NEW MAPPING FROM THE MANZANO PEAK QUADRANGLE, CENTRAL NEW MEXICO

The Manzano Mountains are a ~ 55 km, north-south striking uplift of Proterozoic basement rock that forms the eastern boundary of the Rio Grande rift. The Manzano Mountains preserve a complete stratigraphic sequence of ca.1.67-1.65 Ga supracrustal rocks. In order of decreasing age the sequence is: the Sevilleta metarhyolite (ca. 1.65 Ga), mafic metavolcanic rocks, schist, meta-lithic arenite, metachert, the White Ridge and other quarzites, and the Blue Springs schist. Results of recent mapping of the Manzano Peak Quadrangle for the New Mexico StateMap project indicate a long history of tectonic activity. The Proterozoic involved multiple phases of deformation, which are as follows: D1 (ca. 1.65 Ga) structures are west-verging, isoclinal folds with associated bedding-parallel foliation (S1). D2 involves upright, tight to isoclinal, map-scale folds (F2), and an axial planar foliation (S2) subparallel to S1, that formed during NW-SE regional shortening. D3 (ca. 1.4 Ga) structures are broad folds with parasitic kink-folds, a crenulation cleavage (S3) at a high angle to S1 and S2, and top to the NW shear bands. The Monte Largo Shear zone is a top to the north mylonite zone that places amphibolite grade rocks above greenschist grade rocks. In-situ monazite geochronology constrains regional scale thrusting of this shear zone at ca. 1.65 Ga (D1) and reactivation at ca 1.4 Ga (D3). The amphibolite metamorphism of the hanging wall is associated with the ca. 1.4 Ga intrusion of the Priest Pluton.

Previous work has shown that the Laramide age Montosa fault records both strike-slip and dip-slip movement and may represent a reactivated fault that first moved at ca. 800 Ma. Apatite fission track ages from high elevation samples of the Ojito granite cooled slowly from 30-10 Ma (Kelley et al., 1992) suggesting rift-related exhumation. Miocene normal movement reactivated (inverted) the Laramide age Montosa and other faults.

Kelley, S.A., Chapin, C.E. and Corrigan, J. 1992. Late Mesozoic to Cenozoic cooling histories of the flanks of the northern and central Rio Grande Rift, Colorado and New Mexico. NMBGMR Bulletin 145. p. 39.