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

当热岩羽流从深部地幔上升并融化时，大洋热点轨迹就形成了。大约6000万年前，安通爪哇高原(OJP)在萨摩亚和拉罗通加的羽流上移动。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，以研究羽流与其上覆的大而厚的OJP之间的相互作用。初出茅庐的科学家、研究生和本科生将参加邮轮。在港口，科学团队将带领当地公立学校和媒体参观船只。在海上时，PI将制作一段培训视频，概述如何准备和进行一次成功的巡航。最近的研究提供了诱人的线索，表明目前活跃的萨摩亚热点可能是自白垩纪以来一直活跃的长期地幔熔融异常或热点。位于OJP以北的麦哲伦海山链上的许多87到106 Ma的火山都有萨摩亚热点的地球化学特征。关键的是，它们的年龄和位置与利用绝对板块运动重建的萨摩亚热点的预测相符。这对识别萨摩亚热点的白垩纪段(87-106 Ma)具有深远的意义。首先，使用相同的板块运动模型，重建的萨摩亚热点显示，OJP在~60-30 Ma越过萨摩亚热柱，在~60-50 Ma越过拉罗通加热柱--第二个可能存在时间较长的热点。其次，异常厚的OJP岩石圈通过萨摩亚和拉罗通加热柱将导致较低程度的热柱熔融，具有比沿萨摩亚和拉罗通加热点轨迹的任何其他地方更强烈的富集地幔(EM)特征。与白垩纪萨摩亚有关的麦哲伦海山支持较厚的岩石圈和较强的EM信号之间的假设关系，这些海山显示出较旧(因此较厚)的岩石圈和较强的EM信号之间的牢固关系。为期43天的海上疏浚探险将沿着OJP顶部这两个热点轨迹的模拟踪迹对海山进行采样，将测试OJP是否越过萨摩亚和拉罗通加羽流，以及这是否导致极端EM熔融的产生。地球化学分析和40Ar/39Ar年龄的结合将独特地确定这两个热点的贡献。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.