Rubidium-strontium age determinations from the File-Morton-Woosey Lakes area of the Flin Flon volcanic belt, west central Manitoba
Josse, Genic Raymond
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Rubidium-strontium whole rock isochron ages have been determined on rock units from the File-Morton-Woosey Lakes area of the Flin Flon volcanic belt. A minimum age of emplacement is given by the radiometric age of 1860 +/- 112 m.y. and an 87Sr/86Sr initial ratio of 0.7019 +/- 0.0005 for the Ham pluton, a syn- to late kinematic 'granitic' instrusion (87Rb decay constant of 1.39 x 10-11yr-1). This age also provides a minimum age for the Amisk Group volcanic strata, the Missi Group sedimentary strata, and all other rocks, such as the Morton porphyry, and early deformation that predate the Ham pluton in the study area. The approximate age of 1737 +/- 257 m.y. and an initial ratio of 0.7020 +/- 0.0002 obtained for the Elmes Island Formation dacite flows, (an Amisk Group felsic volcanic), and the radiometric age of 1715 +/- 83 m.y. and an initial ratio of 0.7027 +/- 0.0001 for the Morton porphyry, (a pre- to early kinematic hypabyssal intrusion), are considered to be metamorphic ages and not emplacment ages, and that these units were updated during regional metamorphism. The age of the regional metamorphism that affected the study area is given by the radiometric age of 1760 +/- 43 m.y. obtained for the File gneiss dome, a granitoid paragneiss complex from the Kisseynew sedimentary gneiss belt. The 87Sr/86Sr initial ratio for this unit is 0.7038 +/- 0.0008...