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TitleScapolite and analcime: monitors of magmatic fluid metasomatism in a major shear zone
 
AuthorPe-Piper, G; Piper, D J WORCID logo; Nagle, J
SourceChemical Geology vol. 522, 2019 p. 208-222, https://doi.org/10.1016/j.chemgeo.2019.05.014
Image
Year2019
Alt SeriesNatural Resources Canada, Contribution Series 20180270
PublisherElsevier BV
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
ProvinceNova Scotia
NTS21H/08
AreaClarke Head; Cobequid Highlands; Parrsboro
Lat/Long WENS -64.5000 -64.0000 45.5000 45.3333
Subjectsigneous and metamorphic petrology; mineralogy; tectonics; geochemistry; geochronology; bedrock geology; lithology; igneous rocks; intrusive rocks; syenites; granitic rocks; gabbros; diorites; structural features; shear zones; fault zones; alteration; metasomatism; tectonic environments; tectonic history; intrusions; magmatism; faulting; basins; precipitation; hydrothermal systems; fluid dynamics; fluid flow; scapolite; analcime; hastingsite; veins; sodium chloride; chlorine geochemistry; sodium geochemistry; isotopic studies; oxygen isotopes; titanium geochemistry; zirconium geochemistry; feldspar; potassium geochemistry; biotite; thin section microscopy; mineral assemblages; paragenesis; electron probe analyses; pressure-temperature conditions; radiometric dating; uranium lead dating; argon argon dating; Canadian Appalachians; Potapique Fault; Avalon Terrane; Minas Fault Zone; Meguma Terrane; Cobequid Shear Zone; Phanerozoic; Paleozoic; Carboniferous; Devonian
Illustrationsgeoscientific sketch maps; photographs; photomicrographs; tables; plots; ternary diagrams; geochronological charts
ProgramGSC Atlantic Division
Released2019 05 25
AbstractScapolite and analcime are uncommon alteration minerals in syenite. Here we describe a syenite body in a fault zone that hosts these minerals and we elucidate the unusual chemical conditions that led to their formation. The Clarke Head syenite is part of a regional late Devonian-early Carboniferous back-arc A-type granitoid suite in the Cobequid Highlands of Nova Scotia, Canadian Appalachians. The syenite contains magmatic rutile and analcime. Magmatic K-feldspar has been largely replaced by scapolite of marialite composition, which shows a temporal transition from more Cl rich to more carbonate rich varieties. Scapolite veins cut both the syenite and associated gabbro and diorite. Analcime I occurs as a late stage interstitial magmatic mineral. Analcime II forms by alteration of albite lamellae in perthite replaced by scapolite, analcime III vugs that cross-cut scapolite and analcime IV occurs in late veins cross-cutting earlier analcime phases and scapolite. The regional A-type granite plutonism was Na- and halogen rich, with widespread late-magmatic albitization and F-related mobility of REE minerals. However, only at Clarke Head is there extreme Na- and Cl-rich metasomatism, indicated by scapolite and Cl-rich hastingsite (with>1 wt% Cl content). Cl-rich fluids were derived from regional halite evaporites at faulted basin margins. The main circulating fluids were likely of magmatic origin, based on the delta-18O of both replacement and vein scapolite. As the NaCl supply was reduced, scapolite became more Ca-rich. Halogen-rich fluids also mobilized Ti and Zr, which were reprecipitated in hydrothermal rutile and zircon as the halogen activity diminished. Scapolite replacement of K-feldspar released large amounts of K+ into the circulating fluids, which converted ferromagnesian silicates in fault zones to secondary biotite.
Summary(Plain Language Summary, not published)
A description of the unusual minerals scapolite and analcime in a granitic rock in the Minas Fault Zone near Parrsboro NS, and an interpretation of their origin terms of mineralising systems.
GEOSCAN ID313030

 
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