Basalts samarium isotopes

Beyond the broad major-element constraints afforded by seismic imaging, the abundance of many trace elements in the mantle clearly records the extraction of core (Chapters 2.01 and 2.15) and continental crust (Chapter 2.03). Estimates of the bulk composition of continental cmst (Volume 3) show it to be tremendously enriched compared to any estimate of the bulk Earth in certain elements that are incompatible in the minerals that make up the mantle. Because the crust contains more than its share of these elements, there must be complementary regions in the mantle depleted of these elements—and there are. The most voluminous magmatic system on Earth, the mid-ocean ridges, almost invariably erupt basalts that are depleted in the elements that are enriched in the continental crust (Chapter 2.03). Many attempts have been made to calculate the amount of mantle depleted by continent formation, but the result depends on which group of elements is used and the assumed composition of both the crust and the depleted mantle. If one uses the more enriched estimates of bulk-continent composition, the less depleted estimates for average depleted mantle, and the most incompatible elements, then the mass-balance calculations allow the whole mantle to have been depleted by continent formation. If one uses elements that are not so severely enriched in the continental cmst, for example, samarium and neodymium, then smaller volumes of depleted mantle are required in order to satisfy simultaneously the abundance of these elements in the continental cmst and the quite significant fractionation of these elements in the depleted mantle as indicated by neodymium isotope systematics. 

The Prince Albert Mountains in the northern part of southern Victoria Land consist of a large number of nunataks located on the polar plateau at the heads of Mawson, Harbord, and David glaciers aU of which flow into the Ross Sea. Several of these nunataks are composed of siUs of Ferrar Dolerite although flows of Kirkpatrick Basalt occur on Brimstone Peak (75°48 S, 158°33 E). Molzahn et al. (1996) reported isotope ratios of strontium, neodymium, and osmium as well as trace-element concentrations of five dolerite samples from the nunataks of the Prince Albert Mountains and two basalt samples from Brimstone Peak, including rubidium, strontium, samarium, neodymium, rhenium (Re) and osmium (Os). They also measured isotope ratios of strontium, neodymium, and lead in clinopyroxene and plagioclase of these rocks. 

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