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TitleNet-transfer reactions and modal spaces for ultramafic slivers, Vermont Appalachians, USA
AuthorHonsberger, I WORCID logo; Laird, J
SourceCanadian Mineralogist vol. 56, 2018 p. 1-26,
Alt SeriesNatural Resources Canada, Contribution Series 20180109
PublisherMineralogical Association of Canada
Mediapaper; on-line; digital
File formatpdf
AreaVermont; Stockbridge; Appalachians; Belvidere Mountain; United States of America
Lat/Long WENS -73.0000 -72.0000 44.0000 43.0000
Subjectsmineralogy; igneous and metamorphic petrology; geochemistry; alteration; serpentinization; carbonatization; metasomatism; mineral zoning; carbon dioxide; bedrock geology; lithology; ultramafic rocks; serpentinites; peridotites; metamorphic rocks; schists; structural features; faults; tectonic setting; subduction zones; metamorphism; deformation; veins; metamorphic facies; whole rock analyses; crystallography; phase equilibria; Laurentian Margin; Gondwana; Taconian Orogeny; Acadian Orogeny; Adirondack Massif; Berkshire Massif; Belvidere Mountain Complex; Green Mountain Massif; Red Indian Line; Tillotson Peak Complex; Water
Illustrationsgeoscientific sketch maps; cross-sections; photographs; photomicrographs; tables; schematic representations; graphs
ProgramTargeted Geoscience Initiative (TGI-5) Gold systems
Released2018 10 25
AbstractSerpentinized ultramafic slivers associated with mafic subduction zone rocks in the hinterland of central Vermont preserve talc-carbonate, chlorite-tremolite, and chlorite-talc zones that formed via a series of H2O- and CO2-bearing net-transfer reactions. Reactions took place within both MgO-SiO2-H2O-CO2 (MSHC) and CaO-MgO-Al2O3-SiO2-H2O-CO2 (CMASHC), with MSHC reactions preceding CMASHC reactions. Three linearly independent basis net-transfer reactions were derived for each system. Each set of basis reactions includes one closed system reaction, one reaction open to H2O, and one reaction open to CO2. The basis reactions derived for MSHC are: 9Enstatite+Serpentine=3Forsterite+2Talc; 6Enstatite +3H2O=Talc+Serpentine; 6Enstatite+Serpentine+3CO2=3Magnesite+2Talc. The basis reactions derived for CMASHC are: 2Serpentine+ (VI)Al (IV)AlMg(-1)Si(-1) (TK) = Chlorite; 2Serpentine+ 5Talc + 6CaMg(-1) (CM) = 3Tremolite + 6H2O; 7Talc + 3Dolomite + 3CM = 3Tremolite + 2Serpentine + 6CO2. Modal spaces show that carbonatization of serpentinite occurred in MSHC after serpentinization of peridotite, and that MSHC evolved into CMASHC due to metasomatic addition of Al3+ and Ca2+ during serpentinite carbonatization. The reaction pathway interpreted for CMASHC is dependent primarily on carbonatization and decarbonatization reactions, with chlorite-tremolite and chlorite-talc zones forming via decarbonatization and talc-carbonate zones forming via carbonatization of serpentinite. The modal spaces herein can be utilized for any ultramafic body with comparable zonation. Applying these spaces to ultramafic rocks at Belvidere Mountain in northern Vermont suggests that the mineralogical diversity seen there may result from multiple independent reaction paths within MSHC, NCMASH, CMASH, and CMASHC.
Summary(Plain Language Summary, not published)
Linear algebra is utilized to derive metamorphic reactions for ultramafic rocks in the central Vermont Appalachians that were formed in an ancient subduction zone. Formation of different mineralogical zones is described with respect to an evolving reaction history. The history is described sequentially as follows: 1)hydration of mantle rocks and formation of serpentine; 2)input of CO2 and formation of carbonate minerals; 3)addition of aluminum and calcium during late stage faulting. The reaction history coupled with structural relationships implies that CO2 is prevalent in subduction zones and may be most available for reactions during upward transport of rocks from great depth. Research also highlights the role of faults in transporting ions during deformation of rock. The algebraic framework presented is applicable to any ultramafic rock that was metamorphosed as a result of H2O- and CO2-bearing reactions.

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