Geology and thermal history of the Pliocene Cerro Negro volcanic necks and adjacent Cretaceous sedimentary rocks, west-central New Mexico
R. Bruce Hallett, Philip E. Long, John Lorenz, and Bruce Bjornstad

Abstract:

Two vertical and two angled boreholes were drilled through a Cretaceous–Jurassic section of shale and sandstone adjacent to the Pliocene Cerro Negro necks. One hundred fifty-seven meters of vertical and 575 m of angled core have been recovered, logged, and sampled to establish the section's sedimentologic, depositional, fracture, and thermal characteristics. Detailed core logging from ground surface to the top of the Brushy Basin Member of the Morrison Formation (Jurassic) generally supports published interpretations of depositional environments for this section. Geologic mapping at a scale of 1:2500 identifies a linear array of intrusive features that are roughly parallel to a regional NNE fracture/fault trend. Indirect evidence from drilling suggests the subsurface geometry of the Cerro Negro necks to be unlike the surface expression; additional drilling and geophysical studies will be necessary to map accurately the subsurface geometry. Fracture mapping in surface outcrop and core indicate two dominant, steeply dipping fracture trends, NNE, and a second roughly perpendicular trend of ESE. Although the Cerro Negro necks were not intersected in the angle holes, vitrinite data suggest a thermal aureole associated with the Cerro Negro intrusions of sufficient heat (>125°C) to sterilize local rocks in an approximate 50-m radius.


Citation:

  1. Hallett, R. Bruce; Long, Philip E.; Lorenz, John; Bjornstad, Bruce, 1999, Geology and thermal history of the Pliocene Cerro Negro volcanic necks and adjacent Cretaceous sedimentary rocks, west-central New Mexico, in: Albuquerque Country, Pazzaglia, Frank J.; Lucas, S. G.; Austin, G. S., New Mexico Geological Society, Guidebook, 50th Field Conference, pp. 235-245.

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