柴达木北缘大通沟南山岩体锆石U-Pb同位素年代学及其地质意义

Zircon U-Pb isotope chronology dating of Nanshan rock mass in the Datonggou area,northern margin of Qaidam Basin and its geological significance

大通沟南山岩体出露于柴达木北缘与阿尔金构造带结合部位,侵入于新元古界青白口系索尔库里群之中。岩石化学特征表明,大通沟南山岩体中的二长花岗岩属高钾钙碱性过铝质花岗岩类,稀土表现出较强分异的元素配分模式,具有弱–中等的Eu负异常,反映可能存在弱的斜长石分离结晶作用或部分熔融过程中有斜长石的残留;微量元素结果显示其富集大离子亲石元素Rb、Th、K等和LREE,相对亏损高场强元素Nb、P、Ti、Y、Yb。石英闪长岩属钙碱性准铝质花岗岩类,稀土元素球粒陨石标准化配分曲线显示明显的右倾型,表现出较强分异的元素配分模式;富集大离子亲石元素Rb、Th、K等和LREE,相对亏损高场强元素Nb、P、Ti、Y、Yb,具有明显的Sr、P和Ti负异常。岩体中二长花岗岩的锆石U-Pb同位素年龄为412.4±3.3 Ma,时代属晚志留世;石英闪长岩的锆石U-Pb同位素年龄为272±3.2 Ma,时代属晚二叠世。两岩体可能形成于大洋闭合–陆陆碰撞和碰撞造山晚期到造山后的伸展环境。这一新的成果资料对研究柴北缘与阿尔金结合部位古生代构造演化、造山过程具有重要意义。

The Nanshan rock mass of Datonggou is located at the junction between the northern margin of Qaidam and the Altun tectonic belt,and intrudes into the Suoerkuli Group of Neoproterozoic Qingbaikou system.The petrochemical characteristics show that the monzogranite in the Nanshan rock mass of Datonggou belongs to the high-k calc alkaline peraluminous granite.The REE characteristics show a strong differentiation pattern of element distribution,and have weak to medium negative Eu anomalies,indicating that there may be weak fractional crystallization of plagioclase or residual plagioclase during partial melting.The trace element characteristics show that LILE is enriched in Rb,Th,K and LREE,and relatively depleted in high field strength elements(HFSE)such as Nb,P,Ti,Y and Yb.The quartz diorite belongs to calc alkaline meta-aluminous granite.The normalized REE chondrite distribution curve shows obvious right dipping type,showing a strong differentiation pattern of element distribution.LILE is rich in Rb,Th,K and LREE,and relatively depleted in high field strength elements(HFSE)such as Nb,P,Ti,Y and Yb,with obvious negative Sr,P,and Ti anomalies.The zircon U-Pb isotopic age of monzonitic granite is 412.4±3.3 Ma,indicating a late Silurian origin;the zircon U-Pb isotopic age of quartz diorite is 272±3.2 Ma,indicating a late Permian origin.The two rock bodies may have formed in an extensional environment from ocean closure-continental collision and late collisional orogeny to post orogeny.This new data is of great significance to the study of the Paleozoic tectonic evolution and orogenic process at the junction of the northern Qaidam Basin and Altun tectonic belt.