Earthquake new tool for diamond hunters
doi:10.1038/nindia.2020.27 Published online 12 February 2020
Earth scientists at the Indian Institute of Science Education and Research (IISER) in Pune have proposed1 a new method — which employs seismic imaging of the Earth's crust — for identifying diamond bearing regions in peninsular India.
Diamonds are formed in the mantle of the earth and reach the surface via volcanic rocks such as kimberlites. Diamond prospectors know that the secret of finding these precious stones is to locate these kimberlites, named after the South African town of Kimberley where diamonds were first discovered.
The new method for locating the kimberlites suggested by the IISER team uses the seismic image of lithosphere, the outermost part of the earth comprising the crust and the mantle. The idea exploits a strange behaviour of the "shear waves" generated by earthquakes.
Unlike surface waves, shear waves move through the body of an object. According to the researchers, while shear waves travel at a speed of 4.5 kilometers per second (km/s) through most parts of India, their speed "significantly increases to 4.7 km/s and above" when passing through India's diamond corridor — the 1200-km-long corridor of eastern Dharwar, Bastar and Singhbhum blocks in south-eastern India.
"The observed higher velocity in this corridor could be best explained by the presence of diamond," their report says. The authors claim that their study presents a new geologic model that explains the distribution of 'diamondiferous kimberlites' and suggests that the seismic image of lithosphere can be a guide for exploration of diamonds.
Through high-resolution seismic imaging of the lithospheric mantle, the scientists are further analysing the actual size of the diamond bearing fields that is needed to explain this observed difference in velocities of the shear waves.
1. Saha, G. et al. Occurrence of diamond in peninsular India and its relationship with deep Earth seismic properties. J. Earth Syst. Sci.128, 43c (2019) doi: 10.1007/s12040-019-1088-7