Low-temperature thermochronology in the Brazilian impact structures: dating and thermal evolution

Abstract

At the present, 182 meteorite impact structures have been identified on Earth. In the Brazilian territory, six structures of impact origin are known so far: Araguainha (MT-GO), Vargeão (SC), Vista Alegre (PR), Cerro do Jarau (RS), Serra da Cangalha (TO) and Riachão (MA). Among them, Araguainha impact structure is the one that presents age established by isotopic methods (254±2.5 Ma, U-Pb), the others have estimated age by stratigraphic principles. The importance to know the age of formation of impact structures is (i) correlates them with the causes and effects of impact events in the biosphere and geosphere, (ii) better constraining the impactor flux through geological time and evaluation of potential impact periodicity, and (iii) calibrating the absolute chronostratigraphic time scale. U-Pb and Ar-Ar are the isotopic methods conventionally used to date impact melt rock and neoformed minerals. However, in eroded impact structures there is absence of these materials, precluding the application of such geochronological dating methods. Thus, the application of low-temperature thermochronological methods, such as fission track and (U-Th)/He, both in apatite and zircon, allows obtaining the age of impact and perform the reconstruction of post-impact thermal evolution. In this study, we proposed to apply these thermochronological methods in Araguainha (MT-GO), Serra da Cangalha (TO), Riachão (MA), and Vargeão (SC) impact structures. These impact structures were chosen considering the lithology target, the diameter and the degree of erosion that they present. In this sense, we intent to contribute with the age estimation of the brazilian impact structures and the reconstruction of post-impact thermal evolution on the basis of the results obtained by thermochronological analyses proposals. (AU)