Figure F12. Sr isotope stratigraphy of igneous rocks (bulk rock) at Site 1253, from Chavagnac (pers. comm., 2005) and Dreyer et al. (2005). Excursions to high 87Sr/86Sr, indicative of seawater alteration, are generally observed over limited depth horizons at petrologically defined boundaries between igneous subunits. Arrows labeled N-MORB (normal mid-ocean-ridge basalt) and OIB (ocean island basalt) indicate peak values in histograms showing range of observed isotopic variation in lavas erupted in the two settings (Zindler and Hart, 1986).

Figure F12. Sr isotope stratigraphy of igneous rocks (bulk rock) at Site 1253, from Chavagnac (pers. comm., 2005) and Dreyer et al. (2005). Excursions to high ⁸⁷Sr/⁸⁶Sr, indicative of seawater alteration, are generally observed over limited depth horizons at petrologically defined boundaries between igneous subunits. Arrows labeled N-MORB (normal mid-ocean-ridge basalt) and OIB (ocean island basalt) indicate peak values in histograms showing range of observed isotopic variation in lavas erupted in the two settings (Zindler and Hart, 1986).