沙茨基海隆(Shatsky Rise)白垩纪玄武岩的地球化学特征及其地幔柱-洋中脊相互作用过程  

Geochemical characteristics of Shatsky Rise Cretaceous basalts and implication on the interaction between mantle plume and mid-ocean ridge

作　　者：陈静 陈双双 高锐[1,2] 刘嘉麒 CHEN Jing;CHEN ShuangShuang;GAO Rui;LIU JiaQi(School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519080,China;Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中山大学地球科学与工程学院,广州510275 [2]南方海洋科学与工程广东省实验室(珠海),珠海519080 [3]中国科学院地质与地球物理研究所新生代地质与环境研究室,北京100029

出　　处：《岩石学报》2023年第8期2379-2401,共23页Acta Petrologica Sinica

基　　金：近海海洋环境科学国家重点实验室(厦门大学)访问学者基金(MELRS2233);同济大学海洋地质国家重点实验室开放课题(MGK202302);南方海洋科学与工程广东省实验室(珠海)创新团队建设项目(311021003);广东省引进创新和创业团队、广东省珠江人才项目基金(2017ZT07Z066);中山大学中央高校基本科研业务费专项资金(22qntd2101、2021qntd23);国家自然科学基金重大项目(41590863);国家自然科学青年基金项目(42102333);面上基金项目(41806077)联合资助。

摘　　要：沙茨基海隆(Shatsky Rise)是白垩纪早期形成的西北太平洋大火成岩省,其成因和演化过程目前仍存在较大争议。本次研究对沙茨基海隆白垩纪玄武岩进行了全岩主量、微量元素、Sr-Nd-Pb同位素的分析。沙茨基海隆玄武岩主要属于拉斑玄武岩,具有较亏损的大离子亲石元素和轻稀土元素以及较富集的重稀土元素的特征,没有明显的Eu异常(δEu=0.99~1.29),与正常洋中脊玄武岩(N-MORB)的微量元素配分模式较为相似。然而该系列玄武岩却具有相对较富集的初始^(87)Sr/^(86)Sr(0.702986~0.703991)和^(143)Nd/^(144)Nd(0.513034~0.513194)同位素比值、较富集的^(207)Pb/^(204)Pb(15.439~15.508)和^(208)Pb/^(204)Pb(37.853~38.488)同位素比值,与富集的洋岛玄武岩(OIB)和岛弧火山岩的同位素成分较为相似,且源区混入高U/Pb比值(HIMU型)的富集地幔成分。稀土元素部分熔融模拟反演表明沙茨基海隆火山岩的原始岩浆可能起源于尖晶石相二辉橄榄岩源区,且具有较高程度的部分熔融作用(>10%)。在以上研究基础上,本文提出地幔柱-洋中脊相互作用模型来解释沙茨基海隆拉斑玄武岩较亏损的不相容元素成分和较富集的同位素成分这一特殊地球化学特征。由于来自扩张洋中脊的强大拉张应力的影响,地幔柱岩浆物质将流向洋中脊并发生减压部分熔融,导致不相容元素的高度亏损,但由于放射成因元素(Sm、Rb和U)的半衰期相对较长,同位素成分则难以在较短时间内被改变,因此本文推测沙茨基海隆同位素富集的N-MORB拉斑玄武岩可能是地幔柱-洋中脊相互作用的产物。Shatsky Rise is a large igneous province in the Northwest Pacific that was formed in the Early Cretaceous,and its formation genesis and evolution process are still controversial.This study analyzes the bulk-rock major elements,trace elements,and Sr-Nd-Pb isotopic compositions of Shatsky Rise Cretaceous basalts.Shatsky Rise volcanic rocks mainly belong to tholeiite and are characterized by the depletion of large ion lithophile elements and light rare earth elements(LREEs),the enrichment of heavy rare earth elements(HREEs),and the absence of obvious Eu anomaly(δEu=0.99~1.29),which is similar to the distribution pattern of normal mid-ocean ridge basalt(N-MORB).However,these basalts have relatively enriched 87 Sr/86 Sr(0.702986~0.703991)and^(143)Nd/^(144)Nd(0.513034~0.513194)isotopic ratios,and relatively enriched^(207)Pb/^(204)Pb(15.439~15.508)and 208 Pb/^(204)Pb(37.853~38.488)isotopic ratios,which are similar to the isotopic compositions of enriched ocean island basalt(OIB)and island arc volcanic rocks,and have the involvement of enriched mantle components with high U/Pb ratio(HIMU).The REE partial melting model proves that Shatsky Rise volcanic rocks may originate from a relatively shallow magma source where the spinel iherzolite exists stably,and experience a relatively high degree of partial melting(>10%).We attempt to use the mantle plume-mid ocean ridge interaction model to explain the special geochemical characteristics of Shatsky Rise volcanic rocks with the depleted incompatible element compositions and enriched isotopic compositions.Due to the influence of strong ridge tensile forces,the mantle plume magma would flow to the ridge axis and undergo decompression melting,resulting in the depletion of the highly incompatible elements but the invariability of the isotopic compositions due to the relatively long half-life of the radiogenic elements(Sm,Rb,and U).We speculate that these Shatsky Rise isotopically enriched N-MORB-type tholeiites may be an exclusive product of a mid-ocean ridge-mantle plume interact

关 键 词：SR-ND-PB同位素 拉斑玄武岩 地幔柱 扩张三节点 沙茨基海隆 

分 类 号：P542[天文地球—构造地质学] P588.145[天文地球—地质学]