Age of the Mulcahy Lake Intrusion, Northwest Ontario, and implications for the evolution of greenstone-granite terrains

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doi: 10.1016/0012-821X(85)90079-2
Authors:Morrison, D. A.; Davis, D. W.; Wooden, J. L.; Bogard, Donald D.; Maczuga, D. E.; Phinney, W. C.; Ashwal, L. D.
Author Affiliations:Primary:
NASA/Johnson Space Cent., Houston, TX, United States
Royal Ont. Mus., Canada
Lunar and Planet. Sci. Inst., United States
LEMSCO, United States
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 73(2-4), p.306-316. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:1985
Note:In English. 51 refs.; illus. incl. 2 tables, sketch map
Summary:Zircon data from a 63 km2 layered mafic intrusion in the Wabigoon sub-province, the Mulcahy Lake gabbro, show that the gabbro crystallized at 0712733.2+1.0-0.9 m.y. The largely unaltered gabbro intrudes tholeiites of the Crow Lake-Savant Lake greenstone belt which were generated over a = or >10 m.y. time span. Rb/Sr and Sm/Nd data from pristine whole-rock and mineral separates from the intrusion show disturbances in the system, particularly in pyroxenes. The Sm/Nd age is 2744 + or - 55 m.y., and an epsilonNd value of +2.6 + or - 1.2 indicates a LREE depleted source. The Sm/Nd data show less disturbance than the Rb/Sr data. Granitic and mafic intrusives with similar initial ratios occur 80 km to the S. Primary hornblende was analysed for 40Ar/39Ar, and the age obtained is 2703 + or - 20 m.y., clearly younger than the zircon age, indicating some Ar loss. The Mulcahy lake gabbro is one of four layered mafic plutons of similar petrographic character and stratigraphic age, arrayed in an arc in the Crow Lake-Savant Lake greenstone belt. The plutons appear to represent sub-volcanic chambers which developed simultaneously and crystallized at the end of the volcanic cycle. All intrude basalts and are intruded in turn by the Atikwa batholith, a granitic intrusion >1000 km2 in area. The batholith overlaps the age of the gabbros or is = or <50 m.y. younger. The cessation of mafic magma production and immediate, if not parallel, production of calc-alkaline liquid may represent a process important in the development of greenstone-granite belts. [P.Br.]
Subjects:Absolute age; Amphibole group; Ar/Ar; Argon; Basalts; Chain silicates; Clinoamphibole; Dates; Gabbros; Geochronology; Granites; Greenstone belts; Hornblende; Igneous rocks; Intrusions; Magma chambers; Metamorphic belts; Nesosilicates; Noble gases; Orthosilicates; Petrology; Plutonic rocks; Plutons; Precambrian; Rb/Sr; Silicates; Tholeiite; Volcanic rocks; Zircon; Zircon group; Canada; Eastern Canada; Ontario; Atikwa Batholith; Crow Lake; Evolution; Intrusive rocks; Mulcahy Lake; Northwestern Ontario; Quetico; Savant Lake; Wabigoon
Abstract Numbers:86M/0040
Record ID:1985072077
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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