ANÁLISE MORFOTECTÔNICA DO PLANALTO DO JUQUERIQUERÊ, SÃO SEBASTIÃO

Abstract

MORPHOTECTONIC ANALYSIS OF THE JUQUERIQUERÊ - PLATEAU, SÃO SEBASTIÃO (SP). Geomorphologic, geologic and tectonic surveys carried out in the Juqueriquerê plateau region, which belongs to the southeastern Brazilian rift system, showed that this landform is made up of a discontinuous erosion surface, still recognizable on hilltops at altitudes varying from 700 to 750 m. This plateau stands some 500 m below the Moraes plateau and about 200 m below the Lourenço Velho plateau. The boundary between the Juqueriquerê plateau and the more elevated ones roughly follows the Camburu fault, thus suggesting a tectonic origin for the lowering of the Juqueriquerê plateau. The highest plateau (Moraes plateau) owe its origin to a Paleogene erosion surface, the remains of which can be found on the higher watersheds of the Tietê river, as well as in the highest peaks of the São Sebastião island. Erosional processes increased in the Neogene with the development of the Lourenço Velho plateau at a lower position. The faulting of this latter surface generated the Juqueriquerê plateau. The main regional structural trends originated in the Precambrian and were reactivated in the early Cretaceous, Eocene and early Miocene times. Some of the low intensity earthquakes which have been observed in the area may be related to the latest of these recurrent tectonic movements. The tectonic movements which gave rise to the Juqueriquerê plateau, although most concentrated along the Camburu fault, did not result in a single block, but rather in a series of smaller blocks of varied widths, separated by many smaller faults, which altogether lowered this surface by 200 to 300 meters.