GEOCHEMISTRY AND EVOLUTION OF LATE ARCHEAN PLUTONISM AND ITS SIGNIFICANCE TO THE TECTONIC DEVELOPMENT OF THE SLAVE CRATON

The intrusion of voluminous Late Archean plutonic rocks is the final e vent leading to the stabilization of the Slave craton. Three groups of plutonic rocks are recognized in the central part of the province: Gr oup 1 (approximately 2689-2650 Ma) includes high-Al2O3 (Olga Suite) an d low-Al2O3 (Gondor and Wishbone Suites) trondhjemites and diorite (Ce ntral Belt Suite) all of which are temporally or spatially associated with volcanic rocks; Group 2 (approximately 2610-2600 Ma) includes syn - to late deformation hornblende-biotite monzodiorite through granodio rite (Concession Suite) and trondhjemites (Siege Suite); and Group 3 ( approximately 2599-2580 Ma) consists of post-deformational muscovite-b iotite granites (Contwoyto Suite) and biotite granites (Yamba Suite). Volcanic and associated mafic plutonic rocks are calc-alkaline and hav e trace element characteristics diagnostic of rocks formed in modem su bduction zone settings. The high-Al2O3 and low-Al2O3 trondhjemite suit es may be derived by high and low pressure partial melting of mafic cr ust, respectively. Rocks of the Concession Suite are calc-alkaline, me taluminous and have high contents of Sr, Ba and LREE, high (Ce/Yb)N ra tios and negative Nb anomalies. Parental magmas are derived from melti ng enriched mantle sources and related rocks were produced through ass imilation-fractional crystallization and mixing processes in the crust . The younger granites are derived from mixing and homogenization of m antle- and crust-derived materials (Yamba Suite) and the partial melti ng of metasedimentary protoliths (Contwoyto Suite). Volcanic and Group 1 rocks are interpreted to be remnants of an allochthonous island arc terrane which was accreted to a continental block. The secular evolut ion in the composition of Group 2 and 3 plutonic rocks reflects a chan ge from dominantly mantle- to crustal-derived magmatism during and fol lowing collision. Thickening of the lithosphere during collision, foll owed by lithospheric detachment caused melting of previously subductio n-modified mantle beneath the accreted island arc terranes and generat ion of magmas parental to the Concession Suite. Intrusion of mantle-de rived magmas, in combination with crustal thickening resulted in high T, low P metamorphism, crustal melting and the generation of the two G roup 3 plutonic suites.