青海窑洞山地区晚奥陶世花岗岩岩石地球化学特征及地质意义

Geochemical characteristics and geological significance of Late Ordovician granite in Yadongshan Area of Qinghai Province

对青海省格尔木窑洞山地区四道沟侵入岩进行岩石学、岩石化学、微量元素的分析及研究,主要岩石类型有二长花岗岩、二云母二长花岗岩和白云母花岗岩等,SiO_2含量为65. 65%～77. 32%,K_2O、Na_2O分别含量为2.78%～7.73%和1.26%～5.78%,显示钙碱性系列特征,σ=0.61～2.07,Al_2O_3>CaO+K_2O+Na_2O,A,CNK=1. 09～2.48,为中高钾过铝质岩石。LREE/REE=3. 30～6.24,δEu=0.37～0. 56,均小于1,具明显的负铕异常。K、Rb、Ba、Th、Ce富集,其中Ba具负异常特征,Ta、Zr亏损,具碰撞花岗岩特征。由上述特征表明,窑洞山地区的晚奥陶世花岗岩具壳源花岗岩(S型)特征,是非典型碰撞型花岗岩,形成于岛弧或陆缘弧部位。同时在四道沟西侧的二云母二长花岗岩中获得(471±2)Ma LA-ICP-MS锆石U-Pb年龄,为东昆仑地区古生代多级构造—岩浆演化提供了精确的地质时代证据。

The analysis and study of petrology, petrochemistry and trace elements of the Sidao gou in Yaodongshan area of Golmud City, Qinghai Province, the main rock types are monzonite granites, Biotite-Mus monzonite granites and muscovite granites, the rocks have the following chemical composition:siO2 = 65.65 %~ 77.32 %, K2O and Na2O are different between 2.78%~7.73 % and 1.26%~5.78 %, This indicates the granite rocks with the character of calcium alkalescence siries.σ= 0.61 ~ 2.07, Al2O3 > CaO + K2O + Na2O, A/CNK = 1.09 ~ 2.48, They are medium-high potassium aluminum rocks. LREE/REE = 3.30 ~ 6.24,Δ Eu = 0.37 ~ 0.56, all less than 1, indicate Eu pronounced Obviously negative abnormalty. K, Rb, Ba, Th, Ce are abundant, of which Ba has negative abnormalty, Ta, Zr are loss-making, with collision granite characteristics. From the above characteristics, it is shown that the late Ordovician granites in the Yaodongshan area are Crustal granite(S-type granite), Atypical Syn-Collision granite,formed in island arcs or continental margin arcs. At the same time, We took a sample of the Biotite-Mus monzonite granites in the Yaodongshan area to analys U-Pb age.The LA-ICP-MS U-Pb age analyses show that the granite ages of late Ordovician are (471±2)Ma, the zircon trace elements age provide accurately Geological Age on the Paleozoic multi-stage tectonic-magmatic events of the Eastern Kunlun area.