Kinetics of biotite dissolution and Fe behavior under low O2 conditions and their implications for Precambrian weathering |
| |
| Authors: | Hirokazu Sugimori Takashi Murakami |
| |
| Institution: | Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan |
| |
| Abstract: | Biotite dissolution experiments were carried out to better understand the dissolution kinetics and Fe behavior under low O2 conditions, and to give an insight into the Precambrian weathering. Mineral dissolution with a continuous flow-through reactor was employed at 25 °C for up to 65 days varying partial pressure of atmospheric oxygen (PO2), pH (6.86 and 3.01) and Fe content in mineral (1.06 and 0.11 mol of Fe per O10(OH,F)2 for biotite and phlogopite, respectively) independently for the examination of their effects on biotite dissolution. Low PO2 conditions were achieved in a newly developed glove box (PO2 ? 6 × 10−4 atm; referred to as anoxic conditions), which was compared to the present, ambient air conditions (0.2 atm of PO2; oxic conditions). The biotite dissolution rate was slightly faster under anoxic conditions at pH 6.86 while it was not affected by PO2 at pH 3.01. There was no direct effect of Fe content on dissolution rate at pH 6.86 while there was a small difference in dissolution rate between biotite and phlogopite at pH 3.01. The 1.5 order-of-magnitude faster release rate of Fe under anoxic conditions for biotite dissolution at pH 6.86 resulted from the difference in ratio of Fe3+ precipitates remaining in the reactor to Fe dissolved (about 60% and 100% under anoxic and oxic conditions, respectively), which is caused mainly by the difference in PO2. The results infer that the Fe2+ and Fe3+ contents in the Paleoproterozoic paleosols, fossil weathering profiles, are reflected by atmospheric oxygen levels at the time of weathering. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
