Osmium isotope constraints on lower crustal recycling and pluton preservation at Lassen Volcanic Center, CA

摘要: Osmium isotope compositions of intermediate- to silicic-composition calc-alkaline volcanic rocks from the Lassen region Cascade arc are significantly more radiogenic (QOs = +23 +224) than typical mantle. These evolved in have unradiogenic Sr, Nd, and Pb which overlap with those contemporaneous mafic lavas. Crystal fractionation mafic- intermediate-composition magmas produces Re/Os ratios that high enough evolve very Os only a few million years, providing potential fingerprint for detecting involvement such young, relatively crust magmatic systems. However, will remain constant over short time intervals due low parent/daughter enrichment during evolution. The typically interpreted reflect significant interaction lower crustal material has compositions. Beneath this section arc, large amounts high-QOs may formed been isolated MASH zone mixing homogenization processes Pliocene or Late Miocene. results study indicate isotopes provide unique glimpse into processes, as recycling, primitive orogenic arcs. 9 2002 Elsevier Science B.V. All rights reserved.