雅鲁藏布江缝合带及藏南地区硅质岩微组构特征及其地质意义

在雅鲁藏布江缝合带及藏南地区产出红、绿、黑、褐等多色调的中生代硅质岩.石英是它们的主要矿物,但不同样品的石英晶体微形貌各有特征,X衍射和红外吸收光谱特征表现出细微差别.夏鲁和彭错林分别作为生物成因和热水成因硅质岩的代表,它们在矿物演化路径、石英晶体微形貌和集合体微结构存在差异,为利用微组构区分不同成因硅质岩提供了参考依据.在夏鲁硅质岩中生物化石残骸内存在方英石和玉髓,为反演生物成因硅质岩的矿物演变序列提供了很好的证据.硅质岩成岩过程中微组构演变和元素迁移具有良好的对应关系.石英在重结晶过程中对杂质元素的剔除作用是促使某些微量元素产生富集的重要机制.从微组构角度切入硅质岩研究是一种新的研究思路,它综合运用微区微束手段对硅质岩的微观组构特征进行测试,进而探讨微观组构信息所指示的地质意义.结果对探讨硅质岩的成因、演化和藏南地区硅质岩容矿型Au-Sb-Cs矿床的成矿机理具有重要的指导作用.

Microfabrics of chert from Yarlung Zangbo Suture Zone and southern Tibet and its geological implications.

There exist cherts with red, green, black and brown colors in the Yarlung Zangbo Suture Zone and to its south. Quartz is their predominant mineral component, but differs in crystallinity and micro-texture as well as the XRD and FTIR characteristics, depending on samples from different occurrences. The Xialu chert and the Pengcuolin chert are considered of biogenic origin and hydrothermal origin individually. They are different in the evolution of mineral, and microfabrics, which provides possibility to identify the origin of chert. The existence of cristobalite and chalcedony in fossils of the Xialu profile are significant evidence to reconstruct the mineral evolution in biogenic chert. It is shown that the change of microfabric is well associated with the geochemical migration of elements in diagenesis of chert. That the recrystalization process expels the impurity components from SiO2 crystals may be an effective mechanism to enrich trace elements. The microfabrics of chert is a new direction worthy of paying more attention. Based on advanced testing techniques, such as the XRD, FTIR, RAMAN, SEM and EPMA, it provides with rich microfabric information, helping in revealing the diagenesis and orgin of chert as well as the metallogenesis of the Au-Sb-Cs mineralization belt in southern Tibet.