腾冲地块晚白垩世小龙河花岗岩年龄及其成矿意义

Geochronology and mineralization significance of the Late Cretaceous Xiaolonghe granite in the Tengchong Block

为厘定腾冲地块晚白垩世构造岩浆活动和花岗岩成矿意义,对小龙河花岗岩开展全岩地球化学、年龄和锶-钕-铅同位素研究。小龙河花岗岩由细粒淡色二长花岗岩和似斑状黑云母二长花岗岩组成,锆石U-Pb年龄数据指示它们的岩浆结晶年龄分别为67.0±1.0 Ma和68.5±1.6 Ma,辉钼矿Re-Os模式年龄分别为67.15±0.99 Ma和69.02±1.22 Ma,同为晚白垩世构造岩浆活动产物。锶-钕-铅同位素与主量和微量元素特征表明,细粒淡色二长花岗岩为S型花岗岩((^(87)Sr/^(86)Sr)_(i)=0.757~0.763);ε_(Nd)(t)=-8.89~-8.99,岩浆起源于中元古代(TDM2=1.59~1.60 Ga)上地壳富粘土硬砂岩部分熔融,其与小龙河锡-钨多金属矿床形成密切相关;似斑状黑云母二长花岗岩为I型花岗岩((^(87)Sr/^(86)Sr)_(i)=0.711,ε_(Nd)(t)=-8.72~-9.16),岩浆起源于中元古代(TDM2=1.58~1.62 Ga)下地壳富粘土硬砂岩重熔。腾冲地块晚白垩世小龙河花岗岩及其锡-钨矿化是中特提斯班公-怒江洋闭合后腾冲地块与保山地块碰撞-后碰撞阶段引发的岩浆活动与热液作用的产物。

In order to determine the Late Cretaceous tectonomagmatic activities and the significance of granite mineralization in the Tengchong Block,this study applied the comprehensive methods of geochronology,Sr-Nd-Pb isotopic and whole-rock geochemical analyses to probe Xiaolonghe granites.The results show that the Xiaolonghe pluton is composed of fine-grained leuco-monzogranite and porphyritic-like biotite monzogranite.Zircon U-Pb chronological data indicate that their magmatic crystallization ages are 67.0±1.0 Ma and 68.5±1.6 Ma respectively,and the Re-Os model ages of molybdenite are 67.15±0.99 Ma and 69.02±1.22 Ma respectively,both of which are the products of the Late Cretaceous tectonomagmatic activities.The characteristics of Sr-Nd-Pb isotopes and major and trace elements show that the fine-grained leuco-monzogranite is S-type granite((^(87)Sr/^(86)Sr)_(i)=0.757~0.763,ε_(Nd)(t)=-8.89~-8.99),and the magma originated from the partial melting of clay-rich hard sandstone in the upper crust of Mesoproterozoic(TDM2=1.59~1.60 Ga),which is closely-related to the formation of Xiaolonghe tin-tungsten polymetallic deposit.The porphyritic-like biotite monzogranite is I-type granite((^(87)Sr/^(86)Sr)_(i)=0.711,ε_(Nd)(t)=-8.72~-9.16),and the magma originated from the remelting of clay-rich hard sandstone in the lower crust of Mesoproterozoic(TDM2=1.58~1.62 Ga).The Late Cretaceous Xiaolonghe granites and its tin-tungsten mineralization in the Tengchong Block are the products of magmatic activity and hydrothermal process caused by the collision or post-collision between the Tengchong Block and the Baoshan Block after the closure of the Meso-Tethys Bangong-Nujiang ocean.