Garnet sand reveals rock recycling processes in the youngest exhumed high- and ultrahigh-pressure terrane on Earth.

Rock recycling within the forearcs of subduction zones involves subduction of sediments and hydrated lithosphere into the upper mantle, exhumation of rocks to the surface, and erosion to form new sediment. The compositions of, and inclusions within detrital minerals revealed by electron microprobe analysis and Raman spectroscopy preserve petrogenetic clues that can be related to transit through the rock cycle. We report the discovery of the ultrahigh-pressure (UHP) indicator mineral coesite as inclusions in detrital garnet from a modern placer deposit in the actively exhuming Late Miocene-Recent high- and ultrahigh-pressure ((U)HP) metamorphic terrane of eastern Papua New Guinea.

Tracing ultrahigh-pressure metamorphism at the catchment scale.

Finding traces of ultrahigh-pressure (UHP) metamorphism in the geological record has huge implications for unravelling Earth's geodynamic evolution, such as the onset of deep subduction. Usually, UHP rocks are identified by specific mineral inclusions like coesite and characteristic petrographic features resulting from its (partial) transformation to the lower-pressure polymorph quartz in thin sections of crystalline rocks. This approach relies on very small sample size and is thus limited to a few points within large regions.