Migmatite-like textures in anthracite: Further evidence for low-grade metamorphic melting and resolidification in high-rank coals

Previous studies demonstrated that melting, initiated by supercritical fluids in the 375-400 degrees C range, occurred as part of anthracite metamorphism in the Appalachian Basin. Based on the known behavior of vitrinite at high temperatures and, to a lesser extent, at high pressures, it was determined that the duration of the heating, melting, and resolidification event was about 1 h. In the current study, featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals. By analogy with metamorphosed inorganic rocks, such associations represent diadysites and embrechites, i.e., cross-cutting and layered migmatites, respectively. Even though the temperature of formation of the anthracite structures is several hundred degrees C lower than that seen in metamorphosed inorganic rocks, anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal. (c) 2021 ChinaUniversity of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Automated summary

Previous studies have shown that melting during anthracite metamorphism in the Appalachian Basin is initiated by supercritical fluids in the 375-400 degrees C range, lasting about 1 hour. The current study demonstrates the intimate association of melted and resolidified vitrinite with anthracite-rank macerals. Analogous to metamorphosed inorganic rocks, these associations represent diadysites and embrechites in anthracite structures.