太古宙S型花岗岩:南非Kaapvaal火山口Lekkersmaak和Willie深成岩体的岩石学、地球化学和地质年代

IF 1.2 4区 地球科学 Q2 GEOLOGY
M. Poujol, J. Jaguin, J. Moyen, P. Boulvais, J. Paquette
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引用次数: 2

摘要

s型花岗岩对应于(变)沉积物部分熔融对原有大陆物质和形态的改造。早-中太古宙s型花岗岩较为少见,在新太古宙和太古宙-元古代过渡时期以相对较小的侵入体形式出现。因此,在太古宙地质的背景下,它们的缺乏是重要的,因为它与这一时期过程的不寻常性质相匹配。本文以南非Kaapvaal克拉通北部默奇森绿岩带以南的中太古代晚期威利岩体和新太古代Lekkersmaak岩体为研究对象。这些侵入物代表了该地区迄今为止已知的最古老的s型岩体。通过记录岩石学、矿物学(矿物组成)、地球化学(主微量元素、Sr、Nd和O同位素)和锆石U-Pb年代学,对其岩石成因进行了限定。大的Lekkersmaak和小的Willie岩体代表了两种具有许多地球化学特征的花岗岩;它们均为过铝质、含镁的s型花岗岩,但比典型的s型花岗岩含钠量多,含钾量少。Willie花岗岩的就位时间为2816±9 Ma, Lekkersmaak花岗岩的就位时间为2771±2 Ma。因此,该区在2.82 Ga发生了两次s型岩浆活动,在2.77 Ga发生了40 Myr岩浆活动,涉及相当的未成熟变质沉积岩来源和部分熔融条件。Lekkersmaak岩体无白云母,贫铝,不具有s型特征,定位时间为2 734±11 Ma。这证实了默奇森绿岩带以南岩浆活动的幕式性质。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Archaean S-Type granites: petrology, geochemistry and geochronology of the Lekkersmaak and Willie plutons, Kaapvaal Craton, South Africa
S-type granites correspond to reworking of pre-existing continental material and form by partial melting of (meta)sediments. Early-to-mid Archaean S-type granites are rare and are more frequently found, usually as relatively small intrusions, during the Neoarchaean and the Archaean-Proterozoic transition. In the context of Archaean geology, their paucity is therefore significant, in that it matches the uncommon nature of processes during this period. In this study, we focus on the Late Mesoarchaean Willie pluton and Neoarchaean Lekkersmaak pluton, which crop out to the south of the Murchison Greenstone Belt in the Northern Kaapvaal Craton, South Africa. These intrusions represent the oldest S-type plutons known so far in the region. We constrain their petrogenesis by documenting their petrology, mineralogy (mineral composition), geochemistry (major and trace elements, Sr, Nd and O isotopes) and zircon U-Pb geochronology. The large Lekkersmaak and smaller Willie plutons represent two granites sharing many geochemical characteristics; they are both peraluminous, Ms-bearing S-type granites although they are more sodic and less potassic than typical S-type granites. The Willie granite was emplaced 2 816 ± 9 Ma ago while the Lekkersmaak yielded an emplacement age of 2 771 ± 2 Ma. Therefore, S-Type magmatism in the area occurred twice at 2.82 Ga and then 40 Myr later at 2.77 Ga, involving comparable immature metasedimentary sources and conditions of partial melting. Finally, a sample from the Lekkersmaak pluton devoid of S-type features as it is muscovite-free and aluminum poor was emplaced 2 734 ± 11 Ma ago. This confirms the episodic nature of magmatic activity south of the Murchison Greenstone Belt.
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来源期刊
CiteScore
3.60
自引率
5.60%
发文量
18
审稿时长
>12 weeks
期刊介绍: The South African Journal of Geology publishes scientific papers, notes, stratigraphic descriptions and discussions in the broadly defined fields of geoscience that are related directly or indirectly to the geology of Africa. Contributions relevant to former supercontinental entities such as Gondwana and Rodinia are also welcome as are topical studies on any geoscience-related discipline. Review papers are welcome as long as they represent original, new syntheses. Special issues are also encouraged but terms for these must be negotiated with the Editors.
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