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    内蒙古红花尔基白钨矿矿床赋矿花岗岩Sr-Nd-Pb-Hf同位素特征

    Sr-Nd-Pb-Hf isotopic characteristics of ore-bearing granites in the Honghuaerji scheelite deposit, Inner Mongolia

    • 摘要: 提要:对内蒙古红花尔基白钨矿矿床的赋矿花岗岩进行了全岩Sr、Nd同位素、钾长石Pb同位素以及LA-MC-ICP-MS锆石Hf同位素特征研究。结果表明,从肉红色二长花岗岩、灰白色二长花岗岩到石英二长岩,它们的(87Sr/86Sr)i值依次降低,均值分别为0.70525、0.70517和0.70482,εNd(t)值则依次增加,均值分别为+2.2、+2.3和+3.1。2种二长花岗岩的钾长石Pb同位素值较均一,其中206Pb/204Pb为18.258~18.276,207Pb/204Pb为15.507~15.512;208Pb/204Pb为37.994~38.018。3种花岗岩的锆石Hf同位素特征显示εHf(t)值分别为+5.2~+10.4(均值+8.1)、+3.1~+9.8(均值+7.5)、+5.8~+14.4(均值+9.2)。赋矿花岗岩的Sr-Nd-Pb-Hf同位素特征指示其源岩物质很可能是以新元古代起源于亏损地幔的下地壳物质为主,石英二长岩可能是岩浆混合了少量地幔物质形成的包体。区域构造分析表明,红花尔基白钨矿矿床赋矿花岗岩岩浆源区的形成可能与新元古代古亚洲洋演化过程中俯冲大洋板块与上地幔的相互作用有关;早侏罗世,蒙古—鄂霍次克洋盆在本区闭合后,板块碰撞隆起的挤压环境触发了源岩物质的部分熔融,从而形成了赋矿花岗岩。

       

      Abstract: Abstract: A study of whole-rock Sr-Nd isotopes, Pb isotopes of K-feldspar and Hf isotopic compositions of zircons from the ore-bearing granites in the Honghuaerji scheelite deposit was carried out in this paper. The results show that the average (87Sr/86Sr)i ratios of pink monzogranite, gray monzogranite and quartz monzonite are 0.70525, 0.70517 and 0.70482 respectively, displaying a decreasing trend; however, the average εNd(t) values are +2.2, +2.3 and +3.1 respectively, exhibiting an increasing trend. The Pb isotopic compositions of K-feldspar samples selected from pink and gray monzogranites are relatively uniform, with the 206Pb/204Pb ratios ranging from 18.258 to 18.276, 207Pb/204Pb ranging from 15.507 to 15.512 and 208Pb/204Pb ranging from 37.994 to 38.018. The εHf(t) values of zircons from the three samples are +5.2?+10.4, +3.1?+9.8, +5.8?+14.4 respectively. The Sr-Nd-Pb-Hf isotopic compositions show that the granites-forming materials might have been derived from a depleted mantle during Neoproterozoic. The quartz monzonite was likely the inclusion which was a product of magma mingling. The regional tectonic analysis indicates that the magma resources were probably related to the interaction between the ocean plate and the upper mantle during the closure of Paleo-Asian Ocean before Mesozoic Era; and after the disappearance of Mongolia?Okhotsk marine trough, the compression tectonic setting that had resulted from the collision of plates triggered the partial melting of the resources in early Jurassic epoch.

       

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