Geochemical and Nd isotopic evolution of Paleoproterozoic arc-type granitoid magmatism in the Flin Flon Belt, Trans-Hudson orogen, Canada

摘要

Granitoid magmatism spans three Foin Flon beltevolutionary stages: (i)“evolved”arc (~1920 Ma ) plus earlyjuvenile 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 andsuccessor arc (s) development and; (iii) late (1843-1826Ma )auccessor arc plutonism accompanying successor basinformation and waning arc magmatism. Amphibole-bearingmineralogy, metaluminous compositions, and igneousmicrogranitoid enclaves indicate derivation from infracrustalsources. Predominance of intermediate calc-alkaline compositionsand negative Nb anomalies on normalized patterns over a 46-77wt.% silica tange indicate an arc setting. Basaltic end membersindicate important contributions directly from the mantle. ΕNb(T) values are predominately in the range 0 to +4.3, reflectingmixing between depleted mantle melte and an achean crustalcomponent preserved in evolved arc plutons (-3.9 to -6). Temporalvariations include the following: (i) early juvenile arc plutons arelow K, high field strength element (HFSE) depleted, withrelatively flat rare earth element (REE) patterns and negative Euanomalies, indicative of low-pressure partial melting –fractionation in the mantle wedge, with residualpyroxene andplagioclase; (ii) early and middle successor arc plutonism ismedium K, with steep REE patterns and no Eu anomalies,indicative ot input from melting of basaltic sources (likelysubducted back-arc oceanic crust) under high-pressure canditionswith residual garnet and (or) amphibole and no plagioclase; (iii)late successor arc plutons are high K, more HFSE enriched, withboth variable REE pattern slopes and Eu anomalies, indicative of asignificant prtrogenetic role of recycling of preexisting juvenile arc– accretionary complex crust.