矿床地质2011，Vol.30Issue(5)：773-786,14.
班公湖-怒江缝合带西段改则硅质岩地球化学征及沉积环境
Geochemical characteristics and sedimentary environment of siliceous rocks of Gerze area in western Bangong Co-Nujiang suture zone, Tibet
摘要
Abstract
The Bangong Co-Nujiang suture zone is the second huge ultramafic rock belt in Tibet. Based on detailed geochemical research, this paper discusses the genesis and tectonic setting of siliceous rocks in Gerze area, Tibet. Some conclusions have been reached: ① The SiQ2 content range is 85.23% ~93.73% , and Si/Al ratios vary in the range of 34.08～56.92, indicating that they contain a relatively high proportion of terrigenous muddy sediments; ② Incompatible elements such as Hf, Pb, Nb, Ta, Th and U are obviously depleted; ③ Al/(Fe + Mn + Al) ratios are 0.41～0.69, suggesting bio-genesis. Ba/Sr and U/Th ratios are lower than 1, and Al-Fe-Mn triangular diagram and Zr-Cr diagram show non-hydrothermal characteristics of siliceous rocks; ④ Al2Q3/ (Al2Q3 + Fe2O3) ratios are 0.50 ～0.77, and chondrite-normalized as well as North American shale-normalized REE patterns show that siliceous rocks are enriched with LREE with weak positive Ce anomaly and no obviousCe anomalies; (La/Ce)SN, Ce/Ce* and (La/Lu)SN values are 1.11～1.17, 0.90～0.92 and 1.10～1.62, V< 23 μg/g, and V/Y<2.8. All these features suggest that the siliceous rocks were formed in an environment of relatively weak hydrothermal activity but fairly abundant terrigenous material inputting. In addition, the deposition was dominated by a continental margin environment; ⑤ Si and O isotopes indicate typical characteristics of radiolarian chert. Besides, δ30Si-δ18O assumes positive correlation, indicating that Si and O isotopes had similar kinetic fractionation processes;⑥ Geochemical characteristics of chert implies that it was mainly deposited in a continental margin environment during the closure of the Tethys Ocean.关键词
地质学/地球化学特征/沉积环境/改则硅质岩/班公湖-怒江缝合带Key words
geology/geochemical characteristics/sedimentary environment/siliceous rocks of Gerze area/Bangong Co-Nujiang suture zone分类
天文与地球科学引用本文复制引用
冯彩霞..班公湖-怒江缝合带西段改则硅质岩地球化学征及沉积环境[J].矿床地质,2011,30(5):773-786,14.基金项目
本文受到国家重点基础研究发展计划项目(编号:2009CB421005)和国家自然科学基金(编号.40972071,40773020)联合资助 （编号:2009CB421005）
