J. Otamendi | Universidad Nacional de Rio Cuarto (original) (raw)

Papers by J. Otamendi

Earth and Planetary Science Letters

Revista de la Asociacion Geologica Argentina

RESUMEN Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo... more RESUMEN Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo-barometría de dos complejos máficos que afloran al norte de la sierra de Comechingones. Se aplicaron un conjunto de termómetros y barómetros empíricos con el propósito de determinar los rangos de P y T absolutas de cristalización de estas rocas. Las temperaturas de equilibrio en pares de piroxenos (cpx-opx) se estimaron usando tres termómetros independientes. Dos calibraciones termométricas (Wells 1977, Kretz 1982) dan resultados consistentes y razonables indicando que los piroxenos registran condiciones de cristalización magmática (920-1150ºC), mientras que la tercera calibración (Lindsley 1983) estima temperaturas muy inferiores. Esta discrepancia puede estar relacionada con el hecho de que la última calibración no sería aplicable a rocas que cristalizaron a partir de magmas ricos en hierro. Por su parte, la termometría Amph-Pl sugiere temperaturas de equilibrio comprendidas entre 750-850ºC, para composiciones típicas de núcleos, mientras que para composiciones representativas de los bordes de grano las temperaturas estimadas son significativamente inferiores (< 600ºC) comportamiento que sugiere que el anfíbol cristalizó principalmente en una etapa post-magmática. Las temperaturas de intercambio para Fe-Mg entre opx-bt muestran que este par mineral se equilibró entre dos rangos térmicos bien definidos (430-650ºC y 740-1030ºC), lo que sugiere que las biotitas pueden haber cristalizado tanto en una etapa tardío magmática como post-magmática. Las formulaciones barométricas muestran cierta variabilidad en función de las calibraciones utilizadas, no obstante, sistemáticamente presentan un patrón de valores en el cual las presiones de equilibrio determinadas en el Complejo Suya Taco son inferiores (5,5 ± 1 kbar) a las obtenidas en el Complejo Sol de Mayo (8 ± 1 kbar). En general, este resultado es consistente con las estimaciones barométricas recientemente realizadas en xenolitos de granulitas. Las condiciones de P-T deducidas a partir de las rocas ígneas indican que la secuencia metamórfica encajante se encontraba a temperaturas de la facies de anfibolitas y en niveles de corteza media.

Geologica Acta, 2008

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids hav... more Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fertil calc-alkaline igneous complex, Argentina. Excepcional outcrops with vertical walls of more than 300 m high allow us the study of three-dimensional geometries of individual blobs of mafic magma as well as the geometry of pipe-like structures in which mafic microgranular enclaves are concentrated in more than 50 times the normal abundance in the granodiorite mass. The shape of enclaves and pipe-like structures are interpreted as the ressult of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures are the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. They may account for most of the structures found in microgranular enclaves and magma mingling zones that characterize calc-alkaline batholiths. Synplutonic intrusions from the top is t...

El cinturón trondhjemítico (Formación Cachi) está compuesto por pequeños plutones y diques (Depar... more El cinturón trondhjemítico (Formación Cachi) está compuesto por pequeños plutones y diques (Departamento de La Poma, Salta) que intruyen a metasedimentitas (Formación Puncoviscana). Las trondhjemitas son estériles en elementos económicos, en contraste con las rocas metasedimentarias, con un alto contenido de Ta, Nb, Li y Be. Su origen es por la fusión en la aureola de contacto con los cuerpos intrusivos. Las trondhjemitas desarrollaron una aureola térmica (facies granulitas) con fusión parcial hasta esquistos verdes. Los cuerpos mineralizados (pegmatitas) contienen altos valores de óxidos de tantalio y niobio 10 veces más concentrado en las rocas de caja que en los cuerpos trondhjemíticos. El tantalio y niobio se concentró en zonas con alto metamorfismo, desarrollando cuerpos pegmatíticos dentro de las rocas metasedimentarias. El contenido en elementos litófilos se movilizó desde los metasedimentos a las zonas de fusión parcial. El origen del magma trondhjemítico se asocia con zonas de subducción activas durante la evolución del arco magmático famatiniano (480 a 460 Ma). El contenido rico en Na testifica el probable cambio en su configuración, debido o a la fusión de la corteza baja o a la subducción de corteza oceánica (<25 Ma) o a un cambio del ángulo de subducción originando la fusión parcial de corteza inferior acrecionada. Basado en estas observaciones es posible considerar nuevas exploraciones en la búsqueda de tantalio y niobio en esta área.

Estudios Geológicos, 2017

El presente trabajo expone una síntesis de la geología que comprende al complejo cristalino que c... more El presente trabajo expone una síntesis de la geología que comprende al complejo cristalino que constituye la Sierra de La Aguada, provincia de San Luis, Argentina, desde un enfoque basado en las relaciones de campo, los rasgos petrológico-estructurales y las características geoquímicas. Dicha serranía expone un basamento dominado por rocas plutónicas intermedias-máficas de afinidad calcoalcalina y granitoides félsicos peraluminosos, en conjunto intruidas en metamorfitas de bajo a medio grado metamórfico estabilizadas en condiciones de facies de anfibolita. Todo el conjunto litológico ha sido agrupado dentro del denominado complejo El Carrizal-La Aguada. El análisis de las relaciones de campo, la petrografía y la comparación de las características geoquímicas de las rocas plutónicas del área estudiada y aquellas pertenecientes a la suite ordovícica Famatiniana expuestas en la Sierra Grande de San Luis, sugiere una posible relación genética-temporal vinculada al desarrollo del arco m...

Revista de la Asociacion Geologica Argentina

Geological Society of America Memoirs, 2014

Tectonophysics, 2013

The crustal structure of the Famatinian paleoarc is reconstructed by determining the metamorphic ... more 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 b20 km. Dioritic and tonalitic bodies dominated between 20 and 25 km. The deepest exposed paleodepths are formed by cumulate and non-cumulate gabbroic rocks with interlayered quartz diorites that crystallized below 25 km. The boundary between the crust and the lithospheric mantle is not observed and would have been underneath a depth of 27 km. 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~6.3 km/s to >6.6 km/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 (b6.2 km/s) is 10 km 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 35 km with three distinct layers.

Tectonics, 2012

Bolivia, thickskinned in Argentina) and apparent magnitude of Cenozoic shortening (>100 km more i... more Bolivia, thickskinned in Argentina) and apparent magnitude of Cenozoic shortening (>100 km more in the north). With the aim of evaluating the abruptness and cause of this transition, we conducted a geological and geo-thermochronological study of the Cachi Range ($24-25 S), which is a prominent topographic feature at this latitude. Our U-Pb detrital zircon results from the oldest exposed rocks (Puncoviscana Formation) constrain deposition to mainly Cambrian time, followed by major, Cambro-Ordovician shortening and $484 Ma magmatism. Later, Cretaceous rift faults were locally inverted during Cenozoic shortening. Coupled with previous work, our new (U-Th)/He zircon results require 8-10 km of Miocene exhumation that was likely associated with fault-propagation folding within the Cachi Range. After Miocene shortening, displacement on sinistral strike-slip faults demonstrates a change in stress state to a non-vertically oriented s3. This change in stress state may result from an increase in gravitational potential energy in response to significant crustal thickening and/or lithospheric root removal. Our finding of localized Cenozoic shortening in the Cachi Range increases the estimate of the local magnitude of shortening, but still suggests that significantly less shortening was accommodated south of the thinskinned Bolivian fold-thrust belt. Our results also underscore the importance of the pre-existing stratigraphic and structural architecture in orogens in influencing the style of subsequent deformation.

Lithos, 2011

This study tests the overall consistency of geothermobarometric calibrations and thermodynamic in... more This study tests the overall consistency of geothermobarometric calibrations and thermodynamic internally consistent databases commonly used to retrieve temperature and pressure conditions in metapelitic and igneous mafic protolith metamorphosed at granulite-facies conditions. We examine a lithological sequence characterized by interbedded mafic and metapelitic protoliths that underwent partial melting at the same time during peak T conditions. Textural equilibrium and the lack of complex chemical zoning in rock-forming minerals from the two contrasting protoliths permit the application of commonly utilized ion-exchange and net transfer thermobarometers. By combining garnet-biotite and garnet-cordierite thermometers with the well-known net-transfer barometers, and using thermodynamic properties from both Berman's and Holland and Powell's databases, we demonstrate that temperature and pressure estimated for the metapelitic migmatite are independent of the chosen internally consistent thermodynamic database. Peak pressuretemperature (P-T) estimates in the metapelitic mineral assemblage are also consistent with those inferred from pseudosection models constructed with the whole-rock composition of the metasedimentary migmatite. The most tenable values for the peak temperature-pressure condition retrieved in the metapelitic migmatite are taken to provide the best constraint on which to test thermobarometric results from the mafic migmatites. Two-pyroxene thermometry using the database from Berman (1988) and the amphiboleplagioclase thermometer with the calibration by Holland and Blundy (1994) yields values broadly consistent with those determined in the metapelitic migmatite. By contrast, other calibrations of the two-pyroxene thermometer tend to overestimate temperature by at least several tens of degrees. The construction of a P-T pseudosection for the mafic migmatite composition provides further evidence for both selecting the most accurate thermometer and determining the peak pressure of a mafic migmatite.

Lithos, 2003

Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modif... more Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modification of mafic magma composition by assimilation or reaction with crustal materials. This petrologic process is studied at the Suya Taco Complex where a suite of mafic magmas interacted with metamorphic rocks at 6.6±1 kbar. The Suya Taco Complex consists of close-spaced bodies of biotite-bearing gabbronorites. These magmas intruded into a supracrustal sequence consisting of amphibolite– to granulite–facies gneisses and migmatites. The peak-metamorphic mineral assemblage Bt+Qtz+Pl(An30)+Grt+Kfs±Crd±Sil of supracrustal rocks crystallised before igneous mafic magmatism. Interaction between mafic magmas and metamorphic rocks produces two major hybrid lithologies: diorites made up of Opx+Bt+Pl (An38–50)+Ilm±Cpx±Qtz; and garnet- and orthopyroxene-bearing rocks characterised by the coexistence of Bt+Pl (An30–45)+Grt+Opx+Qtz+Ilm±Spl±Kfs. The latter lithology may locally appear as a quartz-absent and high-aluminous mineral assemblage. The two hybrid rocks occur interlayered at the contact zone between igneous mafic rocks and high-grade gneisses. Individual layers range from centimeter to meter scales; moreover, dioritic and orthopyroxene- and garnet-bearing layers present a spectrum of mineral assemblages and mineral chemistry that spread among those that appear in igneous mafic and metamorphic rocks. The work shows that the changes of mineral assemblages and variations of mineral chemistry in the hybrid diorites and orthopyroxene- and garnet-bearing rocks are the result of interaction processes between mafic magmas and regional metamorphic rocks. Field relationships, petrographic features, mineral compositional changes and qualitative analyses of phase relations suggest that rocks formed by interaction between mafic magmas and metamorphic rocks results from: (1) assimilation of metamorphic rocks by mafic magmas at variable degrees and (2) ion diffusion among mineral assemblages of contrasting composition. The implication of these processes is that Ca is transferred from mafic magmas to metamorphic rocks, which forces the breakdown of garnet and quartz, and induces the crystallisation of plagioclase and orthopyroxene in the resulting hybrid rocks.

Journal of South American Earth Sciences, 2010

The whole Valle Fértil-La Huerta section appears as a calc-alkaline plutonic suite typical of a d... more The whole Valle Fértil-La Huerta section appears as a calc-alkaline plutonic suite typical of a destructive plate margin. New Sr and Nd isotopic whole-rock data and published whole-rock geochemistry suggest that the less-evolved intermediate (dioritic) rocks can be derived by magmatic differentiation, mainly by hornblende + plagioclase ± Fe–Ti oxide fractional crystallization, from mafic (gabbroic) igneous precursors. Closed-system differentiation, however, cannot produce the typical

Journal of South American Earth Sciences, 2012

We obtained detrital zircon ages from three metasedimentary rocks with siliciclastic protoliths t... more We obtained detrital zircon ages from three metasedimentary rocks with siliciclastic protoliths that were buried to paleodepths of 20e27 km during Early Ordovician Famatinian arc magmatism. In all three samples, UePb zircon age distributions are polymodal but the dominant peaks make well-defined clusters, matching the ages of orogenic systems that characterize West Gondwana. The most prominent peaks of constituent age populations at 520 Ma, 600 Ma, and 1050 Ma reflect derivation from sources that are characteristic of the West Gondwana margin. Moreover, grains with Meso-and Paleo-Proterozoic ages appear as small fractions (<5%). The siliciclastic protoliths to metasedimentary rocks from the deep Famatinian crust are dominantly composed of detritus derived from two sources: 1) a nearby magmatic arc or a rapidly exhuming orogen, and 2) sedimentary recycling of Neoproterozoice Lower Cambrian sedimentary successions broadly grouped as Puncoviscana Formation. Our findings reveal that granuliteefacies metasedimentary rocks in the deep crust of the Famatinian arc have detrital zircon patterns closely resembling those found in nearby Middle to Upper Cambrian quartz-rich turbidite sequences from central Famatina, the Cordillera Oriental and the Puna. At the regional scale, these sedimentary successions yield maximum depositional ages corresponding to the Middle Cambrian (<520 Ma). This indicates that metasedimentary rocks in the Sierra de Valle Fértil were rapidly buried to deep levels after deposition. Our results are also consistent with the existence of a crustal scale paleosuture located at the western margin of the Sierras Valle Fértil and La Huerta that explains the differences of detrital zircon age patterns between metasedimentary rocks in the Valle Fértil and age-equivalent sedimentary units in the nearby Cuyania Terrane.

Journal of South American Earth Sciences, 2009

Journal of South American Earth Sciences, 2010

This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and ... more This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and peridotitic layered body that is lens-shaped and surrounded by gabbronorites, diorites, and metasedimentary migmatites. This body exposed at Jaboncillo Valley is one among ...

Journal of South American Earth Sciences, 2005

Journal of Petrology, 2001

Journal of Petrology, 2012

Earth and Planetary Science Letters

Revista de la Asociacion Geologica Argentina

RESUMEN Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo... more RESUMEN Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo-barometría de dos complejos máficos que afloran al norte de la sierra de Comechingones. Se aplicaron un conjunto de termómetros y barómetros empíricos con el propósito de determinar los rangos de P y T absolutas de cristalización de estas rocas. Las temperaturas de equilibrio en pares de piroxenos (cpx-opx) se estimaron usando tres termómetros independientes. Dos calibraciones termométricas (Wells 1977, Kretz 1982) dan resultados consistentes y razonables indicando que los piroxenos registran condiciones de cristalización magmática (920-1150ºC), mientras que la tercera calibración (Lindsley 1983) estima temperaturas muy inferiores. Esta discrepancia puede estar relacionada con el hecho de que la última calibración no sería aplicable a rocas que cristalizaron a partir de magmas ricos en hierro. Por su parte, la termometría Amph-Pl sugiere temperaturas de equilibrio comprendidas entre 750-850ºC, para composiciones típicas de núcleos, mientras que para composiciones representativas de los bordes de grano las temperaturas estimadas son significativamente inferiores (< 600ºC) comportamiento que sugiere que el anfíbol cristalizó principalmente en una etapa post-magmática. Las temperaturas de intercambio para Fe-Mg entre opx-bt muestran que este par mineral se equilibró entre dos rangos térmicos bien definidos (430-650ºC y 740-1030ºC), lo que sugiere que las biotitas pueden haber cristalizado tanto en una etapa tardío magmática como post-magmática. Las formulaciones barométricas muestran cierta variabilidad en función de las calibraciones utilizadas, no obstante, sistemáticamente presentan un patrón de valores en el cual las presiones de equilibrio determinadas en el Complejo Suya Taco son inferiores (5,5 ± 1 kbar) a las obtenidas en el Complejo Sol de Mayo (8 ± 1 kbar). En general, este resultado es consistente con las estimaciones barométricas recientemente realizadas en xenolitos de granulitas. Las condiciones de P-T deducidas a partir de las rocas ígneas indican que la secuencia metamórfica encajante se encontraba a temperaturas de la facies de anfibolitas y en niveles de corteza media.

Geologica Acta, 2008

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids hav... more Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fertil calc-alkaline igneous complex, Argentina. Excepcional outcrops with vertical walls of more than 300 m high allow us the study of three-dimensional geometries of individual blobs of mafic magma as well as the geometry of pipe-like structures in which mafic microgranular enclaves are concentrated in more than 50 times the normal abundance in the granodiorite mass. The shape of enclaves and pipe-like structures are interpreted as the ressult of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures are the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. They may account for most of the structures found in microgranular enclaves and magma mingling zones that characterize calc-alkaline batholiths. Synplutonic intrusions from the top is t...

El cinturón trondhjemítico (Formación Cachi) está compuesto por pequeños plutones y diques (Depar... more El cinturón trondhjemítico (Formación Cachi) está compuesto por pequeños plutones y diques (Departamento de La Poma, Salta) que intruyen a metasedimentitas (Formación Puncoviscana). Las trondhjemitas son estériles en elementos económicos, en contraste con las rocas metasedimentarias, con un alto contenido de Ta, Nb, Li y Be. Su origen es por la fusión en la aureola de contacto con los cuerpos intrusivos. Las trondhjemitas desarrollaron una aureola térmica (facies granulitas) con fusión parcial hasta esquistos verdes. Los cuerpos mineralizados (pegmatitas) contienen altos valores de óxidos de tantalio y niobio 10 veces más concentrado en las rocas de caja que en los cuerpos trondhjemíticos. El tantalio y niobio se concentró en zonas con alto metamorfismo, desarrollando cuerpos pegmatíticos dentro de las rocas metasedimentarias. El contenido en elementos litófilos se movilizó desde los metasedimentos a las zonas de fusión parcial. El origen del magma trondhjemítico se asocia con zonas de subducción activas durante la evolución del arco magmático famatiniano (480 a 460 Ma). El contenido rico en Na testifica el probable cambio en su configuración, debido o a la fusión de la corteza baja o a la subducción de corteza oceánica (<25 Ma) o a un cambio del ángulo de subducción originando la fusión parcial de corteza inferior acrecionada. Basado en estas observaciones es posible considerar nuevas exploraciones en la búsqueda de tantalio y niobio en esta área.

Estudios Geológicos, 2017

El presente trabajo expone una síntesis de la geología que comprende al complejo cristalino que c... more El presente trabajo expone una síntesis de la geología que comprende al complejo cristalino que constituye la Sierra de La Aguada, provincia de San Luis, Argentina, desde un enfoque basado en las relaciones de campo, los rasgos petrológico-estructurales y las características geoquímicas. Dicha serranía expone un basamento dominado por rocas plutónicas intermedias-máficas de afinidad calcoalcalina y granitoides félsicos peraluminosos, en conjunto intruidas en metamorfitas de bajo a medio grado metamórfico estabilizadas en condiciones de facies de anfibolita. Todo el conjunto litológico ha sido agrupado dentro del denominado complejo El Carrizal-La Aguada. El análisis de las relaciones de campo, la petrografía y la comparación de las características geoquímicas de las rocas plutónicas del área estudiada y aquellas pertenecientes a la suite ordovícica Famatiniana expuestas en la Sierra Grande de San Luis, sugiere una posible relación genética-temporal vinculada al desarrollo del arco m...

Revista de la Asociacion Geologica Argentina

Geological Society of America Memoirs, 2014

Tectonophysics, 2013

The crustal structure of the Famatinian paleoarc is reconstructed by determining the metamorphic ... more 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 b20 km. Dioritic and tonalitic bodies dominated between 20 and 25 km. The deepest exposed paleodepths are formed by cumulate and non-cumulate gabbroic rocks with interlayered quartz diorites that crystallized below 25 km. The boundary between the crust and the lithospheric mantle is not observed and would have been underneath a depth of 27 km. 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~6.3 km/s to >6.6 km/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 (b6.2 km/s) is 10 km 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 35 km with three distinct layers.

Tectonics, 2012

Bolivia, thickskinned in Argentina) and apparent magnitude of Cenozoic shortening (>100 km more i... more Bolivia, thickskinned in Argentina) and apparent magnitude of Cenozoic shortening (>100 km more in the north). With the aim of evaluating the abruptness and cause of this transition, we conducted a geological and geo-thermochronological study of the Cachi Range ($24-25 S), which is a prominent topographic feature at this latitude. Our U-Pb detrital zircon results from the oldest exposed rocks (Puncoviscana Formation) constrain deposition to mainly Cambrian time, followed by major, Cambro-Ordovician shortening and $484 Ma magmatism. Later, Cretaceous rift faults were locally inverted during Cenozoic shortening. Coupled with previous work, our new (U-Th)/He zircon results require 8-10 km of Miocene exhumation that was likely associated with fault-propagation folding within the Cachi Range. After Miocene shortening, displacement on sinistral strike-slip faults demonstrates a change in stress state to a non-vertically oriented s3. This change in stress state may result from an increase in gravitational potential energy in response to significant crustal thickening and/or lithospheric root removal. Our finding of localized Cenozoic shortening in the Cachi Range increases the estimate of the local magnitude of shortening, but still suggests that significantly less shortening was accommodated south of the thinskinned Bolivian fold-thrust belt. Our results also underscore the importance of the pre-existing stratigraphic and structural architecture in orogens in influencing the style of subsequent deformation.

Lithos, 2011

This study tests the overall consistency of geothermobarometric calibrations and thermodynamic in... more This study tests the overall consistency of geothermobarometric calibrations and thermodynamic internally consistent databases commonly used to retrieve temperature and pressure conditions in metapelitic and igneous mafic protolith metamorphosed at granulite-facies conditions. We examine a lithological sequence characterized by interbedded mafic and metapelitic protoliths that underwent partial melting at the same time during peak T conditions. Textural equilibrium and the lack of complex chemical zoning in rock-forming minerals from the two contrasting protoliths permit the application of commonly utilized ion-exchange and net transfer thermobarometers. By combining garnet-biotite and garnet-cordierite thermometers with the well-known net-transfer barometers, and using thermodynamic properties from both Berman's and Holland and Powell's databases, we demonstrate that temperature and pressure estimated for the metapelitic migmatite are independent of the chosen internally consistent thermodynamic database. Peak pressuretemperature (P-T) estimates in the metapelitic mineral assemblage are also consistent with those inferred from pseudosection models constructed with the whole-rock composition of the metasedimentary migmatite. The most tenable values for the peak temperature-pressure condition retrieved in the metapelitic migmatite are taken to provide the best constraint on which to test thermobarometric results from the mafic migmatites. Two-pyroxene thermometry using the database from Berman (1988) and the amphiboleplagioclase thermometer with the calibration by Holland and Blundy (1994) yields values broadly consistent with those determined in the metapelitic migmatite. By contrast, other calibrations of the two-pyroxene thermometer tend to overestimate temperature by at least several tens of degrees. The construction of a P-T pseudosection for the mafic migmatite composition provides further evidence for both selecting the most accurate thermometer and determining the peak pressure of a mafic migmatite.

Lithos, 2003

Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modif... more Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modification of mafic magma composition by assimilation or reaction with crustal materials. This petrologic process is studied at the Suya Taco Complex where a suite of mafic magmas interacted with metamorphic rocks at 6.6±1 kbar. The Suya Taco Complex consists of close-spaced bodies of biotite-bearing gabbronorites. These magmas intruded into a supracrustal sequence consisting of amphibolite– to granulite–facies gneisses and migmatites. The peak-metamorphic mineral assemblage Bt+Qtz+Pl(An30)+Grt+Kfs±Crd±Sil of supracrustal rocks crystallised before igneous mafic magmatism. Interaction between mafic magmas and metamorphic rocks produces two major hybrid lithologies: diorites made up of Opx+Bt+Pl (An38–50)+Ilm±Cpx±Qtz; and garnet- and orthopyroxene-bearing rocks characterised by the coexistence of Bt+Pl (An30–45)+Grt+Opx+Qtz+Ilm±Spl±Kfs. The latter lithology may locally appear as a quartz-absent and high-aluminous mineral assemblage. The two hybrid rocks occur interlayered at the contact zone between igneous mafic rocks and high-grade gneisses. Individual layers range from centimeter to meter scales; moreover, dioritic and orthopyroxene- and garnet-bearing layers present a spectrum of mineral assemblages and mineral chemistry that spread among those that appear in igneous mafic and metamorphic rocks. The work shows that the changes of mineral assemblages and variations of mineral chemistry in the hybrid diorites and orthopyroxene- and garnet-bearing rocks are the result of interaction processes between mafic magmas and regional metamorphic rocks. Field relationships, petrographic features, mineral compositional changes and qualitative analyses of phase relations suggest that rocks formed by interaction between mafic magmas and metamorphic rocks results from: (1) assimilation of metamorphic rocks by mafic magmas at variable degrees and (2) ion diffusion among mineral assemblages of contrasting composition. The implication of these processes is that Ca is transferred from mafic magmas to metamorphic rocks, which forces the breakdown of garnet and quartz, and induces the crystallisation of plagioclase and orthopyroxene in the resulting hybrid rocks.

Journal of South American Earth Sciences, 2010

The whole Valle Fértil-La Huerta section appears as a calc-alkaline plutonic suite typical of a d... more The whole Valle Fértil-La Huerta section appears as a calc-alkaline plutonic suite typical of a destructive plate margin. New Sr and Nd isotopic whole-rock data and published whole-rock geochemistry suggest that the less-evolved intermediate (dioritic) rocks can be derived by magmatic differentiation, mainly by hornblende + plagioclase ± Fe–Ti oxide fractional crystallization, from mafic (gabbroic) igneous precursors. Closed-system differentiation, however, cannot produce the typical

Journal of South American Earth Sciences, 2012

We obtained detrital zircon ages from three metasedimentary rocks with siliciclastic protoliths t... more We obtained detrital zircon ages from three metasedimentary rocks with siliciclastic protoliths that were buried to paleodepths of 20e27 km during Early Ordovician Famatinian arc magmatism. In all three samples, UePb zircon age distributions are polymodal but the dominant peaks make well-defined clusters, matching the ages of orogenic systems that characterize West Gondwana. The most prominent peaks of constituent age populations at 520 Ma, 600 Ma, and 1050 Ma reflect derivation from sources that are characteristic of the West Gondwana margin. Moreover, grains with Meso-and Paleo-Proterozoic ages appear as small fractions (<5%). The siliciclastic protoliths to metasedimentary rocks from the deep Famatinian crust are dominantly composed of detritus derived from two sources: 1) a nearby magmatic arc or a rapidly exhuming orogen, and 2) sedimentary recycling of Neoproterozoice Lower Cambrian sedimentary successions broadly grouped as Puncoviscana Formation. Our findings reveal that granuliteefacies metasedimentary rocks in the deep crust of the Famatinian arc have detrital zircon patterns closely resembling those found in nearby Middle to Upper Cambrian quartz-rich turbidite sequences from central Famatina, the Cordillera Oriental and the Puna. At the regional scale, these sedimentary successions yield maximum depositional ages corresponding to the Middle Cambrian (<520 Ma). This indicates that metasedimentary rocks in the Sierra de Valle Fértil were rapidly buried to deep levels after deposition. Our results are also consistent with the existence of a crustal scale paleosuture located at the western margin of the Sierras Valle Fértil and La Huerta that explains the differences of detrital zircon age patterns between metasedimentary rocks in the Valle Fértil and age-equivalent sedimentary units in the nearby Cuyania Terrane.

Journal of South American Earth Sciences, 2009

Journal of South American Earth Sciences, 2010

This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and ... more This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and peridotitic layered body that is lens-shaped and surrounded by gabbronorites, diorites, and metasedimentary migmatites. This body exposed at Jaboncillo Valley is one among ...

Journal of South American Earth Sciences, 2005

Journal of Petrology, 2001

Journal of Petrology, 2012