Vol. 30 No.2 June 2007

Journal of International Geoscience

Published by the International Union of Geological Sciences

by Richard E. Ernst

Mafic-Ultramafic Large Igneous Provinces (LIPs): Importance of the Pre-Mesozoic record

Abstract

           Mafic-ultramafic magmatic provinces are termed Large Igneous Provinces (LIPs) if they are large (>105 km3), are emplaced in a short duration (ca. < 5 myr) (or consist of short duration pulses), and have intraplate characteristics (i.e. are not associated with normal plate boundary processes). This category includes the classic continental flood basalts, oceanic plateaus, bimodal-rift (passive margin) related packages, but also those events, mainly of Phanerozoic-Proterozoic age, where the plumbing system of dykes, sills and layered intrusions has been exposed by erosion. In the Archean, LIPs may be represented by the greenstone belts of the tholeiite-komatiite association. Felsic magmatism is associated with many LIPs and indeed may be dominant in some cases. LIPs are associated with continental breakup, climatic change, extinction events, and major ore deposits especially of the Ni-Cu-PGE type. Continental LIPs occur on average every 20–30 myr since 2.6 Ga; the Archean record is too poorly preserved for generalizations. LIPs occur both as isolated single events (e.g., 2055 Ma Bushveld event), as approximately coeval but widely separated events (e.g., 65 Ma Deccan and 62 Ma NAIP), and as regional clusters associated with supercontinent breakup (e.g., the 830–750 Ma events associated with the breakup of the proposed supercontinent Rodinia). The LIP record represents a key tool for constraining Proterozoic paleocontinental reconstructions.

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