The Guerrero terrane, a para-autochthonous block on the paleo-Pacific continental margin of North America: Evidence from zircon U-Pb dating and Hf isotopes

Abstract

ABSTRACT Two main tectonic scenarios have been proposed for the area corresponding to the Guerrero terrane in western Mexico. The first model suggests that the Guerrero terrane was an allochthonous volcanic arc developed over oceanic substrate, which was accreted to nuclear Mexico. The second tectonic model proposes that the Guerrero terrane was a para-autochthonous volcanic arc developed over continental crust, which was rifted during the extensional phase of the Arperos back-arc basin and then tectonically attached to nuclear Mexico. Based on U-Pb geochronology and Hf isotope analyses of detrital zircon grains extracted from Mesozoic sedimentary successions of the Guerrero terrane and western nuclear Mexico, this study provides new evidence to support the interpretation that the Late Jurassic–Early Cretaceous Guerrero terrane was built above a pre–Late Jurassic continentally sourced basement. Hf isotopic signatures of detrital zircon from Late Jurassic–Early Cretaceous sedimentary rocks of the Guerrero terrane range from –14 to +13 and display depleted mantle model ages (TDMc, using a mean crustal value of 176Lu/177Hf = 0.015) between ca. 2.0 and 0.3 Ga, indicating provenance from both pre–Late Jurassic basement and juvenile crustal components. The most juvenile magmas were formed during the earliest Cretaceous extensional phase, which resulted in the formation of the Arperos basin. Additionally, the negative εHf(t) values are consistent with recycling of Proterozoic and Paleozoic continental materials in Mesozoic magmas.