摘要：
柴达木北缘乌兰地区花岗岩类大多数为镁质类型钙碱性系列,少数为铁质类型碱钙性和碱性系列.其中,早期花岗岩类不仅富集大离子亲石元素,而且还富集部分高场强元素(Zr、Y、Nb等),属A型花岗岩;晚期花岗岩类以富集大离子亲石元素,亏损高场强元素为特征,稀土元素以富集轻稀土、且轻稀土分异明显重稀土分异不明显、不具有或具有弱的负Eu异常为特征,属Ⅰ型花岗岩.同位素地球化学研究表明,早期花岗岩类的n(87Sr)(86Sr)值为0.7108和Nd模式年龄(T1DM)2.10Ga,高于晚期花岗岩(0.7076 ～0.7107,T2DM=1.41～1.58Ga),但晚期花岗岩的εNd(t)值(-11.6)低于早期花岗岩(-4.8～-6.8),表明早期花岗岩可能起源于古元古代的大陆地壳,而晚期花岗岩起源于中元古代玄武质地壳,结合区域地质构造特征,笔者等认为,早期花岗岩类的形成与祁连岩石圈拆沉导致欧龙布鲁克陆块北缘减薄、拉伸有关,也标志着宗雾隆裂陷的开始;而晚期花岗岩类的形成可能与宗雾隆洋壳向南俯冲于欧龙布鲁克陆块之下有关.%Objectives:A large number of granite bodies are exposed in the Wuland area adiacennt to the Dulan UHP terrain.In addition to a few studies,the geochemical characteristics and genesis of these granites and their tectonic significance are almost not much studied.Especially,the genetic relationship between the granites from Wulan and others in the North Qaidam UHP belt remains unclear.Therefore,our research focuses on the petrogenesis of the granite and its regional tectonic significance.Methods:Based on the field work,through the microscope observation,the whole rock chemical analysis and the Sr—Nd isotopic analysis of the granites,we determine the the granite affinity and petrogenesis.Combined with regional tectonic characteristics and other research achievements of granite in North Qaidam,we discuss the tectonic significance of granite from Wulan.Results:Gechemically,most of the granites from Wulan area,northern Qaidam belong to magnesian calc-alkaline series,a few to iron alkali-calc and alkaline series.The early granite is not only enriched in large ion lithophile elements (LILE),but also enriched in part of high field strength elements (HFSE) (such as Zr,Y,Nb),which belongs to A-type granite.The late granitoids are enriched in LILE and light rare earth elements (LREE),depleted in HFSE,and had LREE differentiation to be obvious but heavy rare earth element (HREE),with a weak negative Eu anomalies in REE patterns,which belongs to the I-type granite.The isotopic geochemistry shows that the 87Sr/86Sr ratio of the early granitoids is 0.7108 and Nd model age (T2DM) 2.10Ga,higher than those of late granites (87Sr/86Sr =0.7076 ～ 0.7107,T2DM =1.41Ga ～ 1.58Ga),but εNd(t) value of late granites (-11.6) are lower than that of the early granite (-4.8 to-6.8),indicating that early granite may originate from the Paleoproterozoic continental crust and the late granite from the Middle Proterozoic basaltic crust.Conclusions:This study shows that the early granitoid in Wulan area are related to the Qilian lithospheric delamination,which causes the thinning and stretching of Oulongbuluke continent block,also marks the beginning of Zongwulong rift;and the lategranitoids in the area are related to the oceanic crust subduction of Zongwulong under the Oulongbuluke continent block.
