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Strain localization and fluid-assisted deformation in apatite and its influence on trace elements and U-Pb systematics

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Autor(es):
Ribeiro, V, B. ; Lagoeiro, L. [1] ; Faleiros, F. M. [2] ; Hunter, N. J. R. [3] ; Queiroga, G. [4] ; Raveggi, M. [3] ; Cawood, P. A. [3] ; Finch, M. [3] ; Campanha, G. A. C. [2]
Número total de Autores: 9
Afiliação do(s) autor(es):
[1] Univ Fed Parana, Geol Dept, 100 Francisco Heraclito dos Santos St, Bloco 6, BR-35400000 Curitiba, Parana - Brazil
[2] Univ Sao Paulo, Dept Mineral & Geotecton, Rua Lago 562, BR-05508900 Sao Paulo - Brazil
[3] Ribeiro, B., V, Monash Univ, Sch Earth Atmosphere & Environm Sci, Clayton, Vic 3800 - Australia
[4] DEGEO EM UFOP, BR-35400000 Ouro Preto, MG - Brazil
Número total de Afiliações: 4
Tipo de documento: Artigo Científico
Fonte: Earth and Planetary Science Letters; v. 545, SEP 1 2020.
Citações Web of Science: 0
Resumo

This paper presents electron backscatter diffraction (EBSD), trace element and U-Pb data of apatite grains from a granitic mylonite from the Taxaquara Shear Zone (SE Brazil). The mylonite recrystallized under upper-greenschist facies and presents two types of apatite with distinct microstructures. Type-1 apatite appears in quartz-rich layers and does not exhibit any microstructural, crystallographic, or chemical evidence of deformation/recrystallization, and resembles the original igneous apatite. Type-2 apatite appears in mica-rich layers and exhibits core-and-mantle microstructures, and intragranular subgrain development, suggesting that they have undergone dynamic recrystallization. Recrystallized tails of type-2 apatite grains exhibit a strong c-axis crystallographic preferred orientation parallel to the X-direction (stretching lineation), and lack evidence of dislocation density. This evidence from type-2 apatite grains, combined with REE depletion, high La and a negative Ce anomaly compared to type-1 grains, suggests that type-2 apatite tails underwent recrystallization via dissolution-precipitation creep, whereas parental grains underwent crystal-plastic deformation and subgrain formation through dynamic recrystallization. Phase-equilibrium modelling and quartz CPO opening-angle thermometry are consistent with recrystallization at similar to 480 - 530 degrees C and 2.2 - 5.0 kbar. We were not able to determine precise deformation ages from type-2 apatite because fluid-assisted recrystallization appears to have substantially decreased the U/Pb ratio. We find that preferential fluid flow along high-strain, biotite-rich layers in the mylonite caused type-2 apatite to recrystallise, whereas type-1 apatite in low strain layers was unaffected and retained the characteristics of the protolith. (C) 2020 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 18/10012-0 - Fluxo de fluidos, deformação e significado tectônico de zonas de cisalhamento regionais do Cinturão Ribeira Meridional
Beneficiário:Frederico Meira Faleiros
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 18/00320-9 - Análises cristalográficas, deformacionais e termocronológicas dos milonitos da zona de cisalhamento de Taxaquara (São Paulo)
Beneficiário:Bruno Vieira Ribeiro
Linha de fomento: Bolsas no Brasil - Mestrado