Crustal Geophysics and Geochemistry Science Center

Geophysics of Rio Grande Basins

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Subtask 1 - Subsurface models

Geophysical Model of study area

Subtask 1 Objectives:

Gravity, magnetic, and electromagnetic (EM) geophysical methods are interpreted to determine:

  • thicknesses of Santa Fe Group sediments (the basin-fill aquifer system)
  • locations of basin-bounding and intra-basin faults,
  • the lateral and vertical extents of buried igneous rocks
  • relative grain sizes of the Santa Fe Group with depth
  • subsurface spatial distribution of thick sequences of lacustrine clay

Determining these aspects of the subsurface are key to understanding the hydrogeology, structural framework, rift development, and sedimentation history of Rio Grande basins in the northern and central Rio Grande rift.

Subtask 1 Strategy:

The geophysical interpretations require integration with geologic mapping, seismic data, hydrologic models, and drillhole information.

  • Gravity data, which are key to constraining thickness of low-density basin fill atop denser and older rocks, come from existing regional databases augmented with new data.
  • Aeromagnetic data are the primary data used to locate and delineate igneous bodies within the basin fill. Locating subsurface faults relies primarily on interpretation of high-resolution aeromagnetic data and gravity data.
  • Magnetotelluric (MT) soundings are used to help locate large basin structures and map the basin floor.
  • EM data are the most effective for mapping thick clay layers and can sometimes distinguish variations in grain size of the Santa Fe Group.
  • Very limited seismic information is available.

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