摘要:
本文讨论了中国东南沿海和西南日本两条白垩纪-古近纪火山-侵入岩带的地球动力学特征。两条火山-侵入岩带的下火山岩系岩石经受了左旋走滑的韧性剪切变形而形成片理或片麻理构造。中国东南沿海火山-侵入活动的起始时间、动力变形和结束时间都早于日本约30Ma。西南日本高镁安山岩和埃达克岩(120~105Ma)是在大面积白垩纪岩浆作用的起始阶段由大洋俯冲板片在高温条件下部分熔融形成的。火山-侵入活动的结束标志中国东南沿海岩浆岩带是板内环境的晶洞A型花岗岩和以流纹岩为主的双峰式火山岩;在西南日本岩浆岩带是年轻地壳挤压重熔的S型过铝质石榴石/白云母细粒花岗岩和流纹岩,不存在类似华南的壳源S型花岗岩,中国东南沿海没有代表洋壳俯冲的弧岩浆岩。两条火山-侵入岩带的源区都以幔源为主并有前寒武纪再旋回地壳物质加入,它们的Sr-Nd同位素组成表明:随时间推移,中国东南沿海火山-侵入岩中幔源组分增加,而西南日本则相反。华南中生代大规模岩浆活动的开始(170±5Ma)是在古太平洋板块斜向俯冲背景下,大陆岩石圈减薄,陆内深断裂再活化的结果。东亚大陆边缘在晚中生代(120Ma)进入古太平洋板块正向俯冲构造体系,但不同地段的表现不同。
Abstract:
The paper deals with the evidences of the geodynamic characteristics of the Cretaceous-Pa-leogene volcano-intrusive activities in the Southeast China Coast Magmatic Belts (SECCMB) and the South-west Japan Magmatic Belt (SWJMB) .The volcano-intrusive complexes from the lower volcanic series in the two magmatic belts generally were experienced left lateral strike-slip ductile shearing deformation to form schistosity or gneissosity structures .The starting and terminating of the magmatic activities and dy-namic deformation in the SECCMB were ~30 Ma earlier than those in the SWJMB .The high-Mg andesites and adakites (120~105 Ma) in Southwest Japan were formed by partial melting of subducting oceanic slab under high temperature environment during the early period of voluminous Cretaceous magmatism .The termination marks of magmatic activities in the SECCMB are the within-plate setting miarolitic A-type granites and rhyolite-dominated bimodal volcanic ;w hereas the magmatic activities in the SECCMB are shown by the S-type strong peralumious garnet/muscovite granites and rhyolites formed by compression remelting of the younger crust in an absence of the crust-derived S-type granites w hich are developed in South China .In the SECCMB there have arc magmatic rocks resulted from the subduction of oceanic crust .The source regions of the igneous rocks in the two magmatic belts were dominantly originated from the mantle-derived rocks with the involvement of recycled Precambrian crust . The Sr-Nd isotopic data show that ,with the passage of time ,the mantle-derived components increased in volcano-intrusive rocks of the SECCMB but decreased in those of the SWJMB .The large-scale Mesozoic magmatic activity (170 ± 5 Ma) in South China was resulted from the continental lithospheric thinning and reactivation of intraconti-nental deep fault under the background of oblique subduction of paleo-Pacific Ocean Plate .Asian continent margin during late Yanshanian (<120 Ma) ,the eastern Asian continental margin was belonged to paleo-Pacific Ocean orthogonal subduction-related tectonic system ,but the geodynamic indications varied in dif-ferent segments .
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