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首页> 外文期刊>Contributions to Mineralogy and Petrology >Carbonate metasomatism of the oceanic mantle beneath Fernando de Noronha Island, Brazil
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Carbonate metasomatism of the oceanic mantle beneath Fernando de Noronha Island, Brazil

机译：巴西费尔南多·迪诺罗尼亚岛下方海相地幔的碳酸盐交代作用

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摘要

Evidence is presented for a carbonate-immiscibility phenomena in the upper mantle based on data from a set of strongly metasomatized xenoliths in a basanitic lava flow from Fernando de Noronha Island (southwest Atlantic). A petrological and geochemical study of lherzolitic and harzburgitic xenoliths reveals that the oceanic mantle of this region has been affected by very strong carbonate metasomatism. The metasomatism led to wehrlitization of the primary mantle mineral assemblage (ol, opx, sp). The wehrlitization was the result of interaction between a possibly ephemeral sodic dolomitic melt or fluid with the mantle peridotite according to the following reactions, which include sodic components:4MgSiO_3 + CaMg(CO_3)_2 = 2Mg_2SiO_4 + CaMgSi_2O_6 + 2CO_23CaMg(CO_3)_2 + CaMgSi_2O_6 = 4CaCO_3 + 2Mg_2SiO_4 + 2CO_2The olivine has abundant micro-inclusions consisting of Na-Al-Si-rich glass, Fe, Ni and Cu-monosulfide, Ca-rich carbonate and dense CO_2. The interrelationships between the glass, sulfide and carbonate inclusions permit speculation that silicate, sulfide, and Ca-rich carbonatite melts were in equilibrium with each other and originated from partial melting of metasomatized and wehrlitized peridotite underneath Fernando de Noronha Island. These results support a two-stage model of Ca-rich carbonatite formation: first stage - metasomatic wehrlitization and carbonatization of mantle rocks; second stage - partial melting of the carbonate-bearing wehrlitic rock resulting in the formation of immiscible silicate, sodic carbonate and sulfide liquids and the ultimately generation of calciocarbonatites.
机译：根据来自费尔南多·迪·诺罗尼亚岛（西南大西洋）的玄武岩熔岩流中一组强烈交代的异岩体的数据，提供了上地幔中碳酸盐不溶混现象的证据。岩石和哈茨形异岩的岩石学和地球化学研究表明，该地区的地幔受到强烈的碳酸盐交代作用的影响。交代作用导致原始地幔矿物组合（ol，opx，sp）变湿。蒸发作用是可能的短暂苏打白云岩熔体或流体与地幔橄榄岩根据以下反应相互作用的结果，其中包括苏打成分：4MgSiO_3 + CaMg（CO_3）_2 = 2Mg_2SiO_4 + CaMgSi_2O_6 + 2CO_23CaMg（CO_3）_2 + CaMgSi = 4CaCO_3 + 2Mg_2SiO_4 + 2CO_2橄榄石具有丰富的微夹杂物，包括富含Na-Al-Si的玻璃，Fe，Ni和一硫化铜，富含Ca的碳酸盐和致密的CO_2。玻璃，硫化物和碳酸盐夹杂物之间的相互关系可以推测硅酸盐，硫化物和富含Ca的碳酸盐熔岩彼此平衡，并且是由诺南哈岛费尔南多底下交代和湿润的橄榄岩的部分熔融引起的。这些结果支持了富钙碳酸盐岩形成的两阶段模型：第一阶段-地幔岩石的交代加湿作用和碳化作用;第二阶段-含碳酸盐的辉石岩的部分熔融，导致形成不混溶的硅酸盐，碳酸钠和硫化物液体，并最终生成钙碳石。

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