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Evidence for non-lithostatic pressure in subducted continental crust

机译：底层大陆地壳非岩性压力的证据

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Continental crust buried during collisional orogeny typically records pressures of 3 GPa or lower; however, pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-lithostatic pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme pressures recorded in buried continental crust; however, its occurrence and significance in natural systems is debated. Mechanical pressure heterogeneities were proposed specifically to explain extreme pressures of c. 5.5 GPa obtained in enstatite eclogite veins in the archetypal subducted continental terrane, the Western Gneiss Complex (WGC) in Norway. In this study, we use Lu-Hf garnet geochronology to test when, and thus, in what part of the burial cycle of the WGC the enstatite eclogite assemblages actually equilibrated. The results show that equilibration occurred at c. 393 Ma, which is much later than the typical ages obtained from 'normal' eclogites in the WGC and represents a time when the terrane was already at crustal depths (<2.5 GPa). Finite element modeling of mechanical pressure distribution demonstrates that late extreme pressure excursions are feasible for the given rock system and could explain the seemingly spurious conditions recorded in these unusual rocks. The recognition of non-lithostatic ultrahigh-pressure in deeply buried continental crust allows crucial simplification of models for continental subduction and validates the importance of rock thermo-mechanics in interpreting observations from collision zones.
机译：在碰撞洋葱期间埋没的欧式地壳通常记录3 GPA或更低的压力;然而，远高于这的压力在本地记录，这将建议埋葬地幔深度。在活性Origens中未观察到深度大陆俯冲，并且应该受到唾液外壳相对于地幔的正浮力的阻碍。岩石类型之间的机械对比引起的非岩性压力提供了埋在埋地地壳中的极端压力的替代解释;然而，其在自然系统中的发生和意义是讨论的。提出了机械压力异质性，特别是解释C的极端压力。 5.5 GPA在挪威西部Gneiss Continental Terrane中的山尔特泰特eClogite静脉中获得，挪威西方球茎（WGC）。在这项研究中，我们使用Lu-HF Garnet地理学来测试何时，因此，在WGC的埋葬循环的哪个部分实际平衡。结果表明，平衡发生在C. 393 mA，比WGC中的“正常”eClogites获得的典型年龄在一起，并且代表了地区已经在地壳深度（<2.5GPa）的时间。机械压力分布的有限元建模表明，给定的岩石系统可行的极端压力偏移是可行的，可以解释这些不寻常的岩石中记录的看似虚假的条件。对深埋大陆地壳的非锂电超高压识别允许大陆俯冲模型的重要简化，并验证岩石热门机械在解释碰撞区的观察中的重要性。

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