Ramps, Relays, and Rotation: Interbasin Accommodation Structures in the Northern Rio Grande Rift, New Mexico
Abstract
Structural connections (accommodation zones) between basins in continental rifts control distribution and facies of syntectonic sediments and magmatic rocks, and therefore resources such as groundwater, hydrocarbons, and minerals. These zones are commonly buried beneath rift-filling sediments, thus geophysical methods are of paramount importance in understanding them. In the Summer of Applied Geophysical Experience (SAGE) program we focus on the small Hagan basin, located in an accommodation zone between the right-stepping Albuquerque and Española basins (respectively AB and EB) near the eastern margin of the Rio Grande rift in northern New Mexico. We integrate existing geological mapping and borehole information with geophysical (mainly seismic) data acquired by industry surveys and by SAGE. The broad accommodation zone comprises several north-trending (basin-parallel), right-stepping faults (E to W: La Bajada, San Francisco, and Rincon) downthrown toward the rift axis. Faults partially overlap with each other, serving to "relay" extension between the main AB and EB. Individual basin-parallel faults are dominantly dip slip with an unknown but small amount of lateral slip. Decreasing offset toward fault tips results in plunging hanging-wall ramps. Thus, ramps underwent horizontal-axis rotation and extension, creating normal faults perpendicular to the major relay faults. Extension from the main EB is transferred to the LB fault along an intrabasin northward plunging ramp. Minor footwall uplift ("Cerrillos uplift") along the LB fault created a shallow synform at the southern end of the EB. Major footwall uplift occurring ~10 Ma on the SF and RC faults (master faults of the northern AB) created a narrow basin (Hagan) within the accommodation zone. From the fact that lower Tertiary sediments in the Hagan basin are deformed parallel to underlying Paleozoic and Mesozoic rocks and that uplift of the Sandia Mountains occurred ~10 Ma, we infer that structures in the accommodation zone formed together in the middle to late Tertiary. Much of the deformation was completed by 1.8 Ma. Growth over a substantial period of time is compatible with vertical offset along the LB fault of more than 1000 m on Precambrian rocks but only 200-300 m on 2.8 my old basalt. This work provides data relevant to local groundwater resources and a model of broad interest to rift structures.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T43A1999B
- Keywords:
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- 0530 Data presentation and visualization;
- 1744 Tectonophysics;
- 8109 Continental tectonics: extensional (0905)