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

为了研究岛弧表面地质现象与下地壳和上地幔动力学之间的关系，对上地幔密度不均匀性引起的地壳和上地幔响应与日本东北弧下地震层析成像预期的震级进行了评估。对于低粘度下地壳和低粘度上地幔的流变模型，地幔底辟上升流上方的低密度下地壳物质受到地幔底辟上升流的机械拖动。软流圈剪应力，然后下地壳物质从弧后角向弧前角流动，在5-50 Ma的地质时间尺度上，这一过程的地表沉降量约为300m，并形成沉积盆地。地幔底辟上方的区域（“S”阶段）预计具有与地幔底辟相同的横向尺度，岛弧中的俯冲板片将成为横向运动的障碍。随着这一过程的进展，低密度下地壳物质可能会沿着构造线暴露（阶段“E”）。 ”）。由于下地壳物质沿构造线排出，导致下地壳压力降低，并伴随着加速沉降。日本西南部的白垩纪地质现象预计可以通过这种物理机制及其相关的地表运动和大约 140-120 Ma 时期的下地壳物质流动来解释。在关门沉积盆地中观察到的现象可以解释为“S”阶段的地质事件，从大约110Ma开始，关门沉积盆地受到大量火山沉积物的供给，并同时扩大。大约在同一时间，在关门群以南地区发生了低压高温变质作用和花岗岩活动（Ryoke Belt），这或许可以解释沿中位构造线的这些地质现象。 MTL）作为对应于“E”阶段的地表地质事件，但需要强调的是，这种耦合的时间和空间尺度是由下地壳和上地幔的流变结构以及地幔的规模决定的。少底辟。