摘要
在温度为ｌｌ３０─ｌ４５０℃，压力为０．４─２．０ＧＰａ条件下，实验研究了地幔橄榄岩部分熔融及相转变（尖晶石相→斜长石相）过程中的固相化学成分演变。在部分熔融中，随熔融度的增大，橄榄石的Ｍｇ／（Ｍｇ＋Ｆｅ）尖晶石和斜方辉石的Ｍｇ／（Ｍｇ＋Ｆｅ）及Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；而橄榄石中的Ｃａ含量增至单斜辉石消失后逐渐降低；尖晶石中的Ｔｉ以较低的含量（ＴｉＯ２＜０．１５％）保持不变或稍有降低；斜方辉石中的Ｔｉ含量及单斜辉石的Ｎａ和Ｔｉ含量逐渐降低，直至非常小的值。在从尖晶石橄榄岩向斜长石橄榄岩的相转变过程中，尖晶石强烈富Ｔｉ，且其Ｃｒ／（Ｃｒ＋Ａｌ）逐渐增大；斜方辉石中的Ｔｉ含量和Ｃｒ／（Ｃｒ＋Ａｌ）同时逐渐增大；单斜辉石中的Ｎａ含量降低而Ｔｉ含量升高或保持不变。当斜长石橄榄岩经受了部分熔融（即使很微弱），其在相转变过程中引起的各矿物相的化学成分特征要全部消失，而表现部分熔融作用的特征。这可作为判别橄榄岩在斜长石相域内是否经历了部分熔融的标志。
Over temperature range 1130─1450℃ ,and pressure range 0.4─2.0GPa, the chemical behaviour of soild phases of mantle peridotite during partial melting and spinel-to plagioclase-facies transition was experimentally studied. During partial melting, with increasing in degree of melting, Mg / (Mg+Fe) of olivine, Mg / (Mg+Fe) and Cr/(Cr+Al) of spinel and orthopyroxene increase gradually, but CaO content in olivine increases at first until vanishing of clinopyroxene and then decreases gradually; Ti content which is very low (TiO2<0.15%) in spinel remains unchanged or decreases a little; Ti content in orthopyroxene, and Na and Ti contents in clinopyroxehe decrease gradually until they are very low. During transition from spinel-lherzolite to plagioclase-lherzolite facies, spinel is very rich in Ti and its Cr / (Cr+Al) increases, Ti content and Cr / (Cr+Al) of orthopyroxene increase simultaneously; Na content in clinopyroxene decreases as Ti content increases or remains unchanged. As plagioclase-peridotite underwent partial melting (even very weak),the characteristics of chemical compositions of minerals, which resulted from partial melting,could be observed, instead of that resulted from facies transition. This may be used as an indicator to distinguish if peridotite underwent partial melting with plagioclase facies or not.
出处
《地球化学》
CSCD
北大核心
1996年第1期39-52,共14页
Geochimica
关键词
地幔橄榄岩
部分熔融
相转变
固相化学成分
mantle peridotite
partial melting
facies transition
solid phase's chemical behaviour
experimental study
