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Contact Ca-skarns are formed in the marbles of the Malyovitsa Lithotectonic Unit as a result of emplacement of crosscutting pegmatite injections in the area of the Dzhendemski Ezera, NW Rila Mt. Large (up to 4 cm), well-shaped garnet crystals dominate the mineral association with additional vesuvianite, diopside, scapolite and zoisite. Garnets were selected for mineralogical, geochemical and U-Pb geochronological study. Their crystals show clear zonal pattern due to variation in the octahedral position (Fe3+/Al3+), although the overall composition defines grossular predominance (72–95 mol.% grossular; 4–24% andradite). Trace-element signatures reveal constant isomorphic incorporation of P, V, Zn, Ga, Ge and Y, REE, HFSE, U. Results from the in-situ U-Pb dating of the studied skarn materials suggest the timing of pegmatite intrusion onto the metamorphic rocks and marble-hosted skarn formation at 58.37±0.70 Ma.

The Sierra Nevada de Santa Marta Massif (SNSM) in the Northern Andes affords an insight into lower crustal section structural relations. This polymetamorphic basement comprises high-grade gneisses,...

The Sava suture zone of the internal Dinarides contains Maastrichtian trench-fill sediments, termed “Sava flysch” that record the closure of the northern branch of the Neotethys. Subsequent collision between Adria-derived thrust sheets and blocks of European affinity in Latest Cretaceous to Paleogene times culminated in the formation of the Dinarides fold-and-thrust belt. The suture zone hosts numerous Oligocene plutons of I-type granitic composition. Many of these intrusions are located in the center of metamorphic core complexes (MCCs) that were exhumed in early Miocene times. This phase of post-collisional extension was concomitant with the opening of the northerly adjacent Pannonian Basin and associated with granitic S-type magmatism. Both the processes responsible for extensional deformation and magmatic activity in the internal Dinarides are still a matter of debate. Our Study contributes spatio-temporal constraints to better understand the tectono-magmatic processes of this area. We present field-kinematic, geochronological, and thermobarometric data from two MCCs at the transition between the internal Dinarides and the Pannonian Basin. Both MCCs are characterized by plutonic rocks in the center, surrounded by up to amphibolite-grade mylonites of exhuming shear zones. Heterogeneous extensional reactivation of formerly contractional structures that gave rise to these core complexes as low-angle detachments in the early Miocene is indicated by a variation in deformation ages of 3 Ma, obtained by Ar-Ar in-situ dating of white mica from deformed rocks of the respective shear zones. While Motajica MCC was exhumed from within the Sava zone during E-W extension at approximately 20 Ma, Cer MCC was exhumed as part of the underlying Adriatic basement during N-S extension between 17-16 Ma. For the Cer MCC, a concordia age of 17.6±0.1 Ma (2σ) obtained by U-Pb LA-ICP-MS on zircons from an S-type granite in combination with an Ar-Ar inverse isochron age of 16.6±0.2 Ma (2σ) obtained on white mica from the same sample, indicate a cooling rate of approximately 400°C/Ma. Our results contribute to the idea of rapid exhumation of mid-crustal material in the form of MCCs in response to the opening of the Pannonian Basin. This is further corroborated by results of Raman spectroscopy on carbonaceous material, as the temperature profile across the shear zone implies extremely condensed isotherms of 250°C/km. Additionally, U-Pb analyses show that zircons of the I-type intrusion contain inherited cores with age maxima at 270 Ma and 516 Ma and newly formed rims with an age maximum at 31.7 Ma, indicating the timing of intrusion. The S-type granite of Cer in parts reworks the I-type intrusion, as inherited cores include ages of 31-32 Ma, while the rims show an age of 17-18 Ma, suggesting a syn-extensional emplacement. Our data further shows that zircons of the I-type intrusion contain a significant amount of inherited cores with an age spectrum that resembles the detrital age spectrum from sediments of the Sava zone. This challenges the idea that these I-type melts were solely generated from igneous protoliths, and rather suggests a formation from melting of Paleozoic to Mesozoic successions constituting tectonically buried nappes of the internal Dinarides.

The north Andean block evidences by its shallow to intermediate seismicity a juxtaposition of a southern, relatively steeply dipping slab segment with a correlating volcanic arc and a northern flat slab domain, where a margin-parallel volcanic arc became extinct since the Late Miocene. The clear-cut offset of the seismic pattern suggests the presence of a slab tear, which has its correlative morphological expression by a distinct lineament in the Cauca Valley and separates, within the Eastern Cordillera of Colombia, a southern narrow antiformal cordilleran tract from a northern composite belt with an axial depression that constitutes the High Plain of Bogotá. Faults are consistently blind and associated with tight, basement-cored folds with inverted limbs at the mountain front and distinct domes separated by marginal synclines. These structures belong to a young deformation phase as they were superposed on older cylindrical fold trains. Their ductile deformation style may be associated with a thermal anomaly as evidenced by abnormally high Ro data. In order to assess the age of this folding we extracted zircons from a rhyolitic dike that straddles a marginal syncline of a major dome. U-Pb age data indicate a recycling of these crystals from a Neoproterozoic volcanoclastic sequence that composes the basement of this marginal part of the Cordillera. Euhedral overgrowths yield, however, Quaternary ages that we tentatively associate to the advance of the outer bend of the flat slab to its present position.

The late Eocene-to-early Oligocene Taveyannaz Formation is a turbidite series deposited in the Northern Alpine Foreland Basin (close to the Alpine orogenic front). Double dating of zircons with the fission-track and the U-Pb methods is applied on samples from the Taveyannaz Formation to reconstruct the exhumation history of the Central-Western Alps and to understand the syn-collisional magmatism along the Periadriatic lineament. Three samples from this unit show similar detrital zircon fission-track age populations that center at: 33-40 Ma (20%); 69-92 Ma (30-40%); and 138-239 Ma (40-50%). The youngest population contains both syn-volcanic and basement grains. Combined with zircon U-Pb data, it suggests that the basement rocks of Apulian-affinity nappes (Margna Sesia, Austroalpine) were the major sources of detritus, together with the Ivrea Zone and recycled Prealpine flysch, that contributed debris to the Northern Alpine Foreland Basin. Furthermore, the rocks of the Sesia-Lanzo Zone or of equivalent units exposed at that time presumably provided the youngest basement zircon fission-track ages to the basin. The Biella volcanic suite was the source of volcanogenic zircons. Oligocene sediment pathways from source to sink crossed further crystalline basement units and sedimentary covers before entering the basin from the southeast. The lag times of the youngest basement age populations (volcanic zircons excluded) are about 11 Myr. This constrains average moderate-to-high exhumation rate of 0.5-0.6 km/Myr in the pro-side of the orogenic wedge of the Central Alps during the late Eocene to early Oligocene., International Journal of Earth Sciences, 109 (7), ISSN:1437-3254, ISSN:1437-3262

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Sandstone petrography, detrital zircon geochronology, and sedimentology of Lower Cretaceous to Paleocene strata in the Cuicateco terrane of southern Mexico indicate an evolution from extensional basin formation to foreland basin development. The Early Cretaceous extensional basin is characterized by deposition of deep-marine fans and channels, which were mainly sourced from Mesoproterozoic and Permian crystalline rocks of the western shoulder of the rift basin. Some submarine fans, especially in the northern Cuicateco terrane, record an additional source in the Early Cretaceous (ca. 130 Ma) continental arc. The fans were fed by fluvial systems in updip parts of the extensional basin system. The transition from middle Cretaceous tectonic quiescence to Late Cretaceous shortening is recorded by the Turonian–Coniacian Tecamalucan Formation. The Tecamalucan Formation is interpreted as pre-orogenic deposits that represent submarine-fan deposits sourced from Aptian–Albian carbonate platform and pre-Mesozoic basement. The foreland basin in the Cuicateco terrane was established by the Maastrichtian, when foredeep strata of the Méndez Formation were deposited in the Cuicateco terrane, Veracruz basin, and across the western Gulf of Mexico, from Tampico to Tabasco. In the Zongolica region, these strata were derived from a contemporaneous volcanic arc (100–65 Ma) located to the west of the basin, the accreted Guerrero terrane (145–120 Ma), and the fold belt itself. By the Paleocene, sediments were transported to the foreland basin by drainages sourced in southwestern Mexico, such as the Late Cretaceous magmatic rocks of the Sierra Madre del Sur, and the Chortis block.

This work presents new geochronological and mineralogical data to investigate the provenance of sediments accumulated in deep-water environments in the southern and southwestern regions of the Gulf of Mexico during the Cenozoic. We integrated U-Pb geochronology with heavy and light minerals data to better understand the provenance of the Paleocene–Miocene strata and the evolution of the sediment source terranes. The analyzed samples came from drill cuttings of sandy levels in five exploration wells offshore in the Gulf of Mexico: Puskon-1, Aktum-1, Kunah-1, Kabilil-1, and Chuktah-201. The material contained abundant barite, a component of the drilling mud. Consequently, a semiquantitative approach to discriminate mineral phases and to quantify concentrations was used. Overall, we recognized 10 zircon populations that range from Proterozoic to Cenozoic ages. Proterozoic ages show a prominent peak at ca. 1.0 Ga and a minor peak at ca. 1.8 Ga. The Neoproterozoic to Cambrian population displays a broad distribution with a peak at ca. 600 Ma. Ordovician–Silurian zircons exhibit minor peaks at ca. 460 and 445 Ma. Devonian and Carboniferous zircons are very scarce in our data set. Permian–Triassic zircons are abundant, and they show a prominent peak at ca. 255 Ma and a minor one at ca. 228 Ma. Jurassic zircons are not common and display several minor peaks at ca. 185, 170, and 155 Ma. The Early Cretaceous population displays a noticeable peak at ca. 120 Ma. Late Cretaceous–Paleocene zircons exhibit several peaks at ca. 92, 82, 72, and 65 Ma. Cenozoic zircons also display several prominent peaks at ca. 40, 35, 25, and 18 Ma. Zircons of Proterozoic to Early Cretaceous ages are interpreted to be derived from the Mesozoic sedimentary cover of basement blocks in southern and eastern Mexico terranes due to their rounded to subrounded morphology. Late Cretaceous and Cenozoic zircons are the most abundant populations in the analyzed samples. These zircon populations exhibit euhedral and subhedral morphology indicating derivation from primary sources in the magmatic arcs. This has important implications in assessing the reservoir quality, since the sediments were directly delivered from the magmatic arc into the deep-water environments. Our results allow us to conclude that the sedimentary provenance of the southwestern and southern strata in the Gulf of Mexico was not associated with Laurentian terranes, as has been proposed for Late Cretaceous–Paleogene strata of northern Mexico and the northern Gulf of Mexico, such as the world-class Wilcox-type hydrocarbon reservoirs. We propose that the provenance of the analyzed strata was related to the tectono-magmatic evolution of the southern Mexico terranes during the Cenozoic; therefore, large NW-SE dispersal systems that eroded Laurentian terranes in the southern United States did not deliver sediments into the southern sectors of the Gulf of Mexico, probably constrained by the Tamaulipas Arch and the Gulf Stream.

The Cu-Au deposit of Bor (Serbia) represents a continuum of mineralization styles, from porphyry-style ore occurring in quartz-magnetite-chalcopyrite veins and chalcopyrite disseminations to high-sulfidation epithermal Cu-Au ores in pyrite-chalcopyrite and anhydrite-sulfide veins. Decisive for the great economic importance of Bor is the presence of exceptionally rich high-sulfidation massive sulfide orebodies, composed of pyrite + covellite + chalcocite/digenite and minor anhydrite and enargite. They form irregular bodies measuring 0.5-10 million tons of ore grading up to 7% Cu, hosted by andesites and surrounded by intense argillic alteration. This study focuses on a small but rich underground orebody mined out recently, where limited drillcore is preserved for quantitative geochemical study. This paper documents the vein relationships within the deep porphyry-style orebody of Borska Reka, the transitional porphyry-epithermal veins, and the overlying and laterally surrounding epithermal massive sulfides of the Bor deposit. Geological observations indicate that the formation of massive sulfide orebodies concludes the ore formation. Mass balance calculations, recast into geologically realistic bulk fluid-rock reactions, confirm textural evidence that near-isovolumetric replacement of andesite host rocks is the dominant formation mechanism of massive sulfide orebodies at Bor, whereby all lithophile elements including Si are dissolved and only Ti stays relatively immobile. While net volume changes for individual mineralization styles within the massive sulfide orebody vary from - 16% volume loss to + 127% volume gain, overall volume change for the whole massive sulfide orebody was probably slightly negative. Brecciation is important only as means of creating channelways for reactive fluid that turns the andesite protolith into massive sulfide, whereas net breccia infill occurred only locally., Mineralium Deposita, 56 (8), ISSN:0026-4598, ISSN:1432-1866

The Guajira Arch is located in the northernmost portion of South America and holds the record of several stages of magmatism and metamorphism. We performed LA-ICP-MS U–Pb zircon geochronology coupled with Lu–Hf isotope geochemistry on 11 samples from a high-grade gneissic basement hosting interleaved complexes of younger meta-granitoids and meta-sediments to unravel its tectono-metamorphic evolution. The oldest rocks correspond to a Rodinia-type basement at ca. 1100-880 Ma, affected by mafic magmatism during the Permian at ca. 272 Ma, anatexis during the Carnian at ca. 230 Ma, updoming and the formation of an extensional detachment fault during the Norian at ca. 224 Ma concluding with Jurassic magmatism since ca. 190 Ma. Trace element geochemistry shows that Triassic zircons are depleted in HREE and yield lower Th/U ratios than Jurassic zircons enriched both in HREE, Yb, and Y. Hf systematics indicates a Triassic to Jurassic evolution towards more radiogenic compositions. The lithological associations, structural setting, U–Pb ages, and Hf isotope geochemistry of the Triassic-Jurassic rocks at the Guajira Arch characterize an active margin setting of a hot orogenic belt in NW-Gondwana, comprising the Central Cordillera of Colombia, the Santa Marta Massif, the Merida Andes, the Perija Range, the Santander Massif and the para-autochthonous terranes south of the Ouachita-Marathon Suture (Oaxaquia, Acatlan, and Maya), and thus vindicate the existence of a conjugate margin with Laurentia until the Late Triassic, preceding the breakup of western Pangaea. The Triassic anatectites and Jurassic granitoids from the Guajira Arch yield Proterozoic Hf TDMi ages which are indistinguishable from the autochthonous Proterozoic basement and thus render an allochthonous origin by terrane accretion highly improbable. Instead, these data point to melting of the continental crust by the incorporation of primitive material reflecting a two-stage process at the boundary of a large underlying mantle convection cell (i) Triassic slab steepening, subduction arrest, updoming anatexis at ca. 230-223 Ma and (ii) Early Jurassic arc-magmatism at ca. 190-165 Ma due renewed convergence. Furthermore, we propose that the structural setting, lithology, and isotope geochemistry of the Guajira Arch units, fit into the style of a cordilleran core-complex emplaced in a roll-back extensional setting preceding Pangaea break-up.

The economic significance of pegmatites as a source of strategic rare metals for high-tech products and green energy motivated the present study on Ta–Nb oxides from Vishteritsa rare-element beryl–columbite LCT pegmatites of the Rila–West Rhodopes Batholith in the Western Rhodopes, Bulgaria. Here, we present the first U/Pb age data from columbite with application of the LA–ICP–MS U–Pb technique and a new X36 columbite standard reference material. The obtained Concordia age of 47.57 ± 0.32 Ma with a small spread of the individual 206Pb/238U ages between 45 and 51.3 Ma argues for Early Eocene magmatism and pegmatite formation. The host granite of the rare-element pegmatites is dated 51.94 ± 0.61 Ma with LA–ICP–MS U–Pb technique on zircon and suggests a fertile Early Eocene magmatic period in the Western Rhodopes. EPMA data for the composition of the columbite is used to refine the formula of the mineral (Mn0.554Fe0.427U0.006)0.987(Nb1.826Ta0.085Ti0.116)2.03O6 and define it as columbite-(Mn). Application of the in-situ LA–ICP–MS data technique establishes a series of typical trace elements (Ti, U, Zr, Hf, Y, W, and Zn) that are usually found in content above 500 ppm. The studied columbite is enriched in heavy rare earth elements (HREE sum: 306–697 ppm) and depleted in light REE and Eu. These geochemical characteristics are collectively interpreted as evidence for crystallization from highly fractionated fluid-rich magma. High UO2 content reaching 0.89 wt. % is characteristic for the Vishteritsa columbite. The decrease of U proximal to cracks and in outer crystal zones documents U-mobility during overprinting hydrothermal processes.

Fil: García Morabito, Ezequiel. Universidad Nacional de Río Negro, Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio (IIDyPCa), Río Negro, Argentina. Fil: Beltrán-Triviño, Alejandro. Swiss Federal Institute of Technology in Zurich (ETHZ), Zürich, Switzerland. Department of Geology, Universidad EAFIT, Medellin, Colombia Fil: Terrizzano, Carla Marina. Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland. Fil: Bechis, Florencia. Universidad Nacional de Río Negro, CONICET, Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio (IIDyPCa), Río Negro, Argentina. Fil: Likerman, Jeremías. Universidad de Buenos Aires, CONICET, Instituto de Estudios Andinos "Don Pablo Groeber" (IDEAN), Ciudad de Buenos Aires, Argentina. . Fil: Von Quadt, Albrecht. Swiss Federal Institute of Technology in Zurich (ETHZ), Zürich, Switzerland. Fil: Ramos, Victor Alberto. Universidad de Buenos Aires, CONICET, Instituto de Estudios Andinos "Don Pablo Groeber" (IDEAN), Ciudad de Buenos Aires, Argentina. . Theoretical studies support the idea that the internal dynamics of actively deforming mountain ranges are influenced by spatial and temporal variations in climate. The identification of plausible correlations between orogen behavior and external climatic processes requires, among other factors, that the initiation and duration of any deformation event be precisely constrained. Here, we add new detrital zircon U-Pb ages and 10Be surface exposure dating to the already extensive data set for the low-temperature cooling history, to analyze the spatial patterns of deformation, and their temporal variations across the foreland of North Patagonia, with the aim of evaluating potential feedbacks between climate and deformation. Stratal relationships, together with geomorphic evidences of deformation document the precise timing of individual structures within the fold-thrust belt and the broken foreland. Our data record a progressive decrease of upper-plate shortening rates and subsidence after a first period of widespread deformation and uplift (ca. 13–7 Ma). This “transitional” foreland phase coeval to the onset of glacial conditions at 7.4–5 Ma is followed by a structural reorganization after ca. 3 Ma, marked by the abandonment of the foreland and enhanced slip on interior faults, with the intensification of glacial erosion at this time. We propose that acceleration in erosion rates during the past 7 Ma may have influenced the regional geometry and kinematic history of the orogenic belt. Our empirical results match theoretical predictions and provide compelling evidence at the scale of individual thrust faults for the significant impact of climate change on orogenic behavior. Los estudios teóricos apoyan la idea de que la dinámica interna de las cadenas montañosas que se deforman activamente está influenciada por las variaciones espaciales y temporales del clima. La identificación de correlaciones plausibles entre el comportamiento del orógeno y los procesos climáticos externos requiere, entre otros factores, que el inicio y la duración de cualquier evento de deformación estén limitados con precisión. Aquí, integramos nuevas edades U-Pb de circones detríticos y edades 10Be de exposición de superficies al ya extenso conjunto de datos previos sobre la historia de enfriamiento de baja temperatura, para analizar los patrones espaciales de deformación y sus variaciones temporales en el antepaís de la Patagonia Norte, con el objetivo de evaluar las posibles reacciones entre el clima y la deformación. Las relaciones de estratos, junto con las evidencias geomorfológicas de deformación, documentan la edad precisa de actividad de las estructuras individuales dentro de la faja plegada y corrida y el antepaís roto. Nuestros datos registran una disminución progresiva de las tasas de acortamiento y subsidencia después de un primer período de deformación y levantamiento generalizados (ca. 13–7 Ma). Esta fase de antepaís "de transición", coetánea al inicio de las condiciones glaciales en 7,4–5 Ma, es seguida por una reorganización estructural después de ca. 3 Ma, marcada por la fosilización del antepaís y una mayor actividad registrada en fallas ubicadas en posiciones más internas, con la intensificación de la erosión glaciar en este momento. Proponemos que la aceleración en las tasas de erosión durante los últimos 7 Ma puede haber influido en la geometría regional y la historia cinemática del cinturón orogénico. Nuestros resultados empíricos coinciden con las predicciones teóricas y proporcionan una evidencia convincente a escala de fallas inversas individuales del impacto significativo del cambio climático en el comportamiento orogénico.

Calcic garnets from grossular-andradite (grandite) series have proven their ability to record the conditions and timing of their formation processes. Typically these minerals occur in skarn systems, together with other calc-silicates (diopside, epidote) and commonly host economic Cu, Zn-Pb-Ag, Au, Sn, W or Mo mineralization. Based on the U-content in the garnet structure, we used in-situ LA-ICP-MS U-Pb geochronology to determine the age record in more than 15 skarn deposits from different tectonic zones in Bulgaria. The data is partly complemented with ID-TIMS dating. The mineralogical, geochemical and petrological characteristics of the materials were described additionally. Both contact and infiltration skarns were studied.The obtained data revealed that the garnet composition in terms of major elements does not affect the precision of age determination. Both andradite and grossular members yield age data with very high accuracy. The dating results, however, depend on the geochemical signature of the garnets and especially on the U-content and U/Pb ratio. Our data shows that skarn samples from the vicinities of magmatic bodies or along contacts of causative pegmatite veins usually have increased U-incorporation from several to more than 70 ppm, as suggested by their proximal position to the source. The contact skarn garnets formed by intrusion of silicate melts (or pegmatites) onto carbonate-rich hosts mostly produce precise ages, which are in good agreement with the geochronological zircon data about the magmatism in the studied regions (e.g. Central Pirin, Teshevo, Plana, Gutsal, Rila-West Rhodope, Sv. Nikola etc. plutons). The infiltration skarns, though, generally reveal ages with low accuracy and significant errors, mainly due to U-content below 1 ppm. The reason for the low U-concentration and U/Pb ratio is either connected with a primary U-deficit and its depletion in the garnet-precipitating fluids with time and space but might be also related to garnet retrograde hydrothermal alteration.The time span of the Bulgarian skarn garnets is closely connected with the causative magmatic bodies. The studied skarns reveal Paleogene (~30-42 Ma - Central Pirin and Teshevo plutons and pegmatites from Rila-West Rhodope batholith; Djurkovo, Murzian and Zvezdel Pb-Zn deposits; ~ 58 Ma - skarns from Western Rila Mts., ~ 68 Ma – Babyak Mo-Ag-Au-W-Bi-Cu-Pb-Zn deposit), Cretaceous (~ 76 Ma- Gutsal pluton, 81 Ma - scheelite bearing skarns from the Plana pluton, 86 Ma – Iglika skarn deposit) and Paleozoic (~ 303 Ma – Martinovo Fe-skarn deposit) ages. Given the occurrence of Ca-garnet in contact rocks and hydrothermal ore deposits, our results highlight the potential of grandite as a powerful U-Pb geochronometer for dating magmatism and skarn-related mineralizations.Acknowledgements. The study is partly supported by the DNTS 02/15 bilateral project between Bulgaria and the Russian Federation, financed by the Bulgarian National Science Fund.

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sancakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sancakaya Massif over an area of ca. 12 km by 15 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 +/- 6 to 434 +/- 7 Ma (2 sigma), and on those from a felsic vein an age of 319 +/- 5 Ma (2 sigma) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial cHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of -16 to -9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the PaleoTethyan accretionary complexes, and (ii) the resemblance of the U-Pb age spectra of detrital zircons in the metadastic sequence of the Sancakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the AnatolideTauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sancakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions. (C) 2019 Elsevier B.V. All rights reserved.

Understanding the formation of economically important porphyry Cu–Au deposits requires knowledge of the magmatic-to-hydrothermal processes that act within the much larger magmatic system and the timescales on which they occur. We apply high-precision zircon geochronology (chemical abrasion–isotope dilution–thermal ionisation mass spectrometry; CA–ID–TIMS) and spatially resolved zircon geochemistry (laser ablation inductively coupled plasma mass spectrometry; LA-ICP-MS) to constrain the magmatic evolution of the underlying magma reservoir at the Pliocene Batu Hijau porphyry Cu–Au deposit. We then use this extensive dataset to assess the accuracy and precision of different U–Pb dating methods of the same zircon crystals. Emplacement of the oldest pre- to syn-ore tonalite (3.736±0.023 Ma) and the youngest tonalite porphyry to cross-cut economic Cu–Au mineralisation (3.646±0.022 Ma) is determined by the youngest zircon grain from each sample, which constrains the duration of metal precipitation to fewer than 90±32 kyr. Overlapping spectra of single zircon crystallisation ages and their trace element distributions from the pre-, syn and post-ore tonalite porphyries reveal protracted zircon crystallisation together with apatite and plagioclase within the same magma reservoir over >300 kyr. The presented petrochronological data constrain a protracted early >200 kyr interval of melt differentiation and cooling within a large heterogeneous magma reservoir, followed by magma storage in a highly crystalline state and chemical and thermal stability over several tens of thousands of years during which fluid expulsion formed the ore deposit. Irregular trace element systematics suggest magma recharge or underplating during this final short time interval. The comparison of high-precision CA–ID–TIMS results with in situ LA-ICP-MS and a sensitive high-resolution ion microprobe (SHRIMP) U–Pb geochronology data from the same zircon grains allows a comparison of the applicability of each technique as a tool to constrain dates and rates on different geological timescales. All techniques provide accurate dates but with different precision. Highly precise dates derived by the calculation of the weighted mean and standard error of the mean of the zircon dates obtained by in situ techniques can lead to ages of unclear geological significance that are older than the maximum ages of emplacement given by the CA–ID–TIMS ages of the youngest zircons in each sample. This lack of accuracy of the weighted means is due to the protracted nature of zircon crystallisation in upper crustal magma reservoirs, suggesting that standard errors should not be used as a means to describe the uncertainty in those circumstances. We conclude from this and similar published studies that the succession of magma and fluid pulses forming a single porphyry deposit and similarly rapid geological events are too fast to be reliably resolved by in situ U–Pb geochronology and that assessing the tempo of ore formation requires CA–ID–TIMS geochronology., Geochronology, 2 (2)

Our study is aimed at reconstructing the Palaeozoic&ndash, early Mesozoic plate tectonic development of the Central Asian Orogenic Belt in central and southeast Mongolia (Gobi). We use sandstone provenance signatures including laser ablation U-Pb ages of detrital zircons, their epsilon hafnium isotope signatures, and detrital framework grain analyses. We adopt a well-established terran subdivision of central and southeastern Mongolia. However, according to their affinity and tectonic assemblage we group them into three larger units consisting of continental basement, rift-passive continental margin and arc elements, respectively. These are in today&rsquo, s coordinates: (i) in the north the late Cambrian collage from which the later Mongol-Okhotsk and the Central Mongolia-Erguna mountain ranges resulted, (ii) in the south a heterogeneous block from which the South Mongolia-Xin&rsquo, gan and Inner Mongolia-Xilin belts developed, and (iii) in between we still distinguish the intra-oceanic volcanic arc of the Gurvansayhan terrane. We present a model for paleotectonic development for the period from Cambrian to Jurassic, which also integrates findings from the Central Asian Orogenic Belt in China and Russia. This mobilistic model implies an interplay of rift and drift processes, ocean formation, oceanic subduction, basin inversion, collision and suture formation in space and time. The final assemblage of the Central Asian Orogenic Belt occurred in Early Jurassic.

NMR‐based determination of the configuration of complex molecules containing many stereocenters is often not possible using traditional NOE data and coupling patterns. Making use of residual dipolar couplings (RDCs), we were able to determine the relative configuration of a natural product containing seven stereocenters, including a chiral amine lacking direct RDC data. To identify the correct relative configuration out of 32 possible ones, experimental RDCs were used in three different approaches for data interpretation: by fitting experimental data based singular value decomposition (SVD) using a single alignment tensor and either (i) a single conformer or (ii) multiple conformers, or alternatively (iii) using molecular dynamics simulations with tensorial orientational constraints (MDOC). Even though in all three approaches one and the same configuration could be selected and clear discrimination between possible configurations was achieved, the experimental data was not fully satisfied by the methods based on single tensor approaches. While these two approaches are faster, only MDOC is able to fully reproduce experimental results, as the obtained conformational ensemble adequately covers the conformational space necessary to describe the molecule with inherent flexibility., Ore Geology Reviews, 126

A stratigraphic section in the San Jacinto fold and thrust belt located at northwestern Colombia was studied. This section displays part of the Oligocene-Early Miocene Ciénaga de Oro Formation (COF). This work analyses the sediments provenance using a multi-tool approach which include: (I) conglomerate and sandstone counting clast with mesh, (II) heavy minerals assemblages, (III) paleocurrents and (IV) U/Pb detrital zircon ages. The sedimentary sequence was deposited in deltaic to transitional environment deposition, with reduction in the waves and tidal effect, and increase in the dominance of transitional river processes upward the section. Two main source areas have been identified from a dissected arc province: a main granitic to pegmatitic and a secondary basic igneous source rocks, located to the east and southwest of the current position. Detrital zircon U-Pb geochronology analysis display four age populations: (I) Devonian-Permian, (II) Permian-Triassic, (III) Jurassic and (IV) Cretaceous, with maximum deposition ages of 75.2±0.9 Ma in the lower part of the section, 68.9±0.6 Ma in the middle and 74.5±0.7 Ma for the upper part. It is proposed that COF was sediment-supplied by a south-to-north flvial system, which drained exposed basement blocks and their late Cretaceous to Paleogene sedimentary cover during the Oligocene. This fluvial system carried sediments from late Cretaceous plutons like the Antioqueño Batholith and mafi/ultramafi rocks, which make up the basement of the Western and Central Cordilleras., Boletín de Geología, 42 (3)

The northern margin of the West African Craton preserved in the Anti-Atlas area of southern Morocco, represents an outstanding geological archive covering parts of the Neoproterozoic and the Paleozoic. Despite isolated mentions in the literature, relics of Neoproterozoic glaciations have hitherto not received much attention in this area and tight geochronological constraints had been lacking. This paper documents the sedimentology and stratigraphic context of several occurrences from the eastern and central Anti-Atlas. Based on outcrop-scale sedimentological and microsedimentological investigations, different types of diamictites are distinguished and their origin with reference to modern glacial systems is discussed. The sedimentary record is explained by one single glacial period (albeit interrupted by interglacial phases) affecting both mountainous terrestrial and marine realms. Sedimentary facies and preserved paleotopographies are best accounted for by invoking a fjord-like depositional system with steep-sided valleys being repeatedly drowned by marine water or occupied by valley glaciers. High-precision geochronological constraints suggest that this glacial period must have taken place sometimes between 592 Ma and 579 Ma. Hence it is suggested that this is the first temporally constrained report of the Ediacaran Gaskiers glaciation on the West African Craton (WAC). Existing Ediacaran paleomagnetic data from the WAC are sparse and allow different interpretations regarding paleolatitude of this glaciation. The latter is finally discussed vis-a-vis potential rapid true polar wander events and the possibility that the Gaskiers glaciation was more global in extent than hitherto assumed and might even have brought Earth close to a true pan-glacial state.

Formation and evolution of the Pannonian Basin as part of the Mediterranean region was accompanied by eruptions of compositionally diverse magmas during the Neogene to Quaternary. The long-lasting magmatic activity began with some of the most voluminous silicic eruptions in Europe for the last 20 Myr. This paper describes the eruption chronology of this volcanic activity using new, high-quality zircon U-Pb dates, and provides the first estimates on the volume and areal distribution of the volcanic products, characterizes the magma composition and discusses the silicic magmatism in a region, where the continental lithosphere underwent significant extension. A thorough zircon geochronological study was conducted on samples collected from ignimbrites and pyroclastic fall deposits exposed in the Bukkalja Volcanic Field. In-situ LA-ICP-MS analysis on zircon grains provided a fast, cheap and accurate method for such detailed geochronological work, where the volcanic products occur in scattered outcrops that often have poor stratigraphic constraints. The interpreted eruption ages were determined from the youngest zircon age population within the samples and this methodology was validated by new single zircon CA-ID-TIMS dates and sanidine Ar-Ar ages. The volcanism covers about 4 Myrs, from 18.2 Ma to 14.4 Ma and involved at least eight eruptive phases. Within this, four large eruption events were recognized at 14.358 ± 0.015 Ma (Harsany ignimbrite), 14.880 ± 0.014 Ma (Demjen ignimbrite), 16.816 ± 0.059 Ma (Bogacs unit) and 17.055 ± 0.024 Ma (Mango ignimbrite), which are found in areas across the Pannonian Basin and elsewhere in central Europe. Considering all the potential sources of silicic ash found in the Paratethys sub-basins around the Pannonian Basin and along the northern Alps and in central Italy, we suggest that they were probably derived almost exclusively from the Pannonian Basin as shown by zircon U-Pb dates presented in this paper and published comparable age data from several localities. The new eruption ages considerably refine the Early to Mid-Miocene chronostratigraphy of the Pannonian basin, where the extensive volcanoclastic horizons are used as important marker layers. The cumulative volume of the volcanic material formed during this 4 Myr long silicic volcanism is estimated to be >4000 km3, consistent with a significant ignimbrite flare-up event. Zircon crystallization ages indicate magma intrusions and formations of magma reservoirs in the continental crust for prolonged period, likely >1 Myr prior to the onset of the silicic volcanism accompanied with sporadic andesitic to dacitic volcanic activities. Mafic magmas were formed by melting of the thinned lithospheric mantle metasomatized previously by subduction-related fluids and emplaced at the crust-mantle boundary. They evolved further by assimilation and fractional crystallization to generate silicic magmas, which ascended into the pre-warmed upper crust and formed extended magma storage regions. Zircon Hf isotope and bulk rock Sr-Nd isotopic data indicate a sharp decrease of crustal and/or increase of asthenospheric mantle input after 16.2 Ma, suggesting that by this time the crust, and the lithospheric mantle was considerably thinned. This magmatism appears to have had a structural relationship to tectonic movements characterized by strike-slip and normal faults within the Mid-Hungarian Shear Zone as well as vertical axis block rotations, when the two microplates were juxtaposed. Our new zircon ages helped to refine the age of two major block-rotation phases associated with faulting. This volcanism shows many similarities with other rift-related silicic volcanic activities such as the Taupo Volcanic Zone (New Zealand) and the Basin and Range Province (USA).

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and 176Hf/177Hf(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.

A prominent subduction-related magmatic arc hosting significant mineralization formed in SE Europe during the Late Cretaceous. Previous studies on major magmatic centers and ore deposits suggested that this belt formed through southwards retreat of a subducting Neotethys oceanic slab. However, the timing and the petrologic characteristics of magmatic products from the less mineralized eastern portions of this belt remain largely unknown. The complete lack of radiometric ages and limited geochemical characterization of this magmatism adds considerable uncertainty on existing large-scale geodynamic reconstructions focused on the Late Cretaceous magmatism in SE Europe. Here, we address this question by studying little known Cretaceous lavas and sub-volcanic bodies from the Eastern Balkan, Bulgaria. Major and trace element contents of these volumetrically limited rocks show a clear subduction signature. The most primitive rocks are high-Al basalts, which further differentiated into andesites and dacites via fractional crystallization in relatively small magma chambers. The mineral chemistry and assemblages constrain magmatic conditions prior to crystallization to pressures of 3–7 kb, temperatures of 900–1020 °C, water contents of ~4–7 wt% and high oxygen fugacities. Phenocryst features like reverse zonation of clinopyroxene and amphibole and sieve and patchy textures of plagioclase suggest magma mixing processes. Initial eHf values of Cretaceous zircons (+2 to −2) and inherited, mainly Variscan and older zircons (+3 to −11) provide clear evidence for assimilation of crustal lithologies by mantle-derived Late Cretaceous magmas. Amphibole phenocrysts from an andesite and a dacite give 40Ar/39Ar plateau ages of 94.67 ± 0.40 Ma and 94.56 ± 0.40 Ma, respectively. These dates are the oldest recorded in the entire Late Cretaceous magmatic belt and constrain the onset of the subduction magmatism to the later parts of the Cenomanian stage. Regional correlations based on these results reveal that processes of slab retreat were active also in the eastern part of the magmatic arc. Further, these results outline a clear temporal along-arc trend of progressively younger initiation of the arc magmatism from east to west.

The Sanandaj-Sirjan metamorphic-magmatic Zone (SaSZ) represents the Mesozoic active continental margin of the Neotethys Ocean between the Arabian plate and the Iranian plateau. The zone evolved at the margin of ancient Ediacaran basement, as documented in this paper with an age of 557 Ma for a trondhjemite. The Mesozoic activity of the SaSZ was most intense with sedimentation and magmatism in the Jurassic between 170 and 150 Ma, but this period was then followed by a 20 million years gap with almost no magmatic activity, which has been attributed to flat slab tectonics. The present paper is concentrated on the geochemistry, and zircon CA-ID-TIMS geochronology, of a bimodal, but mainly basaltic, volcanic and subordinate plutonic succession that represents the resumption of magmatism in a deep and gradually shallowing basin in the northern SaSZ between 130 and 110 Ma. The mafic to intermediate volcanic rocks are predominantly calc-alkaline and have eNd values of +0.3 to +3.9. The felsic volcanic rocks are dominantly high-K calc-alkaline with eNd values of −0.5 to +1.9. A suite of Cretaceous trondhjemites yields eNd values of −4.6 to −4.9. Together, the geochemical, lithological and geochronological indications suggest that the thick Barremian-Aptian bimodal magmatic suite represents magmatism in a continental arc to back-arc setting, controlled by extension and probably related to foundering of the flat slab and slab roll-back. These events initiated melting of the mantle in the northern SaSZ, heralding a period of extension and the subsequent development of ophiolites all along the Neothetyan suture.

In the present study, we apply a combination of Sr-isotope whole-rock analyses and LA-ICP-MS U-Pb zircon dating to understand the magmatic evolution of the igneous rocks in the Ruen Zone, western Bulgaria, and bracket the time of their formation. This approach reveals a general interval of magmatic activity from 35.57 ± 0.27 Ма (Pishtilski volcanics) to 28.63 ± 0.58 Ма (cross-cutting dykes in the Osogovo Mountain). The volcanic rocks from the Prekolnitsa Graben are formed with significant (50%) crustal contamination/assimilation. Three major sources of crustal rocks can be outlined, with Triassic, Ordovician and Cambrian age, respectively. For the subvolcanic to plutonic magmatic rocks of the Osogovo Mountain, we suggest maturation and zircon crystallization over 2–4 Ma. The magma was generated dominantly in the continental crust and evolved through mainly fractional crystallization (FC) in the upper crustal chamber, whereas the evolution of the Osogovo dykes requires additional involvement of AFC (Assimilation and Fractional Crystallization) and contamination processes.

The present work aims to contribute to the Cenozoic tectonic setting of the western part of the Makran Accretionary Wedge in SE Iran. We determine the provenance of both deep marine turbiditic and deltaic-shelf Late Cretaceous-Miocene sandstones, describe the sandstone modal framework and heavy minerals and report a new geochronological and isotopic study including 2307 detrital zircons U-Pb ages and 204 in-situ Hf isotopic analyses. Modal sandstone framework compositions indicate that a magmatic arc and recycled accreted sediments were the main sources of Eocene-Oligocene and Miocene sandstones. Cr-spinel and heavy mineral assemblages indicate ultramafic rocks, likely ophiolitic mantle, as a subsidiary source. Detrital zircon U-Pb ages cluster in five main age groups: (1) Neoproterozoic grains suggesting a continental crust provenance within the Central Iran blocks, (2) Jurassic grains with Hf isotopic compositions of continental crust, suggesting a rifting related magmatic provenance, (3) Late Cretaceous and (4) Eocene grains, with Hf isotopic compositions typical of continental crust and non-depleted mantle, suggesting a continental magmatic arc provenance, and (5) Early Miocene grains. The new U-Pb age and Hf isotopic ratios correspond to those obtained in the east Iranian Makran. They fit tectonic reconstructions with Middle Jurassic intracontinental rift, Early Cretaceous to Eocene subduction below Central Iran forming a continental arc to the north of Makran and closure of the related oceanic in the Paleogene. Erosional products of the corresponding magmatic arc are found in the Makran Basin. Our data disprove that provenance characteristics of the Makran sedimentary rocks are consistent with derivation from the Himalayan sources.

On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12 years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~ 9 km. Textural and compositional data from phenocrysts from the erupted products have been integrated with geochemical and isotopic information from bulk rocks to elucidate the magmatic processes responsible for the reawakening of volcanic activity. Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites. Mineral-melt equilibria suggest an origin for the distinct phenocryst populations by mixing between a high- T (~ 1130–1150 °C), basaltic magma with f O 2 (NNO buffer) typical of the lower crust in arc systems and a low- T (~ 1060–1080 °C), basaltic andesitic magma with f O 2 (NNO + 1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg exchange between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low- P (~ 150–250 MPa) and low- T (~ 1000–1050 °C). Mixing between two chemically distinct magmas is also evidenced by the occurrence of reverse zoned plagioclase phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcic mantles. Conversely, plagioclase rims exhibit disequilibrium compositions addressed to decompression kinetics (~ 10 − 3 MPa/s) driven by rapid magma ascent to the surface (~ 0.03 m/s). Major and trace element modelling excludes fractional crystallization as the primary mechanism controlling the bulk rock variability, whereas geochemical data align along a mixing trend between two end-members representative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes of metasomatic fluids and/or melts produced by the subducted slab. The role played by slab-fluid inputs of carbonate origin and slab-melts from the hemipelagic sediments seems to be minimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influenced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crust.

Late Paleogene syn-tectonic magmatic products are known from sandstones contained in the North Alpine (NAFB) and South Alpine (SAFB) foreland basins and in the South Alpine pelagic Trento Basin. The generally turbiditic and mass-flow deposits grade up from marly hemipelagic deeper water series. The source and amount of the reworked volcanic materials have been in debate for a long time. As a proxy for the magma-derived input we use the U–Pb geochronology and geochemistry [176Hf/177Hf(t) and Eu/Eu* ratios] of detrital zircons, and evaluate their temporal and genetic relationships with potential volcanic sources in the Periadriatic magmatic systems (Adamello, Bergell, Biella). The oldest volcanic sources (Lutetian–Priabonian) we identify are in the Trento Basin and Glarus NAFB. During most Rupelian, Bergell and Biella volcaniclastics were delivered to the NAFB in the Glarus, Alpe de Taveyanne and Haute-Savoie. Bergell and minor Adamello magmatic material were supplied to the Villa Olmo Conglomerate in the SAFB. During late Rupelian–Chattian in the entire NAFB, the influx of Paleogene volcanic material faded out. At the same time in the SAFB, the Como Conglomerate shows mixed input from Biella and Bergell. High numbers of old zircons (> 90%) in the NAFB document the asymmetry of the early Alpine orogenic wedge exposing large basement areas to the north of the Periadriatic intrusions. The syn-sedimentary right-lateral movement along the Periadriatic fault system is identified as the main driver of magmatic activity, uplift, and exposure to erosion and transport to the basins. On this base, the dynamics of the early Alpine drainage systems are reconstructed with new accuracy.

The Anti-Atlas area in southern Morocco preserves one of the most complete latest Ediacaran to Cambrian shallow-marine carbonate records in the world and serves as a standard for global chemostratigraphic δ13Ccarb curves. Contrary to the excellent chemostratigraphic coverage, neither metazoan fossils (only stromatolites and calcified algae) nor radiometric age constraints were hitherto available for the basal part of this carbonate record, the Tifnout Member of the Adoudou Formation of the Taroudant Group. We report an Ediacara-type fauna from shallow-marine sandstones from the basal Tabia Member and microfossils from dolostones from both the Tabia and the Tifnout members of the Adoudou Formation. The former are discoidal fossils and share many characteristics with the form genus Aspidella and exhibit a peculiar style of preservation, pointing towards an early diagenetic two-stage (carbonate followed by silica) cementation history, leading to good preservation of these supposedly once soft-bodied organisms. The dolostone-hosted microfossils are preserved as sparite-filled molds enclosed by a thin opaque envelope. Despite their small size, they resemble late Ediacaran calcifying metazoans such as Namacalathus and tubular small shelly fossils. Together, these fossils constitute the oldest known direct evidence for presumably metazoan life from Northwest Africa. We also report new time constraints for the Adoudou Formation and fossils enclosed therein based on combined LA-ICP-MS and high-precision CA-ID-TIMS U-Pb zircon geochronology of detrital and volcanic zircons. Together with new chemostratigraphic (δ13Ccarb) and literature data, these new age constraints suggest a late Ediacaran age (time span between ca. 561 and 542 Ma) for the discoidal Ediacara-type fossils from the basal Tabia Member, and a latest Ediacaran to earliest Cambrian (time span between ca. 544 and 540 Ma) and an early Cambrian age (time span between ca. 528 and 523 Ma) for the two microfossil faunas from the Tifnout Member.

Contributions to Mineralogy and Petrology, 174, ISSN:0010-7999, ISSN:1432-0967

Crystals of the columbite-group minerals (CGM) from 23 rare-element granitic pegmatites of the Pampean Pegmatite Province (PPP) were analyzed by LA-ICP-MS technique. The resulting database shows weighted mean 206Pb/238U ages between 530 and 335 Ma defining two time windows, T1 and T2. T1, from 490 to 440 Ma, spans 75% of the ages of LCT rare-element pegmatites formed during the Famatinian collisional orogeny of peri-Gondwana location. T2, from 370 to 340 Ma, comprises postorogenic pegmatites with lithium-caesium‑tantalum (LCT) and niobium‑yttrium‑fluorine (NYF) or mixed NYF-LCT signatures. The CGM ages of the PPP orogenic pegmatites show a shifting from older in the north to younger in the south. The major elements composition of the CGM shows preference for high #Mn at variable but usually moderate to high #Ta. The normalized, with the Global CGM median, trace elements composition of the CGM of most orogenic LCT (Li-Cs-Ta) pegmatites shows an enrichment in Bi, Pb and U, a remarkable depletion in Sn and sometimes a slight decrease in W (Y ± Yb). The postorogenic pegmatites show CGM with a general enrichment in Y (±Yb), W, Pb, U, and occasionally in Sn. The REEN diagrams of CGM from the northern districts of the PPP show patterns with LREEN HREEN and strong negative Eu anomalies. In the southern districts, there is a bimodal behavior in the total content and distribution of the normalized patterns of REE. The CGM from some pegmatites of the Conlara Pegmatite district have similar features to the ones from the northern districts. It seems that the kind of pegmatite has no definitive control in the type of pattern. The other group shows low contents of REEN mostly comprised between 0.01 and 10 times the chondrite values, flattened patterns, weak to moderate negative anomalies of Eu, and occasionally a weak Ce anomaly. In the southern Totoral district, the CGM of the different kinds of pegmatites also have approximately similar, though relatively lower, total REEN contents and patterns with LRREN

Break-up of western Pangaea initiated a back-arc type tectonic setting along the northwestern margin of Gondwana, which resulted in the accumulation of sedimentary and volcanic deposits in extensional basins during the Middle-Late Triassic. The Sierra Nevada de Santa Marta massif, at the northwestern termination of the Andes, exposes Upper Triassic syn-rift successions beneath a voluminous Lower Jurassic volcanic cover. In this contribution, we present a sedimentological and stratigraphical analysis of the Upper Triassic Los Indios and Corual formations, by integrating whole-rock geochemistry, zircon U–Pb geochronology, and a biostratigraphic revaluation of the conchostracan fossil content. We divide the Los Indios Formation into two sandy to conglomeratic and two muddy members. First and third members were deposited in a coarse-grained delta environment. The second and fourth members are interpreted to represent offshore deposits resulting from the encroachment of gravity-flow lobes. Volcanoclastic and volcanic rocks interbedded with sedimentary deposits of the Los Indios and Corual formations record bimodal basic-acid volcanism with a variably alkaline tendency. Based on their alkaline and calc-alkaline signature, and rare earth and trace element patterns, volcanic rocks display a back-arc affinity. With respect to the age of the Los Indios Formation, we recovered conchostracans diagnostic of Upper Carnian and Lower Norian fauna, bearing similarity with faunal assemblages of other Upper Triassic deposits exposed in the northern Andes. The Los Indios and Corual formations are considered as syn-rift successions in a back-arc extension setting. The development of this back-arc basin coincided with the Late Triassic separation of the Oaxaquia, Acatlan, and Chortis terranes during Pangaea break-up. Finally, the Early to Middle Jurassic evolution of the NW Gondwana margin is marked by the inception of a magmatic arc, which characterizes the establishment of Andean-type subduction coeval to ignimbrite flare-up.

New data on the U–Pb geochronology and Hf-isotopic composition of detrital zircons, along with the geochemistry of garnets, chromian spinel and feldspars from Permian and Triassic volcano-sedimentary sequences in the Southern and Eastern Alps reveal similarities in the nature and tectonomagmatic setting of the Early Permian and the Middle Triassic magmatic events. Detrital zircon U–Pb geochronology displays magmatic activity at 290–280 Ma (Early Permian) and at 245–235 Ma (Middle Triassic). The two-stage Hf-depleted mantle model ages obtained from Permian and Triassic zircons cluster around 1.7–1.6 and 1.3–0.8 Ga. Epsilon Hafnium analysis on dated detrital zircons suggests mixing of mantle and crustal components into the parental magmas of Permian and Triassic magmatism, the latter showing less crustal contribution. The composition of detrital feldspars from the Permian and Triassic volcaniclastic sandstones reveals provenance from intermediate to acidic igneous rocks. Garnet in Middle and Late Triassic beds suggests the incorporation of material comparable to the mafic rocks of the Ivrea-Verbano Zone into the parental melts of the Triassic magmatism. Chromian spinel in syn-magmatic Carnian sandstones indicates an origin associated with MORB-type peridotites and therefore, corroborates a mantle contribution to the Middle Triassic magmatism. The integration of detrital zircon U–Pb ages, Hf isotopes and composition of detrital minerals suggests that continuous lithospheric stretching at the transition from the post-Variscan to the Alpine orogenic cycle, with periods of strike-slip movements, presumably led to an asymmetrical continental rifting process, in which the Middle Triassic magmatic episode represents the earliest stage of the Alpine Tethys oceanic domain.

The Jurassic ophiolites in the South Apuseni Mountains represent remnants of the Neotethys Ocean and belong to the East Vardar ophiolites that contain ophiolite fragments as well as granitoids and volcanics with island-arc affinity. New U–Pb zircon ages, and Sr and Nd isotope ratios give insights into their tectono-magmatic history. The ophiolite lithologies show tholeiitic MOR-type affinities, but are occasionally slightly enriched in Th and U, and depleted in Nb, which indicates that they probably formed in a marginal or back-arc basin. These ophiolites are associated with calc-alkaline granitoids and volcanics, which show trace element signatures characteristic for subduction-enrichment (high LILE, low HFSE). Low 87Sr/86Sr ratios (0.703836–0.704550) and high 143Nd/144Nd ratios (0.512599–0.512616) of the calc-alkaline series overlap with the ratios measured in the ophiolitic rocks (0.703863–0.704303 and 0.512496–0.512673), and hence show no contamination with continental crust. This excludes a collisional to post-collisional origin of the granitoids and is consistent with the previously proposed intra-oceanic island arc setting. The new U–Pb ages of the ophiolite lithologies (158.9–155.9 Ma, Oxfordian to Early Kimmeridgian) and granitoids (158.6–152.9 Ma, latest Oxfordian to Late Kimmeridgian) indicate that the two distinct magmatic series evolved within a narrow time range. It is proposed that the ophiolites and island arc granitoids formed above a long-lived NE-dipping subduction zone. A sudden flip in subduction polarity led to collision between island arc and continental margin, immediately followed by obduction of the ophiolites and granitoids on top of the continental margin of the Dacia Mega-Unit. Since the granitoids lack crustal input, they must have intruded the Apuseni ophiolites before both magmatic sequences were obducted onto the continental margin. The age of the youngest granitoid (~153 Ma, Late Kimmeridgian) yields an estimate for the maximum age of emplacement of the South Apuseni ophiolites and associated granitoids onto the Dacia Mega-Unit.

A multidisciplinary provenance study, including sandstone framework, heavy mineral analysis, in situ U-Pb dating of detrital zircon, and Hf isotopic ratio analysis of dated zircons, was undertaken on Late Cretaceous−Miocene deep-marine turbiditic and deltaic sandstones of Makran accretionary wedge, SE Iran, to determine their sedimentary provenance and tectonic setting. Sandstone framework modes reveal both magmatic arc rocks as a source of Late Cretaceous−Oligocene detritus and recycling of Miocene sandstones. Heavy mineral assemblages, Cr-spinel, and blue amphibole indicate ophiolite and high-pressure−low-temperature metamorphic rocks (blueschists) as a supplementary provenance. In total, 2931 laser-ablation−inductively coupled plasma−mass spectrometry (ICP-MS) U-Pb detrital zircon ages on 21 sandstone samples yielded three major age peaks at ca. 167 Ma, 88.7 Ma, and 48.9 Ma. Also, 241 in situ Hf isotope analyses of dated zircons provide evidence for dominantly igneous source rocks. Two main detrital zircon ages are identified: (1) abundant Middle Jurassic grains with Hf isotopic compositions of continental crust, suggesting a rifting-related magmatic provenance; and (2) Late Cretaceous−Eocene grains with Hf isotopic compositions of continental crust and nondepleted mantle, suggesting a continental magmatic arc provenance. This change in provenance is attributed to the Late Cretaceous convergence between Arabia and Eurasia.

Accessory mineral U–Pb geochronology by isotope dilution thermal ionization mass spectrometry (ID-TIMS) requires precise and accurate determinations of parent–daughter isotope ratios. The small sample size, particularly with respect to radiogenic Pb (Pb*), requires highly sensitive ion detection systems. Most studies therefore employ either secondary electron multipliers (SEMs) or Daly photomultipliers that provide low background noise and high sensitivity but have a limited linear range and require dynamic peak-hopping. We here evaluate the application of new 1013 ohm resistors in a Faraday cup amplifier feedback loop for the static collection of all Pb isotopes (sample and tracer) with 202,205,206,207,208Pb measured on Faraday cups and 204Pb measured in the axial SEM of a Thermo Scientific™ TRITON™ Plus TIMS instrument. We demonstrate long-term stability of the amplifier gain calibration using a secondary Nd standard and test short- and long-term stability and reproducibility of amplifier baselines. Accurate calibration of static detector arrays is demonstrated by repeated analyses of synthetic and natural U–Pb standards (ET100, Temora-2 and AUS_Z7_5) with variable Pb* (0.551 to 699 pg) and comparison with conventional dynamic ion counting data. Excellent agreement between the two detector systems for all analysed standards suggests that our static measurement routine with 1013 ohm resistors produces accurate and precise U–Pb isotopic data with superior external reproducibility. We anticipate that this new technique will push the frontiers of high-precision U–Pb geochronology and may represent a crucial advancement in the quest towards inter- and intra-laboratory reproducibility at the 0.01% level.

The Letseng-la-Terae kimberlite (Lesotho), famous for its large high-value diamonds, has five distinct phases that are mined in a Main and a Satellite pipe. These diatreme phases are heavily altered but parts of a directly adjacent kimberlite blow are exceptionally fresh. The blow groundmass consists of preserved primary olivine with Fo86−88, chromite, magnesio-ulvospinel and magnetite, perovskite, monticellite, occasional Sr-rich carbonate, phlogopite, apatite, calcite and serpentine. The bulk composition of the groundmass, extracted by micro-drilling, yields 24–26 wt% SiO2, 20–21 wt% MgO, 16–19 wt% CaO and 1.9–2.1 wt% K2O, the latter being retained in phlogopite. Without a proper mineral host, groundmass Na2O is only 0.09–0.16 wt%. However, Na-rich K-richterite observed in orthopyroxene coronae allows to reconstruct a parent melt Na2O content of 3.5–5 wt%, an amount similar to that of highly undersaturated primitive ocean island basanites. The groundmass contains 10–12 wt% CO2, H2O is estimated to 4–5 wt%, but volatiles and alkalis were considerably reduced by degassing. Mg# of 77.9 and 530 ppm Ni are in equilibrium with olivine phenocrysts, characterize the parent melt and are not due to olivine fractionation. 87Sr/86Sr(i) = 0.703602–0.703656, 143Nd/144Nd(i) = 0.512660 and 176Hf/177Hf(i) = 0.282677–0.282679 indicate that the Letseng kimberlite originates from the convective upper mantle. U–Pb dating of groundmass perovskite reveals an emplacement age of 85.5 ± 0.3 (2σ) Ma, which is significantly younger than previously proposed for the Letseng kimberlite.