科马提岩研究的回顾与展望

Review and Prospect of the Study of Komatite

科马提岩是一种来源于地幔的镁铁质-超镁铁质火山熔岩,是早前寒武纪绿岩带的重要组成部分,其成分特征可以用来示踪太古宙地幔熔融的深度和温度并反演其形成过程,对研究岩石成因、解译地幔性质及探讨前寒武纪地球动力学背景等方面有着重要意义。本文对科马提岩的时空分布、岩石学和地球化学特征进行分析和总结,进一步厘清了科马提岩的形成时代及各类科马提岩的特征:科马提岩主要形成于太古宙克拉通内部,峰期为新太古代;各古老克拉通的科马提岩多见典型鬣刺结构,主要由辉石和橄榄石组成,部分遭受蛇纹石化过程中发生重结晶;根据地球化学特征的差异,主要分为ADK (贫铝型)和AUK (未贫铝型)型科马提岩;随着地质时代的变化,科马提岩的地球化学组成和地幔源区温度也有规律地变化;通过恢复科马提岩的原始岩浆成分计算得到的地幔潜能温度,指示异常高的地幔熔融温度。已报道科马提岩的形成时代、真实性、成因机制等,仍存在较多争议,需要后续更多的研究解译地球早期地幔性质和壳幔演化等问题。

Komatite is a kind of mafic and ultramafic volcanic lava derived from the mantle,which is an important component of the early Precambrian greenstone belt.Its composition characteristics can be used to trace the depth and temperature of Archean mantle melting and to invert its formation process,which is of great significance for the study of petrogenesis,the interpretation of mantle properties and the discussion of the Precambrian geodynamic background.In this paper,the spatial and temporal distribution,petrology and geochemical characteristics of thekomatites are analyzed and summarized,and the formation age and the characteristics of various komatites are further clarified.The komatites were mainly formed in the interior of the Archean craton,and the peak period was Neoarchean.The komatites of the ancient cratons have typical spinifex texture,mainly composed of pyroxene and olivine,some of which are recrystallized in the process of serpentinization.According to the difference of geochemical characteristics,they are mainly divided into ADK(aluminum-poor type)and AUK(non-aluminum-poor type)Komatites.With the change of geological time,the geochemical composition of the komatites and the temperature of the mantle source area also change regularly.The mantle potential temperature calculated by recovering the original magmatic composition of the komatites indicates an unusually high mantle melting temperature.The formation age,authenticity and genetic mechanism of the komatites have been reported,but there are still many controversies.More studies are needed to interpret the properties of the Earth's early mantle and crust-mantle evolution.