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The Sierra de Famatina of northwestern Argentina contains one of the best Cambro-Ordovician stratigraphic records of the SW Gondwana margin. Two lithotectonic belts (Calalaste–Narváez and Famatina–Valle Fértil), separated by master faults, preserve evidence of two former volcano-sedimentary basins (Eastern and Western, respectively). The Calalaste–Narváez Lithotectonic Belt consists of an Ediacaran to early Cambrian basement unconformably overlain by a 490–480 Ma cover of very low-grade volcano-sedimentary and volcanic succession that presumably formed in an extensional tectonic regime. In contrast, the Famatina–Valle Fértil Lithotectonic Belt comprises a basement consisting of the late-lower-to-middle Cambrian metasedimentary Achavil and Negro Peinado formations unconformably overlain by meta/sedimentary and metavolcanic rocks ranging in age from the late Cambrian to the Middle Ordovician (ca. 490–460 Ma). This belt includes the Famatinian Cordilleran-type magmatic arc active mainly at ca. 473–468 Ma, coeval with andesite to rhyolitic volcanism (Suri and Las Planchadas formations). Rhyolitic tuffs of ca. 473 Ma (εNdi = − 4.1) were found in the La Aguadita Formation, allowing this unit to be re-assigned to the late Floian. The oldest magmatism of the Sierra de Famatina is characterized by isotopically evolved (εNdi = − 5.1) rhyolitic tuffs of ca. 490 Ma in the Bordo Atravesado Formation, which was coeval with deposition of Mn-enriched hydrothermal cherts. This early Famatinan volcanism contrast with that of similar age and isotopically less evolved occurred in the Calalaste–Narváez Lithotectonic Belt suggesting variations of the source of magmas across the space and time within the Famatinan Orogenic Cycle. We propose that both described lithotectonic belts likely diverge northwards into Chile and Peru, wrapping around the Arequipa–Antofalla Proterozoic block. [ABSTRACT FROM AUTHOR]

A sample of micaceous schist of the Cushamen Metamorphic Complex in the Cushamen area (northwestern North Patagonia, Argentina) preserves a complex mineral assemblage, including staurolite, andalusite, garnet, sillimanite, biotite, quartz, and plagioclase. This unit proves an opportunity to analyse a complex mineral association often related to disequilibrium stages or polymetamorphic contexts. Through detailed petrological analysis combining mineral chemistry, X-ray compositional maps, conventional thermobarometry, and phase equilibria analysis, we reconstructed the pressure–temperature (P–T) path of this schist. The schist unit preserves a polymetamorphic history characterized by M1, M2, and M3 events. The M1 event is represented by biotite, muscovite, quartz, and plagioclase. The M2 event, associated with local mid-Carboniferous pluton intrusion, is characterized by andalusite and garnet assemblages, with peak conditions at ~ 3.3 kbar and ~ 563 °C. The main M3 event, at the time of the Carboniferous–Permian boundary, is defined by garnet, staurolite, sillimanite, biotite, muscovite, plagioclase, and quartz. This event records a progressive P–T evolution from ~ 3.5 kbar and ~ 553 °C to ~ 4.9–5.6 kbar and ~ 620–635 °C, nearing peak conditions. This work highlights the importance of comprehensive approaches in P–T trajectory reconstructions and the critical role of selecting the reactive bulk composition, particularly in rocks with complex mineral assemblages. In addition, this study significantly contributes to understanding the metamorphic evolution of the Cushamen Complex, a unit for which there is limited knowledge regarding its structural and metamorphic evolution. This complex is part of the igneous-metamorphic basement of North Patagonia region (Argentina), which records the Paleozoic evolution of the southwestern margin of Gondwana. [ABSTRACT FROM AUTHOR]

This paper focuses on one orogenic belt that formed during the Rinconada phase on the final stage of the Famatinian orogeny, between 445 and 410 Ma, which is well exposed at Sierra de Ramaditas and neighbouring ranges in western Argentina. The Ramaditas Complex is formed by metasedimentary and meta-ultrabasic rocks and amphibolites. This complex forms the upper nappe of a thrust stack resulting from westward thrusting. Deformation consists of an early high-temperature S1 foliation (stromatic migmatites), coeval with thrusting and metamorphism. Metamorphism attained peak P–T conditions of 6.0–6.9 kbar and 795–810 °C, at c. 440 Ma, i.e. coincident with the Rinconada orogenic phase. The lower unit and intermediate nappes crop out in the nearby sierras of Maz and Espinal and underwent low- to medium-grade Silurian metamorphism, respectively, together with the upper nappe, defining an inverted Barrovian-type metamorphism with T decreasing and P increasing downwards across the thrust stack (i.e. westward). We argue that the Rinconada orogenic phase developed near the continental margin of SW Gondwana, during a magmatic lull following accretion of the Precordillera terrane to the continental margin at c. 470 Ma. The active margin jumped to the west after accretion, and flat-slab subduction resumed in the early Silurian, provoking thrusting and imbrication of nappe stack under the still hot root (800–900 °C) of the older Famatinian magmatic arc. This 'hot-iron' process explains both the inverted Barrovian-type metamorphism and the missing overburden of 21 to 24 km implied by the P estimate. [ABSTRACT FROM AUTHOR]

The analysis of major and trace elements in zoned minerals is useful for deciphering parts of the tectonothermal evolution of polymetamorphic tarrain. We applied this approach to the Maz Metasedimentary Series in Western Sierras Pampeanas of Argentina, where polymetamorphism resulted in the overprinting of a Grenvillian basement (the Maz Complex) during the pervasive Rinconada tectonic phase of the Famatinian orogeny. The older metamorphism (M1) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M2) was Silurian to early Devonian, essentially between 440 and 410 Ma. The latter resulted from oceanward migration of the orogenic front relative to earlier late Cambrian to Ordovician (490–470 Ma) tectonic phases of the Famatinian orogeny. The M1 and M2 metamorphic events have been recognized in a staurolite‐garnet schist from the Maz Metasedimentary Series. Most metamorphic minerals from this rock were formed during the M2 event which was of the Barrovian type (±kyanite). Part of the metamorphic P–T evolution is recorded in the complex compositional zoning of garnet porphyroblasts. Three types of garnet were identified based on texture and chemistry, including trace elements (REEs). Phase equilibrium analysis, compositional isopleth, and multi‐equilibrium thermobarometry were applied in order to establish the P–T history. M1 is represented by preservation of Grt1 ± Kfs ± Sil, with peak P–T condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D1 episode represented by a relict S1 foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M2 followed a clockwise P–T path with three mineral growth stages. The earliest occurred at ~585°C and ~8.7 kbar and is represented by Grt2 ± St1 ± Bt1 + Qz. Grt2 was partially coeval with growth of St1, which was stable at ~625°C and 9.0 kbar. Grt2 + St1 are syn‐kinematic to the main S2 foliation (D2 episode). Subsequently, decompression (D3) started as St2 (+ Bt2 + Ms1 + Qz + Pl) crystallized, and garnet was partially consumed at ~612–620°C and ~7.3–7.7 kbar. St3 + Grt3 crystallized at ~608°C and ~6.8 kbar at the end of D3. Increasing P–T conditions during the earlier M2 growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D2). Peak metamorphic conditions were attained during thrust stacking. The tectonic phase (D2) was responsible for the main S2 foliation, which was penetrative at all scales. The nearly isothermal decompression path is compatible with exhumation, probably resulting from extension along discrete shear zones (tectonic phase D3) that produced a mylonitic foliation S3. [ABSTRACT FROM AUTHOR]

Variations in the pressures and temperatures of metamorphism reflect the complexity of collisional orogenic systems. In the north‐west Sanandaj–Sirjan Zone of western Iran, migmatites in the Boroujerd area record earlier dynamothermal metamorphism followed by the development of a contact metamorphic aureole induced by the Jurassic Boroujerd Batholith. Integrated micro‐textural observations, mineral compositions, and the results of phase equilibrium modelling indicate that peak metamorphic temperatures reached 640–660°C in andalusite schists and ~700°C in cordierite–sillimanite migmatites. The pressure does not exceed 3.5 kbar, implying a maximum depth of ~13 km. A hairpin clockwise P–T path in the Boroujerd region was inferred from mineral relations (e.g., replacement of andalusite1 by sillimanite in the migmatites in the heating stage, which was followed by a retrograde episode with growth of andalusite2) and P–T pseudosections. Metamorphism of the Boroujerd area was coeval with voluminous intermediate–mafic magmatism, which provided the heat necessary for partial melting. This study demonstrates that metamorphic sequences of the north‐west Sanandaj–Sirjan Zone developed under similar metamorphic conditions in the Lower to Middle Jurassic and record an extensional back‐arc setting related to the subduction of Neo‐Tethys. [ABSTRACT FROM AUTHOR]

The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545-520 Ma) and Famatinian (490-440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate-siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U-Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Río de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Río de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought. [ABSTRACT FROM AUTHOR]

The Sierra de Guasayán (Eastern Sierras Pampeanas, Argentina) is formed by low to medium grade metamorphic rocks intruded by Cambrian metaluminous (La Soledad quartz-diorite), slightly peraluminous (Guasayán, El Escondido and El Martirizado granodiorite plutons), and strongly peraluminous (Alto Bello granodiorite) granitoids of the Pampean magmatic arc. Chemical compositions of amphibole, plagioclase, biotite, and titanite indicate that these granitoids were emplaced at low pressure (mostly <3 kbar) and temperature (<770 °C) under oxidizing conditions (QFM + 1 and QFM + 2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. Mineral assemblages and whole-rock and mineral chemistry of the granitoids from the Sierra de Guasayán indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, and titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, and sillimanite), and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, and magnetite). This hybrid nature is supported by the presence of abundant mafic microgranular enclaves and rapakivi texture and by published zircon Hf-isotope data (εHfi ranging from −4.76 to −0.12). This suggests, in turn, the involvement of hybridization in the genesis of these granitoids, which seems to be a common mechanism operating in the Pampean magmatic arc. [ABSTRACT FROM AUTHOR]