POST GONDWANA BREAK-UP: CONSTRAINTS FROM APATITE FISSION TRACK THERMOCHRONOLOGY IN SOUTHEAST MARGIN OF THE SANTA CATARINA STATE, BRAZIL

In an attempt to reconstruct the tectono-thermal history in the Southeast portion of Santa Catarina continental margin, apatite fission track thermochronology was applied in a suite of nineteen outcrop samples in order to establish timing and intensity of the paleo-thermal events. The study area is included in the Neoproterozoic to Early Paleozoic Florianópolis Batholith in the Dom Feliciano Belt. The sampling was accomplished along E-W profiles, from the current coastline to the Paraná Basin, considering the tectonic fragmentation of different blocks controlled by WNW-ESE structures. The basement outcrop fission track samples are composed by Neoproterozoic granitoids from the Brasiliano Cycle. Besides were collected additional samples in the line of NNE-SSW and WNW-ESE structures. The apatite fission track thermochronology has been carried out at the Isotope Geology Laboratory of the Universidade Federal do Rio Grande do Sul, Brazil and at the Nuclear Geophysics Laboratory of the Universite Joseph Fourier, France. The fission track ages vary from 68 ± 4 to 46 ± 2 Ma. On the one hand the apparent ages distribution do not present any correlation to the different tectonic blocks. On the other hand, when analyzed with the altitude, the diagram presents two different groups of samples: i) the first group presents a positive correlation between FT ages altitude in the order of 0,01 mm/year, and ii) the second group is constituted by samples collected in the current coastal plain with fission track ages in the same interval of the previous group; however there is no correlation with the altitude. The confined fission track lengths vary between 13.3 ± 0.1 and 10.8 ± 0.3 μm. Based on fission track thermal history modeling, one abrupt regional event has been recognized in the study area, which occurred in the Late Cretaceous with a denudation rate of 1.5 Km. This cooling pattern event is here interpreted as a geomorphic response to the reactivation of NNE-SSW and WNW-ESE basement structures caused by a change in the spresding geometry of the South Atlantic Ocean.