MAKING NUNA AND BREAKING RODINIA: IMPLICATIONS OF SIBERIA-LAURENTIA CONNECTIONS FOR SUPERCONTINENT CYCLES

Multi-faceted geologic and geophysical evidence supports a proposed connection of the Siberian craton to SW Laurentia. The connection began with the Paleoproterozoic assembly of supercontinent Nuna and ended with the Neoproterozoic to Early Cambrian breakup of supercontinent Rodinia. Although significant tectonic adjustments occurred along the proposed Siberia/Laurentia breakaway boundary, the cratons remained loosely connected during the Mesoproterozoic supercontinent cycle defined by breakup of Nuna and assembly of Rodinia; Nuna rift zones and Rodinia (Grenville) collisions did not significantly offset the Paleoproterozoic grain that defines the Siberia-SW Laurentia connection. As Nuna broke up, the 1500 to 1400 Ma Belt-Purcell basin of the northern Rockies filled a deep continental rift along a segment of the eventual Siberia/Laurentia breakaway boundary. Rifting did not proceed to seafloor spreading, as the bulk of Belt-Purcell sediment was derived from an adjacent continental source. Emerging evidence suggests that the Belt-Purcell rift closed slightly during the Grenville orogenic period, producing the enigmatic East Kootenay orogeny. In both SW Laurentia and SE Siberia, basement uplifts and mafic intrusions segmented a Grenville foreland basin; detrital zircons in the Siberian Grenville basin are consistent with sources in SW Laurentia. Renewed rifting along the proposed Siberia/Laurentia breakaway boundary began in the Neoproterozoic, when Laurentian-signature detrital zircons abruptly disappear from Siberian cratonal strata, and deep rift basins appear along the length of the boundary, with most clastics trapped on the Laurentian side. However, close faunal linkages suggest that the cratons remained in proximity during the early Paleozoic. Paleomagnetic evidence supports a model in which the Siberian craton rotated clockwise during late Paleozoic assembly of Pangaea, from a position in SW Laurentia to the Ural Mountains.