| Abstrakt: |
Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench-parallel slab motion through the mantle, recently defined as a form of "slab dragging." We investigate here long-term slab-dragging components of the Tonga-Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga-Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga-Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga-Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga-Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga-Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga-Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga-Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep-slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle. |
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