The Late Archean Magmatic Event (LAME), ca. 2.7 Ga, was the greatest crustal addition event in Earth history. My focus is the Superior Province of Canada, where LAME occurred ca. 2.75 – 2.65 Ga. Mantle plumes impinged on the Abitibi subprovince, where ~ 16 km regional thickness of tonalite-trondhjemite-granodiorite (TTG) melt was produced. Granites (sensu stricto) were the last magmatic phase of LAME, with a Superior-wide regional thickness of ~ 1 – 3 km. Assuming a crustal source for both TTG and granites, I use 1-D thermal models to investigate the origin of TTG in the Abitibi subprovince and that of late granites in the Superior Province. Melting curves appropriate to the source of TTG and granites are used to determine the thickness of melt produced in the models. I show that the incorporation of upward melt transfer into a standard model of lower crustal melting may increase the amount of predicted melt by ~ 1/(1-f), where f denotes the fraction of melt that is on average being extracted from the source rocks. Partitioning of heat producing elements between melt and restite reduces the amount of melt produced, but the effect is secondary compared to the increase in melt production through upward melt transfer. For the Abitibi subprovince, I show that the emplacement of a single plume coupled with the emplacement of a 12-km-thick greenstone cover can generate a maximum of ~ 9-km-thickness of TTG melt. However, the emplacement of a series of plumes, each coupled with the emplacement of a 3-km-thick greenstone cover and a 10-km-thick sill results in ~ 20-km-thickness of TTG melt. My model incorporates delamination of restitic eclogite. Finally, I show that late granites in the Superior Province may have resulted from thickening of a crust that had been “pre-heated” during earlier arc activity and that prolonged granitic magmatism observed in some areas of the Superior Province may be explained by late underthrusting of fertile source rocks into deeper and hotter regions of the crust.

The Late Archean Magmatic Event (LAME), ca. 2.7 Ga, was the greatest crustal addition event in Earth history. My focus is the Superior Province of Canada, where LAME occurred ca. 2.75 – 2.65 Ga. Mantle plumes impinged on the Abitibi subprovince, where ~ 16 km regional thickness of tonalite-trondhjemite-granodiorite (TTG) melt was produced. Granites (sensu stricto) were the last magmatic phase of LAME, with a Superior-wide regional thickness of ~ 1 – 3 km. Assuming a crustal source for both TTG and granites, I use 1-D thermal models to investigate the origin of TTG in the Abitibi subprovince and that of late granites in the Superior Province. Melting curves appropriate to the source of TTG and granites are used to determine the thickness of melt produced in the models. I show that the incorporation of upward melt transfer into a standard model of lower crustal melting may increase the amount of predicted melt by ~ 1/(1-f), where f denotes the fraction of melt that is on average being extracted from the source rocks. Partitioning of heat producing elements between melt and restite reduces the amount of melt produced, but the effect is secondary compared to the increase in melt production through upward melt transfer. For the Abitibi subprovince, I show that the emplacement of a single plume coupled with the emplacement of a 12-km-thick greenstone cover can generate a maximum of ~ 9-km-thickness of TTG melt. However, the emplacement of a series of plumes, each coupled with the emplacement of a 3-km-thick greenstone cover and a 10-km-thick sill results in ~ 20-km-thickness of TTG melt. My model incorporates delamination of restitic eclogite. Finally, I show that late granites in the Superior Province may have resulted from thickening of a crust that had been “pre-heated” during earlier arc activity and that prolonged granitic magmatism observed in some areas of the Superior Province may be explained by late underthrusting of fertile source rocks into deeper and hotter regions of the crust.

<p dir="ltr">The Intermontane terranes represent one of the largest composite accreted terranes that built the northern Cordillera. To better understand the interactions between the continental margin of Laurentia and the Intermontane terranes, this study analyzes twelve detrital zircon samples (n=3232) from a Neoproterozoic (?) to Cretaceous metasedimentary stratigraphic section exposed in central Alaska. Distinct detrital zircon populations have been identified and are interpreted to represent four stages in the geologic development of this part of western North America. Stage 1 extends from the Neoproterozoic (?) to the Early Paleozoic, and is characterized by Proterozoic and Archean detrital zircon populations that correlate with Laurentian sources of sediment. We interpret Stage 1 to represent deposition along the northwestern continental margin of Laurentia. Stage 2 extends from the Silurian (?) to the Devonian and is characterized by a dominant Devonian and Silurian detrital zircon population. We interpret Stage 2 to have been deposited in a backarc basin coeval with active volcanism as the Yukon-Tanana terrane was rifted away from the Laurentian continental margin as the Slide Mountain Ocean opened. Stage 3 extends from the Mississippian to the Jurassic and records a shift back to sediment sources with abundant Proterozoic and Archean zircon. We interpret this stage to represent deposition of Laurentian detritus along the eastern margin of the Slide Mountain Ocean basin. Stage 4 is represented by the Lower Cretaceous strata of the Manley basin that contain one major Late Triassic to Early Jurassic detrital zircon population. We interpret this population to be sourced from the syn-collisional and post-collisional Late Triassic to Early Jurassic plutons and related sedimentary basins of the Intermontane terranes that were exhumed and eroded during the closure of the Slide Mountain Ocean and the subsequent collision with the Laurentian continental margin. We interpret the Manley basin as a syn- to post-collisional extensional basin associated with regional detachment faults that formed because of crustal thickening in the collisional zone. From a regional perspective, an extensive clastic wedge prograded northward away from the zone of crustal thickening and can be identified in a series of Mesozoic sedimentary basins that are discontinuously exposed over 1500 km in southern Alaska. Results of our study better delineate the tectonic processes that set the framework for the construction of the Late Mesozoic and Cenozoic Cordilleran orogen.</p>