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连接扬子地块和华夏地块的江南造山带是华南前寒武纪最重要的构造单元,其形成和演化长期以来备受关注。在江南造山带的范围内广泛发育了新元古代岩浆岩,它们是探讨江南造山带构造演化的重要对象,但其成因和形成的构造背景却备受争论。本文系统收集和分析了江南造山带830~820 Ma花岗岩、800~780 Ma酸性岩和800~750 Ma基性岩的地球化学数据。研究表明,不同时间段的岩石成因类型存在系统差异,830~820 Ma的花岗岩主要为S型花岗岩,800~780 Ma的酸性岩主要为A型酸性岩,而800~750 Ma的基性岩以拉斑系列和碱性系列为主,并在构造判别图中显示了板内玄武岩(WPB)和洋中脊玄武岩(MORB)的特征。综合同位素年代学、岩石地球化学和沉积学等学科领域的研究成果我们认为:扬子北缘和西缘应先于东南缘在1000~900 Ma期间发生碰撞,而此时的东南缘仍为活动大陆边缘;直到~830 Ma,扬子地块与华夏地块沿江南造山带发生拼贴,但只是陆-弧-(微)陆之间的“软碰撞”,而无山脉隆升和高级变质作用,各个块体之间处于“联而不合”的状态,大洋岩石圈拆沉之后的软流圈上涌和由拆沉所引起的拉张作用导致了上覆岩石圈和陆壳发生部分熔融,产生了江南造山带830~820 Ma的S型花岗岩;随着全球Rodinia超大陆的裂解,~820 Ma,华南裂谷盆地开启,并在随后的裂解过程中发育了大量与伸展有关的800~780 Ma A型酸性岩和基性岩脉/墙,而其明显高于同时代MORB源区的地幔潜能温度显示,导致Rodina超大陆裂解的地幔柱可能对该时期岩浆岩的地幔源区有一定影响;随着拉张作用的不断加强,出现了760~750 Ma碱性系列和具MORB特征的基性岩,此时的软流圈地幔既提供热量又有物质供应。
The Jiangnan orogenic belt connecting the Yangtze block and the Cathaysian block is the most important tectonic unit of the Precambrian in South China. Its formation and evolution have drawn much attention for a long time. Neoproterozoic magmatic rocks were extensively developed within the scope of the Jiangnan orogenic belt. They are important targets for the study of the tectonic evolution of the Jiangnan orogenic belt. However, their genesis and formation tectonic setting have been widely debated. This paper systematically collected and analyzed the geochemical data of 830 ~ 820 Ma granite, 800 ~ 780 Ma acidic rocks and 800 ~ 750 Ma basic rocks in the Jiangnan orogenic belt. The study shows that there are systematic differences in rock genetic types in different periods of time. The granite in 830 ~ 820 Ma is mainly S-type granite, the acid rock in 800-780 Ma is mainly A-type acidic rocks, while the 800-750 Ma basic rocks The mottling and alkaline series are the dominant features of the intraplate basalts (WPB) and mid-ocean ridge basalts (MORB). Comprehensive isotopic geochronology, geochemistry and sedimentology and other disciplines of research results we believe that: the northern margin of the Yangtze and the western margin should be before the southeastern margin of 1000 ~ 900 Ma during the collision, while the southeastern margin is still the active continent Margin; until ~ 830 Ma, the Yangtze block and the Huaxia block collapsed along the Jiangnan orogenic belt, but only the “soft collision” between the land-arc and the (micro) land without the upwelling and advanced metamorphism of the mountains. Each block is in a “united and not united” state. Upwelling of the asthenosphere and delamination caused by detachment after the oceanic lithosphere delamination led to the partial melting of the overlying lithosphere and continental crust, resulting in S-type granites from 830 to 820 Ma in the Jiangnan orogenic belt were formed; ~ 820 Ma, South China rift basins were opened up following the global dissolution of the Rodinia supercontinent, and a large amount of stretching-related 800 ~ 780 Ma Type A acidic rocks and basic dykes / walls, and its significantly higher Mh than that of the contemporary MORB source region. The mantle plumes that cause the Rodinale supercontinent cracking may have an impact on the mantle source area of the magmatic rocks during this period. With the increasing role of tension, appeared 7 60 ~ 750 Ma alkaline series and MORB characteristic basic rocks. At this time, the asthenospheric mantle provides both heat and material supply.