冈底斯带加杜早白垩世花岗闪长岩LA-ICP-MS锆石U-Pb测年、地球化学及地质意义

加杜早白垩世花岗闪长岩体侵位最新地层为中晚侏罗世拉贡塘组,后被晚白垩世二长花岗岩及中新世花岗闪长岩、二长花岗岩侵入,岩石具高Al2O3、Na2O和低TiO2、MgO、MnO特征,属准铝质高钾钙碱性系列岩石(KCG)。在球粒陨石标准化稀土元素分布模式上表现为右倾,在原始地幔标准化蛛网图上,富集Rb,Th和亏损Ba,Nb,P,Ti,呈明显与俯冲作用有关的Nb和Ti谷,岩石可能为地幔玄武岩浆在底侵过程中诱发上地壳物质部分熔融形成,岩体在就位过程中分离结晶作用不明显。通过对石英闪长岩进行LA-ICP-MS锆石U-Pb测年,获得岩石结晶年龄为(127.6±1.5) Ma(n=16,MSWD=0.91),形成时代为早白垩世。花岗闪长岩形成构造背景可能与班公湖-怒江洋向南俯冲有关。

LA-ICP-MS Zircon U-Pb Dating,Geochemical Analysis and Geological Significance of the Early Cretaceous Granodiorite in Jiadu,Gangdise

The latest emplacement stratum of the early Cretaceous granodiorite mass in Gardu is the middle-late Juras- sic Lagongtang Group,which was later invaded by late Cretaceous monzogranite,Miocene granodiorite and monzogranite. The mass is characterized by high Al2O3 and Na2O,low TiO2、MgO and MnO,belongs to the quasi aluminum,high potassi- um,calcium alkaline series rock (KCG).Chondrite normalized rare earth elements show relative enrichment of LREE, with right dipping distribution patterns.Primitive mantle normalization spider diagram reveals that the diorite is rich in Rb and Th,deplete in Ba,Nb,P and Ti, and also shows significant Nb and Ti valleys associated with subduction, indicates the mass may be formed by partial melting of upper crust materials induced by mantle basaltic magma during bottom in- vasion and the separation and crystallization are not obvious in the process of emplacement.LA-ICP-MS zircon U-Pb dat- ing of the granodiorite yields an age of (127.6±1.5) Ma (n=16,MSWD=0.91),a magmatic activity product of early Creta- ceous period.The tectonic setting of granodiorite may be related to the southward subduction of Bangonghu-Nujiang ocean.