Nd-Hf Isotopic Decoupling of the Silurian–Devonian Granitoids in the Chinese Altai: A Consequence of Crustal Recycling of the Ordovician Accretionary Wedge?  

作　　者：Yanqiong Huang Yingd Jiang Yang Yu Stephen Collett Sheng Wang Tan Shu Kang Xu 

机构地区：[1]State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China [2]University of Chinese Academy of Sciences,Beijing 100049,China [3]Center for Lithospheric Research,Czech Geological Survey,Prague,Czech Republic

出　　处：《Journal of Earth Science》2020年第1期102-114,共13页地球科学学刊（英文版）

基　　金：supported by the National Key R&D Program of China(No.2017YFC0601205);the Strategic Priority Research Program(B)of the CAS(No.XDB18020203);the NSF China(No.41672056);the Guangdong Special Support Program;GIG-CAS 135 Project(No.135TP201601);A 100 Talents Program of the CAS to Yingde Jiang;a China Postdoctoral Science Foundation to Yu Yang(No.2018M633172)

摘　　要：Voluminous Silurian–Devonian granitoids intruded a greywacke-dominated Ordovician accretionary wedge in the Chinese Altai. These granitoids are characterized by significant Nd-Hf isotopic decoupling, the underlying mechanism of which, so far, has been poorly understood. This issue is addressed in this study by the integration of our new and regional published geological and geochemical data. Geological studies indicated a close spatial relationship between the regional anatexis of the Ordovician wedge and the formation of the granitoids, which is characterized by a gradual textural evolution from the partial molten Ordovician wedge sedimentary rocks(the Habahe Group) to the granitoid bodies. Compositionally, these granitoids and the Ordovician Habahe Group rocks displayed close geochemical similarities, in the form of arclike trace elemental signatures as well as comparable Nd isotopic characteristics. Combined with regional available data, we suggest that the Silurian–Devonian granitoids originated from the immature and chemically primitive Habahe Group rocks. Since Nd and Hf isotopic data for the Habahe Group rocks show significant Nd-Hf isotopic decoupling, we propose that the Silurian–Devonian granitoids inherited the Nd and Hf isotopic signatures from their sources, i.e., the Habahe Group rocks. In other words, the Nd-Hf decoupling in the Habahe Group rocks is the primary causative factor leading to the prevailing Nd-Hf isotopic decoupling of the Silurian–Devonian granitoids in the Chinese Altai.Voluminous Silurian–Devonian granitoids intruded a greywacke-dominated Ordovician accretionary wedge in the Chinese Altai. These granitoids are characterized by significant Nd-Hf isotopic decoupling, the underlying mechanism of which, so far, has been poorly understood. This issue is addressed in this study by the integration of our new and regional published geological and geochemical data. Geological studies indicated a close spatial relationship between the regional anatexis of the Ordovician wedge and the formation of the granitoids, which is characterized by a gradual textural evolution from the partial molten Ordovician wedge sedimentary rocks(the Habahe Group) to the granitoid bodies. Compositionally, these granitoids and the Ordovician Habahe Group rocks displayed close geochemical similarities, in the form of arclike trace elemental signatures as well as comparable Nd isotopic characteristics. Combined with regional available data, we suggest that the Silurian–Devonian granitoids originated from the immature and chemically primitive Habahe Group rocks. Since Nd and Hf isotopic data for the Habahe Group rocks show significant Nd-Hf isotopic decoupling, we propose that the Silurian–Devonian granitoids inherited the Nd and Hf isotopic signatures from their sources, i.e., the Habahe Group rocks. In other words, the Nd-Hf decoupling in the Habahe Group rocks is the primary causative factor leading to the prevailing Nd-Hf isotopic decoupling of the Silurian–Devonian granitoids in the Chinese Altai.

关 键 词：GRANITOIDS crustal recycling Ordovician wedge sediments partial melting Nd-Hf decoupling Chinese Altai geochemistry 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学] P542