滇西加里东期平河复式花岗岩体锆石U-Pb年龄、Hf同位素特征及其风化壳型稀土矿成矿认识

加里东期平河复式花岗岩体位于滇西保山地块西部边缘，其岩石类型主要为二长花岗岩、似斑状二长花岗岩。平河复式花岗岩体主量元素显示岩石全碱（w（K₂O+Na₂O））值分别为6.89%和7.44%，K₂O/Na₂O值分别为1.59和2.65，铝饱和指数（A/CNK）值分别为1.58和1.76，里特曼指数（σ）分别为1.65和1.73；微量稀土元素显示岩石总体上富集Rb、Th等大离子亲石元素，亏损Ta、Nb等高场强元素，轻稀土元素富集，LREE/HREE值分别为1.40和6.43，具低-中等负铕异常（δEu=0.16和0.75）。2件花岗岩样品的锆石U-Pb年龄变化于478~476 Ma，表明这些花岗岩类侵位于早奥陶世；2件样品38颗锆石测点的ε_Hf（t）值显示较大的变化范围，对应的Hf同位素地壳模式年龄集中在2.2~1.7 Ga。这些地球化学特征显示平河复式花岗岩体属钙碱性过铝质S型花岗岩，为泛非运动构造碰撞后应力松弛阶段产物，其形成可能与滇西地区原特提斯地史阶段地块挤压碰撞、裂离过程密切相关。在大团山地区，该期岩体中首次发现含稀土矿物——锰铁铈氧化物，其对全风化岩体稀土氧化物总量贡献最大；岩体风化壳稀土氧化物总量（REO）总体不高，为279.05×10^-6~791.77×10^-6，总体富集Y、La、Ce元素，局部轻稀土元素Nd富集，重稀土镝氧化物配分较高，为2.30%~4.62%。大团山稀土矿点的发现，表明滇西加里东期花岗岩亦有寻找花岗岩风化壳型稀土矿的潜力。

Zircon U-Pb Age and Hf Isotope Characteristics of Caledonian Pinghe Composite Granite Pluton: Its Mineralization of Granite Weathering Crust Type REE Deposit

The Caledonian Pinghe composite granite pluton is located on the western edge of Baoshan block in western Yunnan, which consists mainly of monzonitic granite and porphyritic monzonitic granite. The major elements show that the total alkali (w(K₂O+Na₂O)) values are 6.89% and 7.44%, the K₂O/Na₂O values are 1.59 and 2.65, A/CNK values are 1.58 and 1.76, and the Rittmann indexes (σ) are 1.65 and 1.73; the trace and REE elements show that these rocks are rich in large-ion lithophile elements (Rb、Th) and depleted of high field-strength elements (Ta、Nb), enriched light rare-earth elements with LREE/HREE value of 1.40 and 6.43, and low-middle Eu anomalies (δEu=0.16 and 0.75). The zircon U-Pb ages of 478-476 Ma indicate that this pluton was emplaced during the Early Ordovician. 38 analyses from the two samples provide a wide range of zircon ε_Hf(t) values, and the corresponding Hf-isotope crustal model ages are 2.2-1.7 Ga. The geochemical characteristics show that Pinghe composite granite pluton is calc-alkaline and per-aluminous S-type granite formed in a stress relaxation stage after the tectonic collision of pan-african movement, and closely related to the process of extrusion, collision, and dissociation during the period of original Tethys geological event in western Yunnan. In Datuanshan, ferromanganese cerium oxide, a rare earth mineral, is found in Caledonian Pinghe composite granite pluton for the first time, which contributes the most to REO in the entirely weathered rock mass. The REO is generally not high, ranging from 279.05×10^-6 to 791.77×10^-6, overall enrichment of Y, La, Ce elements, and partial enrichment of Nd. The heavy rare earth dysprosium oxide accounts for a high proportion in all of the fully weathered rock mass, were 2.30% to 4.62%. The discovery of Datuanshan rare earth mine shows that the Caledonian granite also has a potential for the granite weathering crust type REE deposit in western Yunnan.