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The western Argentinian sector of Gondwana has been the focus of several recent studies related to the Famatinian orogeny; however, the geologic history of arc activity in hinterland areas remains poorly understood. We present new data from the Monte Guazú Complex that reveal arc-related magmatism in the Sierras de Córdoba, which we consider part of the Famatinian hinterland. Igneous rocks comprise a diorite unit which includes an amphibole quartz-gabbro/diorite and a tonalite unit comprising amphibole- and biotite-bearing tonalites to minor granodiorites. Both units constitute a medium-K calc-alkaline series ranging in composition from metaluminous to moderately peraluminous. Trace-element signatures show Ti and Nb depletion and strong incompatible element enrichments (large-ion lithophile elements, Pb, Th, U, and light-rare earth elements) relative to normal mid-ocean ridge basalts, suggesting that they formed in an arc setting. U–Pb zircon geochronology constrains magmatism to 455–498 Ma, while weighted mean ages of 474–489 Ma are mostly synchronous with the Famatinian arc beginning. We demonstrate that fractional crystallization of mantle wedge-derived melts controlled the early magmatic evolution, while country rock assimilation and anatectic melt mixing were prevalent in evolved rock members. These results spatially extend the Late Cambrian–Late Ordovician Famatinian retro-arc to the southern Sierras de Córdoba. Our findings show that magmatism involved coeval anatexis of host rocks, conversely to previous geodynamic models. Our data have fundamental implications for Paleozoic tectonic and magmatic processes operating along the western Argentinian sector of Gondwana, demonstrating the importance of crustal reworking and the addition of mantle material in the Famatinian arc inboard sector. [ABSTRACT FROM AUTHOR]

The Chuschín formation is a sedimentary-volcanic succession of the Famatina System subduction-related arc magmatism. This formation developed along the western margin of Gondwana during the early and middle Ordovician. The interpretation of the Chuschín formation is significant for the understanding of the Famatinian arc. This study provides a detailed facies analysis, which allows characterizing the deposits as well as defining some of the characteristics of the volcanism and sedimentation. Coherent, autoclastic, peperitic, pyroclastic and volcaniclastic facies were recognized between the different volcanic facies. The characteristics and relationships between these facies indicate events of effusive subaqueous volcanism as well as explosive volcanism showing predominantly high temperature features. Both types of volcanism are interbedded with volcanogenic deposits and epiclastic sediment that are associated mainly with turbidity currents. The magmatic and volcanic rocks are dominantly subalkaline, weakly peraluminous and silicic. Two new U-Pb zircon crystallization ages on volcanic rocks from the Chuschín Formation show that this section of the Famatinian arc formed between 463 and 469 Ma (Middle Ordovician). [ABSTRACT FROM AUTHOR]

The Laguna Amarga Metamorphic Complex is a major stratigraphic component of the southern Central Andes. The occurrence of crystalline basement pieces extensively exposed in the western Andes of Catamarca (Argentina), has been known for decades, nevertheless, a lack of detailed field-based and geochronological survey has precluded an accurate correlation of the Laguna Amarga Complex with other basement exposures in the Central Andes. The Laguna Amarga Metamorphic Complex outcrops in several fault-bounded blocks spread over about 360 km2, always underlying Neopaleozoic strata and Neogene volcanic strata from the Central Volcanic Zone. The northern part of the complex consists of amphibolite-facies metamorphic rocks derived from sedimentary and igneous precursors grouped in an association named Cazadero Grande. The original stratigraphic succession was interbedded siliciclastic sediments, carbonaceous, and mafic rocks. The southern segment of the complex is dominated by granulite-facies migmatites and ortho-amphibolites grouped in an association called Los Aparejos. In the Cazadero Grande Association, four deformational events are recognized. The first three phases gave rise to an imbricate S-verging over-thrusting system and prevailing tectonic transport to the south in response to progressive non-coaxial strains. The mineral assemblages linked to the metamorphic climax equilibrated coeval with the early stages of fabric-forming deformation. The posthumous fourth phase of deformation produces gentle folds with kilometer-scale wavelengths whose axial planes (non-penetrative) have an NNE strike, and are as related to Andean deformation. Three incremental deformation events coeval with the metamorphic climax are registered in the Los Aparejos Association that indicate a kinematics transport to the east. First U–Pb zircon ages are reported for the Laguna Amarga Metamorphic Complex. Age distributions are polymodal, but the dominant populations make well-defined clusters. The most prominent concord age peak is at 389 Ma, revealing the age of the metamorphic climax. Another noteworthy aspect is the presence of dominant Mesoproterozoic concord age peaks (1119-1082 Ma), interpreted as inheritance ages of their protolith. A point to highlight is the absence of ages reflecting the source with Brasiliano-Pan-African orogenic ages that dominates detrital provenance from the West Gondwana. The Mesoproterozoic protolith ages allow the correlation of this metamorphic complex with nearby basement detached from Laurentian realms. The analysis of the ages shows that the metamorphic peak and the generalized deformation that affected the entire basement of the complex developed in the Middle Devonian (Eifelian), this being a very little known event for the Paleozoic evolution of western Gondwana. The work discusses how a better understanding of the crystalline basement of the high Andes impacts the geodynamic history of the proto-Andean Gondwana margin. It also provides new information on the geodynamic configuration of the Lower to Middle Paleozoic and its link with the processes of accretion-collision of terranes. • Tectonic cover slices from the Cuyania/Precordillera terrane are exposed in the high Andes of Catamarca, Argentina. • Zircon U–Pb dating yields Mesoproterozoic ages in inherited grains while Devonian ages in metamorphic rims. • Structural analyses imply top-S nappe stacking closely following a Devonian metamorphic peak. • A narrow suture zone separating Laurentia-derived crust from the Early Ordovician Famatinian arc. [ABSTRACT FROM AUTHOR]

The Suri Formation is a sedimentary-volcanic succession in the Famatina belt formed during Lower - Middle Ordovician arc magmatism along the western margin of Gondwana. This study reports new lithostratigrafic data relating to the Suri Formation in the Chaschuil valley (Catamarca). The survey defines the main characteristics of volcanism and sedimentation through facies analysis. Epiclastic, volcaniclastic, pyroclastic and peperitic facies were recognized and interpreted in five facies association. The features and relationships of the facies associations indicate environments such as apron volcaniclastic, inner to an outer shelf, and fan distal delta, interbedded with effusive and explosive volcanism. Volcanic activity and relative sea-level changes were controls on sedimentation style in basins adjacent to the volcanic edifice. The study reports U–Pb geochronological analysis of zircon from a sandstone sample of the Suri Formation to infer detrital provenance. The detrital zircon pattern with peaks at 486 Ma points to active Famatinian magmatism as recorded on the nearby Narváez batholith. Eruptive masses experienced rapid reworking, short sedimentary transport and intra-arc deposition. The maximum deposition age of detrital zircon corresponds to a subordinate age cluster at 464.4 ± 4.4 Ma and reflects synchronism between volcano-sedimentary deposition in the Suri Formation and plutonic-volcanic construction of the Las Planchadas Formation. • This study reports a stratigraphic analysis of the Suri Formation in the northern Famatina System. • The Suri Formation reflects apron volcaniclastic, internal to external shelf and fan distal delta. • Variable intensity of volcanism controlled the sedimentary environment of Suri Formation. • Volcanic facies contain abundant proximal deposits suggestive of explosive eruptive activity. • Sedimentation of the Suri Formation reveals a topographic surface with high slope gradient. [ABSTRACT FROM AUTHOR]

The Famatinian arc, over central-western Argentina, is one of the few examples of exposed crustal arc cross-section in the world. This Paleozoic magmatic arc and orogenic system on the Earth's surface offers unique insights into the nature of whole-arc processes, continental crust generation, and preservation. A detailed account of birth, growth, and closure is integrated throughout the region, and the entire geodynamic history of the Famatinian arc is presented. The Famatinian magmatic arc grew during a single-cycle episode that spanned a few tens of million years. Upon waning of the Cambrian Pampean orogen, an Upper Cambrian – Lower Ordovician marginal and open sea basin developed mostly on the recently stabilized Cambrian crystalline crust and was flooded by a turbidite wedge. Typical subduction zone magmatism resumed outboard of the Pampean orogen in the Lower Ordovician. After about 20 My of magmatism driven by subduction zone dynamics at plate scale, magmatism waned and stopped with the entry of a Laurentia-rifted continental microplate in the subduction zone. A full phase of a mountain-building process accompanied the continent-arc collision. The orogenic collapse occurred during the Devonian, ending the Famatinian system after nearly 150 My of magmatic arc, plate convergence, and continent-arc collision development on the proto-Andean Gondwana margin. • Geology shows a well-preserved Paleozoic magmatic arc and orogenic system on the Earth's surface. • A full plutonic crustal section formed in about 20 My of subduction-related magmatism. • A segment of Famatinian arc ended sandwiched between a Laurentian microplate and Gondwanan margin. • The subducting continental crust merged the overriding plutonic arc crust to make stable Continental Crust. [ABSTRACT FROM AUTHOR]

We applied elastic thermobarometry on garnet-bearing migmatites along two transects through the crustal section at Sierra Valle Fértil-La Huerta, Argentina. We performed quartz-in-garnet barometry and zircon-in-garnet thermometry on metapelites from different paleo-depths across the crustal section. Our work recovers entrapment pressures ranging from 240 to 1330 MPa and entrapment temperatures between 691 and 1574 °C. The entrapment conditions are broadly consistent with anticipated pressures and temperatures along the crustal section derived previously using conventional, thermodynamic thermobarometers. The quartz-in-garnet barometer reproduces those conventionally established entrapment conditions when samples only experienced conditions within the alpha-quartz stability field. Raman-derived pressures for samples that experienced beta-quartz reference conditions are commonly much higher than those established by conventional barometry. Samples that preserve compressive (positive) residual pressures best reproduce reference entrapment pressures. Entrapment temperatures show high variability and overestimation of temperature conditions compared to conventional results. These results indicate elastic thermobarometry over- or under-estimates crystallization conditions in rocks crystallized at high temperatures, as is common in the Famatinian Arc deep-crust. We suggest that modeling quartz behavior across the alpha–beta transition may present challenges, as does shape maturation, viscous deformation, and radiation damage in zircon. [ABSTRACT FROM AUTHOR]

Situated in the western Sierras Pampeanas of San Luis, the Nogolí Metamorphic Complex has become a key geological locality for unraveling the construction of the western Gondwana margin on the South American tectonic plate. This study presents a comprehensive analysis, encompassing new petrological and geochronological data, along with a meticulous structural examination of two distinct regions within the Nogolí Metamorphic Complex. Our primary aim is to assess the age and provenance of the protoliths, thereby shedding light on their geodynamic evolution. Detrital zircon U–Pb ages, obtained from a quartz–feldspathic-schist paleosome within a metatexite exposure in the La Barranquita area, disclosed a polymodal distribution. The predominant age population, centered around 616 ± 11 Ma, suggests a late Neoproterozoic source (Brasiliano–Pan African orogen). A secondary, yet significant, age peak at 542 ± 12 Ma points to a late Ediacaran to Early Cambrian origin (Pampean orogen). Additionally, a peak ranging from 930 to 1144 Ma indicates contributions from an early Neoproterozoic source (Grenvillian–Sunsas orogen). The maximum depositional age was determined to be 533 ± 14 Ma, based on the calculation of the youngest grain cluster at 2σ uncertainty. This polymodal zircon-age spectrum indicates that the sedimentary protolith of the Nogolí Metamorphic Complex derived from a Cambrian-age crystalline basement situated along the western margin of Gondwana. Contrary to models invoking continent–continent collision in western Gondwana during the early Cambrian, our findings better support a ridge–trench collision as the most plausible hypothesis for the origin of the Pampean orogeny. [ABSTRACT FROM AUTHOR]

Mass transference from lower to upper crustal levels requires an efficient network of pathways that act as channels for draining melts from the source and transferring magmas through the crust. We report on a mid-crustal section in the Santa Rosa river from the Eastern Pampean Ranges that underwent partial melting under active deformation. The study focuses on the feedback relations between structural features and the position and shape of leucosomes that record the remnant magma network in both metasedimentary and meta-igneous rocks. A complete range of migmatites encompassing from patch to stromatic metatexite to schollen-schlieren and nebulitic diatexite formed during a single high-grade metamorphic event that postdated a previous sub-solid evolution. The diversity in migmatites structures suggests that the layered sequence behaved heterogeneously under a non-coaxial deformational regime of progressive deformation. The relationships between migmatitic structures and the progressive production of melts resulted in feedback relations that persisted as a time-marker during the Pampean event. U-Pb dating of leucogranitic zircons allows constraining the time of melt generation and segregation to the lower Cambrian (534-520 Ma). Migmatites in the lower crust of the Pampean orogen acted as channels of melt migration towards upper crustal levels. • Non-coaxial Pampean deformation and its relationships with migmatitic structures. • A melt transference zone documented from a middle crustal ancient accretionary orogen. • Geochronology shows that syn-deformational migmatites generated during lower Cambrian. • Axial-plane leucosomes work out as melt-removal paths towards upper crustal levels. [ABSTRACT FROM AUTHOR]

The Famatinian arc formed around the South Iapetus rim during the Ordovician, when oceanic lithosphere subducted beneath the West Gondwana margin. We present combined in situ U–Th–Pb and Lu–Hf isotope analyses for zircon to gain insights into the origin and evolution of Famatinian magmatism. Zircon crystals sampled from four intermediate and silicic plutonic rocks confirm previous observations showing that voluminous magmatism took place during a relatively short pulse between the Early and Middle Ordovician (472–465 Ma). The entire zircon population for the four plutonic rocks yields coherent εHf negative values and spreads over several ranges of initial εHf (t) units (−0.3 to −8.0). The range of εHf units in detrital zircons of Famatinian metasedimentary rocks reflects a prolonged history of the cratonic sources during the Proterozoic to the earliest Phanerozoic. Typical tonalites and granodiorites that contain zircons with evolved Hf isotopic compositions formed upon incorporating (meta)sedimentary materials into calc–alkaline metaluminous magmas. The evolved Hf isotope ratios of zircons in the subduction related plutonic rocks strongly reflect the Hf isotopic character of the metasedimentary contaminant, even though the linked differentiation and growth of the Famatinian arc crust was driven by ascending and evolving mantle magmas. Geochronology and Hf isotope systematics in plutonic zircons allow us understanding the petrogenesis of igneous series and the provenance of magma sources. However, these data could be inadequate for computing model ages and supporting models of crustal evolution. [ABSTRACT FROM AUTHOR]

Subduction zone magmatism plays a crucial role in driving the exchange of chemical elements between Earth's interior and surface. This survey focuses on the compositional analysis of primitive mafic rocks within an ancient Early Palaeozoic subduction-related magmatic belt. The primary objective is to assess the petrological processes involved in the cycling of chemical elements from the Earth's surface, through the slab and mantle reservoirs, to the crustal arc magmatic systems. By examining the composition of primitive mafic rocks and utilizing inverse modelling techniques, we estimate the composition of the ambient mantle source, which appears to have undergone depletion due to melt extraction before being metasomatized by slab agents. The inverse approach reveals that fluid-mobile elements (Th, U, La, Ce, and Sr) were primarily derived from the slab contribution and suggests that subduction had influenced the abundances of Nb and Ta in the modified mantle source. Conversely, Zr, Hf, and Ti were sourced from the ambient mantle. However, the available mineral/melt partition coefficients used in inverse modelling may overestimate the contribution of Sr and Nb from the slab. Instead, forward modelling is limited by the incomplete preservation of ancient volcanic arc geology. The forward mixing models that consider the interaction between slab-released sedimentary-derived melts and the ambient depleted mantle can explain the observed variations in Nd and Sr isotopic ratios in primitive mafic rocks. Two-component mixing shows that a small mass fraction (≤1.5 wt%) of average Cambrian continental sediments subducted beneath the Early Ordovician arc into a MORB-depleted mantle source account for the abundance of sedimentary-supplied elements such as Th, La, and Ba, as well as radiogenic isotope ratios of 143Nd/144N and 87Sr/86Sr in the primitive mafic magmas. The chemical and isotopic composition of deep-seated primitive mafic rocks reveals a decoupling between incompatible trace elements, which display minimal variation, and radiogenic isotopic ratios, which exhibit a wide range and reflect contributions from continental crustal reservoirs. To explain the observed variations in trace elements and isotopes, we propose a simple model involving simultaneous bulk assimilation (A) and imperfect fractional crystallization (IFC) in an open igneous system, where crystal accumulation and assimilation occur concurrently. Especially, deep crustal physicochemical interaction of primitive arc magmas with supracrustal host rocks may mask the expected clear signature of subarc mantle petrological processes. Our assessment of the Famatinian-Puna arc, an ancient subduction zone, concurs with estimates from active volcanic arcs, underscoring the general applicability of this study case to subduction zone magmatism. [Display omitted] • The study stresses underlying phenomena complicating the geochemical interpretation. • The pre-arc continental crust is an essential part of the subduction factory. • Crustal contamination could mask the signature of the subducting sedimentary layer. • Lithophile trace elements influx into the mantle wedge comes from subducted sediments. [ABSTRACT FROM AUTHOR]

Abstract: The crustal structure of the Famatinian paleoarc is reconstructed by determining the metamorphic crystallization P–T conditions from metasedimentary rocks at various structural levels in the Valle Fértil section. The bulk section exhibits a 15-km-thick arc crustal section. Thermobarometry shows that nested tonalitic and granodioritic plutons constructed the arc crust at depths <20km. Dioritic and tonalitic bodies dominated between 20 and 25km. The deepest exposed paleodepths are formed by cumulate and non-cumulate gabbroic rocks with interlayered quartz diorites that crystallized below 25km. The boundary between the crust and the lithospheric mantle is not observed and would have been underneath a depth of 27km. P–T estimates throughout the section reveals high geothermal gradients ranging from 25°C/km to 35°C/km. The thermal regime inferred for middle crustal levels is observed in active and ancient magmatic arcs. Thermophysical models predicting the array of retrieved P–T estimates require heat advection conducted by mafic magmas which either emplaced in the lower crust and/or intruded into middle crustal levels. Calculated seismic wave velocities of plutonic rocks dominating progressively deeper paleodepths are used to deduce the internal architecture of the Valle Fértil section. This result indicates that the Famatinian arc had a middle crustal structure very similar to that of the ancient Talkeetna arc; however a rapid increase of seismic wave velocities from ~6.3km/s to >6.6km/s is located at deeper depths in the Famatinian arc than in Talkeetna arc. The thickness of a crustal layer dominated by plutonic rocks with low seismic wave velocities (<6.2km/s) is 10km thinner than the crustal layer with similar physical properties in the Sierra Nevada batholith. A putative model for the whole Famatinian arc suggests a total crustal thickness between 30 and 35km with three distinct layers. [Copyright &y& Elsevier]

Las Cañas Plutonic Complex (LCPC) is a small representative of the Famatinian Ordovician plutonism (470.4 ± 8.1 Ma) located in the northeastern sector of Sierra Grande de San Luis, Argentina. The LCPC was emplaced into a metasedimentary sequence, which reached their metamorphic climax under high-temperature/low-pressure conditions (∼680 ± 37 °C and 550 ± 120 MPa). The bodies of the LCPC are zoned by rocks of different compositions that represent ultrabasic, basic, intermediate and acidic trends (hornblendites, gabbros, tonalites, and granodiorites). Their petrological, mineralogical and geochemical characteristics indicate that multiple processes formed them, mainly crystal fractionation of magnesian, calc-alkaline and metaluminous magmas (typical of arc), but also different assimilation degrees of crustal melts from the fusion of metawackes involving AFC processes. Fieldwork (structural and petrological data), the geochemical characteristics of rocks [eg. Low Sr/Y and (Gd/Yb) C- N ], and thermobarometric results, indicate a relatively shallow fractionalization for the LCPC, which is in line with a pre-collisional arc stage linked to an extensive retro-arc setting for the Famatinian orogeny in Sierra de San Luis. • A new Ordovician absolute age was determined for Las Cañas Plutonic Complex. • The geology and petrology show that the plutons are composed of several facies. • Geochemical modeling indicates multiple processes for the plutonic rocks origin. • The geotectonic setting during the emplacement of the plutons is discussed. [ABSTRACT FROM AUTHOR]

Large masses of turbidite systems have been metamorphosed in orogenic systems during Earth's history. Under granulite-facies conditions, the transformation of turbidite sedimentary successions into metasedimentary sequences drives intracrustal differentiation by anatexis and melt–residuum separation. We report on a migmatite terrane developing from turbidite successions that were buried into the deep crust during the Neoproterozoic to Early Cambrian Pampean orogeny, in central Argentina. At the exposed middle crustal paleodepths, migmatites occur on the regional scale but lithological zones are characterized by (1) bedded migmatites, (2) metatexite, and (3) diatexite. Bedded migmatites are the low-temperature part of the migmatite terrane where the alternating metapelite and metagreywacke layers are traceable among migmatites of different protoliths. The temperature (> 790 °C) was sufficient high for melting the metapelite, but not for melting the metagreywacke. The majority of the migmatite terrane consists of stromatic metatexites in which the limit among different progenitors is either faint or erased by migmatization. Metatexite zone acts as melt transfer in the migmatite terrane. In the stromatic migmatites, the major oxide composition of leucosomes and tabular bodies of leucogranite resembles those of the glasses of experimental petrology. However, leucosomes and leucogranites are crystallized melts that have low Zr, Th and LREE contents and positive Eu anomalies resulting from accessory mineral retention in melting residues. The transformation of metatexite into diatexite is gradational over tens of metres, and related to an accumulated melt fraction that dismembers the stromatic fabric. The most abundant diatexite is mesocratic, and has little or lacks K-feldspar. A subordinate proportion of diatexites is leucocratic, contains K-feldspar phenocrysts, and shows igneous-like textures. Leucogranites and leucocratic diatexites are the potential carriers of an anatectic melt-rich component from granulite-facies migmatite sequences toward shallow crustal levels. Turbidite successions are fertile protoliths that undergo widespread melting under low granulite-facies temperature (< 850 °C), and the development of large diatexite massifs makes them suitable sources of granitic magmatism. [ABSTRACT FROM AUTHOR]

The Ordovician rocks of Sierra Las Planchadas are an exceptionally preserved natural example of a plutonic-volcanic connection. Located in northwestern Argentina, the Las Planchadas Formation consists of a monzogranitic batholith that displays a window into the source of large subvolcanic rhyolitic rocks, cryptodomes and volcanic feeder-dykes. Mafic intrusions and felsic dykes occur cutting the plutonic rocks. Grain-scale relationships, whole-rock compositions and mineral chemistry indicate that monzogranites and rhyolites are two comagmatic members which differentiated within upper crust magma reservoirs. Monzogranites accumulated some plagioclase and trapped a large volume of melt, denoted by a high modal percentage (~64–71%) of near-solidus minerals, comprised of alkali feldspar, albite-rich plagioclase (An <30), and late crystallized quartz. The formation of felsic dykes and rhyolitic cryptodomes is the result of a late melt extraction stage facilitated by the injection of hot mafic magmas from deeper in the system. The mafic-induced thermal reactivation increased the amount of melt-filled pore stored within a highly-crystallized monzogranite reservoir. The breakdown of the low-temperature phases overpressurized the mush and opened a network of microfractures into which residual melts, depleted in feldspar-compatible trace elements (Ba, Sr, and Eu), infiltrated. The draining system involved thin interconnected vein-like channels that merged into wider sheet-like conduits. Our results suggest that channelized segregation of late-stage melts in the subvolcanic environment is a mechanism for triggering rhyolitic eruptions. • Las Planchadas Formation exposes a monzogranitic-rhyolitic stratified magma chamber of the Famatinian magmatic arc. • The plutonic-volcanic construction involved low-pressure crystal fractionation within a single upper-crustal magmatic system. • Thermal reactivation drove late remobilization of residual melts depleted in feldspar-controlled trace elements. • Channelling of felsic melt through a highly crystallized reservoir acted as a potential volcanic feeding mechanism. [ABSTRACT FROM AUTHOR]

Trace element abundances in constituent minerals from mafic and ultramafic rocks of a deep arc crustal section are studied to observe their abundance and distribution. Five cumulate rocks were selected from a sequence that consists of pyroxene hornblende peridotite, olivine hornblende gabbronorite, pyroxene hornblende gabbronorite, hornblende gabbronorite, gabbro and anorthosite. Solid/liquid partition coefficients calculated with the equilibrium distribution model indicate that Cr, Ni, Co, Zn and V are highly compatible with an olivine-dominated mineral assemblage from the mafic and ultramafic cumulates. The compatibility of Ti and Sc would be dependent on the stability of clinopyroxene, amphibole and oxides in the magmatic system. With few exceptions, the other trace elements are incompatible with the minerals that form the cumulate. At most half the mass of Sr carried by a primitive arc magma could be stored in anorthite-rich plagioclase from the mafic cumulates. Magmatic amphibole fractionates Y, middle and heavy REE from other incompatible elements during crystal accumulation of mafic cumulates. In contrast, late magmatic to subsolidus amphibole has no effect on the differentiation of a primitive arc magma. In fact, the trace element variability of amphibole and clinopyroxene is easily related to different stages of magmatic evolution within the cumulate pile. The results presented here are helpful for modelling other cases of arc magma petrogenesis where the cumulate rocks with dominant mafic assemblages are not exposed. [ABSTRACT FROM AUTHOR]

The Sierra Valle Fértil Complex of west-central Argentina represents a section of the Ordovician (~470 Ma) Famatinian arc and exposes a continuous, tilted crustal arc section ranging in depth from ~12 to 32 km (~4-8 kbar pressure). This arc section exposes the complete compositional architecture from ultramafic and mafic rocks to upper crustal granodiorites. Field and compositional data are presented to document the deep (~6-8 kbar) mafic complex of the Sierra Valle Fértil. The mafic complex is composed of many tens to hundreds of plutonic cumulate bodies in a complex and non-regular arrangement. There is no simple compositional, kinematic or age relationship between neighboring plutons throughout the section, as expressed by cumulate compositions, emplacement horizon, size, composition, texture or style of contact. Amphibole gabbronorites and mafic tonalites dominate, but norites, amphibole websterites, troctolites and minor anorthosites are present. Amphibole is common but always as a replacement phase, and is never observed undergoing subsequent dehydration melting. Hence there is no evidence that voluminous tonalites were produced by dehydration melting of mafic precursors. A field-based, cumulate-removal fractionation model is presented that produces the observed compositional variations in five steps. Isotopic compositions of Sr and Nd deviate significantly from primitive mantle values, indicating a crustal contribution; however, this hybridization appears to have played a minor role in the major element evolution of the mafic complex. We interpret this isotopic and elemental decoupling as a byproduct of prolonged, punctuated MASH (melting, assimilation, storage, homogenization) processes in the lower crust. Isotopes may be the only residual evidence of assimilation within the mafic zone. This requires that melt removal from the cumulates was extraordinarily efficient. [ABSTRACT FROM AUTHOR]

The reactivation of existing faults has long been recognized to control the location and style of deformation in orogenic systems including the Sierras Pampeanas in the southern Central Andes; however, it can remain difficult to resolve the timing and fault kinematics across multiple orogenic phases. In the Sierras Pampeanas, basement-cored range-bounding faults mark a Paleozoic terrane boundary and are seismically active; however, the protracted history of deformation along this lithospheric-scale regional fault system - located ~400 km from the plate boundary - has been poorly constrained. In this study, we present new apatite (U–Th-Sm)/He and fission track thermochronology data and thermal history models from ten samples from the Sierra de Valle Fértil-La Huerta in the Western Sierras Pampeanas of Argentina. The spatio-temporal patterns of rock heating and cooling identified by our thermal history models throughout this fault system are consistent with four discrete phases of deformation. Thermal patterns indicative of Mesozoic extensional deformation and latest Miocene - Pliocene compressional deformation corroborate previous interpretations of regional deformation episodes in the Sierras Pampeanas. Our study also identifies a period of middle-Miocene cooling that revises the location of the Andean thrust front. This episode of deformation was previously unrecognized in the Sierras Pampeanas and is contemporaneous with thin-skinned deformation in the adjacent Precordillera thrust belt. A Paleogene phase of cooling may also support a phase of compressional deformation in the Sierras Pampeanas during a period in which neutral tectonic conditions have been proposed along the Andean margin. Our findings outline a history of fault reactivation suggesting that the long-lived fault systems in the Sierras Pampeanas are sensitive to plate-margin processes. • Thermal modeling of AHe-AFT data records fault reactivation across orogenic cycles. • Faults in the Sierras Pampeanas are highly sensitive to distal plate-boundary stress. • Thermal record of Mesozoic extension preserved along Cenozoic reverse fault. • Near-fault cooling shows multi-phase Cenozoic compression events. • High Mio-Pliocene exhumation is identified in nearly all samples in the Sierra Valle Fértil-La Huerta. [ABSTRACT FROM AUTHOR]

The granulite-complexes of the Sierras de Córdoba, inside context of Sierras Pampeanas, expose the deeply-uplifted internal metamorphic zone of an early Cambrian orogen. One of the largest granulite-complexes in the north-central of Sierra de Comechingones consists mainly of a set of stromatic and diatexitic migmatites all derived from metasedimentary progenitors. Migmatites vary over a spectrum of morphologies ranging from patch, net, and stromatic metatexites to schollen-schlieren and nebulite diatexites with widespread interspersed anatectic granites. The granulite-complex subordinately includes amphibolites, marbles, serpentinized ultramafic rocks, and mafic plutonic rocks. Petrographic analysis, textural and structural interpretation, thermobarometric estimates, and inherited and metamorphic zircon dating reveal the metamorphic history of migmatites in the north-central part of the Sierra de Comechingones. Metastable preservation of kyanite reflects that migmatites were buried (0.69–0.78 GPa) and heated (~650 °C) along a prograde trajectory before the onset of extensive anatexis. Then migmatites were further heated to granulite-facies peak temperatures (≥800 °C) at similar pressures (0.77 ± 0.06 GPa) through the sillimanite stability field. Widespread partial melting of the metasedimentary sequence occurred during peak metamorphism. The entire granulite-complex cooled to temperatures below 550 °C and ascended to middle crustal depths (0.3–0.5 GPa). The prograde heating trajectory and decompression during uplift overcoming cooling and tectonic exhumation are compatible with a predominantly compressive deformation. Coeval widespread partial melting with contractional non-coaxial deformation triggered self-reorganization of anatectic melts giving rise syn-deformational migmatites. In all the analyzed migmatites, U–Pb zircon geochronology yields inherited ages corresponding to those of orogenic systems that characterize the West Gondwana supercontinent. Inherited ages show a polymodal distribution pattern with contributions from Neoproterozoic (551–734 Ma; i.e., Brasiliano - Pan-African) and Mesoproterozoic detrital zircons (850–1182 Ma; i.e., Grenvillian), and minor proportions of Paleoproterozoic zircon grains (1751–1839 Ma). Ages interpreted as metamorphism and anatexis suggest the development of a single metamorphic event and restricted anatexis to a relatively short period of about 15 Ma (ca. 540-525 Ma). Metamorphic ages associated with the metamorphic peak trajectory are related to the Cambrian Pampean Orogeny. • P-T- t path shows a clockwise evolution along a single metamorphic event. • U–Pb zircon geochronology constraints granulite-facies metamorphism to ~540-525 Ma. • Metamorphic evolution was coeval with a compressive non-coaxial deformation. • Metatexites and diatexites are Early Cambrian syn-deformational lithological products. [ABSTRACT FROM AUTHOR]

Four major igneous suites with different geochemical characteristics are identified in the accretionary complex of the Pampean orogeny from the southern Sierras de Córdoba, Argentina. Crystallization ages of gabbroic and trondhjemitic plutonic rocks are Early to Middle Cambrian. The plutonic suites include mafic to intermediate alkaline OIB-like rocks, mafic tholeiitic N-MORB rocks, transitional mafic rocks, and minor trondhjemitic rocks with adakitic geochemical signature. The multiple igneous suites are spatially and temporally related to what reveals simultaneous tapping of distinct source reservoirs with their respective melts remaining distinctive from extraction to emplacement at middle crustal depths. The alkaline mafic-intermediate rocks with OIB-like geochemistry were generated by the partial melting of an enriched or metasomatized mantle source. By contrast, tholeiitic mafic rocks with N-MORB geochemical signature came out from a depleted mantle source. Trace element abundances of the transitional mafic magmas reflect variable mixtures between OIB-like and MORB-type magmas. Trondhjemitic rocks exhibit geochemical features highlighting their parent melts formed by low degree melting of a metasomatized subducting oceanic crust. The most reliable setting to generate all these diverse magmatic suites at the same time is a convergent margin where the opening of a slab window followed ridge-trench interaction. A corollary is that widespread mafic magmatism enhanced heat advection and gave rise to extensive intra-crustal anatexis in an accretionary complex of crustal extension. • Coexistence of multiple magmatic sources in the Early to Middle Cambrian Pampean orogen. • Alkaline, transitional and N-MORB mafic magmas intruded into metamorphic sequences. • Trondhjemite silicic adakite magmas spatially associated with alkaline mafic magmas. • Atypical subduction environment driven by slab-window following active ridge subduction. [ABSTRACT FROM AUTHOR]

The Valle Fértil-La Huerta batholith is a differentially tilted, compositionally stacked, calc-alkaline plutonic sequence in the central Famatinian arc of Argentina. It consists of two major lithologic units: these are (1) an intermediate unit largely dominated by amphibole- and biotite-bearing tonalites but encompassing from gabbro to leucogranite; and (2) an overlying silicic unit that shows the same petrological diversity as the intermediate unit, but granodiorite and monzogranite are its prevailing lithologies. The silicic unit is separated into four subunits using lithological changes at regional mapping scale. All the boundaries are gradational among lithologic units and subunits. The internal fabric along the entire batholith is either magmatic or submagmatic and it was developed during the arc formation. The original magmatic foliation is north–south striking and steeply-dipping. The magmatic foliation crosses over and transposes the gradational contacts among lithologic units. Petrological architecture, structural geology, geobarometric estimates and geochronology show that the entire batholith is a comagmatic system exposing more than 13 km of a middle arc crust. Crystallization-fractionation models computed using whole rock and mineral chemistry account for the mineralogy of plutonic rocks and coincide with the results of experimental petrology. Mass-balanced modeling predicts that the unexposed cumulate roots of the Famatinian arc should have been about 1.3 times larger than the intermediate and silicic plutonic batholith. However, the mass of calculated cumulate would diminish significantly if a portion of the host metasedimentary material were consumed in constructing the batholith. The batholith grew progressing upward from the lowest levels and acquired a stratified compositional organization. The driving mechanism was continuous influxes of mantle-derived mafic magmas that made up the lower crust, caused crustal-level melting and magma mixing, and formed intermediate – silicic rocks at increasingly shallower depths. • The plutonic middle crust of the Famatinian arc was at least 13 km thick. • The plutonic crust grew progressing upward and acquiring a stratified organization. • Pre-arc metasedimentary sequences play a role in fertilizing the magmatic system. • Modeling yields a 1.3:1 ratio of cumulates over derivatives to make the magmatic column. • A few tens of kilometers of cogenetic cumulates are lost in the Famatinian arc. [ABSTRACT FROM AUTHOR]