| Title | Scapolite and analcime: monitors of magmatic fluid metasomatism in a major shear zone |
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| Author | Pe-Piper, G; Piper, D J W ; Nagle, J |
| Source | Chemical Geology vol. 522, 2019 p. 208-222, https://doi.org/10.1016/j.chemgeo.2019.05.014 |
| Image |  |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20180270 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®); html |
| Province | Nova Scotia |
| NTS | 21H/08 |
| Area | Clarke Head; Cobequid Highlands; Parrsboro |
| Lat/Long WENS | -64.5000 -64.0000 45.5000 45.3333 |
| Subjects | igneous 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 |
| Illustrations | geoscientific sketch maps; photographs; photomicrographs; tables; plots; ternary diagrams; geochronological charts |
| Program | GSC Atlantic Division |
| Released | 2019 05 25 |
| Abstract | Scapolite 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 ID | 313030 |
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