Geochemical evidence of paleo-pacific slab melting in the big mantle wedge beneath Northeast China during the Early Cretaceous

Abstract

The ‘big mantle wedge’ (BMW) beneath East Asia extends ∼1800 km inland from the trench, yet its formation time and mechanism remain enigmatic. A key challenge is linking subducted slabs to intraplate basaltic volcanism. Here, we present high-precision Ar-Ar dating and Sr-Nd-Hf-Pb isotopic analyses of Mesozoic basalt drill cores (2000–4500 m depth) from the Songliao Basin, NE China. Together with published data, all the Early Cretaceous basalts show transitional character from MORB to basalts derived from sources containing subducted materials, with variable ⁸⁷Sr/⁸⁶Sr_i (0.70311–0.70750), εNd_i (+5.06 to −6.90), ²⁰⁶Pb/²⁰⁴Pb_i (18.10–18.44) and εHf_i (+7.39 to −4.58). For the first time, we identify an Indian-type oceanic crustal signature to the source of Songliao OIB-like basalts (Δ8/4 = 37–58), linked to the subducted Paleo-Pacific (Izanagi) plate. On the other hand, the arc-type basalts across NE China incorporate sedimentary components in their mantle sources, particularly in the Greater Khingan Range, farthest from the paleo-trench but with the earliest age (∼140 Ma). These findings support a flat subduction-rollback model: sediments accumulate ahead during flat subduction while slab rollback induces asthenospheric welling, driving eastward migration of IAB-like magmatism. In contrast, the Ar-Ar dating suggests that the Songliao OIB-like basalts (107–104 Ma) erupted at the terminal stage of IAB-like magmatism (∼140–100 Ma), coinciding with the full development of the BMW and reflecting melts from the stagnant slab.