Structure and metamorphism of the Cushamen Complex in Sañicó and Collón Curá-limay rivers confluence: A Devonian metamorphic event related to the subduction stage of the Gondwanan Patagonian orogen

Abstract

In the North Patagonian Andes and western North Patagonian Massif, the Cushamen Complex is still a matter of interest in order to unravel the Paleozoic evolution of southwestern Gondwana margin. In this contribution we present new petrographic and structural data from the Cushamen Complex cropping out nearby Sañicó town and Collón Curá and Limay rivers confluence together with U–Pb (Q-ICP-MS) detrital zircon ages. In these areas, this metamorphic complex is composed of migmatites, orthogneisses and calcsilicate rocks, with a Late Devonian metamorphic peak age, intruded by Devonian - lower Carboniferous granites. The regional metamorphic peak would also has been accompanied by the development of a pervasive tectonic foliation and associated isoclinal folds. Devonian - Carboniferous granites crosscut the foliation of the migmatites and would have produced a weak contact metamorphism represented by static recrystallization in quartz grains. The regional metamorphic event can be related to the subduction-related Gondwanan orogenic event. At least two more folding phases and related foliations were identified postdating these granitic intrusions, probably related to the collisional event of the Gondwanan orogeny, late Carboniferous - early Permian in age. Evidence of retrograde metamorphism probably related to the previously mentioned foliations and folds are common. Zircons from a mesosome were analyzed by U–Pb Q-ICP-MS yielding a maximum depositional age of 441.79 ± 1.68 Ma (early Silurian/Rhuddanian) indicating a sedimentation for the protholits probably during middle Silurian, age of the pre-orogenic successions of the Gondwanan cycle in Patagonia.