Uplift and subsidence of the RGR: U-Th/He in apatite and EPFT in zircon

Abstract

The Rio Grande Rise (RGR) has key importance for the understanding of the South Atlantic Ocean opening and the evolution associated with lithospheric plate margins. Here we review the last 100 years of scientific work regarding the RGR history and also bring new insights on its evolution based on apatite (U-Th-Sm)/He thermochronology. We have analyzed basalt fragments sampled across the RGR NW-SE rift structure. The samples were dredged during the Rio Grande Rise Project (PROERG) expedition in 2011 from the Brazilian Geological Survey (CPRM). The RGR is interpreted as part of a tectono-sedimentary evolution that extends from the first basaltic flows in the Santonian-Coniacian, until the tectonic reactivations of the South Atlantic Plate, affecting the most recent sediments. The AHe method results address to the continuous reactivation from Late Cretaceous to Neogene and is consistent with a microplate boundary environment.