Sr-Nd isotopes data of the Neoproterozoic-Paleozoic pelites, northwest Argentina and its implications for the early Paleozoic evolution of SW Gondwana margin

APARICIO GONZALEZ PAMELA; NATALIA HAUSER; ANDREA BARRIENTOS; CLAUDIO DE MORISSON VALERIANO; AGNES IMPICCINI; MANUELA DE OLIVEIRA CARVALHO1; MÓNICA HEILBRONT

Río Negro

Congreso; Reunión Argentina de Sedimentología; 2018

AAS

The Sr, Sm and Nd isotopes results of twelve samples from the main pelitic units of Puncoviscana complex, Mesón, Santa Victoria Groups Mojotoro Porphyry Granite are presented.In the analyzed samples were measured values of 143Nd/144Nd between 0.51183 and 0.5121, of 147Sm/144Nd from 0.1077 to 0.1269, of 87Sr/86Sr between 0.7316 and 0.8295, and εNd(t) exhibit consistently negative values varying from -8.7 and -15.7. These intervals plotted in an 87Sr/86Sr versus εNd(t) diagram are concentrated in the field of very radiogenic data, where the more radiogenic values are related to the Chachapoyas Formation rocks and to the Guachos Formation, which has also the less radiogenic sample. A change is observed in the upper units from the Puncoviscana Complex indicating the participation of less radiogenic sediments as compared to the lower Chachapoyas Formation.All units show Meso to Paleoproterozoic TDM model ages of 1.9 Ga for the Mojotoro Granite that intrudes the Chachapoyas Formation; between 1.49 Ga and 1.59 Ga in the Puncoviscana Complex metasediments; of 1.50 Ga in the Campanario Formation; and between 1.49 Ga and 1.90 Ga for the Victoria Group units. The oldest TDM model ages of 1.9 Ga are related to rocks from the Floresta Formation, Santa Victoria Group, and to the Mojotoro Granite.The Nd and Sr isotopic results for the Puncoviscana Complex, the Mesón Group and the Santa Victoria Group are relatively homogeneous, which suggests that most of the lower Paleozoic rocks of the Mojotoro range share similar sources. The average TDM model age of ~ 1,53Ga indicates a strong Mesoproterozoic source of sediments.All units describe mixing lines between old and young isotopic sources that passes through the Mojotoro Granite data.