Rio Grande Rift Gravity
Regional Gravity

      This figure shows the long wavelength Bouger anomaly from a University of Texas, El Paso  and DNAG gravity data. There is a gravity low that trends SW-NE oblique to both the rift and Jemez lineament. The low velocity feature also follows this trend and correlates to the transition zone between the Rio Grande Rift and the Colorado Plateau (Slack et al 1996) and the SKS splitting measurements of the rift (Gao et al 1997). This direction contrasts with the N-S crustal thinning, heat flow and topographic features. It is though that this may be the tectonic expression of an earlier phase of extension (Slack et al 1996).
(Figure from Slack et al 1996)

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Gravity Along the Seismic Profile NW Espanola Basin, Abiquiu

        The observed Bouger Anomaly (+ symbols), regional (dashed line) and calculated gravity are shown along the Abiquiu profile. The solid line is the sum of the calculated and regional anomalies. The model is based on contraints on geologic observations and the seismic profile. Density is in kg/m^3 and was estimated from seismic P-wave velocities (Baldridge et al 1994).
        Constraints in the model use thicknesses of formation at major fault outcrops and the assumption that the El Rito Formation is horizontal and from the seismic profile thicknesses of units. There is some disagreement between the gravity model and the seismic profile at the western end (Balridge et al 1994).
(Figure from Baldrige et al 1994)

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Gravity of the Santa Fe Embayment, Espanola Basin

        The figure shows the observed Bouger anomaly for the Santa Fe Embayment. The 932 gravity stations (+ symbols) were collected during SAGE 1998 and 1997 field season, from Cordell 1979 and others. The 1998 contribution of 336 gravity stations, were taken using G-962 and G-22 Lacoste and Romberg gravimeter and a Scintrex CG-3/3m autograv.
        The Santa Fe Embayment is located in the sorthern portion of the Espanola Basin. The basin is bounded to the east by the Sangre de Cristo Mountains, which are made of Precambrain basement (1.6 - 1.8 by). The western edge of the basin is bounded by the Jemez volcanic field that included the Valles Caldera.

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Depth to Basement of the Santa Fe Embayment, Espanola Basin
        A depth to interface was performed using well data constraints and outcrops of the Precambrian surface. The results show something interesting in that what was expected was a general opening of the embayment to the north as the observed Bouger map alludes to. Though this figure shows that there might have been a lake present to the embayment moving south.
        It is unknown whether the basement topography has been imaged or rather the Paleozoic/Mesozoic boundary. The density contrasts between the basement and the sedimentary rocks are relatively small. Go to a table of physical properties.

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