23 Geophysics of the Rio Grande Rift and Southern Rocky Mountains

Wednesday, 2 May 2001
1:10 PM - 5:00 PM

ARCHITECTURE OF THE SOUTHERN ESPANOLA BASIN (RIO GRANDE RIFT)AND FLANK UPLIFT ADJACENT TO THE LA BAJADA FAULT

Paper number: 23-5
Program: SYMPOSIA
Time: 2:00 PM – 2:15 PM

Authors

Abstract

The Española basin of the Rio Grande rift is a shallow, transitional structural basin between deeper rift basins to the north (Taos) and south (Santo Domingo, Albuquerque). New seismic, gravity, and magnetotelluric data acquired by the Summer of Applied Geophysical Experience (SAGE) program of the Los Alamos National Laboratory have been combined with Mobil (originally Transocean) seismic reflection profiles acquired in 1976-1978 to define the complex stratigraphy and structure of the basin. The Mobile data set consists of numerous parallel and intersecting lines which together provide a robust 3-D image of the basin. Several deep wells allow correlations between reflectors and lithology. Precambrian basement is imaged beneath the entire basin. Pennsylvanian limestone/mudstone, Permian and Triassic redbeds, and younger continental units occur throughout much of the basin. An Eocene redbed unit overlying a post-Laramide unconformity truncates lower units to the east and south. From these data we infer the following:

(1) The southern Española basin is a shallow asymmetrical synclinal basin comprising a ramp dipping westward from the Sangre de Cristo uplift and an east-dipping monoclinal flexure (Cerrillos uplift) adjacent to the La Bajada fault. (2) A thick (2380 m) section of Paleozoic and Mesozoic sedimentary rocks beneath the western limb of the basin is truncated northeastward by a post-Laramide (Eocene) erosional surface, reflecting a Laramide uplift broader than the present Sangre de Cristo range. (3) No evidence exists for a major north-trending fault parallel to the basin axis, nor for a northeast-trending fault parallel to the Santa Fe River. (4) Precambrian rocks and electrically-resistive basement are up to 4 km below the surface in the eastern Santa Domingo basin.

We relate the Cerrillos uplift to flexural uplift adjacent to the La Bajada fault, which was active until less than 3 Ma. The La Bajada fault serves as a relay fault, transferring extension between the Albuquerque and Española basins.