Proterozoic Thermal Evolution of the Southwestern U.S.

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9405696 Bowring Prior research in the Proterozoic of Arizona and New Mexico has resulted in a hypothesis that, after initial accretion, the proterozoic orogenic belt remained stable from 1.7 Ga to 1.4 Ga, with isotherms moving through the rock very slowly, allowing extensive diffusional loss of argon from various minerals, preserved as extreme gradations from cones to rims. An alternative hypothesis of partial resetting by heat from younger intrusions does not fit well with the geologic history, pattern of metamorphism, petrologic aspects of re-metamorphism or known volume of plutons, but remaining an attractive alternative. The project will attempt to test these alternatives in a field and geochronological program. The project offers a strong opportunity to study thermal evolution of newly formed continental lithosphere and to unravel how stable cratonic geotherms are attained.