Basalt weathering in Central Siberia under permafrost conditions

• Main Authors: /Pokrovsky, O.S., /Schott, J., Kudryavtzev, D.I., /Dupré, Bernard
• Format: Text
• Language: English
• Published: 2005
• Subjects: permafrost; Siberia
• Online Access: https://www.documentation.ird.fr/hor/fdi:010035850

Chemical weathering of basalts in the Putorana Plateau, Central Siberia, has been studied by combining chemical and mineralogical analysis of solids (rocks, soils, river sediments, and suspended matter) and fluid solution chemistry. Altogether, 70 large and small rivers, 30 soil pore waters and groundwaters and over 30 solids were sampled during July to August 2001. Analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the Russian Hydrological Survey allowed rigorous estimation of mean annual major element concentrations, and dissolved and suspended fluxes associated with basalt weathering. For the rivers Tembenchi and Taimura that drain monolithologic basic volcanic rocks, the mean multiannual flux of total dissolved cations (TDS_c = Ca + Mg + Na + K) corrected for atmospheric input is 5.7 +/- 0.5 t/km(2)/yr. For the largest river Nizhniya Tunguska-draining essentially basic rocks-the TDS_c is 6.1 +/- 1.5 t/km(2)/yr. The overall CO2 consumption flux associated with basalt weathering in the studied region (similar to 700,000 km(2)) achieves 0.08 x 10(12) mol/yr, which represents only 2.6% of the total CO2 consumption associated with basalt weathering at the Earth's surface. The fluxes of suspended matter were estimated as 3.1 +/- 0.5, 9.0 +/- 0.8, and 6.5 +/- 2.0 t/km(2)/yr for rivers Taimura, Eratchimo, and Nizhniya Tunguska, respectively. Based on chemical analyses of river solutes and suspended matter, the relative dissolved versus particulate annual transport of major components is C-inorg >= C-org > Na + K > Ca > Mg > Si > Fe >= Mn >= Ti >= Al which reflects the usual order of element mobility during weathering. According to chemical and mineralogical soil and sediment analyses, alteration of basalt consists of (1) replacement of the original basaltic glass by Si-Al-Fe rich amorphous material, (2) mechanical desegregation and grinding of parent rocks, leading to accumulation of "primary" hydrothermal trioctahedral ...