甘肃武山鸳鸯镇蛇绿岩构造年代学特征及其构造意义探讨

本文通过对甘肃武山县鸳鸯镇蛇绿岩构造年代学的深入研究,结合野外实测地质剖面对鸳鸯镇蛇绿岩的形成,其代表的构造意义进行了探讨,该带蛇绿岩中采集的蛇纹石Sm-Nd同位素等时线年龄为473±23Ma;在该带硅化碳酸盐化变玄武岩中采用锆石U-Pb法测年,测得模式年龄值为546Ma。研究认为武山蛇绿岩其岩石组合中与显生宙的蛇绿岩大致相近,所不同的是组合中含深水碳酸盐岩;蛇绿岩中基性岩类的REE球粒陨石标准化配分模式接近平坦型及微量元素的环境判别图式都表明该蛇绿岩的生成环境很可能是初始洋盆;武山蛇绿岩代表古生代大陆裂解的产物,两组年龄值基本代表了本次大陆裂解成海盆的时代。

TECTONIC GEOCHRONOLOGY OF OPHIOLITE IN YUANYANGZHEN TOWN OF WUSHAN COUNTY, GANSU PROVINCE

Through the study on tectonic geochronology of ophiolite in Yuanyang Town of Wushan County, Gansu Province, and measured geological section, the authors discussed the formation of opiolite and significance to tectonics. The Sm-Nd isochron age of serpentine sample from ophiolite is 473 ± 23Ma, the model age of carbonatized, silicatized meta-basalt is 546Ma determined by U-Pb isotope dating of zircon. The study show that the rock association of ophiolite in Wushan County is similar with Phanerozoic ophiolite, but the difference between two is that the former contain deep-water carbonates, the forming environment of ophiolite should be likely to be an initial ocean basin according to the nearly flat shape of REE chondrite normalized pattern and the discrimination diagram of trace elements of intermediate -basic rock type within the ophiolite, the ophiolite in Wushan County is the product of Paleozoic continental breakup, both of the above-mentioned ages represent the age when the continent broke up to marine basin.