New Mexico Geological Society Annual Spring Meeting — Abstracts

This abstract reports work in progress involving gravity and magnetics measurements in the eastern portion of the Rio Grande rift directly north of Albuquerque, NM. The study was undertaken to determine local variations in the basement structure. To date, three east-west gravity lines and one magnetics line have been run in a region spanned by the Sandia Mts. to the east and U.S. route 1-25 to the west. Each line is approximately 6 km long with measurements taken every 0.5 km.

The usual "text-book" data reduction methods have been performed on the data. These data show a substantial reduction in gravity of approximately 30.0 to 50.0 mgal from east to West. This result is completely consistent with previous geological and geophysical studies which indicate a westward deepening of the basin by a series of stepped normal fault blocks.

To model the data, a two-dimensional "TaIwani" (computer) modeling scheme is being employed. A mass contrast between basin fill and crystalline basement of 0.5 gm/cc is used. Preliminary results of the modeling assume the westward steeping of the basin from very shallow (10's of meters or less) at the eastern edge of the data lines to 4 to 6 km deep at the western edge of the lines; The modeling seems to indicate a southward steeping of the basin and a "pinching out" of some of the faults between data lines. More analysis and data-gathering is needed before more definative statements can be made.