Isotopic ratios and release rates of strontium measured from weathering feldspars

摘要: Based upon dissolution of feldspars under controlled laboratory conditions, we conclude that Sr release, at pH 3, is neither consistently stoichiometric nor constant for the measured. Bytownite, microcline, and albite all initially release rates which are 5 (bytownite) to 160 (microcline) times faster than steady-state rates. The Sr/Si ratios in early effluents significantly elevated compared bulk mineral values. 87Sr/86Sr measured effluent higher bytownite, but lower microcline albite. feldspar powders also changed markedly during three phases. In part, nonstoichiometric can be explained by presence secondary phases (exsolution lamellae or minute quantities accessory phases) surface leaching. Although infer these eventually with isotopic composition roughly equal steady-state, dissolve extremely different (bytownite releases a rate ∼102 103 3). Therefore, mixture feldspars, other minerals exhibiting vast differences rate, will distinctly from whole rock. addition, initial > albite) differ microcline), complicating analysis weathering solutions. Log (rate constants) albite, decrease −13.5 −16.4 −17.2 (mol cm−2 s−1). Interpretation catchment scale riverine on basis whole-rock isotopes is, therefore, problematic best, would require normalization relative Sr-contributing phases. We argue abraded particles formed naturally, example, glaciation, show this transient release. However, once completed (perhaps 102 yr after abrasion), as long solution chemistry remains relatively constant, cations including Sr, expected. most likely way, increase fluxes major radiogenic create highly flushed (and, far equilibrium) water-rock systems such glacial sediments soils, reactive (e.g., carbonate, plagioclase, biotite) containing significant strontium.