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Your search keyword '"Otamendi, Juan E."' showing total 27 results
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27 results on '"Otamendi, Juan E."'

13. Timing constraints on building an intermediate plutonic arc crustal section: U- Pb zircon geochronology of the Sierra Valle Fertil--La Huerta, Famatinian arc, Argentina

Author

Ducea, Mihai N., Otamendi, Juan E., Bergantz, George, Stair, Kelley M., Valencia, Victor A., and Gehrels, George E.

Subjects
Geochronology -- Research, Zirconium -- Composition, Zirconium -- Environmental aspects, Earth -- Crust, Earth -- Environmental aspects, Earth sciences
Abstract

[1] The Sierra Valle Fertil Range in northwestern Argentina exposes a tilted crustal section through the Ordovician Famatinian arc, from >25 km to shallow crustal paleodepths. Fourteen new U-Pb zircon crystallization ages of magmatic rocks from Sierra Valle Fertil area show that this section of the arc was built over a short time interval during the Ordovician, between 485 and 465 Ma. Zircon rim ages demonstrate that high-grade metamorphism and migmatization were synchronous with magmatic emplacement. Inherited ages in some of the plutonic rocks as well as detrital zircons in the metasedimentary framework suggest that the Famatinian arc was emplaced into a thick miogeoclinal cover to the thinned margin of the proto-South American continent in the Ordovician, which represents a part of Gondwana. Docking of the Precordilleran terrane outboard of proto-South America led to the cessation of arc magmatism in the Valle Fertil area and preservation of the arc in its early stages after

Published
2010

15. Rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth

Author

Otamendi, Juan E., de la Rosa, Jesus D., Patino Douce, Alberto E., and Castro, Antonio

Subjects
Argentina -- Natural history, Rayleigh scattering -- Usage, Rayleigh scattering -- Comparative analysis, Rare earth metals -- Research, Garnet -- Composition, Earth sciences
Abstract

We present laser-ablation microprobe inductively coupled-mass spectrometry analyses of Y, Yb, Er, Dy, and Gd in garnet crystals from high-grade metamorphic and migmatitic rocks from the Sierras Pampeanas of Argentina. These rocks contain large garnet porphyroblasts ([greater than or equal to] 4 mm) that are compositionally zoned. Rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores. A notable feature of this zonation is the inversion of Yb/Er and Yb/Dy ratios, from >1 in the cores to Keywords: Rayleigh fractionation, garnet, heavy rare earth clements, melting.

Published
2002

22. Top-down structures of mafic enclaves within the Valle Fértil magmatic complex (Early Ordovician, San Juan, Argentina)

Author

Castro Dorado, Antonio|||0000-0002-7257-2556, Otamendi, Juan E., Pinotti, Lucio P., D’Eramo, Fernando J., Vujovich, Graciela I., and Tibaldi, Alina M.

Subjects
Enclaves, Calc-alkaline batholiths, Argentina, Synplutonic intrusions, Famatinian belt
Abstract

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fértil 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 the only plausible mechanism to account for the observed structures. The model may be of general application to calc-alkaline batholiths characterized by the presence of mafic microgranular enclaves. An implication of these reverselly stratified magma chambers is the presence of a petrological inversion which may be the consequence of cold diapirs emplaced below the mantle wedge in a suprasubduction setting.

Published
2008

23. Estudio de la Orientación Cristalográfica Preferente del Cuarzo en el Contacto entre Gneises y Metatexitas - Diatexitas del Macizo Cerro Pelado (Sierra de Comechingones, Argentina)

Author

Castellarlni, P., Fernández Rodríguez, Carlos, and Otamendi, Juan E.

Subjects
Quartz c-axis fabrics, Argentina, Migmatites, Sierra de Comechingones
Abstract

The quartz c-axis fabrics measured in the rocks of the high-grade unit of the Cerro Pelado massif (northern Sierra de Comechingones, Sierras Pampeanas, Argentina) allow to deduce a normal-sinistral sense of movement for the south-dipping shear zone separating the diatexite-metatexite domain to the north, from the gneissic terrane to the south. The crystallographic fabrics also indicate that the activity of this shear zone took place under high-T conditions. The deduced kinematics can account for the syn-metamorphic exhumation of the migmatite domain

Published
2003

24. Study of the Crystallographic Preferred Orientation in Quartz at the Contact between the Gneisses and Metatexites-Diatexites of the Cerro Pelado Massif (Sierra de Comechingones, Argentina)

Author

Castellarlni, P., Fernández Rodríguez, Carlos|||0000-0001-5135-7972, and Otamendi, Juan E.

Subjects
Quartz c-axis fabrics, Argentina, Migmatites, Sierra de Comechingones
Abstract

The quartz c-axis fabrics measured in the rocks of the high-grade unit of the Cerro Pelado massif (northern Sierra de Comechingones, Sierras Pampeanas, Argentina) allow to deduce a normal-sinistral sense of movement for the south-dipping shear zone separating the diatexite-metatexite domain to the north, from the gneissic terrane to the south. The crystallographic fabrics also indicate that the activity of this shear zone took place under high-T conditions. The deduced kinematics can account for the syn-metamorphic exhumation of the migmatite domain

Published
2003

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