Publication: Impactos en Mauritania: nuevos datos mineralógicos, texturales y geoquímicos de las megabrechas de Richat y del cráter meteorítico de Aouelloul
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2008
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Sociedad Geológica de España.
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Abstract
Se presentan los primeros resultados de la campaña científica Mauritania’ 2007, en relación con la investigación de cráteres y eventos de impacto. Los estudios se centraron en la caracterización, mediante microscopía de luz transmitida y reflejada, DRX, SEM-EDX, ICP-MS, FT-IR y espectroscopia Raman, de las megabrechas de la espectacular (aunque controvertida) estructura de Richat y en el cráter meteorítico de Aouelloul. Los minerales identificados en las brechas son cuarzo, analcima, goethita, hematites, calcita, dolomita y sulfuros (pirita). Sus texturas incluyen bandeados y agregados colomorfos, texturas anubarradas, rellenos fisurales con recristalizaciones de cuarzo y fragmentos heterométricos de los granos/cristales de cuarzo con bordes y golfos de corrosión. En algunas muestras de Richat se ha observado mosaicismo de los granos de cuarzo y carbón amorfizado. Las brechas muestran heterogeneidad geoquímica con variaciones importantes de algunos elementos (principalmente Na, K, Ti, Cr, V, Co, Cu, Sr, Ba y Ni). En Aouelloul se han caracterizado las rocas intensamente deformadas del interior del cráter (se ha detectado mosaicismo) y los fragmentos ferruginizados (goethita y cuarzo) que aparecen dispersos alrededor de la estructura. También se ha realizado espectroscopia Raman de los fragmentos vítreos ricos en sílice, que muestran clara amorfización.
This contribution presents first results from the research on meteorite impact craters and events in Mauritania. Megabreccias from the remarkable (and controversial) Richat structure and materials from the Aoulloul impact crater were studied by the combination of transmitted and reflected light microscopy, XRD, SEM-EDX, ICP-MS, FT-IR and Raman spectroscopy. Quartz, analcime, goethite, haematite, calcite, dolomite and sulphides (pyrite) were identified as main minerals of the megabreccias. Their textures comprise collomorphous layers and aggregates, cloudy textures, infillings of veins and cracks and quartz recrystallization, and heterometric quartz grains showing corroded gulfs. Some samples from Richat show mosaicism in quartz and amorphized carbon. In general, the megabreccias are geochemically heterogeneous, displaying significant variations in some elements (mainly Na, K, Ti, Cr, V, Co, Cu, Sr, Ba y Ni). Intensely deformed rocks (quartz mosaicism), and iron rich and glass fragments from the Aouelloul impact crater were also studied.
This contribution presents first results from the research on meteorite impact craters and events in Mauritania. Megabreccias from the remarkable (and controversial) Richat structure and materials from the Aoulloul impact crater were studied by the combination of transmitted and reflected light microscopy, XRD, SEM-EDX, ICP-MS, FT-IR and Raman spectroscopy. Quartz, analcime, goethite, haematite, calcite, dolomite and sulphides (pyrite) were identified as main minerals of the megabreccias. Their textures comprise collomorphous layers and aggregates, cloudy textures, infillings of veins and cracks and quartz recrystallization, and heterometric quartz grains showing corroded gulfs. Some samples from Richat show mosaicism in quartz and amorphized carbon. In general, the megabreccias are geochemically heterogeneous, displaying significant variations in some elements (mainly Na, K, Ti, Cr, V, Co, Cu, Sr, Ba y Ni). Intensely deformed rocks (quartz mosaicism), and iron rich and glass fragments from the Aouelloul impact crater were also studied.