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Geophysical constraints on tectonic models of the Taubaté Basin, southeastern Brazil

1991; Elsevier BV; Volume: 196; Issue: 1-2 Linguagem: Inglês

10.1016/0040-1951(91)90294-3

1879-3266

Antônio L. Padilha, N. B. Trivedi, Ícaro Vitorello, José Marques da Costa,

Geological and Geophysical Studies

Abstract Magnetotelluric, gravity and geothermal flux data are analysed to constrain the tectonic evolution of the Taubate Basin, a SW-NE 20 km wide and 170 km long rift-like Tertiary basin in southeastern Brazil. The basin is characterized by half-grabens and contains up to 1000 m of sediments cut by normal faults. The magnetotelluric measurements show the presence of two layers: an upper highly conductive one (less than 10 Ωm from 1-D inversions), associated with Tertiary sediments, and an extremely resistive (more than 10000 Ωm) lower layer, related to the crystalline basement. Gravity anomalies in the region are ascribed to both near-surface sources, sediments and granites, and a deep-seated source associated with crustal thinning towards the continental margin. Available geothermal flux values within the basin are anomalously high; however, they have probably been affected by convective transport because they were determined in water boreholes. These results suggest a stable thermal regime at present and, viewed together with the absence of magmatism and thermal subsidence, indicate that the mechanism related to the basin formation did not originate a deep-seated thermal anomaly in the region. The event can be seen as a shallow one, involving a small area in the upper part of the crust. The region can be characterized typically as a strike-slip mobile zone, with horizontal displacements between juxtaposed blocks. A transtensional model is suggested for the Taubate Basin to explain some of its principal geological features.