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

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194

作者：

T Plank，CH Langmuir

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摘要：

AT ocean trenches, sea-floor sediments may either be scraped off the subducting plate, or accompany it into the mantle. Some of the subducted sediment may then be recycled to the arc crust by magmatism 1 ; the rest may be recycled into the mantle and contribute to mantle heterogeneity 2 . Strong evidence for sediment contributions to arc volcanism has come from isotope tracers, such as 207 Pb and 10 Be (refs 3–5), but a global mass balance requires consideration of element fluxes 6 . Here we report the sedimentary fluxes into eight trenches around the globe of trace elements that are enriched in arc volcanics (Ba, Sr, K, Rb, Cs, La, Th and U) 7 We show that the volcanic outputs clearly reflect the sediment inputs, once the effects of melting are taken into account 8 . Where the sediment flux into a trench is high for a particular element, the associated volcanics are enriched in this same element. Thus, some of the geochemical characteristics of arc volcanics can be traced back to the sediments at the trench. A mass balance of the inputs and outputs will ultimately provide estimates for how much sediment is recycled to the arc and how much to the deeper mantle.

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关键词：

Theoretical or Mathematical, Experimental/ element relative abundance geochemistry sediments tectonics volcanology/ melting effects magma composition seafloor sediments trace elements sediment input volcanic output subduction zones trenches arc volcanics geochemical characteristics mass balance Ba Sr K Rb Cs La Th U/ A9145 Tectonics A9135L Geochemistry A9140 Volcanology/ Ba/el Sr/el K/el Rb/el Cs/el La/el Th/el U/el