山东昌乐蓝宝石的色带微量元素及成因分析

Trace Element and Genesis of Colour Band of Sapphire from Changle, Shandong Province, China

  • 摘要: 色带发育是山东昌乐新生代玄武岩中的蓝宝石主要特征之一,其微量元素不仅影响宝石呈色,也对了解蓝宝石成因和母源岩浆具有重要作用。本研究以色带发育的山东昌乐蓝宝石样品为研究对象,利用紫外-可见光吸收光谱、傅里叶变换红外光谱和激光烧蚀电感耦合等离子体质谱对其谱学特征以及化学成分进行研究。结果表明,昌乐蓝宝石样品具有高Fe、Ga,低Mg、Cr的特征,符合岩浆成因蓝宝石的特征;Fe含量随色带颜色深浅呈规律性变化,指示了蓝宝石结晶过程的动荡性。红外吸收光谱可见和-OH有关的3 310 cm-1处吸收峰,-OH含量和色带颜色深浅呈正相关,深色色带-OH含量最高,浅色色带-OH含量较低。紫外-可见光谱中,黄色核心部分与Fe3+ -Fe3+相关的450 nm处吸收峰较为明显,指示了黄色核心部分为偏氧化条件下产生;蓝色色带部分与Fe2+ -Ti4+相关的570 nm处吸收峰较为明显,指示了蓝色色带部分为偏还原条件下产生。

     

    Abstract: The development of colour band is one of the main features of the sapphire in basalt in Changle, Shandong Province. The trace elements not only affect the colour of the gems, but also play an important role in understanding the genesis of sapphire and the mother source magma. This study takes the sapphires from Changle, Shandong Province as the research objects, and their spectrum characteristics and chemical compositions were tested by UV-visible absorption spectrometer, Fourier transformed infrared spectrometer and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). The results show that the sapphire samples from Changle have the characteristics of high Fe and Ga, low Mg and Cr, which is in line with the characteristics of sapphire in magma; the Fe content changes regularly with the shades of colour bands, indicating the intability of the sapphire crystallization process. The 3 310 cm-1 absorption peak related to -OH can be seen in the infrared absorption spectrum. The -OH content and the shade of the colour band are positively correlated. The darker band has the highest-OH content, and the -OH content of light band is relatively low. In the ultraviolet spectrum, the yellow core part has obvious relationship with the 450 nm absorption peak related to Fe3+ -Fe3+, indicating that the yellow core part is produced under partial oxidizing conditions. The blue colour zone has obvious relationship with the 450 nm absorption peak related to Fe2+-Ti4+, indicating that the blue colour zone is produced under partial reducting conditions.

     

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