摘要
福建南安石井—水头一带出露的中-基性岩墙群主要地球化学特征显示,具低镁、高铝钙碱性特点,SiO_(2)含量为49.26%~61.75%,属中-基性岩范围;(La/Yb)_N比值为9.12~17.30,轻重稀土元素分离较为强烈;大离子亲石元素(LILE) Sr、K、Rb、Ba、Th和Ce等明显富集,而亏损高场强元素(HFSE) Nb、Ta,表现出与岛弧火山岩微量元素相似的地球化学特征。Sr-Nd同位素显示具有高I_(Sr)同位素初始值和低ε_(Nd)(t)值,指示形成中-基性岩墙的岩浆源区为“富集型”地幔源区,是俯冲流体和消减洋壳沉积物交代地幔楔及下地壳的部分熔融等共同参与了地幔源区的混合改造作用,之后再上侵接受地壳物质的混染,在晚白垩世(约90 Ma)拉张的构造环境下迅速上侵到地表冷却最终形成中-基性岩墙群。
The main geochemical characteristics of the exposed medium-base rock wall group in Shijing-Shuitou area of Nan'an,Fujian province show that it has the characteristics of low magnesium and high aluminum calcium alkalinity.The content of Si0,is 49.26%~61.75%,which belongs to the range of medium-basic rocks.(La/Yb)n ratio is 9.12~17.30,the separation of heavy and heavy rare earth elements is strong.Large ion lithophilic elements(LILE)Sr,K,Rb,Ba,Th and Ce are obviously enriched,while high field strength elements(HFSE)Nb and Ta are depleted,showing similar geochemical characteristics to trace elements in island arc volcanic rocks.The Sr-Nd isotope shows a high initial value of Isr isotope and a low&na(t)value,indicating that the magmatic source of medium-basic dike is a"enriched"mantle source region.The subduction fluid and the metasomatic mantle wedge and the lower crust participated in the mixed transformation of the mantle source area,and then accepted the mixed substances in the crust.Under the structural environment of the late Cretaceous(about 90 Ma),it quickly invaded the surface cooling and finally formed the medium-base rock wall group.
作者
童德平
Tong Deping(Western Fujian Geologic Party of Fujian Province,Sangming,365001)
出处
《福建地质》
2023年第3期175-186,共12页
Geology of Fujian
基金
福建省地质矿产勘查开发局地勘费项目“福建安海地区基性岩脉群地球化学特征及构造意义研究”。
