Unraveling the petrogenesis of the Miocene La Peña alkaline intrusive complex, Mendoza, Argentina: Insights from the study of the disregarded late dykes

The La Peña Complex (LPC) is a silica-undersaturated alkaline potassic intrusive system, with a subduction-related signature, linked to the early Miocene retroarc magmatism of the Southern Central Andes, in the flat slab segment. The LPC is composed of several intrusions, predominantly plutonic (clinopyroxenite, malignite and syenite), cross cut by a voluminous swarm of radial and annular dikes with mostly volcanic-subvolcanic textures and variable compositions (foid-bearing alkali feldspar trachyte, trachyte, benmoreite, ledmorite, syenite, tephrite, tephriphonolite and alkaline lamprophyre). In the TAS classification these rocks plot in the alkaline series covering a wide spectrum of compositions following two different trends: 1) alkaline (potassic) strongly silica-undersaturated series, from tephrite, phonotephrite to tephra-phonolite, and 2) mid-alkaline, less silica-undersaturated series, ranging from basaltic trachyandesite to trachyandesite (benmoreite), and trachyte. Dikes from the alkaline series show higher K2O/Na2O ratios and Sr, La, Ce, contents compared to those from the mid-alkaline series. Rocks of the alkaline series are richer in K-feldspar, sodalite, leucite (pseudoleucite), biotite, potassic-ferro-pargasite and garnet than the less silica-undersaturated (trachytic) rocks, reflecting a stronger alkaline potassic affinity. A review of geochemical, isotopic and mineralogical data, and a new geochemical modeling performed on the LPC dikes, suggests that both trends represent separated magmatic series that evolved from two different parental magmas lodged ∼30 km deep in the crust. Our results suggest that the compositional variations observed in LPC dikes, cannot be explained by a simple magmatic evolution via fractional crystallization from a unique parental magma, and that an assimilation and fractional crystallization (AFC) process is required to explain some compositional differences. Our results suggest an upper crustal contaminant (evolved rocks) with a Grenvillian isotope signature. On the other hand, analyses of feldspar crystals from the tephriphonolitic dikes indicate local mixing effects, between an evolved tephriphonolitic melt and a less evolved and hotter mafic magma. The origin of both parental magmas could be explained by different melting degrees of the same mantle source, a phlogopite-bearing spinel lherzolite metasomatized by subduction derived fluids. We consider as a possible explanation that alkaline and coeval calc-alkaline magmatism in this part of the Andes, is due to local heterogeneities in the mantle source, and different degrees of partial melting Similar isotopic compositions of the LPC dikes, with those from other Miocene magmatic occurrences with arc-signature and similar age (e.g., Paramillos de Uspallata, Las Máquinas basalt, Abanico Fm and Farellones Fm) suggest an analogous mantle source for these rocks, from arc and retroarc in the Pampean flat slab regions. However, our results suggest that the isotopic trend contamination of LCP is different from that of Paramillos de Uspallata and other arc rocks of the Southern Volcanic Zone. The crustal contaminant of LPC possibly has another composition that those of Precordillera and Principal Cordillera Miocene rocks. The age of LPC rocks (∼19 Ma) and their arc-related signature agree with the eastward broadening of the arc magmatism between 17 and 19 Ma in this part of the flat slab. According to our interpretations, the LPC is a singular occurrence of two alkaline magmatic series on destructive plate margins, associated with calc-alkaline magmatism, occurring closely in time and space.Fil: Pagano Género, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Enriquez, Eliel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Morosini, Augusto Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Ibañes, Oscar Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Muñoz, Brian Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: D'eramo, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Architecture and kinematics of the Famatinian deformation in the Sierra Grande de San Luis: A record of a collisional history at 33° S latitude

An improved understanding of the evolution of the Famatinian basement in the Sierra Grande de San Luis (SGSL) in Argentina is presented. Combining geological, geophysical and petrological data, a 3D inversion model for the basement rocks and their shear zones in the study area was constructed. The inversion model and the ground data show that the main deformation mechanism that affected the metamorphic complexes is related to a significant number of shear zones which delineate the architecture of the basement. Results suggest that the regional scale shear system (~40 km wide and ~120 km long) and the internal structural elements of the different tectonic domains are the product of an important crustal shortening. A contractional tectonic framework related to the indentation of the Cuyania/Precordillera microcontinent on the western Gondwana margin is proposed to be the cause of the tectonic mechanisms that led to a pop-up megastructure in the western sector of the SGSL and the closing of the Famatinian backarc.Fil: Morosini, Augusto Francisco. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Christiansen, Rodolfo Omar. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Enriquez, Eliel. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Pagano Género, Diego Sebastián. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Perón Orrillo, Juan Matías. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Ortiz Suarez, Ariel Emilio. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Martínez, Myriam Patricia. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Muñoz, Brian Lucas. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; ArgentinaFil: Ramos, Gabriel Alejandro. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentin

Una antigua cordillera

Las sierras de San Luis se encuentran ubicadas en el centro de Argentina sobre el sector noreste de la provincia de San Luis. Constituyen grandes bloques rocosos constituidos principalmente por rocas ígneas y Metamórficas que reflejan la actividad orogénica (formación de una cordillera) que tuvo lugar hace 470 a 320 millones de años. En aquellos momentos dos placas tectónicas que transportaban los continentes de Cuyania, al oeste, y Pampia, al este, colisionaron provocando metamorfismo y fusión. Hoy las rocas que se formaron en aquellos lejanos tiempos forman parte de uno de los mayores atractivos turísticos de la región.Fil: Pagano Género, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; Argentin

Metallogenesis of the Totoral LCT rare-element pegmatite district, San Luis, Argentina: A review

The Totoral Pegmatite District (TPD) is the southernmost rare-element LCT pegmatite field of the Pampean Pegmatite Province. The TPD produced intermittently in the last 60 years Ta-Nb ore minerals, spodumene, beryl and ceramic raw materials. It is located in the southern part of the Eastern Pampean Range of San Luis province. It was developed during the late stage of accretion of the Famatina terrane to the West Gondwana in the Lower Paleozoic (≈450 Ma). The parental S-type leucogranites and rare-element pegmatites of REL-Li subclass form three groups aligned NNE. The leucogranites were originated by muscovite (±incipient biotite) dehydration melting of preferably metapelites (±metagreywackes) of the Pringles Metamorphic Complex (PMC). The resultant bimodal suite of S-type muscovite-tourmaline and muscovite-biotite leucogranites show major, trace elements, and Pb-Ba ratios compatible with both low-T and higher-T collisional leucogranites. These leucogranites were emplaced after regional metamorphism in the upper part of the mica schists unit of PMC at 640–725 °C and ≈400–500 MPa, and they fractionated to their associated pegmatites as is supported by the spatial association, similar age and fractionation trends of leucogranites and pegmatites. The regional integrated pegmatite zoning shows the sequence: leucogranite, pegmatitic leucogranite, barren-transitional to beryl-type, beryl-columbite-phosphate subtype, albite-spodumene type, complex-type spodumene-subtype and albite type rare-elements pegmatites. This zonation follows a path towards decreasing pressure of emplacement. The crystallization of pegmatites was triggered by the rapid undercooling provoked by the thermal contrast due to the fast forced emplacement in the hosting mica schists and the H 2 O and fluxes content of the melts that produced nucleation delay and high crystal growth rate of the minerals. The Li-bearing pegmatites have genetic links with the higher-T leucogranites. The emplacement of the pegmatites was facilitated by a shear zone, and they show synkinematic ductile-state deformation ascribed to the late stage of the Famatina terrane accretion. Later on, most of them were tectonically affected in brittle state by the diastrophism attributed to the westward accretion of the Cuyania terrane.Fil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Pagano Género, Diego Sebastián. Universidad Nacional de San Luis; Argentina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Emplacement of the La Peña alkaline igneous complex, Mendoza, Argentina (33° S): Implications for the early Miocene tectonic regime in the retroarc of the Andes

The La Peña alkaline complex (LPC) of Miocene age (18–19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400–2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km2 and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW–SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N–S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R′), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW–SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by dikes cross-cutting the clinopyroxenite, (3) a malignite facies that causes a small breccia in the clinopyroxenite, (4) a central syenite facies that develops breccias at the contact with the clinopyroxenite and, finally, (5) porphyry necks and a system of radial dikes intruding all units. At the moment of the emplacement different mechanisms would have acted, they summarized in: 1) opening of discontinuities synchronous to the magma circulation as the principal mechanism for formation of dikes and conduits; 2) stoping processes, that play an important role in the development of the breccia zone and enabling an efficient transference of material during the emplacement of the syenitic magma and 3) shear-related deformation (regional stress), affected the internal fabric of the facies, causing intracrystalline deformation and submagmatic flow, which is very evident in the central syenite intrusive. The kinematic analysis of shear planes allows proposing that emplacement of the LPC took place in a transtensive regime, which would have occurred in the back-arc of the Andes orogen, during a long period spanning from Miocene to the present, of the compressive deformation responsible, westward and at the same latitude, for the development of the Aconcagua fold and thrust belt.Fil: Pagano Género, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Artes y Diseño; Argentin

Petrology and mineralogy of the La Peña igneous complex, Mendoza, Argentina: An alkaline occurrence in the Miocene magmatism of the Southern Central Andes

The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32°41´34″ S - 68°59´48″ W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several Cu-Fe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite.The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes.Mineral and whole-rock chemical compositions support the interpretation that a first batch of a tephritic magma produced a cumulate of clinopyroxenite (clinopyroxene + magnetite + apatite) and a residual melt that crystallized as malignite at a shallow emplacement level (<5 km). Fractional crystallization in a deep chamber, coupled with rock assimilation, produced successive magma pulses that gave the composite central syenite, the syenitic and trachitic porphyries, and trachytic dikes. The latest rocks (phonolites) reflect an extreme fractionation with Ca, Al and K removal by feldspars. Mingling relationships between tephrites-basanites and trachytes-phonolites, plus compositional variations linked to the reabsorption surface observed in the K-feldspar from the phonolitic dikes, suggest recharge events with local mixing in the late-stages of the LPC evolution.The emplacement of the LPC melts at a shallow crustal level was favored by the aperture of extensional NNW-SSE fractures genetically linked to a local brittle shear zone, active at 18-19 Ma during a strong compressional event, that initiated the regime of flat-slab subduction in this part of the Andes.Fil: Pagano Género, Diego Sebastián. Universidad Nacional de San Luis. Facultad de Ciencias Físico- Matemáticas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Petrography, mineralogy, and origin of the syenite pegmatitic segregation veins from La Peña alkaline complex, Mendoza, Argentina

The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Pẽna alkaline complex (LPC), Mendoza, Argentina, are emplaced in a malignite body. They occur as veins, parallel layers, and small elliptical bodies 1 to 6 cm wide and 0.2 to 1 m in length. The veins with a pegmatitic to micropegmatitic texture have a thin dark border composed of andradite, potassic-hastingsite, and dark micas and a thicker internal zone of poikilitic Ba-Sr-poor K-feldspar (Or90.3Ab8.9An0.8), nepheline (Ne74.9Ks19.4Qz5.7 to Ne78.7Ks20.0Qz1.3), potassic-hastingsite, dark mica, andradite, scarce clinopyroxene (diopside- hedenbergite), and locally zoned microphenocrysts of Ba-Sr-rich K-feldspar (Or75.6Ab21.7An2.7). Accessory fluorapatite, titanite, interstitial sodalite, and magnetite and secondary abundant Na- And K-rich zeolites, calcite, chlorite-group minerals, and possibly cancrinite have been identified. The textural and mineralogical characteristics of the SPSV show genetic links with the host malignite that belongs to the potassic alkaline series. The SPSV were formed from a residual syenitic melt (malignite) extracted from a parental tephritic magma. In the residual malignite, the concentration of primary crystals (apatite, clinopyroxene, Ba-Sr-rich K-feldspar, and nepheline) formed a crystal network (mush) with the open spaces occupied by small amounts of residual melt enriched in Al, Na, K, and volatiles and depleted in Ba and Sr. Deformation (by shear movements plus magmatic pressures) produced microfractures and fractures which were occupied by residual interstitial melt. In situ crystallization within these fractures resulted in the formation of the SPSV.Fil: Pagano Género, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Geología; ArgentinaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Universidad Nacional de Cuyo. Facultad de Artes y Diseño; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Novák, Milan. Masaryk University; República ChecaFil: Skoda, Radek. Masaryk University; República Chec

A Ta,Ti–rich oxide mineral assemblage from the Nancy beryl–columbite–phosphate granitic pegmatite, San Luis, Argentina

An assemblage of tantalite-(Mn), tantalian rutile, tapiolite-(Fe), titanowodginite, ferrotitanowodginite, and hydroxycalciomicrolite occurs in the Nancy granitic pegmatite, San Luis range, Argentina. The Nancy beryl-type, beryl–columbite–phosphate subtype of LCT (Li-Cs-Ta) rare-element pegmatite was emplaced in the Paleozoic Conlara pegmatitic field. The assemblage occurs at the core margin of the pegmatite, forming an irregularly shaped, 18 by 6 cm nodule. The chemical composition of tantalite-(Mn) shows median Ta# [= (Ta/(Ta + Nb) apfu (atoms per formula unit)] and Mn# [= (Mn/(Mn + FeT) apfu] values of 0.57 and 0.64, respectively; Ti, U and Zr show maximum and [median] contents of: 3.37 [1.25] wt.% TiO2, 0.58 [0.24] wt.% UO2, and 0.72 [0.50] wt.% ZrO2. The unit-cell parameters indicate a moderately ordered structure. Tantalian rutile occurs as anhedral grains replacing tantalite-(Mn), associated with hydroxycalciomicrolite. Its chemical composition shows moderate to high Ti contents, with a maximum and [median] of 64.77 [38.67] wt.% TiO2. The proportion of Ta is very high, with 49.67 [39.59] wt.% Ta2O5. Tapiolite-(Fe), with 82.49 [81.86] wt.% Ta2O5, 2.51 [2.33] wt.% Nb2O5, 0.94 [0.79] wt.% TiO2, and 13.31 [13.18] wt.% FeO, has uniform Ta# and Mn# values, 0.95 and 0.09, respectively. Titanowodginite shows Ta# values ranging from 0.82 to 0.88, whereas in ferrotitanowodginite it ranges from 0.88 to 0.94. The Mn# value is similar in titanowodginite (0.51–0.64), and decreases in the ferrotitanowodginite (0.04 to 0.41). These minerals form a replacement sequence of tantalite-(Mn). Hydroxycalciomicrolite occurs in two generations: I and II. The dominant A cation is Ca, with a median value of 14.39 wt.% CaO. The MnO content, with a median of 1.16 wt.% MnO, is relatively constant. The amount of UO2 is usually below 3 wt.%, but locally attains 6.9 wt.%, and exceptionally 43.6 wt.%, in irregular rims that show a low analytical total, giving compositions that depart from the expected stoichiometry; it is clearly a subsolidus phase. In the more plausible explanation for the evolution of this assemblage, the magmatic crystallization of tantalite-(Mn) was followed during the early subsolidus stage by its partial replacement by tantalian rutile + tapiolite-(Fe) + titanowodginite + ferrotitanowodginte, associated with hydroxycalciomicrolite I, and later, by hydroxycalciomicrolite II produced by the influx of a late Fe–Ti–Ca-bearing fluid phase likely entering the pegmatite from the wall rocks.Fil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquez Zavalia, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Skoda, Radek. Masaryk University; República ChecaFil: Novák, Milan. Masaryk University; República ChecaFil: Copjaková, Renata. Masaryk University; República ChecaFil: Pagano Género, Diego Sebastián. Universidad Tecnológica Nacional. Facultad Regional Mendoza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentin

La Escalerilla pluton, San Luis Argentina: The orogenic and post-orogenic magmatic evolution of the famatinian cycle at Sierras de San Luis

Field relationships, geochemical analysis and two new absolute ages (LA-MC-ICP-MS U/Pb-zircon) allow the division of the La Escalerilla pluton (previously considered to be a single granitic body) into two different plutons: a new La Escalerilla pluton (s.s.), dated at 476.7 ± 9.6 Ma, that represents the northern portion, and the El Volcán pluton, dated at 404.5 ± 8.5 Ma, located in the southern sector. The La Escalerilla pluton is composed of three facies: (1) biotite-bearing granodiorite, (2) porphyritic biotite-bearing granite, and (3) porphyritic two micas-bearing leucogranite, being the presence of late-magmatic dykes in these facies common. The El Volcán pluton is composed of two main facies: 1) porphyritic biotite-bearing granite, and 2) two micas-bearing leucogranite, but amphibole-bearing monzodioritic and tonalititic mega-enclaves are also common, as well as some dykes of amphibole and clinopyroxene-bearing syenites. A peculiarity between the two plutons is that their most representative facies (porphyritic biotite-bearing granites) have, apart from different absolute ages, distinctive geochemical characteristics in their concentrations of trace elements; the La Escalerilla granite is comparatively poorer in Ba, Sr, Nb, La, Ce, P, and richer in Rb, Tb, Y, Tm and Yb. The El Volcán granite is notably enriched in Sr and depleted in Y, resulting in high Sr/Y ratios (12.67–39.08) compared to the La Escalerilla granite (1.11–2.41). These contrasts indicate that the separation from their sources occurred at different depths: below 25 km for the La Escalerilla, and above 30 km for the El Volcán. Moreover, the contrasts allow us to interpret a thin crust linked to an environment of pre-collisional subduction for the first case, and a thickened crust of post-collisional environment for the second, respectively.Fil: Morosini, Augusto Francisco. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ortiz Suarez, Ariel Emilio. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Otamendi, Juan Enrique. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pagano Género, Diego Sebastián. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ramos, Gabriel Alejandro. Universidad Nacional de San Luis; Argentin

Cenozoic orogenic evolution of the Southern Central Andes (32-36°S)

This review explores the complex interactions of endogenic and exogenic processes in the segment of the Andes that straddle a transition from flat slab to normal subduction (32°-36°S). This segment shows remarkable along-strike variations in topographic uplift, structural elevation, amount and rate of shortening, and crustal root geometry. In the flat-slab segment, high elevations, several tectonic provinces and the lack of active volcanism characterize the orogen. Deformation and uplift advanced to the east, together with arc-related magmatic activity, sequentially uplifting the Principal Cordillera (20 to ~8 Ma), the Frontal Cordillera (12 to 5 Ma), the Precordillera (<10 Ma) and the Sierras Pampeanas (<5 Ma). In the normal subduction segment, the Andes are characterized by a decrease in elevation, with a big step in topography at ~35°S and the development of an active magmatic arc straddling the Argentina-Chile border. The Frontal Cordillera is only in the northern part of normal subduction segment, disappearing at 34ºS; south of this latitude, only the Principal Cordillera remains. Deformation progressively advanced to the east, uplifting the Principal Cordillera (20 to 8 Ma), the Frontal Cordillera (<10 Ma) and the San Rafael basement block (<5 Ma). The amount of shortening systematically decreases from north to south, but at the transitional zone between flat and normal subduction segments, there is a sharp decline from ~180 km of shortening (32°S) to ~70 km (33°40´S). South from this latitude, the amount of shortening lineally decreases until it reaches ~30 km at 35°S. Yet, interestingly, the amount of late Miocene surface uplift is opposite that of the trend in crustal shortening. These along-strike variations are best explained by boundary conditions of the subduction system related to interplate dynamics controlling the overall pattern of tectonic shortening. However, local variations in mean topographic elevation, deformation styles and crustal root geometry are more likely to be due upper-plate lithospheric strength variations. These strength variations govern the degree of coupling between brittle upper crust and ductile lower crust deformation. In the flat-slab segment, an initial thick and felsic crust favors the coupling model; while in the normal subduction segment, a thin and mafic lower crust allows the uncoupling model.Fil: Giambiagi, Laura Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mescua, Jose Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Bechis, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio. Universidad Nacional de Río Negro. Instituto de Investigaciones en Diversidad Cultural y Procesos de Cambio; ArgentinaFil: Hoke, Gregory D.. Syracuse University. College Of Arts And Sciences. Department Of Earth Sciences; Estados UnidosFil: Suriano, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Spagnotto, Silvana Liz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Física; ArgentinaFil: Moreiras, Stella Maris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Lossada, Ana Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Mazzitelli, Manuela Amelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Toural Dapoza, Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Folguera, Alicia. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; ArgentinaFil: Mardonez Catalán, Diego José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Pagano Género, Diego Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin