Petrology of Plio-Pleistocene Basaltic Rocks from the Central Rio Grande Rift (New Mexico, USA) and their Relation to Rift Structure

Abstract

Plio-Pleistocene basaltic rocks from the central Rio Grande rift include lavas of both the alkali olivine-and tholeiitic series erupted approximately contemporaneously. The volcanic centers with the greatest diversity of parental compositions and the greatest total range of compositions occur in a complicated transverse structural zone at the offset between the Española and Albuquerque-Belen basins of the rift. The diversity in compositions derives in part from the fact that parental magmas originate at varied depths and in part from fractional crystallization and possibly crustal contamination as magmas move toward the surface. This correlation with structural setting suggests that the transverse shear zone taps partial melts from the mantle diapir beneath the rift at depths greater than along adjacent segments of the rift.

This work has been supported in part by the Los Alamos Scientific Laboratory of the University of California and by a grant from the Caltech Ford/Exxon Energy Research Program.