摘要：AbstractPrevious studies demonstrated that melting, initiated by supercritical fluids in the 375–400 °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 °C lower than that seen in metamorphosed inorganic rocks, anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.Graphical abstractDisplay OmittedHighlights•Anthracite textures from several sources were evaluated.•Several showed signs of melting.•For Pennsylvania anthracite, the structure is described as a migmatite.•Use of a hard rock term is deemed appropriate for highly metamorphosed coals.
关键词：KeywordsIgneousMetamorphic texturePennsylvaniaMesozoic basinsSouth Africa
