Geochemistry and origin of Archean felsic metavolcanic rocks, central Noranda area, Quebec, Canada

Abstract

Felsic magma petrogenesis was studied by analyzing 24 stratigraphically controlled Archean andesite-to-rhyolite lava flows of both tholeiitic and calc-alkalic affinity from the upper Noranda Subgroup, Quebec, using instrumental neutron activation and X-ray fluorescence techniques. The lavas have moderate values of [LaIYb], (0.9-3.8) and low values of 100 X ThlZr ( -I). According to calculations following batch partial melting and Rayleigh fractional crystallization models, both the calcalkalic and tholeiitic felsic volcanic rocks are probably products of shallow-level fractional crystallization of mafic parental magmas formed respectively by lower ( -7 % for calc-alkalic) and higher ( -14% for tholeiitic) degrees of partial melting of a primitive mantle source.Contribution to the magma genesis from plausible crustal materials was negligible. A back-arc-type diapirism is geochemically suggested for the tectonic model of origin of Noranda felsic magmas, in conformity with geological observations. Felsic volcanic rocks with compositions analogous to the studied samples exist in several other Archean terrains of the Canadian Shield, suggesting thereby that the late Archean sialic crust was at least in part produced by volcanic rocks ultimately derived from the primitive mantle.Une Ctude de la pktrogentse du magma felsitique a Ct C effectuCe au moyen d'analyses par les techniques d'activation neutronique instrumentale et de fluorescence des rayons X de 24 coul&s de lave d'andCsine i rhyolite, d'affinitks tholCiitiques et calco-alcalines, du Sous-groupe de Noranda supCrieur, et pour lesquelles la stratigraphie archCenne a Ct C bien vCrifCe. Les laves foumissent des rapports [LaIYb], (0,9-3,8) modCk et 100 x ThlZr ( -1) faible. D'aprbs les calculs fondCs sur les modbles de foumCes de fusion partielle et de la cristallisation fractionnke de Rayleigh, il apparait que les roches volcaniques felsitiques calco-alcalines et tholkiitiques sont probablement les produits de la cristallisation fractionnCe, 21 un niveau ClevC dans les magmas parentaux mafiques formCs respectivement par des degks de fusion partielle plus faibles ( -7% pour calcoalcalines) et plus ClevCs ( -14% pour tholeiitiques) du magma primitif dans le manteau.La contribution i la genbse du magma des matCriaux formant la croQte fut minime. La gCochimie suggbre un diapirisme de type arritre-arc comme modtle tectonique de l'origine des magmas felsitiques de Noranda, conformCment aux observations gCologiques. Les roches volcaniques felsitiques avec des compositions analogues i celles des Cchantillons CtudiCs existent dans plusieurs autres terrains archkens du Bouclier canadien, indiquant par 18 que la crofite sialique de 1'ArchCen supkrieur fut au moins en partie produite par les roches volcaniques dCrivtes fondamentalement du manteau primitif.[Traduit par la revue]Can.

Magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace-element discriminant diagrams

“…Unfortunately, the way in which rocks were classified as calc-alkaline vs. tholeiitic is rarely specified. A notable exception is Ujike and Goodwin (1987) who used iron-enrichment trends as the defining criteria for the series and specifically wrote that most tholeiitic rocks in a certain area of the Blake River Group have [La/Yb] N <2.2, whereas most calc-alkaline ones have [La/Yb] N ≥2.2 (the subscript N denotes chondrite normalization). Ujike and Goodwin (1987) did note, however, that "this particular ratio is not universally applicable to magma series identification".…”

“…A notable exception is Ujike and Goodwin (1987) who used iron-enrichment trends as the defining criteria for the series and specifically wrote that most tholeiitic rocks in a certain area of the Blake River Group have [La/Yb] N <2.2, whereas most calc-alkaline ones have [La/Yb] N ≥2.2 (the subscript N denotes chondrite normalization). Ujike and Goodwin (1987) did note, however, that "this particular ratio is not universally applicable to magma series identification". Laflèche et al (1992), who also worked in the Blake River Group and defined the series based on Fe-Ti enrichment trends, presented REE plots and extended trace-element plots showing steeper overall slopes for calc-alkaline rocks.…”

The LaRonde Penna Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi Greenstone Belt, Quebec: Part II. Lithogeochemistry and Paleotectonic Setting

“…Mantle diapirism also has been proposed, in which variations in magma composition are attributed to variations in the fusion conditions (e.g., Capdevila et al, 1982) or to local variations in mantle composition (e.g., Goodwin, 1982). Mantle diapirism in a back-arc extensional setting was suggested by Ujike and Goodwin (1987), Laflèche et al (1992a, b) and Wyman et al (2002) to explain the tholeiitic to calc-alkaline magmatism of the Blake River Group. Transitional to calc-alkaline magmas in the upper part of the Blake River Group have mostly been attributed to fractionation of mafic magmas, magma mixing, and, in some cases, to crustal contamination.…”

Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 1. Mode of emplacement in three areas1This article is a companion paper to Ross et al. 2011. Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 2. Origin, geochemistry, and geochronology. Canadian Journal of Earth Sciences, 48: this issue.2MRNF Contribution BEGQ 8439-2010/2011-1. Natural Resources Canada, Earth Science Sector Contribution 20100253.

“…After decades of volcanological, structural, geochemical and stratigraphic research on the BRG (e.g., Conolly and Hart 1936;Dimroth et al 1978;de Rosen-Spence et al 1980;Capdevila et al 1982;Cousineau and Dimroth 1982;Gélinas and Ludden 1984;Hubert et al, 1984;Jensen and Langford 1985;Ujike and Goodwin 1987;Paradis et al 1988;Fowler and Jensen 1989;Laflèche et al 1992aLaflèche et al , 1992bSetterfield et al 1995;Péloquin et al 1996;Wyman and Hollings 2006;Dion and Rhéaume 2007;Rogers et al 2010aRogers et al , 2010b; and other papers cited therein), reconstructing the volcanic architecture of the group as a whole remains a work in progress. Since a lot of the deformation in the BRG is inferred to be tectonic in origin rather then syn-volcanic, significant work is still needed to understand the present-day structural architecture of the BRG.…”