Chemical and isotopic compositions of basaltic glasses and crusts from the Mid-Atlantic Ridge rift valley

Data presented in the paper suggest significant differences between thermodynamic conditions, under which magmatic complexes were formed in MAR at 29°-34°N and 12°-18°N. Melts occurring at 29°-34°N were derived by melting of a mantle source with homogeneous distribution of volatile components and arrived at the surface without significant fractionation, likely, due to their rapid ascent. The MAR segments between 12° and 18°N combine contrasting geodynamic environments of magmatism, which predetermined development of a large plume region with widespread mixing of melting products of geochemically distinct mantle sources. At the same time, this region is characterized by conditions favorable for origin of localized zones of anomalous plume magmatism. These sporadic magmatic sources were spatially restricted to MAR fragments with the Hess crust, whose compositional and mechanical properties were, perhaps, favorable for focusing and localization of plume magmatism. The plume source between 12° and 18°N beneath MAR may be geochemically heterogeneous.

本文呈现的数据表明，北纬29°-34°与12°-18°的中大西洋海岭（Mid-Atlantic Ridge，MAR）处形成岩浆杂岩的热力学条件存在显著差异。北纬29°-34°区域的熔体源自挥发组分分布均一的地幔源区熔融，且未发生显著岩浆分异便抵达地表，这大概率缘于其快速上升过程。北纬12°-18°的中大西洋海岭段兼具截然不同的岩浆作用地球动力学环境，这催生了大型地幔柱区域的发育：该区域广泛混合了地球化学特征迥异的地幔源区的熔融产物。与此同时，该区域具备利于异常地幔柱岩浆作用局部富集带形成的条件。这些零星分布的岩浆源仅局限于发育赫斯地壳（Hess crust）的中大西洋海岭片段，该地壳的成分与力学特性或许有利于地幔柱岩浆作用的汇聚与局域化。中大西洋海岭下方北纬12°-18°区域的地幔柱源区可能具有地球化学非均质性。