Oceanic plateaus form by mantle processes distinct from those forming oceanic crust at divergent plate boundaries. Eleven drillsites into igneous basement of Kerguelen Plateau and Broken Ridge, including seven from the recent Ocean Drilling Program Leg 183 (1998^99) and four from Legs 119 and 120 (1987^88), show that the dominant rocks are basalts with geochemical characteristics distinct from those of mid-ocean ridge basalts. Moreover, the physical characteristics of the lava flows and the presence of wood fragments, charcoal, pollen, spores and seeds in the shallow water sediments overlying the igneous basement show that the growth rate of the plateau was sufficient to form subaerial landmasses. Most of the southern Kerguelen Plateau formed at V110 Ma, but the uppermost submarine lavas in the northern Kerguelen Plateau erupted during Cenozoic time. These results are consistent with derivation of the plateau by partial melting of the Kerguelen plume. Leg 183 provided two new major observations about the final growth stages of the Kerguelen Plateau. 1: At several locations, volcanism ended with explosive eruptions of volatilerich, felsic magmas; although the total volume of felsic volcanic rocks is poorly constrained, the explosive nature of the eruptions may have resulted in globally significant effects on climate and atmospheric chemistry during the late-stage, subaerial growth of the Kerguelen Plateau. 2: At one drillsite, clasts of garnet^biotite gneiss, a continental rock, occur in a fluvial conglomerate intercalated within basaltic flows. Previously, geochemical and geophysical evidence has been used to infer continental lithospheric components within this large igneous province. A continental geochemical signature in an oceanic setting may represent deeply recycled crust incorporated into the Kerguelen plume or continental fragments dispersed during initial formation of the Indian Ocean during breakup of Gondwana. The clasts of garnet^biotite gneiss are the first unequivocal evidence of continental crust in this oceanic plateau. We propose that during initial breakup between India and Antarctica, the spreading center jumped northwards transferring slivers of the continental Indian plate to oceanic portions of the Antarctic plate. ß

A palaeomagnetic study has been carried out on three stalagmites from two limestone caves in SW Japan. Remanent magnetizations of the stalagmite samples are weak, but stable enough to record the geomagnetic field. The results indicate an internal consistency between several time-equivalent samples drilled from the same stalagmite. A tentative correlation is suggested between palaeomagnetic data from two stalagmites collected from the same cave, and data from two different limestone caves. Combined curves of declination and inclination variations are constructed on the basis of this tentative correlation between the alternatingfield cleaned results from the three stalagmites. These variation curves can also be tentatively correlated with those deduced from archaeomagnetic studies in SW Japan. In consequence, the curves are believed to represent records of past geomagnetic secular variation. The tentative age of the oldest end of this secular variation curve can be estimated at about 15 OOO yr BP, based on the correlation with the archaeomagnetic results. A possible long period of westerly declination and steep inclination is recognized in the older part of the variation

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