How Are Ultrahigh Temperatures Attained in Continental Crust? A Petrochronological Investigation of the Basin and Range Lower Crust

富含硅元素的大陆地壳似乎是地球独有的，对生命至关重要，但促进这种地壳长期稳定的机制尚不清楚。古大陆岩心中温度超过900°C的岩石被保存下来，这意味着超高温变质作用和相关的地壳部分熔融对地壳稳定至关重要。这项研究将解决一个主要问题：大陆地壳内部的极端温度是如何达到的？该项目将重建正在积极经历超高温变质作用的一段大陆下地壳喷发的岩石的压力-温度-时间历史：美国和墨西哥的盆地和山脉省。分析技术的结合将区分潜在的热源。这项研究将支持一位早期职业科学家，促进研究生的培养，并使本科生参与学术研究。描述地壳如何达到极端温度，与身体力的发展和分布、地壳的流动和地球的化学分异有关。利用一套互补的技术，该项目将使用捕虏体来测试三种假设（地壳增厚、地幔变薄或岩浆底镀），以在活动伸展带下的大陆下地壳中获得超高温。辅助矿物（锆石、独居石、钛矿和金红石）U-Pb定年和微量元素深度剖面将用于推导盆地和山脉省寿命期间下地壳的压力和温度历史。Lu-Hf石榴石日期将用于限定进变质作用的时间。岩石学约束将来自压力-温度伪剖面、最佳热气压测量和微量元素测温。同时，这些技术将用于测量超高温的时间和持续时间，以及部分压力-温度渐进演变。完整的数据集将允许对这三个假设进行严格的测试。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Continental crust that is rich in the element silicon appears to be unique to planet Earth and is critical for life, but the mechanisms that facilitate the long-term stability of this crust are unclear. Preservation of rocks that have attained temperatures greater than 900°C in the cores of old continents implies that ultrahigh temperature metamorphism and associated partial melting of the crust is critical for crustal stabilization. This research will address the primary question: How are extreme temperatures attained within the continental crust? The project will reconstruct the pressure-temperature-time history of rocks that were erupted from a section of continental lower crust that is actively undergoing ultrahigh-temperature metamorphism: the Basin and Range Province of the United States and Mexico. A combination of analytical techniques will discriminate between potential heat sources. The research will support an early career scientist, foster the training of a graduate student, and engage undergraduates in academic research.Characterizing how the Earth’s crust attains extreme temperatures is relevant to the development and distribution of body forces, flow of crust and chemical differentiation of the Earth. Using a suite of complementary techniques, this project will use xenoliths to test three hypotheses (crustal thickening, mantle thinning, or magmatic underplating) for the attainment of ultrahigh temperatures in continental lower crust beneath a zone of active extension. Accessory-mineral (zircon, monazite, titanite, and rutile) U-Pb dating and trace element depth-profiles will be used to derive the pressure and temperature history of the lower crust over the lifespan of the Basin and Range province. Lu-Hf garnet dates will be used to constrain the timing of prograde metamorphism. Petrologic constraints will be derived from Pressure-Temperature pseudo-sections, optimal thermobarometry, and trace-element thermometry. In conjunction, these techniques will be used to measure the timing and duration of ultrahigh temperatures in addition to portions of the prograde Pressure-Temperature evolution. The complete dataset will allow for rigorous testing of the three hypotheses.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.