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TitleMode of emplacement of Archean komatiitic tuffs and flows in the Selkirk Bay area, Melville Peninsula, Nunavut, Canada
AuthorRichan, L; Gibson, H L; Houle, M G; Lesher, C M; Wodicka, NORCID logo
SourcePrecambrian Research vol. 263, 2015 p. 174-196,
Alt SeriesEarth Sciences Sector, Contribution Series 20150021
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
AreaSelkirk Bay; Melville Peninsula
Lat/Long WENS -85.6500 -85.5833 68.1833 68.1500
Subjectsgeochemistry; igneous and metamorphic petrology; greenstone belts; komatiites; tuffs; serpentine; chlorite; amphibole; metamorphism; pyroclastics; magmas; volcanism; ultramafic metavolcanics; volcanic basins; olivine; lavas
Illustrationslocation maps; geologic maps; structural cross-sections; tables; photographs; structural diagrams; graphs
ProgramGEM: Geo-mapping for Energy and Minerals Geomapping for Energy & Minerals (GEM) - Program Coordination
Released2015 07 01
AbstractThe 2.97 Ga Prince Albert greenstone belt (PAGB) of Melville Peninsula (Nunavut, Canada) contains multiple komatiitic flows and laterally extensive units of komatiitic tuff in the Selkirk Bay area. These units are serpentinized, chloritized, amphibolitized, and less commonly, carbonate altered. The tuffs retain element abundances typical of Al-undepleted komatiites, identical to the associated komatiitic flows, indicating that the tuffs and flows are comagmatic. The flows exhibit excellent textural preservation with well-developed upper spinifex and lower cumulate zones typical of differentiated komatiite flows. However, the tuffs do not preserve primary microscale textures and are fine-grained and largely massive to planar-laminated. This, coupled with their extensive nature (up to 10 km laterally; up to 10 m thick vertically), lack of gradational contacts with komatiitic flows, and their komatiitic mineralogical and chemical composition support a pyroclastic origin, deposition via eruption-fed fallout and mass flow, and subaqueous deposition during intervals characterized by lower rates of effusive volcanism. The low volatile content of the komatiitic magma, indicated by lack of vesicles in komatiitic flows and the lack of scoriaceous lapilli in the tuff, suggests an origin through phreatomagmatic pyroclastic eruptions. The Selkirk Bay komatiitic lavas and tuffs have liquid compositions with up to 30 wt% MgO, consistent with their derivation from a high magnesium komatiitic parental magma. There is evidence for up to 15%crustal contamination, which is also supported by slight enrichments in the LREE and Th relative to Nb. Major and minor elemental trends are indicative of olivine being the dominant liquidus mineral during early crystallization. Komatiitic flows of the PAGB were erupted onto massive to pillowed basalt where they formed thick, channelized, massive, undifferentiated flows flanked by spinifex-textured sheet/lobate flows. Synvolcanic structural basins and down-faulting are considered responsible for flow channelization and also controlled the deposition of local, framework-supported, ultramafic mass flow deposits and localized deposits of felsic volcaniclastic rocks. The komatiitic tuffs occur at two stratigraphic intervals indicating that they are a product of at least two pyroclastic eruptions. The uppermost strata document a change to a more mafic-dominated lava sequence interlayered with both differentiated and undifferentiated komatiitic flows, which are overlain by thick deposits of felsic volcaniclastic rock.
Summary(Plain Language Summary, not published)
This article present the results of petrological, geochemical and volcanological study on the 2.97 Ga Prince Albert greenstone belt (PAGB) of Melville Peninsula (Nunavut,Canada) that contains multiple units of differentiated and undifferentiated komatiitic flows and laterally extensive units of komatiitic tuff in the Selkirk Bay area.

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