| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Journal of Petrology | Volume 43 | Number 4 | Pages 663-703 | 2002
© Oxford University Press 2002
Petrogenesis and Implications of Calc-Alkaline Cryptic Hybrid Magmas from Washburn Volcano, Absaroka Volcanic Province, USA
1DEPARTMENT OF EARTH SCIENCES, MONTANA STATE UNIVERSITY, BOZEMAN, MT 59717, USA
2INSTITUTE OF MINERALOGY AND GEOCHEMISTRY, UNIVERSITY OF LAUSANNE, BFSH 2, 1015 LAUSANNE, SWITZERLAND
The petrogenesis of calc-alkaline magmatism in the Eocene Absaroka Volcanic Province (AVP) is investigated at Washburn volcano, a major eruptive center in the low-K western belt of the AVP. New 40Ar/39Ar age determinations indicate that magmatism at the volcano commenced as early as 55 Ma and continued until at least 52 Ma. Although mineral and whole-rock compositional data reflect near equilibrium crystallization of modal phenocrysts, petrogenetic modeling demonstrates that intermediate composition magmas are hybrids formed by mixing variably fractionated and contaminated mantle-derived melts and heterogeneous silicic crustal melts. Nd and Sr isotopic compositions along with trace element data indicate that silicic melts in the Washburn system are derived from deep-crustal rocks broadly similar in composition to granulite-facies xenoliths in the Wyoming Province. Our preferred explanation for these features is that mantle-derived basaltic magma intruded repeatedly in the deep continental crust leading to fractional crystallization, silicic melt production, and homogenization of magmas, followed by ascent to shallow reservoirs and crystallization of new plagioclase-rich mineral assemblages in equilibrium with the intermediate hybrid liquids. The implications of this process are that (1) some calc-alkaline magmas may only be recognized as hybrids on purely chemical grounds, particularly in systems where mixing precedes and is widely separated from crystallization in space and time, and (2) given the role ascribed to crustal processes at Washburn volcano, the variation between rocks that follow calc-alkaline trends in the western AVP and those that follow shoshonitic trends in the east cannot simply reflect higher pressures of fractionation to the east in Moho-level magma chambers in the absence of crustal interaction.
KEY WORDS: petrogenesis; magma mixing; calc-alkaline; Absaroka Volcanic Province; 40Ar/39Ar dates
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. E. Smith, A. R. Carroll, and B. S. Singer Synoptic reconstruction of a major ancient lake system: Eocene Green River Formation, western United States GSA Bulletin, January 1, 2008; 120(1-2): 54 - 84. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. MIRNEJAD and K. BELL Origin and Source Evolution of the Leucite Hills Lamproites: Evidence from Sr-Nd-Pb-O Isotopic Compositions J. Petrology, December 1, 2006; 47(12): 2463 - 2489. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. TATSUMI, T. SUZUKI, H. KAWABATA, K. SATO, T. MIYAZAKI, Q. CHANG, T. TAKAHASHI, K. TANI, T. SHIBATA, and M. YOSHIKAWA The Petrology and Geochemistry of Oto-Zan Composite Lava Flow on Shodo-Shima Island, SW Japan: Remelting of a Solidified High-Mg Andesite Magma J. Petrology, March 1, 2006; 47(3): 595 - 629. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. DUFEK and G. W. BERGANTZ Lower Crustal Magma Genesis and Preservation: a Stochastic Framework for the Evaluation of Basalt-Crust Interaction J. Petrology, November 1, 2005; 46(11): 2167 - 2195. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T.C. Feeley and M.A. Cosca Time vs. composition trends of magmatism at Sunlight volcano, Absaroka volcanic province, Wyoming GSA Bulletin, June 1, 2003; 115(6): 714 - 728. [Abstract] [Full Text] [PDF]
|
|