摘要
对南秦岭北大巴山地区广泛分布的一套基性岩墙群中的辉绿岩进行采样,并进行了锆石U-Pb年代学、全岩地球化学分析。结果显示,岩石形成年龄为435~433 Ma,为早志留世晚期岩浆活动产物。这些辉绿岩具低硅、高碱、高钛的碱性岩特征。岩石微量及稀土元素具板内玄武岩特征,轻稀土元素相对富集,轻重稀土元素分异明显,富集不相容元素Ba、Nb、Ta,而K、Y、Yb相对亏损;K及Rb的负异常表明岩石源区残留角闪石或金云母,部分熔融模拟结果显示岩石起源于尖晶石角闪石岩高程度部分熔融。综合地球化学特征及前人研究结果,认为北大巴山地区在早古生代处于大规模伸展裂陷背景下,岩石圈的拉张诱发了低熔点的交代岩石圈地幔熔融,进而形成了这条碱性岩浆带。
Early Paleozoic basic dike swarms are widely distributed in North Daba Mountain of South Qinling Belt.This paper reports zircon U-Pb age and whole-rock geochemistry for diabase dikes with the purpose of exploring their petrogenesis and geological significance. The results indicate that the dykes were emplaced during the late period of Early Silurian epoch( 435 ~ 433 Ma). These diabases are characterized by low silica but high alkali and titanium content,exhibiting intraplate basalt geochemical characteristics with enrichment of light rare earth elements( LREE) and incompatible trace elements Ba,Nb and Ta but depletion of Rb,K,and heavy rare earth elements( HREE). The negative K and Rb anomalies indicate that amphibole or phlogopite was retained in the mantle source. Partial melting modelling result suggests that diabases were formed by high degrees of partial melting of an enriched spinel hornblendite source. In combination with geochemical characteristics and previous studies,the authors hold that the North Daba Mountain experienced large-scale extension during Early Paleozoic,and the extension of lithosphere induced the partial melting of metasomatized lithospheric mantle with low melting point and formed this alkaline magma belt.
作者
张方毅
赖绍聪
秦江锋
朱韧之
杨航
朱毓
ZHANG Fang-yi;LAI Shao-cong;QIN Jiang-feng;ZHU Ren-zhi;YANG Hang;ZHU Yu(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China)
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2020年第1期35-46,共12页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目(41772052)
国家自然科学基金委创新群体项目(41421002)。
关键词
基性岩墙群
锆石U-PB定年
源区性质
北大巴山
basic dike swarm
zircon U-Pb dating
source region of the magma
North Daba Mountain
