How large are tectonic deviations from lithostatic pressure in a continent-derived, lithologically heterogeneous Alpine UHP nappe (Koralpe-Saualpe-Pohorje Complex, Austria and Slovenia)?

在源自大陆、岩性不均质的高山超高压推覆体（奥地利和斯洛文尼亚的 Koralpe-Saualpe-Pohorje 复合体）中，构造与静岩压力的偏差有多大？

• 批准号: 442578564
• 负责人: Professor Dr. Timm John
• 金额: --
• 依托单位: Arbeitsbereich Mineralogie-Petrologie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/442578564?language=en
• 关键词: How; large; tectonic; deviations; lithostatic

The rheological properties control how rocks deform in a non-uniform stress field. Large differences in the strengths of neighbouring rocks inevitably lead to a deviation of the mean normal stress (i.e. the pressure) from lithostatic pressure. Several theoretical studies have shown that such deviations may reach hundreds of MPa in which case they may influence the petrological pressure record. Since pressures recorded by rocks are commonly used for estimating their burial depth according to a lithostatic pressure-to-depth conversion, such estimates may be biased. On the other hand, unambiguous evidence for tectonic deviations from lithostatic pressure is very scarce and their magnitude and scale at which they occur are poorly known. We propose a novel approach of evaluating the magnitudes by systematically comparing peak pressures of different rock types (mostly eclogites and metapelites) along an orogen-perpendicular transect through an Alpine ultrahigh-pressure nappe. For each rock type, we will determine peak pressure profiles as a function of distance along the transect. If these profiles coincide, there will be no evidence for significant tectonic pressures. If they show a systematic shift, this can be interpreted as an effect of the rheological properties of the different lithologies and can easiest be explained by tectonic pressures. Previous literature data suggest that this may indeed be the case in the Austroalpine Koralpe-Saualpe-Pohorje Complex. A second approach is to investigate if there are outcrop-scale structurally controlled tectonic pressure variations in the near field of rigid lenses and layers surrounded by a weaker matrix. We will investigate samples of the Koralpe-Saualpe-Pohorje Complex with a straightforward thermobarometric methodology that relies as little as possible on complex mineral reactions. If the rock record does not provide evidence for tectonic pressures, this would comply with geodynamic models applying lithostatic pressure-to-depths conversion. If they do, the possibility of tectonic deviation from lithostatic pressure should also be considered for other cases of lithologically diverse (ultra)high-pressure units, both in kinematic and geodynamic models. We will account for potential tectonic overpressure when constraining the maximum burial depth of the Koralpe-Saualpe-Pohorje Complex in a kinematic restoration of an orogen-parallel cross section. By this restoration we aim specifically at estimating the rates of motion of the Koralpe-Saualpe-Pohorje Complex in the Cretaceous Alpine subduction zone and the amount of continental crust that may have been subducted without returning to the surface. These estimates for the Eo-Alpine subduction zone may also give us an idea of the proportion of continental crust in slabs that were imaged below the Alps and are to be resolved in greater detail by seismological methods in SPP 2017.

流变特性控制着岩石在非均匀应力场中如何变形。邻近岩石强度的巨大差异不可避免地导致平均正应力（即压力）偏离静岩压力。一些理论研究表明，这种偏差可能达到数百兆帕，在这种情况下，它们可能会影响岩石学压力记录。由于岩石所记录的压力通常是根据静岩压力-深度换算来估计其埋藏深度的，因此这种估计可能有偏差。另一方面，构造偏离静岩压力的明确证据非常少，其发生的幅度和规模也鲜为人知。我们提出了一种评估震级的新方法，通过系统地比较不同岩石类型（主要是榴辉岩和变长岩）沿造山带垂直样带穿过高山超高压推覆体的峰值压力。对于每种岩石类型，我们将确定峰值压力曲线作为沿样带距离的函数。如果这些剖面相吻合，就没有证据表明存在明显的构造压力。如果它们表现出系统的移动，这可以解释为不同岩性的流变特性的影响，并且可以最容易地用构造压力来解释。先前的文献资料表明，这可能确实是澳大利亚高山Koralpe-Saualpe-Pohorje复合体的情况。第二种方法是研究在刚性透镜体和被较弱基质包围的层的近场是否存在露头尺度的构造控制构造压力变化。我们将用一种简单的热气压测量方法来研究Koralpe-Saualpe-Pohorje复合体的样品，这种方法尽可能少地依赖于复杂的矿物反应。如果岩石记录没有提供构造压力的证据，这将符合应用静压-深度转换的地球动力学模型。如果是这样，在运动学和地球动力学模型中，对于其他岩性多样（超）高压单元的情况，也应考虑构造偏离静岩压力的可能性。在对造山带平行剖面进行运动学恢复时，我们将考虑潜在的构造超压，以限制Koralpe-Saualpe-Pohorje杂岩的最大埋藏深度。通过这种恢复，我们的具体目标是估计白垩纪高山俯冲带的Koralpe-Saualpe-Pohorje复合体的运动速率，以及可能已经俯冲而不返回地表的大陆地壳的数量。这些对古阿尔卑斯俯冲带的估计也可以让我们了解大陆地壳在阿尔卑斯山脉以下的板块中所占的比例，这些板块将在SPP 2017中通过地震学方法进行更详细的解析。