Abstract

The study of the evolution of large igneous provinces showed that the Archean and Early Paleoproterozoic mantle plumes were formed by high-Mg ultramafic rocks and looked like thermal plumes. However, this situation experienced a cardinal change in the mid-Paleoproterozoic ~2.3 Ga, when an irreversible change occurred in the composition of these plumes, providing evidence of an essentially new, geochemically enriched material being involved in the tectonomagmatic processes. Thermochemical plumes like these still exist today and, according to the modern paradigm, they are generated as the lowermost mantle is supplied with fluids released from the liquid outer core. This is in good agreement with the data on the material composition of these plumes containing both fragments of depleted ultramafic rocks of the mantle matrix (green spinel peridotites, mostly lherzolites) and veins of geochemically enriched rocks that were formed during incongruent melting of plume material due to fluids of core origin that were part of the plume material. It is shown that the magmatism during the first half of the Earth’s history (Protogean) was different from that of the second half (Neogean) in being nearly completely devoid of elements related to the core-derived fluids (Ti, Nb, Ta, alkalies, etc.). Possible factors that have contributed to this evolution are considered. We discuss the effect this change has had on the tectonomagmatic processes, and on the ecology and evolution of the biosphere. That is to say, we show how events in the Earth’s deep interiors affect to the surface processes. We show that the amazing stability of mantle plume composition during the last 2.3 billion years is more likely due to the fact that, in this case, crystallization in the core releases fluid components, which control the character of the intraplate magmatism throughout the Neogean. These fluids are constantly released from the solidifying liquid core along with newly generated mantle plumes, thus providing for stability in the composition of the latter.

中文翻译：

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地球历史上火成岩大省的演变：东部波罗的海盾

摘要

对火成岩大省演化的研究表明，太古代和早古元古代地幔柱是由高镁超镁铁质岩石形成的，看起来像是热柱。然而，当这些羽状岩的成分发生了不可逆的变化时，这种情况在古古生代中期〜2.3 Ga发生了主要变化，这为构造构造过程中涉及了一种实质上是新的，地球化学富集的物质提供了证据。像这样的热化学羽流如今仍然存在，根据现代范式，它们是由向最低的地幔提供从液态外核释放的流体而产生的。这与这些羽流的物质组成数据非常吻合，这些羽流包含地幔基质（绿色尖晶石橄榄岩，（多数为锂沸石）和地球化学富集的岩石的脉线，这些岩心是由于羽流材料的一部分来自岩心而产生的，因此在羽流材料的不均匀融化过程中形成的。结果表明，地球历史上半年（原始）的岩浆作用与下半年（Neogean）不同，几乎完全没有与岩心衍生的流体（Ti，Nb，Ta，碱）有关的元素。等）。考虑了促成这种演变的可能因素。我们讨论了这一变化对构造学过程，对生物圈的生态和演化的影响。也就是说，我们展示了地球深层内部的事件如何影响表面过程。我们显示了在最后2个期间，地幔柱组成的惊人稳定性。在这种情况下，可能有30亿年的历史，因为在这种情况下，岩心中的结晶会释放出流体成分，从而控制了整个Neogean板内岩浆作用的特征。这些流体与新产生的地幔柱一起不断地从固化液芯中释放出来，从而为后者的组成提供了稳定性。