摘要
青藏高原东部及邻区新生代钾玄岩系列岩石包括钾质碱性深成岩、火山岩、煌斑岩和偏酸性的斑岩。云母是钾玄岩系列岩石中的主要暗色矿物,分布亦较广泛。我们用单矿物化学分析方法测定本区钾玄岩系四种岩石中云母的化学成分,其结果MF=1.30～1.99,应为金云母-富镁黑云母,属于富碱富镁高铝贫铁类型的云母;云母的红外光谱,在450cm^(-1)和1000cm^(-1)附近都有很强的吸收谱带,显示了四种岩石中的云母具有类似的红外光谱特征;X光衍射测定,本区云母的d(060)为15.32nm～15.41nm,它们的晶胞参数变化不大,均为三八面体1M型云母。以上特征表明,本区钾玄岩系四种岩石中云母均形成于高碱度环境,它们与钙碱性系列岩石中云母形成的环境迥然不同。从四种岩石的云母具有相似的化学成分、红外光谱和晶胞参数,说明它们的寄主岩石具有钾玄岩的特征,其物源来自交代地幔。
The Cenozoic magmatic rocks of shoshonitic series in eastern Qinghai-Tibet plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Mica is the popular mineral in the four different types of rocks. Based on the geochemical characteristics of mica in rocks, the forming environment and source rocks of the micahosted rocks could be determined. The chemical composition of mica was analyzed by wet chemistry and a few mica samples were analyzed by electron-probe analysis. The chemical composition, MF varying from 1.30 to 1.99, suggesting that the micas are phlogopites - Mg-rich biotites, belong to the alkali-rich, Mg-rich, AI-high and Fe-poor type. The infrared spectroscopic analysis of micas was carried out on the PE-621 grating infrared spectrophotometer. The same features of infrared spectrums of micas from four different types of rocks, which have strong absorb spectrum zone at 450cm(-1) and 1000cm(-1),suggest that the mica-hosted rocks belong to the same rocks series. X-diffraction of micas was analyzed by Debye method. The unit cell parameter of micas d(060) ranging from 15. 32nm to 15. 41nm suggests that all the micas from four different types of rocks belong to trisoctahedron 1M micas. On the basis of chemical composition, it could be concluded that the micas were formed in high alkaline environment, which differ from those of micas from calc-alkaline rocks. The features of chemical compositions, X-ray and IR spectrum of micas indicate that four types of mica- hosted rocks are shoshonitic series rocks and the source magmatic material from metasomatized mantle.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2002年第2期205-211,共7页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划项目(编号:G1999043203)
