渝东地区震旦系灯影组硅质岩结构特征与成因机理

Fabric Characteristics and Formation Mechanism of Chert in Sinian Dengying Formation,Eastern Chongqing

通过地表剖面测制，主要应用常规显微镜、扫描电子显微镜详细刻画了渝东地区震旦系灯影组硅质岩显微结构特征，分析了硅质岩的硅、氧同位素特征，探讨了硅质岩的成因机理。结果表明：灯影组硅质岩主要由隐晶石英、玉髓、微晶石英及巨晶石英结构元素组成；具有隐晶、微晶和镶嵌3种结构类型。硅质岩中可见有残存的白云石晶体，代表热水沸腾的针状孔较发育；硅质岩和晶洞石英单矿物的伊。Si值变化范围在-0．6‰～0．8‰，属于热水来源的硅质岩中的δ-30 Si值范围，δ-30值为15‰～23．5‰，利用氧同位素计算得出，研究区硅质岩的形成温度主要分布在70～110℃；微量元素和稀土元素特征揭示研究区硅质岩为热水成因，但也受到构造地理位置和海水的影响；硅质岩为热水与海水、沉积与成岩共同作用的产物，形成时间主要在晚震旦世灯影期早寒武世牛蹄塘期。

Based on profile measuring, applied the microscopy and SEM technology, the micro-texture characteristics of chert in Sinian Dengying Formation in eastern Chongqing has been studied. And features of oxygen isotope are also discussed in this paper. The formation mechanism of chert has been analyzed at last. Four understands have been gotten in this paper, whose are. （1） Chert of Dengying Formation comprise of cryptocrystalline quartz, chalcedony, microcrystalline quartz and megacryst quartz fabric elements,and cryptocrystalline, microcrystalline and poikilotopic fabric types have been found in the chert. Survival dolomite is also found in the chert, and boiling pinholes which respond to hydrothermal fluid are very abundant in chert. （2） Value of δ30Si in chert ranges from-0.6‰ to 0. 8‰ , which belongs to the range of hydrothermal chert. The value of δ18 O in chert ranges from 15‰to 23.5‰. The hydrothermal temperature,which calculated by the oxygen isotope in chert mainly ranges from 70 to ll0℃. （3） Geochemical features of main elements and REEs reveals that chert origins in hydrothermal fluids, and affected by the structural geographic location and sea water. （4） The formation mechanism of chert is controlled by multi factors, sea water, hydrothermal fluid, deposition and diagenesis. The formation time of chert ranges from late Sinian Dengying stage to early Cambrian Niutitang stage.