Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina

The La Aguadita Formation crops out in the core of the Famatina Range (28°39'S) in the southern Central Andes and is interpreted as a relict of a synorogenic Ordovician clastic wedge developed in the retroarc of a collisional-subduction margin built along western Gondwana. This unit, formerly i...

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Detalles Bibliográficos
Publicado:	2005
Materias:	Argentina Berthierine Clay minerals Famatina system Low-grade metamorphism Ordovician Retrograde diagenesis
Acceso en línea:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p283_Collo http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p283_Collo
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

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spelling	paper:paper_10268774_v22_n3_p283_Collo2023-06-08T16:00:15Z Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina Argentina Berthierine Clay minerals Famatina system Low-grade metamorphism Ordovician Retrograde diagenesis The La Aguadita Formation crops out in the core of the Famatina Range (28°39'S) in the southern Central Andes and is interpreted as a relict of a synorogenic Ordovician clastic wedge developed in the retroarc of a collisional-subduction margin built along western Gondwana. This unit, formerly included within the Pampean (Early Cambrian) metamorphic complex, was recently attributed to the middle Ordovician on the basis of U-Pb SHRIMP dating on detrital zircons. La Aguadita Formation comprises two informal members, the lower one is composed of metarkoses with clastic to blastopsammitic textures, whereas the upper member consists of metapelites with subordinated thin-bedded metagraywackes. Mineralogical (XRD) and petrological analyses carried out for the rocks outcropping in Loma de Las Damas indicate that La Aguadita Formation underwent an incipient regional metamorphic event, in which the mineral blastesis was synchronous with the development of the S1, cleavage. According to the XRD study of the <2,μm fraction, the main mineral formed during this event was illite, with subordinate chlorite. Besides, the petrographic study evidences recrystallization processes in quartz and feldespate. The values obtained for the Kübler index of the metapelites correspond entirely to the anchizone (IK= 0.25-0.40 Δ°'2θ), indicating that the main tectono-metamorphic event took place at temperatures around 200-300 °C and depths of 6.5 to 10 km. The existence of blastic epidote and chlorite in some metarkoses and metagraywackes, together with their textural relationships denote a propilitic hydrothermal alteration episode that postdates the main tectono-thermal episode. The clay fraction of the metapelites contains -in addition to the main phyllosilicates- smectite, berthierine, vermiculite, and I/S and Chl/Vm mixed-layered minerals. This group of phyllosilicates is incompatible not only with the grade established for the main metamorphic event, but also with the temperatures estimated for the epidote + chlorite assemblage developed during the hydrothermal alteration. They are interpreted as the result of a retrograde diagenesis episode promted by low-temperature, late-stage hydrothermal fluids or by the interaction between rocks and groundwater after uplift. 2005 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p283_Collo http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p283_Collo
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Argentina Berthierine Clay minerals Famatina system Low-grade metamorphism Ordovician Retrograde diagenesis
spellingShingle	Argentina Berthierine Clay minerals Famatina system Low-grade metamorphism Ordovician Retrograde diagenesis Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
topic_facet	Argentina Berthierine Clay minerals Famatina system Low-grade metamorphism Ordovician Retrograde diagenesis
description	The La Aguadita Formation crops out in the core of the Famatina Range (28°39'S) in the southern Central Andes and is interpreted as a relict of a synorogenic Ordovician clastic wedge developed in the retroarc of a collisional-subduction margin built along western Gondwana. This unit, formerly included within the Pampean (Early Cambrian) metamorphic complex, was recently attributed to the middle Ordovician on the basis of U-Pb SHRIMP dating on detrital zircons. La Aguadita Formation comprises two informal members, the lower one is composed of metarkoses with clastic to blastopsammitic textures, whereas the upper member consists of metapelites with subordinated thin-bedded metagraywackes. Mineralogical (XRD) and petrological analyses carried out for the rocks outcropping in Loma de Las Damas indicate that La Aguadita Formation underwent an incipient regional metamorphic event, in which the mineral blastesis was synchronous with the development of the S1, cleavage. According to the XRD study of the <2,μm fraction, the main mineral formed during this event was illite, with subordinate chlorite. Besides, the petrographic study evidences recrystallization processes in quartz and feldespate. The values obtained for the Kübler index of the metapelites correspond entirely to the anchizone (IK= 0.25-0.40 Δ°'2θ), indicating that the main tectono-metamorphic event took place at temperatures around 200-300 °C and depths of 6.5 to 10 km. The existence of blastic epidote and chlorite in some metarkoses and metagraywackes, together with their textural relationships denote a propilitic hydrothermal alteration episode that postdates the main tectono-thermal episode. The clay fraction of the metapelites contains -in addition to the main phyllosilicates- smectite, berthierine, vermiculite, and I/S and Chl/Vm mixed-layered minerals. This group of phyllosilicates is incompatible not only with the grade established for the main metamorphic event, but also with the temperatures estimated for the epidote + chlorite assemblage developed during the hydrothermal alteration. They are interpreted as the result of a retrograde diagenesis episode promted by low-temperature, late-stage hydrothermal fluids or by the interaction between rocks and groundwater after uplift.
title	Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
title_short	Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
title_full	Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
title_fullStr	Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
title_full_unstemmed	Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina
title_sort	mineralogical and microstructural characterization, and post-depositional history of la aguadita formation, famatina system, la rioja, argentina
publishDate	2005
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_10268774_v22_n3_p283_Collo http://hdl.handle.net/20.500.12110/paper_10268774_v22_n3_p283_Collo
_version_	1768546311571767296

Mineralogical and microstructural characterization, and post-depositional history of La Aguadita Formation, Famatina System, La Rioja, Argentina

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