Igneous fabrics in cumulates can be developed during accumulation (deposition from crystal-laden density flows) or from deformation of a crystal mush during compaction or shearing. These dynamic processes play a fundamental role in determining the final textural and chemical character of cumulates, and therefore have direct bearing on how fractional crystallization proceeds. Unfortunately, the difficulty in acquiring quantitative fabric data has precluded more than relative interpretations of these fabrics. To help remedy this situation, we have been exploring the use of magnetic data as a rapid means for determining petrofabrics and therefore the potential to quantitatively examine a large number of samples. A variety of samples from the Archean Stillwater layered intrusion (Above field photo is from Camp Lake in the Beartooth Range, Montana) have been used to test the correspondence between magnetic fabrics and petrofabrics. Results from one of these samples (a well-foliated gabbronorite) illustrate the close correspondence between the two types of data.



Above Grain boundary tracings from a well-foliated gabbronorite from the Stillwater complex. Tracings of crystallographic features on three orthogonal sections are used to derive a 3D fabric estimate (center; lower hemisphere equal area projection). At right, corresponding remanence anisotropy data for this sample.

Related publications:

Gee, J.S., Meurer, W.P., Selkin, P.A. and M.J. Cheadle, 2004, Quantifying three-dimensional silicate fabrics in cumulates using cumulative distribution functions, J. Petrology, 45: 1983-2009.
Selkin, P.A., Gee, J.S., Tauxe, L., Meurer, W.P. and A. Newell, 2000, The effect of remanence anisotropy on paleointensity estimates: a case study from the Archean Stillwater Complex, Earth Planet. Sci. Lett., 183, 403-416.

Recent and ongoing research projects:

1. A paleointensity record from the ocean crust
2. Mapping sea surface magnetic anomalies
3. Characterizing the time-averaged magnetic field
4. Long term variations in geomagnetic intensity
5. Magnetization of meteorites and lunar samples
6. Applications of magnetic data to fabric development in cumulates