Olivine Water Contents in the Paleozoic Mengyin Kimberlites: Implications for the Destruction of the North China Craton

Abstract

The Mesozoic lithospheric thinning of the North China Craton (NCC) has been linked to water introduced from the subducted Paleo-Pacific oceanic slab. However, the pre-thinning hydration state of the NCC's lithospheric mantle is poorly constrained, leading to uncertainties regarding the impact of subduction-induced hydration. To address this gap, we investigated the petrography and mineral chemistry of olivine from the Paleozoic Mengyin kimberlites in the eastern NCC. These olivines are identified as xenocrysts derived from peridotite disaggregation rather than being primary crystallization products of the kimberlites. Fourier transform infrared spectroscopy analysis revealed that the water content in the olivine ranges from 13 to 281 ppmw, which may represent lower limits due to potential H diffusion loss. The enrichment in water represented by the higher end of this range is attributed to metasomatism by asthenosphere-derived melts. Our findings suggest that the relatively high water contents were a characteristic of the NCC lithospheric mantle since at least the Early Paleozoic. Furthermore, viscosity models show that even with olivine containing 100–600 ppmw water, the viscosity ratios between the cratonic root and the asthenosphere are substantially higher (>300 to 1.4 × 10⁴), supporting a thick lithospheric keel (>200 km) under the NCC during the Paleozoic. These results challenge the notion that olivine hydration is decisive for the stability or destruction of the NCC, suggesting instead that the contribution of water from the subducted Paleo-Pacific slab to the weakening of the NCC lithospheric mantle—and thus to its decratonization—is marginal.