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

点击翻译按钮获取中文摘要

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.