Large-volume, low-δ18O rhyolites of the central Snake River Plain, Idaho, USA
- 1 Department of Geology, Washington State University, Pullman, Washington 99164, USA
- 2 Idaho Geological Survey, P.O. Box 443014, Moscow, Idaho 83844, USA
- 3Department of Geology, Washington State University, Pullman, Washington 99164, USA
Abstract
The Miocene Bruneau-Jarbidge and adjacent volcanic fields of the central Snake River Plain, southwest Idaho, are dominated by high-temperature rhyolitic tuffs and lavas having an aggregate volume estimated as 7000 km3. Samples from units representing at least 50% of this volume are strongly depleted in 18O, with magmatic feldspar δ18OVSMOW (Vienna standard mean ocean water) values between −1.4‰ and 3.8‰. The magnitude of the 18O depletion and the complete lack of any rhyolites with normal values (7‰–10‰) combine to suggest that assimilation or melting of a caldera block altered by near- contemporaneous hydrothermal activity is unlikely. Instead, we envisage generation of the high-temperature rhyolites by shallow melting of Idaho Batholith rocks, under the influence of the Yellowstone hotspot, affected by Eocene meteoric-hydrothermal events. The seeming worldwide scarcity of strongly 18O-depleted rhyolites may simply reflect a similar scarcity of suitable crustal protoliths.
Footnotes
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↵GSA Data Repository item 2005162, Table DR1, major and trace element geochemistry, Table DR2, complete oxygen isotope data, Figure DR1, plots showing A-type characteristics of CSRP and WSRP rhyolites, and Figure DR2, major element compositions of CSRP and WSRP rhyolites, is available online at www.geosociety.org/pubs/ft2005.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
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- Accepted 23 June 2005.
- Received 17 March 2005.
- Revision received 9 June 2005.
- Geological Society of America
