Yao Zhuosen, Mungall James E, Jenkins M Christopher
Department of Earth Sciences, Carleton University, 2115 Herzberg Laboratories, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
Nat Commun. 2021 Jan 21;12(1):505. doi: 10.1038/s41467-020-20778-w.
The Rustenburg Layered Suite of the Bushveld Complex of South Africa is a vast layered accumulation of mafic and ultramafic rocks. It has long been regarded as a textbook result of fractional crystallization from a melt-dominated magma chamber. Here, we show that most units of the Rustenburg Layered Suite can be derived with thermodynamic models of crustal assimilation by komatiitic magma to form magmatic mushes without requiring the existence of a magma chamber. Ultramafic and mafic cumulate layers below the Upper and Upper Main Zone represent multiple crystal slurries produced by assimilation-batch crystallization in the upper and middle crust, whereas the chilled marginal rocks represent complementary supernatant liquids. Only the uppermost third formed via lower-crustal assimilation-fractional crystallization and evolved by fractional crystallization within a melt-rich pocket. Layered intrusions need not form in open magma chambers. Mineral deposits hitherto attributed to magma chamber processes might form in smaller intrusions of any geometric form, from mushy systems entirely lacking melt-dominated magma chambers.
南非布什维尔德杂岩体的勒斯滕堡层状岩体是镁铁质和超镁铁质岩石的巨大层状堆积体。长期以来，它一直被视为熔体主导的岩浆房通过分离结晶作用产生的典型结果。在此，我们表明，勒斯滕堡层状岩体的大多数单元可以通过科马提岩浆与地壳同化的热力学模型推导得出，从而形成岩浆 mush，而无需岩浆房的存在。上区和上主区之下的超镁铁质和镁铁质堆积层代表了上地壳和中地壳通过同化 - 分批结晶作用产生的多晶浆体，而冷却的边缘岩石则代表互补的上清液。只有最上部的三分之一是通过下地壳同化 - 分离结晶作用形成，并在富含熔体的囊袋内通过分离结晶作用演化而来。层状侵入体不一定在开放的岩浆房中形成。迄今归因于岩浆房过程的矿床可能在任何几何形态的较小侵入体中形成，这些侵入体来自完全缺乏熔体主导岩浆房的 mush 系统。
