Low-temperature AMS and the quantification of subfabrics in deformed rocks

Abstract

We evaluate the application and significance of Low-Temperature Anisotropy of Magnetic Susceptibility (LT-AMS) measurements in deformed mudrocks. Originally conceived as a way to enhance paramagnetic relative to ferromagnetic susceptibility, LT-AMS studies offer significant potential in constraining the coexistence of subfabrics that are due to phyllosilicate grains with different preferred orientations. In this study we report a detailed procedure to obtain such directional susceptibilities, measuring samples in multiple orientations at liquid nitrogen temperatures in order to determine the LT-AMS. Due to unequal changes of magnetic susceptibility in micas at low-temperature, the enhancement of standard AMS at low-temperature better separates interacting fabrics in natural rocks, particularly depositional fabrics versus deformational fabrics. LT-AMS is a non-destructive technique that readily offers an ability to separate ferromagnetic and paramagnetic fabrics, and allows the characterization and quantification of multiple fabrics in natural rocks.