滇西南昌宁-孟连构造带晚泥盆世枕状玄武岩和层状硅质岩的特征  

Late Devonian pillow basalts and bedded cherts in Changning-Menglian tectonic belt of southwestern Yunnan,China

作　　者：杨文强[1] 冯庆来[1] 段向东[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《地质通报》2007年第6期739-747,共9页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号:40372105);中国地质调查局<1:25万临沧幅区域地质调查>项目(编号:200413000004)资助

摘　　要：滇西南耿马地区回爱剖面发育有昌宁-孟连构造带最早的枕状玄武岩,与其共生的放射虫硅质岩、硅质泥岩含有晚泥盆世放射虫和牙形石化石。对硅质岩和玄武岩的地球化学研究表明,玄武岩的化学成分具有高P、Ti的特点,轻稀土元素富集,在稀土元素球粒陨石标准化模式图上表现为明显的右倾,微量元素中K、Rb、Ba等大离子亲石元素与Nb、Ta、Zr等高场强元素富集。化学投图结果表明玄武岩形成于洋岛环境。硅质岩的Al／(Al+Fe+Mn)比值大部分介于0.5～0.7之间,Al_2O_3／(Fe_2O_3+Al_2O_3)位于0.41～0.8之间,大部分硅质岩的Ce／Ce*比值小于1,具弱的Ce负异常,总体表现为大陆边缘型硅质岩的特征。这说明研究区晚泥盆世为邻近大陆边缘的洋盆环境,具洋壳性质的昌宁-孟连古特提斯盆地在晚泥盆世已经形成。The earliest pillow basalt of the Changning-Menglian tectonic belt was found at the Hui＇ai section, Gengma area, southwestern Yunnan. Radiolarian chert and siliceous mudstone associated with the pillow basalt contain Late Devonian radiolarians and conodonts. Geochemical study of chert and basalt indicates that the composition of the pillow basalt is characterized by high P and Ti and enrichment in LREE. The chondrite-normalized REE patterns are apparently right-inclined and the trace elements show enrichment in the large-ion lithophile elements such as K, Rb and Ba and high-field strength elements such as Nb, Ta and Zr. Chemical data plots indicate that the pillow basalt formed in an oceanic island environment. The chert in the Hui＇ai section is characterized by high ratios of Al/（Al＋Fe＋Mn） （0.5-0.7） and Al2O3（Fe2O3＋Al2O3） （0.41-0.8） and a weak negative Ce anomaly with most Ce/Ce^＊ ratios 〈1, which implies that the chert was deposited in a continental-margin basin. The above study indicates that study area was located in an oceanic basin environment adjacent to the continental margin in the Late Devonian and that the Changning-Menglian Paleo-Tethys ocean basin of oceanic crustal nature had already formed by that time.

关 键 词：晚泥盆世 洋岛玄武岩 硅质岩 昌宁-孟连构造带 滇西南 

分 类 号：P588.145[天文地球—岩石学] P588.244[天文地球—地质学]