能量约束下的同化混染与分离结晶作用模型(EC-AFC)在超镁铁质岩浆演化过程中的应用——以含铜镍硫化物矿床的四川力马河岩体为例

Application of energy-constrained assimilation-fractional crystallization(EC-AFC) model for ultramafic magmatic systems:A case study of the Limahe intrusion associated with Cu-Ni sulfide ores,Sichuan Province

除极少数情况外,岩浆的演化过程基本为开放体系。AFC模型(同化混染+分离结晶)是模拟岩浆演化过程的经典方法。事实上,岩浆演化过程不仅和围岩有物质交换还存在能量的交换,因此由Spera和Bohrson提出的能量约束下的开放系统岩浆演化过程的同化混染与分离结晶(EC-AFC)模型更加符合地质实际,本文介绍了该模型的方法,在此基础上,以含铜镍矿床的四川力马河岩体为例,运用EC-AFC模型模拟该岩体的岩浆演化过程。结果表明,EC-AFC模型能很好的模拟该岩体的开放系统中岩浆演化过程;Sr同位素的EC-AFC模拟曲线表明岩浆很可能在中下地壳发生混染,岩浆与发生混染的围岩在成分上都具有不均一性。

Magma evolution is an open-system process in many cases with some exceptions.AFC（assimilation-fractional crystallization） model is a ＇classical＇ approach for modeling magma evolution.In fact,there are not only material exchange between magma system and its wall rocks,but energy exchange as well.Therefore the energy-constrained assimilation-fractional crystallization（EC-AFC） model developed by Spera and Bohrson for magma evolution in an open-system is more suitable for nature systems.In this paper,we introduce the principles of EC-AFC model,and evaluate the published datasets of the Limahe intrusion associated with Cu-Ni sulfide ores,and our calculation suggests that EC-AFC model is more consistent with the observed geochemical trends.Furthermore,the isotopic Sr trends of EC-AFC results indicate that the primary magma generated Limahe intrusion are probably contaminated by lower or middle crust,and either parental magmas or wall rocks are compositionally heterogeneous.