东南沿海中生代火山岩带地球化学特征

中国东南沿海位于太平洋板块和欧亚板块的结合处，广泛分布着中生代火山岩，并伴随有大规模的成矿作用。酸性火山岩占绝对优势，基性中性火山岩仅零星出露。酸性和中性火山岩为一套富碱、富钾、富铝、低钛的高钾钙碱性系列，基性火山岩为一套富硅贫碱的高钾和中钾钙碱性系列。从基性到酸性火山岩稀土分馏和铕的负异常逐渐加剧。基性火山岩贫Nb、Zr、Y，弱富集Ba、Hf、Th、Ce。中性火山岩和酸性火山岩贫Ba、Ti、P、Nb、Zr、Ta、Sr，强烈富集Pb。通过主量、微量和稀土元素的研究认为，基性火山岩和酸性火山岩为独立的岩浆起源，在中生代，东南沿海广泛存在着玄武岩的底侵作用，给下地壳提供了大量的热源，从而诱发了下地壳重熔，形成了大量的酸性火山岩。中性火山岩由酸性和基性岩浆混合形成，其地球化学特征主要受酸性岩浆的制约。

Geochemical characteristics of the Mesozoic volcanic belt in southeast coast of China

Southeast coast of China lies in the plate junction between the Pacific and the Eurasian plates,where volcanic rocks are widely exposed and large-scale mineralization were developed in the Mesozoic.There is a large-scale distribution of acidic volcanic rocks while the mafic and intermediate volcanic rocks are exposed sporadically.The acid and intermediate volcanic rocks,which are characterized by high alkali,high K,high Al and low Ti,belong to high-K calc-alkaline series while the mafic volcanic rocks which are characterized by high Si and low alkali belong to high-mid-K calc-alkaline series.The REE fractionation and negative anomaly of europium are more and more obvious from mafic volcanic rocks to acidic volcanic rocks.The mafic volcanic rocks are depleted in Nb,Zr,Y and slightly enriched in Ba,Hf,Th,Ce.The acid and intermediate volcanic rocks are depleted in Ba,Ti,P,Nb,Zr,Ta,Sr and strongly enriched in Pb.The studies of major elements,trace elements and REE suggest that the source of mafic volcanic rocks is separated from the source of acidic volcanic rocks.The remelting of the lower crust caused by heat from basaltic underplating which was widespread in southeast coast of China in the Mesozoic generated a lot of acidic volcanic rocks.The intermediate volcanic rocks,geochemical characteristics of which are controlled by acid volcanic rocks,are generated by mixing of acid magma and mafic magma.