U-Pb and Lu-Hf zircon (SHRIMP-LA-ICPMS-MC) analyses of Cambrian and Silurian-Devonian sequences of Northeastern Patagonia: its tie-up with southern Gondwana.

NAIPAUER MAXIMILIANO; GONZÁLEZ PABLO DIEGO; SATO ANA MARÍA; VARELA RICARDO; LLAMBÍAS EDUARDO; MANASSERO MARCELO

Buzios

Simposio; Gondwana 14. Reuniting Gondwana: East meets West; 2011

Universidad Federal de Río de Janeiro

U-Pb and Lu-Hf isotopic data (SHRIMP and LA-ICP-MS) from previous contributions (Pankhurst et al., 2006; Naipauer et al., 2010; 2011; Uriz et al., 2011) provenance patterns of zircons of early Paleozoic meta- and sedimentary sequences from NE Patagonia are discussed. The older unit is El Jagüelito Fm that is considered to be Early Cambrian because the presence of archeocyath limestone blocks (González et al., 2011). Three samples show main peaks of relative probability at ~523, 535, and 580 Ma, and less frequent at ~970 to 1065 Ma. The Nahuel Niyue Fm previously considered to be correlative with the former one shows a different pattern with a main frequence ~515 Ma (subordinate populations ~635 and 740 Ma) and an important contribution of ~980 Ma. Above the El Jagüelito Fm (angular unconformity) the Silurian–Devonian, Sierra Grande Fm is composed from base to top by the Polke, San Carlos and Herrada Members. Detrital zircon ages of two samples from Polke show peaks at ~500, 570, and a subordinate group ages of ~940 to 1060 Ma. Four samples from San Carlos show patterns significantly different than the previous described. Main frequent ages are Ordovician (~446 to 485 Ma) they also contain peaks at ~516 to 543, 610 Ma, and older (~964 to 1090 Ma). Lu-Hf isotopes from this member show a mixed source, a negative eHf(t) represents a crustal source contribution for the Ordovician to Neoproterozoic zircons populations. Mesoproterozoic zircons show a positive eHf(t) and represent a primitive source for this population. U-Pb and Hf isotopes show a significant coherence with sources of southern Gondwana characterized by Cambrian and Neoproterozoic crustal signature and Mesoproterozoic primitive sources. They are similar to those described for Puncovisvcana Fm (NW Argentina) and Eastern Pampean Ranges as well as Byrd Gp (Transantartic Mountains). This correlation is supported by the archeocyath limestones of Douglas Conglomerate similar to the El Jagüelito Formation not found before in South America. Remarkable is the change in the provenance source evidenced by the Ordovician ages in the San Carlos, these are correlative with the Ordovician plutonic granitoids (~470-478 Ma) from the Patagonia NE (e.g.: Punta Sierra Plutonic Complex).