Abstract

Granitoid magmatism spans three Flin Flon Belt evolutionary stages: (i) "evolved" arc (~1920 Ma) plus early juvenile arc (1904-1880 Ma) plutonism during intraoceanic arc-back-arc formation; (ii) early (1878-1860 Ma) and middle (1860-1844 Ma) successor arc plutonism following accretion and successor arc(s) development and; (iii) late (1843-1826 Ma) successor arc plutonism accompanying successor basin formation and waning arc magmatism. Amphibole-bearing mineralogy, metaluminous compositions, and igneous microgranitoid enclaves indicate derivation from infracrustal sources. Predominance of intermediate calc-alkaline compositions and negative Nb anomalies on normalized patterns over a 46-77 wt.% silica range indicate an arc setting. Basaltic end members indicate important contributions directly from the mantle. εNd(T) values are predominately in the range 0 to +4.3, reflecting mixing between depleted mantle melts and an Archean crustal component preserved in evolved arc plutons (-3.9 to -6). Temporal variations include the following: (i) early juvenile arc plutons are low K, high field strength element (HFSE) depleted, with relatively flat rare earth element (REE) patterns and negative Eu anomalies, indicative of low-pressure partial melting - fractionation in the mantle wedge, with residual pyroxene and plagioclase; (ii) early and middle successor arc plutonism is medium K, with steep REE patterns and no Eu anomalies, indicative of input from melting of basaltic sources (likely subducted back-arc oceanic crust) under high-pressure conditions with residual garnet and (or) amphibole and no plagioclase; (iii) late successor arc plutons are high K, more HFSE enriched, with both variable REE pattern slopes and Eu anomalies, indicative of a significant petrogenetic role of recycling of preexisting juvenile arc - accretionary complex crust.

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