湖南锡田和邓阜仙燕山期花岗岩的源区差异及其意义

Difference of sources of the Yanshanian Xitian and Dengfuxian granites in Hunan Province and their implication

对湖南茶陵锡田和邓阜仙复式岩体燕山期二云母花岗岩进行岩相学、锆石及岩石元素地球化学特征的对比研究,以探讨其源区可能的差异对钨锡多金属成矿的影响。研究结果表明:锡田与邓阜仙二云母花岗岩均显示为高硅、高铝、富碱特征,较高的10 000w(Ga)/w(Al)(分别为3.58~4.20和2.04~4.11,w为质量分数)指示其为A型花岗岩;w(Nd)/w(Th)<15和w(Th)/w(U)>1特征指示两者为壳源,但锡田岩体较邓阜仙岩体含磷低,更富稀土元素,其Eu负异常(δ(Eu)=0.03~0.04)较邓阜仙岩体(δ(Eu)=0.24~0.85)更显著,轻重稀土分馏程度更低,其稀土配分曲线呈"对称"型,而邓阜仙岩体为"右倾"型;由锆石组分计算的锡田与邓阜仙岩浆结晶温度分别为823~945℃和613~922℃,氧逸度lg(fo_2/10~5 Pa)分别为-14.7和-16.8,表明两岩体均为形成伸展背景下的A型花岗岩,是元古宙地壳部分熔融产物;源区以碎屑岩为主,锡田岩体源区应更富火成岩,这表明同为壳源,且同期、空间相邻岩体仍可存在源区和成岩环境的差异,这种物源背景差异对成矿产生影响。

In order to explore the effect of different source regions on W and Sn polymetallic mineralization, comparative studies of petrography and geochemistry of element on zircon and rock were conducted on two-mica granites in Yanshanian complex mass from Xitian and Dengfuxian in Hunan Province. The results show that Xitian and Dengfuxian＇ two-mica granites are rich in silicon, aluminum and alkali. Relative high values of 10 000ω（Ga）/ω（Al） （3.58-4.20 and 2.04-4.11, respectively） indicate that both granites are A-type granites, ω（Nd）/ω（Th）〈 15 and ω（Th）/ω（U）〉 1 suggest that both granites originate from crust. However, Xitian granite has lower phosphorus, higher rare earth elements, more negative Eu anomaly, and lower degree of fractionation between light and heavy rare earth elements than that of Dengfuxian granite. The REE distribution pattern of Xitian granite is symmetrical type while that of Dengfuxian granite is right type. Moreover, magma crystallized temperatures in Xitian and Dengfuxian calculated by using components of zircon are 823-945 ℃ and 613-922 ℃, respectively, and lg（fo2/105 Pa） are -14.7 and -16.8, respectively, which shows that Xitian and Dengfuxian granites are A-type granites formed in an extensional tectonic setting. They are also products of the partial melting of proterozoic crust, and their source regions mainly contain clastic rock. But there are more igneous rocks in the source region of Xitian granite. As a result, two crust-original granites with spatially adjacency and the same period can still come from different sources and diagenetic environments, which has impact on mineralization.