Weathering of a quaternary glass-rich basalt in Bakrit, Middle Atlas Mountains, Morocco. Comparison with a glass-poor basalt
1998; Taylor & Francis; Volume: 11; Issue: 5 Linguagem: Inglês
10.1016/s0985-3111(99)80010-2
ISSN1778-3593
AutoresLhoucine Karrat, Alain Perruchot, Jean-Jacques Macaire,
Tópico(s)earthquake and tectonic studies
ResumoAbstract We compared the disintegration processes and mineralogic and chemical evolution pathways of two Quaternary basalts at Bakrit and Ifrane, weathered in the same physiographic and hydrologic conditions, but differing in texture according to the quantity of glass present. At Bakrit, quite abundant glass favoured the formation of a microfissure network throughout the rock and its disintegration without any distinct weathering front. As a result, basaltic sand with polymineral grains and a clayey-silty matrix were produced. At Ifrane, weathering of a glass-poor basalt produced only a clayey-silty saprolite. In glass-rich basalts, secondary minerals formed in microfissures and were 2/1 clay-mineral rich. In glass-poor basalts, secondary minerals formed mainly within primary minerals and were 1/1 clay-mineral rich. Because glass could be easily dissolved, it protected the minerals of close chemical composition, especially the plagioclases. The order of basalt-mineral weathering (olivine, labrador, augite, Fe-Ti oxides) was modified when glass was abundant (glass, olivine, augite, labrador, Fe-Ti oxides).
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