江西三清山花岗岩体的元素地球化学特征及其地质意义

Element Geochemical Characteristics and Geological Implication of Sanqingshan Pluton in Jiangxi

江西三清山国家地质公园以花岗岩地质与花岗岩峰林地貌著称。通过对岩体各个相带的样品进行主微量元素分析,结果显示,三清山花岗岩体具有较高的硅、铝和碱的含量(SiO2=72.29%～79.26%,Al2O3=11.21%～14.28%,Na2O+K2O=5.25%～10.04%)贫镁铁,总体上为过铝质高钾钙碱性岩系列。三清山花岗岩体微量元素接近陆壳值,富集大离子亲石元素。轻重稀土分馏不明显(LREE/HREE=3.53～13.56,(La/Yb)N=1.80～13.46),属轻稀土富集型(Sm/Nd=0.154～0.292),具有明显的负铕异常(δEu=0.002～0.211)。分析表明,三清山花岗岩体经历了较高程度的演化,系一定程度的斜长石结晶分异的产物。三清山花岗岩具有A型花岗岩的特点,源区为成熟度较高的壳源变泥质岩的部分融熔。在构造环境上指示俯冲已经结束,三清山岩体可能形成于造山后的拉张环境。

Granite geology and granite peak forest landform are well known in Mt.Sanqingshan of Jiangxi.Major trace element analysis of samples in different phases shows that silicon,aluminum and alkali content in Mt.Sanqingshan pluton is high（SiO2 = 72.29%-79.26%,Al2O3 = 11.21%-14.28%,Na2O ＋ K2O = 5.25% 10.04%）,magnesium and iron content is low.Generally they belong to peraluminous high-K calc-alkaline rock series.The trace elements are close to the value of the continental crust,enriched in large ion lithophile elements.Fractionation between HREE and LREE is not obvious（LREE / HREE = 3.53-13.56,（La / Yb） N = 1.80-13.46））,belonging to light rare earth enriched type（Sm / Nd = 0.154-0.292）,with strong negative Eu anomaly（δEu = 0.002-0.211）.Analysis shows that Mt.Sanqingshan pluton is the product of crystallization differentiation of plagioclase,experienced a higher evolution and A-type granite characteristics,with partial melting of matapelite of the crust source region.Tectonic environment subduction ended,entering an extensional environment of post-orogenic.