Archaean granitoid

Martin H. (1999) Adakitic magmas modem analogues of archaean granitoids. Lithos 46, 411—429. 

Rapp, R. P. 1991. Origin of Archaean granitoids and continental evolution. EOS Transactions, American Geophysical Union, 22, 225—229. 

Secular variation in the trace element composition of Archaean granitoids... 

Rapp, R.P., 1997. Heterogeneous source regions for Archaean granitoids experimental and geochemical evidence. In De Wit, M. and Ashwal, L.D. (eds) Greenstone Belts. Oxford University Press, Oxford, pp. 256-66. 

Rollinson, H.R., 1997b. Eclogite xenoliths in West African kimberlites are residues from Archaean granitoids. Nature, 389, 173-6. 

To evaluate these questions further, we have looked again at the variations in Pb/ Pb ratios (and thus pi) of Archaean basalts and granitoids worldwide in the age range 3.7-3.8, 3.5, 3.2, 2.9 to 2.7-2.6 Ga. We show that there are provinces with different Pb/ Pb and pj values, and note that some unexpectedly coincide with Mezosoic continental flood basalts and oceanic DUPAL rocks with similar Pb isotope features. 

Carignan, j., Gariepy, G., Machado, N. Rive, M. 1993. Pb isotopic geochemistry of granitoids and gneisses from the late Archaean Pontiac and Abitibi Subprovinces of Canada. Chemical Geology, 106, 299-316. 

Granitoid magmas in the compositional range Tonalite-Trondhjemite-Granodiorite. These are the magmas which have built the Archaean continental crust... 

In a study which has subsequently had a profound influence on our thinking about Archaean crustal evolution, Martin (1986) showed that the REE chemistry of granitoids has changed with time. He showed that granitoids can be divided into two distinct groups according to their age (Fig. 4.12). These differences can be summarized on a plot of (La/Yb) versus Yb, - the chondrite normalized ratio... 

The dominant rock-types of the Archaean continental crust are those granitoids of the tonalite-trondhjemite-granodiorite (TTG)... 

It has already been shown that the composition of the Earth s continental crust and the Earth s mantle have evolved chemically over time (see Section 4.3 and Chapter 3, Section 3.2.3). Hence, as the continental crust has grown, so has its composition changed, as is apparent from the differences in the REE content and Rb/Sr ratio of granitoids and the Th/La ratio of sediments (Section 4.3.2). These chemical differences could indicate that the mechanism of crust formation has also changed with time. Further support for this hypothesis comes from Plank s 2005 study of crustal Th/La ratios, discussed above. Plank argued that the present-day high Th/La ratio (0.28-0.31) of the continental crust is the product of internal crustal fractionation. However, Archaean continental crust has a much lower Th/La ratio (0.18) than modern continental crust, and does not require intracrustal differentiation, and so may have formed in a different manner. 

Halla, J., 2005. Late Archaean high-Mg granitoids (sanukitoids) in the southern Karelian domain, eastern Finland Pb and Nd isotopic constraints on crust-mantle interactions. Lithos, 79, 161-78. 

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