Authors: Grammatikopoulos, T A.; Clark, A H.; Archibald, D A.

Source: Canadian Journal of Earth Sciences, Volume 44, Number 1, January 2007 , pp. 107-126(20)

Publisher: NRC Research Press

Abstract:

The 1167 ± 2 Ma Leo Lake pluton, located at the southern part of the Frontenac terrane in Central Metasedimentary Belt of southeastern Ontario, is a bimodal pluton that is dominated by olivine gabbro, gabbro, syenite, and lesser monzonite. The adjoining 1166 ± 3 Ma Lyndhurst pluton is composed of syenite and granite, and exhibits magma mingling. Even though geochemical data from both plutons suggest fractional crystallization as the main crystallization process, magma mingling is evident in the Lyndhurst pluton. Hornblende from the Leo Lake syenite yields a ⁴⁰Ar-³⁹Ar age of 1120 ± 6 Ma and titanite from the adjacent St. Lawrence skarn yields a U-Pb age of 1147 ± 8 Ma. The ⁴⁰Ar-³⁹Ar age indicates that the pluton cooled to 550 °C at a rate of ca. <2 °C/Ma following emplacement. The two plutons are similar in petrology to several other granitic, syenitic, and monzonitic intrusions of the Frontenac suite in the Frontenac terrane. Moreover, the spatial distribution, textural features, and geochemistry indicate that the plutons are coeval. The present data indicate that the two plutons may have been produced from evolved mantle-derived melts, and may have assimilated varying proportions of crustal melts.

Le pluton du lac Léo, 1167 ± 2 Ma, situé dans la partie sud du terrane de Frontenac dans la ceinture métasédimentaire centrale du sud-est de l'Ontario, est un pluton bimodale dominé par du gabbro à olivine, du gabbro, de la syénite et des quantités moindres de monzonite. Le pluton de Lyndhurst qui lui est adjacent, 1166 ± 3 Ma, est composé de syénite et de granite et montre des mélanges de magmas. Bien que les données géochimiques des deux plutons suggèrent une cristallisation fractionnée comme principal processus de cristallisation, le mélange des magmas est évident dans le pluton de Lyndhurst. La hornblende de la syénite du lac Léo a donné un âge ⁴⁰Ar-³⁹Ar de 1120 ± 6 Ma et une titanite du skarn St. Laurence adjacent a donné un âge U-Pb de 1147 ± 8 Ma. L'âge ⁴⁰Ar-³⁹Ar indique qu'après sa mise en place, le pluton s'est refroidi jusqu'à une température de 550 ºC à un taux d'environ <2 ºC/Ma. Les deux plutons ont une pétrologie semblable à plusieurs autres intrusions granitiques, syénitiques et monzonitiques de la suite de Frontenac dans le terrane de Frontenac. De plus, la distribution spatiale, les caractéristiques texturales et la géochimie indiquent que les plutons sont contemporains. Ces données indiquent que les deux plutons proviennent possiblement de produits de fusion dérivés du manteau et ils peuvent avoir assimilé des proportions variables de produits de fusion de la croûte.[Traduit par la Rédaction]

Document Type: Research article

Publication date: 2007-01-01

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