CONTRASTING PRECAMBRIAN TECTONIC HISTORIES IN NORTHERN NEW MEXICO AND SOUTHERN COLORADO
It has been known for more than a decade, based on Ar cooling ages, that the triple point terrane in New Mexico has experienced amphibolite facies metamorphism at 1.4 Ga (Grambling and Dallmeyer, 1993). Extrapolating results from Colorado and Arizona to New Mexico has lead to the proposal that the triple point mineral assemblages and associated deformation are the result of superposed tectonic events, with the Ar ages reset during 1.4 Ga intracontinental tectonism. Recently published detrital zircon ages (Jones et al., 2011) and newly obtained Lu/Hf garnet ages (Aronoff et al., this meeting), however, demonstrate sedimentation and prograde metamorphism between 1.49 and 1.4 Ga. These results strongly indicate that the triple point metamorphic terrane experienced a single progressive deformation and metamorphic event at ca. 1.4 Ga that reworked preexisting crust. Structures across the triple point terrane are contractional in nature suggesting deformation driven by collision or convergent margin process. Thus the present data set strongly indicates that Northern New Mexico was affected by a 1.4 Ga orogenic event distinct from the Mazatzal and Yavapai orogenies.