A Time Frame for Construction of the Kerguelen Plateau and Broken Ridge

Abstract

A key element in achieving Ocean Drilling Program Leg 183 science (1) determine the chronology of the Kerguelen Platobjectives is determining the age of volcanism at different locations eau–Broken Ridge magmatism; across the Kerguelen Plateau and Broken Ridge. This paper reports (2) constrain the time scale of melting processes, and crystallization ages derived from Ar–Ar incremental heating post-melting magmatic evolution; experiments, for whole rocks and feldspars separated from basement (3) evaluate the effects of LIP formation on the enunits recovered at Sites 1136, 1137, 1138, 1139, 1140, 1141 vironment; and 1142. The subaerial environment of eruption at most sites and (4) identify and interpret relationships between LIP the generally evolved, high K content of these lava flows contributed development and tectonism. to precise and reproducible age determinations. Volcanic activity at Radiometric ages contribute directly to objectives (1) southern Kerguelen Plateau Site 1136 occurred at 118–119 Ma; and (2) by determining the timing and duration of magat Elan Bank Site 1137, 107–108 Ma; at central Kerguelen matic activity, which allow production rates to be esPlateau Site 1138, 100–101 Ma; at Skiff Bank Site 1139, timated (see Coffin et al., 2002). The most significant 68–69 Ma; at northern Kerguelen Plateau Site 1140, 34–35 Ma; question is, how much magma was erupted over what and at Broken Ridge Sites 1141 and 1142, 94–95 Ma. The period? The answer can be quantified only with precise new ages allow calculation of melt production rates through the radiometric ages distributed widely across the province. >120 Myr history of the Kerguelen plume, adjustments to plate Ages are important in assessing objective (3) by providing reconstructions for the eastern Indian Ocean region in the hotspot a temporal framework for linking magmatic events with reference frame, and assessment of proposed links between large abrupt or gradual environmental changes recorded in igneous province (LIP) magmatism and environmental crises. proximal or distal sediments, such as chemical anomalies (e.g. Sinton & Duncan, 1997) or biological crises (e.g. Erba, 1994). Post-emplacement tectonic events [objective (4)] may have produced synchronous volcanic activity