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

热地壳在造山中的作用：作为地壳地温计测试 α-β 石英转变

• 批准号: 1344582
• 负责人: Vera Schulte-Pelkum
• 金额: $ 8.44万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1344582&HistoricalAwards=false
• 关键词: role; hot; crust; mountain; building

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.

在控制地壳行为的所有物理参数中，温度可以说是最难准确确定的。同时，温度控制着重要过程，例如融化（岩浆的产生），变形过程从脆性（通常是通过地震完成）变化到延性（没有地震）的深度，以及矿物之间的相位过渡会改变地壳的密度，从而更有可能提高高地形（较小的地形（较小的密度）或升入Matersle（Manter）。因此，确定地壳温度的能力对于预测广泛的地壳行为很重要。石英构成了地壳的很大一部分，并在已知温度下经历了矿物结构的变化。可以通过检测横穿材料的地震波速度中的特征模式来测量这种变化，因此可以测量温度。我们使用地震技术的系统组合来查明石英的过渡并确定地壳温度。-晶状体的相位过渡发生在狭窄的温度范围内，该温度范围在580至800°C之间，对于从地球表面看到的压力到〜40 km深度。与其他机制不同的机制（例如熔化和组成边界）不同，相转换产生急剧的压缩地震速度（VP）增加，而没有参与的剪切速度（VS）对比度，这在VP和VP中都会产生对比度。在这项研究中检验的假设是：在具有热felsic中部地壳的Orogens中，可以检测到一个产生P反射但没有P到S转化的界面，并且推断的温度和压力与＆＃945; - ＆＃946的存在一致。石英过渡和缺乏熔化。这项研究使用了一组系统震荡的观察技术（对同一不连续性的P-S转化和P-P反射/转化的发生测试）与岩石物理建模相结合，以研究地壳温度及其在喜马拉雅 - 蒂伯特和台湾牛奶中的地壳温度及其地形动力学后果；如果成功，该方法可以广泛应用以限制全球牛根蛋白的温度。