Convective coupling between lower crust and upper mantle

为了研究岛弧中的地表地质现象与下地壳和上地幔动力学之间的关系，评估了由上地幔密度不均匀性引起的地壳和上地幔响应，其量级与日本东北部岛弧下地震层析成像的预期值相同。对于低粘度下地壳和低粘度上地幔的流变学模型，地幔底辟上涌之上的低密度下地壳物质被软流圈剪切应力沿着机械拖曳，从弧后角部向弧前角部流动。在5-50 Ma的地质时间尺度上，这一过程的地表沉降约为300 m，在地幔底辟之上（S期）可形成横向尺度与地幔底辟相当的沉积盆地。岛弧中的俯冲板片将成为下地壳物质横向运动的屏障。日 ...更多信息 随着这一过程的进行，低密度下地壳物质可能在上覆板块的边缘聚集。在弧前地幔楔压力的临界阶段，高温下地壳物质可能沿构造线沿着出露（E阶段）。由于下地壳物质沿着构造线排出，下地壳压力将降低，沉积盆地将伴随火山活动加速沉降。日本西南部的白垩纪地质现象可以用这种物理机制及其相关的地表地壳运动和下地壳物质流动来解释。在关门沉积盆地中观察到的大约140-120 Ma的相对缓慢的沉积可以解释为“S”阶段的地质事件。从大约110 Ma开始，关门沉积盆地被供给了大量的火山沉积物，同时扩张和突然沉降。大约在同一时期，低压-高温变质作用和花岗岩活动（Ryoke带）发生在沿着Kanmon群南部地区。沿着中构造线（MTL）的这些地质现象可能被解释为对应于“E”阶段的地表地质事件。但这种耦合的时空尺度取决于下地壳和上地幔的流变结构和地幔底辟的规模。少

In order to examine the relationship between surface geological phenomena in island-arcs and lower crustal and upper mantle dynamics, crustal and upper mantle responses induced by the upper mantle density heterogeneities with the magnitude expected from the seismic tomography beneath northeastern Japan arc have been evaluated. For the rheological model with a low-viscosity lower crust and low-viscosity uppermost mantle, low-density lower crustal material above mantle diapiric upwelling is mechanically dragged along by the asthenospheric shear stresses, and then lower crustal material flows from the back-arc corner to fore-arc corner. The surface subsidence for this process is about 300m on the geological time scale of 5-50 Ma, and formation of sedimentary basin with about the same lateral scale as mantle diapir can be expected in the area above the mantle diapir (stage "S"). The subducted slab in island-arc will operate as a barrier to the lateral movement of lower crustal material. Th … More en accumulation of low-density lower crustal material may occur at the edge of the overriding plate as the progress of this process. At a critical stage of the pressure in the mantle wedge of fore-arc region, high temperature lower crustal material may be therefore exposed along the tectonic line (stage "E"). As the result of discharging lower crustal material along the tectonic line, the pressure in the lower crust will be decreased and the accelerated subsidence accompanied by volcanism is expected in the sedimentary basin. The Cretaceous geological phenomena in Southwest Japan may be explained by this physical mechanism and its linked surface crustal movement and the flow of lower crustal material. A relatively slow deposition in the period of about 140-120 Ma observed in the Kanmon sedimentary basin may be interpreted as the geological event of stage "S". From about 110Ma, the Kanmon sedimentary basin was supplied with a large quantity of volcanic sediments, and simultaneously expanded and suddenly subsided. At about the same time, low pressure-high temperature metamorphism and granitic activity (Ryoke Belt) occurred along the areas to the south of the Kanmon Group. It may be possible to interpret these geological phenomena along the Median Tectonic Line (MTL) as the surface geological events corresponding to stage "E". It is, however, stressed that the time and spatial scale for this coupling is determined by the rheological structure of the lower crust and upper mantle and by the scale of mantle diapir. Less