THE MAZATZAL PROVINCE IN SOUTHERN NEW MEXICO: U-PB DATING OF PALEOPROTEROZOIC ROCKS TO ASSESS MAGMATISM, DEPOSITION, METAMORPHISM, AND DEFORMATION
Both regional and contact metamorphism occurred. An undeformed 1631 Ma granite in the San Andres Mtns. is flanked by Qtz-Bt schist with contact metamorphism resulting in Grt growth adjacent to the pluton. These relationships provide evidence for foliation development prior to pluton emplacement and synplutonic static metamorphism. In the Burro Mtns., a 1633 Ma gabbro lies within metamorphic rocks with a field gradient that goes from Grt-Sil schist to andalusite-bearing hornfels.
Most of the 40Ar/39Ar dates from hornblende and biotite in the region are ~1460 Ma and overlap with a U-Pb metamorphic zircon date from amphibolite, monazite dates from schist, and a U-Pb titanite date from amphibolite. These dates are coeval with voluminous granitic magmatism at ~1460–1430 Ma in the region. High-T shear zones are present, but their orientations are not consistent, nor are the orientations of the regional foliations in metamorphic rocks. Proterozoic rocks in the San Andres Mtns. have the least amount of ~1.4 Ga and Paleogene heating and thus are the ongoing focus of our efforts to decipher the Paleoproterozoic history of the southern Mazatzal province.