MARGINS: Controls on Magma Generation at Incipient Spreading Centers

智力上的优点。这项研究旨在确定加利福尼亚州海湾陆上延伸范围内两个年轻的裂谷盆地(Salton Sea和Cerro Prieto)的岩浆多样性控制参数。尽管两个地区的盆地结构和构造环境相似，但岩浆活动却截然不同。索尔顿海表层和地下岩浆岩是双峰型的，而Cerro Prieto的岩浆岩以中间成分为主。由于这两个岩浆系统都与经济上重要的地热资源有关，因此通过地热井穿透实现了密集的三维采样。地热井的钻屑总是受到污染，岩石在高温下暴露在强烈的蚀变中。因此，高空间分辨率的铀系年代学与二次离子质谱仪(SIMS)的锆石氧同位素分析相结合，在提取有关岩浆变化的时空模式方面具有最强的前景。Cerro Prieto的结果将补充索尔顿海的现有数据，这些数据表明，自至少400ka以来，通过热液蚀变玄武岩地壳的重熔而产生了幕式流纹岩。这些结果的综合将有助于深入了解大陆断裂过程中岩石圈结构的变化，裂谷盆地下地壳的成分和热状态，以及新增生地壳在早期海洋扩张过程中的成熟度。这项研究对可再生能源勘探战略产生了影响，并促进了学者和地热行业之间的联系。加州大学洛杉矶分校国家离子探针设施的用户将受益于为低产率样品和现场分析量身定做的SIMS方法开发。该项目为本科生提供了研究经验的机会。

Intellectual merit. This study aims to identify the controlling parameters for magmatic diversity in two young rift basins (Salton Sea and Cerro Prieto) within the on-land extension of the Gulf of California. Despite similarities in basin structure and tectonic setting, magmatism in both locations differs strongly. Salton Sea surface and subsurface magmatic rocks are bimodal, whereas intermediate compositions predominate at Cerro Prieto. Because both magmatic systems are associated with economically important geothermal resources, dense three-dimensional sampling exists through geothermal well penetration. Drill cuttings from geothermal wells are invariably contaminated and rocks were exposed to intense alteration at high ambient temperatures. Thus, high spatial resolution uranium series geochronology coupled with oxygen isotopic analysis of zircon by secondary ion mass spectrometry (SIMS) has the strongest prospects for extracting reliable information on the temporal and spatial patterns of magmatic variability. Results from Cerro Prieto will complement existing data for the Salton Sea that indicate episodic rhyolite generation through remelting of hydrothermally altered basaltic crust since at least 400 ka. The integration of these results will provide insights into the changes in lithospheric structure during continental rupture, the composition and thermal state of the lower crust in rift basins, and the maturation of newly accreted crust during incipient ocean spreading.Broader impacts. This research impacts on strategies for renewable energy exploration, and fosters ties between academics and the geothermal industry. Users of the UCLA National Ion Microprobe facility will benefit from SIMS method development tailored to low-yield samples and in-situ analysis. This project provides opportunities for undergraduate research experience.