Is a cation ordering transition of the Mg‐Fe olivine phase in the mantle responsible for the shallow mantle seismic discontinuity beneath the Indian Craton?

摘要: [1] We use first-principles molecular dynamics simulations to study the behavior of cation ordering in non-equivalent octahedral sites Mg-Fe olivine solid solutions. Our theoretical calculations confirm previous experimental finding that Mg2+ and Fe2+ can invert their site occupancy at a critical temperature. Assuming preference Fe changes discontinuously between two states which it is completely restricted either M1 or M2 sites, we have calculated transition temperature, Tt, extreme states. Under ambient pressure Tt be 520°C agrees fairly with which, however, state changed over much smaller range Fe. found sensitive, showing an increase by 30 100°C per unit GPa, depending upon iron content. Using Indian continental geotherm, estimate depth around 75 Km corresponding temperature ordering, matches well for Hales discontinuity marked jump shear wave velocity ∼4%. For solutions 12.5% iron, increases Vs from 4.5 4.7 Km/s. Both inferences, viz. magnitude find support modeling teleseismic earthquake waveforms recorded broadband seismographs on Dharwar Craton. This leads us infer ferromagnesian might potential factor discontinuity.