摘要
为研究西伯利亚板块东南缘晚古生代板内伸展开始时间及地幔属性。基于1∶5万野外宏微观调查,采用LA-MC-ICP-MS锆石U-Pb定年法对分布于东乌旗西部的角闪石辉长岩进行了年龄测定和岩石地球化学测试。结果表明：角闪辉长岩主要由斜长石、角闪石和单斜辉石组成,锆石U-Pb年龄为280.8±1.5Ma,属早二叠世。地球化学数据显示：岩石具较高SiO2（48.87%~53.70%）、TiO2（0.73%~2.27%）、Al2O3（15.05%~16.69%）的含量,中等至较高的MgO（4.84%~9.25%）、FeOT（6.91%~10.47%）和较低的CaO（5.80%~7.94%）。富Na2O（2.75%~3.90%）,贫K2O（1.01%~1.90%）,为铁质—富铁质碱性和拉斑玄武岩系列岩石组合。稀土总量较高（∑REE为97.50×10-6~251.16×10-6）,轻重稀土分异程度中等[（La/Yb）N=4.23~7.12],Eu异常不明显（δEu=0.85~0.98）。岩石富集大离子亲石元素（LILE）Ba、Sr、K等,相对亏损高场强元素（HFSE）Nb、Ta、Th等,高的Zr（87×10-6~289×10-6）和Zr/Y（4.03~7.66）比值,与板内幔源岩浆作用的产物一致。综上,我们认为角闪辉长岩为板内伸展构造体制下富集型地幔橄榄岩部分熔融形成的玄武质岩浆岩浆经分离结晶作用后形成的,标志着~280 Ma西伯利亚板块东南缘晚古生代造山过程进入到板内非造山阶段。
In this paper,through field investigation,petrography analyses of samples of the bojites,1 sample zircon LA-MC-ICP-MS U-Pb dating and 10 samples geochemical analyses,bojiteson in the southeast margin of Siberian plate have been studied,for their chronology and tectonic implications.In these rocks,main rock forming minerals are plagioclase,hornblende and clinopyroxene.The zircon U-Pb dating suggest that these bojites are formed in Early Permian with detail ages of（280.8±1.5）Ma.Geochemical researches indicate that the bojites are high in silica（SiO2=48.87%~53.70%）,TiO2（0.73%~2.27%）,Al2O3（15.05%~16.69%）,moderate to high MgO（4.84%~9.25%）,FeOT（6.91%~10.47%）and low CaO（5.80%~7.94%）.These rocks are enriched in Na2O（2.75%~3.90%）,especially LILE（Ba,Sr,K）,and depleted in K2O（1.01%~1.90%）and HFSE（Nb,Ta,Th）,with the characteristics of alkaline and tholeiitic series.The rocks have high REE（97.50×10-6~251.16×10-6）,slightly Eu anomalies（δEu=0.85~0.98）,enrichment in LREE and relatively depletion in HREE[（La/Yb）N=4.23~7.12],with the high Zr（87×10-6~289×10-6）and Zr/Y（4.03~7.66）,which is similar to within-plate rocks from mantle magmatism.Thus,we consider that the bojites,in the southeast of Siberian plate,had been formed in extensional tectonics from partial melting of the Enrichment Mantle peridotite,with fractional crystallization,which indicates that ~280Ma may be the tectonic evolution from Post-Orogenic to Anorogenic in southeast margin of the Siberian plate.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2015年第2期262-271,共10页
Acta Geologica Sinica
基金
中国地质调查项目(编号:1212011220446和1212011120697)联合的资助
