Using Loihi Basaltic Rocks to Understand the Hawaiian Plume

利用 Loihi 玄武岩了解夏威夷羽流

基本信息

批准号：
1737284
负责人：
Michael Garcia
金额：
$ 20.99万
依托单位：
University of Hawaii
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-15 至 2023-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737284&HistoricalAwards=false
关键词：
Using Loihi Basaltic Rocks Understand

项目摘要

Hotspot volcanoes are thought to tap the Earth's deep mantle, and to provide fundamental insights into understanding its composition and processes. Hawaii is an excellent venue for studying hotspot lavas because of its distant location from any continent or tectonic plate boundary (2500 km), and the high temperature (1500 degrees C) and volume output (100,000 cubic meters/year) of its hotspot. This proposal focuses on Loihi, the youngest and still underwater Hawaiian volcano. Loihi lavas have the potential to provide important constraints on the mantle plume beneath the islands because: 1) The volcano's youth (preshield stage) allows for the characterization of its mantle source before it has been extensively melted. 2) Loihi basalts are one of the key geochemical end members for Hawaiian basalts. Thus, analyses of its lavas (especially from previously unsampled areas) will provide a unique perspective into melting processes and source heterogeneity within the Hawaiian hotspot, the Earth's hottest mantle plume. Loihi lavas are especially noteworthy for their primordial noble gas signatures. 3) Loihi's interior and early history are exposed by major landslides on its eastern flank (1 km thick stratigraphic section) and in ~300 m deep craters at its summit. 4) An extensive suite (196 samples) of Loihi basalts collected by submersible are available from its summit pit craters, its dissected east flank and the full extent of its two rift zones. Most of these samples have received limited geochemical characterization. These samples will be made available to the Earth science community for other geochemical studies. This project supports the training of a graduate student at the University of Hawaii.The goals of this project are: 1) Determine the lifespan of Hawaiian shield volcanoes using Loihi lavas to document the duration of the early stage, which is the major missing puzzle piece for resolving this issue. Current estimates range widely. 2) Better understand the structure of the Hawaiian plume (e.g., whether it is bilaterally asymmetrical as currently thought). Loihi is at the young end of the LOA trend but paradoxically, it shares geochemical features with KEA trend lavas. 3) Evaluate whether the Hawaiian mantle plume source varies in time and space. Lavas from Loihi deep interior and submarine flanks will provide a new perspective on the Loihi compositional end member of the Hawaiian plume. 4) Determine how crustal contamination works at a submarine Hawaiian volcano. Do rift zone magmas bypass the summit magma reservoir and more faithfully preserve mantle source signatures? Previous studies of Loihi summit lavas showed they were extensively modified by crustal contamination, whereas rare gas compositions of deep south rift lavas suggest they were uncontaminated. Loihi basalts are ripe for geochemical characterization using a new generation of geochemical instruments for determining ages, crustal and mantle processes, and source variations. These analyses will provide fundamental insights into the workings of the Hawaiian hotspot. The newly geochemically characterized Loihi samples, all precisely located and collected by submersible, will be made available to the Earth science community for other complementary future geochemical studies (e.g., Os isotopes, platinum group elements, rare gases).

人们认为热点火山挖掘了地球的深层地幔，并为理解其组成和过程提供了基本的见解。夏威夷是研究热点熔岩的绝佳场所，因为它距离任何大陆或板块边界都很远（2500公里），而且其热点的高温（1500摄氏度）和产量（10万立方米/年）。该提案的重点是洛伊希火山，这是夏威夷最年轻且仍在水下的火山。洛伊希熔岩有可能对岛屿下方的地幔柱提供重要的限制，因为：1）火山的年轻期（盾构前阶段）允许在其广泛融化之前对其地幔源进行表征。 2) Loihi玄武岩是夏威夷玄武岩的关键地球化学端元之一。因此，对其熔岩（特别是来自以前未采样的地区）的分析将为了解夏威夷热点（地球上最热的地幔柱）的熔化过程和来源异质性提供独特的视角。洛伊希熔岩因其原始惰性气体特征而特别值得注意。 3) 洛伊希的内部和早期历史因其东侧（1 公里厚的地层部分）和顶部约 300 米深的火山口的重大山体滑坡而暴露出来。 4) 通过潜水器采集的 Loihi 玄武岩的大量样本（196 个样本）可从其山顶坑坑、解剖的东侧以及两个裂谷带的全部范围中获得。这些样本中的大多数都获得了有限的地球化学特征。这些样本将提供给地球科学界用于其他地球化学研究。该项目支持夏威夷大学研究生的培训。该项目的目标是： 1) 使用 Loihi 熔岩记录早期阶段的持续时间，确定夏威夷盾状火山的寿命，这是主要缺失的拼图为了解决这个问题。目前的估计范围很大。 2）更好地了解夏威夷羽流的结构（例如，它是否像目前认为的那样是双边不对称的）。 Loihi 处于 LOA 趋势的年轻端，但矛盾的是，它与 KEA 趋势熔岩具有相同的地球化学特征。 3）评估夏威夷地幔柱来源是否随时间和空间变化。来自洛伊希内部深处和海底侧翼的熔岩将为了解夏威夷羽流的洛伊希成分端部成员提供新的视角。 4) 确定夏威夷海底火山的地壳污染是如何发生的。裂谷带岩浆是否绕过顶峰岩浆库并更忠实地保存了地幔源特征？先前对洛伊希山顶熔岩的研究表明，它们受到地壳污染的广泛影响，而南部裂谷熔岩的稀有气体成分表明它们没有受到污染。 Loihi 玄武岩的地球化学表征已经成熟，可以使用新一代地球化学仪器来确定年龄、地壳和地幔过程以及来源变化。这些分析将为夏威夷热点的运作提供基本见解。新的地球化学特征的 Loihi 样品全部由潜水器精确定位和收集，将提供给地球科学界用于其他补充的未来地球化学研究（例如 Os 同位素、铂族元素、稀有气体）。