Geochemistry of some ultramafic komatiite lava flows from the Barberton Mountain Land, South Africa☆
Geochemistry of some ultramafic komatiite lava flows from the Barberton Mountain Land, South Africa☆
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南非巴伯顿山区部分超镁铁质科马提岩熔岩流的地球化学☆
DOI：
10.1016/0301-9268(80)90074-1
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发表时间：
1980
影响因子：
3.8
通讯作者：
A. Duncan
中科院分区：
文献类型：
--
作者：
H. Smith;A. J. Erlank;A. Duncan
来自巴伯顿绿岩带科马蒂组的薄超镁铁岩流显示出惊人的结构变化，类似于在安大略和西澳大利亚州芒罗镇的一些超镁铁岩流中发现的结构变化。三齿刺纹理的A2区已被划分为一个A2 rzone组成的短随机取向的橄榄石叶片与囊泡在interblade领域和A2 pzone组成的小册子的橄榄石叶片形成的'趋热'三齿刺纹理。A2带的组成被认为是初始超镁铁液体的代表，而A2 pzone成分的变化反映了流动结晶时残余液体成分的变化。从3.1 m厚流动中获得的主量和微量元素数据的详细模拟表明，挤压后橄榄石的分馏和积累可能产生了观察到的成分范围（25.7- 25.7）。31.7重量% MgO）。从该流动的B区分析的橄榄石核的Ni含量与这些晶体一致，这些晶体与由随机刺状织构A2 r区表示的液体组合物平衡存在。发现这些橄榄石晶体的DCr（橄榄石中的Cr %/“液体”中的Cr %）为0.5，这表明，来自大洋超镁铁质熔岩的橄榄石的高Cr含量是由于它们结晶的液体中的Cr含量非常高。纹理和化学数据相结合，开发一个冷却和结晶模型，这种流动。
Thin ultramafic flows from the Komati Formation in the Barberton Greenstone Belt show striking textural variations similar to those found in some ultramafic flows from Munro Township, Ontario and Western Australia. The spinifex textured A2zone has been divided into an A2rzone consisting of short randomly oriented olivine blades with vesicles in the interblade areas and an A2pzone made up of booklets of olivine blades forming a ‘thermotactic’ spinifex texture. The composition of the A2rzone is considered to be representative of the initial ultramafic liquid, while the variation in the composition of the A2pzone reflects the evolving residual liquid composition as the flow crystallized.Detailed modelling of major and trace element data obtained from a 3.1 m thick flow demonstrates that olivine fractionation and accumulation after extrusion probably generated the observed compositional range (25.7–31.7 wt.% MgO). The Ni content of olivine cores analysed from the B zone of this flow are consistent with these crystals having existed in equilibrium with a liquid composition represented by the random spinifex textured A2rzone. A DCr(Cr % in olivine/Cr % in ‘liquid’) of 0.5 found for these olivine crystals suggests that the high Cr content of olivines from Archaean ultramafic lavas is due to the very high Cr content of the liquids from which they crystallized. The textural and chemical data are combined to develop a cooling and crystallization model for this flow.