The southwesternmost piece of the Grenville Orogen in Laurentia – New U-Pb and Sm-Nd ages, and P-T estimates from the Sierra del Cuervo, Chihuahua, Mexico

Abstract

This paper elucidates the origin and tectonic setting of Mesoproterozoic metaigneous rocks of the Sierra de Cuervo, Chihuahua, Mexico, providing new evidence for the southwestern extension of the Grenville Orogeny in North America. Several geochronological approaches were used, including U-Pb zircon dating by LA-ICP-MS and the Sm-Nd isochron technique, using ID-TIMS. Igneous zircon domains reveal crystallization ages for felsic igneous protoliths ranging from ∼ 1.38 Ga to ∼ 1.33 Ga, with ∼ 1.42 b.yr. old inherited zircon. Whole-rock Sm-Nd isotopic data define an isochron at 1.52 ± 0.03 Ga, suggesting crustal growth during the early Mesoproterozoic. The timing of metamorphism is constrained by Sm-Nd leached garnet-whole-rock isochrons and by U-Pb zircon dates between ∼ 1.06 and ∼ 1.05 Ga. Metamorphic pressure and temperature conditions were estimated from a metamafic rock sample at 6.4 ± 1 kbar and 520 ± 20 °C using conventional geothermobarometry and pseudosection modeling. The results contextualize the Precambrian rocks of the Sierra del Cuervo with metamorphic rocks of the West Texas Uplift thrust over the Laurentian margin. We propose that this thrust represents a remnant of the unexposed Grenville Front and that the Chihuahua and West Texas metamorphic basement is characterized by contemporaneous magmatism and reworked from the Granite-Rhyolite Province of the North American midcontinent during the Grenville Orogeny, comparable to the low-medium pressure allochthonous Ottawan metamorphic belt of the Grenville Province in Canada.