LARGE IGNEOUS PROVINCES - CRUSTAL STRUCTURE, DIMENSIONS, AND EXTERNAL CONSEQUENCES

Large igneous provinces (LIPs) are a continuum of voluminous iron and magnesium rich rock emplacements which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts. Such provinces do not originate at ''normal'' seafloor spreading centers. We compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts. Crustal thicknesses range from 20 to 40 km, and the lower crust is characterized by high (7.0-7.6 km s(-1)) compressional wave velocities. Volumes and emplacement rates derived for the two giant oceanic plateaus, Ontong Java and Kerguelen, reveal short-lived pulses of increased global production; Ontong Java's rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system. The major part of the North Atlantic volcanic province lies offshore and demonstrates that volcanic passive margins belong in the global LIP inventory. Deep crustal intrusive companions to continental flood volcanism represent volumetrically significant contributions to the crust. We envision a complex mantle circulation which must account for a variety of LIP sizes, the largest originating in the lower mantle and smaller ones developing in the upper mantle. This circulation coexists with convection associated with plate tectonics, a complicated thermal structure, and at least four distinct geochemical/isotopic reservoirs. LIPs episodically alter ocean basin, continental margin, and continental geometries and affect the chemistry and physics of the oceans and atmosphere with enormous potential environmental impact. Despite the importance of LIPs in studies of mantle dynamics and global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features.