Leg 183 will penetrate igneous basement to depths of ~200 m at several
morphologically and tectonically diverse locations on the Kerguelen
Plateau-Broken Ridge Large Igneous Province (LIP) in the Southeast Indian
Ocean. This leg will build on results obtained by basement drilling at four
Ocean Drilling Program (ODP) sites on the Central and Southern Kerguelen
Plateau during Legs 119 and 120. LIPs are important to understand
because the very large amounts of magma entering the crust in a
relatively short time interval reflect mantle processes that differ from
those causing magmatism at diverging and converging plate margins (e.g.,
LIPs may result from decompression melting of a mantle plume). A major
objective of this leg is to infer eruption rates (km3/yr) by
determining the eruption ages of the uppermost igneous crust at several
locations. Additional goals are to determine the mechanism of plateau
growth and the tectonic history of the plateau by integrating seismic data
with studies of the sedimentary and igneous cores. Specifically, these
cores will be used to address the following issues: (1) the timing and
extent of initial uplift; (2) the relative roles of subaerial and submarine
volcanism; (3) the cooling and subsidence into a submarine environment;
and (4) the multiple episodes of post-emplacement deformation. A unique
aspect of this LIP is its clear association with a long hot-spot track that
formed from ~82 to 38 Ma (i.e., the Ninetyeast Ridge with seven Deep Sea
Drilling Project and ODP drill holes that penetrated igneous basement),
and the Kerguelen Archipelago and Heard Island, which have a volcanic
record from ~40 Ma to the present. Studies of the subaerial lavas from
these islands and submarine lavas recovered by drilling provide a 115-Ma
record of volcanism that can be used to understand the origin and
evolution of the large and long-lived Kerguelen Plume. This plume is
particularly important because it is a source of the "enriched isotopic
component" that forms an end-member in the isotopic arrays defined by
ocean island basalts, and it may have been important in creating the
distinctive isotopic characteristics of Indian Ocean ridge basalts.
Determination of the spatial and temporal variations in geochemical
characteristics of the basalts forming the Kerguelen Plateau and Broken
Ridge are essential for understanding the early history of the Kerguelen
Plume.
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