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。海底高度超过1公里的海山有2万多座，较小的海山还有数十万座。在大小范围的另一端，海洋岛屿代表了数量有限的出现在海面之上的巨大海山。太平洋中海山和海洋岛屿的线性排列很常见，其中突出的代表是夏威夷-皇帝和路易斯维尔热点路径，这两者都被称为主要热点路径，每条路径都被认为是在其自身的长期存在之上形成的地幔柱，起源于地幔深处。然而，超过 80% 的太平洋已知海山踪迹性质截然不同，可分为二级和三级热点。令人惊讶的是，我们对这些和其他类似的线性火山路径知之甚少，尽管它们比主要路径更常见。这项研究提高了我们对次生和第三次热点的认识，以获得洋盆火山作用的基础知识。这项工作的目标是库克-澳大利亚地区的火山岩。该地区是最神秘的热点系统之一，拥有多达 4 条热点轨迹，这些轨迹的历史均小于 3000 万年，并且共同展现出复杂的年龄和地理格局。 研究涉及对来自八个库克南方大洋岛屿的新样本进行 40Ar/39Ar 年龄测定，并对来自库克南方海山和海洋岛屿的其他样本进行重新分析，这些样本的年龄是通过不太精确的测年方法 (K/Ar) 确定的。 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-南方地区地幔柱几何形状的了解。 这项工作的更广泛影响包括学生培训以及科学和工程领域代表性不足的群体参与研究计划。对于太平洋热点路径中最年轻的火山岛和海山，有相对大量的地质年代学数据，但大多数都是不准确的 K/年龄。这阻碍了我们回答主要悬而未决的问题的能力，即为什么年轻的 0-3000 万岁的次要热点路径在其年龄进程中表现出如此大的变异性。因此，库克-南方热点在板块运动模型中经常被忽略，但这些次要热点的性质却是地幔柱争论的核心。这项研究使用现代 40Ar/39Ar 年龄测定和样品处理和浸出方法，这将允许：（1）更准确地确定鲁鲁图和麦克唐纳库克-澳大利亚热点路线当前的年龄进展，（2）确定某些火山呈现双峰年龄分布，以及（3）这对太平洋构造板块运动有何影响。 所有样品都将通过俄勒冈州立大学氩地质年代学实验室的 ARGUS-VI 多接收器质谱仪采用最新的 40Ar/39Ar 增量加热方法进行分析。