The occurrence of large dominantly felsic plutons not obviously associated with a distinct tectonic event or "orogeny", particularly in deeply eroded Precambrian terranes, has long been problematic in the plate tectonic puradym. This project will examine widespread plutonism in the Southwest at 1.4Ga to evaluate the kinematic and metamorphic history of these intrusion. The work will focus of selected 1.5Ga plutons in Arizona and Colorado . These data will supplement ongoing studies in New Mexico and provide a regional database from which to evaluate the nature of the 1.4Ga tectonism, and particularly test the current competing tectonic models of 1, anorogeny-a stationary Laurentian supercontinent insulated its mantle and induced mantle upwelling, underplating and resulting granitoid plutonism, 2. extensional tectonism or 3. contractional tectonism. Each model predicts different regional-scale kinematics, timing and thermal histories thereby providing the basis for a test of the hypotheses. The results are expected to resolve the tectonic setting of these plutons and to shed light on the origin of the anomalous "anorogenic" tracts in general.
