Geochemical and chronological constraints on the mantle plume origin of the Caroline Plateau
Geochemical and chronological constraints on the mantle plume origin of the Caroline Plateau
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关于卡罗琳海台地幔柱成因的地球化学与年代学限制
DOI：
10.1016/j.chemgeo.2020.119566
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发表时间：
2020-05
期刊：
影响因子：
3.9
通讯作者：
Guoliang Zhang;Ji Zhang;Shuai Wang;Jian-xin Zhao
中科院分区：
文献类型：
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作者：
Guoliang Zhang;Ji Zhang;Shuai Wang;Jian-xin Zhao
大洋高原的成因为研究深部地幔的成分和熔融动力学提供了重要信息。加罗林海隆由东、西加罗林海脊组成，在西太平洋俯冲系统的演化中发挥了重要作用;然而，对加罗林海隆的性质和起源知之甚少。在这里，根据海底采样，我们首次确认卡罗琳海隆代表了一个海洋高原（卡罗琳高原），该高原形成为一个大的火成省。加罗林高原与加罗林海山链在东部相连，海山链形成于一个根深蒂固的热点之上。为了探讨加罗林高原地幔源区的性质及其与加罗林海山/岛链的成因关系，对加罗林高原玄武岩样品进行了年龄测定，并对其主量元素、微量元素和Sr-Nd-Pb-Hf同位素进行了分析。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 ~ 19.26 ± 0.35 Ma）比碱性玄武岩（8.13 ± 0.81 Ma）和以东加罗林海山/群岛的火山岩年龄大。拉斑玄武岩的微量元素模式与Ontong Java高原的玄武岩相似。我们认为拉斑玄武岩代表加罗林高原火山作用的主要阶段，碱性玄武岩代表火山作用的晚期阶段。高原碱性玄武岩的同位素组成与加罗林群岛的玄武岩相似，表明其来源于同一富集地幔端元。拉斑玄武岩的亏损地球化学特征表明其地幔源区有亏损组分参与，其Sr-Nd-Pb-Hf同位素组成可通过碱性玄武岩与亏损的MORB地幔组分的混合来再现。根据两组玄武岩相对较低的Sm/Yb比，推断卡罗琳高原形成于岩石圈较薄的年轻卡罗琳板块上。我们认为，在加罗林高原/海山系统的火山岩的地球化学和年龄可以解释的加罗林热点的活动。加罗林高原和岛屿火山岩的碱度和Sm/Yb比值随时间增加，反映了岩石圈增厚和加罗林地幔柱活动减少。
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.