闽东北晚侏罗世南园组火山岩地球化学特征及构造意义

Geochemical Characteristics and Tectonic Significance of Volcanic Rocks of Late Jurassic Nanyuan Formation in the Northeastern Fujian

通过福建1∶5万漳湾镇、溪南镇幅区域地质调查,对闽东北福安和霞浦晚侏罗世南园组火山岩组合、地球化学特征、岩浆起源及构造环境进行了分析。结果表明,研究区南园组火山岩共分为中性-中酸性、酸性及中性-中酸性3个岩性段,分别对应南园组第一段、第二段和第三段。南园组中性火山岩具有高铝、低镁铁特征,酸性火山岩具有高硅、高铝、低镁、低铁、低钛特征,且南园组酸性火山岩表现出更为强烈的不相容元素Ba、Sr、P、Ti等的亏损和负Eu异常特征,显示了更高的分异程度。南园组火山岩总体地球化学特征与大陆边缘岛弧火山岩相似,可能形成于晚侏罗世-早白垩世太平洋板块向欧亚大陆板块俯冲下的陆缘弧环境。

Through the regional geological survey of 1∶50,000 Zhangwan Town and Xinan Town,the volcanic rock combination,geochemical characteristics,magma origin and structural environment of Late Jurassic Nanyuan Formation were analyzed in Fuan city and Xiapu county of the northeast Fujian.The results show that the volcanic rocks in the study area are divided into three neutral-medium acid,acid and neutral-medium acid sections,respectively corresponding to the first,second and third sections of the Nanyuan Formation.Neutral volcanic rocks of Nanyuan group have characteristics of high aluminum and low Magnesium,and acid volcanic rocks have characteristics of high silicon,high aluminum,low magnesium,low iron and low titanium.Moreover,the acid volcanic rocks in the Nanyuan group showed a stronger loss and negative Eu abnormalities of Ba,Sr,P,Ti,showing a higher degree of divergence.The overall geochemical characteristics of the Nanyuan Formation are similar to the continental marginal island arc volcanic rocks,possibly forming in the terrestrial margin arc environment where the Late Jurassic-Early Cretaceous Pacific Plate dives into the Eurasian Plate.