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，温度控制着熔化（岩浆的产生）、变形过程从脆性转变的深度等重要过程。 （通常伴随地震）到延性（不发生地震），矿物之间的相变改变了地壳的密度，使其更有可能抬升高地（密度较小）或沉入地幔（密度较大）的能力。决定因此，地壳温度对于预测各种地壳行为非常重要。石英构成了地壳的很大一部分，并在已知温度下经历了矿物结构的变化。这种变化以及温度可以通过以下方式测量。检测穿过材料的地震波速度的特征模式我们使用地震技术的系统组合来查明石英转变并确定地壳温度。“-”到“-”相。石英的相变发生在从地球表面到约 40 公里深度的压力范围内的 580 至 800°C 之间的狭窄温度范围内。相变产生了压缩地震速度 (Vp) 的急剧增加，但没有伴随的剪切速度。 (Vs) 对比，与其他机制（例如熔融和成分边界）不同，它们在 Vp 和 Vs 中产生对比。本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 β- 石英转变的存在和不存在熔化一致。一套系统的远震观测技术（测试相同不连续性的 P-S 转换和 P-P 反射/转换的发生）与岩石物理模型相结合，以研究地壳温度及其地球动力学后果在喜马拉雅-西藏和台湾造山带中；如果成功，该方法可以广泛应用于全球造山带的温度约束。