Subduction zone carbon cycling is a key process that regulates the carbon balance between Earth’s deep interior and shallow reservoirs. The pathways and timescales of this cycling directly influence the long-term evolution of the atmosphere. Previous studies have predominantly focused on identifying individual carbon pathways, leaving the coexistence and evolution of multiple pathways within a single tectonic system poorly understood. To address this, we conducted an integrated petrological, geochemical, and zircon U-Pb geochronological study on marbles from the Yuka terrane and carbonatites from the Lülangshan terrane in the North Qaidam ultrahigh-pressure (UHP) metamorphic belt. Our results show that the Yuka marbles recorded a UHP metamorphic age of ~443 Ma. Their low phosphorus contents and low rare earth element (REE) abundances suggest a sedimentary carbonate protolith. In contrast, the Lülangshan carbonatites display a dominant detrital zircon age peak of 430~410 Ma. Their geochemical features including enrichment in large-ion lithophile elements (LILEs), depletion in high-field-strength elements (HFSEs), and REE patterns consistent with global average crust-derived carbonatites collectively support a crust-derived igneous origin. Combined with the regional tectonic setting, we propose that the Yuka marbles represent a solid-state return pathway, where subducted carbonates were metamorphosed under UHP conditions and subsequently exhumed via a subduction channel. In contrast, the Lülangshan carbonatites likely represent a melt pathway, formed by the partial melting of carbonate rocks detached from the subducted slab during the post-collisional stage, facilitated by upwelling asthenosphere. These two distinct rock types reveal diverse mechanisms solid versus melt for the return of carbon from depth to the surface in an orogenic belt, providing new constraints for understanding the fate of carbon in subduction zones and orogenic carbon cycling.