The origin of water in the large igneous provinces: constraints from hydrogen isotope

Large igneous provinces (LIPs), characterized by massive basaltic lava flows and rapid formation over short time frames, exert profound effects on Earth's environment, climate, and mineral resources. Although prior studies have revealed that high water content in the mantle sources would be a critical factor for the genesis of LIPs, the origin of water in their mantle sources remains debated, posing a critical challenge for understanding the geodynamic context of LIP formation and associated deep mantle processes. The water can derive from the primordial components that build the earth, or from the earth surface carried by the subducted oceanic slabs. Here, we conducted coupling analysis of water contents and hydrogen isotopes of the melt inclusions and quenched glasses from the high ³He/⁴He picrites in Western Greenland and low-Ti type picrites from Emeishan large igneous province. The results show that the high H₂O/Ce (>1300) and normal mantle like D/H ratio of the primary magma are distinct to that of the oceanic island basalts and Archean komatiites. Combining the high mantle potential temperature and non-arc like trace elemental patterns, we suggest that the ELIP taps highly hydrous reservoirs in the deep mantle, potentially with water inherited from earth-building materials or the less dehydrated subducted oceanic lithosphere. Our work also raises the caution that the traditionally combined water content and δD analysis for OHMs does not necessarily allow the accurate determination of water concentration of the primary magma. For Western Greenland picrites, the results show water contents from 850 to 1050 ppm by weight, but large variable δD from -75± to -140±8 ‰, which forms the trends well modeled by the kinetic fractionation driven by inward water diffusion into the melt inclusions. The primary δD of the these picrites were inferred to be around -80 ‰, consistent with the recent results for the high 3He/4He submarine basaltic glasses from Loihi, Hawaii. Thus, our work may support a globally consistent primordial water in the origin of chondritic material.