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LOVE, D.W., DUNBAR, N., MCINTOSH, W.C., MCKEE, C., CONNELL, S.D., JACKSON-PAUL, P.B., New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, 801 Leroy Pl., Socorro, NM 87801; and SORRELL, J., Environment Department, Pueblo of Isleta, P.O Box 1270, Isleta, NM 87022

Flows and tephra from several local basaltic volcanic edifices, and pumice, tuff clasts, and fallout ash from silicic eruptions in the Jemez Mountains are buried within Albuquerque basin fill on and near Isleta Pueblo lands. Geochemical "fingerprints" and 40/39Ar-ages of many of these volcanic rocks help correlate deposits exposed on different fault blocks and in different depositional settings, leading to a more complete geologic understanding of erosion and deposition in this part of the Albuquerque Basin. The correlation of deposits on different fault blocks also helps explain some of the hydrogeochemical anomalies associated with the area. The oldest exposed basaltic tephra is an undated hawaiite found near the base of exposures on the highest uplifted block. Subsurface drilling for water supplies and aeromagnetic surveys (Grauch, 1999) have revealed several buried volcanic edifices south and west of Isleta Volcano (Perea Mesa). Isleta Volcano and at least three smaller eruptive centers are tilted to the southeast west of the Rio Grande valley (Kelley and Kudo, 1978). 40/39Ar-ages for Isleta volcano tightly constrain the eruptive history: 2.79±0.04 Ma (A large block within base-surge in the tuff-cone), 2.75±0.03 Ma (flow 1 of Kelley and Kudo, 1978), 2.78±0.06 Ma (flow 2 of Kelley and Kudo, 1978), 2.73±0.04 Ma (flow exposed along Highway 85), 2.68±0.04 Ma (Black Mesa flow northeast of Isleta Volcano). Base surge and cinders from four localities on the east side of the Rio Grande valley have similar chemistry to these dated units. One tephra crops out on the lowest fault block at an elevation of 4910 ft. Two exposures of similar tephras crop out on intermediate fault blocks at elevations of 5050 and 5080 ft. The highest of these similar tephras is near the top of the highest uplifted block at an elevation of 5200 ft.

Love, D.W., Dunbar, N., McIntosh, W.C., McKee, C., Connell, S.D., Jackson-Paul, P.B., and Sorrell, J., 2001, Late-Miocene to early-Pleistocene geologic history of Isleta and Hubbell Spring Quadrangles based on ages and geochemical correlation volcanic rocks [abstract]: New Mexico Geology, v. 23, n. 2, p. 58.

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