Paleoproterozoic arc magmatism imposed on an older backarc basin: Implications for the tectonic evolution of the Trans-Hudson orogen, Canada

摘要

Compositional data from 72 granitoids and associatedmafic rocks in the Paloproterozoic Kisseynew domain, Trans-Hudson orogen, Canada, were used to evaluate the tectonic setting of magma generation between 1840 and 1820 Ma. These data thus provide insights into the development of the Trans-Hudson orogen just prior to amphibolite-grade metamorphism and the final stages of continental collision. The granitioid rokcs are hornblende-or orthopyroxene-bearing, medium-to high-K calc-alkalic, and weakly peraluminous. The trends on Harker variation diagramsare consistent with crystal-fractionation proconsistent with crystal-fractionation processes, although the range in values is related to the temporal and spatial distribution os samples. The extent of LRE (light rare earth elemetn) enrichment increaes with increasing SiO_2, as does variability in HREE (heavy rare earth element) fractionation and magnitude of Eu anomalies. Most samples have (Gd/b)_n<10 (suite Ia), although five have (Gd/Yb)_n=17-24, suggesting the presence of garnet residua (suite Ib). The range in rock types, calc-alkalic character, and negative nb and Ti anomalies are all characteristic of arc enivironments. Magma generation within the Trans-Hudson orogen, including the Kisseynew domain, betwen 1.84 and 1.82 Ga was related to interaction between th Sask craton and the Flimn Flon-Glennie compelx. A decreae in subduction angle likely resulted from northward-directed subducton of more buoyant crust, with associated changes in termal conditions leading to melting over a wide area. Most magmas formed in a slab-dehydriation-dominated regime, although localized slab