Archaean High-Mg Granitoids of Mantle Origin in the Eastern Dharwar Craton of Andhra Pradesh

A few xenoliths of high-Mg granitoids occur in the Archaean granodiorite and granite of Eastern Dharwar craton. They are composed of quartz, plagioclase, K-Feldspar, clinopyroxene, biotite, ore and occasionally orthopyroxene. They show wide variation in silica content from 61.4 to 73 wt.%. The Mg-Numbers in the units which contain 61.4 to 63.5 wt.% silica vary from 0.44 to 0.57; in the Total Alkalis-Silica diagram, these units plot in the fields of andesite, dacite and trachy-dacite, and in the QAP diagram they show quartz-Monzodiorite composition. In the units which contain >65 wt.% silica, the Mg-Numbers range from 0.43 to 0.51 and, in the normative Ab-An-Or diagram, they show granodiorite and tonalite compositions. These high-Mg granitoids show enrichment of Ba and Cr, and their chondrite-Normalised REE patterns display moderate slopes indicating LREE enrichment and HREE depletion. Quartz-Monzodiorite reveals sanukitoidal geochemistry and it is likely to have been derived from a source which is LREE-Rich and having high Mg-Number such as the products of mantle peridotite. Fractional crystallisation of sanukitoid would have generated high-Mg granodiorite and tonalite.