Abstract

In the Bandera lava field of western New Mexico both alkalic and tholeiitic basalts were erupted within a short period of time. The lava field is located at the intersection of two major lineaments which have also controlled the location of individual volcanic centers within the field. Both fissure flow and pyroclastic activity were common, although most of the material was ejected quiescently from fissures. Chemically both basalt types are impoverished in total strontium when compared to other basalts. Strontium isotopic ratios are low, and in contrast to many oceanic basalts the alkali basalts have the lowest ratios. Despite impoverishment of total strontium in both basalt types the alkali basalts have strontium contents sufficiently high to make them relatively insensitive to crustal contamination. If the higher ratios of the tholeiitic basalts are the result of crustal contamination, then the source material for both basalt types must have been impoverished in rubidium early in the history of the mantle.

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