Sequential extraction of labile elements and chemical characterization of a basaltic soil from Mt. Meru,Tanzania |
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| Institution: | 1. Faculty of Geology, Moscow State University, Leninskie Gory 1, Moscow, 119991, Russia;2. V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia;3. ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia;4. Institute of Experimental Mineralogy, Russian Academy of Sciences, ul. Institutskaya 4, Chernogolovka, 142432, Moscow Region, Russia;5. School of Earth Sciences, the University of Melbourne, Parkville, VIC 3010, Australia;6. Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh’yanovoi 6a, Ulan-Ude, 670047, Russia;7. Buryat State University, ul. Smolina 24a, Ulan-Ude, 670000, Russia |
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| Abstract: | We conducted a modified Bureau Commun Reference (BCR) sequential extraction on a basaltic soil (phono-tephrite) from Mt. Meru in Northern Tanzania in order to determine the relative contribution of water soluble, carbonate and exchangeable, oxide and organic fractions to the bulk composition of the soil. Elemental compositions were determined by ICP-MS and corrected for loss on ignition. Relatively immobile elements, such as Zr, Hf and Al, are enriched by 10–30% compared to the unweathered protolith, consistent with soil formation being accompanied by mass loss due to chemical weathering. However, superimposed on this mass loss appears to be enrichment of elements such as Fe, Ca and Mg, especially towards the surface. In some cases, the bulk concentrations of these elements at the surface exceed that of the protolith. These data suggest that the surface of the Meru soil columns may have experienced “re-fertilization” by the deposition of volcanic ash. From the carbonate and exchangeable extraction, we found evidence of clay rich horizons which may sequester as much as 5% of the bulk K. The concentration of calcium carbonate appears to decrease with depth, but the largest incorporation of Sr and Ba into carbonates occurs below 114 cm. Fe and Mn oxides scavenge more than 10–20% of total Ti, V, Co, Cu, Zr and Pb below 114 cm. The organic fraction sequestered significant fractions of total Al, Cu, REE’s and Pb throughout the soil column. |
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