A estrutura de impacto do Cerro do Jarau, Quaraí, RS

Abstract

The Cerro do Jarau is located in Quaraí region, in the southwestern portion of the RS state and represent one of the rare astrobleme of the south region of Brazil. The structure presents circular and structurally complex form, with a diameter of approximately 14 km. The central core of the structure is uplifted and has around shape with 7 km of diameter, with steep-topographic gradients of up to 160 meters between the high portions of its edge until the levels more deep in the external portion. The circular features showed by its structure is compound by a morphological group of concentric rings, constituted by topographic depressions in the external and central areas, separated in the north and central portion of the structure by an elongated topographic elevation in half moon shape. These features are reminiscent of weathering and erosive process of an impact crater generated by collision of a meteoritic body of large dimensions. These impact effects under the sandstones of Botucatu Formation (Triassic-Jurassic) and basaltic lava flows of Serra Geral Formation (Jurassic-Cretaceous) generated a group of extensional normal faults and transcurrent ruptile shear zones moreover the structural uplift of the sedimentary rocks in central portion of the Cerro do Jarau structure. The observed features of impact metamorphism are PDF’s and PF’s structures in quartz and plagioclase of impacted sandstones and basalts, as well, probably and rare impact breccias and injection breccias. The circular shape seems today to represent the weathering and erosion remnants of the original crater.