Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)

The Vendian-Early Cambrian Puncoviscana Formation is a pelite-greywacke turbidite sequence affected by polyphase deformation cropping out extensively in the Cordillera Oriental of northwestern Argentina. Previous X-ray diffraction and analytical high-resolution TEM studies on southern locations foun...

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Autores principales:	Do Campo, M., Collo, G., Nieto, F.
Formato:	JOUR
Materias:	Chlorite, phengite EDX Kübler Index P-T-time paths Scanning electron microscopy Thermobarometry Cambrian chemical composition chlorite diagenesis geobarometry geothermometry metamorphic rock mica mineralogy P-T-t path pelite phengite scanning electron microscopy unconformity Vendian X-ray diffraction Argentina Cordillera Oriental [Argentina]
Acceso en línea:	http://hdl.handle.net/20.500.12110/paper_09351221_v25_n3_p429_DoCampo
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	todo:paper_09351221_v25_n3_p429_DoCampo
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spelling	todo:paper_09351221_v25_n3_p429_DoCampo2023-10-03T15:48:35Z Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina) Do Campo, M. Collo, G. Nieto, F. Chlorite, phengite EDX Kübler Index P-T-time paths Scanning electron microscopy Thermobarometry Cambrian chemical composition chlorite diagenesis geobarometry geothermometry metamorphic rock mica mineralogy P-T-t path pelite phengite scanning electron microscopy unconformity Vendian X-ray diffraction Argentina Cordillera Oriental [Argentina] The Vendian-Early Cambrian Puncoviscana Formation is a pelite-greywacke turbidite sequence affected by polyphase deformation cropping out extensively in the Cordillera Oriental of northwestern Argentina. Previous X-ray diffraction and analytical high-resolution TEM studies on southern locations found anchizonal grade and proposed medium-high pressure metamorphism followed by higher thermal conditions. We have determined the chemical composition of mica and chlorite with EDX on small uncontaminated areas selected using SEM in backscattered electron mode. The application of mica-chlorite geothermobarometry to mineral grains defining two different foliations has produced consistent pressure/temperature results based on the intersection of six reactions: 9 kbar/250 °C peak conditions were followed by an isothermal decompression to 3 kbar and a successive increase of temperature to nearly 350 °C at 1.5 kbar. The shales from the overlying Mesón and Santa Victoria Cambro-Ordovician groups do not contain chlorite, thus chlorite-mica geothermobarometry could not be applied. According to the range of KICIS obtained (0.41-0.68Δ°2θ) and their mineralogical assemblage (illite ± kaolinite ± corrensite + Qtz + Pl ± Kfs), these rocks have not surpassed diagenetic conditions, which implies a minimum temperature difference with the Puncoviscana Formation of 100 °C, consistent with the sharp angular unconformity between the two units. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart. Fil:Do Campo, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_09351221_v25_n3_p429_DoCampo
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Chlorite, phengite EDX Kübler Index P-T-time paths Scanning electron microscopy Thermobarometry Cambrian chemical composition chlorite diagenesis geobarometry geothermometry metamorphic rock mica mineralogy P-T-t path pelite phengite scanning electron microscopy unconformity Vendian X-ray diffraction Argentina Cordillera Oriental [Argentina]
spellingShingle	Chlorite, phengite EDX Kübler Index P-T-time paths Scanning electron microscopy Thermobarometry Cambrian chemical composition chlorite diagenesis geobarometry geothermometry metamorphic rock mica mineralogy P-T-t path pelite phengite scanning electron microscopy unconformity Vendian X-ray diffraction Argentina Cordillera Oriental [Argentina] Do Campo, M. Collo, G. Nieto, F. Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
topic_facet	Chlorite, phengite EDX Kübler Index P-T-time paths Scanning electron microscopy Thermobarometry Cambrian chemical composition chlorite diagenesis geobarometry geothermometry metamorphic rock mica mineralogy P-T-t path pelite phengite scanning electron microscopy unconformity Vendian X-ray diffraction Argentina Cordillera Oriental [Argentina]
description	The Vendian-Early Cambrian Puncoviscana Formation is a pelite-greywacke turbidite sequence affected by polyphase deformation cropping out extensively in the Cordillera Oriental of northwestern Argentina. Previous X-ray diffraction and analytical high-resolution TEM studies on southern locations found anchizonal grade and proposed medium-high pressure metamorphism followed by higher thermal conditions. We have determined the chemical composition of mica and chlorite with EDX on small uncontaminated areas selected using SEM in backscattered electron mode. The application of mica-chlorite geothermobarometry to mineral grains defining two different foliations has produced consistent pressure/temperature results based on the intersection of six reactions: 9 kbar/250 °C peak conditions were followed by an isothermal decompression to 3 kbar and a successive increase of temperature to nearly 350 °C at 1.5 kbar. The shales from the overlying Mesón and Santa Victoria Cambro-Ordovician groups do not contain chlorite, thus chlorite-mica geothermobarometry could not be applied. According to the range of KICIS obtained (0.41-0.68Δ°2θ) and their mineralogical assemblage (illite ± kaolinite ± corrensite + Qtz + Pl ± Kfs), these rocks have not surpassed diagenetic conditions, which implies a minimum temperature difference with the Puncoviscana Formation of 100 °C, consistent with the sharp angular unconformity between the two units. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart.
format	JOUR
author	Do Campo, M. Collo, G. Nieto, F.
author_facet	Do Campo, M. Collo, G. Nieto, F.
author_sort	Do Campo, M.
title	Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
title_short	Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
title_full	Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
title_fullStr	Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
title_full_unstemmed	Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)
title_sort	geothermobarometry of very low-grade metamorphic pelites of the vendian-early cambrian puncoviscana formation (nw argentina)
url	http://hdl.handle.net/20.500.12110/paper_09351221_v25_n3_p429_DoCampo
work_keys_str_mv	AT docampom geothermobarometryofverylowgrademetamorphicpelitesofthevendianearlycambrianpuncoviscanaformationnwargentina AT collog geothermobarometryofverylowgrademetamorphicpelitesofthevendianearlycambrianpuncoviscanaformationnwargentina AT nietof geothermobarometryofverylowgrademetamorphicpelitesofthevendianearlycambrianpuncoviscanaformationnwargentina
_version_	1807323776550961152

Geothermobarometry of very low-grade metamorphic pelites of the Vendian-Early Cambrian Puncoviscana Formation (NW Argentina)

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