Paper No. 12
Presentation Time: 11:45 AM
CERROS DEL RIO VOLCANIC FIELD—LINKS TO THE GEOLOGY OF BANDELIER NATIONAL MONUMENT
The Pliocene to Quaternary (~2.6-1.14 Ma) Cerros del Rio volcanic field of northern New Mexico forms a dissected basaltic plateau punctuated by eroded cinder cones astride the eastern boundary of Bandelier National Monument. Mostly separated from the monument by the deeply incised White Rock Canyon of the Rio Grande, well-exposed lava flows and related volcaniclastic deposits record precursory, contemporaneous and ensuing eruptive periods of basaltic volcanism marginal to the Quaternary caldera-forming eruptions of the Jemez volcanic field. This moderately voluminous (~180 km3
), predominantly basaltic to andesitic volcanic field reflects the petrologic and geochemical character typical of volcanic fields of northern Rio Grande rift basins. However, by virtue of its geographic, stratigraphic and temporal association with large volume ash flow sheets of the Otowi (1.6 Ma) and Tshirege (1.25 Ma) members of the Bandelier Tuff, this field may represent the leaky margins of the basaltic underpinnings of the large volume Jemez silicic magma system. Consequently, the co-eruption of mafic magmas and large volume rhyolites to the west may reflect the impact of pre-eruptive basaltic triggers.
We present a new 1:50,000-scale geologic map compilation reflecting the eruptive and tectonic history of the Cerros del Rio Volcanic field of southeastern Jemez Mountains. This compilation is based on new 1:24,000-scale geologic mapping of the Montoso Peak and Cochiti Dam quadrangles and recompilation and reinterpretation of parts of the previously published White Rock, Agua Fria, and Tetilla Peak quadrangles. Geologic mapping and new geochronologic, paleomagnetic and geochemical data constrain; 1) new or revised stratigraphic interpretations that record the spatial and temporal eruptive history of Cerros del Rio volcanic deposits, 2) the temporal and spatial association of contemporaneous rift faulting associated with volcanism and, 3) the compositional range of mafic magmas erupted on the margins of a large volume Jemez silicic system.