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  1. The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada [Download]

    Title: The evolution of calcite-bearing kimberlites by melt-rock reaction: evidence from polymineralic inclusions within clinopyroxene and garnet megacrysts from Lac de Gras kimberlites, Canada
    Creator: Stachel, Thomas
    Description: Megacrystic (>1 cm) clinopyroxene (Cr-diopside) and garnet (Cr-pyrope) xenocrysts within kimberlites from Lac de Gras (Northwest Territories, Canada) contain fully crystallized melt inclusions. These ‘polymineralic inclusions’ have previously been interpreted to form by necking down of melts at mantle depths. We present a detailed petrographical and geochemical investigation of polymineralic inclusions and their host crystals to better understand how they form and what they reveal about the evolution of kimberlite melt. Genetically, the megacrysts are mantle xenocrysts with peridotitic chemical signatures indicating an origin within the lithospheric mantle (for the Cr-diopsides studied here ~4.6 GPa, 1015 °C). Textural evidence for disequilibrium between the host crystals and their polymineralic inclusions (spongy rims in Cr-diopside, kelyphite in Cr-pyrope) is consistent with measured Sr isotopic disequilibrium. The preservation of disequilibrium establishes a temporal link to kimberlite eruption. In Cr-diopsides, polymineralic inclusions contain phlogopite, olivine, chromite, serpentine, and calcite. Abundant fluid inclusion trails surround the inclusions. In Cr-pyropes, the inclusions additionally contain Al-spinel, clinopyroxene, and dolomite. The major and trace element compositions of the inclusion phases are generally consistent with the early stages of kimberlite differentiation trends. Extensive chemical exchange between the host phases and the inclusions is indicated by enrichment of the inclusions in major components of the host crystals, such as Cr2O3 and Al2O3. This chemical evidence, along with phase equilibria constraints, supports the proposal that the inclusions within Cr-diopside record the decarbonation reaction: dolomitic melt + diopside → forsterite + calcite + CO2, yielding the observed inclusion mineralogy and producing associated (CO2-rich) fluid inclusions. Our study of polymineralic inclusions in megacrysts provides clear mineralogical and chemical evidence for an origin of kimberlite that involves the reaction of high-pressure dolomitic melt with diopside-bearing mantle assemblages producing a lower-pressure melt that crystallizes a calcite-dominated assemblage in the crust.
    Subjects: Kimberlite, Cr-rich megacrysts, Polymineralic inclusions, Melt inclusions, Decarbonation reaction, Kimberlite evolution
    Date Created: 2016/07
  2. One tree hill/Maungakiekie: Contesting the iconography of an Auckland landscape.

    Title: One tree hill/Maungakiekie: Contesting the iconography of an Auckland landscape.
    Creator: Kearns, R. A.
    Subjects: race relations, auckland, European, politics, Maori, one tree hill
    Date Created: 2000
  3. Late Paleozoic strike-slip faults in Maritime Canada and their role in the reconfiguration of the northern Appalachian orogen [Download]

    Title: Late Paleozoic strike-slip faults in Maritime Canada and their role in the reconfiguration of the northern Appalachian orogen
    Creator: Waldron, JWF
    Description: Major late Paleozoic faults, many with documented strike-slip motion, have dissected the Ordovician-Devonian Appalachian orogen in the Maritime Provinces of Atlantic Canada. Activity alternated between east-west faults (Minas trend) and NE-SW faults (Appalachian trend). NW-SE faults (Canso trend) were probably conjugate to Minas-trend faults. Major dextral movement, on faults with Appalachian trend, in total between 200 and 300 km, began in the Late Devonian. This movement initiated the Maritimes Basin in a transtensional environment at a releasing bend formed around a promontory in the Laurentian margin and thinned the crust, accounting for the major subsidence of the basin. Appalachian-trend strike slip continued in the Mississippian but was accompanied by major movement on E-W Minas-trend faults culminating around the Mississippian-Pennsylvanian boundary, juxtaposing the Meguma and Avalon terranes of the Appalachians close to their present-day configuration. However, strike slip continued during the Pennsylvanian-Permian interval resulting in transpressional deformation that reactivated and inverted earlier extensional faults. A final major episode of transtension, mainly sinistral, occurred during the Mesozoic opening of the Atlantic Ocean. Restoration of movements on these faults, amounting to several hundred kilometers of slip, explains anomalies in the present-day distribution of terranes amalgamated during early Paleozoic Appalachian tectonism. In the restored geometry, the Nashoba and Ellsworth terranes of Ganderia are adjacent to one another, and the Meguma terrane lies clearly outboard of Avalonia. A restored post-Acadian paleogeography, not the present-day geometry of the orogen, should be used as a basis for reconstructions of its earlier Paleozoic history.
    Subjects: Tectonics
    Date Created: 2015/11/26
  4. Smoking environments in transition: The experiences of recent Chinese migrants to Canada [Download]

    Title: Smoking environments in transition: The experiences of recent Chinese migrants to Canada
    Creator: Li, J.
    Description: International migrants experience first-hand differences between countries in terms of the social meanings, spatial regulation and prevalence of smoking. This research centred on the smoking-related perceptions, experiences and behaviours of recent migrants from China to Canada. Eight focus groups were held in Edmonton, Alberta, in July–October 2013 to explore migrants' understandings of the practices and meanings of smoking in both countries. There were 58 participants (37 non-smokers and 21 smokers), most of whom were international students. Qualitative content analysis of focus group transcripts was undertaken to identify key themes. Participants observed that smoking remains almost ubiquitous in China due to ineffective spatial restrictions and the social importance of smoking among men. By contrast, smoking bans in Canada were perceived as effective due to widespread compliance and expectations of enforcement. They were conscious that male smoking was both less prevalent and less socially valued in Canada; conversely, female smoking was perceived as more accepted in Canada than in China. There was broad agreement that smoking was tolerated in Canada, provided it occurred in appropriate places. Complying with widespread spatial restrictions brought about changes in smokers' behaviours: they smoked less often, and consumed fewer cigarettes. Because smoking was more difficult to perform, participants thought the Canadian context supported quitting. Non-smokers were enthusiastic about smoke-free environments in Canada, and had become acculturated to air that did not smell of smoke. These findings affirm the importance of comprehensive smoking bans, backed by enforcement, in contributing to the denormalisation of smoking and the protection of non-smokers.
    Subjects: second-hand smoke, migration, Canada, tobacco control, smoking, China
    Date Created: 2015