皖南泾县章渡岩体的年代学、地球化学及成因研究

A Study of Chronology,Geochemical Characteristics and Genetic Analysis of the Zhangdu Pluton in Jingxian County,Anhui Province

为探讨章渡岩体的成岩时代、源区特征及构造背景,对其进行了年代学和岩石地球化学研究。结果表明,该岩体岩性主要为花岗闪长岩,形成于早白垩世(135 Ma),为皖南地区燕山早期大规模岩浆活动的产物。岩体岩石的SiO_(2)含量为65.18%~67.38%,A/CNK为0.93~0.98,属准铝质高钾钙碱性系列岩石。岩石富集Th、U、La与K元素,相对亏损Ba、Nb、Sr、P与Ti元素,微量元素蛛网图与稀土元素配分曲线均呈明显的右倾型,具明显的Eu负异常(δEu为0.72~0.81)。其ε_(Hf)(t)值为-11.1~-10,Mg^(#)为38.86~43.58,Nb/U值为2.32~3.74,表明章渡花岗闪长岩的源岩主要以古老的下地壳壳源物质为主,并经历了幔源组分的加入和板片俯冲流体的交代作用,岩浆主要受部分熔融作用控制。结合前人研究成果,推断章渡岩体应形成于中生代太平洋板块向欧亚板块俯冲背景下的陆缘弧构造环境。

In order to explore diagenetic timing,provenance chracteristics,and tectonic background of the Zhangdu pluton,a study of chronology and petro-geochemistry of the Zhangdu pluton has been carried out in this paper.The results show that the pluton,mainly consists of granodiorite,was formed in the Early Cretaceous(135 Ma),as the product of large-scale magmatic activity in early Yanshanian in the southern Anhui.Their SiO_(2) contents range from 65.18%to 67.38%and their aluminum saturation indexes vary from 0.93 to 0.98,indicating that the pluton belongs to the metaluminous,high K calc-alkaline series rock.In addition,samples of the pluton are enriched in Th,U,La,and K elements,relatively depleted in Ba,Nb,Sr,P,and Ti elements,with right-declined spidergrams of trace elements and REE patterns,and obvious negative Eu anomalies(δEu values varying from 0.72 to 0.81).The zircon Hf isotopes(ε_(Hf) values varying from-11.1 to-10),Mg^(#)values ranging from 38.86 to 43.58,and Nb/U values varying from 2.32 to 3.74 show that the magma of the Zhangdu granodiorite was mainly derived from the partial melting of the ancient lower crust sourced materials,which had experienced the addition of mantle sourced components and the metasomatism of plate subduction fluid.Combined with previous research results,the authors believe that the Zhangdu pluton was formed in the continental arc tectonic environment under the background of the subduction of the Pacific plate to the Eurasian plate during the Mesozoic.