Phase equilibria involving humite minerals in impure dolomitic limestones |
| |
Authors: | Jack M Rice |
| |
Institution: | (1) Department of Geology, University of Oregon, 97403 Eugene, Oregon, USA |
| |
Abstract: | The natural occurrence of critical assemblages among the phases clinohumite, calcite, dolomite, tremolite, forsterite, diopside,
chlorite, and spinel in metamorphosed impure limestones, together with experimental and thermodynamic data, permits the calculation
of phase equilibria governing the stability of clinohumite in terms of the variables P, T, and composition of a CO2-H2O-HF fluid. Equilibrium constant expressions are given for 23 equilibria that describe the stable phase relations between
the above phases. Pure OH-clinohumite is considered to be metastable at relatively low pressures. The occurrence of clinohumite
in natural marbles is the result of nonideal fluorine substitution which increases the stability of clinohumite. The stability
field for clinohumite +calcite, governed primarily by the equilibrium 4forsterite+dolomite+H2O = clinohumite+calcite +CO2, expands to more CO2-rich fluid compositions with increasing fluorine contents and decreasing total pressure. The F/(F+OH) ratio of clinohumite
coexisting with calcite, dolomite, and forsterite is a sensitive indicator of the composition of the mixedvolatile fluid phase.
The thermodynamic model is in good agreement with observed phase relations and can be used to gain useful information concerning
the P-T-X
fluid conditions responsible for the formation of clinohumite. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|