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

海山是地球上最丰富的火山地貌之一。海底有2万多座高于1公里的海山，还有数十万座较小的海山。在大小范围的另一端，海洋岛屿是出现在海面上的数量有限的特大海山。太平洋海山和海洋岛屿的线性排列很常见，夏威夷-皇帝和路易斯维尔热点痕迹是其中的突出代表，这两个热点痕迹都被称为原始热点痕迹，据信每个热点痕迹都是在其长期存在的地幔柱上方形成的，地幔柱来源于地幔深处。然而，太平洋80%以上的已知海山步道的性质截然不同，可归类为二级和三级热点。令人惊讶的是，我们对这些和其他类似的线性火山痕迹知之甚少，尽管它们比原始痕迹更常见。这项研究提高了我们对第二和第三纪热点的理解，以获得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。该地区是最神秘的热点系统之一，拥有多达四个热点轨迹，年龄小于3000万年，共同表现出复杂的年龄和地理模式。 研究包括对来自八个库克-奥斯特拉尔海洋岛屿的新样品进行40 Ar/39 Ar年龄测定，并对来自库克-奥斯特拉尔海山和海洋岛屿的其他样品进行重新分析，这些样品的年龄是通过不太精确的定年方法（K/Ar）确定的。 新的日期将使我们能够确定西太平洋目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认识。 这项工作的更广泛的影响包括学生培训和参与研究计划中科学和工程领域代表性不足的群体。相对大量的地质年代学数据可用于太平洋热点小径中最年轻的火山岛和海山，但大多数都是不准确的K/Ar年龄。这妨碍了我们回答一个主要的悬而未决的问题的能力，即为什么年轻的0- 3000万年的次级热点轨迹在它们的年龄进程中表现出如此大的变化。因此，库克-南方热点往往被忽略在板块运动模型，但这些次级热点的性质是地幔柱辩论的核心。本研究使用现代40 Ar/39 Ar年龄测定和样品处理及沥滤方法，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峰年龄分布的原因，以及（3）太平洋构造板块运动的含义。 所有样品将在俄勒冈州州立大学氩地质年代学实验室采用最新的40 Ar/39 Ar增量加热方法，使用ARGUS-VI多收集器质谱仪进行分析。

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.