Geology of the northern Valles Caldera and Toledo embayment, New Mexico
Jamie N. Gardner and Fraser E. Goff
Detailed geologic mapping supported by geochronology and petrography shows that the northern Valles caldera records a complex history of pre-caldera volcanism and Rio Grande rift-related sedimentation, caldera collapse and mass wasting, ring-fracture volcanism and structurally focused volcanism within the Toledo embayment, and formation of intracaldera lacustrine deposits and alluvial terraces. The prominent northeastern grain of the Jemez lineament is locally defined by the Jemez fault zone, Redondo Creek graben, Toledo embayment, a structural discontinuity, the Embudo fault zone, and short faults in the map area. The main ring fracture collapse structures of the Toledo and Valles calderas were nearly coincident. Although the origin of the Toledo embayment is not entirely resolved, geologic arguments constrain its formation between 2.3 and 1.5 Ma. Based on geomorphic and other field relations of domes and flows, the structural history of the area, and timing constraints, we argue that the Toledo embayment formed during collapse of the Toledo caldera (1.61 Ma) along a structurally controlled zone that had hosted a northeasterly-elongated offshoot from the main Toledo caldera magma body. Field and laboratory data suggest that the hypabyssal rocks of the Cerro Rubio hills are shallow remnants of earlier Tschicoma volcanoes that covered the present area of the embayment before formation of Toledo caldera. The embayment became the site of structurally focused rhyolitic extrusions and explosive eruptions after caldera formation.
- Gardner, Jamie N.; Goff, Fraser E., 1996, Geology of the northern Valles Caldera and Toledo embayment, New Mexico, in: The Jemez Mountains Region, Goff, Fraser; Kues, Barry S.; Rogers, Margaret Ann; McFadden, Les D.; Gardner, Jamie N., New Mexico Geological Society, Guidebook, 47th Field Conference, pp. 225-230.