Author(s)

Sunki Amarendhar^1*, Valluri Sai Krishna Priya², Malintee Vittal², Madabhhoshi Srinivas²

¹Department of Geology, University College of Science Saifabad, Osmania University, Hyderabad, India.
²Department of Geology, Osmania University, Hyderabad, India.

The charnockites of Marandahalli, Dharmapuri District, Tamil Nadu India, form a part of the southern granulitic terrain in the Salem Block (SB). The charnockites are medium to coarse grained, inequigranular, with porphyroblastic and granophyric textures. They are composed of plagioclase feldspars (49 - 66 vol.%), K-feldspar (1 - 5 vol.%) and quartz (21 - 34 vol.%). The mafic minerals include pyroxene (2 - 7 vol.%) and biotite (1 - 12 vol.%). The accessory minerals include magnetite and apatite. Orthopyroxene compositions (MgO 16 - 22 wt.%) fall within the hypersthene series (En_55.03Fs_43.57Wo_1.4) and yield peak metamorphic temperatures of 800˚C - 1000˚C. Biotites show K₂O, MgO, FeO, TiO₂, and Al₂O₃ concentrations consistent with magmatic formation, and Ti-in-biotite thermometry suggests temperatures of ~740˚C - 800˚C. Plagioclase compositions (An_26-33) plot in the oligoclase field, while K-feldspar (Or_93-99) plots in the orthoclase/microcline field. A ternary feldspar geothermometer indicates a retrograde temperature of <700˚C for the rocks. The rocks are originated from the Mg rich amphibolite source and garnet free. The rocks are calc-alkaline with high SiO₂ (65 - 68 wt.%), Na₂O > K₂O, high CaO (3 - 5 wt.%), MgO (2.5 - 4 wt.%) and Fe₂O₃ (2 - 6 wt.%). The concentration of V, Rb and Ni, and LREE-rich and HREE-depleted patterns of the rocks indicate low degree of partial melting.

Charnockite, Salem Block, Fractional Crystallization, Amphibolite, Marandahalli, Peninsular Gneissic Complex (PGC)

Amarendhar, S. , Priya, V. , Vittal, M. and Srinivas, M. (2024) Mineral Chemistry and Geochemistry as Proxy for Petrogenetic Evaluation of Charnockites: Evidences from Marandahalli, Salem Block of Southern India. Open Journal of Geology, 14, 963-987. doi: 10.4236/ojg.2024.1411043.