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(2017) The amphiboles of the REE-rich A-type peralkaline Strange Lake plutonfingerprints of magma evolution. Lithos 288:156-174.

Abstract:It is well established that A-type granites enriched in high field strength elements, such as Zr, Nb and the REE, form in anorogenic tectonic settings. The sources of these elements and the processes controlling their unusual enrichment, however, are still debated. They are addressed here using neodymium and oxygen isotope analyses of samples from the 1.24 Ga Strange Lake pluton in the Paleoproterozoic Core Zone of Québec-Labrador, an A-type granitic body characterised by hyper-enrichment in the REE, Zr, and Nb. Age-corrected εNd values for bulk rock samples and sodic amphiboles (mainly arfvedsonite) from the pluton range from -0.6 to -5.7, and -0.3 to -5.3, respectively. The εNd values for the Napeu Kainiut quartz monzonite, which hosts the pluton, range from -4.8 to -8.1. The 147Sm/144Nd ratios of the suite and the host quartz monzonite range from 0.0967 to 0.1659, large variations that can be explained by in-situ fractionation of early LREE-minerals (Strange Lake), and late hydrothermal HREE remobilization. Oxygen isotope analyses of quartz of both Strange Lake and the host yielded δ18O values between +8.2 and +9.1, which are considerably higher than the mantle value of 5.7 ± 0.2 ‰. Bulk rock oxygen isotope analyses of biotite-gneisses in the vicinity of the Strange Lake pluton yielded δ18O values of 6.3, 8.6 and 9.6 ‰. The negative εNd values and positive δ18O values of the Strange Lake and Napeu Kainiut samples indicate that both magmas experienced considerable crustal contamination. The extent of this contamination was estimated, assuming that the contaminants were sedimentary-derived rocks from the underlying Archean Mistinibi (para-) gneiss complex, which is characterized by low εNd and high δ18O values. Mixing of 5 -15 % of a gneiss, having an εNd value of -15 and a δ18O value of +11, with a moderately enriched mantle source (εNd = +0.9, δ18O = +6.3) would produce values similar to those obtained for the Strange Lake granites. Based on analogies between the Nain Plutonic Suite and the Gardar alkaline igneous province (SWGreenland), we conclude that the Strange Lake pluton and associated REE- Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporationmineralized anorogenic bodies formed from a combination of subduction-induced fertilization of the sublithospheric mantle, crustal extension and in-situ magma evolution.Response to Reviewers: RESPONSE TO REVIEWERS We are encouraged that Editor Timothy L. Grove and Reviewer #1 consider our manuscript, which presents a hypothesis for the generation of the Strange Lake pluton and other HFSE mineralized silicate bodies of the Nain Plutonic Suite, to have merit and be worthy of publication after appropriate revision. Reviewer #2 questions our model that mantle-derived fertile melts were important and requests additional proof. Below, we systematically address the minor points raised by Reviewer #1 and then the more substantial criticisms of the manuscript by Reviewer #2. REVIEWER # 1General comments/questions of Reviewer # 1: Revi...