甘肃龙首山西山头窑地区中酸性岩体年代学、地球化学特征及构造意义  

Geochronology,Geochemistry and Tectonic Significance of Intermediate Acid Magmatic Rocks in Shantouyao Area,West of Longshou Mountain,Gansu Province

作　　者：董国强[1] 余君鹏[1] 李通国[1] 刘涛 张炜[1] Dong Guoqiang;Yu Junpeng;Li Tongguo;Liu Tao;Zhang Wei(Geological survey of Gansu Province,Lanzhou,Gansu,730000,China)

机构地区：[1]甘肃省地质调查院,甘肃兰州730000

出　　处：《新疆地质》2022年第3期425-433,共9页Xinjiang Geology

基　　金：甘肃省基础地质调查项目(甘国土资勘发[2017]64号)资助。

摘　　要：阿拉善地块南缘龙首山西段石炭—二叠纪岩浆活动受控于南侧祁连造山作用,还是与北侧的中亚造山带相关,一直存在争议。该问题直接影响到对本区构造属性的确定及进一步找矿方向。为此,作者通过野外露头及岩心观察、结合室内薄片鉴定、岩石化学分析及年龄测试,对该区中酸性岩体的岩相学、年代学、地球化学等方面进行了综合研究,认为山头窑地区有3个期次岩浆侵入,第一期次侵入岩为白岗岩,为钙性-钙碱性、强过铝质花岗岩,^(206)Pb/^(238)U加权平均年龄为(304.3±2.2)Ma,^(87)Sr/^(86)Sr初始值为0.712568,^(143)Nd/^(144)Nd初始值为0.512205,具壳幔混合型花岗岩特征,可能与俯冲环境有关;第二期次侵入岩为石英闪长岩,为偏铝质、钙性-钙碱性岩系,显示火山弧花岗岩特点,^(206)Pb/^(238)U加权平均年龄为(287.5±2.4)~(285.2±1.6)Ma;第三期次侵入岩为二长花岗岩体,为碱钙性-钙碱性岩系,过铝质,具后造山花岗岩特征,^(206)Pb/^(238)U加权平均年龄为(281.2±1.7)Ma。研究认为,山头窑地区中酸性岩体形成于华里西期,与阿拉善陆块霍尔森-查干楚鲁西端弧后洋盆扩张、俯冲及闭合过程相关,为古亚洲洋向南俯冲的结果,与阿拉善中北部广泛分布的中酸性岩浆岩形成时代相近,特点相似,可做对比。It has been controversial whether the Carboniferous Permian magmatic activity in the Western Longshou section of the southern margin of the Alxa block was controlled by the Qilian orogeny in the South or related to the Central Asian orogenic belt in the north.The solution to the problem directly affects the determination of structural attributes and the selection of further ore-prospecting direction in this area.By studying field outcrops and cores,combined with thin section identification,petrochemical analysis and age test,the author acquitted some data on the petrography,chronology and geochemistry of medium acid rock mass in this area.The shantouyao area magmatic intrusion could be divided into three stages.The first stage was alaskite with the^(206)Pb/^(238)U weighted average age of(304.3±2.2)Ma.Its initial data of^(87)Sr/^(86)Sr is 0.712568 and^(143)Nd/^(144)Nd is 0.512205.They are characterized by calc alkaline,strongly peraluminous belongs to crust-mantle mixed type granite.It may be related to subduction environment.The second stage is quartz diorite with the^(206)Pb/^(238)U weighted average age of(287.5±2.4)Ma-(285.2±1.6)Ma,which belongs to aluminous calc alkaline rock series,showing the characteristics of subduction related volcanic arc granite.The third stage is monzonitic granite with a weighted average age of(281.2±1.7)Ma,peraluminous with the characteristics of post orogenic granite.According to the study,the Variscan intermediate acid pluton in Shantouyao area is related to the expansion,subduction and closure of the back arc ocean basin at the western end of halsen-chaganchulu,Alxa landmass,resulting from the southward subduction of the paleo Asian Ocean.It is similar to the formation age and characteristics of intermediate acid magmatic rocks widely distributed in the north central Alxa,and can be compared.

关 键 词：岩浆岩 锆石U-PB定年 SR-ND同位素 地球化学 龙首山 阿拉善 

分 类 号：P597.3[天文地球—地球化学] P59[天文地球—地质学]