HR: 1340h
AN: V13B-1461    [Abstracts]
TI: Constraints on P-T Conditions and Evolution of Granulite and Ultramafic Xenoliths From Prindle Volcano, Alaska
AU: * Ghent, E D
EM: ghent@ucalgary.ca
AF: Edward D. Ghent, Dept. of Geology and Geophysics, University of Calgary, Calgary, AB T2N 1N4 Canada
AU: Edwards, B R
EM: edwards@alpha.dickinson.edu
AF: Benjamin R. Edwards, Dept. of Geology, Dickinson College, Carlisle, PA 17013 United States
AU: Russell, J K
EM: krussell@eos.ubc.ca
AF: James K. Russell, Igneous Petrology Laboratory, Dept. of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
AB: Prindle volcano is an isolated, inactive basanitic cone located just across the Alaska-Yukon border (Lat. 63.72 øN; Long. 141.82 øW) at the northern edge of the northern Cordilleran volcanic province. The cone contains crustal and mantle xenoliths, including crustal granulites. The basement to Prindle volcano comprises Mesozoic metamorphic rocks (greenschist to amphibolite facies), but no granulites have been detected. The crustal xenoliths contain orthopyroxene (opx)-plagioclase (pl)-quartz (qtz) +/- mesoperthite (msp) and clinopyroxene (cpx). Geothermometry using opx-cpx yields T's ranging from 770 to 1015 C at 10 kbar. Integrated feldspar geothermometry yields 855 to 964 C at 10 kbar. Pl-cpx-qtz geobarometry yields P's ~10-11 kbar. Opx-cpx geothermometry on mantle ultramafic rocks yields 915-970 C at 15 kbar. Isochemical P-T phase diagrams for spinel lherzolite suggest a maximum P of 11.5 kbar at 950 C, but experimental work suggests higher pressures, ~15 kbar (+). Present Moho conditions are estimated to be 900 +/- 100 C and ~10 kbar. The calculated liquidus for the host basanite lava is ~1450 C at 15 kbar. Our results suggest that the crustal xenoliths were metamorphosed under relatively dry conditions with crustal thicknesses not significantly greater than present day; however, rocks at the present-day surface are high-pressure amphibolites. Geothermal gradients during Mesozoic metamorphism are near the higher estimates of the present geothermal gradient, ~25 +/- 3øC /km. P-T constraints from mantle xenoliths are consistent with present day geothermal gradients. Basanite liquidus temperatures, which are significantly higher than the lherzolite temperatures, are consistent with an asthenospheric source region.
DE: 8499 General or miscellaneous
DE: 9350 North America
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting