New Mexico Geological Society Annual Spring Meeting — Abstracts

A 17-station broadband (10³ – 10^-3 Hz) magnetotelluric survey over the Central Rio Grande rift has been modelled using 1D, 2D and 3D inverse methods. The results have been interrogated using 3D forward modelling routines. The resistivity models are dominated by sedimentary structures related to the Albuquerque, Socorro and La Jencia Basins. Evidence of evolved brines hosted in syn-rift basin fill are apparent by bulk resistivity values less than 1 ohm-m, most notably in the southern Albuquerque and northern Socorro Basins. Along the so called ‘Socorro Constriction’, where a rise in inferred low-permeability basement marks the transition between the Albuquerque and Socorro Basins, these brines appear to interact with the Loma Pelada fault and the San Acacia spring system. Conduits such as these may allow for evolved basin brines to mix with the Rio Grande near this point, which has been suggested by previous researchers. The survey is also located over a zone of vertical surface uplift (1-3 mm/yr) related to the Socorro Magma Body, although only minimal structures are imaged below 10 km depth. Rock units in the upper 10 km and under this area of uplift exceed 10³ ohm-m, suggesting these units are both dry and competent. An anomalous conductor has been identified on the eastern edge of the La Jencia Basin, although interrogation of the feature is ongoing. It is likely that the presence of conductive basins masks out finer details in the resistivity structure beneath them, but to what extent is currently unknown.