New Mexico Geological Society Annual Spring Meeting
April 7, 2017

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3D Inverse Models of Magnetotelluric Data in the Central Rio Grande Rift Illuminate Rift Basin Geometry and Possible Interactions Between Deep Brines and Surface Waters

Matthew Folsom1, Jeff Pepin1, Jared Peacock2, Mark Person1, Shari Kelley3 and David Love3

1New Mexico Institute of Mining and Technology, Socorro, NM, New Mexico, 87801, United States,
2United States Geological Survey
3New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech, Socorro, NM, 87801

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.


magnetotelluric, inverse methods, sedimentary basin, Rio Grand rift, basin brines

pp. 29

2017 New Mexico Geological Society Annual Spring Meeting
April 7, 2017, Macey Center, New Mexico Tech campus, Socorro, NM