Estruturas rúpteis e expressão topográfica na terminação norte da Serra da Mantiqueira, Sudeste do Brasil

Abstract

Elevated Passive Continental Margins (EPCMs) are characterized by extensive topographic elevations, such as sharp escarpments, located at the transition between a low-relief elevated inland plateau and narrow coastal plains. However, the location of the escarpment, as well as its morphology, can vary considerably, and in some cases, along the same EPCM. This situation is observed in Brazil’s southeast margin, where the southern region exhibits sharp escarpments of the Mar and Mantiqueira ranges marking regional drainage divides near the coast, and the northern region is marked by the absence of prominent escarpment, with regional divides positioned more than 100 km inland. In particular, on the northern end of the Mantiqueira Range, the interpretation of neotectonic events from the study of Neogene sediments close to the coast contrasts with the post-Miocene tectonic quiescence indicated by ages of denudation and uplift in portions of the continental interior. This study explores the patterns of topography and tectonics to investigate the post-rift geological evolution and the influence of brittle structures on topographic evolution in the northern end of the Mantiqueira Range. To this end, we performed quantitative geomorphic analyses to extract metrics from the topography, an extensive field survey to survey for brittle geological structures and mineralogical analyses of filling materials in brittle structures. The results indicate a large number of NE-SW and NW-SE oriented brittle structures formed by the concentration of local stresses developed in discontinuities of the Precambrian basement. Brittle faults with slickensides marked in the filling materials originated after mineral precipitation (in the case of manganese oxides) or during (in the case of illite), with a maximum age of deformation in the Miocene. We inferred three post-rift tectonic events: an E-W sinistral strike-slip and a WNW-ESE distension, both active between the Miocene and Pliocene; and a NE-SW to NNE-SSW distensive event, positioned in the Pleistocene. Patterns of topography, drainage, and brittle deformation indicate the presence of a NE-SW-oriented knickzone anchored to reactivated structural boundaries, associated with a topographic rejuvenation more recent than the Miocene. However, the large-scale landscape morphology, particularly the origin of the regional drainage divides, must predate post-Miocene brittle deformation and rejuvenation, implying that older and more recent topographic elements coexist in the landscape. The northern termination of the Serra da Mantiqueira, an EPCM not characterized by a prominent escarpment, underwent relatively recent topographic rejuvenation and brittle deformation, and these processes are not necessarily linked to the formation or persistence of a “Great Escarpment”.