摘要
赵卡隆铁铜多金属矿区发育一套与成矿密切相关的安山岩。为了研究其成因,对安山岩的主量、微量、稀土元素及同位素进行分析。研究结果表明：安山岩以英安岩类为主,主成分以低硅（SiO2质量分数为47.79%~61.51%,平均为55.41%）、高铝（Al2O3质量分数为15.44%）、高钠（Na2O平均质量分数为4.81%）、低钾（K2O平均质量分数为1.60%）含量为特征,岩石分异指数（DI）为39.63~72.52,火山岩QAPF图落入英安岩、安山岩区;轻稀土元素富集,Eu无异常,Ce呈弱的负异常,Y和Yb元素有显著的亏损（w（Y）〈20μg/g,w（Yb）〈1.93μg/g）;硫同位素比值δ34SCDT范围为-1.60‰~15.32‰;地球化学数据分析显示出其大洋安山岩的特征,属于亚碱性-拉斑玄武岩系列,喷发环境为海相,具有岛弧安山岩的性质及弧后扩张盆地火山岩的双重性质;微量元素以富集大离子亲石元素和亏损高场强元素为特征,且高场强元素的比值（w（Zr）/w（Nb）,w（Hf）/w（Ta））具有类似MORB的特性;安山岩构造位置应偏于岛弧中的内弧火山活动,安山岩岩浆应为地幔来源,并混染了大陆壳物质,为壳幔两种岩浆混合的产物,其形成与岛弧东侧的大洋消减作用及岛弧西侧的弧后扩张作用有关;安山岩虽然在某种程度上表现出岛弧安山岩的特征,但实际揭示了弧后扩张盆地的大地构造背景。
The Zhaokalong andesite from the back-arc rift sedimentary basin is closely related to the Fe-Cu polymetallic mineralization.In order to study the petrogenesis,the major,trace,rare earth elements and isotopes were analyzed.The results show that the andesite belongs to dacite,and it has an uncommon chemical composition with a characteristic of low silica（SiO2 47.79%-61.51%,average 55.41%）,high alumina（Al2O3 average 15.44%）,high sodium（Na2O average 4.81%） and low potassium（K2O average 1.60%）.Rock differentiation index（DI） is 39.63-72.52,and the spots of Q-A-P-F diagram situate in the dacite-andesite zone.In addition,the andesite has an enrichment of light-rare-earth elements（LREE）,and its LREE/HREE ratio is 3.97-9.13.Eu shows no anomaly（δEu 0.92-1.10）,while Ce shows weak negative anomalies（δCe 0.68-0.84）,Y and Yb are depleted greatly（w（Y）20 μg/g,w（Yb）1.93 μg/g）.Furthermore,the andesite has high abundances of large-lithophile trace elements（e.g.Ba,Th,Rb） and low abundances of high-strength-field elements（HFSE,e.g.Ta,Nb,P,Ti）,and the ratios of HFSE（e.g.w（Zr）/w（Nb）,w（Hf）/w（Ta）） have similar characteristics to MORB.δ34SCDT（sulfur isotope ratios） of the andesite range from -1.60 ‰ to 15.32 ‰.Geochemistry indicates that the andesite erupted in a marine environment,with the characteristics of ocean andesite,belongs to the subalkaline-tholeiite series.The andesite has a dual nature of island-arc andesite and back-arc volcanic,and the eruption location of the andesite may be biased towards to inner arc（back-arc rift）.Andesite magma,which is related to oceanic subduction and arc spreading,should be crust-mantle mixing magma originated from the mantle and contaminated by the continental crust.The andesite shows the characteristics of island-arc andesite to some extents,but in fact it originates in a tectonic setting of back-arc expansion basin.
出处
《中南大学学报（自然科学版）》
EI
CAS
CSCD
北大核心
2012年第9期3524-3534,共11页
Journal of Central South University:Science and Technology
基金
国家留学基金委资助项目(留金发[2011]3005)
关键词
赵卡隆矿床
安山岩
岛弧
弧后盆地
Zhaokalong deposit
andesite
island arc
back-arc basin
