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Kilbourne Hole is a maar, a low-relief, broad volcanic center formed by multiple shallow explosive pyroclastic surge eruptions. Kilbourne Hole, like most maars, is surrounded by a crater ring made of pyroclastic surge deposits. Kilbourne Hole is about 2.7 km north-south by 1.6 km east-west. This maar formed in the late Pleistocene. Kilbourne Hole and the others maars nearby are part of the Potrillo volcanic field, which is on the west margin of the Rio Grande Rift. Kilbourne Hole is noted for the presence of mantle xenoliths in the pyroclastic surge deposits. Some are up to 90 cm in diameter. The xenoliths help geologist learn about the lithosphere beneath the southern Rio Grande Rift.
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Hunts Hole maar is about 3 km south of Kilbourne Hole and located along the same north-south trace of the Fitzgearald-Robledo fault system. A third maar, Potrillo, is 8 km to the southwest. The Rio Grande Rift is characterized by anomalously high heat flow, recent volcanism, deep sedimentary basins, and Quaternary faulting. Rifting started about 32 million years ago. Volcanism (alkali olivine basalt) started about 13 million years ago, possibly as the result of crustal stretching and upwelling mantle. Crustal thinning at higher rates began 8 million years ago and probably caused an increase in volcanism about 5 million years ago. See additional references in Padovani and Reid.
Perry and others (1987) wrote an elegant paper about the role of the asthenosphere and lithosphere in the genesis of basaltic rocks from the Rio Grande Rift and adjacent regions of the southwestern United States. Wood and Kienle (1993) have additional information about Kilbourne Hole and the Potrillo monogenetic cone field.
Sources of Information: Padovani, E.R., and Reid, M.R., 1989, Field guide to Kilbourne Hole maar, Dona Ana County, New Mexico in Chapin, C.E. and Zidek, J., eds., Field excursions to volcanic terranes in the western United States, Volume I: Southern Rocky Mountain Region; Memoir 46, New Mexico Bureau of Mines & Mineral Resources, p. 174-185.
Perry, F.V., Baldridge, W.S., and DePaolo, D.J., 1987, Role of the asthenosphere and lithosphere in the genesis of basaltic rocks from the Rio Grande Rift and adjacent regions of the southwestern United States: Jour. of Geophysical Research, v. 92, p. 9193-9213.
Wood, C.A., and Kienle, J., 1993, Volcanoes of North America: Cambridge University Press, New York, 354 p.
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