Zircon Hf isotopic composition and source characteristics of the Wudang Group in the Qinling orogenic belt,western Henan province
Zircon Hf isotopic composition and source characteristics of the Wudang Group in the Qinling orogenic belt,western Henan province
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发表时间：
2009
影响因子：
1.8
通讯作者：
Zhu Xiyan;Chen Fukun;Yang Li;Wang Wei;H. P. Trung;Miao Laicheng;Zhang Fuqin
中科院分区：
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作者：
Zhu Xiyan;Chen Fukun;Yang Li;Wang Wei;H. P. Trung;Miao Laicheng;Zhang Fuqin
武当群变质火山-沉积岩系是南秦岭陆块基底的重要岩石单元，其形成时代和地球化学特征可为认识秦岭造山带的构造演化提供重要信息。本文报道了武当群上部沉积岩和下部火山岩的全岩Sm-Nd和锆石Lu-Hf同位素组成，武当山沉积岩锆石Hf初始值为-30 ~+10，模式年龄（tDM 2）为1.0 ~ 3.2Ga;全岩的Nd初始值变化范围为-4.0 ~-6.0，沉积物源为亲扬子基底岩和武当群下部火山岩，火山岩中锆石的Hf初始值变化范围为-35 ~+15，对应的t_（DM 2）值约为0.8 ~ 3.5Ga，而聚集在1.5~1.8Ga和2.2~2.4Ga之间。两个火山岩石英角斑岩样品的Nd初始值分别为-9.2和-10.7，与湖北省武当玄武岩安山岩的Nd初始值不同，湖北省武当玄武岩安山岩的Nd初始值大多为正值，因此，武当群不同类型的火山岩具有不同的成因，以低Nd、低Hf为特征的火山岩具有不同的成因类型。结果表明，部分样品的初始Hf值主要来源于地壳物质的重熔，而其他样品的初始Hf值变化范围较大（-35 ~+15）或正初始_（Nd）值，表明武当火山岩岩浆中有地幔物质或新生地壳岩石与老地壳岩石的共同贡献。武当群的Hf同位素组成和碎屑锆石年龄模式表明，南秦岭扬子陆块在元古宙可能经历了多阶段的地壳增生改造历史。
The metamorphosed volcanic-sedimentary sequences of the Wudang Group belong to an important rock unit of the basement in the South Qinling block.Formation ages and geochemical features of the Wudang Group can provide essential information for understanding of the tectonic evolution of the Qinling orogenic belt.In this study,we report whole-rock Sm-Nd and zircon Lu-Hf isotopic composition of sedimentary rocks in the upper part and volcanic rocks in the lower part of the Wudang Group,and provide discussion on petrogenesis of the volcanic rocks and source characteristics of the sedimentary rocks.Zircon grains from the Wudang sedimentary rocks give initiale_(Hf) values ranging from-30 to+10,corresponding to model age values(t_(DM2)) between about 1.0Ga and 3.2Ga,initiale_(Nd) values of whole-rocks vary from-4.0 to-6.0.The sedimentary sources originated from basement rocks of a Yangtze-affinity and volcanic rocks of the lower part of the Wudang Group.Initiale_(Hf) values of zircon grains from the volcanic rocks vary from-35 to+15,corresponding to t_(DM2) values of about 0.8Ga to 3.5Ga,but clustering around 1.5～1.8Ga and 2.2～2.4Ga. Initiale_(Nd) values of two quartz-keratophyre samples of volcanic rock are-9.2 and-10.7,different from the reported values for the Wudang basaltic-andesitic rocks exposed in Hubei Province,where most of the volcanic rocks have positivee_(Nd) values.Therefore, different origins can be proposed for different volcanic rock types of the Wudang Group.Those volcanic rocks characterized by low initiale_(Nd) ande_(Hf) values originated mainly from re-melting crustal material,while others have a broad range of initiale_(Hf) values(-35 to+15) or positive initiale_(Nd) values,which indicate significant contribution of mantle material or juvenile crustal rocks together with old crustal rocks to the magma(s) of the Wudang volcanic rocks.Evidence of Nd-Hf isotopic compositions and detrital zircon age patterns of the Wudang Group suggests that the South Qinling terrane of Yangtze-affinity probably underwent multi-stage history of crustal accretion and reworking during the Proterozoic time.