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Proto-Laurentia (i.e. pre-Grenvillian Laurentia) is an aggregate of six or more formerly independent Archean cratons that amalgamated convulsively in geons 19 and 18 (Orosirian Period), along with non-uniformly distributed areas of juvenile Paleoproterozoic crust. Subduction polarities and collision ages have been provisionally inferred between the major cratons (and some minor ones), most recently between the Rae and Hearne cratons. The oldest Orosirian collisions bound the Rae craton: 1.97 Ga (Taltson-Thelon orogen) in the west, and 1.92 Ga (Snowbird orogen) in the southeast. All other Orosirian collision ages in proto-Laurentia are < 1.88 Ga. The Rae craton was the upper plate during (asynchronous) plate convergence at its western and, tentatively, southeastern margins. Subsequent plate convergence in the Wopmay and Trans-Hudson orogens was complex, with the Rae craton embedded in the lower plate prior to the first accretion events (Calderian, Reindeer and Foxe orogenies), but in the upper plate during major subsequent convergence and terminal collisions, giving rise to the Great Bear and Cumberland magmatic arcs, respectively. The ‘orthoversion’ theory of supercontinental succession postulates that supercontinents amalgamate over geoidal lows within a meridional girdle of mantle downwellings, orthogonal to the lingering superswell at the site of the former supercontinent. If the downwelling nodes develop through positive feedback from the descent of cold oceanic slabs, then viscous traction should contribute to drawing the cratons together over the downwelling node. Viewed in this way, the Rae craton was the first to settle over the downwelling node and became the backstop for the other cratons that were drawn towards it by subduction. It was, literally, the origin of Laurentia. Whether the Rae craton was also the origin of Nuna, the hypothetical cogenetic supercontinent, depends on ages and subduction polarities of Orosirian sutures beyond proto-Laurentia.SOMMAIRELa proto-Laurentie (c.-a-d. la Laurentie pre-grenvillienne) est un agregat d’au moins six cratons archeens independants qui se sont amalgames convulsivement durant les geons 19 et 18 (Orosirien), le long de zones de croutes juveniles paleoproterozoiques reparties de maniere heterogene.  Les polarites de subduction et les âges de collision entre les grands cratons (et d’autres moins grands) ont ete provisoirement deduits, le plus recemment entre le craton de Rae et le craton de Hearne.  Les plus anciennes collisions orosiriennes ont soude le craton de Rae : 1,97 Ga (orogene de Taltson-Thelon) dans l’ouest, et 1,92 Ga (orogene de Snowbird) dans le sud-est.  Tous les autres âges de collision en proto-Laurentie sont inferieurs a 1,88 Ga.     Le craton de Rae constituait la plaque superieure durant la convergence de plaque (asynchrone) a sa marge ouest, et peut-etre aussi a ses marges sud-est.  La convergence de plaque subsequente dans les orogenes de Wopmay et Trans-Hudson a ete complexe, le craton de Rae etant encastre dans la plaque inferieure avant les premiers evenements d’accretion (orogenes calderienne, de Reindeer et de Fox), puis dans la plaque superieure durant la grande convergence subsequente et les collisions terminales, ce qui a cree les arcs magmatiques de Great Bear et de Cumberland respectivement.     La theorie de « l’orthoversion » de la succession des supercontinents presuppose que les supercontinents s’amalgament au-dessus de creux geoidaux en deca d’une gaine meridienne de convections manteliques descendantes, a angle droit d’un super-renflement persistant au site d’un ancien supercontinent.  Si le nœud de convection descendante s’etablit par retroaction positive de la descente de plaques oceaniques froides, la traction visqueuse devrait contribuer a entrainer les cratons ensembles au-dessus du nœud de convection descendante.  Vu de cette facon, le craton de Rae a ete le premier a s’etablir au-dessus du nœud de convection descendante, ce qui en a fait la butee des autres cratons entraines par la subduction.  Litteralement, telle a ete l’origine de la Laurentie.     Quant a savoir si c’est le craton de Rae qui a ete a l’origine de Nuna, cet hypothetique surpercontinent cogenetique, cela depend des âges et des polarites de subduction des sutures orosiriennes au-dela de la proto-Laurentie.

The Origin of Laurentia: Rae Craton as the Backstop for Proto-Laurentian Amalgamation by Slab Suction