Volcanic Arc of Kamchatka: a Province with High-␦18O Magma Sources and Large-Scale 18O/16O Depletion of the Upper Crust
Geochimica et Cosmochimica Acta, Vol. 68, No. 4, pp. 841–865, 2004 Copyright © 2004 Elsevier Ltd Pergamon Printed in the USA. All rights reserved 0016-7037/04 $30.00 ϩ .00 doi:10.1016/j.gca.2003.07.009 Volcanic arc of Kamchatka: a province with high-␦18O magma sources and large-scale 18O/16O depletion of the upper crust 1, 2 3 1 ILYA N. BINDEMAN, *VERA V. PONOMAREVA, JOHN C. BAILEY, and JOHN W. VALLEY 1Department of Geology and Geophysics, University of Wisconsin, Madison, WI, USA 2Institute of Volcanic Geology and Geochemistry, Petropavlovsk-Kamchatsky, Russia 3Geologisk Institut, University of Copenhagen, Copenhagen, Denmark (Received March 20, 2003; accepted in revised form July 16, 2003) Abstract—We present the results of a regional study of oxygen and Sr-Nd-Pb isotopes of Pleistocene to Recent arc volcanism in the Kamchatka Peninsula and the Kuriles, with emphasis on the largest caldera- forming centers. The ␦18O values of phenocrysts, in combination with numerical crystallization modeling (MELTS) and experimental fractionation factors, are used to derive best estimates of primary values for ␦18O(magma). Magmatic ␦18O values span 3.5‰ and are correlated with whole-rock Sr-Nd-Pb isotopes and major elements. Our data show that Kamchatka is a region of isotopic diversity with high-␦18O basaltic magmas (sampling mantle to lower crustal high-␦18O sources), and low-␦18O silicic volcanism (sampling low-␦18O upper crust). Among one hundred Holocene and Late Pleistocene eruptive units from 23 volcanic centers, one half represents low-␦18O magmas (ϩ4 to 5‰). Most low-␦ 18O magmas are voluminous silicic ignimbrites related to large Ͼ10 km3 caldera-forming eruptions and subsequent intracaldera lavas and domes: Holocene multi-caldera Ksudach volcano, Karymsky and Kurile Lake-Iliinsky calderas, and Late Pleistocene Maly Semyachik, Akademy Nauk, and Uzon calderas.
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