Circular 156—Volcanoes and related basalts of Albuquerque Basin, New Mexico

By V. C. Kelly and A. M. Kudo, 1978. Reprinted 2001.
30 pp., 16 tables, 32 figures, 2 oversize sheets.

This reissue honors the collaboration 25 years ago to two great New Mexico geologists. In 1975, Vincent C. Kelly and Albert M. Kudo submitted a manuscript describing the late Cenozoic volcanic rocks of the central Rio Grande rift. Circular 156 laid the groundwork for a quarter of a century of research.

During the Pliocene-Pleistocene, numerous eruptions (alkali basaltic, olivine tholeiitic, and minor andesitic) occurred within the Albuquerque Basin of the Rio Grande rift. The principal volcanic fields — San Felipe, Albuquerque, and the Cat Hills-Wind Mesa group — appear to trend about N. 15° E., roughly paralleling the axis of the basin. To the west of these fields is a lesser alignment of volcanoes that includes Benevidez diatreme, Mesita Negra, and Mohinas Mountain. Volcanism at Los Lunas, Tome Hill, and Black Butte, all east of the main alignment, is andesitic. Quaternary erosion in the inner valley has exposed a variety of formations and volcanic features. At least 5 or 6 flows and explosive phases are found in many of the volcanic centers. Usually the earliest eruptions are low in viscosity and form widespread fissures. Later eruptions are thicker, are less expansive, have greater surface irregularity, and are restricted to central vents. Many of the eruptions culminate with the formation of cinder cones. The olivine tholeiite at the Albuquerque volcanoes becomes increasingly hypersthene normative with time and has a differentiation trend consistent with the mode of the basalts containing olivine and plagioclase phenocrysts. The olivine tholeiite could have differentiated at depths less than 24 km by settling out of olivine and plagioclase. The alkali basalts at Cat Hills and Isleta must have differentiated at pressures in excess of 8 kb. Modally, the basalts contain olivine and plagioclase phenocrysts with minor augite. The generation of these basalts may be related to the degree of partial melting in the mantle at pressures well in excess of 8 kb. The hypersthene normative lavas that erupted first may have come from mantle partially melted by more than 20 percent whereas the later nepheline normative eruptions tapped mantle less melted. The origin of the andesites in the Albuquerque Basin is uncertain; a shallow origin under hydrous conditions is possible.