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Using apatite to resolve the age and protoliths of mid-crustal shear zones: A case study from the Taxaquara Shear Zone, SE Brazil

Texto completo
Autor(es):
Ribeiro, V, B. ; Mulder, J. A. [1] ; Faleiros, F. M. [2] ; Kirkland, C. L. [3] ; Cawood, P. A. [1] ; O'Sullivan, G. [4] ; Campanha, G. A. C. [2] ; Finch, M. A. [1] ; Weinberg, R. F. [1] ; Nebel, O. [1]
Número total de Autores: 10
Afiliação do(s) autor(es):
[1] Ribeiro, B., V, Monash Univ, Sch Earth Atmosphere & Environm Sci, Clayton, Vic 3800 - Australia
[2] Ribeiro, B., V, Univ Sao Paulo, Dept Mineral & Geotecton, Rua Lago 562, BR-05508900 Sao Paulo - Brazil
[3] Curtin Univ, Timescales Mineral Syst Grp, Ctr Explorat Targeting Curtin Node, Sch Earth & Planetary Sci, Perth, WA 6102 - Australia
[4] Univ Coll Dublin, UCD Sch Earth Sci, Dublin 4 - Ireland
Número total de Afiliações: 4
Tipo de documento: Artigo Científico
Fonte: LITHOS; v. 378, DEC 15 2020.
Citações Web of Science: 0
Resumo

Shear zones accommodate strain and facilitate migration of hydrothermal fluid and magma through the crust. Unravelling the deformation history of shear zones requires correspondence between the closure temperature of mineral geochronometers and the temperature of deformation. Here, we adopt apatite U-Pb-trace element analysis as a tool for dating deformation and tracing the protoliths of mid-crustal shear zones through a case study of the Taxaquara Shear Zone (TSZ), a major transpressional shear zone in the southern Ribeira Belt of SE Brazil. Apatite from mylonites in the TSZ yield U-Pb ages of 558-536 Ma, considering uncertiainties, which slightly overlap with Ar-40/Ar-39 ages of 538 +/- 2 Ma from muscovite in the lower limit. The closure temperature of apatite is estimated at 500-460 degrees C, which is slightly higher than that estimated for syn-kinematic muscovite (445-420 degrees C). Apatite from shear zone mylonites has Sr/Y and LREE systematics typical of apatite from S- and I-type granitoids, suggesting the adjacent and undeformed Pilar do Sul and Piedade granites are the likely protoliths of the mylonites. This interpretation is supported by new U-Pb ages of ca. 605 Ma from prekinematic zircon and titanite from mylonites, which corresponds closely with new U-Pb apatite ages and previously published U-Pb monazites ages fromthe Pilar do Sul Granite. Wesuggest the U-Pb systemof apatite in the TSZ was reset via volume diffusion during rapid cooling given that it preserves the igneous geochemical signatures. Moreover, this interpretation is consistent with the lower apatite closure temperature (500-460 degrees C) relatively to the temperature of deformation (530-480 degrees C). The revised similar to 560-535 Ma age for the TSZ demonstrates that it post-dates the collisional phase of the Ribeira Belt (620-595 Ma and 595-565 Ma), indicating protracted strain accommodation during the Brasiliano-Pan African orogeny, and supports correlation with the 600-550Ma and 570-550 Ma transpressional Dom Feliciano and Kaoko Belts. This study demonstrates that apatite is a powerful tool for unravelling the history of mid-crustal shear zones as it is stable in a wide range of lithotypes, has trace element compositions that are sensitive to the environment of formation, and Pb closure temperatures typical of mid-crust conditions. U-Pb-trace element analysis of apatite provides a robustmeans to date shear zones that can be complimentary to, or independent of, more traditional 40Ar/39Ar analysis of mica or amphibole. (C) 2020 Elsevier B.V. All rights reserved. (AU)

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
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: 15/03737-0 - O Cráton Rio de la Plata e o Gondwana Ocidental
Beneficiário:Miguel Angelo Stipp Basei
Linha de fomento: Auxílio à Pesquisa - Temático
Processo FAPESP: 18/16307-1 - Avaliação da idade de deformação da Zona de Cisalhamento de Taxaquara, Faixa Ribeira (Brasil), através de análises geocronológicas e termocronológicas
Beneficiário:Bruno Vieira Ribeiro
Linha de fomento: Bolsas no Exterior - Estágio de Pesquisa - Mestrado