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首页> 外文期刊>Journal of Asian earth sciences >Petrogenesis of coexisting high-silica aluminous and peralkaline rhyolites from Yunshan (Yongtai), southeastern China
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Petrogenesis of coexisting high-silica aluminous and peralkaline rhyolites from Yunshan (Yongtai), southeastern China

机译：中国东南部云山（永泰）共存的高硅铝硅酸盐和高碱性流纹岩的成因

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摘要

The Late Cretaceous bimodal Yunshan (Yongtai) volcanics in Fujian province contain peralkaline rhyolites, the only presence of such rhyolites in southeastern China. Whole-rock and mineral chemical compositions are analyzed for the coexisting aluminous (metaluminous to weakly peraluminous)-peralka!ine high-silica rhyolites from the Yunshan volcanics. They are sparsely porphyritic, and contain K-feldspar, ferromagnesian minerals, quartz, magnetite, and titanomagnetite phenocrysts, as well as accessory minerals such as fayalite, chevkinite, apatite and zircon. The mineral assemblage indicates an oxidizing preemption condition. These rhyolites exhibit diagnostic geochemical features of A-type granites, such as elevated 10~4 * Ca/Al (mostly greater than 2.6) and FeO~T/(FeO~T + MgO) ratios, enrichment in high field strength elements (HFSE) such as Zr (>400ppm) and Nb, and strong depletion in Al_2O_3 (<13 wt%), CaO, Ba and Sr. On the basis of their petrographic and geochemical characteristics, it is suggested that the rhy-olite magmas are derived from partial melting of H_2O-poor (meta) granitic igneous rocks in the deep crust, and cannot be fractionated from the coeval Yunshan mafic magmas. Geochemical variations of major and trace elements indicate the possible fractionation of K-feldspar, calcium-rich pyroxene, Fe-Ti oxides and minor chevkinite during the magma evolution. In peralkaline rhyolites, we found that the pre-existing Fe-Ti oxide and hedenbergite phenocrysts had been transformed into aegirine + oxide and aegirine + oxide + fluorite assemblages, respectively. These mineral assemblages are the products of the subsolidus reaction of pre-existing phenocrysts and extraneous Na-F-rich fluids. Such Na-F-rich fluids may be derived from the degassing of the subvolcanic rocks. The reactions indicate that the Yunshan peralkaline rhyolites could be generated through the reaction of highly fractionated aluminous silica magmas and Na-F-rich fluids.
机译：福建省晚白垩世双峰云山（永泰）火山岩含有碱性碱性流纹岩，这是中国东南部唯一的此类流纹岩。分析了云山火山岩中共存的铝质（金属铝质至弱铝质铝质）-高铝钾盐流纹岩的全岩石和矿物化学成分。它们是稀疏的斑状的，含有钾长石，铁锰矿，石英，磁铁矿和钛磁铁矿斑晶，以及辅助矿物，如铁橄榄石，雪佛兰，磷灰石和锆石。矿物组合表明存在氧化先占条件。这些流纹岩表现出A型花岗岩的诊断地球化学特征，例如升高的10〜4 * Ca / Al（大多大于2.6）和FeO〜T /（FeO〜T + MgO）比，富含高场强元素（HFSE） ）（如Zr（> 400ppm）和Nb），以及Al_2O_3（<13 wt％），CaO，Ba和Sr中的强耗竭。根据它们的岩石学和地球化学特征，建议形成流纹岩浆岩浆H_2O贫（元）花岗岩火成岩在深地壳中的部分融化，而不能从云山基性岩浆岩中分离出来。主要和微量元素的地球化学变化表明，在岩浆演化过程中可能会分馏钾长石，富钙辉石，铁钛氧化物和次氯钒铁矿。在高碱性流纹岩中，我们发现先前存在的Fe-Ti氧化物和Hedenbergite晶状体分别被转化为Aegirine +氧化物和Aegirine +氧化物+萤石组合。这些矿物组合是预先存在的表晶和多余的富含Na-F的流体的亚固相反应的产物。这种富含Na-F的流体可以来自火山岩的脱气。反应表明云山高碱性流纹岩可以通过高度分馏的硅铝岩浆和富Na-F的流体反应生成。

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  • 来源
    《Journal of Asian earth sciences》 |2013年第25期|316-329|共14页
  • 作者

    Wentao Hong; Xisheng Xu; Haibo Zou;

  • 作者单位

    State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China;

    State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China,State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China;

    Department of Geology and Geography, Auburn University, Auburn, AL 36849, USA;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Peralkaline; Aluminous; Rhyolites; Fluid-rock reaction; Bimodal; SE China;

    机译：过碱性铝流纹岩;流体-岩石反应;双峰中国东南;

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