Limited arc magmatism and seismicity due to extensive mantle wedge serpentinization in the Makran subduction zone

Abstract

Highlights • We present a new integrated seismic, magnetic, gravity and isostatic model across the Makran subduction zone. • Slow low-angle Makran subduction has 60–65% serpentinization in the peridotitic shallow mantle wedge. • A large volume of rheologically weak serpentinite reduces seismicity by lowering the slab friction. • Little fluid left in the slab at the melting depth (70–100 km) explains the limited arc magmatism. • Around 100 km depth, the low-angle subduction changes to an almost vertical dip. Subduction processes usually involve extensive seismicity and create voluminous magmatic arcs by mantle wedge melting caused by dehydration of the subducting slab, but the Makran subduction zone has anomalously low seismicity and magmatism. Here we explain these anomalous features by 60-65% serpentinization in the peridotitic shallow mantle wedge based on our new integrated seismic, magnetic, gravity and isostatic model across the Makran subduction zone. The low-angle, slow Makran subduction provides ample time for the slab to release sufficient amounts of fluids for creating a large volume of rheologically weak serpentinite. This reduces seismicity by lowering the friction between the slab and surrounding rocks. Further, very little fluid is left in the slab when it reaches the melting depth, which explains the limited arc magmatism. Around 100 km depth, the subduction switches from low-angle to almost vertical. Our model demonstrates the combined effects of subduction rate and dip on mantle serpentinization with implication for assessment of seismic and volcanic hazards in subduction systems.