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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

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

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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]
Total Authors: 10
[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
Total Affiliations: 4
Document type: Journal article
Source: LITHOS; v. 378, DEC 15 2020.
Web of Science Citations: 0

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)

FAPESP's process: 18/00320-9 - Crystallographic, deformational and thermocronological analysis of mylonites of Taxaquara shear zone (São Paulo)
Grantee:Bruno Vieira Ribeiro
Support type: Scholarships in Brazil - Master
FAPESP's process: 18/10012-0 - Fluid flow, deformation and tectonic significance of regional shear zones from the southern Ribeira Belt
Grantee:Frederico Meira Faleiros
Support type: Regular Research Grants
FAPESP's process: 15/03737-0 - The Rio de La Plata Craton and the Western Gondwana Assembly
Grantee:Miguel Angelo Stipp Basei
Support type: Research Projects - Thematic Grants
FAPESP's process: 18/16307-1 - A geochronological and thermochronological approach to assess timing of deformation of Taxaquara Shear Zone, Ribeira Belt (Brazil)
Grantee:Bruno Vieira Ribeiro
Support type: Scholarships abroad - Research Internship - Master's degree