GEOLOGIC MAPPING OF THE CAPILLA PEAK STATE QUADRANGLE, CENTRAL NEW MEXICO

Geologic mapping (1:12,000) of the Capilla Peak Quadrangle was done for the STATEMAP project. This quadrangle is located within the Manzano Mountains, central New Mexico, which makes up the eastern flank of the Rio Grande rift. Field mapping and structural analyses of the Precambrian rocks portrays a complex polyphase deformation history within this region. At least three different deformations are recognized. D1 is associated with the development of an S1 foliation that is often bedding parallel and axial planar to rare isoclinal F1 folds. D2 formed map-scale tight to isoclinal folds; S2, the dominant fabric of the rocks in the study area, is NE striking with variable NW and SE dips. Based on style, overprinting relationships, and general attitude, most folds seen in the area are interpreted to be of D2 generation. D3 structures are broad folds, crenulations and kink-folds and are characterized by an S3 crenulation cleavage at high angles to S2 and S1. Due to this complex nature of deformation, stratigraphy is difficult to ascertain. However, our structural cross-sections suggest that the Capilla Peak stratigraphy may be compatible with the following regional sequence (oldest to youngest): Sevilleta metarhyolite, amphibolitic metavolcanic rocks, schist, metalithic arenite, a prominent metachert layer, White Ridge and related quartzites, and Blue Springs schist. Competent quartzite and metachert ridges define a ~10km synclinorium under the Monte Largo shear zone (MLSZ). This shear zone in the E-central portion of the area records top-to-the-NW movements associated with all three deformations. Additional petrologic and geochronologic studies are currently underway to our understanding of kinematics and timing of each deformational event.