Volcanic and sedimentary stratigraphy of the Rio Grande gorge and the late Cenozoic geologic evolution of the southern San Luis Valley
M. A. Dungan, W. R. Muehlberger, L. Leininger, C. Peterson, Nancy J. McMilan, G. Gunn, M. Lindstrom, and L. Haskin


The Taos Plateau volcanic field (TPVF) is one of several dominantly basaltic volcanic fields erupted along the Jemez lineament over the last 10 m.y. These volcanic fields comprise a regional magmatic event that was coincident with regional uplift and tectonic rejuvenation of the Rio Grande rift postdating late Miocene time. TPVF volcanism was dominated by extensive floods of the highly fluid olivine tholeiites (1,500 km2) of the Servilleta Basalt. Andesites and dacites erupted from shields scattered throughout the field are lesser in volume, but coeval with the basalts. The main phase of basaltic and intermediate volcanism ( --4.5- 3.5 m.y.) was succeeded by a period of low-volume alkalic basalts (>1.8 m.y.).

Post-volcanic erosion by the Rio Grande has cut a canyon up to 180 m deep along the southern edge and northward through the TPVF. Exposures the length of the canyon reveal the interplay between volcanism, sedimentation, and deformation during an approximately onetotwo- million-year period. Earlier history is exposed only along the southeastern margin of the TPVF and in the Tusas Mountains to the west of the study area. The widespread floods of Servilleta Basalts, which appear to have been erupted from vents located along the western margin of the field, record voluminous, short-lived, effusive episodes interspersed with longer intervals during which gravel fans prograded to the west from the Sangre de Cristo Mountains and north—northwest from the Picuris Mountains. Olivine andesites and two-pyroxene dacites erupted from cones both east and west of the Rio Grande and Red River gorges are also locally interlayered with basalts. The entire volcanic section was tilted to the southeast during and following volcanic activity. Deformation during and after volcanism is also recorded by reoccurring movements on intra-rift and rift-boundary faults, differential subsidence of the narrow Velarde and Taos grabens, and local warping of the volcanic units. Local zones of reverse faulting along the eastern segment of the Embudo fault and warping of the plateau surface (Taos graben) demonstrate a shift to local compression late in the evolution of the basin.


  1. Dungan, M. A.; Muehlberger, W. R.; Leininger, L.; Peterson, C.; McMilan, Nancy J.; Gunn, G.; Lindstrom, M.; Haskin, L., 1984, Volcanic and sedimentary stratigraphy of the Rio Grande gorge and the late Cenozoic geologic evolution of the southern San Luis Valley, in: Rio Grande rift--northern New Mexico, Baldridge, W. S.; Dickerson, P. W.; Riecker, R. E.; Zidek, J., New Mexico Geological Society, Guidebook, 35th Field Conference, pp. 157-170.

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