Investigações tectônicas no embasamento da sub-bacia do Jandiatuba (bacia do Solimões)

Abstract

Through this work, we sought to understand the structural framework of the continental crust of the western portion of the Solimões Basin called Jandiatuba Sub-basin. With this approach, the nature of the basement and intrabasement structural systems of the basin was characterized based on the geometry and depth of the reflectors. The analysis of conventional seismic sections, used in oil prospecting, and of three versions of a deep seismic profile, with records from 15 to 19 seconds (double time), provided the definition of the following structural elements. (a) inverse faults in the Jandiatuba sub-basin sedimentary package; (b) fault zones that dip following a pattern in the form of ramps, which may be related to shear zones or back-thrusts, especially in the upper crust; (c) detachments that permeate the crust and project into the crust-mantle interface; (d) imbrications in the middle and lower intervals of the ductile crust expressed through a strongly anastomotic signature; (e) seismic “transparency” of the brittle upper crust evidenced by the absence of reflectors, in addition to “transparent” lenses in the deeper crustal levels; (f) the discontinuity of the Moho characterized by several anastomotic beams of reflectors, the differentiation of reflectivity and the decrease in amplitude and frequency in the range of 38 to 45 km. The analysis of the collection of results of the different programs existing on the various continents on deep reflection seismic (COCORP, BIRPS, DEKORP and ECORS), helped in the interpretation of the set of reflectors and was fundamental for the comparison and correlation between the different seismic signatures. The complexity of the seismic signatures of this crustal segment of Amazonia was mainly related to the geometry of structural systems of thrust belts and transcurrents, as well as extensional basins. In other words, seismic arrangements resulting from the action of compressive, directional and extensional regimes were identified. The defined structural framework was discussed through three models that consider compression and imbrication in the Precambrian, stretching in the early Paleozoic and transpression in the Jurassic. Therefore, the Jandiatuba sub-basin region corresponds to a crustal segment that experienced at least three main tectonic movements during its geotectonic evolution.