The basic assumptions made in the interpretation of the anisotropy of magnetic susceptibility (AMS) of lava flows, dykes and other tabular intrusive rocks have changed with time. This paper presents a historical account of those changes. Because several aspects of the AMS of these types of rocks are still open to debate, the historical perspective helps us to appreciate better the limitations that had to be faced at different times, therefore providing some clues that can be used to solve such controversies. Also, by benefiting from hindsight it is possible to devise alternative approaches that can be employed to interpret the AMS of these types of rocks. Although some adjustments to current models will be made as new results become available, it seems that at present the main commponents of the basic model of AMS in lava flows and tabular intrusive rocks have been finally reached, leaving behind most of the apparent contradictions found in earlier works. This progress is undoubtedly an important advance in our understanding of the nature of AMS in general.
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Magnetic Fabric: Methods and Applications
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.