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A recipe for microcontinent formation

¹ University of Sydney, School of Geosciences, Building F05, Sydney, New South Wales 2006, Australia
² Geological Survey of Canada, 615 Booth Street, Ottawa, Ontario K1A 0E9, Canada
³ Department of Earth Sciences, University of Aarhus, DK 8200 Aarhus N., Denmark

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

Key Words: microcontinents • plumes • crustal accretion • sea-floor spreading • terranes

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