RODINIA, COEVAL JUVENILE CRUST FORMATION AND THEIR PALEOZOIC LEGACIES

The supercontinent Rodinia formed between 1.2 and 1.0 Ga as a result of a number of continent-continent collisions and dispersed between 0.75 and 0.6 Ga. The existence of Rodinia implies the presence of a Panthalassa-like ocean (the Mirovoi Ocean) between ca. 1.0–0.75 Ga within which juvenile crust developed. Following the breakup of Rodinia, vestiges of this juvenile crust were accreted to the leading edges of the dispersing continents where they are preserved as terranes in Late Neoproterozoic orogens. These terranes are characterized by abundant ca. 1.2 to 0.75 Ga Sm-Nd (T_DM) model ages, i.e. model ages coeval with the existence of Rodinia, in complexes ranging from Neoproterozoic to Late Paleozoic in age. They include ca. 0.8 Ga ophiolites and ensimatic arc complexes, and ca. 0.8 to 0.6 Ga recycled mafic to felsic arc complexes, as well as Paleozoic rift-related complexes. For example, along the northern margin of Gondwana, Late Neoproterozoic and Early Paleozoic mafic complexes derived from a sub-continental lithospheric mantle have 1.2 to 0.75 Ga T_DM ages, consistent with an origin within the Mirovoi Ocean. A potential Mesozoic-Cenozoic analogue is the accretion of juvenile terranes to the leading edge of North America during the breakup of Pangea, which influenced the composition of post-accretionary magmatism in the western Cordillera. More generally, periods of juvenile crust formation in oceans that surround supercontinents can be recognized by Sm-Nd T_DM model ages that overlap the life-span of the supercontinent. The rocks that record these ages are recycled from this juvenile crust and their location provides constraints on the geometry of supercontinent breakup.