Eastern Shandong is an important exposure of the Early Precambrian basement in the North China craton,and the stratigraphic study in this area could provide important information for the early continental crustal formation and evolution.In the west of the Jiaobei Terrane,a suite of quartzite,named Shanyangcun quartzite,has been traditionally considered as part of the Paleoproterozoic Xiaosong Formation of the Fenzishan Group.But no precise geochronological constraint is obtained.This paper presented zircon U-Pb ages and Hf isotopes from detrital zircons obtained from this quartzite and associated metasedimentary rocks.The detrital zircons from the Shanyangcun quartzite show a major age peak at 2501 ± 16Ma,which is also the minimum age obtained from this rock.Such an age spectra is different from that of the Paleoproterozoic Fenzishan Group.According to comprehensive analysis of age spectra,field occurrence and rock association and previous studies,we suggest a new lithographic unit for the Shanyangcun quartzite and the Xiaosong Formation probably belong to the Archean Jiaodong Group.The prominent ～ 2.5Ga zircons from the Shangyangcun quartzite show positive εHf(t) values following the evolutionary trend of the ～ 2.7Ga crust,suggesting the protolith of these zircons comes from the recycling of a ～ 2.7Ga juvenile crust.Minor ca.2.7 ～3.0Ga zircons with positive εHf(t) values indicate a continuous recycling of ancient crust since ～3.1Ga,＞ 3.0Ga zircons show negative εHf(t) values,indicating the protolith rocks formed by recycling of more ancient crust.The Hf isotopic signatures of the ＞ 3.0Ga zircons indicate that the continental crust has probably existed in North China Craton before 4.1Ga and crustal remelting occurred in ～ 4.1 Ga,which may be an important early evolutionary stage of the earth crust.In addition,detrital zircon studies from the metamorphic clastic rocks from the associated Wugezhaung Formation or the Xiaoweijia Formation suggest they formed during Paleoproterozoic and could be the bottom of the Fenzishan Group.The Hf isotopic systematics of ～2.1 Ga granitic gneiss indicates that its source is a mixture of old and new crust (ca.2.5 ～2.9Ga).%基底古老地层的研究可以为探索地球早期陆壳形成与演化历史提供重要支持,胶东地区是华北克拉通变质基底重要的出露区之一,在胶北地体的西缘有一套高成熟度的古老石英岩-山阳村石英岩,前人将其划归古元古代粉子山群的小宋组,但缺乏明确的年代学限定.本文对山阳村石英岩的碎屑锆石进行U-Pb年代学和Hf同位素分析,获得年龄谱的最大峰值为2501±16Ma,且是最小峰值年龄.与古元古的粉子山群和中元古的芝罘群的碎屑锆石年龄谱均不同.综合年龄谱特征、野外产状以及岩石组合,本文认为山阳村石英岩是新太古代的岩石建造,建议为其单独建立新太古代岩石地层单位.结合本次研究及前人工作本文认为应将原粉子山群小宋组划到太古代归属胶东岩群.山阳村石英岩中,～2.5Ga锆石Hf同位素εHf(t)＞0且从下方靠近亏损地幔演化线并在～2.7Ga地壳演化线附近分布,显示其原岩来自～2.7Ga新生地壳的重熔;ca.2.7～3.0Ga的锆石Hf同位素εHf(t)＞0且在～3.1Ga地壳演化线附近,意味着其母岩的源区为～3.1Ga的新生地壳,且在ca.2.7～3.0Ga发生了持续的地壳再熔融;＞3.0Ga碎屑锆石的Hf同位素εHf(t)＜0,源区岩石形成于更古老陆壳物质的再循环.已知的胶北地块＞3.0Ga锆石的Hf同位素特征暗示华北克拉通在4.1Ga前就存在地壳,而且在～4.1Ga发生了重熔.
展开▼
