福州盆地西缘霏细斑岩脉锆石U-Pb年龄及其地质意义

Zircon U-Pb age of the felsite porphyry veins in western Fuzhou basin of Fujian Province and its geological significance

通过对福州盆地西北缘发育的霏细斑岩脉野外地质特征、锆石U-Pb测年及地球化学研究,讨论其与福州复式花岗岩体的成因联系。研究区霏细斑岩呈紫灰色,局部可见明显的流动构造,主要由正长石斑晶组成,脉体呈北东向侵入于早期福州复式岩体中。研究结果显示,霏细斑岩脉形成于97.4Ma,具有钙碱性I型花岗岩的特征。该期岩浆活动形成于福州复式岩体的过渡期,且其地球化学特征与早白垩世钙碱性I型花岗岩、晚白垩世碱性A型花岗岩之间存在连续过渡的关系,反映其为福建东南沿海构造体制从弧后扩张向陆内伸展转换的产物,暗示该构造体制的转换时间约为97Ma。

This paper presents U-Pb zircon geochronology,petrology,and major and trace elements of Cretaceous felsite porphyry veins in western Fuzhou basin,Fujian Province.These data were used to investigate the genetic relationship between felsite porphyry and Fuzhou composite granite body.Felsite porphyry shows purplish gray color and is mainly composed of orthoclase phenocrysts,and the well-developed flow structure is present on the margin.Felsite porphyry veins have a NE-trending strike and intruded into Fuzhou composite granite body.Felsite porphyry shows the features of calc-alkali and I-type granites,with the emplacement age being 97.4Ma;it was formed in the transition period between early Fuzhou composite granite body(111~100Ma)and late Fuzhou composite granite body(95~90Ma).The geochemical characteristics between the above three phase rock types present a graduallychanged transitional relation on the time scale.That is,this felsite porphyry is the product of the tectonic regimes conversion between Early and Late Cretaceous in southeastern China.The authors thus hold that the transformation age may be 97Ma.