Arizona Geological Society: The Ghost of Sutures Past – A Re-evaluation of the Yavapai-Mazatzal Province Boundary in central Arizona

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 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 are isotopically juvenile at ca. 1.75-1.74 Ga, with εHf(t) values near +10. 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.

Presented by

Mark Holland

Arizona Geological Survey