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    海南石碌铁矿外围花岗岩类成因及形成的构造环境

    Origin and rock-forming environment of the granitoids in the periphery of the Shilu iron deposit

    • 摘要: 提要:石碌铁矿床外围的印支期花岗岩属于昌江岩体的一部分。这些花岗岩岩性为二长花岗岩,为准铝质-弱过铝质,属于高钾钙碱性系列和钾玄岩系列。岩石稀土元素总量较低,变化不大,∑REE介于134.96×10-6~241.05×10-6;轻重稀土分异明显,LREE/HREE变化于4.44~9.67,(La/Yb)N变化于3.95~10.69;具有中等负Eu异常(δEu=0.28~0.57),Ba、Nb(-Ta)、Ce、Sr、P、Ti具明显负异常。Ba、Sr、Eu的明显负异常表明源区有斜长石的大量残留或岩石经历了斜长石的结晶分异作用。花岗岩87Sr/86Sr初始比(ISr)主要变化于0.710 852~0.715 492(1个样品ISr值为0.706 364)。εNd(t)=–7.3~-9.1,TDM2模式年龄变化于1.5~1.9 Ga。总体来说,ISr值、εNd(t)值和TDM2值比较均匀,表明源区是均匀的,由中元古代抱板群部分熔融作用所形成。花岗岩形成于后碰撞环境。笔者在探讨海南岛与俯冲有关的弧岩浆活动、同碰撞岩浆活动和与后碰撞有关的岩浆活动基础上,认为海南岛海西—印支期花岗岩可与北越南海西—印支期花岗岩进行对比。

       

      Abstract: Abstract:The Indosinian granites in the periphery of the Shilu iron deposit belong to the Changjiang granitic body. These granites are mainly monzonitic granites. They lie between metaluminous field and weakly peraluminous field, and belong to high-K calc-alkaline series and shoshonitic series. The granites have ∑REE values of 134.96-241.05 ppm and show relatively strong enrichment of light rare earth elements (LREE/HREE=4.44-9.67), with higher (La/Yb)N ratios of 3.95-10.69 and negative Eu anomalies (δEu=0.28-0.57). Mantle-normalized trace element spidergrams of all samples show obvious negative anomalies of Ba, Nb, Ta, Ce, Sr, P and Ti. The obvious negative Ba, Sr and Eu anomalies indicate that plagioclase existed in the source region or the granites experienced plagioclase crystallization and fractionation. The granites have a range of (87Sr/86Sr)i from 0.710852 to 0.715492 except for one sample (SL10-136) whose (87Sr/86Sr)i value is 0.706364 , a narrow εNd(t) value range of -7.3 to -9.1 and TDM2 model ages of 1.5–1.9 Ga, indicating a homogeneous source and partial melting of the Mid-Proterozoic Baoban Group. The granites were formed in a post-orogenic environment. Based on previous investigation of granite in Hainan Ireland, this paper deals with ireland-arc, syn-orogenic and post-orogenic granitoids in Hainan Ireland. The Hercynian to Indosinian granitoids can be compared with granitoids in northern Vietnam.

       

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