Dharwad Granitoids

Published: 26-04-2020| Version 1 | DOI: 10.17632/hbm49gzmrk.1
Chandan Kumar Boraiaha


Bulk-rock geochemical data of Dharwar Granitoids. The Dharwad granitoids are intermediate to felsic in composition with a narrow range of silica, low to moderate potassium and considerably higher sodium oxides. They have moderate to higher alumina content and higher alkali ratio, characteristic of transitional tonalite-trondhjemite-granodiorites (TTGs). These granitoids have moderate alkali contents and spreads across the fields of diorite and granite in the total-alkali silica [TAS] diagram. The quartz-monzodioritic variety of Dharwad granitoids occupy diorite field while the granitic varieties fall on the boundary line between granodiorite and granite. The MgO content of the quartz-monzodiorites is higher than the granites due to the predominance of mafic silicate phases in the former. The Dharwad granitoids have Fe* greater than 0.5 (and < 1) and have higher mole proportions of Fe than Mg and are hence, classified as ferroan. These rocks are metaluminous with molar Na+K < 1 and ASI (Alumina Saturation Index) < 1. All these features indicate that the Dharwad granitoids do not represent mantle-derived primary magma composition. The transitional elements (Co, Ni and V) are enriched in quartz-monzodiorite due to the dominant mafic silicate phases in them. Except Sr, the analyzed compatible elements (Rb and Cs) and the incompatible elements (Nb, Ta, Zr, Hf and Y) are enriched in granites than quartz-monzodiorites. There is no particular increasing or decreasing trends exhibited by the trace elements between the grey and pink granites, however, in general, the incompatible elements tend to increase in pink granites. The total rare earth element concentration increases from quartz-monzodiorite to granite. The quartz-monzodiorite display light REE (LREE) fractionation with no europium anomalies and negligible heavy REE (HREE) depletion. The fractionation trends of the granites are similar to the quartz-monzodiorite, except moderate negative europium anomalies in the former.