Abstract: Slab dehydration hydrates overlying mantle atop subducting slab, which lowers mantle melting points and causes partially melting of the hydrated mantle. Once melts in the partially melting mantle are extracted to surface, volcano explodes and new crust forms at the surface. Therefore, spatial and temporal activities of the partially melting mantle with relatively small density and viscosity in the mantle wedge controls volcanisms in space and time. We used 3-D petrological-thermomechanical model to simulate spatial and temporal volcanisms closely related to the slab dehydration in subduction zone. Our results show that effective viscosity and density of partially melting mantle are the main factors for different patterns of the 3-D mantle plumes atop the subducting slab. In high-viscosity models (10²⁰~10²¹ Pa·s ) trench-subparalleled plumes become rather sheet-like/wave-like, and the spacing between them increases to 70~100 km, while in low-viscosity models (10¹⁸~10¹⁹ Pa·s) the typical spacing of finger-like/ridge-like plumes is about 30~50 km. In contrast, a low density contrast of 0~50 kg/m3 between partially melting mantle and ambient mantle (i.e. high to complete melt removal) suppresses pronounced plumes and is associated with low-amplitude (50~100 km wide and 10~15 km high) domal structures. Periodic melt productivity (5 Myrs) shows the periodicity of volcanism in subduction zone. The higher subduction velocity favors bigger partially melting mantle at bigger depths ( i.e.120 km), and the higher melt extraction efficiency increases the total amount of new crust. The lower subduction velocity and lower melt extraction efficiency increase the ratio of upper (granitic) and middle (dacitic) crust to lower(basaltic) crust. Our results may explain the periodicity and clustering of volcanic activity observed in magmatic arcs such as in North-East Japan, New Zealand and Southern Alaska.

Key words: Subduction zone, Slab dehydration, Mantle plumes, Volcano, 3-D numerical modeling