LIPs are a significant type of planetary volcanism found on the Earth, Moon, Venus, and Mars (Coffin and Eldholm, 1994; Head and Coffin, 1997). They represent voluminous fluxes of magma emplaced over relatively short time periods, as would be expected from decompression melting of an ascending, relatively hot, mantle plume. Terrestrial LIPs are dominantly mafic rocks formed during several distinct episodes in Earth history, perhaps in response to fundamental changes in the processes that control energy and mass transfer from the Earth's interior to its surface. The ocean basins contain two very large Cretaceous LIPs, the Kerguelen Plateau/Broken Ridge in the Indian Ocean (Fig. 1) and the Ontong Java Plateau in the Pacific Ocean. Both are elevated regions of the ocean floor encompassing areas of ~2 x 106 km2 (Coffin and Eldholm, 1994). These LIPs are important for several reasons. First, they provide information about mantle compositions and dynamics that are not reflected by volcanism at spreading ridges. For example, today LIPs account for only 5% to 10% of the heat and magma expelled from the Earth's mantle, but the giant LIPs may have contributed as much as 50% in Early Cretaceous time (Coffin and Eldholm, 1994), thereby indicating a substantial change in mantle dynamics from the Cretaceous to the present (e.g., Stein and Hofmann, 1994). Also, because magma fluxes represented by oceanic plateaus are not evenly distributed in space and time, their episodicity punctuates the relatively steady-state production of crust at seafloor spreading centers. These intense episodes of igneous activity temporarily alter the flux of magma and heat from the mantle to the crust, hydrosphere, and atmosphere, possibly resulting in global environmental change, such as excursions in the chemical and isotopic composition of seawater (e.g., Larson, 1991; Ingram et al., 1994; Jones et al., 1994; Bralower et al., 1997). Finally, because oceanic LIPs may be resistant to subduction, they may be future building blocks of continental crust.

Despite their huge size and distinctive morphology, oceanic plateaus remain among the least understood features in the ocean basins. This drilling leg is focused on sampling the Kerguelen Plateau/Broken Ridge LIP with the objectives of determining the age and composition of the basement volcanic rocks in all major parts of the LIP, mass transfer and chemical fluxes between the volcanic crust and the atmosphere-hydrosphere-biosphere system, and the tectonic history of the LIP beginning with the mechanisms of growth and emplacement and continuing with the multiple episodes of post-constructional deformation that created the present complex bathymetry (Figs. 2, 3, and 4).

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