Surface uplift due to thermal expansion around the Socorro Magma Body: preliminary results
Jolante van Wijk, Gary Axen, Rediet Abera, and S. Yao
The Socorro magma body is the second largest known magma body on Earth: a partially molten sill with a thickness of ~130 m and a surface area of ~3400 km2 that lies at ~19 km depth below central New Mexico. The largest known magma body is a similar sill of ~1 km thickness and ~5000 km2 area in South America. Both cause active surface uplift. Understanding the emplacement and deformation histories of these large magma bodies is significant for understanding neotectonics, volcanic hazards and mid-crustal magma processes. We report the results of two-dimensional elastic crustal models (200 km wide by 30 km thick) of surface uplift due solely to conductive heat loss from a sill (60 km wide, 100 m thick, 19 km depth) and attendant thermal expansion of the surrounding host rocks, allowing us to separate surface uplift due to thermal expansion from uplift due to other causes, such as sill inflation, volume loss caused by crystallization of the sill, volume gain or loss due to melting or recrystallization of the host rocks, or isostatic adjustments. The sill is heated linearly in time from ambient temperature to 1200°C over 100 years. Net surface uplift during this heating stage is domical, somewhat wider than 140 km in diameter and ~3.5 m in amplitude, and accumulates at a nearly constant rate of ~30 mm/yr in the center. When heating ceases at 100 yr, the central uplift rate drops dramatically to <1 mm/yr and continues to decline until ~100,000 years have passed. The magnitude and rate of uplift across ~140 km of the dome remain above noise levels of repeated geodetic surveys (~1 mm/yr) for >100 yr but are well below noise levels after 1000 yr. As the uplift rate falls below the geodetic noise level, the diameter of the measurably uplifting dome decreases, an effect that is consistent with the Socorro magma body being about as wide as the zone of measurable surface uplift and intruded >100 yr ago.
- van Wijk, Jolante; Axen, Gary; Abera, Rediet;Yao, S., 2016, Surface uplift due to thermal expansion around the Socorro Magma Body: preliminary results, in: The Geology of the Belen Area, Frey, Bonnie A.; Karlstrom, Karl E.; Lucas, Spencer G.; Williams, Shannon; Zeigler, Kate; McLemore, Virginia; Ulmer-Scholle, Dana S., New Mexico Geological Society, Guidebook, 67th Field Conference, pp. 217-223.