“Ages and Hf isotopic compositions of detrital zircons in the Pinal schist, southern Arizona, USA: Provenance, tectonic setting, and evidence for pre-1.7 Ga crust in SW Laurentia”

Abstract

The Pinal basin of southern Arizona is best known for the widely distributed Paleoproterozoic Pinal schist. Most detrital zircons from the Pinal schist yield ages in the 1.68–1.77 Ga range, suggesting provenance in the proximal Mazatzal and Yavapai Provinces. Hf isotopic compositions of these zircons yield εHf values that are positive, but less than estimated depleted mantle at this time, and yield single-stage depleted mantle model ages that indicate a minimum age of 1.85–2.0 Ga for an older crustal component in the source. New Sm-Nd data from Pinal schist whole rocks are compatible with the source(s) of the pelitic component of Pinal sediment being derived from a terrane with a component older than the 1.68–1.77 Ga granitoids in the Mazatzal and Yavapai Provinces, as suggested by the Lu-Hf data. If the Pinal sediments were derived from the Mazatzal and/or Yavapai arcs, these arcs should thus be considered continental arcs. The composition and age of the older crustal component(s) indicated by the Sm-Nd and Lu-Hf systematics is not uniquely defined by these data, but options on a Laurentian margin include the cryptic older crust of the Colorado Province, e.g., an extension of Trans-Hudson-Penokean age crust. If the arcs were built on non-Laurentian crust and accreted as exotic terranes several possibilities are viable in the SWEAT, AUSWUS, and other models for conjugates to southwestern Laurentia in the Nuna supercontinent.