Yang Junlong, Wang Chao, Jin Zhenmin, Jing Zhicheng
Department of Earth and Space Sciences, Southern University of Science and Technology, 518055, Shenzhen, China.
State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, 430074, Wuhan, China.
Nat Commun. 2025 Jun 6;16(1):5276. doi: 10.1038/s41467-025-60619-2.
The composition of ocean island basalts (OIBs) is key to understanding mantle differentiation and quantifying intra-plate carbon outflux. Existing petrogenesis models fail to simultaneously reproduce the low SiO and low SiO/FeO characteristics of alkalic OIBs and ignore melt-orthopyroxene reactions in the lithosphere that may further elevate the SiO content of primary magmas. Here we show experimentally that high-degree (>50%) high-pressure crystallization of carbonated primary magmas at the base of lithosphere drastically reduces both the SiO content and SiO/FeO ratio, due to the combined effects of clinopyroxene and garnet precipitation and carbonates dissolution. The major-element chemistry of alkalic OIBs can be quantitatively reproduced by considering varying degrees of crystallization, melt-orthopyroxene reactions, and source CO content. Our results imply high intra-plate carbon outfluxes and support the observed association of low OIB SiO contents with low mantle potential temperatures, as slower magma transport at lower temperatures leads to more extensive crystallization and reaction.
大洋岛玄武岩（OIBs）的成分是理解地幔分异和量化板内碳通量的关键。现有的岩石成因模型无法同时再现碱性OIBs的低SiO和低SiO/FeO特征，并且忽略了岩石圈中熔体-斜方辉石反应，而这种反应可能会进一步提高原生岩浆的SiO含量。在此，我们通过实验表明，由于单斜辉石和石榴石的析出以及碳酸盐的溶解共同作用，岩石圈底部碳酸化原生岩浆的高度（>50%）高压结晶会大幅降低SiO含量和SiO/FeO比值。通过考虑不同程度的结晶、熔体-斜方辉石反应和源CO含量，可以定量再现碱性OIBs的主元素化学特征。我们的结果意味着板内碳通量较高，并支持观察到的OIBs低SiO含量与低地幔势温度之间的关联，因为在较低温度下岩浆运移较慢会导致更广泛的结晶和反应。
