Effects of Pressure and Temperature Changes on Shock Remanence Acquisition for Single-Domain Titanomagnetite-Bearing Basalt

Knowledge of the shock remanent magnetization (SRM) property is crucial for interpreting the spatial change in a magnetic anomaly observed over an impact crater. This study conducted two series of impact-induced SRM acquisition experiments by varying the applied field intensity (0-400 mu T) and impact conditions. Systematic remanence measurements of cube-shaped subsamples cut from shocked basalt containing single-domain titanomagnetite were conducted to investigate the effects of changes in pressure and temperature on the SRM acquisition. The peak pressure and temperature distributions in the shocked samples were estimated using shock-physics modeling. SRM intensity was proportional to the applied field intensity of up to 400 mu T. SRM intensity data for peak pressure and temperature of up to 8.0 GPa and 530 K, respectively, clearly show that it increases with increasing pressure and decreases with increasing temperature. The SRM has unblocking temperature components up to a Curie temperature of 510 K, and it easily demagnetizes with alternating field demagnetization. The observed SRM properties can be explained by the pressure-induced microcoercivity reduction and temperature-induced modification of the blocking curve. Although the remanence acquisition efficiency of the SRM is significantly lower than that of the thermoremanent magnetization (TRM), the magnetic anomaly originating from the SRM distribution in a broader region may show a contribution comparable to that of the impact-induced TRM distribution in a narrow region. Crustal rocks on terrestrial planets acquire remanent magnetization at the time of an impact event as shock remanence. Magnetic field data observed over impact craters play a key role in reconstructing the magnetic field histories of terrestrial planets. Knowledge of shock remanence is crucial for interpreting the spatial changes in the magnetic field observed over an impact crater. In this study, a suite of shock remanence acquisition and evaluation experiments were conducted to investigate the effects of pressure and temperature changes during shock wave propagation on shock remanence acquisition. The experimentally observed characteristics of shock remanence, such as the stability with respect to thermal and alternating field demagnetization and the systematic intensity changes with respect to pressure and temperature changes, are qualitatively explained by the pressure- and temperature-induced changes in magnetic properties during shock wave propagation. The shock remanence intensity with respect to impact conditions was evaluated using newly obtained experimental data, which enabled us to quantitatively evaluate the shock remanence distributions and their contribution to the magnetic field over impact craters. The shock remanence contribution is estimated to be comparable to that of the impact-induced thermoremanent magnetization, considering the intensity and volume of these remanences. Shock remanence acquisition and evaluation experiments are conducted to evaluate the effects of pressure and temperature changes Characteristics of shock remanence can be explained by a pressure-induced microcoercivity reduction and a temperature effect on it Contribution of shock remanence to magnetic anomaly over crater is estimated to be comparable with that of impact-induced thermoremanence