New structural interpretation, microstructural analyses, and preliminary monazite geochronology of Proterozoic rocks in the central Manzano Mountains, New Mexico
The Manzano Mountains of central New Mexico, on the east flank of the Rio Grande Rift, provide excellent outcrops of Proterozoic basement. Rock types in the area include Sevilleta metarhyolite, amphibolitic metavolcanic rocks, schist, meta-lithic arenite, banded metarhyolite, the White Ridge and related quartzites, and the Blue Springs schist. Plutonic activity included the emplacement of the Monte Largo (1656Ma) and Priest (1427Ma) plutons. Proterozoic metavolcanic and metasedimentary rocks were multiply deformed during at least three deformation events. D1, D2, D3 of rocks in the Manzano Mountains have all produced movement along the NE striking Monte Largo shear zone (MLSZ). The movement sense within this shear zone is consistently top-to-the-northwest. Analysis of microstructures from the MLSZ, combined with studies of overprinting relationships of folded rocks of the area provides a better understanding of the kinematics associated with each deformation event. Geochronologic studies of metamorphic monazite grains will place time constraints on when movement occurred within the area. Metamorphic monazite grown during tectonic deformation can have incremental growth patterns such as rim and core features. The ability to relate grain orientation to overall fabric of the rocks combined with the ability to obtain geochronological information of individual grains (and individual parts of each grain, i.e rim/core features) helps in interpreting how and when deformation occurred. Examination of thin sections of quartzites within the MLSZ as well as from the folded quartzites within the metasedimentary package provides information to help understand the kinematics and time constraints of each deformational event.
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