New Mexico Geological Society Annual Spring Meeting — Abstracts

Neotectonic analysis in the Abiquiu embayment of the Rio Grande rift, northern New Mexico, was conducted to determine the kinematics, timing, magnitude, and rate of faulting along this margin of the rift. Kinematic information derives from (1) structural geometry and style of rift-fault zones; and (2) analysis of over 450 fault-plane attitudes (main, antithetic, and cross faults; and the Rl and R2 planes to main, antithetic, and cross faults); and (3) approximately 300 fault-plane lineations (slickensides, striations, oriented mineral growths, and aligned particles). Geologic constaints on the timing, magnitude and rate of rift-faulting derive from stratigraphic and topographic offset of radiometrically-dated units. [NOTE: A failure to locate true piercing points precludes calculation of true slip rates.]

Six fault zones were examined in the Abiquiu embayment, named from west to east: Canones FZ, Garcia FZ , Cerrito Blanco FZ , Plaza Colorado FZ , Madera Canon FZ and Embudo FZ. Faults in nearly all cases are high-angle, normal. Many fault zones are demarcated along some fault segments by small asymmetric grabens that are 10s to 100s of meters wide at the earth's surface. Principal component of offset on most faults is dip slip with minor sense of strike slip. In contrast, the Embudo FZ displays a large component of lateral slip. Compression features (S and Z folds; nearly vertical bedding near fault planes; high-angle reverse faults) are common along the Embudo FZ in the vicinity of Arroyo de la Presa. Characteristics of the fault zones are summarized below:

Calculated slip rates are of the same order to two-orders of magnitude less than slip rates calculated on faults south of the Embudo FZ and in the western Espanola basin (Slemmons, 1977; Gardner and House, 1987; Wachs et al., 1988). The Embudo FZ structurally segments the Abiquiu embayment from the rest of the Espanola basin. The Abiquiu embayment apparently has been tectonically inactive with a few minor exceptions during the mid- to late Quaternary, and is structurally shallower than the rest of the Espanola basin. Analysis of the neotectonic details of this segment of the rift development in northern New Mexico.

* indicates informal names used in this study. Names of fault zones derive from local residents or nearby geographic features found on the U.S.G.S. 7 1/2 minute topographic map of Abiquiu, New Mexico.