The role of hydraulic fractures and intermediate-depth earthquakes in generating subduction-zone magmatism

Article Abstract:

Magmatism at subduction zones is unexpected as subduction of cool oceanic lithosphere makes the regions the coldest in the mantle. A current subduction-zone magmatism model is based on water from the subducting slab entering the warmer mantle wedge, resulting in a reduction in melting temperature and magmatism. However it is believed that water does not leave the slab through porous flow to enter the wedge. Intermediate depth seismicity is explained by high pore-pressure that could facilitate faulting by a decrease in the friction. A hypothesis asserts that non-percolating water gives high pore-pressure and faulting interconnects the water ores, producing a hydrofracture that transports the water out into the wedge.

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Tracing trace elements from sediment input to volcanic output at subduction zones

Article Abstract:

The sedimentary fluxes in eight trenches around the globe were examined using the trace elements Ba, Sr, K, Rb, Cs, La, Th and U. The study tests the assumption that during subduction into open trenches, sea-floor sediments may either be scraped off or accompany the subducting plate into the mantle. Subducted sediment may then be either recycled to the arc crust by magmatism, or recycled into the mantle and contribute to mantle heterogeneity. The results indicate that sediment input into trenches is reflected in volcanic output.

Marine sediments, Volcanism

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The brine of the Earth

Article Abstract:

Sea water is likely the fluid mechansism that is responsible for the chemistry of arc volcanic magmas at subduction zones. At a subduction boundary, crustal material and ocean water are pulled down into the mantle, enter a fluid phase and are erupted in arc volcanos. Researchers were able to simulate the fluid thermodynamics of such a melt with results that agreed with both the thermodynamics of formation and the partitioning of trace elements in observed arc magmas.

Sea-water, Seawater

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