Role of Magma Ocean Differentiation in the Formation and Long-Term Preservation of Distinct Geochemical Domains Within the Deep Mantle

We modeled the evolution of the terrestrial Magma Ocean using the short-lived ¹⁸²Hf-¹⁸²W isotope system (t_1/2 = 8.9 Myr) in a multi-reservoir early Earth. We start with a chondritic Earth at T₀ = 4.567 Ga. Core segregates and attains its present-day mass, W elemental and isotopic (¹⁸²W/¹⁸⁴W) composition by the end of core formation (T_CF). The duration and rate of core formation constrain the starting composition of the silicate Earth and magma ocean that formed at the last stages of the core formation. Crystallization of magma ocean results in the formation of crystals/cumulates of mass M_CX, leaving behind a residue with mass M_RES. A series of differential equations describing the changing mass and abundance of ¹⁸²Hf, ¹⁸²W, and ¹⁸⁴W nuclides in each reservoir are solved numerically at 0.1 Myr time-step for the initial 200 Myr of Earth's history. Our results constrain the depth of the early magma ocean to be ∼38–70% of the total mantle mass, corresponding to a depth of ∼770–1,600 km and the timing of magma ocean crystallization over a duration T_CX of ≤50 Myr after core formation, which successfully reproduces the present-day Hf and W concentrations and ¹⁸²W/¹⁸⁴W ratios in M_RES reservoir similar to the deep mantle sources sampled by ocean island basalts. The model-derived results suggest that leftover residual (liquid) magma ocean after magma ocean crystallization could partly or fully represent the present-day large low shear velocity provinces, LLSVPs.