Supporting Information S2 (Tables S1 to S6) in "Quantitative Estimation of Leucosome Volume in Migmatized Eclogite and Implications for Exhumation Dynamics of Mafic Crust"

Numerical experiments have shown that the presence of melt during exhumation of deeply subducted ultrahigh-pressure (UHP) eclogite significantly reduces the bulk strength and density, promoting exhumation. However, quantitative studies of the leucosome volume in natural migmatitic eclogites as a proxy for melt volume during exhumation are rare. Here, we report results from an extensive outcrop of migmatized eclogite within host gneisses at General's Hill in the Sulu belt, China. Two types of leucosome are distinguished: one type was derived exclusively from eclogite and the other represents a blend of melts derived from eclogite and gneiss. We develop a comprehensive set of quantitative methods to estimate the total leucosome volume and the proportion derived from eclogite, and to evaluate the density change of mafic crust due to the presence of melt and effects of retrogression during exhumation. Based on linear proportion or area as a proxy for volume, we identified leucosome types and estimated leucosome proportion using one-dimensional transects totaling ~239 meters and two-dimensional drone-based orthophotos covering ~4000 m². Leucosome forms 20–30 vol.% of the migmatized mafic crust with ~83% sourced from eclogite. Retrogression reduces eclogites density by 5–19% on a per sample basis compared to representative unmigmatized UHP eclogites from the adjacent Yangkou Bay outcrop, and overall, the presence of leucosome leads to 18–20% density reduction of the local mafic crust investigated in this study. These results provide critical parameterized constraints for use in geodynamic models of exhumation of eclogite-dominated tectonic units in continental subduction zones.