Titanium isotopes as a tracer of eclogite in the mantle sources of continental intraplate basalts

Recycled oceanic crust and sediments play a crucial role in generating the chemical and lithological heterogeneity of the Earth's mantle. However, unequivocally identifying the lithological properties of these recycled crustal materials in the mantle sources of basalts remains a challenge, despite its significant implications for mantle dynamics and the generation of magma diversity. Here, we explore titanium (Ti) stable isotopes as a novel method for tracing eclogite melting in the source of intraplate basalt. We present new Ti isotope data for a suite of well-characterized intraplate basalts from northeast (NE) China, which were thought to be formed through interaction between primitive low-MgO melts derived from eclogitic recycled crust and the local lithospheric mantle peridotite. Results show that these basalts display large Ti isotopic variation, with δ^49/47Ti values ranging from −0.05‰ to 0.14‰. The δ^49/47Ti values are well correlated with radiogenic Sr–Nd–Pb isotopes and stable Fe isotopes, suggesting the mixing of two endmembers with distinct Ti isotopic compositions. The low-δ^49/47Ti endmember exhibits depleted Sr–Nd isotopic compositions that resemble those of the local lithospheric mantle peridotite. The high-δ^49/47Ti endmember (δ^49/47Ti ≥ 0.14‰) is characterized by an elevated δ^57/54Fe value (≥ 0.3‰) and low values of MgO (≤ 5 wt.%), CaO/Al₂O₃ (≤ 0.4), Nb/Nb* (≤ 0.7), and Ti/Ti* (≤ 0.6), which require an eclogite melt component in equilibrium with residual rutile in the source. Our thermodynamic modeling and mass balance calculations further suggest that such a melt can be produced by partial melting of a rutile-bearing eclogite, which has a protolith of mixed recycled oceanic crust and sediments. Therefore, this study highlights that Ti isotopes can serve as a novel tool for identifying the contribution of rutile-bearing eclogite to intraplate basalts.