西藏班公湖怒江结合带中段恐弄拉地区卡来花岗闪长斑岩岩石地球化学特征、锆石U-Pb年代学及其构造背景

Rock geochemistry,Zircon U-Pb Geochronology and Structural Background For Granodiorite Porphyry of Kalai of Kongnongla Area in the Middle Part of the Bangong Lake-Nujiang Belt,Tibet

卡来花岗闪长斑岩是班怒带演化的重要岩浆活动记录,通过采用LA-MC-ICP-MS技术对其进行锆石U-Pb同位素年龄测定,年龄为175.0±2.7Ma(n=15,MSWD=3.4)。微量元素原始地幔标准化数据显示岩石具富集K、Rb、Th大离子亲石元素,亏损Nb、Ta、Zr、Hf、P高场强元素的特征。ΣREE平均203.67×10-6,LREE平均149.12×10-6,HREE平均21.53×10-6,LREE/HREE平均为6.93,属典型轻稀土富集型,稀土元素球粒陨石标准化显示轻稀土高分馏而重稀土微弱分馏—无分馏。通过各类适用于中酸性岩石的地球化学图解判定,认为该岩体是班公湖—怒江洋盆萎缩过程中于中侏罗世早期(阿林期)向南侧冈底斯地块俯冲环境下的岛弧岩浆产物,物质来源主要为地壳熔融产物,并混入了靠近俯冲带的深海沉积物。

The Kalai granodiorite porphyry is an important magmatic activity record of the evolution of the Bangong Lake-Nujiang Belt The zircon U-Pb isotopic age of granodiorite porphyry was determined by LA technique at 175 0±2 7 Ma Trace Elemental mantle normalization data show that the rocks are enriched with large ion lithophile elements including K and Rb and Th,loss high field strength elements including Nb and Ta and Zr and Hf and P The mean values ofΣREE,LREE,HREE and LREE/HREE of the rocks are 203 67×10-6,149 12×10-6,21 53×10-6 and 6 93 respectively,the rocks are light rare earth type Standardization of rare earth element chondrites shows that rocks have a rare fraction of light rare earth and a heavy fraction of heavy rare earth fractions According to geochemical illustrations,the author thinks that the granodiorite porphyry is an island arc magmatic product in the subduction of the Bangong Lake-Nujiang ocean basin during the early Jurassic(Aalenian),and The main source of matter is the crustal melting product and the deep sea sediments of the subduction zone.