TEMPORAL, STRATIGRAPHIC AND STRUCTURAL CONTROLS ON THE EVOLUTION OF THE CERROS DEL RIO VOLCANIC FIELD, NORTHERN RIO GRANDE RIFT, NEW MEXICO

The Plio-Pleistocene Cerros del Rio volcanic field (CdRVF) in northern New Mexico is one of the largest (>700 km²) basaltic volcanic fields in the Rio Grande rift and preserves a record of late-stage, volcano-tectonic evolution of the southwestern part of the Española rift basin. Mostly flat-lying lava flows and pyroclastic deposits of the CdRVF erupted from multiple basaltic to dacitic volcanoes in three main phases. First-phase eruptions formed large volcanoes with constructive topography, such as Montoso Peak and Cerro Colorado, formed from magma erupted between 2.8 and 2.6 Ma during the normal-polarity Gauss magnetic chron and are associated with positive aeromagnetic anomalies. Second-phase eruptions were from numerous smaller-volume vents; these lava flows commonly filled topographic lows between the older, larger volcanoes. These lavas were erupted between 2.5 and 2.2 Ma during the reversed-polarity Matuyama magnetic chron, and where sufficiently thick, are associated with negative aeromagnetic anomalies. A final 1.5- to 1.1-Ma phase of CdRVF eruptions is represented by 1.46-Ma basaltic andesite of the Cochiti Cone and even smaller-volume, younger volcanic centers in the western third of the CdRVF. A north-striking series of faults traverse the CdRVF. Lava flows of the first and second phase eruptions were down-dropped into the actively subsiding western margin of the basin. Down-to-west offset along the Cochiti Cone fault and the La Bajada fault are locally mantled by deposits from Cochiti Cone and likely controlled the emplacement of feeder dikes and edifice conduits. Older inferred faults, based on topographic lineaments, are sub-parallel to these young faults and cut some second stage volcanic centers. Younger second stage centers form isolated and aligned zones of volcanic vents on strike with these inferred faults. Feeder dikes for these localized eruptive centers appear to have utilized fault zones within the underlying sediments of the Santa Fe Group.