Geochronologic and paleomagnetic evidence defining the relationship between the Miocene Hiko and Racer Canyon tuffs, eccentric outflow lobes from the Caliente caldera complex, southeastern Great Basin, USA |
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Authors: | Sherman Gromme Alan M Deino Myron G Best Mark R Hudson |
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Institution: | (1) United States Geological Survey, 345 Middlefield Road, MS 937, Menlo Park, California 94025, USA, US;(2) Berkeley Geochronology Center, 2453 Ridge Road, Berkeley, California 94709, USA, US;(3) Department of Geology, Brigham Young University, Provo, Utah 84602, USA, US;(4) United States Geological Survey, P.O. Box 25046, MS 913, Denver, Colorado 80225, USA, US |
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Abstract: | Outflow sheets of the Hiko tuff and the Racer Canyon tuff, which together extend over approximately 16 000 km2 around the Caliente caldera complex in southeastern Nevada, have long been considered to be products of simultaneous or near-simultaneous
eruptions from inset calderas in the west and east ends, respectively, of the caldera complex. New high-precision 40Ar/39Ar geochronology and paleomagnetic data demonstrate that emplacement of the uppermost part of the Racer Canyon tuff at 18.33±0.03 Ma
was nearly synchronous with emplacement of the single outflow cooling unit of the much larger overlying Hiko tuff at 18.32±0.04 Ma.
Based on comparison with the geomagnetic polarity time scale derived from the sea-floor spreading record, we conclude that
emplacement of the first of several outflow cooling units of the Racer Canyon tuff commenced approximately 0.5 m.y. earlier.
Only one paleomagnetic polarity is found in the Hiko tuff, but at least two paleomagnetic reversals have been found in the
Racer Canyon tuff. The two formations overlap in only one place, at and near Panaca Summit northeast of the center of the
Caliente caldera complex; here the Hiko tuff is stratigraphically above the Racer Canyon tuff. This study demonstrates the
power of combining 40Ar/39Ar and paleomagnetic data in conjunction with phenocryst compositional modes to resolve problematic stratigraphic correlations
in complex ash-flow sequences where use of one method alone might not eliminate ambiguities.
Received: 13 January 1997 / Accepted: 7 May 1997 |
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Keywords: | Ash-flow tuff Welded tuff Caldera Geochronology Paleomagnetism Great Basin USA |
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