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

合作提案：构造控制弧演化和岩石形成，内华达山脉中部祖先喀斯喀特弧，加利福尼亚州

• 批准号: 1917361
• 负责人: Cathy Busby
• 金额: $ 38.85万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1917361&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Tectonic; controls; arc

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.

最近对活火山的研究表明，火山喷发通常是由地震引发的，地震是对板块构造力的响应。但这类火山上的活动断层无法直接检测，因为它们被沉积物和较早喷发的火山物质深深地埋藏着。这项研究的PI在加利福尼亚州东部发现了三个中新世火山中心，位于一个名为沃克巷的地区，该地区通过隆起和侵蚀，暴露了罕见的喀斯喀特火山的根源。他们的工作对科学和社会都有更广泛的影响。首先，由于加利福尼亚州北部的拉森活火山中心也在沃克巷地区，他们提出的工作将直接适用于了解那里和其他活跃级联火山的喷发触发机制。他们最近的工作还发现了已知的现代或古代瀑布中最大的火山喷发速度，他们的新工作将划定允许发生超大规模火山喷发的构造条件。此外，PIS还将培训新一代科学家。弗雷斯诺州立大学的本科生将参与到这项工作的各个方面。他们大多是第一代大学生，往往来自代表不足的群体和低收入家庭。NSF的这种支持对于将研究经验带给一个服务不足的社区至关重要。通过弗雷斯诺州立大学和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现场和实验室助理合作。学生不仅将在研究项目上发挥带头作用，而且将在专业会议上发表演讲，并将成为论文的合著者或主要作者。大多数弗雷斯诺州立大学的学生毕业后还将在加州中央山谷担任地质学家，从事从地震灾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拨款结束后多年后会给中央山谷带来红利。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。PI和他们的学生将研究的加州中部的原始喀斯喀特火山是活火山的古代类似物，例如加州北部的拉森峰和沙斯塔山，或称Mt.华盛顿的圣海伦斯。祖先级联形成于大约1600万至500万年前，并在内华达山脉的东部边缘隆起。抬升和侵蚀暴露了三个火山中心长达5公里的构造起伏。PI将利用这些深度暴露来绘制允许这些祖先级联火山发展的地质断层图。他们早期的工作表明，火山在所谓的伸展盆地中发展；形成这些盆地的断层允许岩浆到达地表。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类型(爆炸性和爆发性)是否与断层活动的规模直接相关。他们的假设之一是，活动的扭张断层活动将允许更深、更热的岩浆喷发。PI将分析熔岩流的成分，并使用热力学模型来确定喷发前岩浆是储存在深层还是浅层水库中。PI还发现了一套熔岩，它们代表了现代或古代瀑布中有史以来最大的单一喷发速度。他们的新数据将确定这种大规模喷发是否利用了异常深或异常热的来源，以及这种喷发是否受到断层活动的控制。有了这些结果，就有可能对现代火山的地震进行研究，以预测喷发量和喷发类型。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。