University of Kentucky UKnowledge Center for Applied Energy Research Faculty Publications Center for Applied Energy Research 5-2021 Migmatite-Like Textures in Anthracite: Further Evidence for Low- Grade Metamorphic Melting and Resolidification in High-Rank Coals James C. Hower University of Kentucky, [email protected] Susan M. Rimmer Southern Illinois University Carbondale Maria Mastalerz Indiana University Nicola J. Wagner University of Johannesburg, South Africa Follow this and additional works at: https://uknowledge.uky.edu/caer_facpub Part of the Geology Commons Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Repository Citation Hower, James C.; Rimmer, Susan M.; Mastalerz, Maria; and Wagner, Nicola J., "Migmatite-Like Textures in Anthracite: Further Evidence for Low-Grade Metamorphic Melting and Resolidification in High-Rank Coals" (2021). Center for Applied Energy Research Faculty Publications. 37. https://uknowledge.uky.edu/caer_facpub/37 This Article is brought to you for free and open access by the Center for Applied Energy Research at UKnowledge. It has been accepted for inclusion in Center for Applied Energy Research Faculty Publications by an authorized administrator of UKnowledge. For more information, please contact [email protected]. Migmatite-Like Textures in Anthracite: Further Evidence for Low-Grade Metamorphic Melting and Resolidification in High-Rank Coals Digital Object Identifier (DOI) https://doi.org/10.1016/j.gsf.2020.12.004 Notes/Citation Information Published in Geoscience Frontiers, v. 12, issue 3, 101122. © 2020 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by- nc-nd/4.0/). This article is available at UKnowledge: https://uknowledge.uky.edu/caer_facpub/37 GSF-01122; No of Pages 9 Geoscience Frontiers 12 (2021) 101122 Contents lists available at ScienceDirect Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Migmatite-like textures in anthracite: Further evidence for low-grade metamorphic melting and resolidification in high-rank coals James C. Hower a,⁎, Susan M. Rimmer b, Maria Mastalerz c, Nicola J. Wagner d a University of Kentucky Center for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, USA b School of Earth Systems and Sustainability, Southern Illinois University Carbondale, Carbondale, IL 62901, USA c Indiana Geological & Water Survey, Indiana University, Bloomington, IN 47405, USA d Department of Geology, University of Johannesburg, Johannesburg, South Africa article info abstract Article history: Previous studies demonstrated that melting, initiated by supercritical fluids in the 375–400 °C range, occurred as Received 6 November 2020 part of anthracite metamorphism in the Appalachian Basin. Based on the known behavior of vitrinite at high tem- Received in revised form 2 December 2020 peratures and, to a lesser extent, at high pressures, it was determined that the duration of the heating, melting, Accepted 16 December 2020 and resolidification event was about 1 h. In the current study, featureless vitrinite within banded maceral assem- Available online 23 December 2020 blages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals. Handling Editor: M. Santosh 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 anthra- Keywords: cite structures is several hundred °C lower than that seen in metamorphosed inorganic rocks, anthracites are Igneous metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal. Metamorphic texture © 2020 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ Pennsylvania licenses/by-nc-nd/4.0/). Mesozoic basins South Africa 1. Introduction high maturity coals in cases where structural and textural features re- semble closely those in metamorphic rocks. While there have been many attempts to correlate mineral and Metamorphic and tectonic structural techniques and nomenclature maceral metamorphic parameters, Kisch (1987) noted that the accuracy (after Ramsay, 1967; Spry, 1969; Bucher and Grapes, 2011)havebeen of the parameters and refinement of the correlations is limited by the applied to high to low volatile bituminous coals in western Pennsylva- nature of the starting materials and many other factors including, but nia by Hower (1978) and Zhang and Davis (1993); to an anthracite not limited to, oxidation conditions, supply of cations, SiO2 supersatura- from a mine in the Southern Anthracite field, Pennsylvania by Hower tion, permeability and porosity of rocks, partial pressure of CO2,changes (1978) and Hower and Davis (1981); to semi-anthracite- and in the composition of interstitial solutions with time, persistence of non- anthracite-rank coals in the Pennsylvania Anthracite fields by Levine equilibrium mineral assemblages,and the selection of theappropriate and Davis (1989a); to medium and low volatile coals in the Broad Top vitrinite type for reflectance measurements. Basically, as the “coalifica- coalfield, Pennsylvania by Levine and Davis (1989b);andtoseverallo- tion experiment” was run several hundred million years ago (in the cations in Alberta and British Columbia by Kalkreuth et al. (1990) and case of the Pennsylvania anthracites), it cannot be replicated by exper- Langenberg and Kalkreuth (1991). At a very fine scale, the occurrence imental heating and in most, if not all cases, there are more variables of nanotubes in anthracites and meta-anthracites with Rmax>5%isare- than can be reliably defined. Therefore, not only is it difficult to relate flection of the metamorphic temperatures and pressures (Silva et al., structural and textural characteristics of high maturity coals to those 2020). A similar mechanism was noted in anthracites intruded by igne- present in metamorphic rocks, it is even more difficult to interpret tex- ous rocks (Li et al., 2017), but the Silva et al. (2020) discovery appears to tural similarities in anthracite and those in metamorphic rocks in terms be the first for regionally metamorphosed coals. of temperature and pressure conditions. Considering that organic mat- The theories on metamorphic events in the Pennsylvania Anthracite ter is more sensitive to metamorphic processes than minerals, the ques- Fields and, indeed, elsewhere in the Appalachians and beyond, evolved tion remains whether metamorphic rock terminology can be applied to from traditional views of the imposition of coal rank by folding pres- sures (White, 1925; Turner, 1934), a view that persisted at least to the ⁎ Corresponding author. work of Wood et al., 1969 despite Teichmüller and Teichmüller's E-mail address: [email protected] (J.C. Hower). (1966) advocacy for the influence of geothermal heating. In contrast, https://doi.org/10.1016/j.gsf.2020.12.004 1674-9871/© 2020 Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article as: J.C. Hower, S.M. Rimmer, M. Mastalerz, et al., Migmatite-like textures in anthracite: Further evidence for low-grade metamorphic melting and resoli..., Geoscience Frontiers, https://doi.org/10.1016/j.gsf.2020.12.004 J.C. Hower, S.M. Rimmer, M. Mastalerz et al. Geoscience Frontiers 12 (2021) 101122 more recent works emphasize the static influence of heating at depths 2. Methods of several kilometers accompanying the folding (Hower, 1978; Hower and Davis, 1981; Levine, 1983, 1986; Levine and Davis, 1989a, b; Samples of the Pennsylvanian Buck Mountain vein from a mine in Roden and Miller, 1989; Kisch and van den Kerkhof, 1991; Hulver, western Schuylkill County, Pennsylvania, were examined. The epoxy- 1997; Faill, 1998)1and/or the influence of hydrothermal fluids bound pellets were made from the broken remnants, generally >1- (Gresley, 1896; Reeves, 1928; Oliver, 1986, 1992; Juster et al., 1987; mm size, of a 5 cm × 5 cm block sample that had been subjected to Daniels and Altaner, 1990; Daniels et al., 1990, 1994, 1996; Hower strength testing and from a 1-mm-thick oriented wafer prepared for et al., 1993; Hower, 1997, 2013; Hower and Gayer, 2002; Harrison thermal testing (Weisenberger et al., 2020). As such, the maceral com- et al., 2004; Ruppert et al., 2010; Ruppert et al., 2014). Higher vitrinite position and chemistry of the test pellets are not representative of the reflectances in the Pennsylvanian anthracites (Ruppert et al., 2010) whole coal. Both pellets were prepared to a final 0.05-μm alumina slurry compared to those in the underlying Devonian black shales (Repetski polish. All other samples cited in the study were previously prepared for et al., 2008)suggestthathydrothermalfluids might have preferentially other studies. flowed through the Pennsylvanian rocks rather than the Devonian Reflectance measurements were taken on epoxy-bound particulate rocks. Coal, however, records higher reflectance than vitrinite in associ- pellets using a 50×, reflected-light, oil-immersion objective utilized in- ated clastic sediments around the same intrusive body (Quaderer et al., coming light polarized at 45°. The reflected light passed across a grating 2016). Based on the above observations, it is hypothesized thatthe esti- monochrometer set at 547 nm on the path to the photomultiplier tube. mated peak temperature ranged from 200 °C