CA. 850 MA BIMODAL VOLCANIC ROCKS IN NORTHEASTERN JIANGXI PROVINCE, SOUTH CHINA: INITIAL EXTENSION DURING THE BREAKUP OF RODINIA?
CA. 850 MA BIMODAL VOLCANIC ROCKS IN NORTHEASTERN JIANGXI PROVINCE, SOUTH CHINA: INITIAL EXTENSION DURING THE BREAKUP OF RODINIA?
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DOI：
10.2475/09.2010.08
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发表时间：
2010-11-01
影响因子：
2.9
通讯作者：
Li, Z. X.
中科院分区：
文献类型：
--
作者：
Li, W. X.;Li, X. H.;Li, Z. X.
华南地区多次中新元古代岩浆事件被认为记录了构造体系从罗迪尼亚超大陆的聚合到解体的转变。我们最早在这篇论文中记录了大约。 850Ma华南双峰式火山活动可能预示着大陆伸展和裂谷的开始。使用二次离子质谱 (SIMS) U-Pb 锆石法对珍珠山双峰式火山岩进行定年，年龄为 849 +/- 6 Ma。该系列的镁铁质成员是硅饱和拉斑玄武岩，大多数不相容微量元素中度富集，ε Nd(T) 值高达 2.1 至 4.8。这表明玄武岩可能源自拉张环境中耗尽的软流圈地幔源，并且岩浆在上升到地表的过程中经历了低度的分异结晶和地壳污染。长英质成分是过铝质成分，其特征是负 epsilon Nd(T) 值为 -0.3 至 -1.9，其地球化学特征与邻近的约 100 岩层相似。 820 Ma 过铝质花岗岩源自中元古代至最早的新元古代沉积源。结合华南地区850~830Ma火成岩和沉积岩序列的分布，我们认为扬子地块南缘的大陆裂谷可能始于850Ma。在罗迪尼亚超大陆的其他地区也有报道称同期的造山岩浆活动，可能代表了罗迪尼亚超大陆完全组装后，对环罗迪尼亚地幔雪崩的响应，罗迪尼亚超级地幔柱的早期阶段。
Multiple Meso- to Neoproterozoic magmatic events in South China are believed to record the transition in tectonic regime from the assembly of the supercontinent Rodinia to its breakup. We document in this paper the earliest, ca. 850 Ma bimodal volcanism in South China which may indicate the beginning of continental extension and rifting. The Zhenzhushan bimodal volcanic rocks were dated at 849 +/- 6 Ma using the secondary ion mass spectrometry (SIMS) U-Pb zircon method. The mafic members of the succession are Si-saturated tholeiitic basalts with moderate enrichment in most incompatible trace elements and high epsilon Nd(T) values of 2.1 to 4.8. This suggests a likely derivation of the basalts from a depleted asthenospheric mantle source in an extensional environment, and that the magma experienced low-degree fractional crystallization and crustal contamination during its ascent to the surface. The felsic members are peraluminous and are characterized by negative epsilon Nd(T) values of -0.3 to -1.9 with geochemical features similar to those of the adjacent ca. 820 Ma peraluminous granitoids derived from a Mesoproterozoic to earliest Neoproterozoic sedimentary source. In combination with the distribution of 850 to 830 Ma igneous and sedimentary successions in South China, we suggest that continental rifting along the southern margin of the Yangtze Block probably started by 850 Ma. Coeval anorogenic magmatism has also been reported in other parts of the Rodinia supercontinent, and may represent the early stage of the Rodinia superplume in response to a circumRodinia mantle avalanche after the complete assembly of the supercontinent.