A interação tectônica embasamento/cobertura em aulacógenos invertidos: um exemplo da Chapada Diamantina Ocidental

Abstract

A basement-involved fold-trust belt is exposed along the western border of the Chapada Diamantina, a high plateau underlain by proterozoic units in the interior of the northern Sao Francisco craton. This NNW-trending and ENE-verging fold fold-thrust belt encompasses a substantial part of the eastern portion of the Paramirim aulacogen, which corresponds to a intracratonic rift basin that experienced a long history of development starting at ca. 1.75 Ga with sedimentation of Espinhaco Supergroup. After the deposition of its second major fill unit, the Neoproterozoic (Tonian-Cryogeninan) Sao Francisco Supergroup, the Paramirim rift experienced a vigorous positive inversion that generated the system of NNW-trending faults and folds. Aiming to contribute to better understanding of basement-involved inversion tectonics, we carried out a field based structural analysis along the western Chapada Diamantina. Our results indicated that the inversion process took place according to four coaxial phases of progressive deformation. Under an overall WNWESE oriented shortening, the first phase of deformation (D pdesc ) nucleated a thin-skinned system of ESE-verging structures, including layer controlled detachments, blind imbricate fans, strata-confined duplexes and a variety of small-scale structures. Reactivating pre-exiting structures, the subsequent deformation phases (D p1/p2 ) were responsible for the generation of basement-involved reverse faults, reverse to oblique-slip ductile shear zones and large-scale NNW-trending folds that dominate the structural picture of the western Chapada Diamantina. During the D p3 -phase trains of NNW-oriented and WSW-verging folds associated with a prominent crenulation cleavage overprint the previously mentioned structures in the high strain zones of the western border of the Chapada Diamantina.