Petrogenesis Isotopic Evidence

Many of the trace element and isotopic characteristics compare more closely with those of continental crustal rocks than with typical mantle-derived materials, indicating the dominance of a crustal component in the petrogenesis of these tholeiites. 

The evidence we have already presented includes the anomalously high initial Sr/ Sr ratios (Figs. 12.21, 12.33,12.34), the Sr-isotopic mixing lines (Figs. 12.23, 12.35), and the correlation of initial Sr/ Sr ratios with major-element concentrations including SiO (Fig. 12.36) and MgO (Fig. 12.37). 

The most direct way to recognize the crustal character of these rocks is by means of the initial isotope ratios of strontium and neodymium in Fig. 12.38. The Sr-Nd plane in this diagram is divided into four quadrants by the ratio of the Chondritic 

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Zhang M., Stephenson J., O Reilly S. Y., McCulloch M. T., and Norman M. (2001) Petrogenesis of Late Cenozoic basalts in North Queensland and its geodynamic implications trace element and Sr—Nd—Pb isotope evidence. J. Petrol. 42, 685-719. 

Chen B., Jahn B. M., and Wei C. (2002) Petrogenesis of Mesozoic granitoids in the Dabie UHP complex. Central China trace element and Nd-Sr isotope evidence. Lithos 60, 67-88. 

McCulloch M. T. and Woodhead J. D. (1993) Lead isotopic evidence for deep crustal-scale fluid transport during granite petrogenesis. Geochim. Cosmochim. Acta 57, 1837-1856. 

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