GSA Connects 2022 meeting in Denver, Colorado

Paper No. 79-3
Presentation Time: 8:40 AM


CHAPMAN, James, Earth, Environmental, and Resource Sciences, University of Texas at El Paso, 500 W University Ave, El Paso, TX 79968, PRIDMORE, Cody J., Geology and Geophysics, University of Wyoming, 1000 East University Avenue, Laramie, WY 82071, CHAMBERLAIN, Kevin R., Department of Geology and Geophysics, University of Wyoming, 1000 University Avenue, Laramie, WY 82071, HAXEL, Gordon B., U.S.G.S., Flagstaff, AZ 86001 and DUCEA, Mihai N., Faculty of Geology and Geophysics, University of Bucharest, Bucharest, 011004, Romania

The southern U.S. and northern Mexican Cordillera experienced crustal melting during the Laramide Orogeny. The metamorphic and migmatitic sources of melt are not exposed at the surface, however, anatectic leucogranites are present throughout the region, providing an opportunity to investigate the tectonic and metamorphic processes associated with this orogeny. A detailed geochemical and petrochronological analysis of the Pan Tak Granite from the Coyote Mountains core complex in southern Arizona suggests that prograde metamorphism, melting, and melt crystallization occurred from 62-42 Ma. Ti-in-zircon temperatures (Tzr) correlate with zircon HREE concentrations and indicate prograde heating, garnet breakdown, and melt generation took place from 62-53 Ma. Tzr increases from ~600 to 850 °C during this interval. A prominent gap in zircon ages is observed from 53-51 Ma and is interpreted to reflect the timing of peak metamorphism and melting, which caused zircon dissolution. The age gap is an inflection point in several geochemical-temporal trends that suggest crystallization and cooling dominated afterwards, from 51-42 Ma. Supporting this interpretation in an increase in zircon U/Th and Hf, a decrease in Tzr and zircon HREE, and textural evidence for coupled dissolution-reprecipitation processes that resulted in zircon (re)crystallization. In addition, whole rock REE, LILE, and major elements suggest that the Pan Tak Granite experienced advanced fractional crystallization during this time. High silica, muscovite + garnet leucogranite dikes that cross-cut two-mica granite represent more evolved melt compositions. Geochemically, the Pan Tak Granite is consistent with mica dehydration melting or fluid-deficient melting, although the exact tectonic mechanisms that led to melting remain uncertain. Regardless, metamorphism and anatexis was not a short, punctuated event, but a protracted process that affected the deep crust for ~20 Myr. The characteristics of the Pan Tak Granite are strikingly similar to intrusive suites in the Himalayan leucogranite belt and further support the association between the North American Cordilleran anatectic belt and the development of a mature orogenic system and/or plateau.