Continental flood-basalts isotopic compositions

The problem of crustal contamination is particularly acute for low mg continental flood basalts and smaller volume continental tholeiitic basalts, both of which have low trace-element concentrations (see Sections 3.03.3.2.3 and 3.03.3.3). The issue is less critical for many smaller volume continental rocks, such as kimberlites and alkali basalts, which have much higher abundances of many trace elements. As a result of their high strontium and neodymium content, for example, the isotopic compositions of these elements in kimberlites and alkali basalts are relatively insensitive to modification during crustal contamination. Conversely, the osmium and lead concentration of basaltic magmas are so low that these isotope systems are particularly vulnerable to modification by interaction with cmstal rocks (McBride et al, 2001 Chesley et al, 2002) hence these systems provide relatively sensitive indicators of crustal assimilation. 

Table 3 Major element, trace element, and isotopic compositions of continental flood basalts. 

Fig. 13.39 The magmatic activity that was initiated by the rifting of Gondwana during the Mesozoic Era occurred in a belt that now extends across four continents of the southern hemisphere. The chemical and isotopic compositions of the resulting continental flood basalts and intrusives depend on the make-up of the...

Fig. 14.1 Queen (or Dronning) Maud Land is located in East Antarctica along the east coast of the Weddell Sea. It is not considered to be an extension of the Transantarctic Mountains, although it does include flat-lying sandstones of the Permian Amelang Formation which are overlain by continental flood basalts of the Jurassic Kirwan Volcanics. The chemical and isotopic compositions of the basalt flows and sills resemble the Karoo Basalt of southern Africa which was adjacent to Queen Maud Land before the break-up of Gondwana (Adapted from Fumes et al. (1987))...

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