Magma/mantle interaction and genesis of primitive magnas

研究了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：高度贫化的橄榄岩可能是多成因的。巴布亚蛇绿岩中高镁辉石中尖晶石的Cr#含量高于Kamuikotan带。kamukotan褐辉辉岩的熔融条件为含水熔融，巴布亚蛇绿岩的熔融条件为无水熔融。阿曼蛇绿岩的莫霍过渡带基本由辉锌矿与MORB相互作用的产物组成。这些岩石类似于来自太平洋赫斯深的同类岩石，这是一个快速扩张的山脊系统。原始MORB可能与莫霍过渡带的泥质岩（和橄榄岩）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。洋质橄榄岩的岩石学特征变化不大，而地幔橄榄岩的岩石学特征则随扩展速率的变化而变化很大。橄榄岩/熔体相互作用产生的次生熔体可同时富集部分相容元素，也可富集不相容成分，形成脚状铬铁矿沉淀。脚状铬铁矿的特征为含少量cpx的中度贫辉锌矿和中等Cr（约0.5）的铬尖晶石。它们的铬尖晶石通常具有较高的Cr#s（约0.8），表明它们形成于超俯冲带环境。苦橄岩玄武岩是橄榄岩/熔体相互作用的产物。橄榄岩捕虏体与其寄主碱性玄武岩的反应产物与苦橄质混合物很相似。

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.