Chen Chunfei, Foley Stephen F, Shcheka Svyatoslav S, Liu Yongsheng
State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, 430074, Wuhan, China.
School of Natural Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.
Nat Commun. 2024 May 21;15(1):4311. doi: 10.1038/s41467-024-48304-2.
The oxygen fugacity (fO) of the lower cratonic lithosphere influences diamond formation, melting mechanisms, and lithospheric evolution, but its redox evolution over time is unclear. We apply Cu isotopes (δCu) of ~ 1.4 Ga lamproites and < 0.59 Ga silica-undersaturated alkaline rocks from the lithosphere-asthenosphere boundary (LAB) of the North Atlantic Craton to characterize fO and volatile speciation in their sources. The lamproites' low δCu (-0.19 to -0.12‰) show that the LAB was metal-saturated with CH + HO as the dominant volatiles during the Mesoproterozoic. The mantle-like δCu of the < 0.59 Ga alkaline rocks (0.03 to 0.15‰) indicate that the LAB was more oxidized, stabilizing CO + HO and destabilizing metals. The Neoproterozoic oxidation resulted in an increase of at least 2.5 log units in fO at the LAB. Combined with previously reported high fO in peridotites from the Slave, Kaapvaal, and Siberia cratonic roots, this oxidation might occur in cratonic roots globally.
下地壳克拉通岩石圈的氧逸度（fO）影响钻石形成、熔融机制和岩石圈演化，但其随时间的氧化还原演化尚不清楚。我们对来自北大西洋克拉通岩石圈-软流圈边界（LAB）的约1.4 Ga钾镁煌斑岩和<0.59 Ga硅不饱和碱性岩石应用铜同位素（δCu），以表征其源区的fO和挥发性物质形态。钾镁煌斑岩的低δCu（-0.19至-0.12‰）表明，在中元古代期间，LAB以CH + HO作为主要挥发性物质处于金属饱和状态。<0.59 Ga碱性岩石类似地幔的δCu（0.03至0.15‰）表明，LAB氧化性更强，使CO + HO稳定并使金属不稳定。新元古代的氧化作用导致LAB处的fO至少增加2.5个对数单位。结合之前报道的来自斯拉维、卡普瓦尔和西伯利亚克拉通根部橄榄岩中的高fO，这种氧化作用可能在全球克拉通根部发生。
