Hf Isotopic Compositions of Zircons from 2.7 Ga Metasedimentary Rocks and Biotite-Plagioclase Gneiss in the Mengjiatun Formation Complex,Western Shandong Province
Hf Isotopic Compositions of Zircons from 2.7 Ga Metasedimentary Rocks and Biotite-Plagioclase Gneiss in the Mengjiatun Formation Complex,Western Shandong Province
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2010
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通讯作者：
Du Lilin
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作者：
Du Lilin
采用La-MC-ICP-MS方法对鲁西新泰市孟家屯组杂岩中的石榴石英岩（M08）、含十字石的石榴黑云母石英片岩（D242-Y2）和TTG片麻岩中的黑云母斜长片麻岩（M03）进行了锆石Lu-Hf同位素组成分析。石榴石英岩碎屑成因锆石的岩浆核给出的176 Lu/177 Hf和176 Hf/177 Hf分别为0.001730~0.002546和0.281249~ 0.281360，锆石边的~（176）Lu/~（177）Hf和~（176）Hf/~（177）Hf分别为0.000123~0.002070和0.281241~0.281318，含十字石石榴子石-黑云母-石英片岩中碎屑成因锆石的岩浆岩芯测得176 Lu/177 Hf和176 Hf/177 Hf值分别为0.001334~ 0.001334和0.001334~ 0.001334。黑云母斜长片麻岩中岩浆锆石的比值为0.000315 ~ 0.000847，岩浆锆石的比值为0.002169 ~ 0.281226~ 0.281324，片岩中岩浆锆石的比值为0.000445 ~ 0.001375，片岩中岩浆锆石的比值为0.281227 ~ 0.281309。0.281186~ 0.281265。孟家屯组杂岩的石榴石英岩、含十字石的石榴黑云母石英片岩和正片麻岩中的（碎屑）锆石分别为3.75~ 7.26、2.31 ~7.26和3.21~ 6.27。所有样品的锆石TDM 1年龄与SHRIMP锆石U-Pb年龄接近，表明它们来自于年轻地壳物质的部分熔融，结合区域地质资料，推测2.7Ga岩浆活动是鲁西地区一次重要的岩浆构造事件，即使在华北克拉通也是如此，变质沉积岩中的许多锆石表现出变质增生边缘具有较低的176 Lu/177 Hf而较高的176 Hf/177 Hf的趋势。177 Hf值高于岩浆核，说明变质石榴石对锆石Lu-Hf同位素体系有重要影响。
Lu-Hf isotopic compositions of zircons separated from the garnet quartzite(M08),staurolite-bearing garnet-biotite-quartz schist(D242-Y2)of the Mengjiatun formation complex and biotite plagioclase gneiss(M03)of the TTG gneisses at Mengjiatun village,Xintai City,western Shandong Province,have been analyzed through the La-MC-ICP-MS method.All the rocks mentioned above were formed 2.7Ga ago.Among them,the magmatic cores of detrital origin zircons of the garnet quartzite give the 176Lu/177Hf and 176Hf/177Hf ranges 0.001730～0.002546 and 0.281249～0.281360,respectively,and the zircon rims of the sample have the 176Lu/177Hf and 176Hf/177Hf ranges 0.000123～0.002070 and 0.281241～0.281318,respectively.The magmatic cores of detrital origin zircons from the staurolite-bearing garnet-biotite-quartz schist yield the 176Lu/177Hf and 176Hf/177Hf values 0.001334～0.002169 and 0.281226～0.281324,respectively,and the metamorphic rims of the zircons from the schist 0.000445～0.001375,0.281227～0.281309,respectively.While the ratios of magmatic zircons from the biotite plagioclase gneiss are 0.000315～0.000847,0.281186～0.281265,respectively.eHf(t)values of the magmatic(detrital)zircons from garnet quartzite and staurolite-bearing garnet-biotite-quartz schist of the Mengjiatun formation complex and the orthogneiss are 3.75～7.26,2.31～7.26 and 3.21～6.27,respectively.In addition,the TDM1 ages of the zircons of all the samples are close to the SHRIMP zircon U-Pb ages,suggesting they were derived from partial melting of the juvenile crustal materials.Combining with the regional geology information,the authors deduce that the 2.7Ga magmatism is an important magmatic tectonothermal event in western Shandong Province area,even in the North China Craton.Many zircons in the metasedimentary rocks show the tendency that the metamorphic overgrowing rims have lower 176Lu/177Hf but higher 176Hf/177Hf values than that of the magmatic cores,demonstrating the substantial influence of the metamorphic garnet on the Lu-Hf isotopic system of zircons.