扬子板块北缘阳坝岩体锆石饱和温度的计算及其意义
Zircon saturation temperatures of Yangba granodiorite and mafic microgranular enclaves in northern margin of Yangtze Block and its significance
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摘要: 通过对阳坝花岗闪长岩和暗色微粒包体中锆石饱和温度的计算反演岩浆源区的温度。计算结果表明,阳坝花岗闪长岩的锆石饱和温度介于762~773℃,平均值为769℃,暗色微粒包体的锆石饱和温度介于752~770℃,平均值为760℃。这表明阳坝花岗闪长岩可能是增厚下地壳在有外来流体注入的条件下发生低温(770℃)部分熔融的产物,而外来流体则可能是底侵作用早期由富含挥发分的偏基性岩浆发生去气作用的产物。Abstract: Assessing temperatures of magma that solidified to form plutonic rocks is notoriously problematic,because of:①scarcity of appropriate mineral pairs with temperature-sensitive exchange reaction and ② reequilibration during cooling. Zircon saturation thermometry provide a simple and robust means of estimating magma temperatures,because solubility of zircon is extremely sensitive to temperature.But in most cases,only weakly sensitive to other factors. Yangba pluton located in Yangba town,southern Kangxian,Gansu Province,NW China. In this paper,we calculate the zircon saturation temperatures for Yangba granodiorite and mafic microg ranular enclaves to inverse the temperature in magma source. The result indicated that the zircon saturation temperatures for host granodiorite range in 762～773℃,the average is 769℃,and the zircon saturation temperatures for mafic microg ranular enclaves range in 752～770℃,the average is 760℃.The temperatures suggested that Yangba granodiorites are derived from partial melting of thickened lower crust whichis in low temperature(770℃)with the participation of fluid which richin volatiles,and the fluid was possibly the results of gas discharge of mantle-derived magmas during early stage of underplating.
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