Early Paleozoic ridge subduction in the Chinese Altai: Insight from the abrupt change in zircon Hf isotopic compositions

作     者：SUN Min LONG XiaoPing CAI KeDa JIANG YingDe WANG BuYun YUAN Chao ZHAO GuoChun XIAO WenJiao WU FuYuan 

作者机构：Department of Earth SciencesThe University of Hong KongPokfulam RoadHong KongChina Key Laboratory of Isotope Geochronology and GeochemistryGuangzhou Institute of GeochemistryChinese Academy of SciencesGuangzhou 510640China State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2009年第52卷第7期

页      面：1345-1358页

核心收录：

学科分类：070902[理学-地球化学] 0709[理学-地质学] 07[理学] 

基　　金：Supported by National Basic Research Program of China (Grant No. 2007CB411308) Hong Kong RGC Grants (Grant Nos. HKU704307P and 704004P) National Natural Science Foundation of China (Grant Nos. 40772130, 40803009) CAS/SAFEA International Partnership Program for Creative Research Teams 

主　　题：Paleozoic ridge subduction Hf isotope granite Altai 

摘      要：Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified in composition by a rapid addition of melt from the mantle. We suggest that this dramatic change was due to the onset of ridge subduction, which can account not only for the formation of voluminous granitoids, mafic rocks with complex compositions, and the association of adakite + high-Mg andesite + boninite + Nb-enriched basalt, but also for the coeval high-T, low-P metamorphism.