Glacially-crushed quartz grains in late Quaternary deposits in the Virunga Mountains,Rwanda -indicators of wind transport from the north? |
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| Authors: | WILLIAM C MAHANEY |
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| Institution: | Geomorphology and Pedology Laboratory, Geography Department, Atkinson College, York University, 4700 Keele Street, North York, Ontario, Canada, M3J IPS |
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| Abstract: | Quartz sand grains in late Quaternary deposits of the Virunga Mountains, northwestern Rwanda, were found to contain glacial-crushing microtextures. Glacially-crushed subangular grains generally lack sharp edges, and carry mainly low frequency, linear crushing features. Because there are no known tills in the Virunga Volcanoes (and because quartz is rare in volcanic terrain), it is likely the grains were delivered by aeolian transport from the Ruwenzori Massif, -150 km to the north. All the grains studied are consistent with crushing under low shear stress, and over short transport distances, in alpine glaciers. An increase in the percentage of glacially-crushed quartz from Holocene to Pleistocene beds likely reflects on the increased strength of the paleowind system (trade winds) during the last glacial maximum. Alternatively, it could reflect on the increased source area for glacially-crushed grains resulting from an increase in the extent of the Afroalpine belt during the last glaciation. |
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