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Kyanite preserves prograde and retrograde metamorphic events as revealed by cathodoluminescence, geochemistry, and crystallographic orientation
Date: 2021-01-01
Creator: Emily M. Peterman
Michael J. Jercinovic
Rachel J. Beane
Cameron B. de Wet
Access: Open access
- Cathodoluminescence (CL) images of kyanite reveal several internal textures, including sector zoning, oscillatory zoning, and cross-cutting relationships among different domains. Many textures observed in kyanite correspond to discrete events, thereby connecting kyanite textures to the pressure–temperature (P–T) history of the rock. To evaluate the record of metamorphism preserved by kyanite, metapelites were selected from three different orogens that reflect P–T conditions ranging from amphibolite to ultrahigh-pressure (UHP) facies. Cross-correlation of variations in CL intensity, chemistry, and crystal orientation within kyanite indicate the following findings. First, the preservation of original growth zones in kyanite from poly-metamorphic rocks demonstrates that growth zoning in kyanite persists through metamorphic events and is not erased by diffusion or complete recrystallization. In some samples, kyanite retains evidence of its reaction history during growth. Second, measured changes in absolute crystallographic orientation do not correspond with changes in CL intensity in any of the measured samples, including kyanite twins. Third, both kink banding and undulatory extinction are present across all samples, consistent with rotation about in the (100)[001] slip system. Kyanite from (U)HP samples exhibits higher amplitude undulations than kyanite from lower-grade lithologies, suggesting that crystallographic orientation data may provide complementary insight about deformation along the P–T path. Fourth, specific CL and trace element signatures in kyanite can be correlated with discrete metamorphic histories; yet, CL intensity and colour are affected by multiple elements, not a single controlling element. In sum, multiple generations of kyanite can be identified by careful cross-correlation of CL and geochemical data, and when combined with crystal orientation data, kyanite provides a robust record of a rock's P–T evolution.
The organization (re)invented by its blogs
Creator: Alex Primo
Access: Open access
- This article discusses how interactions in organizational blogs participate in the emergence of the organization itself. Based on the principles of The Montreal School of organizational communication, the paper reflects on how the recursive relationship between texts and conversations in blogs, according to their affordances, mobilizes the organization and contributes to its continuing creation. In order to conduct this argument, the concept of social media, uses of organizational blogs and the main contributions of The Montreal School are analyzed. Finally, this article demonstrates how blogs contribute to the definition of the organization. Beyond their promotional potential, the blog’ role as co-creator of the organization is highlighted.