Magma/mantle interaction and genesis of primitive magnas

研究了深部岩石和热液岩石中上地幔橄榄岩与熔体的相互作用。我们的研究结果总结如下。高度亏损的橄榄岩可能是多成因的。高镁方辉橄榄岩中尖晶石的铬含量在巴布蛇绿岩中高于Kamuikotan带。在Kamuikotan纯橄榄岩-方辉橄榄岩中，熔融条件是含水的，而在巴布亚蛇绿岩中是无水的。阿曼蛇绿岩的莫霍面过渡带基本由方辉橄榄岩与莫氏蛇绿岩相互作用的产物组成，与快速扩张的海脊体系--太平洋赫斯深海的莫霍面过渡带岩石相似。原始的MORB可能与莫霍面过渡带的纯橄榄岩(和榴辉岩)处于平衡状态，后者是更原始的MORB与地幔橄榄岩相互作用的产物。大洋纯橄榄岩的岩石学特征略有变化，而地幔橄榄岩的岩石学特征随扩张速率的不同而变化很大。橄榄岩/熔体相互作用产生的二次熔体可同时浓缩部分相容元素和不相容组分，形成豆荚状铬铁矿。豆荚状铬铁矿的特征是赋存于中等亏损的方辉橄榄石和少量的cpx和中等铬#的铬尖晶石(约0.5)。它们的铬尖晶石往往具有高的铬#S(约0.8)，指示其形成的上俯冲带环境。苦橄岩玄武岩是橄榄岩/熔体相互作用产物的热液相。橄榄岩包体与其寄主碱性玄武岩的反应产物是苦橄岩混合物的良好类似物。

The interaction between upper mantle peridotite and melt has been studied both for deep-seated rocks and for effusive rocks. Our results are summarized as follows.1. The highly depleted peridotite is possibly polygenetic. The Cr# of spinel in high-Mg harzburgite is higher in the Papuan ophiolite than in the Kamuikotan zone. the melting condition was hydrous in the Kamuikotan dunite-harzburgite and was anhydrous in the Papuan ophiolite.2. The Moho transition zone of the Oman ophiolite is basically composed of the interaction product between harzburgite and MORB.The rocks are similar to the equivalents from Hess Deep, the Pacific Ocean, a fast-spreading ridge system.3. The primitive MORB is possibly in equilibrium with dunite (and troctolite) of the Moho transition zone, an interaction product between more primitive MORB and mantle peridotite. The oceanic dunite is slightly variable in petrological characteristics whereas the mantle peridotite is highly variable depending on the spreading rate.4. The secondary melt produced by the peridotite/melt interaction can concentrate both some compatible elements simultaneously and incompatible components, leading to precipitate podiform chromities.5. The podiform chromitite is characteristically hosted by moderately depleted harzburgite with small smount of cpx and chromian spinel of moderate Cr# (around 0.5). Their chromian spinel often has high Cr#s (around 0.8), indicating supra-subduction zone environment for their formation.6. The picrite basalt is an effusive facies of the peridotite/melt interaction product. The reaction product between peridotite xenolith and its host alkali basalt is a good analogue of the picritic mixture.