Convective coupling between lower crust and upper mantle

下地壳与上地幔之间的对流耦合

基本信息

批准号：
05640469
负责人：
NAKADA Masao
金额：
$ 1.22万
依托单位：
KYUSHU UNIVERSITY (1994)Kumamoto University (1993)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1993
资助国家：
日本
起止时间：
1993 至 1994
项目状态：
已结题

项目摘要

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

为了检查岛 - 弧形和下地壳和上地幔动力学的表面地质现象之间的关系，由上地幔密度异质性引起的地壳和上地幔反应，日本东北部的地震层析成像的幅度预期。对于低粘液质性低地壳和低粘度最高地幔的流变学模型，高密度的下地壳材料在地幔透明上升上升的上方是机械地沿着小圈剪切应力沿机械拖动，然后较低的地壳材料从后排角向前拐角流到了前角。在5-50 mA的地质时间尺度上，此过程的表面沉降约为300m，在地幔底底（阶段“ S”）上方的区域中，可以预期具有与Mantle Diapir的横向尺度大致相同的沉积盆地的形成。岛上岛上的俯冲平板将作为下层地壳材料侧向运动的障碍。随着该过程的进展，低密度下地壳材料的加速度可能会发生更多的加速度。因此，在前弧区域的地幔楔的临界阶段，高温下地壳材料可以沿构造线（阶段“ E”）暴露。由于沿着构造线排放下层地壳材料的结果，下层地壳中的压力将得到改善，预计在沉积盆地中，火山造成的加速沉降。日本西南部的白垩纪地质现象可以用这种物理机制及其连接的表面地壳运动和下层地壳材料的流动来解释。在Kanmon沉积盆地观察到的大约140-120 MA期间，相对较慢的沉积物可以解释为“ S”阶段的地质事件。从大约110mA开始，为Kanmon沉积盆地提供了大量的火山沉积物，并简单地扩展并突然补贴。大约同时，沿着坎蒙组南部的区域发生了低压力高温变质和花岗岩活性（Ryoke带）。可以将这些地质现象沿中位构造线（MTL）解释为与阶段“ E”相对应的表面地质事件。但是，这强调，这种耦合的时间和空间尺度取决于下层外壳和上地幔的流变结构以及地幔底底的尺度。较少的