辽东大东沟金矿岩浆岩LA-ICP-MS锆石U-Pb年龄及岩石地球化学特征

    LA-ICP-MS zircon U-Pb age and petrochemical characteristics of magmatite from the Dadonggou gold deposit in east Liaoning

    • 摘要: 大东沟金矿位于华北克拉通北缘东段。对矿区内的岩浆岩进行了锆石U-Pb年代学和岩石地球化学研究。用LAICP-MS方法,测得花岗闪长岩和石英闪长岩中锆石207Pb/206Pb年龄加权平均值分别为2147±10Ma和140.8±1.2Ma,花岗闪长岩经历了1874±18Ma的后期热液活动事件。元素地球化学测试结果显示,两者均为高钾钙碱性I型花岗岩类。石英闪长岩稀土元素配分模式为明显的右倾模式,具有弱负Eu异常,而花岗闪长岩为平坦的右倾模式,具有明显的正Eu异常,两者呈现轻稀土相对富集的特征。微量元素均富集Rb、Ba、K等大离子亲石元素。石英闪长岩表现为亏损Nb、Ta、Zr、Hf、Ti等高场强元素,而花岗闪长岩表现为Th、Nb、Ta、Ti等高场强元素亏损。结合区域大地构造背景及相关研究认为,花岗闪长岩形成于大陆弧后盆地的构造背景,主要是由约2.2Ca的岩浆底侵加热导致下地壳基性火成岩部分熔融而成;石英闪长岩形成于伊佐奈岐板块向华北板块斜向俯冲的构造背景,具有壳幔混合的特征,为俯冲带流体交代地幔,使其部分熔融,形成基性岩浆与地壳熔融物质混合而成的产物。

       

      Abstract: The Dadonggou gold deposit is located in the east of the northern margin of North China craton.In this paper, zircon UPb chronology and petrochemistry of magmatite from the Donggou gold deposit were studied. The LA-ICP-MS method was used and the ages of zircon in granodiorite and quartz diorite are 2147±10Ma(207Pb/206Pb age-weighted mean, n=17, MSWD=0.59) and 140.8 ±1.2Ma(206Pb/238U age-weighted mean, n=22, MSWD=0.48) respectively; nevertheless, the granite diorite experienced late hydrothermal events of 1874 ±18Ma.Elemental geochemical test results show that both granodiorite and quartz diorite are high potassium calc-alkaline I type granite. Quartz diorite is a right-dipping model with weak negative Eu anomalies, but granodiorite is a relatively flat right-dipping model with obvious positive Eu anomalies; they both show characteristics of relatively rich light rare earth elements. As for trace elements, they are all enriched in large ion lithophile elements Rb, Ba and K. Quartz diorite is characterized by depletion of high field strength elements such as Nb, Ta, Zr, Hf and Ti, but the granodiorite shows the depletion of high field strength elements such as Th, Nb, Ta and Ti. Combined with regional tectonic evolution and related studies, the authors have reached the conclusion that granodiorite was formed in the tectonic background of continental back-arc basin, mainly caused by partial melting of the lower crustal igneous rocks due to the magmatic heating action of ~2.2Ca. However, quartz diorite was formed in the tectonic background of the oblique subduction of Izanagi plate to the North China plate, which had the feature of crust-mantle mixing.It was the fluid metasomatic mantle in the subduction zone, and the basic magma formed by partial melting was mixed with the crust molten material.

       

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