LIPs are enormous constructions that present considerable challenges for adequate sampling to address the major questions outlined in the preceding sections. Our knowledge of oceanic Cretaceous LIPs is rudimentary, similar, perhaps, to that of mid-ocean ridges before the general acceptance of the plate tectonics paradigm in the late 1960s. Geophysical surveys and a grid of shallow (100 to 200 m) basement drill holes are necessary to address Cretaceous mantle dynamics, the physical and chemical processes involved in construction of these LIPs, and their environmental consequences. Understanding the temporal and compositional history of the Kerguelen Plateau and Broken Ridge requires a multifaceted drilling strategy (Fig. 14), including (1) transects of shallow basement holes across the surface of the LIP; (2) offset drilling in tectonic windows that expose deeper levels of the LIP that are otherwise inaccessible; (3) intermediate (1000-2000 m) and deep (>2000 m) basement holes at carefully chosen locations; and (4) reference holes on older adjacent oceanic crust. Leg 183, complemented by Legs 119 and 120, is part of the fundamental and necessary reconnaissance phase of sampling. To obtain a comprehensive database of eruption ages and lava compositions for the entire LIP, we sampled igneous basement to depths of ~100 to 150 m at as many morphologically and tectonically distinct regions of the Kerguelen Plateau-Broken Ridge LIP as possible during one drilling leg (Table 1; Figs. 3, 4, 5, 6). In addition, the sedimentary section immediately overlying the basement provides estimates of minimum ages for extrusive basement, important information regarding eruption and weathering in a subaerial vs. submarine environment, and evidence for tectonic events in the plateau's history. Neogene to Cretaceous sediments overlying basement also provided significant paleoceanographic information for high southern latitudes. At some
sites, tephra horizons of various ages provide information on explosive eruptions at nearby islands (McDonald, Heard, and Kerguelen Archipelago) and perhaps more distant volcanoes.

Leg 183 Principal Results - Sites 1135/1136
Leg 183 Table of Contents