Pangea assembly (Permian-Triassic), the Antarctic Peninsula crustal block formed part of Patagonia as evidenced the detrital zircons record in the Permian-Triassic arc-flank basins. Deformation and metamorphism of these late Paleozoic-early Mesozoic basins could have occurred during the latest Triassic-Early Jurassic Chonide event. Fil: Suárez, Rodrigo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Gonzalez, Pablo Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Ghiglione, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

New structural data from a mid-crustal segment in the Eastern Sierras Pampeanas, coupled with geochronological methods and P–T estimates, reveal polyphase contractional deformation and metamorphism during the Famatinian Orogeny overalongperiodoftime.Peaksofmetamorphicmonaziteandzirconagesarerecordedatc.500 Ma,between484and465 Ma and at c. 440 Ma. Between 484 and 465 Ma the region attained high-temperature (HT) low-pressure (LP) conditions that resulted in widespread partial melting (peak at c. 470 Ma). A contractional phase occurred during this event, as suggested by syn-anatectic structures, as well as folding at subsolidus conditions. Renewed contraction under subsolidus conditions is evidencedbyreverseductileshearingandfoldingatc.440 Ma.ThrustingalongtheLaChilcaShearZonecausedmetamorphic inversion. The consistent orientation of folds in the Quebrada del Molle Metamorphic Complex, El Portezuelo Metamorphic– Igneous Complex and the La Chilca Shear Zone as well as WSW-directed thrusting at the later shear zone indicate uniform WSW–ENE-directedshortening.ThislatedeformationrecordstheOcloyictectonicphaseandbroughttheFamatinianOrogeny to an end in the Late Ordovician to Early Silurian. Fil: Larrovere, Mariano Alexis. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de la Rioja; Argentina. Universidad Nacional de La Rioja; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: de Los Hoyos, Camilo Raul. Srk Consulting; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Willner, Arne P.. Instituto de Geología, Mineralogía y Geofísica, Universidad del Ruhr; Alemania Fil: Verdecchia, Sebastián Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Baldo, Edgardo Gaspar Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Casquet, César. Universidad Complutense de Madrid; España Fil: Stipp Basei, Miguel Angelo. Universidade de Sao Paulo; Brasil Fil: Hollanda, Maria H.. Universidade de Sao Paulo; Brasil Fil: Rocher, Sebastián. Universidad Nacional de La Rioja; Argentina Fil: Alasino, Pablo Horacio. Universidad Nacional de La Rioja; Argentina. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de la Rioja; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Moreno, Gabriel Gastón. Geoconsult; Argentina

The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545–520 Ma) and Famatinian (490–440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate–siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U–Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Río de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Río de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought., Funding was through Argentine public Grants PUE 2016 CONICET-CICTERRA, CONICET PIP 2015–2018 11220150100901CO, FONCYT PICT 0472, SECyT 2016–2017 Tipo A No. 30720150100517CB, and Spanish grants (CGL2009-07984), GR58/08 UCM-Santander and CGL2016-76439-P of MINECO.

New U–Pb and Lu–Hf detrital zircon data together with whole-rock geochemical and Sm–Nd data were obtained for paragneisses of the Austroalpine basement south of the Tauern Window. Geochemically immature metasediments of the Northern–Defereggen–Petzeck (Ötztal–Bundschuh nappe system) and Defereggen (Drauzug–Gurktal nappe system) groups contain zircon age populations which indicate derivation mainly from Pan-African orogens. Younger, generally mature metasediments of the Gailtal Metamorphic Basement (Drauzug–Gurktal nappe system), Thurntaler Phyllite Group (Drauzug–Gurktal nappe system) and Val Visdende Formation (South Alpine Basement) were possibly derived from more distant sources. Their significantly larger abundances of pre-Pan-African zircons record a more advanced stage of downwearing of the Pan-African belts and erosion of older basement when the Austroalpine terrane was part of the Early Palaeozoic Northern Gondwana passive margin. Most zircon age spectra are dominated by Ediacaran sources, with lesser Cryogenian, Tonian and Stenian contributions and subordinate Paleoproterozoic and Neoarchean ages. These age patterns are similar to those recorded by Cambro–Ordovician sedimentary sequences in northeastern Africa between Libya and Jordan, and in some pre-Variscan basement inliers of Europe (e.g. Dinarides–Hellenides, Alboran microplate). Therefore, the most likely sources seem to be in the northeastern Saharan Metacraton and the Northern Arabian–Nubian Shield (Sinai), further supported by whole-rock Sm–Nd and zircon Lu–Hf data. Fil: Siegesmund, Siegfried. Universität Göttingen; Alemania Fil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Heinrichs, T.. Universität Göttingen; Alemania Fil: Stipp Basei, Miguel Angelo. Universidade de Sao Paulo; Brasil Fil: Nolte, N.. Universität Göttingen; Alemania Fil: Hüttenrauch, F.. Universität Göttingen; Alemania Fil: Schulz, B.. Technische Universitat Bergakademie Freiberg; Argentina

The Pampean orogeny of northern Argentina resulted from Early Cambrian oblique collision of the Paleoproterozoic-Mesoproterozoic MARA block, formerly attached to Laurentia, with the Gondwanan Kalahari and Rio de la Plata cratons. The orogen is partially preserved because it is bounded by the younger Córdoba Fault on the east and by the Los Túneles-Guacha Corral Ordovician shear zone on the west. In this review we correlate the Pampean Belt with the Saldania orogenic belt of South Africa and argue that both formed at an active continental margin fed with sediments coming mainly from the erosion of the Brasiliano–Pan-African and East African–Antarctica orogens between ca. 570 and 537 Ma (Puncoviscana Formation) and between 557 and 552 Ma (Malmesbury Group) respectively. Magmatic arcs (I-type and S-type granitoids) formed at the margin between ca. 552 and 530 Ma. Further right-lateral oblique collision of MARA between ca. 530 and 520 Ma produced a westward verging thickened belt. This involved an upper plate with high P/T metamorphism and a lower plate with high-grade intermediate to high P/T metamorphism probably resulting from crustal delamination or root foundering. The Neoproterozoic to Early Cambrian sedimentary cover of MARA that was part of the lower plate is only recognized in the high-grade domain along with a dismembered mafic–ultramafic ophiolite probably obducted in the early stages of collision. Uplift was fast in the upper plate and slower in the lower plate. Eventually the Saldania and Pampean belts detached from each other along the right-lateral Córdoba Fault, juxtaposing the Rio de la Plata craton against the internal high-grade zone of the Pampean belt., Financial support for this paper was provided by Argentine public grants CONICET PIP0229, FONCYT PICT 2013-0472 and Spanish grants CGL2016-76439-P and GR58/08 UCM-Santander.

The association of trace fossils from the Late Silurian Río Seco de los Castaños Formation in central-western Argentina (San Rafael Block) is mainly composed of Dictyodora, including Dictyodora scotica, Dictyodora tenuis and a new ichnospecies named Dictyodora atuelica. The latter shows a tendency to migrate to a deeper level - analogous to Dictyodora liebeana's - which reflects more sophisticated behavioural patterns. The Dictyodora ichnospecies (one of the most diverse assemblages in Gondwana) coexists with Nereites. SEM observations and EDS analyses suggest that the wall structure of Dictyodora could be the result of an activity other than the traditional suggestion of respiration, e.g., feeding. The succession, including some of the levels containing Dictyodora, presents microbially induced sedimentary structures (MISS) that would indicate a photic zone. This discovery favours previous deltaic interpretations instead of the deep-sea fan deposits traditionally suggested for the Siluro-Devonian greywackes of the Cuyania terrane, and particularly for this unit. The abundant Dictyodora, Nereites, Zoophycos and undermat miners ichnofossils, as well as the scarce arthropod trackways, resemble older records in Europe and North America. The studied section is very well age-constrained, and the autochthonous Gondwana ichnofauna permits to cast doubt on previous interpretations, suggesting that after the Ordovician, microbial mats retreated to marginal marine environments and then spread later in the Carboniferous. More importantly, the occurrence of Dictyodora and Nereites in beds that bear abundant wrinkle structures or records of biofilms in some places is challenging with regard to deep-sea interpretations. Dictyodora is probably not a good stratigraphic indicator, and the provincialism suggested for this ichnogenus may be an artefact of the lack of more complete records in Gondwana. Fil: Pazos, Pablo Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Heredia, Arturo Miguel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fernández, Diana Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Gutiérrez, Carolina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Comerio, Marcos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

The pre-Carboniferous evolution of the San Rafael Block is described in different stages. The first one is referred to the Mesoproterozoic basement derived from a complex plutonic and volcanic protolith of Cerro La Ventana Formation. The signature of this basement indicates a common origin with the present eastern part of Laurentia. The carbonate platform of Cuyania terrane has been drifted away during Early Cambrian to Early Ordovician times. The Ordovician silico-carbonate sequences of the San Rafael Block are unconformably deposited over the basement near the present eastern slope of the Cuyania terrane. Detrital zircon ages show a provenance derived from Mesoproterozoic source. The El Nihuil dolerites with a tholeiitic ocean floor signature considered the southern end of the Famatinian ophiolites were interpreted as a Late Ordovician–Early Silurian extensional event. The collision of Cuyania produced a new west polarity subduction and a magmatic arc, represented by the Devonian Rodeo de la Bordalesa tonalite and the granitoids of the “Agua Escondida Mining District”. The Late Silurian–Early Devonian sequences of La Horqueta and Río Seco de los Castaños formations were deformed during the collision and accretion of the Chilenia terrane against the proto-Andean margin, and recorded an east vergent cleavage developed on the previous deformed rocks. This collision produced the strong angular unconformity between the La Horqueta/Río Seco de los Castaños Formations and the El Imperial Formation (Upper Paleozoic). The new subduction with east polarity characterized the beginning of the Gondwanian cycle. The new magmatic arc was interrupted by the intense Lower Permian deformation of the San Rafael tectonic phase. Fil: Cingolani, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina

The largest igneous body in the Sierras Pampeanas (the Achala batholith) is composed by several magmatic intrusions. How many plutons form this batholith and its intrusive history remains unclear. The emplacement of the batholith began at ca. 380 Ma; the Characato suite, in the northern extreme of the body, represents a relatively young intrusive phase in its construction (ca. 360 Ma). This suite, composed mainly of two-mica monzogranites, correspons to a strongly peraluminous A-type magma (A/CNK > 1.1) with fractionated compositions (high Rb/Sr and Rb/Ba). The parental magma corresponds to a high temperature melt generated by biotite dehydration melting, which was then differentiated to form the Characato monzogranites. These monzogranites have crustal Nd and Srisotope signatures (εNdt −6.0 to −6.1 and 87Sr/86Srt 0.7074 to 0.7131) and abundant inherited zircons (ca. 90%). The inherited ages are mainly Early Cambrian, and to a lesser extent Mesoproterozoic, Neoproterozoic and Ordovician, all they recognized in the basement of the Sierras de Córdoba. The Nd-isotope composition, added to the inherited zircon ages of the Characato suite, indicate that these magmas derived from partial melting of a heterogeneous crust composed by the S-type Pampean granites and migmatites, Famatinian granitoids, and probably the low-to medium-grade metamorphic rocks of the Puncoviscan Series. The high variability and positive εHft values of the inherited Cambrian zircons found in the Characato suite could have been transferred from the Neoproterozoic grains of the Puncaviscana Series to the Early Cambrian S-type granites and migmatites during the Pampean, Financial support was provided by Grant CONICET-FAPESP 2013–2014, FonCyT PICT-2013 0226, PICT-2016 0843, PIP07178 CONICET, FAPESP 2018/06837-3 and CGL- 2016-76439-P (Spain).

The Eastern Sierras Pampeanas were structured by three main events: the Ediacaran to early Cambrian (580–510 Ma) Pampean, the late Cambrian–Ordovician (500–440 Ma) Famatinian and the Devonian-Carboniferous (400–350 Ma) Achalian orogenies. Geochronological and Sm–Nd isotopic evidence combined with petrological and structural features allow to speculate for a major rift event (Ediacaran) dividing into two Mesoproterozoic major crustal blocks (source of the Grenvillian age peaks in the metaclastic rocks).This event would be coeval with the development of arc magmatism along the eastern margin of the eastern block. Closure of this eastern margin led to a Cambrian active margin (Sierra Norte arc) along the western margin of the eastern block in which magmatism reworked the same crustal block. Consumption of a ridge segment (input of OIB signature mafic magmas) which controlled granulite-facies metamorphism led to a final collision (Pampean orogeny) with the western Mesoprotrozoic block. Sm–Nd results for the metamorphic basement suggest that the TDM age interval of 1.8–1.7 Ga, which is associated with the less radiogenic values of εNd(540) (−6 to −8), can be considered as the mean average crustal composition for the Eastern Sierras Pampeanas. Increasing metamorphic grade in rocks with similar detrital sources and metamorphic ages like in the Sierras de Córdoba is associated with a younger TDM age and a more positive εNd(540) value. Pampean pre-540 Ma granitoids form two clusters, one with TDM ages between 2.0 and 1.75 Ga and another between 1.6 and 1.5 Ga. Pampean post-540 Ma granitoids exhibit more homogenous TDM ages ranging from 2.0 to 1.75 Ga. Ordovician re-activation of active margin along the western part of the block that collided in the Cambrian led to arc magmatism (Famatinian orogeny) and related ensialic back-arc basin in which high-grade metamorphism is related to mid-crustal felsic plutonism and mafic magmatism with significant contamination of continental crust. TDM values for the Ordovician Famatinian granitoids define a main interval of 1.8–1.6, except for the Ordovician TTG suites of the Sierras de Córdoba, which show younger TDM ages ranging from 1.3 to 1.0 Ga. In Devonian times (Achalian orogeny), a new subduction regime installed west of the Eastern Sierras Pampeanas. Devonian magmatism in the Sierras exhibit process of mixing/assimilation of depleted mantle signature melts and continental crust. Achalian magmatism exhibits more radiogenic εNd(540) values that range between 0.5 and −4 and TDM ages younger than 1.3 Ga. In pre-Devonian times, crustal reworking is dominant, whereas processes during Devonian times involved different geochemical and isotopic signatures that reflect a major input of juvenile magmatism. Fil: Steenken, André. Universität Greifswald; Alemania Fil: Lopez, Monica Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Martínez Dopico, Carmen Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotopica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Drobe, Malte. Universität Göttingen; Alemania Fil: Wemmer, Klaus. Universität Göttingen; Alemania Fil: Siegesmund, Siegfried. Universität Göttingen; Alemania

The central-eastern part of the Sierra de Velasco (Sierras Pampeanas, NW Argentina) is formed by the large Huaco (40 x 30 km) and Sanagasta (25 x 15 km) granite massifs and the small La Chinchilla stock (2 x 2 km). The larger granites intrude into Ordovician metagranitoids and crosscut Devonian (?) mylonitic shear zones, whereas the small stock sharply intrudes into the Huaco granite. The two voluminous granites are biotitic-muscovitic and biotitic porphyritic syeno- to monzogranites. They contain small and rounded tonalitic and quartz-dioritic mafic microgranular enclaves. The small stock is an equigranular, zinnwaldite- and fluorite-bearing monzogranite. The studied granites are silica-rich (SiO2 > 70%), potassium-rich (K2O > 4%), ferroan, alkali-calcic to slightly calk-alkalic, and moderately to weakly peraluminous (A/CNK = 1.06-1.18 Huaco granite; 1.01-1.09 Sanagasta granite; 1.05-1.06 La Chinchilla stock). They have moderate to strong enrichments in several LIL (Li, Rb, Cs) and HFS (Nb, Ta, Y, Th, U) elements, and low Sr, Ba and Eu contents. U-Pb monazite age determinations indicate Lower Carboniferous crystallization ages: 350-358 Ma for the Huaco granite, 352.7 ± 1.4 Ma for the Sanagasta granite and 344.5 ± 1.4 Ma for the La Chinchilla stock. The larger granites have similar eNd values between ?2.1 and ?4.3, whereas the younger stock has higher eNd of ?0.6 to ?1.4, roughly comparable to the values obtained for the Carboniferous San Blas granite (?1.4 to ?1.7), located in the north of the sierra. The Huaco and Sanagasta granites have a mainly crustal source, but with some participation of a more primitive, possibly mantle-derived, component. The main crustal component can be attributed to Ordovician peraluminous metagranitoids. The La Chinchilla stock derives from a more primitive source, suggesting an increase with time in the participation of the primitive component during magma genesis. The studied granites were generated during a post-orogenic period in a within-plate setting, possibly as a response to the collapse of the previous Famatinian orogen, extension of the crust and mantle upwelling. They are part of the group of Middle Devonian-Lower Carboniferous granites of the Sierras Pampeanas. The distribution and U-Pb ages of these granites suggests a northward arc-parallel migration of this mainly post-orogenic magmatism with time. Fil: Grosse, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Söllner, Frank. Ludwig-Maximilians-Universität; Alemania Fil: Báez, Miguel Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Toselli, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Rossi, Juana Norma. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: de la Rosa, J. D.. Universidad de Huelva; España

En la Sierra de Cachi, situada en Salta (NO de Argentina), afloran rocas neoproterozoicas y paleozoicas de los Andes en un domo plutono-metamórfico flanqueado por rocas sedimentarias mesozoicas y cenozoicas. Estas rocas registran un metamorfismo de alta temperatura y baja presión, que alcanzó condiciones de fusión parcial y fue coetáneo del emplazamiento de plutones de granitos y trondhjemitas. El metamorfismo y el emplazamiento de los plutones se produjo en condiciones extensionales. Nuevos análisis de U-Pb en zircones, por los métodos TIMS y SHRIMP, proporcionan edades similares para la migmatización (479,7 ± 3,5 Ma) y el emplazamiento de los granitos (472,1 ± 11 Ma), acotando el evento extensional al Ordovícico Inferior. También describimos el hallazgo de bloques de gabros que dan una edad U-Pb SHRIMP en circones semejante, de 477,5 ± 3,9 Ma. Por lo tanto, se propone que el evento extensional descrito en la Sierra de Cachi tuvo lugar en una zona de retro-arco asociada a la subducción famatiniana del borde occidental de Gondwana. El acortamiento producido por los pliegues más jóvenes vergentes al E refleja la superposición de un campo de esfuerzos compresivos, probablemente relacionados con la orogenia Oclóyica (Ordovícico Medio/Superior-Devónico). The Cachi mountain ranges, located in Salta (NW Argentina), form an inlier where Neoproterozoic and Paleozoic materials of the Andes crop out in a plutono-metamorphic dome surrounded by Mesozoic and Cenozoic sedimentary rocks. The pre-Mesozoic rocks record a regional metamorphism of low pressure and high temperature conditions, which reached partial melting conditions and was coeval with the intrusion of sheeted granite and trondhjemite plutons. The metamorphic evolution and the emplacement of the plutons took place in an extensional tectonic setting. New U-Pb zircon dating by TIMS and SHRIMP methods yields similar ages for the migmatization (479.7 ± 3.5 Ma) and the emplacement of granites (472.1 ± 11 Ma), constraining the extensional event to Early Ordovician times. We also report the finding of gabbro boulders, which also yield a similar U-Pb SHRIMP zircon age of 477.5 ± 3.9 Ma. So, we propose that the extensional event recognized in Sierra de Cachi took place in a retro-arc setting linked to the Famatinian subduction along the western border of Gondwana. The shortening produced by younger east-verging folds evidences the superposition of a compressional stress field, probably related with the Ocloyic orogeny (Middle/Late Ordovician-Devonian) Fil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina Fil: Tubía, J. M.. Universidad del Pais Vasco; España Fil: Esteban, J. J.. Universidad del Pais Vasco; España Fil: Aranguren, A.. Universidad del Pais Vasco; España Fil: Vegas, N.. Universidad del Pais Vasco; España Fil: Sergeev, S.. Centre of Isotopic Research; Rusia Fil: Larionov, A.. Centre of Isotopic Research; Rusia Fil: Basei, M.. Universidade de São Paulo. Instituto de Geociências; Brasil

El Granito Los Cuartos aflora sobre la ladera occidental de Cumbres Calchaquíes, al E de la localidad de Tafí del Valle, provincia de Tucumán, Argentina. Es de composición granítica a granodiorítica, con desarrollo de dos micas, predominando la biotita. Es de grano medio e inequigranular, con megacristales de feldespato potásico raros o ausentes. Contiene xenolitos de la roca de caja con diferentes grados de digestión. Este cuerpo desarrolla fenómenos de metamorfismo de contacto en el basamento al que intruye, con desarrollo de porfiroblastos de andalucita y biotita poiquiloblástica. El granitoide presenta características calcoalcalina, peraluminosos, rico en K y P y con contenidos comparativamente más bajos en Ca y Na que los granitoides del área; poseen rasgos tardío-tectónicos con respecto a la deformación y su emplazamiento se habría producido durante el Ordovícico (Ciclo Famatiniano). Los Cuartos Granite crops out on the western flank of the Cumbres Calchaquíes, east of Tafí del Valle, Tucumán Province, Argentina. It has a granitic to granodioritic composition, of two micas, being biotite dominant. The granite is medium grained and inequigranular, with rare K-feldspar megacrysts. It contains host-rock xenoliths with different degrees of assimilation. The granite intrusion produced con- tact metamorphism in the surrounding basement, with development of andalucite porphyroblasts and poikiloblastic biotite. The granite is calk-alkaline and peraluminous, and is K- and P-rich and Ca- and Na- poor compared to other granitoids of the region. The pluton shows late-tectonic features with regard to the regional deformation. The granite possibly intruded during the Ordovician (Famatinian Cycle) and its emplacement was structurally controlled by the Tafí Megafracture. Los Cuartos Granite and other intrusi- ve bodies of the region share similar petrographical, geochemical, structural and geochronological cha- racteristics. Fil: Lopez, Jose Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Bellos, Laura Iudith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina

The evolution of the provenance areas for Late Neoproterozoic,Cambrian and Early Ordovician sedimentary and meta-sedimentaryrocks of north central and northwest Argentina is discussed using 123maximum ages of detrital zircons from 42 samples from this andpreviously published studies. Most detrital zircon ages fall into twogroups: 1,200–900 Ma and 670–545 Ma. These ages are essentiallyidentical for the non- to very low grade metamorphic lateNeoproterozoic to Early Cambrian Puncoviscana Formation and thelow to high grade metamorphic rocks of Eastern Sierras Pampeanas.Hence, both units are related to similar provenance areas at thesame time of sedimentation. The time span from zirconcrystallization in the Earth’s crust to exhumation and erosion may bevery long. This is important when determining maximum ages ofsedimentary rocks. Variation of zircon maxima may also beinfluenced by concurrent sedimentary cover of proposed provenanceareas. For the late Mesoproterozoic to early Neoproterozoic zirconage group, an active mountain range of the southwest BrazilianSunsás orogen is the most probable provenance area. The younger,late Neoproterozoic zircons are related to the continuouslydeveloping mountains of the Brasiliano orogen of southwest and southcentral Brazil. Young zircons, up to 514 Ma, from fossil-bearingPuncoviscana and Suncho Formation outcrops are related to late EarlyCambrian volcanism contemporaneous with sedimentation. Thissituation continues through the Late Cambrian to the EarlyOrdovician, but the Sunsás orogen provenance diminishes as possibleRío de la Plata craton origins become important.Keywords West Gondwanaland – Neoproterozoic – Cambrian – Detrital Fil: Miller, Hubert. Ludwig-Maximilians-Universität; Alemania Fil: Adams, Christopher. GNS Science; Nueva Zelanda Fil: Aceñolaza, Florencio Gilberto. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina Fil: Toselli, Alejandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina

Middle Tremadocian cephalopods from the Sierra de Mojotoro, Cordillera Oriental, NW Argentina, are assigned to Saloceras cf. sericeum (Salter) based on the siphuncle morphology and general shape of the conch. Saloceras sericeum (Salter) is known from the Upper Tremadocian and Floian of England and Wales, a region that formed part of eastern Avalonia during the Early Ordovician, located at a high southern latitude to the north of the Gondwanan margin. This is the oldest record of this genus and of the family Eothinoceratidae, and extends the geographical range of Saloceras, being the first positive record of its presence in Argentina and the Central Andean Basin. These remains are amongst the oldest cephalopods described from NW Argentina. They represent the third mid Tremadocian record of nautiloids at relatively high palaeolatitudes and away from the low latitude carbonate platform palaeoenvironments where the bulk of the earliest cephalopods resided. Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Vaccari, Norberto Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

We studied the P-T-t evolution of a mid-crustal igneous-metamorphic segment of the Famatinian Belt in the eastern sector of the Sierra de Velasco during its exhumation to the upper crust. Thermobarometrical and geochronological methods combined with field observations permit us to distinguish three tectonic levels. The deepest Level I is represented by metasedimentary xenoliths and characterized by prograde isobaric heating at 20-25 km depth. Early/Middle Ordovician granites that contain xenoliths of Level I intruded in the shallower Level II. The latter is characterized by migmatization coeval with granitic intrusions and a retrograde isobaric cooling P-T path at 14-18 km depth. Level II was exhumed to the shallowest supracrustal Level III, where it was intruded by cordierite-bearing granites during the Middle/Late Ordovician and its host-rock was locally affected by high temperature-low pressure HT/LP metamorphism at 8-10 km depth. Level III was eventually intruded by Early Carboniferous granites after long-term slow exhumation to 6-7 km depth. Early/Middle Ordovician exhumation of Level II to Level III (Exhumation Period I, 0.25-0.78 mm/yr) was faster than exhumation of Level III from the Middle/Late Ordovician to the Lower Carboniferous (Exhumation Period II, 0.01-0.09 mm/yr). Slow exhumation rates and the lack of regional evidence of tectonic exhumation suggest that erosion was the main exhumation mechanism of the Famatinian Belt. Widespread slow exhumation associated with crustal thickening under a HT regime suggests that the Famatinian Belt represents the middle crust of an ancient Altiplano- Puna-like orogen. This thermally-weakened over-thickened Famatinian crust was slowly exhumed mainly by erosion during ~180 Myr. Fil: de Los Hoyos, Camilo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Willner, Arne P.. Ruhr-universität; Alemania Fil: Larrovere, Mariano Alexis. Universidad Nacional de La Rioja; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Rossi, Juana Norma. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Toselli, Alejandro Jose. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Stipp Basei, Miguel Angelo. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina

The U–Pb and Lu–Hf isotopic analyses of the different sedimentary sequences of the Ventania System, an old Paleozoic orogenic belt exposed in the southern region of the Río de la Plata Craton in the province of Buenos Aires, Argentina, provide new evidence for the understanding of the tectonic evolution of the western sector of the Gondwanides mountain belt. These ranges formed as result of the late Paleozoic collision of the Patagonia terrane against the continental margin of Gondwana. The provenance analysis together with the sedimentary paleocurrents confirm a dominant source from the Tandilia System, a Paleoproterozoic mountain belt formed during the amalgamation of the Río de la Plata Craton at about 1800–2200 Ma, and incorporated to Western Gondwana during the Brasiliano Orogeny at 550–530 Ma. The local dominant source at the base of the early Paleozoic changed to more distant supplies toward the top of the sequences, when an increasing participation of detritus from first, Cambrian (560–520 Ma) zircons from the Pampean Orogen, and later on Ordovician (480–460 Ma) zircons from the Famatinian Orogen is recorded. The detrital zircon patterns and the maximum age of the units shed light on some previous discrepancies in the early Paleozoic stratigraphy. The Balcarce Formation, an early Paleozoic sedimentary cover of the Tandilia metamorphic and igneous basement, shows striking differences when compared with the new data from the Ventania System. The two data-sets reveal different sources for the two regions. The late Paleozoic foreland basin deposits mark an abrupt change of 180° in the paleocurrent directions, in the petrographic composition of the sediments, and in the provenance of detrital zircons. These data indicate a southern provenance with the first evidence of Carboniferous and Permian magmatic zircons. The oldest Archean zircons together with the finding of clasts with archeocyathids support the provenance from Patagonia, which was derived from Eastern Gondwana. The U–Pb ages of the ash-fall tuffs in the Tunas Formation confirm the Early Permian age of the Eurydesma Fauna in the Ventania System. The U–Pb data together with the Lu–Hf isotopic data enhance the comprehension of the tectonic evolution of the Ventania System as part of the larger Gondwanides Belt that amalgamated to Western Gondwana during Late Permian times with some independent pieces derived from Eastern Gondwana. Fil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos ; Argentina Fil: Chemale, Farid. Universidade Do Brasilia; Brasil Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos ; Argentina Fil: Pazos, Pablo Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos ; Argentina

U-Pb zircon data (secondary ion mass spectrometry [SIMS] and thermal ionization mass spectrometry [TIMS] analyses) from igneous rocks with differing structural fabrics in the Sierra Norte de Córdoba, western Argentina, suggest that the sedimentary, tectonic, and magmatic history in this part of the Eastern Sierras Pampeanas spans the late Neoproterozoic–Early Cambrian. A deformed metarhyolite layer in metaclastic sedimentary rocks gives a crystallization age of 535 ± 5 Ma, providing a limit on the timing of the onset of D1 deformation and metamorphism. The new data coupled with published Neoproterozoic zircon dates from a rhyolite beneath the metaclastic section and detrital zircon ages from the section indicate a late Neoproterozoic to Early Cambrian depositional age, making this section time equivalent with the Puncoviscana Formation (sensu lato) of northwest Argentina. A synkinematic granite porphyry gives a crystallization age of 534 ± 5 Ma, providing a limit on the age of dextral mylonitization in the Sierra Norte area (D2 event). The new age is consistent with ages of 533 ± 4 Ma from a mylonitic granite with dextral sense-of-shear fabrics and 531 ± 4 Ma from a late-synkinematic dacitic porphyry, which broadly indicates the final age of dextral deformation. A crystallization age of zircons from the postkinematic, high-level El Tío granite (530 ± 4 Ma) suggests that both stages of Pampean deformation and regional metamorphism, accompanied by synkinematic intrusions, were followed by uplift and took place during a very short time span in the Early Cambrian. This is supported by zircon dates of 523 ± 5 Ma from a rhyolite to dacite in the western part of the Rodeito area and dates from the undeformed El Escondido rhyolite and granite of 519 ± 4 Ma and 521 ± 4 Ma, respectively. These three crystallization ages also indicate that ductile dextral shearing and mylonitization associated with the Pampean D2 event terminated in the Early Cambrian. Both stages of Pampean deformation in this segment of the western pre-Andean Gondwana margin seem to represent a continuous event that can be related to oblique dextral convergence between the overriding plate in the east and the subducting and finally colliding plate in the west. The postkinematic intrusions and extrusions are related to the late stage of the Pampean magmatic history, which terminated before Early Ordovician (Famatinian) time. Fil: Von Gosen, W.. Friedrich-Alexander-Universität; Alemania Fil: McClelland, W. C.. University of Iowa; Estados Unidos Fil: Loske, W.. Ludwig-Maximilians-UNiversität München; Alemania Fil: Martinez, Juan Cruz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Prozzi, Carlos. Universidad Nacional del Sur. Departamento de Geologia. Catedra de Petrologia; Argentina

The Cerro Durazno, Brealito, and Cobres granitoid plutons belong to the eastern Ordovician magmatic belt of northwestArgentina and are associated with a network of NW- and N-striking ductile shear zones. A structural analysisof these plutons and their metamorphic host rocks was conducted to elucidate mid- to upper-crustal magmatism andtectonism at the western margin of Gondwana. Pluton emplacement took place at 480?455 Ma, toward the end ofa ca. 75-Ma-long episode of regional deformation and high-temperature metamorphism. The Cerro Durazno andBrealito plutons were probably emplaced as NE-SW-striking, vertical magma sheets that coalesced into large magmabodies under overall E-W shortening that generated SW-dipping metamorphic foliations at a later stage of plutonformation. These fabrics were superimposed to the magmatic structures in the granite plutons and to the high-grademetamorphic structures of the host rocks. At the northern pluton margins, ductile high-strain zones, notably theAgua Rosada Shear Zone north of the Cerro Durazno pluton, further localized ascent of granitoid magma. Similarly,emplacement of the Brealito and Cobres plutons is genetically related to prominent shear zones. Geometry andmetamorphic character of the shear zone network in the eastern Ordovician magmatic belt point to orogen-parallelextension and transverse shortening of the belt under variable metamorphic conditions. The width as well as protracteddeformation, high-temperature metamorphism, anatexis, and granitoid magmatism of the magmatic belt are keycharacteristics of a hot, wide orogen that evolved during the lower Paleozoic at the western margin of Gondwana.Remarkable geotectonic similarities with respect to the modern Andes point to comparable plate-tectonic conditionsat the lower Paleozoic and the Cenozoic convergent plate margins. Fil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Riller, Ulrich. Universität zu Berlin; Alemania

New U–Pb radiometric dates for K-bentonite horizons within the Lower Cambrian to Middle Ordovician platform carbonates from the Precordillera terrane of NW Argentina provide further constraints on models for the allochthonous or parautochthonous accretion of this terrane. Two K-bentonite layers from the Talacasto section yield indistinguishable sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon dates of 469.5 ± 3.2 Ma and 470.1 ± 3.3 Ma respectively. These are within uncertainty of the U–Pb SHRIMP zircon date of 468.3 ± 3.4 Ma for a porphyritic rhyolite from the Famatinian magmatic arc, Sierra de las Planchadas, near Rio Chaschuil. Geochemical and isotope data also demonstrate the similarity of the K-bentonite and Chaschuil rhyolite parent magmas. Thus, it is highly probable that the Famatinian arc volcanoes provided the ash for the K-bentonite horizons, suggesting proximity to the Precordillera terrane during the deposition of the Lower Cambrian to Middle Ordovician platform carbonates. This implication supports a mid-Ordovician collision model, but could also be compatible with a parautochthonous model for docking of the Precordillera terrane, by movement along the Pacific margin of Gondwana, rather than across the Iapetus Ocean., Facultad de Ciencias Naturales y Museo, Centro de Investigaciones Geológicas

The giant Almaden mercury deposit (Spain) is hosted by the Lower Silurian Criadero Quartzite; in turn this ore-bearing rock unit is cross-cut by the so-called Frailesca unit, a diatreme body of basaltic composition. The geochemical characteristics of the Silurian to Devonian Almaden District volcanic units indicate that these rocks originated from an enriched, evolving mantle source that ultimately yielded basanites–nephelinites to rhyolites, through olivine-basalts, pyroxene-basalts, trachybasalts, trachytes, very scarce rhyolites, and quartz-diabases. The Silurian intraplate alkaline volcanism developed in submarine conditions which triggered widespread hydrothermal activity resulting in Hg ore formation and pervasive alteration to carbonates. The δ 18 O, δ 13 C, and δ 34 S isotopic signatures for carbonates and pyrite suggest different sources for carbon and sulfur, including magmatic and organic for the former and magmatic and sea water for the latter. The most important and efficient natural source of mercury on Earth is by far the volcanic activity, which liberates mercury via quiescent degassing and catastrophic (Plinian) events when eruptions can overwhelm the atmospheric budget of Hg. Thus, we suggest that CO 2 degasification and coeval distillation of mercury from the volcanic rocks fed the huge hydrothermal system that led to massive deposition of mercury at Almaden. Build up of Hg 0 gas in magmatic chambers during waning rifting in the Late Ordovician, followed by renewed volcanism in the Early Silurian, would have resulted in massive degasification of the accumulated mercury. Part of this mercury went into the Criadero Quartzite leading to formation of the huge Almaden deposit and others (e.g., El Entredicho) along the same stratigraphic level. Progressive depletion of the deep seated magmatic Hg stock would have resulted in a drastic reduction in ore deposit size after the Lower Silurian when smaller deposits formed (e.g., Las Cuevas).