New Mexico Geological Society Annual Spring Meeting — Abstracts

Detailed aeromagnetic surveys were conducted in November and December, 1996 over two areas within the Middle Rio Grande Basin: (1) north and west of Albuquerque in the Rio Rancho area, and (2) west of Albuquerque in the West Mesa area. The overall objective of these surveys, in conjunction with airborne electromagnetic surveys planned for February and March, 1997, is to improve the understanding of the geologic and hydrogeologic framework of the Middle Rio Grande Basin. This improved understanding will lead to refinements in the hydrologic model of the Basin.

The Rio Rancho high-resolution aeromagnetic survey was flown with 100-m flight-line spacing and 100 m above ground level (AGL) except over urban areas, where heights reached about 300 m AGL. The primary purpose of this survey is to map structures within the basin fill, which is not a common use of aeromagnetic surveys within the public sector. More commonly, aeromagnetic surveys have been used to understand bedrock areas, where rocks are fairly magnetic. A preliminary magnetic map from the survey indicates overall success: evidence of faults that offset basin fill are numerous. These faults generally strike north, and many are sinuous in pattern. Evidence for geologically mapped northeast-striking structures is not clear, although some of the north-striking faults abruptly end or change character near the mapped structures. The magnetic map also shows expressions of exposed and buried bedrock blocks on the edges of the Rio Grande Rift and manmade features (primarily buildings).

The survey west of Albuquerque was flown with lower resolution than the Rio Rancho survey, with 150-m spacing and heights 150 m AGL (300 m over urban areas). The primary purpose of this survey is to map basalt and structures related to the Albuquerque volcanoes. Preliminary results from this survey support the idea of a north-striking basalt-filled graben at Albuquerque volcanoes with fault-controlled vents. Faults parallel to the vents are expressed in the basalt to the east, and the fault system bounding the graben on the east appears to extend at least 15 km further south.

Preliminary results from the aeromagnetic surveys are promising for further use of aeromagnetic data in the Middle Rio Grande Basin to map faults that offset basalt or alluvial units. Especially promising is the identification of fault traces where surface outcrops have been covered by thin sheets of eolian sand. Locating and mapping the faults is important for development of the hydrologic model of the Basin, especially to the north and south of Albuquerque where subsurface information is sparse.