Geoquímica y petrología de las metabasitas del Complejo Arquía (Municipio de Santafé de Antioquia y Río Arquía, Colombia)implicaciones geodinámicas

Abstract

The Arquía complex metabasites (Central Cordillera, Colombia) correspond to Mesozoic rocks of oceanic affi nity tectonically juxtaposed against the Colombian paleo-margin in upper cretaceous times and subsequently deformed by the Romeral fault system. These rocks are partially covered by clastic rocks of the Oligo-Miocene Amagá Formation and locally intruded by Mio-Pliocene subvolcanic rocks. The composition of metabasites indicates a tholeiitic affi nity (basalts and basaltic andesites; SiO2: 45.86 - 49.69 wt%; FeO+MgO: 14.6-25.26 wt%; K2O+Na2O: 1.8-2.91 wt% with Nb/Y=0.017-0.216 ratios) with slightly depleted LREE patterns followed by less fractionated and fl at HREE patterns. The HFSE, in turn, shows in general fl at patterns, close to 1. Trace element plots yields fractionated patterns for LILE´s, with markedly enrichment in Cs, Ba, Pb and a slightly negative Nb anomaly for some samples. On the other hand, a genetic relationship with abyssal and back-arc magmatism can be envisaged through Th/Yb - Nb/Yb ratios. It is suggested that the protolith for metabasites are MORB, formed in the Andean back-arc (i.e., the colombian seaway) in lower cretaceous times. These ideas reinforce the interpretation that Arquia Complex is a tectonic melange formed during an arc-continetal collision in upper cretaceous times.