DRILLING STRATEGY
LIPs are enormous igneous constructions that present considerable challenges for adequate sampling to address our first-order questions. Our knowledge of LIPs is rudimentary, similar, perhaps, to that of mid-ocean ridges before general acceptance of the plate tectonics paradigm in the late 1960s. Considerable shallow basement drilling and significant geophysical surveying are necessary to begin to address issues of Cretaceous mantle dynamics and environmental consequences. Understanding the complete temporal and compositional history of the Kerguelen Plateau and Broken Ridge will require several approaches, including (1) transects of shallow (~200 m) 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 utilizes approach 1 and should complete the fundamental and necessary reconnaissance phase of Kerguelen sampling, which has included Legs 119 and 120. To obtain a comprehensive database of eruption ages and lava compositions for the entire LIP, Leg 183 will sample igneous basement to depths of =150-200 m using single rotary core barrel (RCB) holes at as many morphologically and tectonically distinct regions of the Kerguelen Plateau/Broken Ridge LIP as possible on one leg (Tables 1, 2; Figs. 2, 3, 4). In addition, the sedimentary section immediately overlying the basement will provide estimates of minimum ages for extrusive basement, important information regarding eruption and weathering in a subaerial vs. submarine environment, and possibly evidence for tectonic events in the plateau's history.
Leg 183 is scheduled to start and finish in Fremantle, Australia. Transit time from Fremantle to the first site on the southern Kerguelen Plateau, KIP-13B, is projected at 8.1 days (Table 1). KIP-13B is the only Leg 183 site located where icebergs may present an operational hazard; completing our drilling objectives at the site may or may not be possible depending on ice conditions. Drilling (RCB) and logging time at the site is estimated at 7.7 days. Transit from KIP-13B to the next site, KIP-6C on Elan Bank, will require 2.2 days; drilling (RCB) and logging time at KIP-6C is expected to be 4.7 days. KIP-7B on the central Kerguelen Plateau is a 1.1-day transit from KIP-6C; drilling (RCB) and logging time is estimated at 7.5 days. Transit to the next site, KIP-3F on the central Kerguelen Plateau, will take 0.8 days. RCB drilling and logging time at KIP-3F is estimated at 5.0 days. KIP-2E, on the northernmost Kerguelen Plateau, is a 1.3-day transit from KIP-3F; drilling (RCB) and logging time is estimated at 6.7 days. Transit time to the final primary site, KIP-9B on Broken Ridge, is projected at 6.3 days, and 4.8 days have been estimated to drill and log the site. Fremantle is a 3.8-day transit from KIP-9B.