滇西腾冲-梁河地块石英闪长岩-二长花岗岩锆石U-Pb年龄、Hf同位素特征及其地质意义

U-Pb Dating and Hf Isotopic Compositions of Quartz Diorite and Monzonitic Granite from the Tengchong-Lianghe Block,Western Yunnan, and Its Geological Implications

高黎贡-腾梁花岗岩带是冈底斯花岗岩带的东延部分。腾梁花岗岩中辉长-闪长质包体、花岗岩、石英闪长岩密切共生。辉长-闪长质包体的结构构造、矿物学特征表明,它们是岩浆快速冷凝结晶的产物。地球化学数据显示,辉长-闪长质包体为钙碱性系列,具有低SiO2、高MgO和Mg#的特征,富集Rb、Sr、Th、Ba和Ce,亏损Nb、Ta、P、Zr、Yb和Y;寄主花岗岩为中钾—高钾钙碱性系列,准铝质到弱过铝质,富集Rb、Th、Zr和Hf,亏损Nb、Ta、Ti、Sr、P和Ba,具有中等程度的负Eu异常;石英闪长岩介于二者之间。锆石U-PbLA-ICP-MS定年显示,石英闪长岩形成年龄为127.10±0.96Ma,花岗岩形成年龄为123.8±2.5Ma。结合辉长-闪长质包体形成年龄为122.6Ma,三者年龄基本一致,从年代学角度为花岗岩、辉长-闪长质包体和石英闪长岩岩浆混合作用成因提供了证据。石英闪长岩锆石εHf(t)值变化于-7.61～-3.80。结合辉长-闪长质包体、花岗岩的εHf(t)值及地球化学特征,认为花岗岩来源于古老地壳的部分熔融,辉长-闪长质包体来源于地幔楔橄榄岩部分熔融,石英闪长岩为幔源岩浆与古老地壳部分熔融的岩浆完全混合的产物。腾梁地块早白垩世侵入岩很可能与班公湖-怒江洋壳岩石圈向南俯冲的动力学背景有关。

The Tengcong-Lianghe magmatic belt is the eastward extension of the Gangdese granite belt.Gabbro-diorite enclaves,granite,and quartz diorites in the Tengcong-Lianghe area have close spatial and temporal relationship.Morphological,structural,textural and mineralogical characteristics of gabbro-diorite enclaves indicate that these enclaves were the products of rapid condensation and crystallization of the intermediate and mafic magmas.Geochemical data show that the gabbro-diorite enclaves are calc-alkaline series, characterized by low SiO2,high MgO and Mg#,enrichment in the Rb,Sr,Th,Ba and Ce,depletion in Nb,Ta,P,Zr,Yb and Y.Host granites belong to medium to high-K calc-alkaline series,metaluminous weak peraluminous,and are enriched Rb,Th,Zr and Hf,depleted in Nb,Ta,Ti,Sr,P and Ba,with medium Eu negative anomaly.The quartz diorites lie between the gabbro-diorite enclaves and host granites.Zircon LA-ICP-MS dating indicates that the quartz diorites and monzonitic granites were emplaced at 127.10±0.96Ma and 123.8±2.5Ma,respectively,coeval with emplacement age（122.6± 0.8Ma）of gabbro-diorite enclaves,and this provides evidence for the mixing magmatic origin.Zircons from quartz diorite yieldεHf（t）values of-7.61to-3.80.Combined with gabbro-diorite enclaves,granite εHf（t）and their geochemical features,it is concluded that granite may be derived from partial melting of ancient crust,gabbor-diorite enclaves from partial melting of mantle-wedge peridotite,and quartz diorite from the mixing of mantle-derived magma and partial melting crust.Early Cretaceous intrusive rocks in the Tengchong-Lianghe block may be related to southward subduction of the Bangonghu-Nuiang oceanic lithosphere.