闽北邵武地区玄武安山岩的成因和意义——来自年代学、地球化学及Nd-Hf同位素的约束  

Petrogenesis and Significance of Basaltic Andesite in the Shaowu Area,Northern Fujian:Constraints from Geochronology,Geochemistry and Nd-Hf Isotopes

作　　者：周伏顺 林鑫[1] 王郅睿 邵程波 Zhou Fushun;Lin Xin;Wang Zhirui;Shao Chengbo(School of Earth Sciences and Resources,Chang’an University,Xi’an 710054,China)

机构地区：[1]长安大学地球科学与资源学院,西安710054

出　　处：《吉林大学学报（地球科学版）》2024年第3期840-861,共22页Journal of Jilin University：Earth Science Edition

基　　金：陕西省重点研发计划(2024GH-ZDXM-26);国家重点研发计划(2016YFC0600601);中央高校基金项目(300102271206)。

摘　　要：东南沿海地区中生代火山岩研究成果颇丰,但有关中侏罗世晚期基性火山岩的报道较少,限制了对该区域中生代构造-岩浆活动及大地构造演化的深入理解。本文对江绍断裂带东南侧邵武地区的中生代火山岩开展了系统的岩石学、锆石U-Pb年代学、锆石Lu-Hf同位素、地球化学和Sm-Nd同位素研究。结果显示:邵武地区玄武安山岩喷发年龄为(161.0±2.0)Ma;同位素地球化学结果显示,这些样品中—晚侏罗世锆石的ε_(Hf)(t)值介于-14.33~-10.41之间,ε_(Nd)(t)值较低(-9.2~-8.4),反映富集Nd同位素的特征;岩石地球化学结果表明,该套火山岩具有高w(Al_(2)O_(3))、w(Na_(2)O)、低w(MgO)、w(TFe_(2)O_(3))等特征,稀土总量较低,稀土配分曲线为右倾型,且具弱的Eu负异常,大离子亲石元素Rb、Ba和K相对富集,高场强元素Nb、Ta、Ti、P等相对亏损。综合岩石学和地球化学研究结果,本文认为邵武玄武安山岩起源于交代岩石圈地幔的部分熔融,并经历一定结晶的分异作用,其大地构造背景总体为板内环境。结合前人对区域构造-岩浆活动的认识,本文认为在中侏罗世晚期,太平洋俯冲板片发生回撤、撕裂,导致幔源岩浆底侵并置换了古老壳源岩石,从而东南沿海地区虽整体处于挤压背景,但仍存在局部拉张环境。Among the Mesozoic volcanic rocks along the southeast coast of China,Middle Jurassic rocks are seldom reported,yet they hold significant importance for understanding Mesozoic magmatic activities and tectonic evolution in this region.The Shaowu basaltic andesite,exposed in the southeast of the Jiangshao fault zone,provides an ideal opportunity for study.This paper systematically presents petrological,zircon U-Pb geochronological,Lu-Hf isotopic,whole-rock geochemistry and Sm-Nd isotopic analyses of the basaltic andesite,indicating an eruption age of(161.0±2.0)Ma.The isotopic data shows that all samples are characterized byε_(Hf)(t)values ranging from-14.33 to-10.41 and lowε_(Nd)(t)values between-9.2--8.4.The geochemical results shows high w(Al_(2)O_(3))and w(Na_(2)O)contents,along with low levels of w(MgO)and w(TFe_(2)O_(3))etc.The total rare earth elements(REE)content is low,with chondrite-normalized REE patterns showing LREE enrichment and weak Eu negative anomalies.Furthermore,large ion lithophile elements such as Rb,Ba and K are enriched,while the high field strength elements such as Nb,Ta,Ti and P are relatively depleted.The geochemical and petrological characteristics of the basaltic andesite imply that it originated from partial melting of a metasomatic mantle wedge,underwent certain crystallization differentiation,and formed in an intraplate tectonic environment.Based on previous studies on regional tectonic-magmatic activities,it is proposed that Pacific subducted plate retreat and tearing,resulting in encroachment of mantle-derived magma and the replacement of ancient crust-derived rocks,occurred amidst local extension within the broader compressional background of the south-eastern coast of China during the Middle Jurassic.

关 键 词：中侏罗世 地球化学 伸展背景 玄武安山岩 东南沿海 

分 类 号：P588.145[天文地球—岩石学]