Magnetic Fabric of Freshly Consolidated Lacustrine Mudstones Constrains the “Present-Day” Strain Field

The anisotropy of magnetic susceptibility (AMS) has great potential in deciphering weakly deformed fabrics that may be related to tectonic stress. Previous studies have suggested that magnetic lineation is a good indicator of paleostrain direction. It is unclear whether the magnetic fabric can also be used to indicate the present-day strain field. To verify this idea, we measured the AMS of freshly consolidated lacustrine fine-grained and horizontal-bedding sediments at 11 locations in the Qaidam and Chaka-Gonghe basins of the northeastern Tibetan Plateau and compared it with the present-day strain field deduced from the Global Position System (GPS) velocity field. The AMS of these sediments appears a weakly deformed fabric with clear foliation and lineation. The optical and scanning electron microscope (SEM) images of the thin sections show that the elongated particles display an orientation parallel or subparallel to the magnetic lineation direction, confirming the effectiveness of magnetic lineation. The magnetic lineations of both room-temperature and low-temperature AMS are roughly perpendicular to the GPS-derived tectonic shortening direction within the error range, suggesting that the AMS of freshly consolidated muds is an effective indicator of the present-day strain field, even if the sediments appear undeformed at the outcrop scale.