Abstract

Field observations in the Meatiq Dome, Eastern Desert, Egypt, show that amphibolite weathers to form massive outcrops and dense desert pavements that are extensively varnished. Laboratory-based reflectance spectra of representative samples (covering 5 cm2) and spectra extracted from Landsat thematic mapper data (covering 2.25 x ∼104m2) confirm that varnish dominates the reflectance properties of amphibolite outcrops. Field, laboratory, and Landsat data indicate that granite gneiss weathers to expose mainly bare rock, whereas granitic out-crops evolve to a mix of rock and locally generated sediment. Penetrative foliation in quartz phyllonite leads to production of slab-shaped clasts that cover the surface. The data show that mass wasting of the slabs results in a mix of rock, varnish, and sediment exposures. Outcrop reflectance properties for arid regions are thus dependent on both rock mineralogy and texture, because both parameters modulate bedrock weathering and erosion.

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