Freya Roxanne George, Daniel R Viete, Janaína N. Ávila, Gareth G. E. Seward, George L. Guice, Mark B. Allen, Michael J. Harrower

Subduction facilitates the transfer of volatiles from the Earth’s surface to its interior. However, the rock-scale processes that govern the efficiency of deep volatile transfer are not fully understood. Garnets from subduction zone rocks commonly have fine-scale, oscillatory elemental zoning that is typically considered to record external fluid ingress/transfer. Elemental and oxygen-isotope zoning in garnets from five exhumed subduction zone complexes show that in subduction zone rocks these records are not necessarily coupled; oxygen isotope evidence of ingress of buffering fluids, obvious only in rare cases, is decoupled from shorter length scale elemental and oxygen isotope zonings (which also show no coupling with each other). This finding suggests multiple mechanisms of internal chemical transfer operate at the grain and rock scale during subduction, and that rocks may commonly experience only limited interaction with external fluids. The results presented are consistent with a picture of volatile transfer in subduction that is spasmodic, highly localized, and variably efficient at evacuating fluids inherited from the surface then released by metamorphic dehydration.