摘要
采用现代高精度中子活化分析方法分析研究了内蒙集宁群麻粒岩相中石榴石的痕量稀土,原岩为火山质岩石和原岩为正常沉积岩中的石榴石显示出完全不同的稀土配分型式,认为变质岩中的石榴石,其稀土元素特征可用来判别深变质岩的原岩性质,区分正副变质岩。
The Jining Group in Inner Mongolia consists of a suite of hypometamorphic rocks of granulite facies, with the lower part being mainly two-pyroxene-plagio-clase gneiss originating from volcanic rocks and the upper part, sillimanite-garnet- potash feldspar gneiss from normal sedimentary rocks. The garnet samples collected from different parts of fining Group belong chemically to similar species and are composed mainly of almandine (50-60 norm％) and pyrope (34-42 norm％), with less andradite and spessartite.The trace and rare earth elements in garnets from granulites of Jining Group have been determined by means of modern highprecision neutron activation analytical technique.Experimental results show that the chondrite-normalized pattern of rare earth elements is mainly affected by the properties of original rocks instead of by the composition of garnets. In the process of metamorphism the garnets from metamorphic volcanic rocks mostly retain the distribution characteristics of magmatic type garnets, showing considerable enrichment of heavy rare earth elements, while those from metasedimentary rocks fail to show obvious LREE and HREE separation but have relatively strong negative Eu anomalies.It is considered that the rare earth element characteristics of the garnets in metamorphic rocks might serve as an indicator for distinguishing ortho-rocks from para-rocks, and for determining properties of original rocks.
出处
《岩石矿物学杂志》
CAS
CSCD
1989年第2期173-180,共8页
Acta Petrologica et Mineralogica
关键词
麻粒岩
岩相
石榴石
稀土元素
garnet
rare earth element
granulite
Inner Mongolia
