【摘要】 拉萨地块中-南部广泛分布着三叠—早侏罗世花岗岩,拉龙松多花岗岩为其中一个岩体,通过对该岩体样品的U-Pb年代学和地球化学测试分析发现,拉龙松多花岗岩中的岩浆锆石U-Pb加权平均年龄为178.3 Ma±2.3 Ma,MSWD=1.4,表明拉龙松多花岗岩的形成时代为早侏罗世。岩石地球化学方面,拉龙松多花岗岩具富w（SiO₂）77.62%～78.94%,w（K₂O）3.34%～4.35%,w（Na₂O）1.86%～2.28%,贫w（CaO）0.05%～0.48%,w（Ti₂O）0.09%～0.10%,富w（Al₂O₃）11.78%～12.80%的特征;属于强过铝质高钾钙碱性系列-钙碱系列（A/CNK=1.43～1.61）。拉龙松多花岗岩轻稀土元素（LREE）含量介于82.01×10^-6～91.97×10^-6之间,重稀土元素（HREE）含量介于12.67×10^-6～15.94×10^-6之间,LREE/HREE介于5.49～6.58之间,具明显轻稀土相对富集,重稀土相对亏损特征,Eu负异常明显（δEu=0.25～0.34）,球粒陨石标准化分布模式呈典型的右倾V型。微量元素显示,拉龙松多花岗岩样品中的大离子亲石元素（Rb,Th,U等）相对富集,高场强元素（Nb,Ta,Sr,P,Ti等）相对亏损,同时相对Rb而言亏损Ba。上述岩石地球化学特征显示出其具有S型花岗岩的特征;在相关地球化学图解中样品位于S型花岗岩区域。综合分析,认为拉龙松多S型花岗岩应该形成于洋壳俯冲向高角度转换,俯冲带之上出现的伸展环境下。更多还原

【Abstract】 Triassic to early Jurassic granite is widely distributed in the middle-south Lhasa terrane.U-Pb dating geochronology and geochemical analysis are carried out to study the formation age and geochemical characteristics of the Lalongsong granite in the area.Magmatic zircon U-Pb age dating for Lalongsong granite yields a weighted mean age of 178.3 Ma±2.3 Ma（MSWD=1.4）,an early Jurassic magmatic product.Geochemical analysis reveals that Lalongsong granite is rich in w（SiO₂） 77.62%～78.94%,w（K₂O） 3.34%～4.35%,w（Na₂O）1.86%～2.28%,w（Al₂O₃）11.78%～12.80%; poor in w（CaO）0.05%～0.48%,w（Ti₂O）0.09%～0.10% and belongs to strong aluminous high potassium calc-alkaline series-calcium base series（A/CNK=1.43～1.61）.Light rare earth element（LREE） content of the rock is in the range of 82.01×10^-6～91.97×10^-6,and heavy rare earth element（HREE） content is between 12.67×10^-6～15.94×10^-6,with LREE/HREE ranging from 5.49 to 6.58,showing obvious enrichment of light rare earths,relative loss of heavy rare earths and obvious Eu negative anomaly（δEu=0.25～0.34）.The normal distribution pattern of chondrite of the Lalongsong granite is typical right-inclined V-type.Trace element analysis shows that the large ion lithophile elements（Rb,Th,U,etc.） in the Lalongsong granite are relatively enriched,and the high field strength elements（Nb,Ta,Sr,P,Ti,etc.） are relatively depleted,while Ba is depleted relative to Rb.The geochemical characteristics and relevant geochemical diagrams of the Lalongsong granite display characteristics of S-type granites.Based on the comprehensive analysis,it is considered that the Lalongsong S-type granite is formed in the extension environment on the upper slab of the subduction zone.更多还原