T39 Evaluation of Proterozoic Tectonic Styles in North America and Their Influence on Phanerozoic Structures and Mineralization

Sunday, 9 October 2022
1:30 PM - 5:30 PM
507

REASSESSING THE TECTONIC SIGNIFICANCE OF PROTEROZOIC SHEAR ZONES IN CENTRAL ARIZONA: MESOPROTEROZOIC (CA. 1.5 GA) DEFORMATION CONSTRAINED BY PAIRED ZIRCON AND APATITE GEO-THERMOCHRONOLOGY

Paper number: T39-10
Program: Technical Sessions
Time: 3:30 PM – 3:50 PM

Authors

Abstract

Proterozoic rocks of central Arizona comprise multiple km-scale blocks with distinctive lithologic, structural, and metamorphic features bounded by shear zones. This architecture has long been attributed to the assembly of disparate crustal fragments with shear zones delineating allochthonous blocks. Here we synthesize kinematic analysis of two block-bounding shear zones, utilizing new zircon and apatite U-Pb geo-and-thermochronology, and a compilation of detrital zircon U-Pb and Hf-isotope data from multiple unconformity-bound metasedimentary successions throughout the region into a revised tectonic model for Proterozoic orogenesis. The north-south trending Shylock shear zone deforms lower amphibolite grade metasedimentary rocks across a ~2 km wide zone east of the Crazy Basin pluton. Stretching lineations are primarily subvertical, though a localized zone of greenschist facies mylonites displays shallowly north-plunging lineations attributed to sinistral shear. On either side of the Shylock shear zone, apatite and zircon from the Crazy Basin and Badger Springs plutons yield overlapping U-Pb dates which we interpret as rapid cooling after emplacement at ca. 1685 and 1740 Ma respectively. In contrast, apatite from metasedimentary rocks within the shear zone yield discordant dates at ca. 1500 Ma, which we attribute to fluid-mediated isotopic resetting during Mesoproterozoic deformation, possibly related to localized sinistral shear. Stretching lineations in the southwest striking Moore Gulch shear zone plunge steeply to the northeast and record top to the southwest shearing in an oblique sinistral reverse fault geometry. Detrital zircon from two unconformity bound packages of metasedimentary rocks that straddle both shear zones show identical age populations and Hf-isotope compositions, which constrains shearing after ca. 1490 Ma. These observations preclude interpretation of either structure as a terrane bounding shear zone. Rather, block-bounding shear zones accommodated ca. 1.5 Ga northwest-southeast directed shortening. We explore potential links between Mesoproterozoic trans-Laurentian magmatism and the origins of the ca. 80-45 Ma Southwestern North America Porphyry Copper Province.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379888

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