摘要
通过LA-(MC)ICP-MS碎屑锆石微区U-Pb定年和Hf同位素分析,对鄂尔多斯盆地东胜地区中侏罗统直罗组砂岩型铀矿层进行了同位素定年物源示踪研究。结果显示,四个样品的锆石年龄分布均表现出良好的一致性,总体呈现出2500～2300Ma,2000～1750Ma和450～250Ma三个主峰值年龄与2300～2000Ma、1750～1400Ma的次峰期年龄。年代学对比研究揭示,东胜地区砂岩型铀矿的物源主要来自华北克拉通西部陆块阴山地块和中部造山带北部的TTG片麻岩、麻粒岩和孔兹岩,以及海西期的大量火成岩体。碎屑锆石的εHf(t)值由负到正,变化范围较大,显示了古老地壳的再循环过程。其中,1.9Ga和2.5Ga的部分锆石其Hf分析点位于亏损地幔线附近,指示该时期有新生地壳的形成。锆石的二阶段Hf模式年龄分布范围3.8～0.7Ga,但集中于3.0～2.3Ga,在2.8～2.6Ga出现一峰值,说明华北克拉通地壳主要形成于中、新太古代。本文所获得的锆石Hf同位素模式年龄与华北克拉通西部陆块的Hf和Nd同位素模式年龄分布特征非常接近,而与东部陆块有很大差别,从而进一步证实了东、西部陆块在古元古代拼合之前是独立发展的。
Research result of provenance tracing and tectonic setting for sandstone-type uranium deposit in Zhiluo Formation of the Middle Jurassic in Dongsheng area,Ordos basin,using LA-（MC） ICP-MS in situ U-Pb dating and Hf isotope analysis of the detrital zircons from the sandstones indicates that zircon ages from four samples yield consistent characteristics,with three major age peaks at 2500 ～ 2300Ma,2000 ～ 1750Ma and 450 ～ 250Ma,and two subordinate age peaks at 2300 ～ 2000Ma and 1750 ～ 1400Ma. By comparative study of isotopic chronology with the potential parent rocks,it can be concluded that the provenance of the sandstone-type uranium deposit in Dongsheng area mainly came from the TTG genesis,granulite,khondalite and the Hercynian igneous bodies from Yinshan terrain in western block,and the northern part of the Trans-North China Orogen. The ε Hf（t） values of the detrital zircons vary in a wide range,from positive to negative,indicating a recycling of the old continent curst. Some Hf data points of the zircons with ages of ～ 1. 9Ga and ～ 2. 5Ga lie around the depleted mantle reference line in the εHf（t）-age figure,implying new crust formation from the mantle. The t DM2 values of the zircons vary from 3. 8Ga to 0. 7Ga,but cluster around 3. 0 ～ 2. 3Ga,with a peak at 2. 8 ～ 2. 6Ga, illustrating that crust of the North China Craton was formed mainly from Mesoarchean to Neoarchean. The research also shows that Hf isotopic model ages of the detrital zircons from the study area consistent with the published Hf and Nd isotopic model ages from the Western Block,but different from that of the Eastern Block,which is also an important direct evidence that the two blocks of the North China Craton developed independently from each other until they finally combined into one in the Late Paleoproterozoic.
出处
《岩石学报》
SCIE
CAS
CSCD
北大核心
2013年第8期2746-2758,共13页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40872083
41272138)
国家科技重大专项(2011ZX05008-004-61)
国家大学生创新性实验计划项目(国200711)联合资助
