Large igneous provinces (LIPs) are a significant type of planetary volcanism found on Earth, the moon, Venus, and Mars (Coffin and Eldholm, 1994; Head and Coffin, 1997). They represent large volumes of magma emplaced over relatively short time periods, such as expected from decompression of upwelling, relatively hot or wet mantle. This process explains hot spot magmatism at the Earth's surface and is conceptually described by various plume head and tail models applicable to the Earth's sublithospheric mantle. In such models, the plume head leads to oceanic plateaus and continental flood basalts, and the tail leads to volcanic chains known as hot spot tracks. Terrestrial LIPs are dominantly mafic rocks formed during several distinct episodes in Earth's 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 several Cretaceous LIPs; the two largest are the Kerguelen Plateau-Broken Ridge in the Indian Ocean (Fig. F1) and the Ontong Java Plateau in the Pacific Ocean. Both are elevated regions of the ocean floor encompassing areas of ~2 106 km2 (Coffin and Eldholm, 1994). These giant LIPs are important for several reasons. They provide information about mantle compositions and dynamics that are not revealed by volcanism at spreading ridges. For example, today's plume-associated volcanism (principally, oceanic islands) accounts for only 5% to 10% of the mass and energy expelled from 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 Cretaceous to present time (e.g., Stein and Hofmann, 1994). 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 increase the flux of magma and heat from the mantle to the crust, hydrosphere, and atmosphere, possibly resulting in global environmental changes, such as excursions in the composition and isotope characteristics of seawater (e.g., Larson, 1991; Ingram et al., 1994; Jones et al., 1994; Bralower et al., 1997). Finally, because oceanic LIPs apparently resist subduction, they contribute to the growth of continents.

The Kerguelen Plateau-Broken Ridge LIP is interpreted to represent voluminous Cretaceous volcanism associated with the arrival of the Kerguelen plume head below young Indian Ocean lithosphere (Fig. F2) (e.g., Morgan, 1971; Duncan and Storey, 1992; Pringle et al., 1994; Storey et al., 1996). Subsequently, rapid northward movement of the Indian plate over the plume formed a 5000-km-long, ~82- to 38-Ma, hot spot track, the Ninetyeast Ridge (Duncan, 1991). At ~40 Ma the westward-propagating Southeast Indian Ridge (SEIR) intersected the plume's position. As the SEIR migrated northeast relative to the plume, hot spot magmatism became confined to the Antarctic plate. From ~40 Ma to the present, the Kerguelen Archipelago, Heard and McDonald Islands, and a northwest-southeast-trending chain of submarine volcanoes between these islands were constructed on the northern and central sectors of the Kerguelen Plateau (Figs. F1, F2, F3, F4). Thus, an ~115-m.y. record of volcanism is attributed to the Kerguelen plume (e.g., Mahoney et al., 1983; Weis et al., 1992; Pringle et al., 1994; Storey et al., 1996).

Despite their huge size and distinctive morphology, oceanic plateaus remain among the least understood features in the ocean basins. This drilling leg focused on sampling the Kerguelen Plateau-Broken Ridge LIP to determine (1) the age and composition of the basement volcanic rocks in all major parts of the LIP, (2) the mantle and crustal components that contributed to the magmatism, (3) the mass transfer and chemical fluxes between the volcanic crust and atmosphere-hydrosphere-biosphere system, and (4) the tectonic history of the LIP beginning with the mechanisms of growth and emplacement and continuing with the multiple episodes of postconstructional deformation that created the present complex bathymetry (Figs. F3, F4).