粤北地区河口岩体次英安斑岩地球化学特征及地质意义

Geochemical Characteristics of Porphyritic Dacite of Hekou Pluton in North Guangdong

河口岩体位于粤北地区贵东岩体中部的北缘。在系统研究河口岩体次英安斑岩的岩相学和地球化学特征基础上,探讨其成因类型、岩浆源区及形成的构造环境。河口岩体次英安斑岩SiO2含量为68.15%~69.66%,里特曼指数δ值为1.50~2.42,平均值为2.12,具有高硅、富碱、富铝的特征,为亚碱性高钾钙碱性过铝质系列;轻稀土元素富集,重稀土元素相对亏损,轻重稀土元素分异明显;富集大离子亲石元素Rb、Nd、Sm等,亏损Sr、Nb、Ti、Zr等元素,显示壳源S型花岗岩的特征,其源岩来自上部地壳,可能是砂质岩。河口岩体次英安斑岩形成于主碰撞造山阶段结束之后的后碰撞造山构造环境。

Hekou pluton is located in the northern margin of the central part of Guidong pluton in the northern part of Guangdong province.Based on the systematic study of the lithographic and geochemical characteristics of the porphyritic dacite in the Hekou pluton,this paper discussed the genetic type,magmatic source region and tectonic environment of formation.The SiO2 content of the porphyritic dacite in the Hekou pluton is of 68.15%~69.66%,and the δ value is 1.50~2.42 with the average of 2.12.The porphyritic dacite is of high silicon,rich alkaline and aluminum,which falls into the subalkaline high potassium calc-alkaline praluminous series.It is rich in LREE,depleted in HREE and distinct in the differentiation between LREE and HREE,relative rich of large ion lithophile elements Rb,Nd,Sm,etc.and relative loss of Sr,Nb,Ti,Zr and other elements,bears the characteristics of the shell-source S-type granite.The source rock may come from the upper crust derived from the sandy rock.The Hekou pluton was believed formed in the post-collisional orogenic tectonic environment after the end of the main collision orogeny.