东昆仑扎玛休玛地区含矿花岗闪长斑岩LA-ICP-MS锆石定年及地质意义

LA-ICP-MS U-Pb ZIRCON DATING AND GEOLOGICAL SIGNIFICANCE OF ORE-BEARING GRANODIORITE PORPHYRY IN ZAMAXIUMA AREA,EAST KUNLUN

东昆仑东段扎玛休玛地区中—酸性岩浆活动较为发育,但受其交通限制,研究程度较低,特别是与铜铅锌多金属矿化有关的花岗闪长斑岩前人鲜有研究。本次针对扎玛休玛地区的含矿花岗闪长斑岩进行了研究,通过LA-ICP-MS锆石U-Pb测年和岩石地球化学研究。明确了扎玛休玛地区含矿花岗闪长斑岩侵位年龄为229.5±1.3 Ma,属于晚三叠世。地球化学研究表明含矿花岗闪长斑岩w(SiO_(2))含量在67.22%-70.21%之间,w(Al_(2)O_(3))为13.51%-15.28%,w(K_(2)O)为3.48%-4.27%,全碱含量w(K_(2)O+Na_(2)O)为5.98%-7.41%,w(K_(2)O/Na_(2)O)=1.20-1.52,显示富钾贫钠特点,里特曼指数σ值为1.33-2.23,在w(SiO_(2))-w(K_(2)O)关系图上落入高钾钙碱性系列,A/CNK值为1.02-1.14,平均1.07,属过铝质岩石;ΣREE=147.42-202.29×10^(-6),LREE/HREE=11.15-15.29,(La/Yb)_(N)=13.42-20.11,具轻稀土富集、重稀土亏损的右倾曲线,δEu介于0.34-0.43,显示负异常特征,大离子亲石元素Rb,K,Ba,Th等相对富集,高场强元素Nb,Ta,P,Ti相对亏损特征,具有火山弧花岗岩特征;结合构造背景判别图解及区域构造背景,认为花岗闪长斑岩为晚三叠世形成后碰撞构造阶段的火山弧花岗岩。

The intermediate-acid magmatic activity is relatively well developed in Zamaxiuma area in the eastern part of east Kunlun,but the research degree,especially granodiorite porphyry related to the copper-lead-zinc polymetallic mineralization,is relatively low due to the traffic restriction.In this study,LA-ICP-MS zircon U-Pb dating and petrogeochemical analysis have been used to study the ore-bearing granodiorite porphyry in the Zamaxiuma area.Geochronology study reveals that the emplacement age of granodiorite porphyry is 229.5±1.3 Ma,which belongs to late Triassic period.Geochemical analyses show that the content of w(SiO_(2))is 67.22%-70.21%,w(Al_(2)O_(3))is 13.51%-15.28%,w(K_(2)O)is 3.48%-4.27%,and the total alkali content of w(K_(2)O+Na_(2)O)is 5.98%-7.41%.w(K_(2)O/Na_(2)O)=1.20-1.52,indicating the characteristics of rich potassium and poor sodium.Its Litterman indexσvalue ranges from 1.33 to 2.23.In the w(SiO_(2))-w(K_(2)O)diagram,the rock falls into the high potassium calc-alkaline series with the A/CNK value(1.02-1.14,average 1.07),indicating that the granodiorite porphyry belongs to peraluminous rock.Trace element and rare earth element analysis reveal that theΣREE=147.42-202.29×10^(-6),LREE/HREE=11.15-15.29,(La/Yb)N=13.42-20.11,with right-leaning curve of LREE enrichment and HREE depletion.δEu is between 0.34-0.43,showing negative anomaly characteristics.Large ion lithophile elements such as Rb,K,Ba and Th are relatively enriched,while high field strength elements,such as Nb,Ta,P and Ti,are relatively depleted,which is characterized by volcanic arc granite.Based on the comprehensive analysis of regional tectonic setting,combined with the tectonic setting discrimination diagram of the area,it is considered that the granodiorite porphyry belongs to volcanic arc granite which was formed in the collision tectonic stage in late Triassic period.