A recipe for microcontinent formation

Accreted slivers of continental margins are common in the geologic record, but the processes that lead to their formation are poorly understood, We ob serve an association of plume-related microcontinent isolation and subseque nt long-term asymmetries in oceanic crustal accretion based on four recent examples: the Seychelles in the Indian Ocean, Jan Mayen in the Norwegian-Gr eenland Sea, and the East Tasman Plateau and the Gilbert Seamount Complex i n the Tasman Sea. These microcontinents formed by rerifting of a young cont inental margin (<25 m.y. old) in the vicinity of a mantle-plume stem, follo wed by asymmetric seafloor spreading. Two-dimensional numerical stochastic basin modeling suggests that a yield-strength minimum along the landward ed ge of a rifted margin, thermally enhanced by heating from a mantle plume, m ay cause a spreading ridge to jump onto this zone of weakness. This action isolates a passive-margin segment. The association of large igneous provinc es and microcontinents should be useful for identifying similar events in t he geological record.