RUI: Inflation Cycles of the Resurgent Dome, Long Valley Caldera, California

RUI：复苏圆顶的通货膨胀周期，长谷火山口，加利福尼亚州

• 批准号: 9628115
• 负责人: John Reid
• 金额: $ 6.82万
• 依托单位: Hampshire College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-08-01 至 1998-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9628115&HistoricalAwards=false
• 关键词: RUI; Inflation; Cycles; Resurgent; Dome

Reid 9628155 Since 1979, the resurgent dome of Long Valley caldera, California has risen more than 50 cm apparently due to the injection of 0.2 km3 of magma at depth. Floodplain geomorphology suggests that the Owens River, that circumvents the dome, oscillates between two parallel meander belts depending on whether the dome is inflated or deflated, and that the current uplift is part of a long term inflation that may total 15-35 meters. The central goal of the renewal proposal is to understand the inflation history of Long Valley and the nearby Inyo Crater eruptions over the past several millenia. The hope is that patterns between eruptions and Owens River avulsions in the past will clarify the potential for future eruptive activity. Efforts with NSF-RUI 91-17474 funding to determine a chronology for these oscillations have revealed three major findings: (1) In dating plant remains in abandoned channel system, with live aquatic plant "ages" as high as 13.3 kyr. Cation geochemistry and 13C in plants and waters suggest predominantly magmatic sources for the "dead" CO2 feeding these plants. Tree kills at Mammoth Mountain also manifest this CO2 release (Farrar et al, 1995) (2) Inyo Crater pumice fills an abandoned channel of the Owens River and contains charcoal apparently derived from trees charred during the pumice eruptions. This suggests a connection between Owens River avulsions and eruptions in the Inyo Craters. The chemical and petrographic stratigraphy of these pumices and the proposed AMS dates on their charcoals will allow the timing of past eruptions and avulsions to be determined, and estimates to be made of where the caldera stands today in terms of potential for similar activity in the future. (3) The topography of deformed shorelines of Pleistocene Long Valley Lake has been measured. The shorelines have recorded caldera floor deformation over longer time periods than the river channels; the data suggest that relatively little net uplift of the dome has occurred over the life of the lake. The proposed research seeks to complete the work that has been begun and includes: (1) synoptic14C, pH, alkalinity, dissolved ion determinations and discharge measurements with finer resolution at sites of major springs to quantify the "dead" CO2 emanations entering the streams, (2a) AMS 14C age determinations on charcoal in the pumice to time earlier river avulsions and associated pumice eruptions, (2b) XRF analyses of a large suite of pumicies to fingerprint them as to their site of origin, and (3) completion of the topographic surveying of the lake shores and dating of tufa cements in them by U-series dating to better understand the longer history of the dome. The results of this study offer valuable information about the recent tectonic history of Long Valley caldera, and perhaps give an indication of the caldera's potential behavior in the near future. They are thus of central concern to residents of Mammoth Lakes, CA. The study offers undergraduate students an excellent opportunity to investigate in the field and in the laboratory an important example of silicic volcanism.

里德9628155自1979年以来，加利福尼亚州长谷火山口复活的穹顶由于在深处注入了0.2km3的岩浆，显然已经上升了50厘米以上。泛滥平原地貌表明，绕过穹顶的欧文斯河在两个平行的曲流带之间摆动，这取决于穹顶是膨胀的还是泄气的，目前的抬升是长期通货膨胀的一部分，总长度可能为15-35米。更新建议的中心目标是了解过去几千年来朗谷和附近的因约陨石坑喷发的通胀历史。人们希望，过去火山喷发和欧文斯河撕裂之间的模式将澄清未来喷发活动的可能性。利用美国国家科学基金会-瑞瑞91-17474基金确定了这些振荡的年表，发现了三个主要发现：(1)在测年中，植物遗骸在废弃的航道系统中，活的水生植物的年龄高达13.3KYR。植物和水中的阳离子地球化学和~(13)C表明，供应这些植物的“死”二氧化碳主要来自岩浆。猛犸山的树木死亡也体现了这种二氧化碳释放(Farrar等人，1995)(2)Inyo陨石坑浮石填充了欧文斯河的一条废弃河道，其中含有显然来自浮石喷发期间烧焦的树木的木炭。这表明欧文斯河的撕裂和因约陨石坑的喷发之间存在联系。这些浮岩的化学和岩石学地层学及其木炭上拟议的AMS日期将有助于确定过去喷发和撕裂的时间，并就未来类似活动的可能性对火山口今天所处的位置进行估计。(3)对更新世长谷湖的变形岸线进行了地形测量。海岸线记录的火山口底部变形时间比河道长；数据表明，在湖的整个生命周期中，穹顶的净隆起相对较少。拟议的研究旨在完成已开始的工作，其中包括：(1)对主要泉水地点的14C、pH、碱度、溶解离子的测定和以更高分辨率进行的流量测量，以量化进入溪流的“死亡”二氧化碳排放；(2a)对浮石中的木炭进行14C年龄测定，以确定早期河流撕裂和相关的浮石喷发的时间；(2b)对一大批浮石进行XRF分析，以确定它们的起源位置；(3)完成对湖岸的地形测量，并通过U系列测年对其中的凝灰岩进行测年，以更好地了解穹顶的更长历史。这一研究结果为了解长谷火山口的现代构造历史提供了有价值的信息，并可能为该火山口在不久的将来的潜在行为提供指示。因此，它们是加利福尼亚州猛犸湖居民最关心的问题。这项研究为本科生提供了一个在野外和实验室进行调查的绝佳机会，这是硅质火山作用的一个重要例子。