THE EARLY PALEOZOIC EXTENSIONAL HISTORY OF THE CUYANIA TERRANE: AN APPROACH TO UNDERSTANDING ITS TECTOSEDIMENTARY EVOLUTION

The origin of Cuyania Terrane, Western Argentina, is currently under discussion considering both allochthonous and para-autochthonous models respectively. Additional information concerning the Early Paleozoic evolution of the Precordillera, allow us to recognize, at least four successive extensional stages: Stage 1, Lower Cambrian, is represented by Cerro Totora Formation (Guandacol area), composed of evaporites and reddish siliciclastics capped by glauconite sandstone and greenish mudstone bearing Olenellid trilobites. Stage 2, Middle to Upper Ordovician, is related to complex pull-apart system, and it is represented by the Las Vacas Formation (Guandacol basin) (C. bicornis time), La Cantera Formation (Villicum basin) (N. gracilis time), and Estancia San Isidro Formation (San Isidro Basin) (P. tentaculatus time). These units are composed of thinning-fining upward sequences, with olistostrome and conglomerates dominating in the lower part. Stage 3, Hirnantian to Emsian, is related to yo-yo tectonic, and it is represented by the Hirnantian to Early Wenlock La Chilca Formation, the Middle Wenlock to Lochkovian Los Espejos Formation, the Lochkovian to Emsian Talacasto Formation and the Emsian Punta Negra Formation. Each of these units are composed by thickening-coarsening upward successions, that may represent repeated tectonic subsidence events. Stage 4, Emsian-Eifelian, is related to pull-apart system, and it is represented by olistostrome of the Los Sombreros and Rinconada formations. Middle and Upper Devonian deposits are not known at present in the Eastern and Central Precordillera, like in the Famatina System, which could indicate up-lift of this block on that time. We conclude that Cuyania reached its present position, relative to Famatina, during the Middle to Upper Devonian, pointing out the starting of the Chánica tectonic phase. Currently, the northern and southern boundaries of the Cuyania terrane, coincides with the extension of the flat-slab subduction zone, which is related to the Cenozoic up-lift of the Precordillera and Sierras Pampeanas.