SOURCES OF THE MEALY MOUNTAINS AND ATIKONAK RIVER ANORTHOSITE-GRANITOID COMPLEXES, GRENVILLE PROVINCE, CANADA

作者：Hegner Ernst^*; Emslie Ronald F; Iaccheri Linda M; Hamilton Michael A

来源：The Canadian Mineralogist, 2010, 48(4): 787-808.

DOI：10.3749/canmin.48.4.787

• anorthosite massifs
• AMCG association
• megacrysts
• radiogenic isotopes
• Proterozoic
• Mealy Mountains
• Atikonak River
• Grenville Province
• Canada

The report geochemical and isotopic data for anorthosite - mangerite - granite samples of the similar to 1.65 Ga Mealy Mountains Intrusive Suite (MMIS) and the similar to 1.13 Ga Atikonak River Complex (ARC), located in the northeastern Grenville Province of Canada. Initial Pb isotopic ratios for feldspar samples from the ARC indicate assimilation of an old residual lower crustal component by all rock types. Monzodiorite and some granites with initial epsilon(Nd) in the range -2.0 to -3.8 are interpreted as products of fractional crystallization and mixing in a lower crustal sill of mixed melts derived from depleted mantle and early Paleoproterozoic crust (t(DM) = 2.4 Ga). For the anorthositic rocks, with systematically higher initial epsilon(Nd) of +2.0 to -1.3 than in the granitoids, we suggest a parental melt comprising assimilated plagioclase-pyroxene cumulates and mantle-derived melt. The inferred plagioclase cumulates are hot remnants of the collapsed magma-chambers after granite extraction. If the ferrodiorite sample of the ARC represents a residual melt after anorthosite separation, additional contamination of the magma by older material is required. Anorthositic and granitic rocks of the MMIS show mostly depleted-mantle epsilon(Nd) values up +3.6 that overlap the composition of the juvenile Labradorian basement. Enriched (87)Sr/(86)Sr values in the samples were probably inherited from mantle sources modified during Labradorian plate subduction. Trace-element data support incompatible-element-enriched garnet-bearing mantle sources for the inferred parental basaltic melt. Crustal contamination of the mantle-derived melts is well documented by distinct Pb isotopic compositions, similar to those for the Labradorian basement. High Th and U concentrations relative to La and HREE depletion in the granite (s.s.) samples support melting of fertile garnet-bearing lower crust. Low abundances of Th and U in the monzodiorite and monzonite samples can be reconciled with a component derived from residual lower crust.

• 出版日期2010-8