Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 7
Presentation Time: 8:00 AM-5:30 PM


GOFF, Fraser, Earth and Planetary Sciences Dept, University of New Mexico, Albuquerque, NM 87131, GARDNER, Jamie N., Gardner Geoscience, 14170 Hwy 4, Jemez Springs, NM 87025, RENEAU, S.L., Ees-16, Los Alamos National Laboratory, Los Alamos, NM 87544, KELLEY, Shari A., New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, NM 87801, KEMPTER, Kirt A., 2623 Via Caballero del Norte, Santa Fe, NM 87505 and LAWRENCE, John R., Lawrence GeoService Ltd. Co, 2321 Elizabeth NE, Albuquerque, NM 87112,

Valles caldera (1.25 Ma) is famous as the type locality of large resurgent calderas, the location of a classic 260-300 °C liquid-dominated geothermal system, and the site of a long-lived late Pleistocene lake (South Mountain lake, ca. 550 to 370 ka). We have published a detailed color geologic map of the Valles caldera and surrounding areas at 1:50,000 scale obtainable from New Mexico Bureau of Geology and Mineral Resources ( The new Valles map has been compiled from all or parts of nine 1:24,000 geologic maps completed between 2004 and 2008 (Bland, Cerro del Grant, Jarosa, Jemez Springs, Polvadera Peak, Redondo Peak, Seven Springs, Valle San Antonio, and Valle Toledo). Our map provides more detailed geology on the resurgent dome, caldera collapse breccias, post-caldera lava and tuff eruptions, intracaldera sedimentary and lacustrine deposits, and precaldera volcanic and sedimentary rocks than previous maps. We also show structural relations between Valles and the earlier, comparably sized Toledo caldera (1.62 Ma). Furthermore, the map documents the distribution of pre- and post-caldera hydrothermal alteration styles, including recently recognized zeolite-type alteration. Three cross sections supported by surface geology, geophysical data and deep borehole logs (≤4500 m) show an updated view of the caldera interior, depict a modern interpretation of caldera collapse and resurgence, and provide caldera-wide subsurface isotherms (≤300 °C). The map incorporates recent stratigraphic revisions to the geology of the Jemez Mountains volcanic field (JMVF). East (9-10 Ma) to west (7-9 Ma) to east (2-5 Ma) migration of the volcanic centers in the northern JMVF is preserved along the northeast caldera margin. In addition, 40Ar/39Ar dates from the northeast side of the caldera reveal three episodes of rhyolite emplacement at ca. 7.1, 4.8, and 1.6 Ma. Finally, we present a generalized model showing our interpretation of intracaldera structure and subjacent magma chambers, and relations of Valles to earlier Quaternary-Precambrian units.