Print this pageBasement-Cored Uplifts Related to Meso-Cenozoic Tectonism in the Amazonas and Solimões Basins - Northern Brazil
Basement-cored uplifts are often described as structures related to the reactivation of basement faults due to friction of low-angle subducting plates beneath the lithosphere of active continental margins. The products are huge basement highs controlled by reverse faults with kilometric throws and associated forced folds. The aim of this paper is to show that similar products occur in different tectonic settings not only related to shallow subduction, e.g. in interior basins.
The Paraguá-Jutaí High, at the western part of the Solimões Basin, is a basement high controlled by a 1.7km throw reverse fault. It is the product of regional transpression during the Juruá Event (Upper Jurassic) within the Solimões Mega-Shear Zone, a deformational belt where basement faults focused the strain due to differential rotation and translation of the South American Plate during the break up of Gondwana.
The Monte Alegre Dome, at the mid-eastern Amazonas Basin, is an asymmetrical fold forced by the uplift of a basement block. It has an elliptical topographic expression where the Devonian rocks of the Ererê Formation crop out in its core, surrounded by Carboniferous rocks of the Monte Alegre Formation at its flanks. A N45E-trending reverse fault throws the Paleozoic rocks of the hanging wall over the Cretaceous rocks of the Alter do Chão Formation in the foot-wall. Surface geology and data from foot-wall wells show that the fault throw is around 3.3km. There is a positive gravity anomaly whose shape fits almost perfectly the dome. This dome occurs in front of the hinge line of a huge and southward plunging open anticline deforming the Paleozoic rocks cropping out at the northern edge of the basin. Radar images and geological mapping of the terrain surface show that this big fold is controlled by a N30W-trending basement block which was uplifted during Cenozoic strike-slip reactivation of ancient faults, in response to remote tensions from the Caribbean margin of the South American Plate. The Monte Alegre Dome was probably caused by a basement cored uplift that exploded near the crest of the regional northern basin flank anticline.
The tectonic features described above show that the term “basement-cored uplift” which has been used with a strong genetic connotation (associated with low-angle subduction) should be used in a descriptive sense, once the same products may occur in other tectonic settings.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil