湖南衡阳燕山早期川口过铝花岗岩地球化学特征、成因与构造环境  

Geochemistry,petrogenesis and tectonic setting of the early Yanshanian peraluminous granites in the Chuankou region,Hengyang,Hunan

作　　者：柏道远[1] 汪永清 王先辉[1] 马铁球[1] 张晓阳[1] 

机构地区：[1]湖南地质调查研究院,湖南湘潭411100 [2]湖南省地勘局413队,湖南常德415000

出　　处：《沉积与特提斯地质》2007年第2期49-59,共11页Sedimentary Geology and Tethyan Geology

基　　金：中国地质调查局地质调查项目(200213000035)

摘　　要：川口过铝花岗岩为二云母二长花岗岩,高硅、中碱,SiO2和K2O含量分别平均为75.71%和4.39%,Na2O＋K2O平均为7.57%,K2O/Na2O平均为1.43,Al2O3平均为13.28%,总体属过铝—强过铝质钙碱性花岗岩类。Ba、Nb、Sr、Eu、Ti等元素表现为较强烈的亏损,Rb、U、Ta、Nd、Hf、Sm、Y＋Yb等则相对富集;ΣREE平均仅67.18×10^-6,（La/Yb）N平均为2.21,δEu值平均为0.16。ISr为0.75093,εSr（t）为659,εNd（t）为-11.82,t2DM为1.92Ga,与湘桂内陆带花岗岩的背景值（2.4~1.8Ga）和区域基底的时代（2.7~1.7Ga）相吻合。川口岩体岩浆来源为中地壳结晶基底,属典型S型花岗岩;岩浆存在源于泥质岩的“低温”和源于砂岩的“高温”两种不同类型,至少有两个岩浆来源;岩体形成于后造山构造环境。分析认为,深部岩石圈拆沉与壳幔相互作用的规模差异,是造成湘东南燕山早期花岗岩一般为准铝-弱过铝质并有幔源物质加入,而川口岩体为过铝-强过铝质壳源花岗岩的原因。The Chuankou peraluminous granites in Hengyang, Hunan consist dominantly of two-mica monzonitic granites which have high Si and moderate alkali contents, average SiO2 and K2O contents ranging from 75.71% and 4.39%, average Na2O ＋ K2O content of 7.57%, average K2O/Na2O ratio of 1.43, and average Al2O3 content of 13.28%, indicating that these granites should be assigned to the peraluminous and strongly peralurninous calc-alkaline granites. The elements Ba, Nb, Sr, Eu and Ti are strongly depleted, while the elements rb, U, Ta, Nd, Hf, Sm and Y ＋ Yb are relatively enriched. These granites are also marked by average ∑REE content of only 67.18 × 10^-6the average （La/ Yb）N value of 2.21, the average δEu value of 0.16, the average Isr value of 0.75093, the εSr（t） value of 659,εNd（t） value of - 11 .82, t2DM of 1.92 Ga coinciding with the ages for the granites from Hunan and Guangxi （2.4- 1.8 Ga） and for the basement of the study area （2.7- 1.7 Ga）. The magmas of the Chuankou granites are derived from the mid- dle crustal crystalline basement, typical of the S-type granites. The magmas may be divided into two types： ＂low-temper- ature＂ type from mudstones and ＂high-temperature＂ type from sandstones. The Chuankou granites were formed from the post-orogenic tectonic setting. The detachment of the deep-seated lithosphere and crust-mantle interaction suggest the evidences that the early Yanshanian granites in southeastern Hunan are metalunfinous and weakly peraluminous whereas the Chuankou granites belong to the crest-derived peraluminous and strongly peraluminous granites.

关 键 词：衡阳 燕山早期 过铝花岗岩 地球化学 湖南 

分 类 号：P588.121[天文地球—岩石学]