安哥拉东北部地区Inkisi组碎屑锆石U- Pb年龄、地球化学特征及其地质意义

Inkisi组是刚果盆地西南缘最古老的沉积地层之一，岩性主要为一套紫红色、红褐色细粒、细中粒长石砂岩、杂砂岩。通过对安哥拉东北部Inkisi组长石砂岩开展碎屑锆石测年、岩石地球化学研究，探讨其沉积时代、物质来源、沉积环境和大地构造背景，为研究刚果盆地演化提供科学依据。结果表明，碎屑锆石206Pb/238U年龄主要集中于3个年龄峰值区间2350~1900 Ma、1150~850 Ma、850~500 Ma，最年轻的锆石峰值年龄为531±9 Ma，据此，本文认为Inkisi组的沉积时代上限应厘定为早寒武世。Inkisi组砂岩地球化学特征显示，物源具有长英质物源近源搬运特征，沉积时期的水体为陆相开阔的淡水环境。通过碎屑锆石年龄谱特征、主微量元素物源判别及构造判别图解，本文认为，West Congo构造带为安哥拉东北部地区Inkisi组主要物源区，Lufilian构造带、Angola 地盾等是其次要物质来源，物源区构造环境主要为活动大陆边缘和被动大陆边缘构造环境背景。

U- Pb dating of detrital zircons and geochemical characteristics of Inkisi Formation in the northeastern Angola area

The sedimentary age, material source, sedimentary environment and tectonic setting of the arkose of Inkisi Formation in northeast Angola are discussed through detritonal zircon dating and petrogeochemistry, which provide scientific basis for the study of the evolution of Congo Basin.Methods: We performed the zircon SHRIMP U- Pb isotopic dating, major elements and trace elements compositions of the arkose from Inkisi Formation in northeastern of Angola. Results: The results show that the 206Pb/238 U age of detrital zircon is mainly concentrated in three peak age ranges of 2350~1900 Ma, 1150~850 Ma, and 850~500 Ma, with the youngest zircon having a peak age of 531±9 Ma.Conclusions: The upper limit of depositional age of Inkisi Formation in this area is the Early Cambrian. The geochemical characteristics of the sandstone of Inkisi Formation show that the provenance has the characteristics of near- source transport of felsic provenance, and the water in the sedimentary period was an open freshwater environment of continental facies. Based on the age spectrum of detrital zircon, source identification of major trace elements and structure identification diagram, the results show that the West Congo tectonic zone is the main provenance zone, followed by the Lufilian tectonic zone and Angola shield. The tectonic environment of its provenance area is mainly active continental margin and passive continental margin tectonic environment background.