Abstract
Backscattered scanning electron micrograph and ultra small- and small-angle neutron scattering data have been combined to provide statistically meaningful data on the pore/grain structure and pore evolution of combustion metamorphic complexes from the Hatrurim basin, Israel. Three processes, anti-sintering roughening, alteration of protolith (dehydration, decarbonation, and oxidation) and crystallization of high-temperature minerals, occurred simultaneously, leading to significant changes in observed pore/grain structures. Pore structures in the protoliths, and in low- and high-grade metamorphic rocks show surface ( Ds) and mass ( Dm) pore fractal geometries with gradual increases in both Ds and Dm values as a function of metamorphic grade. This suggests that increases in pore volume and formation of less branching pore networks are accompanied by a roughening of pore/grain interfaces. Additionally, pore evolution during combustion metamorphism is also characterized by reduced contributions from small-scale pores to the cumulative porosity in the high-grade rocks. At high temperatures, small-scale pores may be preferentially closed by the formation of high-temperature minerals, producing a rougher morphology with increasing temperature. Alternatively, large-scale pores may develop at the expense of small-scale pores. These observations (pore fractal geometry and cumulative porosity) indicate that the evolution of pore/grain structures is correlated with the growth of high-temperature phases and is a consequence of the energy balance between pore/grain surface energy and energy arising from heterogeneous phase contacts. The apparent pore volume density further suggests that the localized time/temperature development of the high-grade Hatrurim rocks is not simply an extension of that of the low-grade rocks. The former likely represents the "hot spots (burning foci)" in the overall metamorphic terrain while the latter may represent contact aureoles.
| Original language | English |
|---|---|
| Pages (from-to) | 339-362 |
| Number of pages | 24 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 121 |
| DOIs | |
| State | Published - Nov 15 2013 |
Funding
Effort by H.-W.W., L.M.A., L.F.A., A.G.S., and G.R. was sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy . We acknowledge the support of the NCNR/NIST , U.S. Department of Commerce in providing the research neutron facilities used in this work. This work utilized facilities supported in part by the National Science Foundation under agreement No. DMR-0944772. Certain commercial equipment, instruments, materials and software are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the NIST, the Department of Energy, or the Oak Ridge National Laboratory, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. We would also like to thank Dr. Michael Schmid, Institut für Angewandte Physik, Technische Universität Wien, for his help with the ImageJ plugins for calculating the autocorrelation functions and scattering curves from the SEM/BSE images, and Prof. Yehoshua Kolodny, Institute of Earth Sciences, Hebrew University of Jerusalem, for his help with sample collection and for sharing his astonishing knowledge of the Hatrurim phenomenon. We also thank Dr. Mei Ding and the other anonymous journal reviewer for their comment on the manuscript.