Publication Type
Journal
Journal Name
Geochimica et Cosmochimica Acta
Publication Date
Page Numbers
339 to 362
Volume
121
Issue
121
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 lowand
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.