Trondhjemite and Granodiorite Assemblages from West of Barmer: Probable Basement for Malani Magmatism in Western India

The pre-Malani basement, occurring to the southwest of the Malani Igneous Suite in western India is represented by an older, biotite trondhjemite (gneiss) and a younger, hornblende granodiorite. These granitoid assemblages (hitherto mentioned as unclassified granitoids) denote tectonically uplifted basement for the volcano-plutonic Malani magmatism. Biotite trondhjemite with well-developed gneissic fabric is significantly deformed as compared to hornblende granodiorite, which is slightly deformed. The basement granitoids exhibit a well-defined temporal and spatial relationship with each other, and are further intruded by Malani rhyolite/basic dykes. Well-preserved magmatic fabric of rhyolite/basic dykes suggests that the intrusive activity post-dated any deforrnational event. The geochemical signatures of the basement granitoids - moderate silica, high Sr, low FeO/MgO ratio and moderate alkali abundance, are quite distinct from the A-type geochemistry of Malani rhyolite dykes - high silica, high HFSE abundance, high FeO/MgO ratio and high alkali abundance, thus invoking different sources and emplacement history.