Polyphase tectonics and metamorphism and their relation to movement on the Monte Largo shear zone in the Manzano Mountains, central New Mexico

The Proterozoic rocks of the Manzano Mountains of central New Mexico preserve evidence of multiple deformation events. The dominant foliation is the northeast-trending S2 that overprints the older S1 foliation in most places. Later S3 fabrics are present in many areas as well as S4 crenulations in rocks from Monte de Abajo Canyon. Petrographic and field studies were performed on rocks from Monte Largo Canyon, which contains the Monte Largo shear zone, and rocks from Monte de Abajo Canyon ~3km south of the shear zone. These studies were done to help constrain the timing of the movement on the shear zone as well as to explain the deformation and metamorphism related to movement. From these studies it was recognized that 1) multiple generations of top-to-the-northwest shear sense implies that there were multiple episodes of movement on the shear zone, 2) metamorphic minerals in the upper plate (south of the shear zone) indicate amphibolite facies conditions, 3) these minerals overgrew earlier S1 and S2 fabrics that probably developed during shearing, but were synchronous with development of S3 fabrics that were formed during reoccurring movement on the shear zone, and 4) some deformation continued after mineral growth.GeologyMastersUniversity of New Mexico. Dept. of Earth and Planetary SciencesKarlstrom, KarlSelverstone, JaneCrossey, Laur