Resolving pressure differences within the Grand Canyon Precambrian basement: Implications for Proterozoic tectonics

Abstract

Burial pressures (depths) within mountain belts place fundamental constraints on the growth and stabilization of continental crust. We report precise metamorphic pressures for ca. 1.7 Ga rocks from the Upper Granite Gorge (UGG) of the Grand Canyon (southwestern United States) and, for the first time, resolve pressure variations across this continuous exposure of mid-crustal rocks. We applied quartz-in-garnet (QuiG) barometry and pseudosection modeling to determine pressures in domains (“blocks”) with evidence of higher and lower peak metamorphic grades. New pressure-temperature (P-T) paths constructed using this integrated approach show that a hot block sample reached 7 kbar and a cold block sample never surpassed 5 kbar, revealing an ∼2 kbar P difference between hot and cold blocks and delineating distinct P-T paths for these domains in the UGG. Our findings suggest that hot and cold blocks were likely metamorphosed at different crustal levels within a pre-Yavapai, Paleoproterozoic orogen and were subsequently juxtaposed during and/or after the Yavapai Orogeny at mid-crustal levels. The deformation that produced differential vertical displacement of crustal blocks post-dated peak metamorphism and could reflect extensional collapse of a large orogen and/or renewed folding and thrusting at the Paleoproterozoic Laurentian plate margin.