An integrated geophysical and geological investigation of the transition zone between the Colorado Plateau, Rio Grande Rift and Basin and Range provinces: Arizona and New Mexico.

Robert Vincent Schneider, The University of Texas at El Paso

Abstract

The southeastern margin of the Colorado Plateau (CP) lies in southwestern New Mexico and southeastern Arizona. It is defined as the boundary between the CP, the Rio Grande Rift and the Basin and Range (BRP) provinces. Along its western and southern margins, the CP is physically distinguishable from the BRP by major escarpments. Because of a thick cover of volcanic material associated with the Mogollon-Datil Volcanic Field (MDVF), no such demarcation exists in the study area. Like the western and southern margins, the geophysical boundary between the provinces appears to be transitional in nature.

To accurately determine lithospheric structure in this area, two seismic refraction lines that intersect within the MDVF were studied. Gravity data collected within 1000m of these lines were simultaneously examined. Based on these data, velocity and density profiles were created via iterative forward modeling processes. Major crustal boundaries for each paired gravity/refraction profile were constrained to agree at the point of intersection. Structurally, the CP margin appears as an abrupt northward deepening of the Moho just south of Datil, NM. This lies beneath a major low density--low velocity upper crustal body, interpreted to be a plutonic complex approximately 230 by 155 by 6 km. This complex may have provided the source material for the MDVF. Stoping appears to be the vehicle for emplacement of this body, implying a major crustal reorganization.

Anomalously slow velocities and low densities required by this model support previous suggestions that elevated temperatures occur at depth throughout the region. High geothermal gradients throughout the Cenozoic are evidenced by regional deformation and igneous activity. A 2D finite difference algorithm for temperature conduction was generated in order to predict present day thermotectonic setting. Surface heat flow and isostatic uplift values were generated in the program and compared to present day observations. Results require two thermal perturbations, one at the base of the lithosphere (BOL) and the second at the base of the crust (BOC). The BOL is long-standing ($\geq$28 Ma) and dominates uplift, while the BOC is of shorter duration ($\geq$5.4 Ma) and controls present day surface heat flow.

Subject Area

Geophysics

Recommended Citation

Schneider, Robert Vincent, "An integrated geophysical and geological investigation of the transition zone between the Colorado Plateau, Rio Grande Rift and Basin and Range provinces: Arizona and New Mexico." (1990). ETD Collection for University of Texas, El Paso. AAI9117783.
https://scholarworks.utep.edu/dissertations/AAI9117783

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