RUI: Collaborative Proposal: Tectonic controls on arc evolution and petrogenesis, central Sierra Nevada Ancestral Cascades arc, California

最近对活火山的研究表明，火山爆发通常是由地震引发的，地震是对板块构造力的反应。但是这些火山上的活动断层无法直接检测，因为它们被沉积物和早期喷发的火山物质深埋。这项研究的PIs在加利福尼亚东部一个叫做沃克巷的地区发现了三个中新世的火山中心，通过隆起和侵蚀，暴露出了罕见的喀斯喀特火山的根部。他们的工作具有更广泛的科学和社会影响。首先，由于加州北部活跃的拉森火山中心也在沃克莱恩地区，他们提出的工作将直接适用于了解那里的喷发触发机制，以及其他活跃的喀斯喀特火山。他们最近的工作还揭示了在现代或古代喀斯喀特山脉中已知的最大火山爆发率，他们的新工作将划定允许大规模火山爆发发生的构造条件。此外，pi还将培养新一代科学家。弗雷斯诺州立大学的本科生将参与这项工作的各个方面。他们大多是第一代大学生，通常来自代表性不足的群体和低收入家庭。NSF的支持对于将研究经验带给服务不足的社区至关重要。通过弗雷斯诺州立大学与加州大学戴维斯分校的合作，弗雷斯诺州立大学的学生将有机会与加州大学戴维斯分校的博士生以及本科生和实验室助理合作。学生不仅将在研究项目中发挥领导作用，还将在专业会议上发表演讲，并将成为论文的共同作者或主要作者。大多数弗雷斯诺州立大学的学生毕业后也将作为地质学家在加州中央山谷工作，从事从地震危害到地下水质量的各种项目。因此，这种对他们研究经验的早期支持在资助结束多年后为中央谷带来了红利。该项目得到了岩石学与地球化学和构造学两个项目的支持。加州中部的喀斯喀特火山的祖先，pi和他们的学生将研究的是活火山的古代类似物，如加州北部的拉森峰和沙斯塔山，或华盛顿的圣海伦斯山。喀斯喀特山脉的祖先形成于大约1600万到500万年前，在内华达山脉的东部边缘隆起。隆起和侵蚀使三个火山中心的5公里的构造地形暴露出来。pi将利用这些深度暴露来绘制地质断层图，这些地质断层使这些古老的喀斯喀特火山得以发展。他们早期的研究表明，火山是在所谓的张拉盆地中发育的；形成这些盆地的断层为岩浆到达地表提供了通道。他们的新地质图和年龄日期将限制断层活动和火山喷发的时间，并将允许测试火山喷发的数量和风格（爆炸性与喷涌性）是否与断层活动的大小直接相关。他们的一个假设是，活跃的张拉断层会使更深、更热的岩浆喷发出来。pi将分析熔岩流的成分，并使用热力学模型来确定岩浆在喷发前是储存在深部还是浅层。pi还发现了一套熔岩，这些熔岩代表了现代或古代喀斯喀特山脉有记录以来最大的一次喷发速率。他们的新数据将确定如此大规模的喷发是否来自异常深或异常热的源头，以及此类事件是否受到断层活动的控制。有了这些结果，就有可能检查现代火山的地震，以预测喷发的数量和方式。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。

Recent studies of active volcanoes show that volcanic eruptions are often triggered by earthquakes, which occur in response to plate tectonic forces. But the active faults on such volcanoes cannot be directly examined as they are deeply buried by sediments and earlier erupted volcanic materials. The PIs of this study have discovered three Miocene-age volcanic centers in eastern California, in a region called the Walker Lane that, through uplift and erosion, have exposed the rarely-seen roots of Cascade volcanoes. Their work has both scientific and societal broader impacts. First, because the active Lassen Volcanic Center in northern California is also in the Walker Lane region, their proposed work will be directly applicable to understanding eruption triggering mechanisms there, and at other active Cascade volcanoes. Their recent work has also uncovered the largest volcanic eruption rates known in either the modern or ancient Cascades, and their new work will delimit the tectonic conditions that allow for very large volcanic eruptions to occur. In addition, the PIs will be training a new generation of scientists. Fresno State undergraduate students will be involved in all aspects of the work. They are mostly first generation college students, and are often from under-represented groups and low income families. This NSF support is crucial to bringing research experiences to an underserved community. Through the Fresno State-University of California Davis collaboration, Fresno State students will have the opportunity to collaborate with a PhD student as well as undergraduate field and lab assistants at UC Davis. Students will take the lead not only on research projects, but on presentations at professional meetings, and will be co-authors or lead authors on papers. Most Fresno State students will also serve California's Central Valley as Geologists after graduation, working on projects that range from earthquake hazards to groundwater quality. This early support for their research experiences thus pays dividends to the Central Valley many years after the grant is over. The project is supported by both the Petrology & Geochemsitry and Tectonics programs.The ancestral Cascade volcanoes of central California that the PIs and their students will study are the ancient analogs of active volcanoes, such as Lassen Peak and Mt Shasta in northern California, or Mt. St. Helens in Washington. The ancestral Cascades formed from about 16 to 5 million years ago and have been uplifted at the eastern edge of the Sierra Nevada Mountain range. Uplift and erosion have exposed 5 km of structural relief on three volcanic centers. The PIs will take advantage of these deep exposures to map the geologic faults that allowed these ancestral Cascade volcanoes to develop. Their earlier work showed that volcanoes develop in what are called transtensional basins; the faults that form these basins allow pathways for magmas to reach the surface. Their new geologic maps and age dates will constrain the timing of both fault activity and volcanic eruptions, and will allow a test whether the volume and style (explosive vs. effusive) of volcanic eruptions is directly related to the magnitude of fault activity. One of their hypotheses is that episodes of active transtensional faulting will allow deeper, hotter magmas to be erupted. The PIs will analyze the compositions of the lava flows, and use thermodynamic models, to determine whether the magmas were stored in deep or shallow reservoirs prior to eruption. The PIs have also discovered a suite of lavas that represent the single largest eruption rates ever recorded in either the modern or ancient Cascades. Their new data will determine whether such large eruptions tapped sources that are unusually deep or hot, and whether such episodes are controlled by fault activity. With these results, it may be possible to examine earthquakes at modern volcanoes to predict eruption volume and style.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.