Thermobaric and kinematic evolution of Anta Gorda Anticlinorium, Ribeira Belt: metamorphism record and shear deformation in a transpressional setting

Author(s)

Maria Thereza Akemi Guimarães Yogi

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
• Defense date: 2019-12-16

Examining board members

Frederico Meira Faleiros; Vinicius Tieppo Meira; Brenda Chung da Rocha

• Advisor: Frederico Meira Faleiros

Abstract

The Ribeira Belt is an important orogen that is part of the history of Western Gondwana assembly. The southern part of the orogen comprehends important domains as the Apiaí, Curitiba and Embu terranes, that comprise units that date from Late Paleoproterozoic to the Cambrian periods. The existence of Mesoproterozoic and Paleoproterozoic rocks in the Ribeira Belt opens the possibility whether these domains record evidences of a tectonic event prior to the Gondwana assembly. Metamorphic ages constitute important missing piece in the knowledge of the Apiaí Terrane and therefore are important object of investigation on whether different Ribeira domains present similar or distinct metamorphic and tectonic overprints. This work comprehends a multi-method approach to decipher the tectono-metamorphic evolution of an area knowns as the Anta Gorda Anticlinorium in the Apiaí Terrane. Statherian orthogneissic rocks from the Tigre Gneiss and a Calymmian metasedimentary succession from the Votuverava Group constitute the object of study. Metamorphic conditions coupled with microstructural and geochronological analysis were performed to derive P-T-D-t paths for these rock units. Structural analysis showed the exhumation of Tigre Gneiss cores is result of regional scale folding in response to transpressive tectonics. A mylonitic quartzite unit in contact with Tigre Gneiss rocks indicates a simple shear dominated late deformation overprint of greenschist facies conditions. P-T-D-t paths of Votuverava Group metapelites were obtained by coupling phase equilibria modelling and monazite geochronology. P-T conditions of ~600-625°C and 9kbar, 625-650°C and 8-10 kbar and ~650-660°C and 10kbar were yielded to the garnet, staurolite and kyanite metamorphic zones, respectively. A decompression stage of at least ~6kbar kbar recorded in kyanite-bearing metapelites produced late cordierite and andalusite. Monazite and hornblende geochronology indicate progressive metamorphic stage around 615-610 Ma and peak conditions reached at ~570-580 Ma. Late stages of exhumation are constrained by monazite ages of 560-565 Ma. When compared to other terranes from the Southern Ribeira Belt, the Apiaí Terrane records distinct P-T-t path with younger and slower exhumation rate trajectories. (AU)

• FAPESP's process: 17/02769-0 - Thermo-kinematic evolution of the Anta Gorda anticlinorium basement and metasedimentary cover, southern Ribeira Belt
• Grantee: Maria Thereza Akemi Guimarães Yogi
• Support Opportunities: Scholarships in Brazil - Master