Abstract
Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using 57Fe synchrotron Mössbauer spectroscopy. Spatial resolution of ~10–20 μm was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1 h. Spectra were recorded every 5–10 μm, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the “cloudy zone.” Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X‐ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed.
Highlights
There has been increased interest in the magnetism of meteoritic Fe-Ni alloys (Uehara et al 2011; Bryson et al 2014a, 2014b, 2015; Dos Santos et al 2015; Nichols et al 2016)
As the matrix was found to be nonmagnetic, there remains an unresolved issue of discrepancy between Mo€ssbauer spectroscopy measurements and methods such as X-ray photoemission electron microscopy (XPEEM) and electron holography
The use of the cloudy zone” (CZ) to extract paleomagnetic data by Bryson et al (2015) was based on a simple thermodynamic argument, linking the biased populations of the six possible magnetic states of tetrataenite islands to the applied magnetic field and the island volume. These calculations did not consider explicitly the magnetic state of the matrix phase, the presence of a magnetic matrix phase was included in the image simulations in order to better reproduce the experimental XPEEM images
Summary
There has been increased interest in the magnetism of meteoritic Fe-Ni alloys (Uehara et al 2011; Bryson et al 2014a, 2014b, 2015; Dos Santos et al 2015; Nichols et al 2016). More advanced, higher resolution magnetic imaging methods, as well as chemical extraction of particular metal phases, have shown that there are hard ferromagnetic phases present that can potentially retain useful paleomagnetic signals (Bryson et al 2014a; Dos Santos et al 2015). This discovery has renewed interest in meteorite magnetism, with attention focusing most intensely on the nanoscale intergrowth known as the “cloudy zone” (CZ) (Reuter and Williams 1988; Yang et al 1997a, 1997b; Bryson et al 2014b).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
