Geocronologia U-Pb em zircões detríticos de sedimentos da Bacia do Rio Piratini, RS

Abstract

The Piratini River basin is located in the southeastern region of the state of Rio Grande do Sul and is composed of detrital sediments derived from granitic rocks of Pelotas Batholith. The region has a predominance of calc-alkaline proterozoic rocks, with a minimum age of 206Pb / 207Pb, previously suggested, of ± 650 Ma. From the U-Pb LAICP-MS dating method (Laser ablation inductively coupled plasma mass spectrometer) applied in the collected sediment samples, the data obtained were analyzed and interpreted and can be used as a basis for geochronology studies in the region. The work began with fieldwork, where sediments from samples JG-01, JG-02 and JG-03 were collected, respectively at the margin downstream of the confluence between the Piratini river and the Basílio river, at the margin of the Basílio river and at the margin of the Piratini River. Of the 413 detrital zircon grains selected from the samples, 236 have an agreement greater than 5%. The U/Pb ages of the detritic zircons show a contribution of sediments from source areas of neoproterozoic ages, with populations of more frequent ages of 622 Ma, 625 Ma and 640 Ma. The results obtained coincide and reinforce the ages of other bibliographies, making it possible to complement the region's geochronological data.