【作者】 孔会磊；

【导师】 董国臣；

【作者基本信息】 中国地质大学（北京） ， 矿产普查与勘探， 2011， 硕士

【摘要】 滇西三江地区南澜沧江带的临沧花岗岩体是云南省出露面积最大的复式岩基,它是古特提斯构造域中的重要单元。但对其成因和形成时代尚存在争议。本论文在野外调研的基础上,对临沧花岗岩体进行了系统的U-Pb同位素年代学、岩石学、元素地球化学以及锆石Hf同位素等方面的研究,结合区域上已有的U-Pb年代学,旨在对其成因和形成时代以及区域构造岩浆演化提供约束。本论文共选用样品19件,岩性主要为黑云母二长花岗岩,研究结果表明,该花岗岩的SiO₂含量为66.07-73.99%,平均为68.88%,K₂O/Na₂O值高,为1.41-2.21,平均为2.06,Al₂O₃含量为12.94-15.23%,平均为14.30%,铝饱和指数A/CNK为0.97-2.01,平均为1.27,为高钾钙碱性过铝-强过铝花岗岩。岩石总体上富集大离子亲石元素和Pb,明显亏损高场强元素。稀土总量173.58-359.16×10^-6,平均为240.13×10^-6,具有明显的轻稀土富集,重稀土亏损的特征,（La/Yb）_N为6.69-15.72,平均11.54,δEu为0.41-0.75,平均0.53,球粒陨石标准化配分模式显示明显的负Eu异常。六件样品的锆石U-Pb年龄分别为227.00±0.80Ma、219.19±0.99、219.69±0.67 Ma、203.38±0.70 Ma、211.9±1.8Ma和214±2Ma,属晚三叠世。SiO₂-Zr判别图、ACF图解等花岗岩成因类型判别图指示临沧花岗岩为S型花岗岩,其物质来源为贫粘土的砂屑岩。微量元素Rb-Y+Nd判别图中,临沧花岗岩体投影点全部落入后碰撞花岗岩区。在Sr-Yb判别图中,投影点全部落入低Sr高Yb型花岗岩区,与我国东南沿海花岗岩特征一致,应形成于挤压向伸展转换的后碰撞阶段。锆石Hf同位素组成比较均一,εHf（t）均为负值（集中于-14^-10之间）,Hf地壳模式年龄集中于1.90².15Ga,推断其为古老地壳部分熔融的产物。结合锆石定年结果及岩体产出的区域地质背景,我们认为临沧花岗岩形成于缅泰马陆块与思茅地块大陆碰撞造山过程的后碰撞阶段,应形成于晚三叠世。更多还原

【Abstract】 The Lincang granite in southern Lancangjiang zone of Sanjiang area, located in West of Yunnan Province, has the largest area of outcrop in Yunnan Province. The composite granite batholith is an important part in the paleo-Tethyan Tectonic Region. However, its petrogenesis and age are still in dispute. Based on Field investigation, the Lincang granite is systematically researched in this study, in which the subjects of U-Pb isotope chronology, petrology, elemental geochemistry and zircon Hf isotopic geochemistry are involved. Correlated with the known U-Pb dating, the purpose of this study endeavors to bring up the geological constraints for its petrogenesis, age and regional magmatic evolution under the tectonic setting.The Lincang granite is mostly biotitic monzogranite in terms of lithology. The 19 representative samples have shown that SiO₂ and Al₂O₃ of the granitoid range 66.07-73.99% and 12.94-15.23%, averagely 68.88% and 14.30% respectively,The K₂O/Na₂O ratio is high,ranging 1.41-2.21, with average of 2.06,A/CNK varies from 0.97 to 2.01,averagely 1.27,and mostly >1.1. So Lincang granites are high-K calc-alkaline and peraluminous to strongly peraluminous series. They are also enriched in LILE and Pb,but strongly depleted in HFSE. The REE content is between 173.58×10^-6 and 359.16×10^-6(average 240.13×10^-6), with （La/Yb）_N ratios of 6.69-15.72 （average 11.54） andδEu of 0.41-0.75（average 0.53）. The intrusion is remarkably characterized by enriched LREE and depleted HREE. The chondrite-normalized REE patterns show strong negative Eu anomalies. The zircon U-Pb age of the six samples is 227.00±0.80 Ma、219.19±0.99 Ma、219.69±0.67 Ma、203.38±0.70 Ma、211.9±1.8Ma and 214±2Ma, belonging to Late Tertiary. The SiO₂-Zr relationship and ACF plot indicated that the Lincang granite was S type granite. It mainly derives from clay-poor psammite. Lincang granite can be classified into the group of post-collisional granites in the Rb-Y+Nd discrimination diagram. In addition, Lincang granites are plotted into the low-Sr and high-Yb granites in the Sr-Yb discrimination diagram, in accordance with the granites in Southeast China, and should be formed during the transferring setting from compression to extension. Lincang granites have homogeneous zircon Hf isotopic composition. Their zircons have negativeεHf（t） Values（-14^-10） and old Hf-isotope Crust model ages （1.90².15Ga）, suggesting that Lincang granite was formed by partial melting of old crust. Therefore we consider that Lincang granite was formed in post-collisional stage between the Burma-Thai-Malaysia and Simao block in the late Triassic.更多还原