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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Exhumation of UHP/LT rocks due to the local reduction of the interplate pressure: Thermo-mechanical physical modelling
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Exhumation of UHP/LT rocks due to the local reduction of the interplate pressure: Thermo-mechanical physical modelling

机译：由于板间压力的局部降低而造成的UHP / LT岩石的发掘：热机械物理模型

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摘要

Spatial distribution of UHP/LT terrains suggests that their exhumation is essentially a three-dimensional process that occurs only locally in specific sites along mountain belts. On the other hand, the continental subduction resulting in the formation of UHP/LT rocks takes place along the whole belt. The previously performed by the authors 2-D thermo-mechanical laboratory modelling of continental subduction has shown that exhumation of deeply subducted continental crust is possible only when the effective interplate pressure p(n) is lower than the lithostatic pressure (low compression subduction regime). At the same time, this modelling showed that for the deeply subducted continental crust to be preserved at low temperature at great depth, the continental subduction should be accompanied by the subduction of the fore-arc block or the arc plate. The latter process occurs only when p(n) is high (high compression regime). To reconcile both processes we suggest that within the background of a generally high compression regime the interplate pressure can be locally reduced in some specific situations which would then allow the local exhumation of UHP/LT material. Using physical modelling technique we investigate one of such situations that occurs when the frontal part of the overriding plate undergoes (subduction induced or not) extension parallel to the plate boundary with activation or formation of a strike-slip transform fault oblique to the plate boundary (to the interplate zone). The displacement along this fault results in a local reduction of the interplate pressure at the intersection of the fault with the interplate zone. This pressure reduction permits the rise of the deeply subducted low-density continental crust and sediments submitted to UHP/LT conditions under buoyancy force. A 10 km-thick slice of crust detaches at similar to 150 km-depth and moves up along the interplate zone with a starting rate of ca. 3 cm/yr. The ascent rate reduces when the unit reaches crustal depth. The deformation of this unit is small when it first detaches and starts rising, but increases when reaching the base of the overriding plate. The exhuming material is sheared and stretched in a narrow passage at similar to 70 km-depth. Therefore in real conditions the deformation is mainly recorded when the unit is submitted to HP and not UHP conditions.
机译：UHP / LT地形的空间分布表明，它们的挖掘本质上是一个三维过程，仅局部发生在沿山带的特定位置。另一方面，导致整个UHP / LT岩石形成的大陆俯冲发生在整个带上。作者先前进行的大陆俯冲的二维热机械实验模型表明，只有当有效板间压力p（n）低于岩石静压时（低压缩俯冲方式），才可能挖掘深俯冲的大陆壳。 。同时，该模型表明，要在低温下大深度保存深俯冲的大陆壳，大陆俯冲应伴随前弧块或弧形板的俯冲。仅当p（n）高（高压缩状态）时，才会发生后一个过程。为了调和这两个过程，我们建议在一般高压缩状态的背景下，板间压力可以在某些特定情况下局部降低，从而允许局部挖掘UHP / LT材料。使用物理建模技术，我们研究了以下一种情况，当上覆板块的前部平行于板块边界经历（俯冲诱发与否）延伸而激活或形成倾斜于板块边界的走滑转换断层时（到板间区域）。沿着该断层的位移导致断层与板间区域相交处的板间压力局部降低。这种压力的降低使得在浮力作用下，深层俯冲的低密度大陆壳和沉积物在UHP / LT条件下上升。一块厚约10 km的地壳以约150 km的深度分离，并沿板间区向上移动，起始速率约为。 3厘米/年当单位达到地壳深度时，上升速度会降低。初次分离并开始上升时，该单元的变形很小，但在到达上覆板的底部时，变形增加。挖掘材料在狭窄的通道中被剪切和拉伸，深度约为70公里。因此，在实际条件下，变形主要是在将设备置于HP条件下而不是UHP条件下记录的。

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