大别山造山带东南部天柱山花岗岩类侵入体的特征及其LA-ICP-MS锆石U-Pb年龄  

Characteristics and LA-ICP-MS zircon U-Pb ages of the Tianzhushan granitoid intrusive body,southeastern Dabie orogen

作　　者：薛怀民[1] 马芳[2] 赵逊[3] 吴维平[4] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]中国地质科学院,北京100037 [4]安徽省地质调查院,安徽合肥230001

出　　处：《岩石矿物学杂志》2011年第5期935-950,共16页Acta Petrologica et Mineralogica

基　　金：中国地质调查局地质调查项目(1212010711814);地质矿产调查评价专项(1212011121116);天柱山国家地质公园资助项目

摘　　要：大别山造山带内广泛发育晚中生代的花岗岩类侵入体,天柱山岩体是其中的一个典型代表,位于分隔南大别超高压变质带与北大别杂岩之间的五河-水吼断裂带附近。该岩体是个由多期次侵位构成的复式岩体,自早到晚依次为闪长岩→石英正长岩/花岗闪长岩→碱长花岗岩。整个杂岩体属高钾钙碱性系列,但碱长花岗岩的地球化学性质与构成杂岩体的其他类型岩石之间存在着显著的差异,拥有A型花岗岩的很多地球化学特征,但大量存在的包裹体(围岩俘虏体及暗色细粒包体)和低的Zr饱和温度又明显不同于典型的A型花岗岩,推测属高度演化的I型花岗岩。地球化学特征显示天柱山花岗岩类的成因与整个大别山造山带内晚中生代的花岗岩类似,来自古老下地壳物质的部分熔融,形成于晚中生代整个中国东部岩石圈减薄的构造背景下。测得该复式岩体中花岗闪长岩和碱长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为127.8±0.7 Ma和127.7±1.0 Ma,两者的侵位年龄几乎完全一致,岩相特征也显示,碱长花岗质岩浆侵位时,花岗闪长岩尚未完全固结。The Tianzhushan intrusive body is one of the representative plutons in the Dabie orogen,where late Mesozoic granitoid intrusive bodies are widely distributed,locates near the Wuhe-Shuihou fault which separates the UHP metamorphic complex of South Dabie from the block of North Dabie.This intrusive body is a composite intrusion consisting of three generations of intrusions： diorite,quartz syenite/granodiorite,and alkali-feldspar granite respectively from early to late.All the complexes belong to high-K calc-alkaline series,but the geochemical characteristics of the alkali-feldspar granite are remarkably different from other types of rocks and similar to things of A-type granite to a considerable degree.The alkali-feldspar granite has abundant enclaves and lower Zr saturation temperature,showing great difference from typical A-type granite and probably belonging to a highly evolved I-type granite.The geochemical characteristics of the Tianzhushan intrusive body are similar to those of other late Mesozoic granitoid intrusive bodies in the Dabie orogen,derived from partial melting of ＂old＂ lower crust under the tectonic backdrop of all eastern China lithospheric thinning in late Mesozoic.The granodiorite and alkali-feldspar granite are similar to each other in the emplacement age,and their zircon LA-ICP-MS U-Pb ages are 127.8 ±0.7 Ma and 127.7±1.0 Ma respectively,corresponding to the lithofacies features.It is thus held that the granodiorite had not been entirety concreted during the intrusion of the alkali-feldspar granitic magma.

关 键 词：花岗岩类 中生代 锆石年龄 天柱山 大别山造山带 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]