Constraining the age of the Mitu Group, South-East Peru: U-Pb ages of detrital and igneous zircons

Abstract

The present study investigates the Mitu Group of south-east Peru (13-16°S), which consists of continental clastic sedimentary rocks and interbedded basaltic to andesitic lavas. There is a paucity of geochemical and geochronological data from the Mitu Group, and the interpretation of its evolution is complicated by i) rapid changes in fault structure along-strike of the graben system, and ii) inversion during Andean orogenesis. Due to dominating coarsegrained clastics, the Mitu Group is devoid of fossils and its age is poorly bracketed to the Permo-Triassic, based on its stratigraphic relationships with the underlying Copacabana and overlying Pucará groups. The upper strata of the Copacabana Group have been constrained by palynology to the Artinskian, while marine fossils at the base of the Pucará Group indicate a Norian age. The Pucará Group is only present in northern Peru, whereas the Mitu Group has an erosional contact with overlying Cretaceous sandstones in the study area. Preliminary data suggest that the lower Mitu Group is middle Triassic, leaving a significant hiatus between the Copacabana and Mitu groups.