A geophysical-geological transect of the Silent Canyon caldera complex, Pahute Mesa, Nevada

Journal Article · Thu Mar 10 04:00:00 EST 1994 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JB02447· OSTI ID:243986

Ferguson, J F ^[1]; Cogbill, A H; Warren, R G ^[2]

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1. Univ. of Texas at Dallas, Richardson, TX (United States)
2. Los Alamos National Lab., NM (United States)

Revision of lithological logs for boreholes penetrating the volcanic center at Pahute Mesa, Neveda, has led to a thorough review of the volcanic stratigraphy and geologic structure. The authors have combined this review with a compilation of old and newly acquired gravity and seismic travel time data, producing a unified interpretation along a northwest to southeast profile. The analysis supports a new interpretation of the Silent Canyon caldera complex. The caldera is found to be more asymmetric than previously suggested, with the southeastern boundary formed by linear, high-angle normal faults and a more gently sloping northwestern boundary. The total thickness of volcanic units within the caldera complex does not appear to exceed 5 km. The shallow structure at Pahute Mesa could have a profound effect on the seismic response for regional and teleseismic signals from this nuclear test site. The Silent Canyon caldera complex is actually a set of nested calderas first filled by thick (>1 km) postcaldera lavas and subsequently buried by outflow sheets of the Timber Mountain caldera to the south. Thick, postcaldera lavas filled a half-graben structure formed west of the West Greeley fault, dropping the tops of the youngest caldera-forming units to depths in excess of 2 km. Therefore the western boundary of the caldera complex is poorly defined. East of the West Greeley fault, two overlapping calderas are defined, and stratigraphic data suggest the presence of even older calderas. The youngest caldera, the calc-alkaline Area 20 caldera, is well defined from drill hole data. The Area 20 caldera overlaps the 13.6 Ma peralkaline Grouse Canyon caldera, which is less well defined, but apparently collapsed in trap-door style along the Almendro fault. For both these calderas, collapse continued after the main caldera-forming eruption, concurrent with the accumulation of thick (>1 km) lavas within the peripheral collapse zones. 67 refs., 13 figs.

• OSTI ID: 243986
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B3 Vol. 99; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
58 GEOSCIENCES
CALDERAS
GEOLOGIC STRATA
GEOLOGY
NEVADA TEST SITE
STRATIGRAPHY