How deformed are weakly deformed mudrocks? Insights from magnetic anisotropy
Josep M. Parés, 2004. "How deformed are weakly deformed mudrocks? Insights from magnetic anisotropy", Magnetic Fabric: Methods and Applications, F. Martín-Hernández, C. M. Lüneburg, C. Aubourg, M. Jackson
Download citation file:
For over thirty years the anisotropy of magnetic susceptibility (AMS) has been exploited in rock fabric studies. Our knowledge of the mechanisms leading to magnetic fabric development in deformed rocks has grown substantially, even though some details are still under debate. This paper reviews recent developments in AMS studies applied to the characterization of early deformation stages in mudrocks. From the current data set of AMS in rocks deformed at low temperature and low pressure it is possible to revisit the concept of weakly deformed rocks. We contend that weak deformation in mudrocks and the appearance of magnetic cryptofabric are concatenated. Furthermore, magnetic anisotropy studies in weakly deformed rocks suggest that cleavage fabric, the most common planar fabric in deformed mudrocks, builds up gradually from the earliest stages of deformation rather than suddenly at some strain threshold.
Figures & Tables
Fabric is a ubiquitous and significant feature of geological materials. The processes involved in the formation and deformation of rocks and sediments leave their mark on the orientations of the constituent mineral grains. Petrofabrics thus provide essential keys to understanding the history of geological materials. Magnetic anisotropy is directly related to petrofabric, and has become one of the most rapid, sensitive and widely used tools for its characterization. The relationship between magnetic fabric and petrofabric is complex and depends on various factors including the composition, concentration and grain size of mineral grains. Ongoing research in geological applications is paralleled by studies of the fundamental mineral magnetic phenomena involved.
The papers in this book represent the current state of investigations in magnetic anisotropy studies as a discipline that integrates geological interpretations, mineral fabric development, technical advances and rock-magnetic properties.