阿尔金岩群大理岩地球化学特征、锆石U-Pb年龄及地质意义

Geochemical Characteristics,Zircon U-Pb Dating and Geological Significance of the Marble in the Altyn Tagn Group

通过对原古元古代阿尔金岩群大理岩进行岩石地球化学分析及LA-ICP-MS锆石U-Pb测年研究,确定了大理岩成因和原岩沉积年龄。地球化学数据显示,岩石Ca O含量高,为26.05%~51.08%、Mg O与Si O2变化较大,分别为4.40%~21.51%、0.90%~21.11%,低Na2O、K2O、Mn O、Ti O2、P2O5(小于1%),低ΣREE,4.69×10^-6~54.36×10^-6,弱的负Eu异常,为0.73~0.94,轻重稀土分馏不强,LaN/YbN=6.58~10.57,富集大离子亲石元素,亏损高场强元素,岩石地球化学特征与沉积碳酸盐相近,异于火成碳酸岩。锆石U-Pb测年显示沉积年龄介于929~536 Ma,经历了阿尔金地区早古生代多次构造运动改造。综合分析认为大理岩为沉积-变质成因,原岩沉积时代为新元古代,非先前认为的古元古代。

Based on the petrogeochemical analysis and LA-ICP-MS zircon U-Pb dating of the protoproterozoic Altun group marble,the genesis and protolith sedimentary age of the marble are determined.Geochemical data show that the content of CaO is high,ranging from 26.05%to 51.08%in rocks.MgO and SiO2 vary greatly,ranging from 4.40%to 21.51%and 0.90%to 21.11%respectively,low contents of Na2O、K2O、MnO、TiO2、P2O5(<1%),lowΣREE(4.69~54.36),weakly negative Eu anomalies(0.73~0.94),moderately fractionated REE patterns(LaN/YbN=6.58~10.57).The rocks are enriched in LILE and depleted in HFSE.,the geochemical characteristics of rocks are similar to those of sedimentary carbonates and different from those of igneous carbonates.Zircon U-Pb dating shows that the sedimentary age is between 929 and 536 Ma,and there are many tectonic activities in Early Paleozoic in Altyn Tagn area..According to comprehensive analysis,the marble is of sedimentary-metamorphic origin,and the sedimentary age of the protolith is Neoproterozoic,it is not Paleoproterozoic as previously thought.