The Xiong'er volcanic belt at the southern margin of the North China Craton: Petrographic and geochemical evidence for its outboard position in the Paleo-Mesoproterozoic Columbia Supercontinent
The Xiong'er volcanic belt at the southern margin of the North China Craton: Petrographic and geochemical evidence for its outboard position in the Paleo-Mesoproterozoic Columbia Supercontinent
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DOI：
10.1016/j.gr.2009.02.004
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发表时间：
2009-10
影响因子：
6.1
通讯作者：
Guochun Zhao;Yanhong He;M. Sun
中科院分区：
文献类型：
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作者：
Guochun Zhao;Yanhong He;M. Sun
沿着北中国克拉通南缘占地6万多平方公里的熊耳火山带，长期以来一直被认为是大陆内裂谷带，最近被解释为由地幔热柱形成的大型火成岩省的一部分，地幔热柱导致了古-中元古代超大陆哥伦比亚的解体。然而，这种解释不能用带内火山岩的岩性、矿物学、地球化学和年代学来解释。在岩石学上，熊耳火山岩带以玄武岩安山岩和安山岩为主，并有少量英安岩和流纹岩，不同于与大陆裂谷或地幔柱有关的岩石组合，后者一般为双峰型，以镁铁质成分为主。然而，它们与现代大陆边缘弧中的岩石组合非常相似。在一些玄武质安山岩和安山岩中，角闪石是常见的斑晶相，表明富含H2O的流体参与了熊耳火山岩的成因。在地球化学上，熊耳火山岩属于钙碱性系列，在大多数构造-岩浆判别图上，大多数熊尔火山岩都与岩浆弧有亲缘关系。在原始地幔归一化微量元素图解中，熊耳火山岩表现出LILE和LREE的富集性，Nb-Ta-Ti负异常，类似于交代地幔楔体水合熔融产生的弧型火山岩。熊耳火山岩的Nd同位素组成表明，在太古代至古元古代，有5-15%的老地壳通过俯冲作用的再循环进入岩石圈上地幔。SHRIMP和LA-ICPMS锆石年龄数据表明，熊耳火山岩在1.78~1.75(Ga)、1.76-1.75(Ga)和1.65(Ga)~1.45(Ga)之间断续喷发，但火山活动主期发生在1.78~1.75(Ga)。这种多次和间歇性的火山活动与地幔热柱驱动的裂谷事件不一致，但在古代和现存的大陆边缘弧中并不少见。综上所述，熊耳火山带极有可能是形成于北中国克拉通南缘的古-中元古代大陆岩浆弧。在劳伦西亚南部和东南部边缘、波罗的海南缘、阿蒙佐尼亚西北边缘和北澳大利亚克拉通南部和东部边缘也存在类似的古中元古代大陆岩浆弧，它们被认为代表了古中元古代哥伦比亚超大陆大陆边缘与俯冲有关的幕式外展。因此，在哥伦比亚超大陆的任何构型中，北中国克拉通南缘不可能像最近提出的那样与任何其他大陆块相连，而是一定面临着一个开阔的大洋，其岩石圈被俯冲到北中国克拉通南缘之下。
The Xiong'er volcanic belt, covering an area of more than 60,000 km2along the southern margin of the North China Craton, has long been considered an intra-continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the Paleo-Mesoproterozoic supercontinent Columbia. However, such interpretations cannot be accommodated by lithology, mineralogy, geochemistry and geochronology of the volcanic rocks in the belt. Lithologically, the Xiong'er volcanic belt is dominated by basaltic andesite and andesite, with minor dacite and rhyolite, different from rock associations related to continental rifts or mantle plumes, which are generally bimodal and dominated by mafic components. However, they are remarkably similar to those rock associations in modern continental margin arcs. In some of the basaltic andesites and andesites, amphibole is a common phenocryst phase, suggesting the involvement of H2O-rich fluids in the petrogenesis of the Xiong'er volcanic rocks. Geochemically, the Xiong'er volcanic rocks fall in the calc-alkaline series, and in most tectono-magmatic discrimination diagrams, the majority of the Xiong'er volcanic rocks show affinities to magmatic arcs. In the primitive mantle normalized trace-element diagrams, the Xiong'er volcanic rocks show enrichments in the LILE and LREE, and negative Nb–Ta–Ti anomalies, similar to arc-related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge. Nd-isotope compositions of the Xiong'er volcanic rocks suggest that 5–15% older crust has been transferred into the upper lithospheric mantle by subduction-related recycling during Archean to Paleoproterozoic time. Available SHRIMP and LA-ICP-MS U–Pb zircon age data indicate that the Xiong'er volcanic rocks erupted intermittently over a protracted interval from 1.78 Ga, through 1.76–1.75 Ga and 1.65 Ga, to 1.45 Ga, though the major phase of the volcanism occurred at 1.78–1.75 Ga. Such multiple and intermittent volcanism is inconsistent with a mantle plume-driven rifting event, but is not uncommon in ancient and existing continental margin arcs. Taken together, the Xiong'er volcanic belt was most likely a Paleo-Mesoproterozoic continental magmatic arc that formed at the southern margin of the North China Craton. Similar Paleo-Mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of Laurentia, the southern margin of Baltica, the northwestern margin of Amonzonia, and the southern and eastern margins of the North Australia Craton, which are considered to represent subduction-related episodic outbuilding on the continental margins of the Paleo-Mesoproterozoic supercontinent Columbia. Therefore, in any configuration of the supercontinent Columbia, the southern margin of the North China Craton could not have been connected to any other continental block as proposed in a recent configuration, but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the North China Craton.