甘肃北祁连武威地区莲花山花岗岩体的单颗粒锆石U-Pb年龄及其地质意义

Single-grain zircon U-Pb ages and geological significance of the Lianhuashan granites from Wuwei (Gansu) in the Northern Qilian orogenic belt

在1：25万武威幅区域地质调查中对北祁连莲花山花岗岩体进行了调查研究,通过高精度单颗粒锆石 U-Pb同位素测年,获得w（206Pb）/w（238U）表面年龄统计权重平均值为426±15 Ma,属加东晚期.岩石化学和地球化学特征表明莲花山岩体属钙碱性系列,少量为高钾钙碱性系列.σ=0.6～2.3, A/CNK=0.81～1.04,ΣREE=68.58～188.76, LREE/HREE=2.80～5.09,δEu=0.60～0.87.研究表明莲花山岩体形成于陆？陆碰撞造山阶段后期,可能形成于加厚地壳的部分熔融.

Petrological and geochemical characteristics as well as formation ages of the Lianhuashan granitic pluton were investigated during the regional geological survey （scale 1：250 000） in Wuwei, Qilian Mountains. High-precision single-grain zircon U-Pb dating results yielded weighted an average age of 426±15 Ma for fine-to middle-grained granodiorite and porphyritic adamellite in the Lianhuashan pluton, respectively, indicating that the pluton was formed in the late Caledonian. The Lianhuashan granitic rocks are calc-alkaline in major elements and are plotted in the field of volcanic arc and syn-collisional granite,σ=0.6～2.3, A/CNK=0.81～1.04,ΣREE=68.58～188.76, LREE/HREE=2.80～5.09, δEu=0.60～0.87. It is proposed that the Lianhuashan pluton was formed by partial melting at the late stage of a continent-continent collision.