Figure F11. Subsidence estimates for various parts of the Kerguelen Plateau plotted as a function of eruption age of basement basalts (from Wallace, 2002). The subsidence for Site 1140 is calculated using H2O and CO2 data for glassy pillow rims. For all other sites, the basement basalts were erupted in a subaerial environment, so there is no information on the original elevation above sea level at the time of eruption. Therefore, to estimate subsidence, we have assumed that (1) these other sites subsided like normal Indian Ocean lithosphere from the time of eruption until the time represented by the oldest marine sediments on top of basement, and (2) at the time of the oldest marine sediment, the site was at sea level. Note that assumption 1 only affects the first 10-35 m.y. following the initiation of subsidence. For each site, subsidence from the time of the oldest marine sediment to the present day is shown as a thin blue line. For reference, the heavy solid line shows the subsidence curve for normal Indian Ocean lithosphere (Hayes, 1988). Eruption ages were determined by 40Ar/39Ar dating (Duncan, 2002; Pringle et al., 1994). Biostratigraphic ages are from Coffin, Frey, Wallace, et al. (2000) and references therein. For all sites, including Site 1140, the present-day depth of the top of igneous basement has been corrected for sediment loading (i.e., the actual present-day depth is greater than would have occurred due to thermal subsidence alone because of the additional effect of sediment loading). The corrected basement depth (Dc) is obtained from the equation of Crough (1983): Dc = dw + ts (

Figure F11. Subsidence estimates for various parts of the Kerguelen Plateau plotted as a function of eruption age of basement basalts (from Wallace, 2002). The subsidence for Site 1140 is calculated using H₂O and CO₂ data for glassy pillow rims. For all other sites, the basement basalts were erupted in a subaerial environment, so there is no information on the original elevation above sea level at the time of eruption. Therefore, to estimate subsidence, we have assumed that (1) these other sites subsided like normal Indian Ocean lithosphere from the time of eruption until the time represented by the oldest marine sediments on top of basement, and (2) at the time of the oldest marine sediment, the site was at sea level. Note that assumption 1 only affects the first 10-35 m.y. following the initiation of subsidence. For each site, subsidence from the time of the oldest marine sediment to the present day is shown as a thin blue line. For reference, the heavy solid line shows the subsidence curve for normal Indian Ocean lithosphere (Hayes, 1988). Eruption ages were determined by ⁴⁰Ar/³⁹Ar dating (Duncan, 2002; Pringle et al., 1994). Biostratigraphic ages are from Coffin, Frey, Wallace, et al. (2000) and references therein. For all sites, including Site 1140, the present-day depth of the top of igneous basement has been corrected for sediment loading (i.e., the actual present-day depth is greater than would have occurred due to thermal subsidence alone because of the additional effect of sediment loading). The corrected basement depth (D_c) is obtained from the equation of Crough (1983): D_c = d_w + t_s (

_s -

_m)/(

_w -

_m), in which d_w = water depth in meters, t_s = sediment thickness in meters,

_s = average sediment density (1.90 g/cm³),

_m= upper mantle density (3.22 g/cm³), and

_w = seawater density (1.03 g/cm³). Error bars show uncertainty in the subsidence estimates. For Site 1140, this uncertainty is based on uncertainty of the original eruption depth due to variations in the H₂O and CO₂ data for glassy pillow rims. For all other sites, error bars show an estimate of the combined uncertainties resulting from assumptions 1 and 2 above and the correction for effects of sediment loading on subsidence.