地质学报2018，Vol.92Issue(3)：545-559,15.
青藏高原拉萨地块中西部超钾质岩Ca-Mg同位素特征及其地质意义
Ca-Mg Isotopic Compositions of Ultra-Potassic Volcanic Rocks in the Lhasa Terrane, Southern Tibet and Their Geological Implications
摘要
Abstract
To better understand the compositions of enriched mantle source of ultra-potassic rocks in southern Tibet,here we report Ca and Mg isotopic compositions of eight ultra-potassic rock samples from the Mibale and Maiga areas in the Lhasa Terrane.Excluding the effect of weathering,crustal contamination,fractional crystallization and partial melting on ultra-potassic rocks' Ca and Mg isotopic compositions,it is determined that some carbonate sediments from subducted Neo-Thethy oceanic crust may join into the mantle source of ultra-potassic rocks.The ultra-potassic rocks show significantly lower δ44 Ca values ranging from 0.59 to 0.75 (average=0.68±0.04),which are distinctly lower than the upper mantle (1.05 ±0.04),bulk silicate earth (0.94±0.05) and igneous rocks (0.80±0.10).All these features indicate that the mantle source of ultra-potassic rocks might contain materials with low δ44Ca value.The δ26 Mg values of ultra-potassic rocks display limited varication from-0.33 to-0.24 (mean =-0.29 ± 0.03),which are similar to the upper mantle (δ26Mg=-0.25±0.07) within the analytical uncertainty.The Ca-Mg isotopic compositions of ultra-potassic rocks are positively correlated,indicating their source might be metasomatized by the materials with low δ44 Ca and δ26 Mg value.Considering the tectonic evolution of Lhasa Terrane,we suggest that the low Ca-Mg isotopic materieals are very likely marine carbonate sediments derived from subducted Neo-Tethyan oceanic crust.关键词
拉萨地块/超钾质岩/Ca-Mg同位素/地幔源区/特提斯俯冲Key words
Lhasa Terrane/ultra-potassic rocks/Ca-Mg isotopic composition/Mantle source/Tethyan subduction引用本文复制引用
刘峪菲,许继峰,张兆峰,王桂琴,陈建林,黄丰,祝红丽,刘芳..青藏高原拉萨地块中西部超钾质岩Ca-Mg同位素特征及其地质意义[J].地质学报,2018,92(3):545-559,15.基金项目
本文为国家自然科学基金项目(编号41373007、41603033),国家重点基础研究发展计划(编号2016YFC0600304)和博士后创新人才支持计划(编号BX201700213)联合资助成果. （编号41373007、41603033）
