Evaluating the Complex 40Ar/39Ar Age Progressions Along the Cook-Austral Ocean Islands Representing Archetype Secondary Hotspot Volcanism

评估代表次生热点火山活动原型的库克-南大洋群岛沿线复杂的 40Ar/39Ar 年龄演化

• 批准号: 1533827
• 负责人: Anthony Koppers
• 金额: $ 19.97万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-12-01 至 2021-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1533827&HistoricalAwards=false
• 关键词: Evaluating; Complex; 40Ar; 39Ar; Age

Seamounts are among the most abundant volcanic features on Earth. There are more than 20,000 seamounts on the seafloor that are taller than 1 kilometer, and there are hundreds of thousands of smaller seamounts. On the other end of the size spectrum, ocean islands represent a limited number of extremely large seamounts that have emerged above the sea surface. Linear arrangements of seamounts and ocean islands in the Pacific are common and these are prominently represented by the Hawaiian-Emperor and Louisville hotspot trails, both of which are called primary hotspot trails, each of which is believed to have formed above its own long-lived mantle plume that is sourced deep in the mantle. However, more than 80% of the known seamount trails in the Pacific are of quite a different nature and can be classified as secondary and tertiary hotspots. We know surprisingly little about these and other similar linear volcanic trails, although they are more common than primary trails. This research improves our understanding of secondary and tertiary hotspots in order to obtain fundamental knowledge of ocean basin volcanism. The work targets volcanic rocks in the Cook-Austral region. This region is home to one of the most enigmatic hotspot systems, harboring up to four hotspot trails that are younger than 30 million years and that, together, exhibit a complex age and geographic pattern. Research involves 40Ar/39Ar age dating of new samples from eight Cook-Austral oceanic islands and reanalysis of other samples from Cook-Austral seamounts and ocean islands whose ages were determined by a less precise dating method (K/Ar). The new dates will allow us to determine the validity of the current volcanic age patterns in the western Pacific Ocean and improve our knowledge of the mantle plume geometry in the Cook-Austral region. Broader impacts of the work include student training and engagement of groups under-represented in science and engineering in the research program.Relatively large amounts of geochronological data are available for the youngest volcanic islands and seamounts in Pacific hotspot trails, but most are inaccurate K/Ar ages. This impedes our ability to answer the major outstanding question as to why young 0-30 million year old secondary hotspot trails exhibit such a large variability in their age progressions. As a result, the Cook-Austral hotspots are often ignored in plate motion modeling, yet the nature of these secondary hotspots lies at the heart of the mantle plume debate. This research uses modern 40Ar/39Ar age dating and sample processing and leaching methods that will allow: (1) more accurate determinations of the current age progressions for the Rurutu and Macdonald Cook-Austral hotspot trails, (2) determination of the causes of the present bi-modal age distributions on certain volcanoes, and (3) what are the implications are for Pacific tectonic plate motions. All samples will be analyzed by employing the latest 40Ar/39Ar incremental heating methods using ARGUS-VI multi-collector mass spectrometers in the Oregon State University Argon Geochronology Lab.

海山是地球上最丰富的火山特征之一。海底有2万多座高度超过1公里的海山，还有数十万座较小的海山。在尺寸谱的另一端，海洋岛屿代表了出现在海面上的数量有限的超大型海山。太平洋中海底山和海洋岛屿的线性排列是常见的，夏威夷皇帝和路易斯维尔热点路径是突出的代表，它们都被称为主要热点路径，每个热点路径都被认为是在其自身长期存在的地幔柱之上形成的，地幔柱来源于地幔深处。然而，在太平洋已知的海山小径中，超过80%的性质完全不同，可以被归类为第二和第三热点。令人惊讶的是，我们对这些和其他类似的线性火山轨迹知之甚少，尽管它们比原始轨迹更常见。该研究提高了我们对二、第三系热点的认识，从而获得了海洋盆地火山作用的基础知识。这项工作的目标是库克-南方地区的火山岩。这个地区是最神秘的热点系统之一的所在地，拥有多达四个热点路径，这些热点路径的年龄小于3000万年，它们共同展示了一个复杂的年龄和地理模式。研究包括对来自8个库克-南大洋岛屿的新样品进行40Ar/39Ar年龄测定，并对来自库克-南大洋海底山和海洋岛屿的其他样品进行重新分析，这些样品的年龄由一种不太精确的测年方法（K/Ar）确定。新的日期将使我们能够确定西太平洋当前火山年龄模式的有效性，并提高我们对库克-南太平洋地区地幔柱几何形状的认识。这项工作的更广泛影响包括学生培训和参与研究项目中科学和工程领域代表性不足的群体。对于太平洋热点路径上最年轻的火山岛和海底山，有相对大量的地质年代学数据，但大多数是不准确的K/Ar年龄。这阻碍了我们回答一个主要悬而未决的问题的能力，即为什么年轻的0- 3000万年前的次要热点轨迹在它们的年龄进展中表现出如此大的变化。因此，库克-南方热点在板块运动建模中经常被忽略，然而这些次级热点的性质是地幔柱争论的核心。本研究采用现代40Ar/39Ar年龄测年和样品处理和浸出方法，将允许：(1)更准确地确定Rurutu和Macdonald Cook-Austral热点路径的当前年龄进展，(2)确定某些火山当前双模态年龄分布的原因，以及(3)对太平洋构造板块运动的影响。所有样品将采用最新的40Ar/39Ar增量加热方法，使用俄勒冈州立大学氩地球年代学实验室的ARGUS-VI多收集器质谱仪进行分析。