Cenozoic strontium isotope ratios

Os/ Os ratio remains relatively constant for the majority of this time interval, with the notable exception of the Eocene-Oligocene transition itself. During the Paleocene and Eocene (35-65 Ma), it appears that the osmium record exhibits considerably more variability than does the strontium record. Neither record shows clear evidence of systematic change to more or less radiogenic isotope compositions during this early part of the Cenozoic. 

Information concerning the origin of the alkali-rich lavas of the Erebus volcanic province is derivable from the isotopic composition of strontium and the concentrations of rubidium and strontium. The first measurements of the Sr/ Sr ratios of the Cenozoic volcanic rocks in the Erebus province by Jones and Walker (1972) ranged from 0.7022 to 0.7048 with a mean of 0.70365 0.0024 (2o). These measurements demonstrated that the Cenozoic lavas are only moderately enriched in radiogenic Sr in marked contrast to the basalt flows and dolerite sills of the Eerrar Group. These results were later confirmed by Stuckless and Ericksen (1976) whose measured Sr/ Sr ratios in Figs. 16.6a, b, and c have a nnimodal distribution with a mean of 0.70332 0.00005 (2. ... 

Fig. 16.9 The values and initial Sr/ Sr ratios at 900 Ma of granulite inclusions in the Cenozoic volcanic rocks in the Ross Embayment and in the Transantarctic Mountains form separate clusters. These differences indicate that the inclusions originated from distinctly different crustal sources that are separated from each other by a discontinuity (Kalamarides et al. 1987). The isotope compositions of oxygen and strontium of the Kirkpatrick Basalt in the Transantarctic Mountains (Hoefs et al. 1980) define a third cluster having low values and high initial Sr/ Sr ratios. The evidence in this diagram implies that a tectonic boundary exists in the deep crust underlying the Transantarctic Mountains and the Ross Embayment. The isotopic data also rule out a connection between the granulite inclusions in the Cenozoic lavas and the Kirkpatrick Basalt of the Transantarctic Mountains (Adapted from Fig. 1 of Kalamarides and Berg (1991))...

The HIMU component typically has a high 206pb/204pb j. bo between 20.5 and 21.5 and a low Sr/ Sr ratio between 0.7025 and 0.7030 which places it in Fig. 16.42 on an extension of the hyperbolic Sr-Pb isotopic mixing line loosely defined by the Cenozoic volcanic rocks of the Hallett volcanic province. The volcanic rocks on the Balleny Islands and on Scott and Peter I islands have isotopic compositions of strontium and lead that overlap those of the Hallett volcanic province. However, the Sr/ Sr ratios of the Balleny/ Scott islands are low (0.7025-0.7030), whereas those of Peter I Island (0.7038-0.7040) are normal for oceanic island basalts. 

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