Several types or grain sizes of ferromagnetic minerals can contribute to a rock's remanence and anisotropy of remanence. Each subpopulation may have a different fabric. Measuring anisotropy of partial anhysteretic remanent magnetization (ApARM) allows one to determine the anisotropy contribution of subpopulations with different coercivity distributions. Separating these contributions to remanence anisotropy can provide information about early versus late stages of deformation in fabric studies and is the basis for improved anisotropy corrections in paleomagnetic studies. Unfortunately, collecting multiple ApARM tensors on each specimen is time-consuming and not often done. Measuring a smaller number of carefully chosen ApARM tensors and obtaining the remaining tensors of interest by tensor calculation would be more efficient. This can only be done, however, when ApARM tensors are additive. Here we investigate the additivity of ApARM tensors in a range of lithologies, by measuring a total of seven ApARM and anisotropy of anhysteretic remanent magnetization (AARM) tensors for each specimen, and comparing the tensors calculated from a combination of ApARM tensors to the corresponding measured AARM. Differences in principal directions between measured and calculated tensors are often smaller than the confidence angles of the measurements. Mean anhysteretic remanences are additive to within ±5%. The anisotropy degree varies by ±30% (k′) or ±0.15 (P), and the shape parameter U by ±0.4. These error limits will help to determine whether or not it is necessary to measure each ApARM tensor in future fabric or paleomagnetic studies, or if these tensors can be calculated from a smaller set of measurements.
Bibliographical noteFunding Information:
We thank Frantisek Hrouda and two anonymous reviewers for their critical evaluation of the manuscript. This study was supported by the Swiss National Science Foundation (SNSF) project 167608. Measurements were performed at the Institute for Rock Magnetism (IRM) at the University of Minnesota. The IRM is a U.S. National Multi-user Facility supported through the Instrumentation and Facilities program of the National Science Foundation (NSF), Earth Sciences Division, and by funding from the University of Minnesota. Specimens were collected for previous studies supported by SNSF project 155517, NSF-EAR 0309686 (to Paul Renne and Gary Scott), NSF-0911683 (to Joshua M Feinberg and Julie Bowles), and Norwegian Research Council 222666 (to Suzanne McEnroe). Archaeological specimens courtesy of the Tel Hesi Regional Project. This is IRM publication 1805. Data can be obtained from the supporting information of this paper, or downloaded from the MagIC database, https://doi.org/10.7288/V4/MAGIC/16724.
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- magnetic fabric
- remanence anisotropy