Geology of the Cerro del Medio moat rhyolite center, Valles Caldera, New Mexico
— Jaime N. Gardner, M. Magdalena Sandoval, Fraser Goff, Erin Phillips, and Ariel Dickens


The Cerro del Medio moat rhyolite center is the oldest postresurgence flow and dome complex in Valles caldera. The center consists of five distinctive lava flows and an upheaved dome, amounting to about 5 km3 of rhyolite. At least two of the effusive phases had associated pyroclastic activity with deposits preserved in the caldera. Additional pyroclastic activity from the Cerro del Medio center can be inferred from pyroclasts in sedimentary deposits in the caldera and fallout and reworked tephras to the east of the caldera. New 40Ar/39Ar dates range from 1.229 +/- 0.017 Ma on one of the complex’s older flows to about 1.17 Ma on a unit stratigraphically in the middle of the Cerro del Medio sequence. These data indicate volcanism in the Cerro del Medio complex spanned at least 50 to 80 kyr, and other data may imply it spanned more than 100 kyr. Topographic features and sedimentary deposits on the flanks of Cerro del Medio, neighboring moat rhyolite domes, and on the southeastern and southern rim of Valles caldera argue very strongly for an ancient caldera-hosted lake >800 ka with the highest stand at about 2800 m above sea level.

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Recommended Citation:

  1. Gardner, Jaime N.; Sandoval, M. Magdalena; Goff, Fraser; Phillips, Erin; Dickens, Ariel, 2007, Geology of the Cerro del Medio moat rhyolite center, Valles Caldera, New Mexico, in: Geology of the Jemez Region II, Kues, Barry S.; Kelley, Shari A.; Lueth, Virgil W., New Mexico Geological Society, Guidebook, 58th Field Conference, pp. 367-372.

[see guidebook]