Some geochemical constraints on hot fingers in the mantle wedge: evidence from NE Japan
Y. Tamura, 2003. "Some geochemical constraints on hot fingers in the mantle wedge: evidence from NE Japan", Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes, R. D. Larter, P. T. Leat
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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 decreasing 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 87Sr/86Sr of NE Japan volcanoes are interpreted as resulting from transport of fertile and high-87Sr/86Sr mantle material into the 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/86Sr magmas along the volcanic front. Conveyor-like return flow carries the sheet-like remnants of the fingers to depth along the top of the subducting slab.
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Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes
Recycling of oceanic plate back into the Earth’s interior at subduction zones is one of the key processes in Earth evolution. Volcanic arcs, which form above subduction zones, are the most visible manifestations of plate tectonics, the convection mechanism by which the Earth loses excess heat They are probably also the main location where new continental crust is formed, the so-called ‘subduction factory’. About 40% modern subduction zones on Earth are intra-oceanic. These subduction systems are generally simpler than those at continental margins as they commonly have a shorter history of subduction and their magmas are not contaminated by ancient sialic crust. They are therefore the optimum locations for studies of mantle processes and magmatic addition to the crust in subduction zones.
This volume contains a collection of papers that exploit the relative simplicity of intra-oceanic subduction systems to provide insights into the tectonic, magmatic and hydrothermal processes associated with subduction.