Natural graphite from neoproterozoic psammitic gneiss, Inanalo mountain, southern Madagascar

Abstract

We report here, for the first time, powder X-ray diffraction, and laser-Raman spectroscopic data on the graphite samples from Inanalo mountain (S24°24′31.2″ E45°23′18.3″), 20 km east of the Ampanihy shear zone of the southern Madagascar. Oar experimental results show that the graphite is highly crystalline, and syngenetic with the degree of graphitisation varying from 148 to 180, yielding the peak metamorphic temperatures of 750 to 850°C. Laser Raman spectroscopic studies show only ordered peak at around 1580 cm-1 in the frequency range from 1000 to 2000 cm-1. The commonly observed disordered peak in natural graphite is found to be absent in the studied sample, indicating high-temperature metamorphism. There is no fluid deposited graphite (epigenetic graphite) in the sample. The peak metamorphic temperature obtained in the present study is found to be in good agreement with that obtained from the conventional geothermometry studies on the sample from the Beraketa shear zone or the Betroka tectonic belt.