Discrimination diagrams for granites based upon Hf-Rb-Ta variations

2 Discrimination diagrams for granites based upon Hf-Rb-Ta variations 

Brown et al. (1984) found that with increasing maturity, volcanic-arc granites are enriched in the elements Rb, Th, U, Ta, Nb, Hf and Y and depleted in the elements Ba, Sr, P, Zr and Ti. They showed that a bivariate plot of the ratio Rb/Zr 

Twist and hhirmer (1987) applied the Rb-(Y + Nb) and Nb-Y diagrams to the Proterozoic Bushveld granites and associated felsite lavas. Their study raises two rather different but important points. Firstly, these diagrams can be applied to felsidc Lavas as well as to plutonic felsic rocks, provided the lavas are not contaminated. Secondly, they found that differences in trace element chemistry could be just as much a function of variable source chemistry as of differences in tectonic environment. 

Plate tectonic processes impart a distinctive geochemical signature to sediments in two separate ways. Firstly, different tectonic environments have distinctive provenance characteristics and, secondly, they are characterized by distinctive sedimentary processes. Sedimentary basins may be assigned to the following tectonic settings (Bhatia and Crook, 1986)  

Oceanic island-arc — fore-arc or back-arc basins, adjacent to a volcanic-arc developed on oceanic or thin continental crust. 

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