摘要
广西东南部钦防海槽地区晚古生代硅质岩十分发育。对硅质岩主量元素、微量元素及稀土元素的分析结果表明:该区晚古生代硅质岩含有较高的SiO2,硅化程度较高;除上泥盆统弗拉斯阶及下石炭统硅质岩具有较低的Al/(Al+Fe+Mn)值(0.14～0.24;0.07～0.81)及较高的U/Th值(0.34～5.09;0.16～10.1)外,其他层位硅质岩具有较高的Al/(Al+Fe+Mn)值(0.4～0.95)及较低的U/Th值(0.1～2.1);上泥盆统硅质岩稀土元素比值Ce/Ce*、LaN/YbN及LaN/CeN值分别为0.78～1.08、0.4～1.52和0.88～1.35,而下石炭统硅质岩具有较低的Ce/Ce*值(0.55～0.91)、LaN/YbN值(0.12～1.8)及较高的LaN/CeN值(1.12～1.79),中下二叠统硅质岩Ce/Ce*、LaN/YbN及LaN/CeN值分别为1.01～1.62、0.72～2.71和0.62～1.9。钦防海槽晚古生代硅质岩地球化学特征表明:晚泥盆世钦防海槽发生扩张,热液活动比较强烈,处于大陆边缘海环境;早石炭世钦防海槽再次发生扩张,热液活动强烈,硅质岩形成于远离陆源的深海海盆环境;早中二叠世,钦防海槽逐渐收缩,海水变浅。钦防海槽晚古生代并没有出现真正的洋壳,可能属于晚古生代古特提斯分支洋盆的一个坳拉槽盆地。
The Late Paleozoic siliceous rocks in the Qingfang Trough were well developed. Based on the analyses of major elements, trace elements and rare earth elements, it was concluded that the Late Paleozoic siliceous rocks contain high content of SiO2 and high silicification degree; the Upper DevonianFrasnian and Lower Carboniferous siliceous rocks have lower A1/（AI＋Fe＋Mn） value （0. 14-0.24; 0.07 0. 81） and higher U/Th value （0.34 - 5.09; 0. 16-10. 1） , whereas the Famennian and Lower-Mid- dle Permian siliceous rocks have higher A1/（AI＋Fe＋Mn） value（0.4-0.95） and lower U/Th value （0. 1 2. 1） , illustrating that the Frasnian and the Lower Carboniferous siliceous rocks were influenced by the hydrothermal process but the Famennian and the Lower-Middle Permian siliceous rocks were biogenic ori- gin; Ce/Ce＊ , LaN/YbN , and LaN/CeN values for the Upper Devonian siliceous rocks are 0.78- 1.08, 0. 4- 1.52 and O. 88- 1.35, whereas these values for the Lower Carboniferous siliceous rocks are 0.55 - O. 91, 0. 12- 1.8 and 1.12 - 1.79, and the Lower-Middle Permian siliceous rocks have Ce/Ce＊ , Lax/ YbN, and LaN/CeN values of 1.01 - 1.62, 0.72-2.71 and 0.62 - 1.9; Geochemical characteristics of the Late Paleozoic siliceous rocks in the Qinfang Trough indicated that the Qinfang Trough expanded within an epicontinental sea environment during the Late Devonian with hydrothermal activity, then expanded a- gain in the Early Carboniferous with siliceous rocks formed in deep sea basin environment, and in the Ear- ly Permian the Qinfang Trough shrinked gradually to a continental margin basin. In a conclusion, the Qin- fang Trough is more like a sea basin and may be belong to the Aulacogen of Paleo-Tethys Ocean in Late Paleozoic, and an ocean crust had never been formed.
出处
《古地理学报》
CAS
CSCD
北大核心
2014年第1期77-87,共11页
Journal of Palaeogeography：Chinese Edition
基金
国家自然科学基金项目(编号:41272120)
中央高校基本科研业务费专项资金资助项目共同资助
关键词
钦防海槽
硅质岩
地球化学
晚古生代
Qinfang Trough, siliceous rocks, geochemistry, Late Paleozoic
