U-PB Age and Hf Isotopic Study of Detrital Zircons from the Liaohe Group: Constraints on the Evolution of the Jiao-Liao-Ji Belt, North China Craton

This dissertation, "U-Pb Age and Hf Isotopic Study of Detrital Zircons From the Liaohe Group: Constraints on the Evolution of the Jiao-Liao-Ji Belt, North China Craton" by Yan, Luo, 羅彥, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled U-Pb AGE AND Hf ISOTOPIC STUDY OF DETRITAL ZIRCONS FROM THE LIAOHE GROUP: CONSTRAINTS ON THE EVOLUTION OF THE JIAO-LIAO- JI BELT, NORTH CHINA CRATON Submitted by Luo Yan for the degree of Doctor of Philosophy at The University of Hong Kong in December 2005 The North China Craton (NCC) is the largest and oldest known continental block in China. The Jiao-Liao-Ji mobile belt along the eastern margin of the NCC is one of the rarely preserved Paleoproterozoic integrities in the world. As an important Paleoproterozoic sedimentary sequence of this belt, the Liaohe Group consists of an assemblage that includes a lower arkose- and volcanic-rich sequence (Langzishan, Li'eryu /Gaojiayu Formations), through a middle carbonate-rich sequence (Dashiqiao Formation) to an upper argillaceous sequence (Gaixian Formation). Traditionally, this group was subdivided into the North and South Liaohe Groups. Associated with the Liaohe Group are large volumes of granitoid rocks (Liaoji Granite), whose emplacement age has been dated at 2.1-2.2 Ga. Regionally, the Liaohe Group and the associated Liaoji Granite extend along a NEE-trending belt that is flanked by 2.45-2.55 Ga basement gneisses. Because of the lack of knowledge about the timing of deposition and metamorphism, nature of the sedimentary provenance and the basement, controversy exists on several issues including the depositional environment and tectonic significance of these rocks. The present work aims to constrain key issues by studying U-Pb, Hf isotopic and trace elemental compositions of detrital zircons from the Liaohe Group. Modern analytical technology such as cathodoluminescence (CL) imaging, laser ablation inductively coupled plasma mass spectrometry and laser ablation multiple collector inductively coupled plasma mass spectrometry were employed. CL images reveal that most detrital zircon grains from the Liaohe Group are characterized by concentric oscillatory zoning, suggesting magmatic origin. However, a small number of zircon grains have structureless recrystallization rims, indicating metamorphic origin. Results of this study show that the zoned zircon grains of the Langzishan Formation, the lowest sequence of the Liaohe Group, have concordant U-Pb ages ranging from 2.24-2.05 Ga, suggesting that the minimum depositional time of the Liaohe Group is at 0.2815 and 0.2813), similar Hf model ages (T, peaks at 2.66 Ga 2.75 DM Ga, and 2.8 3.0 Ga) and similar εHf values ( -5 +9 and -7 +5). Data of this study suggest that the metasedimentary rocks of the Liaohe Group were deposited between 2.05 and 1.93 Ga, a short time after emplacement of the Liaoji Granite. The provenance of the Langzishan, Li'eryu and Gaixian Formations, is particularly dominated by the Liaoji Granite. Furthermore, the protoliths of the North and South groups may have formed simultaneously and could have developed on a single late Archean basement rather than two different blocks. This