The role of hot crust in mountain building: Testing the alpha-beta quartz transition as a crustal geothermometer

在所有控制地壳行为的物理参数中，温度可以说是最难准确确定的。与此同时，温度控制着重要的过程，如熔化（岩浆的产生），变形过程从脆性（通常伴随着地震）转变为韧性（没有地震）的深度，以及改变地壳密度的矿物之间的相变，使其更有可能提升高地（密度较低）或沉入地幔（密度较高）。因此，确定地壳温度的能力对于预测广泛的地壳行为非常重要。石英构成了地壳的很大一部分，并在已知的温度下经历矿物结构的变化。这种变化，以及由此产生的温度，可以通过检测穿过材料的地震波速度的特征模式来测量。我们使用地震技术的系统组合来精确定位石英的转变和确定地壳温度。石英的#945;-到#946;-相变发生在一个狭窄的温度范围内，从地球上看到的压力在580到800°C之间。s表面~40 km深度。相变产生了一个急剧的压缩地震速度（Vp）增加，没有伴随的剪切速度（Vs）的对比，不像其他机制，如熔化和成分边界，这创造了Vp和Vs的对比。在这项研究中测试的假设是：在具有热长英质中地壳的造山带中，可以检测到产生P反射但没有P到S转换的界面，并且推断的温度和压力与石英转变的存在&&和熔化的不存在相一致。本研究使用一套系统的地壳温度观测技术（测试P-S转换和来自同一不连续面的P-P反射/转换的发生）结合岩石物理模拟来研究喜马拉雅-西藏和台湾造山带的地壳温度及其地球动力学后果;如果成功的话，该方法可以广泛应用于全球造山带的温度约束。

Of all physical parameters that control the behavior of the Earth's crust, temperature is arguably the most difficult to determine accurately. At the same time, temperature controls important processes such as melting (generation of magma), the depth at which deformation processes change from brittle (usually accompanied by earthquakes) to ductile (without earthquakes), and phase transitions between minerals that change the density of the crust, making it more likely to lift high terrain (less dense) or sink into the mantle (denser). The ability to determine crustal temperature is therefore important for the prediction of a wide range of crustal behaviors. Quartz makes up a large portion of the Earth's crust and undergoes a change in mineral structure at a known temperature. This change, and therefore the temperature, can be measured by detecting a characteristic pattern in the velocity of seismic waves traversing the material. We use a systematic combination of seismic techniques to pinpoint the quartz transition and determine crustal temperature.The α- to β-phase transition of quartz occurs in a narrow temperature range that lies between 580 to 800°C for pressures seen from the Earth?s surface to ~40 km depth. The phase transition generates a sharp compressional seismic velocity (Vp) increase with no accompanying shear velocity (Vs) contrast, unlike other mechanisms such as melting and compositional boundaries, which create contrasts in both Vp and Vs. The hypothesis tested in this study is: In orogens with a hot felsic middle crust, an interface can be detected that generates P reflections but no P to S conversions, and the inferred temperature and pressure are consistent with the presence of the α-β quartz transition and the absence of melting. This study uses a systematic set of teleseismic observation techniques (tests for the occurrence of P-S conversions and P-P reflections/conversions from the same discontinuity) in combination with petrophysical modeling to investigate crustal temperature and its geodynamic consequences in the Himalaya-Tibet and Taiwan orogens; if successful, the method can be widely applied to constrain the temperature of orogens worldwide.