Sedimentary provenance analysis of the Early Paleozoic units of the arroyo El Leoncito area, Southern Precordillera, province of San Juan.

Abstract

In the Arroyo El Leoncito area, northern sector of the Southern Precordillera, the Cabeceras Formation and Ciénaga del Medio Group crop out. These units consist of marine siliciclastic successions and tholeiitic mafic rocks developed on a continental margin during the Ordovician-Devonian. In order to characterize this setting and its source areas, this work presents a sedimentary provenance analysis using modal composition of metasandstones of the Cabeceras Formation and Ciénaga del Medio Group, as well as other units of the Southern Precordillera (Portezuelo del Tontal, Peñasco, Garganta del León and Sandalio formations). Analyzed detrital modes suggest that mainly low-grade metamorphic and sedimentary rocks acted as source. To a lesser extent, intermediate-acid igneous rocks and/or medium- to high-grade metamorphic rocks of similar composition also participated. The contribution of volcanic rocks was subordinated. Discrimination diagrams indicate a recycled orogen as the main provenance zone, with the participation of a dissected arc zone. These results can be explained in a context where the Ocloyic orogen would have acted as source and, at the same time, as a barrier that prevented the transport of detritus from regions located further east (i.e. Famatinian arc and/or cratonic areas). Detritus provenance from the west is not totally ruled out. The similarity of the detrital modes of the formations involved in the segment of the Southern Precordillera analyzed  (31°45'-32°15'S) suggests that there were no significant changes in source areas during the Ordovician-Devonian.