Some geochemical constraints on hot fingers in the mantle wedge: evidence from NE

Abstract: Mantle melting and the production of magmas along the NE Japan arc may be controlled by hot regions in the mantle wedge (hot fingers) that move toward the volcanic front along upward-sloping trajectories. At depths equivalent to 1-2 GPa, where magmas are expected to segregate from mantle diapirs, the hot-finger structures result in a decreas-ing thermal gradient away from volcanic front. Low-alkali tholeiite is therefore formed by the greater degree of diapiric melting near the volcanic front; high-alumina basalt and alkali olivine basalt are produced by lesser degrees of diapiric melting to the west. The grouping of volcanoes at the volcanic front is interpreted as being controlled by thermal structure in the mantle wedge, and groups are concentrated above the tips of the hot fingers. Map-view variations of minimum S7Sr/S6Sr of NE Japan volcanoes are interpreted as resulting from transport of fertile and high-S7Sr/S6Sr mantle material into he magma source region in the hot fingers. Given that mantle diapirs are formed in the lower part of the mantle wedge, a greater proportion of fertile material will be contained in the diapirs at the tips of the hot fingers, resulting in higher 87Sr/S6Sr magmas along the volcanic front. Conveyor-like r turn flow carries the sheet-like remnants of the fingers to depth along th