XRD-based crystallinity degrees and formation temperature of graphite in some regional-metamorphic rocks from the Central and Eastern Rhodopes, Bulgaria: a test of the new graphitization degree GD(0–30) scale

Graphitization degrees and temperatures of the regional metamorphism in Central Eastern Rhododpes have been determined by values structural parameter d002 (Å) graphite graphite-bear¬ing marbles shists, from Vacha Madan-Erma Reka areas (Madan lithotectonic unit), Ardino–Nedelino area (Startsevo Chernichevo–Boturche (Byala unit). Equations different authors, formulated between 1951 2021, were used. They are integrated one system, allowing a conversion results deriving new quantitative correlations temperature metamorphism, degree crystallinity order semi-graphite graphite. The com¬parison data allows creation scheme, GD(0–30), based on natural carbon matter. validity range this geothermometer is large, 84 °C to 804 (from zeolite granulite facies metamorphism). peak studied 660 (i.e., upper limit amphibolite facies), lowest 468 °C, which charac¬teristic for lower part greenschist P-T field. graphitization regressive Rhodopes are: C (GD(0–30) = 24, well-crystallized graphite); 588 21, 564 (GD(0-30) 20, 516 18, 492 17, 16, graphite). calculated Rhodopes, equations all correspond conditions established other methods without using GD(0-30) sys¬tem determination simple, informative functional. It more convenient than earlier schemes showing correlation: metamorphic − degree. In addition influence temperature, also include effect secondary factors processes.