Geochemical characteristics of the metapelites from the Xingxingxia group in the Eastern Segment of the Central Tianshan
Metapelites from the Mesoproterozoic Xingxingxia group in the Eastern Segment of the Central Tianshan, Northwestern China, were analyzed for major and trace elements, including rare earth elements. Compared with post-Archean shales, the metapelites are enriched in Sr, Hf and Zr. The other elements are similar to the compositions of the Phanerozoic North American Shale Composite and the Post-Archean Australian average Shale (PAAS). The characteristics of Al2O3/TiO2, Cr/Zr, Cr/Th, Th/Sc and high Zr concentration suggest that these pelites could be derived from a significant proportion of felsic and a few proportion of participation of mafic materials in nature. These rocks display highly fractionated REE patterns, and average (La/Yb)n = 18.6. Several samples have slightly negative Eu anomalies (Eu/Eu* = 0.7―0.84) in comparison with PAAS (Eu/Eu* = 0.65), indicating contribution from young immature materials. The low K2O/Al2O3 values of these metapelites suggest that their source materials could contain minimal alkali feldspar. In the A-CN-K triangular diagram, the sample data array intersects the feldspar join, indicating that the source had a plagioclase: K-feldspar ratio of approximately 5:1, representing weathered products from components that could approximately correspond to granodiorites and tonalites. The low Chemical Index of Alteration (CIA) and high Index of Compositional Variability (ICV) values suggest low degrees of weathering of the source and low compositional maturity of the sediments, respectively. The geochemical characteristics of the metapelites from the Xingxingxia group also demonstrate that these sediments were deposited in a back-arc background within a continental-arc system.
作 者： LI Qiugen LIU Shuwen HAN Baofu WANG Yueran DANG Qingning 作者单位： The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China 刊 名： 中国科学D辑（英文版） SCI 英文刊名： SCIENCE IN CHINA SERIES D (EARTH SCIENCES) 年，卷(期)： 2005 48(10) 分类号： P3 关键词： Eastern Segment of the Central Tianshan metapelites from the Xingxingxia group geochemistry provenance paleoweathering tectonic setting