Tectonic Overpressures in High-Strain Zones: A Quantitative Investigation

江西构造超压是地质学中一个古老、根本性但仍有争议的问题。最近的工作清楚地表明，在非安德森应力状态下，构造超压的大小不受岩石强度的限制。韧性高应变区是非安德森应力区。人们对如此重要的构造环境中的超压知之甚少。这项研究使用数值和分析建模技术来解决两个问题：(1)在现实的流变学和自然变形条件下，高应变区能否产生高超压？(2)如果产生高超压，能否在重要的地质时期动态保持，以影响变质反应？无论答案是肯定的还是否定的，研究结果都将具有重大的科学价值。对任何一个问题的否定回答都将使目前广泛使用的压力-深度转换建立在严格的基础上。对这两个问题的肯定回答意味着，来自高应变带岩石的压力数据不能在没有资格的情况下转换到深度。目前对地温气压数据的构造解释需要重新考虑。由于许多高压和超高压岩石显示出高应变带起源的证据，显著的超压将意味着这些岩石可能形成于比目前认为的要浅得多的深度。由于超压堆积而导致的高于岩石静压力梯度的压力梯度可能是流体流动、熔体提取和迁移以及岩体侵位的驱动力。

0003315JiangTectonic overpressure is an old, fundamental but still controversial problem in geology. Recent work clearly demonstrates that, in non-Andersonian stress regimes, the magnitude of tectonic overpressures is not limited by the rock strength. Ductile high-strain zones are non-Andersonian stress domains. Little is known of overpressures in such important tectonic environments. This investigation uses numerical and analytical modeling techniques to address two questions: (1) Can high overpressures be generated in high-strain zones, given realistic rheology and natural deformation conditions? (2) Can high overpressures,if generated, be dynamically maintained for significant geological times to affect metamorphic reactions? Regardless of whether the answers are positive or negative, the research results will have significant scientific merit. A negative answer to either question would place the now widely-practiced pressure-depth conversion on a rigorous basis. A positive answer to both questions implies that the pressure data from high-strain zone rocks cannot be converted to depths without qualification. Current tectonic interpretation of geothermobarometric data needs to be reconsidered. Since many high-pressure and ultrahigh-pressure rocks show evidence of a high-strain zone origin, a significant overpressure would imply that these rocks may have formed at depths considerably shallower than currently believed. A higher-than-lithostatic pressure gradient as a result of overpressure buildup is a possible driving force to be considered for fluid flow, melt extraction and migration, and pluton emplacement.