Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil

Micaschists that host the Acari batholith (Ediacaran age, 572 to 577 My) are characterized by a large number of quartz veins. The veins are more abundant in higher-temperature metamorphic zones and, together with lower metamorphic zones, form an aureole centered in the batholith. Most of the fluid...

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Autores principales:	Laécio Cunha de Souza, Regina Celia de Oliveira Brasil Delgado, Heitor Neves Maia
Formato:	article
Lenguaje:	EN PT
Publicado:	Universidade de São Paulo 2021
Materias:	Fluid inclusions Quartz veins Micaschists Thermal aureole Fluid composition Salinity Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/e3928bbc96734c1797e73480c7bc7421
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id	oai:doaj.org-article:e3928bbc96734c1797e73480c7bc7421
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spelling	oai:doaj.org-article:e3928bbc96734c1797e73480c7bc74212021-11-23T16:28:41ZFluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil2316-9095https://doaj.org/article/e3928bbc96734c1797e73480c7bc74212021-11-01T00:00:00Zhttps://www.revistas.usp.br/guspsc/article/view/192784https://doaj.org/toc/2316-9095 Micaschists that host the Acari batholith (Ediacaran age, 572 to 577 My) are characterized by a large number of quartz veins. The veins are more abundant in higher-temperature metamorphic zones and, together with lower metamorphic zones, form an aureole centered in the batholith. Most of the fluid inclusions are two-phase (H2O-CO2 and liquid/vapor), but three-phase varieties (liquid/vapor/salt cubes; liquid/liquid/vapor) occur locally. The analyzed veins come from the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite metamorphic zones. CO2 melting temperatures (TmCO2) vary from -62.6 to -56.7°C, suggesting CH4 and/or N2. Eutectic temperatures (Te) in quartz veins show average values of -30.8°C in the biotite + chlorite + muscovite and biotite + garnet zones, and -38.6°C in the cordierite + andalusite and cordierite + sillimanite zones. Ice-melting temperatures (Tmice) are lower in the higher-temperature metamorphic zones. The mode values are -3.8, -5.5, -5.6, and -7.3°C, corresponding respectively to the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite zones. A fluid characterized by the H2O-Na-Cl (KCl)-MgCl2-FeCl2-CaCl2 system is defined by: Tmice from near -1.9 to -32°C, the presence of salt cubes mainly in the cordierite + andalusite and cordierite + sillimanite zones, and recorded eutectic temperatures (Te) from -16.5 to -59.1°C. In addition, total homogenization temperatures (Tht) ranging from 117 to 388°C were obtained for primary aqueous fluid inclusions. This indicates a long period of fluid circulation under conditions of falling temperatures. Our results are consistent with an increase in the salinity of the aqueous fluid across the thermal aureole toward the granitic batholith. Laécio Cunha de SouzaRegina Celia de Oliveira Brasil DelgadoHeitor Neves MaiaUniversidade de São PauloarticleFluid inclusionsQuartz veinsMicaschistsThermal aureoleFluid compositionSalinityGeologyQE1-996.5ENPTGeologia USP. Série Científica, Vol 21, Iss 4 (2021)
institution	DOAJ
collection	DOAJ
language	EN PT
topic	Fluid inclusions Quartz veins Micaschists Thermal aureole Fluid composition Salinity Geology QE1-996.5
spellingShingle	Fluid inclusions Quartz veins Micaschists Thermal aureole Fluid composition Salinity Geology QE1-996.5 Laécio Cunha de Souza Regina Celia de Oliveira Brasil Delgado Heitor Neves Maia Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
description	Micaschists that host the Acari batholith (Ediacaran age, 572 to 577 My) are characterized by a large number of quartz veins. The veins are more abundant in higher-temperature metamorphic zones and, together with lower metamorphic zones, form an aureole centered in the batholith. Most of the fluid inclusions are two-phase (H2O-CO2 and liquid/vapor), but three-phase varieties (liquid/vapor/salt cubes; liquid/liquid/vapor) occur locally. The analyzed veins come from the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite metamorphic zones. CO2 melting temperatures (TmCO2) vary from -62.6 to -56.7°C, suggesting CH4 and/or N2. Eutectic temperatures (Te) in quartz veins show average values of -30.8°C in the biotite + chlorite + muscovite and biotite + garnet zones, and -38.6°C in the cordierite + andalusite and cordierite + sillimanite zones. Ice-melting temperatures (Tmice) are lower in the higher-temperature metamorphic zones. The mode values are -3.8, -5.5, -5.6, and -7.3°C, corresponding respectively to the biotite + chlorite + muscovite, biotite + garnet, cordierite + andalusite, and cordierite + sillimanite zones. A fluid characterized by the H2O-Na-Cl (KCl)-MgCl2-FeCl2-CaCl2 system is defined by: Tmice from near -1.9 to -32°C, the presence of salt cubes mainly in the cordierite + andalusite and cordierite + sillimanite zones, and recorded eutectic temperatures (Te) from -16.5 to -59.1°C. In addition, total homogenization temperatures (Tht) ranging from 117 to 388°C were obtained for primary aqueous fluid inclusions. This indicates a long period of fluid circulation under conditions of falling temperatures. Our results are consistent with an increase in the salinity of the aqueous fluid across the thermal aureole toward the granitic batholith.
format	article
author	Laécio Cunha de Souza Regina Celia de Oliveira Brasil Delgado Heitor Neves Maia
author_facet	Laécio Cunha de Souza Regina Celia de Oliveira Brasil Delgado Heitor Neves Maia
author_sort	Laécio Cunha de Souza
title	Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
title_short	Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
title_full	Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
title_fullStr	Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
title_full_unstemmed	Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil
title_sort	fluid evolution from quartz veins in micaschists from the thermal aureole around the acari batholith, northeast brazil
publisher	Universidade de São Paulo
publishDate	2021
url	https://doaj.org/article/e3928bbc96734c1797e73480c7bc7421
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Fluid evolution from quartz veins in micaschists from the thermal aureole around the Acari batholith, Northeast Brazil

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