Figure 7
From: Genesis of ultra-high-Ni olivine in high-Mg andesite lava triggered by seamount subduction
Cross section of northern subduction zone of the Kamchatka Peninsula and schematic model of EC magma generation. Right figure shows overall cross-sectional view of the subduction zone and it represents why the subducted seamount is the cause of efficient slab dehydration just beneath the EC area (<80 km), via the following effects: thinning of the lithosphere5, plate rejuvenation from a mantle plume40, 41, and formation of fluid pathway along cracks formed by the collapse of the subducted seamount. Left figure (black frame part in right figure) focuses on the mantle wedge beneath the EC and it represents the genesis of EC lavas. Based on these effects, ①silica-enriched slab fluids are dehydrated from the subducted seamount and ② form pyroxenite veins in the mantle wedge, which are formed locally along fluid pathways. Its melting would ③ generate ultra-high-Ni melt (HMA) and ④ crystallize ultra-high-Ni olivine (~6300 ppm Ni) at the initial stage of crystallization in the mantle. Cpx also starts to crystallize from the initial stage and pargasitic hornblende (Hb) breakdown by subsequent decompression. For subsequent stages, ⑤ the residual Si-less fluid would cause flux melting of peridotite to produce basalt with moderate–high-Ni olivine (~2900 ppm Ni) ⑥ and ⑦. The black dashed lines indicate temperature contours from 200 to 1200 °C with a contour of 200 °C intervals. The seamounts and EC are not drawn to scale.
