U-Pb, Hf isotopes and trace elements of zircon reveals a Mesoproterozoic crustal source for the Jurassic Caopas sub-volcanic intrusion: Northern part of the Nazas Igneous Province in Mexico

Abstract

The Caopas sub-volcanic intrusion crops out in the northern area of the Nazas Igneous Province. Due to its extension (∼70 km²), this intrusion is the largest igneous body within this province. At the same time, its location, close to the boundary between the Central terrane and Oaxaquia microcontinent, highlights its relevance to understanding the role that the basement plays in the genesis of the Caopas sub-volcanic intrusion. In this paper we present whole rock geochemical data of major and trace elements, U-Pb ages, Hf isotopes and trace elements in single zircon grains from samples of the Caopas sub-volcanic intrusion (U-Pb zircon age: ∼166.97 ± 0.96 Ma). Geochemical data indicate that the rocks studied are peraluminous (Al/CNK ≥1). The analyzed zircon grains exhibit enriched Hf isotopic compositions (εHf_(t) from −1.6 to 2.5), high U/Yb values and negative Eu anomalies, suggesting, along with the geochemical data, that these magmas were formed by significant volumes of crustal melts during their genesis. The Hf model ages in zircon grains are consistent with a Mesoproterozoic crustal source for the magmas that formed the intrusive (∼1023 Ma to ∼1282 Ma), which coincides with ages reported for rocks in the crystalline basement of the area (i.e. the Oaxaquia microcontinent).