Since Graham [1954; 1967] demonstrated in the 1950s and 1960s that magnetic anisotropy was a quick and non-destructive way of measuring rock fabric, magnetic fabric measurements have become increasingly prevalent in the study of earth and environmental processes (see Table 1 for definitions of magnetic terms). The accomplishments of U.S. workers over the past 4 years show that the U.S. community continues to contribute to the growth and development of the field. In addition to the more traditional anisotropy of magnetic susceptibility (AMS) measurements work is branching out to include anisotropy of remanence studies, particularly anisotropy of anhysteretic remanence (AAR) [ McCabe et al., 1985] and anisotropy of isothermal remanence (AIR), since these parameters can be tied directly to the remanence-carrying grains in a rock and hence have relevance to the effects of magnetic fabric on natural remanent magnetization (NRM). Along with this shift is the realization, as a result of combining nonmagnetic observations (e.g.. scanning electron microscopy (SEM), finite strain measurements) with rock magnetic measurements (e.g. hysteresis parameters), that magnetic mineral composition (paramagnetic and ferromagnetic) has an important control on magnetic anisotropy.
There has also been growth in the number of U.S. workers and laboratories conducting magnetic fabric studies in the last four years. In the last quadrennium Jackson and Tauxe [1991] reported less than 10 U.S. workers involved in magnetic fabric research. Now there are more than twice that number working in about a dozen U.S. laboratories. This review will emphasize the work done in U.S. laboratories over the past 4 years. Work done by non-U.S. scientists has been included to set the proper context for the U.S. studies.
Magnetic fabric measurement of bulk rock strain has been the major thrust of the U.S. community in the past quadrennium. Over half of the magnetic anisotropy publications in the last four years have been concerned with the measurement and quantification of rock deformation. Correction of NRMs affected by deformation has been a significant part of this work, particularly burial compaction effects. The major strategic goal of these studies has been to develop a quick, nondestructive method of measuring both the orientation of the principal strain directions in a rock and the magnitude of strain so that the extent and character of major tectonic events (folding and faulting, mountain building) could be established.
The remaining magnetic fabric activity during the past four years involved about equal numbers of studies of igneous flow fabrics and the development of new measurement and sampling techniques. The igneous fabric studies involved both intrusive rocks (dikes) and extrusive rocks (predominately tuffs). One of the strategic goals in these studies was to locate ancient, now completely eroded, volcanic sources of major ash fall events.
Only two studies in the last quadrennium addressed sedimentary fabrics, however, these studies show the great potential of magnetic fabric measurements for studying ancient and present day environmental systems.
Finally, several excellent reviews of magnetic fabric work have appeared in the last four years. Jackson [1991] provides a summary which emphasizes the complexity of mineralogic sources that can control magnetic anisotropy. Rochette et al. [1992] review how rock magnetic experiments may be used to interpret magnetic fabric results. During the quadrennium a new book, Magnetic Anisotropy of Rocks [ Tarling and Hrouda, 1993] has appeared. It is a reference for magnetic fabric measurement and statistical analysis techniques and also provides examples of how magnetic fabric studies can be applied to deformed, igneous and sedimentary rocks.