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首页> 外文期刊>Chemical geology >Tourmaline B-isotopes as tracers of fluid sources in silicified Palaeoarchaean oceanic crust of the Mendon Formation, Barberton greenstone belt, South Africa
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Tourmaline B-isotopes as tracers of fluid sources in silicified Palaeoarchaean oceanic crust of the Mendon Formation, Barberton greenstone belt, South Africa

机译：电气石B同位素作为南非Barberton绿岩带Mendon组硅化的古太古洋壳中流体源的示踪剂

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摘要

Pervasive silicification is a common phenomenon in Early Archaean volcano-sedimentary sequences, reflecting the interaction between Si-rich fluids and the Archaean oceanic crust. In the Palaeoarchaean Barberton greenstone belt, South Africa, the silicified zones locally contain abundant tourmaline. In order to constrain the source of fluids responsible for the alteration, six tourmaline-bearing samples from the 3.3 Ga Mendon Formation were investigated by in-situ analyses of mineral chemistry and boron isotopes. The samples comprise a silicified, finely laminated sedimentary chert and five highly altered and silicified komatiites. Electron microprobe analysis (EMPA) indicates that tourmaline is mostly dravitic, with one sample between dravite and Mg-foitite. Tourmaline has a weakly-developed patchy colour-and chemical zonation, with variations in Al, Fe and Mg composition. Some samples show strong zoning in Cr-concentration with Cr enrichment in the core, and locally the high-Cr domains are at contacts with other Cr-rich phases such as magnesiochromite and chromian muscovite ("fuchsite").
机译：普遍的硅化作用是早古生代火山沉积序列中的一种普遍现象，反映出富硅流体与古生大洋地壳之间的相互作用。在南非的古生巴伯顿绿岩带中，当地的硅化带含有丰富的电气石。为了限制造成这种变化的流体源，通过矿物化学和硼同位素的原位分析研究了来自3.3 Ga Mendon组的六个含电气石的样品。样品包括硅化的，精细层压的沉积石和五种高度蚀变和硅化的科马提岩。电子微探针分析（EMPA）表明，电气石主要是德拉威，其中一个样品介于德拉威和镁镁橄榄石之间。电气石的色斑和化学区带较弱，Al，Fe和Mg组成有所变化。一些样品显示出Cr浓度强的带状分布，且岩心中有Cr富集，并且局部高Cr域与其他富铬相（如镁铬铁矿和铬白云母（“铁矾土”）接触）。

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