Asymmetric dynamics at subduction zones derived from plate kinematic constraints |
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| Institution: | 1. Sapienza Università di Roma, Dipartimento di Scienze della Terra, Rome, Italy;2. Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy;3. Istituto Nazionale di Geofisica e Vulcanologia, INGV, Rome, Italy;1. Geosciences and Technology Division, CSIR – North East Institute of Science and Technology, Jorhat, Assam, India;1. Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Wuhan), Wuhan 430074, China;4. Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China;5. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;1. National Institute of Natural Hazards, Ministry of Emergency Management, 100085 Beijing, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 100029 Beijing, China;3. Department of Mathematical Sciences, Tsinghua University, 100084 Beijing, China;4. School of Mathematics and Statistics, Ningxia University, 750021 Yinchuan, China;1. Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy;2. Dipartimento di Scienze della Terra, Sapienza Università di Roma, Rome, Italy;3. Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy |
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| Abstract: | The lithospheric sinking along subduction zones is part of the mantle convection. Therefore, computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced, for the mass conservation criterion. The rate of subduction is constrained by the convergence rate between upper and lower plates and the motion of the subduction hinge H that may either converge or diverge relative to the upper plate. Here, starting from the analysis of the slab hinge kinematics, we evaluate the subduction rate at 31 subduction zones worldwide, useful to compute volumes of sinking lithosphere into the mantle. Our results show that ∼190 km3/yr and ∼88 km3/yr of lithospheric slabs are currently subducting below H-divergent and H-convergent subduction zones, respectively. We also propose supporting numerical models providing asymmetric volumes of the subducted lithosphere, using the subduction rate instead of plate convergence, as boundary condition. Furthermore, H-divergent subduction zones appear to be coincident with subductions having “westward”-directed slabs, whereas H-convergent subduction zones are mostly compatible with those that have “eastward-to-northeastward”-directed slabs. On the basis of this geographical polarity, our lithospheric volume estimation gives ∼214 km3/yr and ∼88 km3/yr of subducting lithosphere, respectively. This entails that W-directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to E-to-NE-directed ones. In accordance with the conservation of mass principle, this volumetric asymmetry in the mantle suggests a displacement of ∼120 km3/yr of mantle material from west to east, providing a constraint for global asymmetric mantle convection. |
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