Rapid early Permian tectonic reorganization of Laurentia’s plate margins: Evidence from volcanic tuffs in the Permian Basin, USA

Abstract

Early Permian arc magmatism is critical to understanding the final assembly of the supercontinent Pangea and subsequent plate reorganization. Here we report the geochronology and geochemistry of Cisuralian and Guadalupian volcanic tuffs in southwestern Laurentia and infer the magmatic sources and plate reorganization related to Laurentia-Gondwana collision. Zircon CA-ID-TIMS U-Pb dates of tuffs in the Wolfcamp B, Wolfcamp A and lower Spraberry units in the Permian Basin provide the first set of absolute ages of Cisuralian deposits in this basin. Zircon geochemistry data further show that the parent melts of these tuffs were granitic melts that formed in continental arcs. Syn-depositional zircons from the Wolfcamp B tuff beds (288.2 ± 1.7 Ma) have an average εHf value of +5.5 and TDM2 model ages between 675 and 1207 Ma, reflecting a mixture of juvenile mantle melts and Precambrian crust. The isotopic signature is consistent with Mississippian Laurentian tuffs derived from a northern Gondwana arc formed by the subduction of the Rheic oceanic plate. However, zircons from a Wolfcamp A tuff bed (287.2 ± 0.5 Ma) show an average εHf value of −4.5, much more evolved than the inferred northern Gondwana arc, but consistent with granitoids of similar or younger age in the Oaxaquia terrane. This change in εHf most likely reflects magmatism related to subduction of a paleo-Pacific oceanic plate beneath western Pangea. Our interpretation suggests a late Cisuralian plate reorganization that was caused by plate reorganization following Pangea assembly led to rapid (∼1 Myr) initiation of subduction beneath western Pangea. This study also compares tuff dates from LA-ICPMS and CA-ID-TIMS U-Pb dating and concludes that the weighted mean date of the youngest dominant KDE mode (WMYDM) is the best way to approximate LA-ICPMS dates to true depositional ages.