A time frame for construction of the Kerguelen Plateau and Broken Ridge

A key element in achieving Ocean Drilling Program Leg 183 science objectives is determining the age of volcanism at different locations across the Kerguelen Plateau and Broken Ridge. This paper reports crystallization ages derived from 40Ar-39Ar incremental heating experiments, for whole rocks and feldspars separated from basement units recovered at Sites 1136, 1137, 1138, 1139, 1140, 1141 and 1142. The subaerial environment of eruption at most sites and the generally evolved, high K content of these lava flows contributed to precise and reproducible age determinations. Volcanic activity at southern Kerguelen Plateau Site 1136 occurred at 118-119 Ma; at Elan Bank Site 1137, 107-108 Ma; at central Kerguelen Plateau Site 1138, 100-101 Ma; at Skiff Bank Site 1139, 68-69 Ma; at northern Kerguelen Plateau Site 1140, 34-35 Ma; and at Broken Ridge Sites 1141 and 1142, 94-95 Ma. The new ages allow calculation of melt production rates through the similar to120 Myr history of the Kerguelen plume, adjustments to plate reconstructions for the eastern Indian Ocean region in the hotspot reference frame, and assessment of proposed links between large igneous province (LIP) magmatism and environmental crises.