Systematic variations in the composition of volcanic rocks in tectono-magmatic seamount chaines in the Brazil Basin
Systematic variations in the composition of volcanic rocks in tectono-magmatic seamount chaines in the Brazil Basin
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巴西盆地构造岩浆海山链火山岩成分的系统变化
DOI：
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发表时间：
2014
影响因子：
0.8
通讯作者：
S. Skolotnev
中科院分区：
文献类型：
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作者：
A. Peyve;S. Skolotnev
巴西盆地线性构造岩浆隆升岩石组成资料表明，维多利亚-特林达德海山链火山岩是在接近亚碱性微玄武岩的熔体作用下不均匀富集磷的地幔储层形成的。由于地幔柱物质受到大陆岩石圈成分的污染，这些熔体含有大量的EM - I地幔成分。整个构造，包括Trindade和Martin Vaz群岛以及Abrolhos高原，都具有典型的长寿命同位素均匀性。据报道，Fernando de Noronha群岛岩石的类似同位素比率可以用类似的熔体衍生机制和地幔柱物质的类似演化来解释，地幔柱物质最初位于南美洲大陆之下。与本文讨论的所有其他海山的火山岩熔体相比，维多利亚-特林达德海山的火山岩母熔体是在较深的富集源物质熔融程度较低的情况下形成的。巴伊亚海山北链的绝大多数火山岩是由HIMU型物质参与形成的熔体形成的。同时，我们的一个岩石样品的成分来源接近DM，其中含有一定的EM I等富集物质。Pernambuco海山岩石的地幔源由DM和HIMU物质的混合物组成，其中含有一定的EM I（或者可能是EM II）混合物。10°-11°S海山形成于靠近MAR轴向带的化学均质地幔源减压熔融过程中，该地幔源由DM物质与EM I（或EM II）组分混合组成。
Data on the composition of rocks in linear tectono-magmatic rises in the Brazil Basin indicate that volcanic rocks in the Vitoria—Trindade seamount chain were derived from a mantle reservoir unevenly enriched in phosphorus under the effect of melts close to subalkaline picrobasalt. These melts contained much of the EM I mantle component because the plume material was contaminated with continental lithospheric component. A long-lived isotopic homogeneity of the source is typical of the whole structure, including the Trindade and Martin Vaz Islands and the Abrolhos Plateau. The analogous isotopic ratios of rocks at the Fernando de Noronha Islands are reportedly explained by a similar mechanism of melt derivation and the similar evolution of the mantle plume material, which was originally situated beneath the South American continent. Compared to the melts of volcanic rocks of all other seamounts discussed herein, the parental melts of volcanics at the Victoria—Trindade Seamounts were derived at lower degrees of melting of enriched source material at a greater depth. The overwhelming majority of volcanic rocks at the northern chain of the Bahia Seamounts were produced by melts generated with the involvement of material of the HIMU type. At the same time, one of our rock samples was derived from a source of composition close to DM with a certain admixture of enriched material like EM I. The mantle source of rocks of the Pernambuco Seamounts consisted of a mixture of DM and HIMU material with a certain admixture of EM I (or, perhaps, EM II). The 10°–11° S Seamounts were formed near the MAR axial zone at the decompressional melting of chemically homogeneous mantle source that consisted of DM material with an admixture of EM I (or, perhaps, EM II) component.