New Finding of Silica-deficient Sapphirine-bearing Granulites from NNE of Suranganar Village, Southern Madurai Block, India

An infrequent occurrence of sapphirine from metapelite rocks of the Cardamom hills of South India has been reported. This report of sapphirine may not be the first from the Southern Granulite Terrane (SGT) but is essentially from a new locality. The studied metapelites are silica-undersaturated devoid of garnet and the sapphirine symplectites. The symplectites of orthopyroxene + cordierite, orthopyroxene + K-feldspar + cordierite, orthopyroxene + sapphirine + cordierite ± K-feldspar ± biotite, orthopyroxene + biotite + cordierite + K-feldspar are discernible. The textural patterns show partial to complete pseudomorphism of the initially formed orthopyroxene and sapphirine and their succeeding decomposition to present stage. The relative XMg calculated for the key minerals show the trend as: Crd > Spr > Bt > Opx. The pseudosection modelling and the calculated P-T diagram drawn from the average bulk composition of the studied metapelite connote isothermal decompression with peak pressure and temperature conditions stable at ∼10 Kbar and ∼985 °C respectively. The assemblage reported in this study has an important bearing on the crustal evolution of the high-grade metamorphism exhumed from a deeper level of the crust.