Abstract The genesis of an oceanic plateau provides important information on the composition and melting dynamics of the deep mantle. The Caroline Rise, consisting of the West and the East Caroline Ridges, has played an important role in the evolution of the subduction system of the western Pacific; however, the nature and origin of the Caroline Rise are poorly known. Here, on the basis of seafloor sampling, we confirm for the first time that the Caroline Rise represents an oceanic plateau (the Caroline Plateau) that formed as a large igneous province. The Caroline Plateau is connected with the Caroline Seamount Chain to the east, and the seamount chain formed above a deep-rooted hotspot. To investigate the nature of the mantle source of the Caroline Plateau and its genetic relationship with the Caroline Seamount/Island Chain, we age-dated basalt samples from the Caroline Plateau and analyzed their major and trace elements and Sr–Nd–Pb–Hf isotopes. The samples can be classified as alkali or tholeiitic basalt. The tholeiitic basalts (15.62 ± 3.16 to 19.26 ± 0.35 Ma) are older than the alkali basalts (8.13 ± 0.81 Ma) and the volcanics of the Caroline Seamounts/Islands to the east. The tholeiitic basalts have trace element patterns similar to those of basalts of the Ontong Java Plateau. We suggest that the tholeiitic basalts represent the main stage of volcanism on the Caroline Plateau and the alkali basalts the late stage. The alkali basalts of the plateau have isotopic compositions similar to those of the basalts of the Caroline Islands, indicating an origin from the same enriched mantle end-member. The tholeiitic basalts with a MORB-like depleted geochemistry indicate the involvement of depleted components in their mantle source, and the Sr–Nd–Pb–Hf isotope compositions of the tholeiitic basalts can be reproduced by mixing alkali basalt with a depleted MORB mantle component. Based on the relatively low Sm/Yb ratios of the two groups of basalts, the Caroline Plateau is inferred to have formed on a young Caroline Plate with a thin lithosphere. We suggest that the geochemistry and ages of formation of volcanic rocks in the Caroline Plateau/Seamount system can be explained by the activities of the Caroline hotspot. The volcanic rocks of the Caroline Plateau and Islands show increasing alkalinity and Sm/Yb ratios with time, which reflect thickening of the lithosphere and decreasing activity of the Caroline mantle plume.

中文翻译：

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卡罗琳高原地幔柱起源的地球化学和年代学约束

摘要 大洋高原的成因为深部地幔的组成和熔融动力学提供了重要信息。由西、东卡罗林海脊组成的卡罗林海隆在西太平洋俯冲系统的演化过程中发挥了重要作用；然而，卡罗琳隆起的性质和起源却鲜为人知。在这里，在海底采样的基础上，我们首次确认卡罗琳隆起代表了一个形成为大型火成岩省的海洋高原（卡罗琳高原）。卡罗林高原东面与卡罗林海山链相连，海山链形成于一个根深蒂固的热点之上。研究卡罗林高原地幔源的性质及其与卡罗林海山/岛链的亲缘关系，我们对来自卡罗琳高原的玄武岩样品进行了年龄测定，并分析了它们的主要和微量元素以及 Sr-Nd-Pb-Hf 同位素。样品可分为碱性玄武岩或拉斑玄武岩。拉斑玄武岩 (15.62 ± 3.16 至 19.26 ± 0.35 Ma) 比碱性玄武岩 (8.13 ± 0.81 Ma) 和东部卡罗林海山/岛屿的火山岩更古老。拉斑玄武岩具有与 Ontong Java 高原玄武岩相似的微量元素模式。我们认为拉斑玄武岩代表了卡罗林高原火山作用的主要阶段，碱性玄武岩代表了晚期阶段。高原碱性玄武岩的同位素组成与卡罗林群岛的玄武岩相似，表明其起源于同一富集的地幔端部。具有类似 MORB 贫化地球化学的拉斑玄武岩表明其地幔源中涉及贫化组分，拉斑玄武岩的 Sr-Nd-Pb-Hf 同位素组成可以通过将碱性玄武岩与贫化 MORB 地幔组分混合来再现。基于两组玄武岩相对较低的 Sm/Yb 比值，推测卡罗林高原形成于岩石圈较薄的年轻卡罗林板块上。我们认为，卡罗林高原/海山系统火山岩的地球化学和形成年龄可以用卡罗林热点的活动来解释。卡罗林高原和群岛火山岩的碱度和 Sm/Yb 比值随时间增加，反映了岩石圈的增厚和卡罗林地幔柱活动的减少。