Carbonatite Genesis: The Example of the Oceanic Nephelinite-Phonolite-Carbonatite Volcanic Suite on Brava, Cape Verde Islands

佛得角的布拉瓦岛是一个第四纪 霞石-响岩-碳酸盐岩火山碎屑序列 喷发 主导音位的风格明显偏离那些 典型的长英质岩浆，绘制矿床将增加 我们对高碱性岩浆喷发行为的了解 声子晶体通常严重缺乏稀土元素 元素，并承担相关的互补关系 富含稀土的碳酸岩火山岩 最可能的 其机理是碳酸盐岩的不混溶分离 来自硅酸盐岩浆的液体，碳酸盐以 火山岩堆为碳酸岩熔岩和凝灰岩。 语音学 似乎是通过管线分离结晶的产物 橄榄石霞石-霞石-响岩，但 主要问题仍然存在，特别是关于 响岩成因中的硫酸盐岩型匙形鼻状突。 造岩 建模将基于矿物化学和主要的微量元素， 一套完整岩石的元素和同位素测定 和矿物从新鲜的浮石碎屑中分离出来， 研究了火山碎屑岩单位。 密切相联 霞石质、玄武质、响岩质和碳酸岩质火山岩 在一个暴露良好的第四纪中心单位提供了一个不寻常的 有机会进一步了解的起源和行为 碳酸岩岩浆及其与 碱性硅酸盐岩浆

The island of Brava, Cape Verdes, eshibits a Quaternary nepheline-phonolite-carbonatite pyroclastic sequence. Eruptive styles of the dominant phonolites depart markedly from those typical of felsic magmas, and mapping the deposits will add to our knowledge of the eruptive behavior of highly alkaline magmas. Phonolites are typically strongly depleted in rare-earth elements, and bear a complementary relationship to associated rare-earth-enriched carbonatite volcanics. The most probable mechanism for this is the immiscible separation of a carbonatite liquid from silicate magma, the carbonate being represented in the volcanic pile as carbonatite lavas and tuffs. The phonolites appear to be products of fractional crystallization via the line of descent, olivine nephelinite - nephelinine - phonolite, but major questions remain, especially regarding the role of the sulphate feldspathoid nosean in phonolite geneses. Petrogenetic modelling will be based on mineral chemistry and major, trace element, and isotopic determinations of a suite of whole rocks and mineral separates from fresh pumice clasts in carefully studied pyroclastic units. The close association of nephelinitic, basanitic, phonolitic and carbonatitic volcanic units at a well-exposed Quaternary center provides an unusual opportunity to advance understanding of the genesis and behavior of carbonatite magmas, and their relationship to associated alkaline silicate magmas.