INTEGRATED GEOLOGIC, GEOCHRONOLOGIC AND GEOPHYSICAL STUDIES OF THE NORTHEASTERN TAOS PLATEAU, NEW MEXICO, USA—NEW CONSTRAINTS ON THE EVOLUTION OF RIFT STRUCTURES, BASIN EVOLUTION, AND PLIOCENE VOLCANIC ERUPTION HISTORY

The Taos Plateau volcanic field (TPVF) in the southern San Luis Basin of northern New Mexico and southern Colorado is the most voluminous of the predominantly basaltic Neogene (6-1 Ma) volcanic fields of the Rio Grande rift. Coincident with extensional tectonism, volcanic deposits of the TPVF are intercalated with alluvial deposits of the Santa Fe Group and reflect the time-integrated magmatic response to basin- and sub basin-scale structural accommodation of regional extension. New data constraining the eruptive history of mafic to intermediate composition Pliocene volcanic rocks of the northeastern Taos Plateau volcanic field are presented based on integrated geologic mapping, ⁴⁰Ar/³⁹Ar geochronology, geochemistry, and aeromagnetic data. Mapped stratigraphy and faulting is linked to new regional gravity model interpretations to establish the location of deeper basin and sub-basin geometry relative to mapped eruptive centers.

Two representative clusters of eruptive centers in the northeastern Taos Plateau area of the San Luis Basin (Ute Mtn., and Guadalupe Mtn./Red River areas) range in composition from basaltic andesite to dacite but are volumetrically dominated by high-silica andesite to dacite. Eruptive cycles for each cluster are: Ute Mtn. (andesite – 3.95 Ma, high silica andesite – 3.90 Ma); Guadalupe Mtn./Red River (Guadalupe Mtn. dacite – 5.04 Ma, Hatchery volcano basaltic andesite to andesite – 4.90 Ma) and Red River (high silica andesite – 4.64 Ma). Deposits of each cluster are stratigraphically intercalated with Servilleta Basalt (5.26-3.36 Ma) but not necessarily coeval with these lavas. Each mapped cluster is spatially associated with mapped or inferred basin- or sub basin-bounding structures largely derived from a new gravity model and interpretation of aeromagnetic data.

Mapped eruptive centers are interpreted to reflect; 1) discrete pulses of volcanic activity characterized by limited, but zoned compositional range, 2) relatively short life cycles and, 3) spatial association with known faults or inferred basin boundaries. The latter may result from coupled partitioning of extensional strain reflected as local expressions of sub basin development and contemporaneous volcanism.