Nd isotopic evidence for Early to Late Archean (3.4-2.7 Ga) crustal growthin the Western Superior Province (Ontario, Canada)

New Sm-Nd analyses of Archean metavolcanic, plutonic, gneissic and metasedi mentary rocks from Sachigo and Berens River subprovinces (North Caribou ter rane) and Winnipeg River and Wabigoon subprovinces in conjunction with prev iously published data are used to trace the crustal evolution of the Wester n Superior Province (WSP) from ca. 3.4 to 2.7 Ga. The extensive WSP geochro nological database, which contains 3.17-2.55 Ga plutonic rocks, allows the calculation of precise is an element of(Nd)(t) values and the identificatio n of the main periods of new crustal addition at 3.4 +/- 0.1, 3.02-2.92 and 2.76-2.69 Ga. Mass-balance calculations indicate that the Western Superior Province represents a collage of Archean crusts comprising 7%, 44% and 48 wt% of crust created at 3.4, 3.0 and 2.7 Ga, respectively. Although these c alculations depend on the isotopic signatures of the mantle and those of th e average crust at different times, several important observations can be m ade: (1) the importance of pre-2.7 Ga terranes recycled in the 2.7 Ga oroge n; (2) the existence of time intervals of 150-300 Ma dominated by intra-cru stal processes resulting in a large range of crystallization ages (U-Pb zir con ages) that do not reflect new additions from the mantle; (3) much of th e new crustal additions at 2.7 Ga were contaminated by crustal material sub ducted into the source region (TTG suites) or were contaminated during intr usion into the crust (sanukitoids). (C) 2000 Elsevier Science B.V. All righ ts reserved.