Elastic properties of amphibolite and granulite facies mid-crustal basement rocks of the Deccan volcanic covered 1993 Latur-Killari earthquake region, Maharastra (India) and mantle metasomatism

Present study provides a new data set of P- and S‐wave velocities and density of metasomatized mid-crustal amphibolite and granulite facies basement rocks of the 1993 Latur-Killari earthquake region of Maharashtra (India), which is concealed below a thick suite of Deccan volcanics. This includes laboratory tests, geochemical analysis and petrographic examination on 29 fresh cored samples, selected from the depths between 351.7 m and 616.8 m of the KLR-1 borehole, drilled in the earthquake epicentral zone. These samples show a wide range in SiO2 content from 52.2 to 70.0 wt.%. Majority of these samples are characterized by intermediate composition with a mean density of 2.85 g/cm3 (range, 2.72-3.06 g/cm3) and average P- and S-wave velocities of 6.23 km/s (5.83-6.61 km/s) and 3.56 km/s (3.21-3.96), respectively. They also contain quite high amount of FeOT and CaO with respective means of 9.76 and 6.59 wt.%. Average Poisson's ratio is 0.25, together with respective values of Young's, bulk and rigidity modulus at 90.8 GPa, 62.0 GPa and 36.3 GPa. Inspite of having higher densities, some of the biotite and FeO-rich samples, exhibit unusually low velocities consequent to metasomatic activity. Our study demonstrates that the mantle metasomatic alteration and retrogression of the underlying high‐velocity mafic crust under the Latur-Killari earthquake region, accompanied by geodynamic process of uplift and erosion during the geologic past, has led to severe changes in the petrophysical and elastic properties of the studied rocks.

► Presents first results of elastic properties of amphibolite and granulite facies basement below Killari earthquake region. ► Discusses the effect of metasomatism on measured elastic properties of rock. ► The study investigates the possible causes of velocity inversion in mafic rocks. ► Adds a new dimension to the nature of geodynamic evolution of Killari earthquake region.