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地幔楔（mantle wedge)，是大洋板块在海沟（板块汇聚边界）处向地幔俯冲时与上盘的大陆板块（非潜没板块）之间夹杂的三角楔形的地幔舌部。可用地震波速成像来辨识。^[1]

俯冲的洋壳携带了大量挥发性水分（水合矿物的分解与渗透的海水），水分的上升将降低其上的地幔楔的熔化温度。^[2]^[3]^[4] 地幔楔的流动导致的减压也有助于其熔化。熔融的地幔楔上升形成了火山活动。^[5]

弧前地幔扩展至俯冲带与地幔楔较冷的鼻部相遇之处，深度约为10–40 km.^[1]俯冲带之处的地震波衰减低，波速快。^[6]地幔楔区域的地震波断层成像显示为低速高衰减区域，Vp= 7.4 km·s⁻¹ ，Vs= 4 km·s⁻¹.^[1] 没有火山弧的地幔楔就没有这种低速。这反映了地幔楔是否熔融。

参考文献

^ ^1.0 ^1.1 ^1.2 Weins, A. D.; Conder, A. J.; Faul H. U. The seismic structure and dynamics of the mantle wedge. Annual Review of Earth and Planetary Sciences. 2008,. 10.1146.
^ Kelley, K.; Plank, T.; Newman, S.; Stolper, E.; Grove, T.; Parman, S.; Hauri, E. Mantle melting as a function of water content beneath the Mariana arc. Journal of Petrology. 2010, 51 (8): 1711–1738. doi:10.1093/petrology/egq036.
^ Van Keken, Peter E. The structure and dynamics of the mantle wedge (PDF). Earth and Planetary Science Letters. 2003, 215 (3–4): 323–338 [2016-08-20]. Bibcode:2003E&PSL.215..323V. doi:10.1016/S0012-821X(03)00460-6. （原始内容 (PDF)存档于2011-07-21）.
^ Kimura, J.; Yoshida, T. Contributions of slab fluid, mantle wedge and crust to the origin of quaternary lavas in the NE Japan arc. Journal of petrology. 2006, 47 (11): 2185–2232. doi:10.1093/petrology/egl041.
^ Hirshmann, M. M. Ironing out the oxidation of earth's mantle. Science Magazine. 2012,. 10.1126.
^ Stachnik, J. C.; Abers, A. G. Seismic attenuation and mantle wedge temperatures in the Alaska subduction zone. Journal of geophysical research. 2004, 10 (B10304).