西天山阿吾拉勒成矿带察汉乌苏铁矿赋矿玄武岩的成因:锆石U-Pb年代学、地球化学及Hf同位素约束

Genesis of the Host Basalt of the Chahanwusu Iron Deposit in the Awulale Metallogenic Belt of the Western Tianshan Mountains:Zircon U-Pb Chronology,Geochemistry and Hf Isotope Constraints

西天山为中亚成矿域的重要组成部分,是我国重要的富铁矿资源基地。察汉乌苏铁矿位于阿吾拉勒成矿带东段,赋存于石炭系大哈拉军山组火山岩中,目前火山岩成因认识还存在较大分歧,通过探讨火山岩成因,为深入找矿及区带研究提供新资料。通过对赋矿玄武岩岩石地球化学分析发现,玄武岩具相对较高Al_(2)O_(3),Na_(2)O,K_(2)O,低MgO,CaO,TiO_(2),里特曼指数(σ)为0.46~3.03,均小于3.3,岩石系列为钙碱性系列;玄武岩富集大离子亲石元素Rb,Th,U,K,亏损高场强元素Nb,Ta,P,Ti;微量、稀土元素分布模式介于OIB和EMORB之间。赋矿玄武岩形成于大陆岛弧火山岩环境。通过对玄武岩锆石U-Pb测年,获得^(206)Pb/^(238)U加权平均年龄为(325.3±2.8)Ma,属早石炭世末期。玄武岩锆石Lu-Hf同位素单阶段模式年龄tMD1为(522.24~642.70)Ma;二阶段模式年龄tMD2为(634.66~830.79)Ma,表明成岩成矿物质来源于亏损地幔并有新元古代基底物质加入。结合区域构造背景认为,察汉乌苏铁矿成矿作用发生于早石炭世末期北天山古洋盆向南侧俯冲和消亡过程地球动力学背景下。

As an important component of the Central Asian metallogenic domain,the West Tianshan Mountains are an important iron ore rich resource base in China.Chahanwusu iron ore deposit is located in the eastern part of the Awulale metallogenic belt.The iron ore deposit occurs in the volcanic rocks of the Carboniferous Dahalajunshan Formation.At present,there are still big differences in the understanding of the origin of volcanic rocks.In order to explore the origin of volcanic rocks,new data will be provided for in-depth ore prospecting and regional research.Based on the geochemical analysis of the host basalt rocks,it is found that the basalt has relatively high Al_(2)O_(3),Na_(2)O,K_(2)O,and low MgO,CaO,TiO_(2),and Littman index(σ)0.46 to 3.03 are all less than 3.3,and the rock series is a calcium alkaline series;Basalt is rich in large ion lithophile elements Rb,Th,U,K,and lacks high field strength elements Nb,Ta,P,Ti;The distribution patterns of trace and rare earth elements are between OIB and EMORB.The host basalt was formed in a continental island arc volcanic environment.Through zircon U-Pb dating of basaltic rocks,a weighted average age of^(206)Pb/^(238)U was obtained to be 325.3±2.8 Ma,indicating a late Early Carboniferous period.The single stage model age tMD1 of zircon Lu Hf isotopes in basalt ranges from 522.24-642.70 Ma;The second stage model age tMD2 is 634.66-830.79 Ma,indicating that the diagenetic and diagenetic materials are derived from depleted mantle and added by Neoproterozoic basement materials.Combined with the regional tectonic background,it is believed that the mineralization of Chahan Wusu iron ore occurred in the Geodynamics background of the southern subduction and extinction process of the northern Tianshan ancient ocean basin at the end of the Early Carboniferous.