柴北缘滩间山地区独树沟金矿花岗斑岩锆石U-Pb年代学、地球化学和Hf同位素

Zircon U-Pb geochronology, geochemistry, and Hf isotope of the granite porphyry in the Dushugou gold deposit, Tanjianshan area, North Qaidam

本文报道了柴北缘滩间山地区独树沟金矿区花岗斑岩的地球化学、锆石U-Pb定年和Hf同位素的研究结果。全岩化学分析显示岩石具有富硅(SiO2=75.23%~77.28%)、钠(Na2O/K2O=1.71~2.41),贫铁(TFe2O3=1.04%~3.24%)、镁(MgO=0.28%~0.39%)、钙(CaO=0.23%~0.75%)、铝(Al2O3=13.09%~13.73%)的特征;样品富集大离子亲石元素如Rb、K、Th和U,明显亏损高场强元素Nb、Ta、Ti和P,富集轻稀土元素,亏损重稀土元素,岩石具有较强的Eu负异常(δEu=0.49~0.53),分异指数DI为90.76~93.71,指示岩石发生了较强的结晶分异作用,通过与邻区花岗岩进行特征对比,判断独树沟花岗斑岩为高分异I型花岗岩;锆石U-Pb定年显示,独树沟花岗斑岩形成于350.8±1.7Ma;锆石Hf同位素显示,独树沟花岗斑岩的锆石ε(Hf)(t)值为+1.82^+9.19,平均值为+6.85,二阶段模式年龄(t(DM2))为768~1238Ma,独树沟花岗斑岩的Hf同位素组成变化较大,指示其源区物质组成较为复杂,以新元古代新生地壳物质为主,有中元古代甚至更古老的地壳物质存在。结合柴北缘古生代构造演化历史,认为独树沟花岗斑岩形成于早古生代碰撞造山之后的伸展环境。

In this article, we report the geochemical, zircon U-Pb dating, and Hf isotope data from granite porphyry in the Dushugou gold deposit, Tanjianshan area, in the North Qaidam. Bulk-rock analyses show that this intrusion is characterized by the enrichment in silica(SiO2=75.23%~77.28%), sodium(Na2O/K2O=1.71~2.41), and depletion in iron(TFe2O3=1.04%~3.24%), magnesium(MgO=0.28%~0.39%), calcium(CaO=0.23%~0.75%), and aluminum(Al2O3=13.09%~13.73%). The rocks are enriched in large-ion lithophile elements, such as Rb, Th, U, and K, and depleted in the high-field-strength elements, such as Nb, Ta, Ti and P. The rocks are enriched in light rare earth elements relative to heavy rare earth elements, and have obvious negative Eu anomaly(δEu=0.49~0.53). Furthermore, the differentiation index(DI) of the Dushugou granite porphyry ranges between 90.76 to 93.71, which is the characteristic of strong crystallization differentiation. Based on the comparison of the characteristics with the adjacent granite, we propose that the Dushugou granite porphyry is highly differentiated I-type granite.Zircon U-Pb dating of the Dushugou granite porphyry yields magmatic crystallization ages of 350.8±1.7 Ma, with the εHf(t) values ranging from +1.82 to +9.19, with an average value of +6.85, and a two-stage Hf model age(tDM2) range from 1238 to 768 Ma. The variation range of Hf isotopic composition of the Dushugou granite porphyry is large, suggesting that the material composition of its source area is relatively complex.The magma source was dominated by Neoproterozoic juvenile accreted crustal materials, mixed with Mesoproterozoic and even older crustal materials.Based on the Paleozoic tectonic evolution history of the Northern Qaidam, it is concluded that the Dushugou granitic porphyry was formed in the extensional environment after collisional orogeny in Early Paleozoic.