摘要
在西藏罗布莎蛇绿岩块的豆荚状铬铁矿中 ,存在包裹体矿物镁橄榄石。这些镁橄榄石为无色透明多晶面组成的自形晶 ,Fo值可达到 97～ 98,具富镁端员组分。选取一代表性颗粒的单晶进行X单晶衍射分析 ,表明其为斜方晶系 ,空间群Pbnm ,镁橄榄石晶胞参数a、b、c以及M 1— 0和M 2— 0键长均小于地幔包裹体和一般地幔岩中橄榄石的对应值。测试出的晶胞参数与人工合成镁橄榄石的一致。镁橄榄石具有橄榄石族中已知最小的晶胞参数 。
The forsterite mineral inclusions in chromite of podiform chromitite occur in mantle peridotite of Luobusa ophiolite in the Indo_Yarlung Zangbo tectonic unit. The forsterite inclusions from chromite grains have Fo number of 97～99 and assume the form of colorless, transparent and euhedral grains with abundant small faces. The crystal of forsterite used for X_ray analysis was measured to be approximately 0.15 mm×0.15 mm×0.15 mm. Crystal system of this forsterite is orthorhombic, space group Pbnm , α, β and γ is 90°, a =4.7597, b =10.205, c = 5.9831. The unit cell parameters of forsterite, a , b , c as well as M1—O and M2—O bond lengths are smaller than those of some olivines from mantle xenolith and mantle peridotites. The unit cell parameters of the forsterite in the study area are the same as those of the synthetic forsterite. According to experimental study cited in the literature, the small unit cell andcation_oxygen bond distances of olivine suggest a high pressure of its crystallization.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2001年第1期1-10,共10页
Acta Petrologica et Mineralogica
基金
国家自然科学基金项目! ( 49972 0 73)的部分成果
