北祁连山早古生代硅质岩稀土元素特征及环境指相意义  

Tectonic Setting Implications of Rare Earth Elements in Early Paleozoic Siliceous Rocks from the Northern Qilian Mountains

作　　者：徐学义[1] 赵江天[1] 夏林圻[1] 夏祖春[1] 何世平[1] 

机构地区：[1]中国地质调查局西安地质矿产研究所,710054

出　　处：《地质论评》2003年第6期605-609,共5页Geological Review

摘　　要：本文通过对北祁连山不同地质环境与火山岩相伴生硅质岩稀土元素特征的分析,证明产于不同地质环境硅质岩的稀土元素,特别是∑REE、Ce/Ce*、LaN/YbN具有特定的规律性变化.该研究为利用硅质岩稀土元素判定古老造山带构造环境提供了参考标准.This paper presents researches on the REE characteristics of siliceous rocks occurring in different tectonic settings. We have measured the REE contents in 23 siliceous rock samples collected from different Early Paleozoic tectonic settings, such as continental rift, mid-ocean ridge, island-arc and back-arc basin settings inthe northern Qilian Mountains. The results show that analyses of the REEs,especially ∑REE, Ce/Ce* and LaN/YbN change regularly, which are closely related to the tectonic settings. From mid-ocean ridge,back-arcbasin, island arc,fissure-type continental rift to central-type continental rift, the REE values vary from 7. 64X×10-6, 8. 2×10-6, 23.74×10-6, 28. 4×10-6 to 69. 4×10-6, the Ce/Ce* from 0.63, 0.68, 0.72, 0.75 to 0.95 and the LaN/YbN from 0.37, 0.41, 0.59, 0.76 to 1.08. These studies have verified the following law:At the beginning of continental rifting (corresponding to the central-type continental riftsetting), the Ce/Ce* values are close to 1 and the ∑REE values are very high with less ∑REE distillation or relative LREE enrichement; at the late stage of the continental rifting (corresponding to the fissure-type continental rift setting), the ocean crust appeared and the Ce/Ce* values fall within the range of ocean settingwith low ∑REE contents and enriched HREE. On the other hand, siliceous rocks occurring in oceanicsettings (including mid-ocean ridge, island arc and back-arc basin) have relatively low ∑REE, Ce/Ce* , LaN/ YbN values than those in continental rift, those in mid-ocean ridge setting have the lowest Ce/Ce * values andREE contents as well as highly-enriched HREE;whereas siliceous rocks occurring in back-arc basin settingwith less HREE enrichment have normal ocean setting Ce/Ce* values and REE contents, which are higher than those in mid-ocean ridge setting. Siliceous rocks in island-arc setting have higher Ce/Ce* values andREE contents than those in back-arc basin setting with decreasing HREE enrichment. The authors consider that the studies can provide a refe

关 键 词：早古生代 硅质岩 稀土元素 环境指相 

分 类 号：P595[天文地球—地球化学]