Sedimentological, geochemical and chronological characteristics of Puncoviscana Formation in Palermo, Cachi and Molinos ranges. Eastern Cordillera, Argentina

Abstract

Palermo, Cachi and Molinos ranges, of Salta province, are part of the Eastern Cordillera, which is composed of a meta-sedimentary basement assigned to the
Puncoviscana Formation, with an age of sedimentation and lepto-metamorphism that corresponding to the Ediacaran-Terreneuvian. The psammites and pelites are represented essentially by greywackes, litharenites, shales and wackes, which would have been deposited in a continental island-arc to an active continental margin. The area source would have been constituted essentially by siliceous sediments and felsic to intermediate igneous rocks, typical of Upper Continental Crust (UCC) that would have undergone relatively brief hydraulic transport that allowed its alteration but not an efficient granulometric selection. The ages and morphological characters of detrital zircons show different origins and ages, euhedral volcanic ones of 527 My and others rounded by erosion with ages of 583 My. The fossil traces corresponding to the associations of Nereites saltensis, which one is coherent with the deposition ages of >540 My obtained in detrital zircons, and the levels of Oldhamia radiate with ages <540 My is not observed in these mountains. The Puncoviscana Formation is subsequently affected by a regional metamorphic event that culminates with the Tilcárica orogeny (~520 My), which develops conditions of Sub-Green Schist Facies eventually reaching Green-Schist Facies. Another posterior tectonic-thermal event occurs between 488 and 453 My (Upper Cambrian - Upper Ordovician) that produce the intrusion of the tonalitic-trondhjemitic and granodioritic-granitic plutons of the Cachi Formation, with which the gneisses and migmatites are associated to phyllites and spotted schists of La Paya Complex, in Amphibolite and Granulite Facies. The U-Pb ages were in zircons and monazites determined the sedimentation epoch, as well as by the strontium isotopes.