Basement controls on cover deformation in eastern Chapada Diamantina, northern São Francisco Craton, Brazil : insights from potential field data.

Abstract

The Proterozoic sedimentary cover in eastern Chapada Diamantina recorded positive inversion tectonics at the Paramirim aulacogen during Neoproterozoic times. Additionally, geological evidence suggests that although the basement was not involved in the contractional tectonics, it exerted control on cover deformation. The Euler deconvolution, based on aeromagnetic and gravimetric databases, integrated with geological framework, was used to delineate the structures and deep architecture of the crystalline basement and to understand their relationships with cover deformation. The 3D view of Euler deconvolution profiles show a graben and horst geometry in the basement architecture. Horsts and grabens are limited by NNW-SSE, N-S and E-W normal faults, which nucleated during two extensional events and favored for deep Archean-Paleoproterozoic discontinuities. The first event was related to the development of a half-graben that had a NNE-SSE-oriented eastern boundary and that was filled with rocks of the Chapada Diamantina Group. The second event gave rise to an asymmetrical graben that evolved from dextral strike-slip displacement and was filled by rocks of the Una Group in the Irecê domain. In the late Neoproterozoic, two contractional, thin-skinned cover deformations with ENE-WSW and N-S shortening directions affected the Chapada Diamantina and Irecê domains. Our geophysical models reveal a parallelism between the thin-skinned structures and N-S and E-W normal faults, interpreted in the crystalline basement, suggesting a control on strain and stress distribution during cover deformation. During the second contractional tectonic event, the NNW-SSE and N-S lineaments at the boundaries of the Irecê domain were reactivated, producing Ubiaí and Serra da Babilônia brittle shear zones in the sedimentary cover, respectively. In summary, the superposed intracratonic basin formation was controlled by older structures in the crystalline basement, while the inversion tectonics was controlled by the geometry of these basins.