湘东南瑶岗仙岩体岩石化学特征、成因与构造环境

Geochemistry,Petrogenesis and Tectonic Setting of Early Yanshanian Yaogangxian Granite Pluton,Southeastern Hunan province

湘东南燕山早期瑶岗仙岩体主要由黑云母二长花岗岩组成。岩石SiO2和K2O平均含量分别为75.83%和4.78%,Na2O+K2O平均8.02%,K2O/Na2O比值平均为1.53,Al2O3平均为12.98%。总体属弱过铝质钙碱性花岗岩类。εNd(t)值为-11.13^-9.13;t2DM为1.70~1.86Ga,与湘桂内陆带花岗岩的背景值(1.8~2.4Ga)和区域基底的时代(1.7~2.7Ga)相吻合。上述特征表明,瑶岗仙岩体岩浆来源为中地壳结晶基底,属典型S型花岗岩。氧化物构造环境判别图解及区域构造演化背景反映瑶岗仙岩体形成于后造山构造环境。

The Early Yanshanian Yaogangxian granite pluton in southern Hunan province is composing dominantly of biotite monzogranites. Their mean content of SiO2 is 75.83 wt%, K2O 4.78 wt%, Na2O ＋ K2O 8.02 wt% with mean K2O/Na2O ratio 1.53 and Al2O3 12.98 wt%. Thus, the rocks belong to weakly perluminous granite of calc -alkaline series, εNd （t） value of - 11.13 - -9.13, t2DM of 1.70 - 1.86 Ga, coinciding with the ages for the granites from Hunan and Guangxi interior continental belt （ 1.8 - 2.4 Ga） and the basement formation ages of the study area （1.7 -2.7 Ga）, The magmas of the Yaogangxian granites are derived from the middle crustal crystalline basement, typical origin of the S - type granites. Multiple oxide -diagrams for discrimination of tectonic setting and regional tectonic evolution analysis indicate that the rocks are formed in the post- orogenic extension environment.