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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.)

Deformation conditions and quartz c-axis fabric development along nappe boundaries: The Andrelandia Nappe System, Southern Brasilia Orogen (Brazil)

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Author(s):
de Oliveira Rodrigues, Sergio Wilians [1] ; Cacador Martins-Ferreira, Marco Antonio [1] ; Faleiros, Frederico Meira [2] ; Campos Neto, Mario da Costa [2] ; Akemi Guimaraes Yogi, Maria Thereza [2]
Total Authors: 5
Affiliation:
[1] UFG, Fac Ciencias & Tecnol, Setor Conde Arcos, Rua Mucuri S-N, Aparecida De Goiania, Go - Brazil
[2] Univ Sao Paulo, Inst Geociencias, Dept Mineral & Geotecton, Rua Logo 562, BR-05508080 Sao Paulo, SP - Brazil
Total Affiliations: 2
Document type: Journal article
Source: TECTONOPHYSICS; v. 766, p. 283-301, SEP 5 2019.
Web of Science Citations: 0
Abstract

The Liberdade and Andrelandia nappes, SE Brazil, record the western Gondwana amalgamation in the Southern Brasilia Orogen during the Ediacaran. The Liberdade Shear Zone acted as the boundary between these two overlapping nappes. Quartz c-axis fabrics and strain data from quartzite samples and petrological data from hosting metapelite rocks were analyzed to investigate the tectonic processes involved in nappe development. Further constraints were achieved by conducting petrological modeling and geothermobarometry using P-T isochemical phase diagram approaches. Quartz axis plots show consistency with different kinematic criteria verified in the field in meso and macroscale. The fabrics are associated to both coaxial deformation and non-coaxial deformation. Quartz microstructures, metamorphic assemblages and c-axis concentrations primarily around Y and X structural directions suggest that deformation was accommodated by grain boundary migration recrystallization under temperature above 500 degrees C. Disregarding pressure effects the opening angles of quartz c-axis fabrics suggest temperatures between 480 and 640 degrees C (muscovite quartzite) and 650-720 degrees C (sillimanite quartzite). Considering pressure data, the opening angles indicate conditions of 550-650 degrees C and 7-10 kbar (muscovite quartzite) and 600-730 degrees C and 4-7 kbar (sillimanite quartzite), reflecting primarily distinct baric regimes. Sillimanite-bearing samples estimatives are supported by ubiquitous presence of chessboard subgrain patterns in quartz and by modeled isochemical phase diagrams that constrain conditions of 660-730 degrees C and 6-7 kbar for garnet-sillimanite-biotite schist samples. Altogether, these results indicate progressive tectonic evolution linked to oblique convergence between tectonic units represented by the Andrelandia and Liberdade nappes and the Paleoproterozoic basement. Besides recording distinct thermal and baric regimes, the nappes also present different structural styles, suggesting that pressure and temperature are important boundary conditions for the nappe structural style. (AU)

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 Opportunities: Regular Research Grants