福建新生代玄武岩及其地幔包体的矿物学特征——对岩石圈地幔性质的制约  

Mineralogical Characteristics of Cenozoic Basalts and Mantle Xenoliths in Fujian:Constraints on Properties of Lithospheric Mantle

作　　者：颜雪 王力圆 陈洲鑫 张文慧 Yan Xue;Wang Liyuan;Chen Zhouxin;Zhang Wenhui(Zijin School of Geology and Mining,Fuzhou University,Fuzhou 350108,China)

机构地区：[1]福州大学紫金地质与矿业学院,福州350108

出　　处：《吉林大学学报(地球科学版)》2025年第2期463-482,共20页Journal of Jilin University:Earth Science Edition

基　　金：国家自然科学基金项目(41873012,41903007)。

摘　　要：福建新生代玄武岩广泛发育且携带了大量地幔包体,其矿物元素特征能够反演岩石圈地幔性质。本文对福建沿海的厦门及内陆地区的明溪、闽清等地新生代玄武岩及其橄榄岩包体中的矿物进行了电子探针、单斜辉石LA-ICP-MS微量元素和原位Sr同位素分析,探究福建地区岩石圈地幔属性特征及演化历史。结果表明:玄武岩及其橄榄岩包体中单斜辉石主要为透辉石,橄榄岩包体根据矿物学特征分为A、B两组,A组(Mg^(#)>90)代表了古老难熔岩石圈地幔,B组(Mg^(#)<90)代表了经改造后年轻饱满岩石圈地幔。A组橄榄岩包体中的单斜辉石高场强元素Nb、Ti轻微负异常,Hf、Zr、Ta强烈负异常。B组橄榄岩包体中的单斜辉石有所不同,高场强元素Zr、Hf轻微负异常,大离子亲石元素Ba强烈负异常。玄武岩斑晶和基质中的单斜辉石均呈现LREE富集、HREE亏损的特征,且单斜辉石斑晶边部比核部亏损高场强元素Th、Nb,富集大离子亲石元素Sr、Eu。橄榄岩包体中大部分A组和B组单斜辉石都经历了硅酸盐熔体交代,少数A组单斜辉石介于硅酸盐熔体交代和碳酸盐熔体交代之间。单斜辉石原位Sr同位素范围在0.70257~0.70367之间,大多单斜辉石边部的^(87)Sr/^(86)Sr值比核部要高,可能受到了高^(87)Sr/^(86)Sr值物质交代作用。福建橄榄岩包体很可能代表的是太平洋板块俯冲软流圈地幔经历减压上升后新改造的岩石圈地幔。The Cenozoic basalts in Fujian are widely developed and contain abundant mantle xenoliths,whose mineralogical characteristic provide insights into the properties of lithospheric mantle.This study conducted electron microprobes,clinopyroxene LA-ICP-MS trace element,and in-situ Sr isotopes analyses on the minerals in Cenozoic basalts and peridotite xenoliths from Xiamen along the Fujian coast,as well as Mingxi and Minqing in the inland region.The results indicate that the clinopyroxenes in both basalt and peridotite xenoliths are predominantly diopside.The peridotite xenoliths are divided into two groups based on mineralogical characteristics:Group A(Mg^(#)>90),representing an ancient,refractory lithospheric mantle,and Group B(Mg^(#)<90),representing a younger,modified enriched lithospheric mantle.Group A clinopyroxene exhibit slight negative anomalies in high-field strength elements Nb and Ti,and strong negative anomalies in Hf,Zr,and Ta.In Group B peridotite,clinopyroxene shows differences,with slightly negative anomaly in high high-field strength elements Zr and Hf and a pronounced negative anomaly in the large ion lithophile element Ba.The clinopyroxene in both the phenocrysts and matrix of the basalt exhibits LREE enrichment and HREE depletion,with the rims showing greater depletions in high-field strength elements Th and Nb compared to the cores,along with enrichments in large ion lithophile elements Sr and Eu.Most clinopyroxenes in both Group A and Group B xenoliths have experienced silicate melt metasomatism,while a few Group A clinopyroxene suggest a mix between silicate and carbonate melt metasomatism.In-situ Sr isotope ratios for clinopyroxene range from 0.70257 to 0.70367,with most rims showing higher^(87)Sr/^(86)Sr ratios than the cores,like due to interaction with materials of higher^(87)Sr/^(86)Sr ratios.The Fujian peridotite probably represents a newly modified lithospheric mantle of the Pacific plate subduction asthenosphere mantle,following decompression ascent.

关 键 词：新生代玄武岩 橄榄岩包体 矿物学 原位Sr同位素 岩石圈地幔 

分 类 号：P588.145[天文地球—岩石学]