Collaborative Research: Was early Cenozoic Samoa and Rarotonga volcanism suppressed when the Ontong Java Plateau drifted over the hotspots?

当热岩柱从地幔深处上升并融化时，海洋热点轨迹就形成了。大约6000万年前，Ontong爪哇高原（OJP）在萨摩亚和拉罗汤加火山羽流上移动。OJP是地球上最大的火山结构。该项目将对OJP顶部的海山进行采样，以研究羽流与上覆的大而厚的OJP之间的相互作用。初入职场的科学家、研究生和本科生将参加这次航行。在港口，科学小组将带领船只参观当地的公立学校和媒体。在海上，pi将制作一个培训视频，概述如何准备和执行一次成功的巡航。最近的工作提供了诱人的暗示，目前活跃的萨摩亚热点可能是一个长期存在的地幔融化异常，或热点，自白垩纪以来一直活跃。位于OJP北部的麦哲伦海山链上的许多87至106 Ma火山都具有萨摩亚热点地球化学特征。至关重要的是，它们的年龄和位置与利用绝对板块运动重建得出的萨摩亚热点预测相符。这对确定萨摩亚热点的白垩纪段（87-106 Ma）意义深远。首先，使用相同的板块运动模型，萨摩亚热点的重建表明，OJP在~60-30 Ma时经过萨摩亚羽流，在~60-50 Ma时经过拉罗汤加羽流——第二个可能存在很长时间的热点。其次，异常厚的OJP岩石圈经过萨摩亚和拉罗汤加火山柱会导致较低程度的火山柱融化，并且比萨摩亚和拉罗汤加火山热点轨道上的其他任何地方都有更强的富集地幔（EM）特征。白垩纪与萨摩亚相关的麦哲伦海山支持了厚岩石圈与强电磁信号之间的假设关系，这些海山显示出更古老（因此更厚）的岩石圈与强电磁信号之间的牢固关系。一项为期43天的海上疏浚考察将沿着OJP顶部这两个热点轨迹的模拟痕迹对海山进行采样，以测试OJP是否经过了萨摩亚和拉罗汤加羽流，以及这是否导致了极端EM融化的产生。地球化学分析和40Ar/39Ar年龄的结合将唯一地确定这两个热点的贡献。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Oceanic hotspot tracks form when plumes of hot rock upwell from the deep mantle and melt. Approximately 60 million years ago the Ontong Java Plateau (OJP) moved over the Samoan and Rarotonga plumes. The OJP is the largest volcanic structure on Earth. This project will sample seamounts on top of the OJP to study the interactions between plumes and the overlying large and thick OJP. Early-career scientists, graduate students, and undergraduate students will take part in the cruise. In port the science team will lead ship tours for local public schools and media. While at sea the PIs will make a training video that outlines how to prepare for and carry out a successful cruise. Recent work offers tantalizing hints that the currently active Samoan hotspot may be a long-lived mantle melting anomaly, or hotspot, that has been active since the Cretaceous. Many of the 87 to 106 Ma volcanoes in the Magellan Seamount Chain, located north of the OJP, have Samoan hotspot geochemical signatures. Critically, their ages and locations match predictions for the Samoan hotspot made using absolute plate motion reconstructions. The implications for identifying a Cretaceous segment (87-106 Ma) of the Samoan hotspot are profound. First, using the same plate motion models, reconstructions of the Samoan hotspot show that the OJP passed over the Samoan plume at ~60-30 Ma, and over the Rarotonga plume—a second, possibly-long-lived hotspot—at ~60-50 Ma. Second, passage of the extraordinarily thick OJP lithosphere over the Samoan and Rarotonga plumes would have resulted in lower degree plume melts with stronger enriched mantle (EM) signatures than anywhere else along the Samoan and Rarotonga hotspot tracks. The hypothesized relationship between thicker lithosphere and stronger EM signatures is supported by the Cretaceous Samoa-related Magellan Seamounts, which exhibit a robust relationship between older (and therefore thicker) lithosphere and stronger EM signatures. A 43-day seagoing dredging expedition to sample the seamounts along the modeled traces of these two hotspot tracks on top of the OJP will test whether the OJP passed over the Samoan and Rarotonga plumes, and whether this resulted in generation of extreme EM melts. A combination of geochemical analyses and 40Ar/39Ar ages will uniquely identify contributions from these two hotspots.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.