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 

机构地区：[1]Department of Earth Sciences,The University of Hong Kong,Pokfulam Road,Hong Kong,China [2]Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China [3]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China

出　　处：《Science China Earth Sciences》2009年第9期1345-1358,共14页中国科学（地球科学英文版）

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

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.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 significantly 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.

关 键 词：PALEOZOIC ridge SUBDUCTION Hf ISOTOPE GRANITE ALTAI 

分 类 号：P597.3[天文地球—地球化学]