Early Proterozoic Assembly of Tectonostratigraphic Terranes in Southwestern North America

Abstract

A 500 km wide early Proterozoic orogenic belt in Arizona and adjacent areas is divided into lithotectonic blocks by northeast- and north-trending shear zones. Structural and U-Pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike-slip movements on shear zones. A northwestern province, here called the Yavapai Province, is composed of at least five tectonic blocks and was assembled at about 1700 Ma. A southeastern province, here called the Mazatzal Province, is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the Mazatzal orogeny, between 1695 and 1630 Ma. The diversity of seemingly incompatible 1700 Ma tectonic regimes now in close proximity to each other, and the absence of systematic cross-strike changes in age and character of deformation, plutonism, and metamorphism, suggest a model whereby the orogenic belt developed, and North America grew, by assembly of diverse tectonostrati-graphic terranes. Such a model provides an alternate working hypothesis to previous models of progressive southward growth of North America. This model provides a better explanation for the rapid development of the orogenic belt (1700-1630), the accretion of large volumes of juvenile crust, and the complexity in timing and styles of Early Proterozoic tectonism in southwestern North America.