Slab devolatilization and Os and Pb mobility in the mantle wedge of the Kamchatka arc

Os-, Nd-, and Pb-isotope measurements were performed on a suite of eleven Kamchatka peridotite mantle xenoliths in volcanics from the southern (Avachinsky) and central (Sheveluch and Kharchinsky) segments of the Kamchatka peninsula. Peridotites with higher Os content (1.3-5.2 ppb) show a narrow 187Os / 188Os range between 0.1182 and 0.1272 while the xenoliths with lower Os content (< 1 ppb) show a wider variation and more radiogenic 187Os / 188Os values (0.1287-0.1585). 187Os / 188Os and 3He / 4He (R / Ra) values of the xenoliths indicate that the xenoliths are metasomatized by the slab-derived fluids from the subducting altered oceanic crust. The original Os signature of some of the mantle wedge xenoliths seems to be eradicated and imprinted by the slab fluids from the subducting crust. The Nd-isotopic (+ 8.7-+ 9.3) and Pb-isotopic ratios (206Pb / 204Pb = 18.25-18.76; 207Pb / 204Pb = 15.43-15.55; 208Pb / 204Pb = 37.68-38.24) of the xenoliths are similar to those of the Pacific MORB. Pb and Ba contents of the xenoliths increase with increasing 187Os / 188Os. Thus the mantle-wedge beneath Kamchatka was infiltrated by slab-derived fluids with Os, Pb, and other volatile and fluid-mobile elements.