Chemistry of igneous rocks--[Part] 1, Differentiation index

Petrogenetic modeling of a potential uranium source rock, Granite Mountains, Wyoming

“…Most of the samples are close to the average composition for all the samples as shown by the small standard deviations for the major elements (table 4). The compositions are highly evolved as indicated by the differentiation indices (Thornton and Tuttle, 1960) which range from 76 to 97 with all but five analyses greater than 90. All but one of the analyzed samples are peraluminous ( fig.…”

“…The granite is highly evolved as indicated by the high differentiation index of Thornton and Tuttle (1960), the strongly enriched light REE, the large negative Eu anomaly for most of the samples, the high Rb in relation to K or Sr (K/Rb=200 to 400, Rb/Sr=2 to 6), and high contents of incompatible elements such as U and Th. Although all these features can result from either high degrees of fractional crystallization or low degrees of partial melting, partial melting of a granitic (and already evolved) source appears to be necessary to account for such a highly evolved character.…”

Petrology of the bimodal Cenozoic volcanism of the Kapsiki plateau (northernmost Cameroon, Central Africa)

“…3) according to their differentiation index (Thornton and Tuttle, 1960). Ma®c lavas include basalts, ankaramite-type basalts and hawaiite.…”

“…Differentiation indices (Thornton and Tuttle, 1960) of the lavas range from 22 to 97 with a large gap in the range 34±82. Some basalts are primitive (530 ppm Ni, 1100 ppm Cr).…”

“…Two types of trachytes occur: peralkaline trachytes, with Ti-, Na-and F-rich aegirine augite, richterite, arfvedsonite phenocrysts and non-peralkaline trachytes, with an aenigmatite-type undetermined mineral, Ti-rich biotite and zircon phenocrysts. Similarly, two types of rhyolites occur: peralkaline with quartz and arfvedsonite phenocrysts and non-peralkaline with quartz and biotite phenocrysts.Differentiation indices (Thornton and Tuttle, 1960) of the lavas range from 22 to 97 with a large gap in the range 34±82. Some basalts are primitive (530 ppm Ni, 1100 ppm Cr).…”