辽东盖州-庄河地区榆树砬子岩组碎屑锆石U-Pb年代学与Hf同位素研究:对华北克拉通陆壳演化的制约

出露于辽东地区盖州-庄河一带的榆树砬子岩组,作为该区不整合覆盖于古元古代辽河群之上最早的稳定沉积盖层,其沉积时代、物源区及沉积环境的研究对了解华北克拉通的构造演化具有重要科学意义。目前该地区依然缺乏关于榆树砬子岩组形成时代和区域地层对比的数据。本文在详细野外地质调查基础上,通过碎屑锆石U-Pb定年、Hf同位素示踪等手段,对该岩组的沉积环境及时限、物源区及与燕辽裂谷带内中元古代地层的时空关系等问题进行了讨论。通过对榆树砬子岩组与燕辽裂谷带内常州沟组对比,发现尽管锆石U-Pb定年结果表明榆树砬子岩组沉积时代晚于1803Ma,但二者在锆石年龄谱、物源成分、岩石组合及沉积旋回序列等方面具有一定相似性。龙岗地块及辽南陆块太古宙基底、古元古代辽吉花岗岩以及古元古代同碰撞或碰撞后岩浆岩可能为榆树砬子岩组提供了物源。同时,锆石Hf同位素特征表明华北克拉通东北缘记录了自～4. 1Ga以来的一系列地壳生长事件,其峰期主要发生于31～27亿年,与华北克拉通其他地区的数据一致,为华北克拉通太古代的陆壳演化提供了新的佐证。

Detrital zircon U-Pb and Hf isotopic study of the Yushulazi Formation in the Gaizhou-Zhuanghe area of the eastern Liaoning: Constraints on the crustal evolution of the North China Craton

As the oldest stable sedimentary cover sequences on the crystalline basement of eastern Liaoning Province, the Yushulazi Formation outcrops in the Gaizhou-Zhuanghe area and unconformably overlies the Paleoproterozoic Liaohe Group. Therefore, its depositional age, provenance and sedimentary environment can provide important information for the understanding of the crustal evolution. However, very few data about its depositional age and provenance information have been reported. Based on our new detail field geological mapping results, in this study we carried out zircon U-Pb dating and Hf isotopic analysis on typical samples from the lower, middle and upper levels of the Yushulazi Formation. U-Pb zircon dating results show that the Yushulazi Formation deposited sometime after~1803Ma. It shows a large similarity with the adjacent Changzhougou Formation of the Mesoproterozoic Changcheng System in age spectrum, provenances and sedimentary cycles. The adjacent Archean basement of Longgang and Liaonan blocks, the Paleoproterozoic Liao-Ji granitoids may provide the major source for the Yushulazi Formation. Moreover, detrital zircon Hf isotopes reveal an old Hf model age of~4.1Ga, and a peak model age of 3.1~2.7Ga, indicating that the North China Craton experienced the multiple crustal growth events during the Meso-and Neo-Archean.