Fluid flow and water–rock interaction across the active Nankai Trough subduction zone forearc revealed by boron isotope geochemistry

Autor: Tomohiro Toki, Andre Hüpers, C. Geoffrey Wheat, Ryuichi Shinjo, Achim J Kopf, Simone A Kasemann, Anette Meixner, Chen-Feng You
Rok vydání: 2016
Předmět:
Zdroj: Geochimica et Cosmochimica Acta. 193:100-118
ISSN: 0016-7037
Popis: Compositional changes, dehydration reactions and fluid flow in subducted sediments influence seismogenesis and arc magmatism in subduction zones. To identify fluid flow and water–rock interaction processes in the western Nankai Trough subduction zone (SW Japan) we analyzed boron concentration and boron isotope composition (δ11B) of pore fluids sampled across the subduction zone forearc from depths of up to ∼922 m below seafloor during four Integrated Ocean Drilling Program (IODP) Expeditions. The major structural regimes that were sampled by coring include: (1) sedimentary inputs, (2) the frontal thrust zone, (3) the megasplay fault zone, and (4) the forearc basin. From mass balance consideration we find that consumption of boron (B) by ash alteration and desorption of B from the solid phase, mediated by organic matter degradation, produces a net decrease in B concentrations with depth down to ∼120 μM and variable δ11B values in the range of ∼+20‰ and +49‰. Interstitial water in sediments on the incoming oceanic plate are influenced by more efficient mobilization of exchangeable B from the solid phase due to higher temperatures and alteration of the oceanic crust that acts as a sink for 10B. At the tip of the megasplay fault zone, elevated B concentration and B isotopic composition suggest that underthrust coarse-grained slope sediments provide a pathway for fluids out of the upper (
Databáze: OpenAIRE
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