TY - JOUR
T1 - Dissolution of primary basaltic minerals in natural waters
T2 - saturation state and kinetics
AU - Gislason, Sigurdur R.
AU - Arnórsson, Stefán
N1 - Funding Information: The work described in this article has been supported by the Icelandic Science Foundation and the Research Foundation of the University of Iceland. Audur Andr6st6ttir is thanked for performing some of the ICP chemical analyses. Reviews of an earlier version of this paper by Scott A. Wood and an anonymous reviewer is sincerely appreciated.
PY - 1993/3/15
Y1 - 1993/3/15
N2 - The state of saturation of olivine, orthopyroxene and plagioclase of variable composition has been assessed in various types of natural waters in Iceland including river waters, groundwater and geothermal waters with temperatures up to 250°C. The stability of olivine and orthopyroxene decreases with increasing Mg content. Similarly, the stability of plagioclase decreases with increasing anorthite content. The river waters which are representative of the weathering environment are always undersaturated with both olivine and orthopyroxene, the degree of undersaturation being dominated by the water pH. All river waters tend to dissolve olivine of the composition encountered in basalts according to the linear rate law and orthopyroxene when the pH is < 8. Groundwaters, which have a higher pH, appear to dissolve orthopyroxene and Fc-rich olivine according to the slower near-equilibrium dissolution rate law. In river waters and groundwaters Na-rich plagioclase is stable but when Ca-rich it is close to equilibrium or slightly undersaturated. The state of saturation is independent of pH in the range occurring in these waters (pH 7-10). Geothermal waters of high temperature (> 200°C) are undersaturated with olivine, orthopyroxene and plagioclase, the first two particularly when Fe rich, and sufficient to cause olivine to dissolve according to the linear rate law. At intermediate temperatures (50-150°C) the geothermal waters are close to equilibrium with these minerals except for Mg-rich olivine. It seems likely that dissolution of glass from basalt, which is very reactive, will favor stability of the igneous minerals.
AB - The state of saturation of olivine, orthopyroxene and plagioclase of variable composition has been assessed in various types of natural waters in Iceland including river waters, groundwater and geothermal waters with temperatures up to 250°C. The stability of olivine and orthopyroxene decreases with increasing Mg content. Similarly, the stability of plagioclase decreases with increasing anorthite content. The river waters which are representative of the weathering environment are always undersaturated with both olivine and orthopyroxene, the degree of undersaturation being dominated by the water pH. All river waters tend to dissolve olivine of the composition encountered in basalts according to the linear rate law and orthopyroxene when the pH is < 8. Groundwaters, which have a higher pH, appear to dissolve orthopyroxene and Fc-rich olivine according to the slower near-equilibrium dissolution rate law. In river waters and groundwaters Na-rich plagioclase is stable but when Ca-rich it is close to equilibrium or slightly undersaturated. The state of saturation is independent of pH in the range occurring in these waters (pH 7-10). Geothermal waters of high temperature (> 200°C) are undersaturated with olivine, orthopyroxene and plagioclase, the first two particularly when Fe rich, and sufficient to cause olivine to dissolve according to the linear rate law. At intermediate temperatures (50-150°C) the geothermal waters are close to equilibrium with these minerals except for Mg-rich olivine. It seems likely that dissolution of glass from basalt, which is very reactive, will favor stability of the igneous minerals.
UR - https://www.scopus.com/pages/publications/0027456209
U2 - 10.1016/0009-2541(93)90122-Y
DO - 10.1016/0009-2541(93)90122-Y
M3 - Article
SN - 0009-2541
VL - 105
SP - 117
EP - 135
JO - Chemical Geology
JF - Chemical Geology
IS - 1-3
ER -