The “lost” aqueous supercritical fluids recorded in highly refractory mantle peridotites

Supercritical fluids, including silicate-enriched and aqueous varieties, are crucial for material circulation and energy exchange within Earth’s layers. Although silicate-enriched supercritical fluids are well-documented in ultra-high-pressure rocks, the nature of aqueous supercritical fluids remains elusive because they are easily “lost” during transport processes and their signals are often obscured in natural materials. Here, we report the geochemical compositions of the ultra-refractory mantle wedge peridotites that underwent extreme melt extraction and metasomatism to identify aqueous supercritical fluid signatures. These peridotites are enriched in fluid-mobile elements, and light rare earth and high-field strength elements, implying metasomatism by silicate-depleted aqueous rather than silicate-enriched supercritical fluids. The δ^138/134Ba of peridotites range from -0.11‰ to +0.52‰, indicating that the aqueous supercritical fluids may be derived from a cold subducted plate or through the silicate loss of silicate-enriched supercritical fluids. These water-enriched liquids can play a key role in cryptical metasomatism and long-distance element migration, providing new insights into the dynamics of Earth’s interior.