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首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >Formation and emplacement of two contrasting late-Mesoproterozoic magma types in the central Namaqua Metamorphic Complex (South Africa, Namibia): Evidence from geochemistry and geochronology
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Formation and emplacement of two contrasting late-Mesoproterozoic magma types in the central Namaqua Metamorphic Complex (South Africa, Namibia): Evidence from geochemistry and geochronology

机译：中部纳马夸变质复合体（南非，纳米比亚）中晚生代古代岩浆的两种形成对比：来自地球化学和年代学的证据

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摘要

The Namaqua Metamorphic Complex is a Mesoproterozoic low-pressure, granulite fades belt along the southern and western margin of the Kaapvaal Craton. The NMC has formed between similar to 13 and 1.0 Ga and its central part consists essentially of different types of granitoids intercalated with metapelites and calc-silicate rocks. The granitoids can be subdivided into three major groups: (i) mesocratic granitoids, (ii) leucocratic granitoids and (iii) leucogranites. The high-K, ferroan mesocratic granitoids (54-75 wt% SiO2) have a variable composition ranging from granitic to tonalitic, and contain biotite and/or hornblende or orthopyroxene. They are strongly enriched in REE and LIE, indicating A-type chemical characteristics, and are depleted in Ba, Sr, Eu, Nb, Ta and Ti. The leucocratic granitoids and leucogranites (68-76 wt% SiO2) differ from the other group in having a granitic or slightly syenitic composition containing biotite and/or gamet/sillimanite. They have lower REE and MgO, FeOt, CaO, TiO2, MnO concentrations, but higher Na2O and K2O contents. Compositional variations in mesocratic granitoids indicate their formation by fractional crystallization of a mafic parental magma. Leucocratic granitoids and leucogranites lack such trends, which suggests melting of a felsic crustal source without subsequent further evolution of the generated magmas. The mineralogical and geochemical characteristics of the mesocratic granitolds are consistent magmatic differentiation of a mantle derived, hot (>900 degrees C) parental magma. The leucocratic granitoids and leucogranites granites were formed from low-temperature magmas (<730 degrees C), generated during fluid-present melting from metasedimentary sources.
机译：Namaqua变质复合体是沿着Kaapvaal Craton的南缘和西缘的中元古代低压，粒状褪色带。 NMC的形成类似于13 Ga和1.0 Ga之间，其中心部分基本上由不同类型的花岗岩组成，这些花岗岩之间夹有偏橄榄石和钙硅酸盐岩石。花岗岩可分为三大类：（i）中层花岗岩，（ii）白云质花岗岩和（iii）白云岩。高K，亚铁的中晶花岗岩（54-75 wt％SiO2）具有从花岗岩到tonalitic范围的可变组成，并且包含黑云母和/或角闪石或邻位辉石。它们富含REE和LIE，表明A型化学特征，而Ba，Sr，Eu，Nb，Ta和Ti贫化。白云岩花岗岩和白云母（68-76 wt％SiO2）与另一类的区别在于其花岗岩或轻度亚硒酸盐成分含有黑云母和/或配子/硅线石。它们的REE和MgO，FeOt，CaO，TiO2，MnO浓度较低，但Na2O和K2O含量较高。介孔花岗岩的成分变化表明它们是由镁铁质母岩浆的分级结晶形成的。白垩纪花岗岩和白垩纪花岗岩缺乏这种趋势，这表明长英质地壳源融化而没有随后产生的岩浆进一步演化。中克拉通花岗岩的矿物学和地球化学特征是源自地幔的热（> 900摄氏度）父母岩浆的一致岩浆分异。白云岩花岗岩和白云岩花岗岩是由低温岩浆（<730摄氏度）形成的，低温岩浆是在沉积过程中由沉积物来源产生的流体熔解而成的。

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