Axial focusing of impact energy in the earth's interior: A possible link to flood basalts and hotspots

摘要

We present the results of shock physics and seismological computational simulations that show how energy from a large impact can be coupled to the interior of the Earth. The radially-diverging shock wave generated by the impact decays to linearly elastic seismic waves. These waves reconverge (minus attenuation) along the axis of symmetry between the impact and its antipode. The locations that experience the most strain cycles with the largest amplitudes will dissipate the most energy and have the largest increases in temperature (for a given attenuation efficiency). We have shown that the locus of maximum energy deposition in the mantle lies along the impact axis. Moreover, the most intense focusing is within the asthenosphere at the antipode, within the range of depths where mechanical energy is most readily converted to heat. We propose that if large impacts on the Earth leave geological evidence anywhere other than the impact site itself, it will be at the antipode. We suggest that the most likely result of the focusing for a sufficiently large impact, consistent with features observed in the geological record, would be a flood basalt eruption at the antipode followed by hotspot volcanism. A direct prediction of this model would be the existence of undiscovered impact structures whose reconstructed locations would be antipodal to flood basalt provinces. One such structure would be in the Indian Ocean, associated with the Columbia River Basalts and Yellowstone; another would be a second K/T impact structure in the Pacific Ocean, associated with the Deccan Traps and Reunion.