table4_A Possible Roll-Over Slab Geometry Under the Caroline Plate Imaged by Monte Carlo Finite-Frequency Traveltime Inversion of Teleseismic SS Phases.docx

The shape of a subducting slab varies as a function of trench motion. Two end-members of subduction modes are geodynamically possible: roll-back mode underneath neighboring plates and roll-over mode underneath the plate itself. Whereas most of major slabs seem to roll back while the Pacific plate shows a slab piling behavior down to ∼1,000 km depth under the Mariana trench, no clear evidence of slab roll-over in nature has been reported so far. Here we show a possible roll-over slab beneath the Caroline microplate, revealed from its three-dimensional seismic velocity structure derived by analyzing teleseismic reverberating SS phases. We suggest that slab roll-over is driven by at least two factors: 1) the overall buoyancy and fragility of the Caroline microplate at the surface, induced by a thin hot mantle plume that rises from depths ≥800 km; and 2) the pushing force of the Pacific plate acting on the trailing edge of the Caroline plate.

俯冲板片（subducting slab）的形态随海沟运动（trench motion）发生变化。地球动力学上存在两种可行的俯冲模式端元（end-members）：邻侧板块下方的后撤模式（roll-back mode），以及板块自身下方的翻转模式（roll-over mode）。多数大型俯冲板片均表现出后撤特征，而太平洋板块（Pacific plate）在马里亚纳海沟（Mariana trench）下方约1000公里深度处则呈现板片堆积行为，但截至目前，自然界中尚未有板片翻转（slab roll-over）的明确证据被报道。本文通过对远震SS反射震相（teleseismic reverberating SS phases）的分析得到三维地震波速结构（three-dimensional seismic velocity structure），并据此揭示了加罗林微板块（Caroline microplate）下方存在一例可能的板片翻转结构。我们认为，板片翻转至少受两个因素驱动：1）源自深度≥800公里的薄而炽热的地幔柱（mantle plume）所引发的加罗林微板块表层整体浮力与脆性特征；2）太平洋板块施加于加罗林板块后缘的挤压力。