Petrology and Geochemistry of the Mount Abu Granites, Southwestern Rajasthan

摘要

The Neoproterozoic mount Abu batholith comprises medium to coarse-grained, grey and pink porphyritic to non-porphyritic biotile granites. Chemically and mincralogically, these are sub-aluminous and potash-rich granites. They are characterized by high SiO_2, Na_2O + K_2O, Fe/Mg, Rb, Nb, Zr, Y, Zn, Ga and Th, and low MgO, Fe_2O~t_3, CaO and Sr contents, and show close affinity to the A-type granites. High K/Rb, Rb/Sr, Ba/Sr and Ga/Al ratios of these granites are suggestive of crustal origin, which were most likely derived by low-degree partial melting of pre-existing depleted lower crustal source. The mount Abu granites were emplaced at 650°-700°C ai an assumed pressure of around 5 kb.