浙闽相邻区白垩纪上下火山岩系成因与壳幔作用对比研究  

Comparison Study of Petrogeneses and Crust-Mantle Interactions between Cretaceous Lower and Upper Volcanic Series in the Adjacent Area of Zhejiang-Fujian Provinces

作　　者：段政[1] 赵希林[1] 邢光福[1] 杨祝良[1] 余明刚[1] 陈志洪[1] 靳国栋[1] 姜杨[1] 李亚楠[1] 

机构地区：[1]南京地质矿产研究所,南京210016

出　　处：《地质学报》2015年第2期319-338,共20页Acta Geologica Sinica

基　　金：中国地质调查局基础地质综合研究项目(编号:1212011120134;1212011121136;1212011085446);国家自然科学基金资助项目(批准号41002024)的成果

摘　　要：浙闽相邻区广泛出露的白垩纪火山岩划分为上下火山岩系。下火山岩系为大面积展布的早白垩世早期长英质火山岩,属弱过铝质高钾钙碱性系列,富集大离子亲石元素Cs、Rb、Ba、Pb等和LREE,无明显Eu异常,亏损高场强元素Nb、Ta、Ti、P等,εHf(t)值较低(-20.43^-6.39),锆石Hf同位素二阶段模式年龄TDM2集中在1.8~2.2Ga之间。上火山岩系为局限于断陷盆地内的早白垩世晚期长英质火山岩,属偏铝质高钾钙碱性系列,相对贫硅贫碱但同样富集LREE和大离子亲石元素,负Eu异常明显,εHf(t)值较高(-10.00^-4.51)。研究表明,上下火山岩系均表现出随时代变新ΣREE和LREE分异程度降低的趋势,均形成于活动大陆边缘环境,主要为幔源岩浆底侵导致古元古代陆壳基底部分熔融形成的低Sr流纹岩类,但上火山岩系成岩过程中经历了更强烈的壳幔作用;例外的是下火山岩系西山头组上部熔岩,属东南沿海罕见的橄榄玄粗岩系列高Sr粗面英安岩,以富集Sr、Ti、Co、Ni和低的εHf(t)为特征,推断由幔源基性岩浆结晶分异形成。区域晚中生代火山岩的综合对比表明,东南沿海深部壳幔作用具有从中—晚侏罗世到早白垩世晚期逐渐增强、自南往北依次减弱的时空演化规律。Cretaceous volcanic rocks outcrop expensively in the adjacent area of Zhejiang-Fujian provinces and can be subdivided into the Lower ＆ Upper Volcanic Series.The earlier Lower Volcanic Series are widelyspread felsic volcanic rocks formed at early stage of Early Cretaceous.They belong to weakly peraluminous high-K calc-alkaline series,are enriched in LILE（such as Cs、Rb、Ba、Th、K、Pb）and LREE without evident Eu anomalies,depleted in HFSE（such as Nb、Ta、Ti、P）,show lowεHf（t）values（-20.43^-6.39）and old crustal model ages（TDM2mostly between 1.8and 2.2Ga）.The later Upper Volcanic Series are felsic volcanic rocks which formed at late stage of Early Cretaceous and expose only in faulted basins.They belong to metaluminous high-K calc-alkaline series,contain similar LILE and LREE to the Lower ones,but have evident Eu anomalies,lower SiO2＆ total alkaline contents and higherεHf（t）（-10.00^-4.51）.Both the Lower and Upper Volcanic Series show decreasingΣREE and differentiation degrees of LREE with time,they are mostly high-Sr rhyolitic rocks formed in active continental margin setting,and derived from partial melting of Proterozoic basements caused by underplating of mantle magmas.However,the Upper Volcanic Series underwent more crust-and mantle-derived magmatic mixings.Different from above rocks,the lava at the top of Xishantou Formation is Shoshonite series highSr trachyandesite.It is a kind of very rare rock in coastal Southeast China,enriched in Sr,Ti,Co,Ni but lowerεHf（t）values,and is inferred to result probably from fractional crystallization of mantle-derived basic magma.Based on comprehensive comparisons of Late Mesozoic volcanic rocks,it is summarized that the crust-mantle interactions in Southeast Coast of China incerased temporally from Middle-Late Jurassic to late stage of Early Cretaceous,and weakened spatially from south to north.

关 键 词：对比研究 成因与壳幔作用 上下火山岩系 白垩纪 浙闽相邻区 

分 类 号：P588.14[天文地球—岩石学]