且干布拉克早寒武世硅质岩岩石学、地球化学特征及地质意义

摘要

通过对西山布拉克组第一岩性段硅质岩岩石学、地球化学特征研究，探讨其沉积环境和成因，推测其与库鲁克塔格早古生代地壳演化关系。研究区硅质岩夹泥质硅岩、流纹质晶屑凝灰岩的岩石组合，硅质岩的Al/（Al+Fe）值（~0.6）、Ce/Ce*值（~0.57）、（La/Yb）n值（~0.66）等特征指示为欠补偿、缺氧的深水盆地沉积环境。其Fe/Ti值（~29.2），Al/（Al+Fe+Mn）值（~0.54），（Fe+Mn）/Ti值（~31.3），富集Ag，As，Sb，Ba元素等特征，表明该区硅质岩为热水和海水混合成因，形成过程中海水有较高的生产力。硅质岩∑REE在剖面底部为14.9×10-6，向上减小为8.6×10-6，至顶部增加到105.6×10-6，表明剖面底部到顶部热水活动强度呈减弱趋势。早寒武世硅质岩岩石学、地球化学特征表明，硅质岩形成于裂陷槽盆地中，是上升洋流将海底热水物质带至沉积地点与海水发生不同程度混合的产物，为库鲁克塔格早寒武世早期处于拉张裂解环境提供了岩石学和地球化学证据。%The systematic analyses of petrology and geochemistry of Xishanbulake Formation cherts in Lower Cambri-an of Kuruktag, Xinjiang have been made in this work. The purpose of this paper is to dissuss depositional environment and orign of cherts and infer the relationship with crustal evolution of Kuruktag in the Early Paleozoic. The characteris-tics of rock association composed of black cherts interbedded with argillous cherts, crystal tuff, ratios of Al/(Al+Fe) (~0.6), Ce-anomalies(~0.57) and ratios of (La/Yb)n(~0.66) represent for abyssal, anoxic and insufficient compensation envi-ronment. The characteristics of ratios of Fe/Ti(~29.2), ratios of Al/(Al+Fe+Mn)(~0.54), ratios of (Fe+Mn)/Ti(~31.3) and rich Ag, As, Sb, Ba elements indicate that cherts are hybrid origin from hydrothermal sediments and hydrogenous sedi-ments, and there are high yields in the seawater.∑REEs in the cherts decrease from 14.9ppm at the bottom to 8.6ppm in the middle, then increase to 105.6ppm at the top. These REE parrerns suggest that activities of hot water would be weak-ened from the bottom to the top. Combining with regional geological background, the cherts deposit in rift trough basin which result from mixturing by hot water and seawater through ascending current. These provide petrologic and geo-chemical evidence for extensional background of Kuruktag in the Early Cambrian.