An In Situ Detection System for Obtaining IRM Acquisition Curves and Alternating Field Demagnetization Remanence Curves of Rocks.

A correct understanding of the magnetic properties of rocks is essential to obtain reliable records of paleomagnetism and environmental magnetism. However, the original orientation of cores can be easily lost during drilling, which represents the main source of error when measuring the magnetic properties of rocks. In this study, we develop an in situ detection system to obtain isothermal remanent magnetization (IRM) acquisition curves and alternating field demagnetization (AFD) remanence curves of rocks. This system eliminates the need to collect cores and allows the rock to be magnetized, demagnetized, and measured in situ. This system uses a magnetic field generator to generate pulsed magnetic fields and alternating magnetic fields for in situ magnetization and demagnetization of rocks. The remanence data are collected using an anisotropic magnetoresistance magnetometer. To achieve remote control and real-time data transmission, the system's corresponding host computer software is also configured. The system has high magnetization (0-1 T, 8 ms) and demagnetization (0-300 mT, 62.5 Hz) capabilities; in addition, the linearity and stability of the magnetometer are almost unaffected by strong magnetic fields. In this article, the remanence inversion formula for the in situ detection system is given. When the rock is measured in situ and close to the bottom of the coil, the z-component of the flux density measured by the magnetometer can be used to calculate the rock's remanence based on the inversion formula. Three cylindrical rock samples of the same material and different sizes were tested using the in situ detection system, and their corresponding IRMB and AFDB curves were obtained. The Br c and saturation IRM parameters of the samples obtained by inversion are essentially the same as those measured using a vibration sample magnetometer (VSM). This system provides a new measurement method for the detection of remanence of rocks in the field and provides a strong foundation for the future development of in situ measurement technology for the magnetic properties of seafloor rocks and sediments.