GSA Connects 2021 in Portland, Oregon

Paper No. 65-6
Presentation Time: 9:30 AM


HOLLAND, Mark, Life Earth and Environmental Sciences, West Texas A&M University, 2403 Russell Long Blvd, Canyon, TX 79015, VELASQUEZ Jr., Jason A., Department of Life, Earth, and Environmental Sciences, West Texas A&M University, 2304 Russell Long Blvd., Canyon, TX 79105, REGAN, Sean, Geophysical Institute, University of Alaska Fairbanks, 900 Yukon Dr, Fairbanks, AK 99775-9702, DOE, Michael, Colorado School of Mines, Golden, CO 80401 and KARLSTROM, Karl E., Earth and Planetary Sciences, University of New Mexico, Northrop Hall, Albuquerque, NM 87131

The Proterozoic crust of southern Laurentia has been considered an archetype of continental growth via the accretion of exotic crustal fragments for over 30 years. In a broadly accepted model, Laurentia grew by the sequential addition of the ca. 1.8-1.7 Ga Yavapai and ca. 1.7-1.6 Ga Mazatzal provinces. These provinces were originally defined in central Arizona, USA, where the Yavapai and Mazatzal provinces are distinguished by marked differences in lithology, metamorphic grade, and structural style across a proposed suture coincident with the Moore Gulch shear zone (MGsz). Here, we test the hypothesis that rocks of the Mazatzal province are allochthonous with respect to the Yavapai province, and that the MGsz is a reactivated hinge-zone that marks the approximate province suture. We present: 1) field and microstructural analysis of the MGsz, 2) combined zircon U-Pb and Hf-isotope analysis and bulk rock major and trace element geochemical analysis of plutonic rocks across the MGsz, and 3) a compilation of detrital zircon U-Pb and Hf-isotope data from multiple unconformity-bound metasedimentary successions on either side of the MGsz. Stretching lineations in the northeast striking MGsz plunge steeply to the west-northwest and record top to the southeast shearing in an oblique dextral reverse fault geometry. In addition, ca. 1.75-1.74 Ga plutonic rocks across the MGsz show enriched high-field strength elements relative to large ion lithophile elements with pronounced negative Nb, Ta, P, and Ti anomalies. Both suites of rocks are isotopically juvenile at ca. 1.75-1.74 Ga, with depleted εHf(t) values. Finally, detrital zircon data from metasedimentary rocks of the ca. 1.75 Yavapai Supergroup and the ca. 1.65 Ga Mazatzal Group, and its regional correlates, are indistinguishable across the MGsz. These results do not support the presence of a crustal suture across the MGsz. Instead, we favor the interpretation that metasedimentary rocks of the Mazatzal province were deposited unconformably across those of the Yavapai province, and that the difference in lithotectonic character between the two provinces is due to the juxtaposition of different crustal levels across the MGsz. Juxtaposition of different crustal levels may have occurred during the Mesoproterozoic Picuris orogeny.