New Mexico Geological Society Annual Spring Meeting — Abstracts

Newly determined high-precision ⁴⁰Ar/³⁹Ar ages of basaltic lava flows and cinder cones, in conjunction with previously published low-precision ages, suggest that vent locations within individual volcanic fields of the Rio Grande rift and Jemez lineament have migrated from the west or southwest to the east or northeast during the late Quaternary. Although many volcanic fields in the rift and lineament were active during the late Cenozoic, the migration pattern is only observed in the six fields with eruptions during the last 1 Ma. The vent migration rate and direction for most fields is between 2 to 5 cm/yr to the east or northeast (~ N70°E ± 45°). The pattern of vent migration in some volcanic fields has been fairly regular. For example, the oldest vents in the Zuni Bandera volcanic field are the Chain of Craters, located along the continental divide and in the most western part of the field. Activity here began as early as 783 ka with most eruptions occurring between 260 and 100 ka. Vent locations then migrated eastward to the northwest corner of the present-day El Malpais National Monument and southern Zuni Mountains. Here, at least ten cinder cones erupted between 65 and 11 ka, including the well known Bandera crater and flow. The youngest and most eastern vent erupted the McCartys flow 3.9 ka. Vent migration in other fields has not been constant and continuous, but instead is best characterized by an abrupt, “step-like” jump in vent location. The oldest vents in the Potrillo field are exposed in the West Potrillo Mountains, which were active between 916 and 262 ka. Activity then migrated eastward where at least nine vents erupted between 190 and 17 ka. Both the older, western vent cluster and younger, eastern vent cluster display irregular vent migration patterns. The eastward migration of volcanism is also apparent at fields with infrequent eruptions. The Carrizozo lava flow erupted at 5.2 ka. This Holocene eruption was preceded by two eruptions at 345 and 252 ka from vents 12 km to the west-northwest. The magnitude and direction of vent migration within fields of the rift and lineament is similar to the established migration patterns at other Quaternary fields in the western US. Furthermore, the rift and lineament vent migration patterns are also moderately consistent with the absolute North American plate motion relative to a fixed mantle source. Continued work will focus on quantifying the volcanic hazards and connecting the temporal-spatial patterns of late Quaternary volcanism within the rift and along the lineament with geochemical data that suggest an increasing contribution from an asthenospheric mantle source.