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Peter Hackspacher, State University São Paulo- UNESP (Brazil)
Elton Dantas, University of Brasilia (Brazil)
Ivaldo Trindade, State University São Paulo (Brazil)
Richard Armstrong, Australian National University (Australia)
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The southeastern Brazilian coastline comprises different lithologies of origins and ages strongly affected by the Ribeira Belt (RB), related to the Brasiliano-Pan-African orogeny. Late-collisional northeast-southwest dextral strike-slip shear zones are responsible for the lateral juxtaposition of different crustal levels. The present work will focus on and present shrimp U/Pb data which confirm the importance of vertical displacement during the lateral escape in a transpressive regime of the RB.
The late-collisional phase, around 600 Ma, affected calc-alkaline to alkaline granites of the I-type, locally S-type. Pos-tectonic phase is represented by the Itu granite, (Rapakiwi Province) at 580 Ma and the beginning of the extensional phase and future structuring of the Paraná basin.
Metasediments, in greenshist facies, of the São Roque Group (sedimentation at 630 Ma) were positioned laterally to migmatitic and granitic rocks of the Embu Complex (metamorphism between 620- 600 Ma) by the dextral Taxaquara strike-slip shear zone. Zircons of the São Roque Group performs Paleoproterozoic ages without metamorphic rims, otherwise zircons of the Embu Complex shows zircons with Paleoproterozoic cores and 600 Ma old rims, also the age of the shear zone. This shear zone put side by side rocks of the São Roque Group (metamorphism at 400 oC) and the Embu Complex (metamorphism around 650 oC) with difference of 250 oC between boths. For a geothermal gradient of 40 oC/km a vertical displacement around 6 km can be considered.
It is considered that the Taxaquara shear zone represent part of a regional transpressive system with significant vertical displacement. The vertical displacement was responsible for the side by side setting of different crustal levels, and can be considered as an important process during the post- collisional regime of the Brazilian/Pan-African Cycle in southeastern Brazil. Probably this process formed high mountains, the Brasiliano-Pan-African Alps. Younger reactivations can be found in strong deformed metaconglomerate of Vendian ages.
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