Dharwad Granitoids

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.

德干（Dharwar）花岗岩类全岩地球化学数据。该类花岗岩类成分为中性至长英质，二氧化硅含量区间狭窄，钾含量介于低至中等水平，而氧化钠含量显著偏高；其氧化铝含量中等至偏高，碱度比值更高，具备过渡性英云闪长岩-奥长花岗岩-花岗闪长岩（TTGs）的典型特征。该类花岗岩类碱含量中等，在总碱-硅（Total-Alkali Silica，TAS）图解中分布于闪长岩与花岗岩的区间范围内。德干花岗岩类中的石英二长闪长岩亚种落入闪长岩区间，而花岗岩亚种则位于花岗闪长岩与花岗岩的分界线上。石英二长闪长岩的氧化镁含量高于花岗岩，这是由于前者中铁镁质硅酸盐矿物相占主导地位。德干花岗岩类的全铁摩尔比值（Fe*）介于0.5至1之间，且铁的摩尔占比高于镁，因此被归类为富铁质岩石。该类岩石为准铝质，其钠+钾的摩尔比值小于1，铝饱和指数（Alumina Saturation Index，ASI）同样小于1。上述所有特征表明，德干花岗岩类并非幔源原生岩浆的组成。过渡元素（钴Co、镍Ni及钒V）在石英二长闪长岩中富集，这同样源于其铁镁质硅酸盐矿物相占主导。除锶（Sr）外，本次分析的相容元素（铷Rb与铯Cs）及不相容元素（铌Nb、钽Ta、锆Zr、铪Hf及钇Y）在花岗岩中的富集程度均高于石英二长闪长岩。灰色花岗岩与粉色花岗岩之间的微量元素未呈现明确的增减趋势，但总体而言，不相容元素在粉色花岗岩中含量有所升高。从石英二长闪长岩到花岗岩，稀土元素总浓度逐渐升高。石英二长闪长岩表现出轻稀土元素（LREE）分馏特征，无铕异常，且重稀土元素（HREE）亏损程度极微。花岗岩的分馏趋势与石英二长闪长岩相似，仅前者存在中等程度的负铕异常。