1,1,2,1- 1Badong National Observation and Research Station of Geohazards, State Key Laboratory of Geological Processes and Mineral Resources, and Center for Global Tectonics, China University of Geosciences, Wuhan, China (yanchao@cug.edu.cn)
- 2Laboratory for Crustal Petrology, Department of Geology University of Maryland, College Park, MD, USA (mbrown@umd.edu)
Numerical experiments have shown that the presence of fluid or 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 the amount of melt present during exhumation are rare, hindering a deeper understanding of exhumation dynamics of mafic crust. Here, we report results of a systematic study 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 at outcrop and thin-section scales: one type was derived exclusively from UHP eclogite and the other represents a blend of melts derived from both eclogite and host 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. First, we identified leucosome types, subsequently verified by petrographic analysis, and estimated leucosome proportion along one-dimensional transects totaling ~239 meters in length. Second, we estimated the area of different leucosome types using two-dimensional drone-based orthophotos covering ~4000 m2 in area. Based on linear proportion or area as a proxy for volume, the total leucosome amount in the migmatized mafic crust varies from 20 to 30 vol.% with ~83% of the leucosome sourced from eclogite. Retrogression during exhumation leads to between 5 and 19% density reduction of the eclogites 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 between 18 and 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.
How to cite: Yan, C., Wang, L., Chen, Z., Brown, M., Yang, X., and Zhang, M.: Quantitative Estimation of Leucosome Volume in Migmatized Eclogite and Implications for Exhumation Dynamics of Mafic Crust, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-268, https://doi.org/10.5194/egusphere-egu26-268, 2026.
