New Mexico Geological Society Annual Spring Meeting — Abstracts

Timescales of processes related to mid-crustal magma intrusion are poorly understood. The Socorro magma body (SMB) in the central Rio Grande rift is one of the largest known active mid-crustal intrusions and offers a unique opportunity to study the timing of processes associated with its emplacement. Surface uplift and seismicity above the SMB demonstrate ongoing magmatic unrest. Nearby Holocene volcanism illustrates the potential for a longer-lived magmatic system that was active during Holocene or pre-Holocene times. Quaternary river terraces preserved at the surface and above the SMB provide paleo-geodetic markers to interrogate the longevity of magmatism. We use high-resolution terrace elevations in the Rio Salado, a Rio Grande tributary that crosses surface-uplift contours, and new ³⁶Cl surface-exposure and ¹⁴C ages to document a prehistoric surface-uplift event above the SMB. We observe longitudinal terrace patterns consistent with an arching event that began after 26 ka and ceased before 3 ka which cannot be explained by tectonic or fluvial mechanisms. This late Pleistocene-early Holocene surface uplift is related to a magma-emplacement event that predates modern magmatism and is co-located with geodetic uplift. We interpret the two temporally distinct surface-uplift events as recording episodic intrusion below the Socorro area since late-Pleistocene time. We propose that rejuvenation of magmatic activity occurs via a stationary plumbing system inferred from seismic data. This study shows that the magmatic source-feeder system is stable and active over timescales of 10⁴ yrs and demonstrates the utility of terraces as strain markers of low-amplitude, large-wavelength deformation caused by mid-crustal magmatic activity.