Regional geology and geophysics of the Jemez Mountains Page: 6 of 12
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REGIONAL GEOLOGY AND GEOPHYSICS OF THE JEMEZ MOUNTAINS
Francis G. West
The western margin of the Rocky Mountain tectonic belt
is the initial site for the Los Alamos Geothermal Project.
Igneous activity in the area culminated with the formation
of a collapsed volcanic caldera and the deposition of thick.
beds of tuff. Geophysical studies indicate that the region
is one of relatively high-terrestrial heat flow, low-crustal
density, low-crustal seismic velocities, low-crustal magneto-
electric impedance, and thin crust.
The Los Alamos Scientific Laboratory
has initiated a program for the research and
development of geothermal energy. Potential
for development of geothermal energy varies
areally and with depth below the earth's
surface. This spatial distribution of geo-
thermal energy is the culmination of all
geological processes that were ever active.
Assessment of the geothermal potential of an
area requires at a minimum all available
geological and geophysical information. The
following is a brief review of that informa-
tion for the proposed project area with an
attempt by the author to assemble it into
the most reasonable picture.
The area proposed for initial experi-
ments in the development of a man-made geo-
thermal-energy system, the Jemez Mountains,
lies in the southern part of the Rocky Moun-
tain belt in what is known as the Rio Grande
trough or rift. . The trough is bounded geo-
logically on the east by the Texas foreland,
on. the west, by the Colorado Plateau, and on
the southwest by the Basin and Range prov-
ince. This cordilleran system, the Rocky
Mountain belt, extends northward into Canada
and southward into Mexico. The Rio Grande
trough extends from central Colorado through
southern New Mexico.1
The Rockies have a long history of
structural activity, which was culminated
during the Laramide orogeny with a dramatic
uplift of the belt by compressional forces
of global magnitude. The uplifted belt has
a width of 50 to 100 miles in New Mexico.
The east limb of the New Mexico part of the
uplift characteristically exhibits more
folding and is wider than the west limb,
which is flatter and terminates more abruptly.
The east limb has been folded to the extent.
that it was described as a synclinorium.2
The uplift was eroded to an undulating plain,
the remnants of which cap many of the peaks
of the present Rockies. Subsequently, parts
of the belt went into tension causing linear-
collapse features such as the Rio Grande Val-
ley, a complex structural trough. The trough
was formed by en echelon blocks faulted down
in a stair-step fashion, as is indicated in
Fig. 1, with an occasional relatively up-
thrown block in the sequence. It was during
this period in geologic time that extensive
volcanic extrusion and intrusion began to
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West, F.G. Regional geology and geophysics of the Jemez Mountains, report, August 1, 1973; New Mexico. (digital.library.unt.edu/ark:/67531/metadc1036044/m1/6/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.