Supplementary Figure Legends.
Fig. S1. Two diagrams are shown illustrating the stretching of a viscous band by shear
strain (A) and normal strain (B). The lines correspond to different degrees of stretching
(/0) of a band of initial thickness 0. Three cases are illustrated that represent 10%
stretching (blue), 50% stretching (green) and 90% stretching (red). As an example, after
40 Myrs recycled crust or lithosphere would have been stretched and thinned to about
50% of its original thickness via shear strain, and after 300 Myrs to about 10%. Time
scales for the same stretching by normal strain are correspondingly shorter, at ~25 and 80
Myrs, respectively. Layer thinning is described by /0=1/(1+t) for shear strain and by
/0=exp(- t) for normal strain, where  is strain rate and t is time.
Fig. S2. Hf ‘isochron’ diagram for Southeast Indian Ridge MORB glasses and basalts
from Amsterdam and St. Paul islands. The trendline corresponds to an age of 400 Myr,
equivalent to the linear regression of the new SEIR data (slope=0.00769, r2=0.23). Data
sources are [1-2] for the Australian-Antarctic Discordance (AAD), [3] for the SEIR west
of the ASP Plateau, and [4] for Amsterdam and St. Paul islands. SEIR data in dark blue
are from this study, with Lu and Hf concentration data from [5].
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Australian-Antarctic Discordance and origin of the Indian MORB source. Geochem.
Geophys. Geosyst. 3, doi:10/1029/2002GC000320 (2002).
2. Hanan, B., Blichert-Toft, J., Pyle, D. G. & Christie, D. M. Contrasting origins of the
upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge.
Nature 432, 91-94 (2004).
3. Chauvel, C. & Blichert-Toft, J. A hafnium and trace element perspective on melting of
the depleted mantle. Earth and Planet. Sci. Lett. 190, 137-151 (2001).
4. Doucet, S., Weis, D., Scoates, J. S., Debaille, V. & Giret, A. Geochemical and Hf-PbSr-Nd isotopic constraints on the origin of the Amsterdam-St. Paul (Indian Ocean)
hotspot basalts. Earth Planet. Sci. Lett. 28, 179-195 (2004).
5. Christie, D. M., Pyle, D. G. and Sylvander, B. A. Major and trace element composition
of basalts from the Southeast Indian Ridge (Westward cruise, leg 10). LDEO
Petrological Database, submitted data set (2004).