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TitleMafic whole-rock geochemistry and neodymium isotopes, Green Mountain and Rowe/Prospect Rock slices, Vermont Appalachians
AuthorHonsberger, I WORCID logo; Coish, R A; Laird, J; Zhang, S
SourceAmerican Journal of Science vol. 319, 2019 p. 287-314,
Alt SeriesNatural Resources Canada, Contribution Series 20180200
PublisherAmerican Journal of Science (AJS)
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
AreaAppalachian Mountains; Green Mountains; Vermont; United States of America
Lat/Long WENS -73.5000 -71.5000 45.5000 42.5000
Subjectstectonics; geochemistry; structural geology; mineralogy; igneous and metamorphic petrology; bedrock geology; lithology; mafic rocks; ultramafic rocks; igneous rocks; volcanic rocks; basalts; ophiolites; metamorphic rocks; metavolcanic rocks; schists; greenschist facies; eclogites; amphibole; structural features; faults; faults, thrust; faults, normal; fault zones; folds; antiforms; anticlinoria; whole rock geochemistry; minor element geochemistry; trace element geochemistry; major element geochemistry; isotopic studies; neodymium; mass spectrometer analysis; tectonic evolution; crustal evolution; provenance; lithosphere; mantle; magmatism; rifting; partial melting; subduction zones; metamorphism; alteration; chloritization; albitization; crystallization; models; Appalachian Province; Neoproterozoic; Rodinia; Iapetus Ocean; Laurentian Margin; Green Mountain Massif; Rowe-Prospect Rock Slice; Tillotson Peak Complex; Humber Zone; Dunnage Zone; Gander Zone; Red Indian Line; Laurentian Drift; Moretown Terrane; Taconic Orogen; Belvidere Mountain Complex; Grenville Orogen; Hinesburg-Underhill Slice; Lincoln Mountain Massif; Prospect Rock Fault; Whitcomb Summit Thrust; Acadian Orogen; Honey Hollow Fault; New Boston Antiform; Phanerozoic; Paleozoic; Precambrian; Proterozoic
Illustrationsgeoscientific sketch maps; cross-sections; tables; photomicrographs; plots; ternary diagrams
ProgramTargeted Geoscience Initiative (TGI-5) Gold systems
Released2019 04 01
AbstractMafic rocks containing sodic-calcic amphibole in the Green Mountain slice (GMS) and Rowe/Prospect Rock slice (R/PRS), Vermont Appalachians were originally subalkaline basalts emplaced as melts during Neoproterozoic rifting of Rodinia that led to the formation of the Iapetus Ocean basin. Relatively high degrees of partial melting of asthenosphere that was highly depleted in incompatible elements produced R/PRS magma(s), which may have been contaminated locally by continental crust and/or fluids. Trace element chemistry suggests that mafic bodies from different locations in the R/PRS may be fractionated magmatic equivalents. Mafic rocks in the GMS formed from magmas produced by relatively low degrees of partial melting of mantle that was relatively enriched in incompatible elements compared to depleted mantle. These enriched melts may have been derived from a plume and/or enriched lithospheric components, potentially continental crust, embedded in depleted upper mantle. A depleted mantle signature preserved locally in the GMS probably reflects increasing asthenospheric input during crustal thinning, opposed to crustal or fluid contamination.
Whole-rock minor and trace element data from the GMS and R/PRS are distinct from analyses of glaucophane schist from the Tillotson Peak Complex in northern Vermont, which may be exhumed Iapetan ocean floor. Exhumed mafic rocks in the GMS and R/PRS were formed as lower plate melts prior to relatively high pressure subduction zone metamorphism, providing evidence for subduction of the Laurentian margin, not subduction erosion. Low pressure greenschist facies mafic rocks that occur structurally between the GMS and R/PRS were sourced from depleted or highly depleted mantle in a supra-subduction zone environment, potentially a forearc or backarc basin; an ophiolitic origin is equivocal. Geochemical and isotopic data and interpretations are compatible with rift-related tectonomagmatic models for the peri-Laurentian realm of the northern Appalachians.
Summary(Plain Language Summary, not published)
This manuscript presents new whole-rock geochemistry and neodymium isotopes for mafic rocks that were subducted in the Early Paleozoic. Our work shows that the metamorphic rocks of study formed originally as igneous rocks during late stages of continental rifting prior to the establishment of the proto-Atlantic ocean basin (Iapetus), and are not ophiolitic. The data presented in the manuscript capture interaction of incompatible element enriched and incompatible element depleted mantle sources that resulted from progressive asthenospheric input leading to ocean ridge development. An implication of this research is that relatively high pressure subduction zone metamorphism of the rocks of study resulted from subduction of the Laurentian margin, not subduction erosion of the upper plate.

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