The Famatinian Orogen Along the Protomargin of Western Gondwana: Evidence for a Nearly Continuous Ordovician Magmatic Arc Between Venezuela and Argentina

Abstract

The continental protomargin of Western Gondwana in South America records an important Early-Middle Ordovician magmatic activity associated with the development of the Famatinian orogen. Almost the entire margin has evidence of a magmatic arc preserved as orthogneisses in the high-grade metamorphic domains up to volcanic rocks of the same age interfingered with sedimentary facies. These subduction-related calcalkaline rocks have new U-Pb zircon dates that show striking similar ages bracketed between 490 and 460 Ma. The different domains along the continental margin are compared taking the western Sierras Pampeanas as the type locality, showing an alternation among high-grade metamorphic—greenschist facies—sedimentary facies. There are three deeply exhumed segments preserved as orthogneisses in high-grade amphibolite facies, the Sierras Pampeanas, the Maranon, and the Santander-Merida domains. These domains are flanked by greenschist facies such as the Quetame in Colombia, the Vilcabamba in Peru, and the Puna Eruptive Belt in northern Argentina. Some segments are characterized by sedimentary facies as the Altiplano domain of Bolivia and the Olmos-Loja domain between Peru and Ecuador. The location and metamorphic grade are controlled by the amount of shortening and uplift, responsible for the different crustal levels exposed, as a consequence of the characteristics of the distinct terranes that collided against the continental margin. As a final remark, the time span of the Famatinian episode when globally compared has a widespread development in Laurentia, Baltica, and Australia, as a consequence of a period of high mobility of the plates during Early-Middle Ordovician times.