Rapid Recycling of Subducted Sediments in the Subcontinental Lithospheric Mantle.

This article focuses on the geochemical and isotopic study of Cenozoic potassic–ultrapotassic lavas from the western Kunlun area of northwestern Tibet to investigate the recycling of subducted sediments in the subcontinental lithospheric mantle (SCLM) during continental subduction. The lavas exhibit enriched mantle-2 (EM2) isotopic signatures—characterized by high ^87Sr/^86Sr (>0.7080), low ε_Nd (≤ −4.8), high ^206Pb/^204Pb (≥18.704), and low ε_Hf (≤ −2.6)—and arc-like trace-element patterns, indicating a mantle source enriched by recycled terrigenous sediments derived from the subducted Indian continental lithosphere during the India–Eurasia collision. Geochemical modeling suggests these magmas formed by low-degree (1–5%) partial melting of a phlogopite-bearing garnet lherzolite in the lithospheric mantle, consistent with a mélange melting process where buoyant subducted sediments detach from the slab and diapirically ascend into the overlying mantle lithosphere. The findings imply that subducted sediments can be rapidly recycled into the SCLM (likely within 50 million years), highlighting the SCLM as a significant reservoir for recycled sediments and providing insights into mantle circulation and chemical heterogeneities in continental subduction zones.