Chemistry, reaction mechanisms and micro-structures during retrograde metamorphism of gedrite-biotite-plagioclase bearing rocks from Bergslagen, south-central Sweden |
| |
Authors: | Embaie A Ferrow Magnus Ripa |
| |
Institution: | a Department of Mineralogy and Petrology, University of Lund, Sölvegatan 13, S-223 62, Lund, Sweden b Geological Survey of Sweden, Box 670, S-751 28, Uppsala, Sweden |
| |
Abstract: | The Proterozoic rhyolitic volcanics constituting the foot-wall rocks in the Stollberg ore-field, Bergslagen, south-central Sweden, locally contain gedrite altered to chlorite and serpentine, biotite altered to chlorite and plagioclase altered to epidote. The intergrowths between the host gedrite and the chlorite/serpentine inclusions are oriented with the a* of gedrite parallel to the c* of serpentine and chlorite. The biotite has been altered to chlorite by brucitization of both the K-interlayer and talc-like layer. In both cases the net change in volume during chloritization is small. The assumption that Al is conserved during alteration of gedrite and biotite agrees very well with the micro-structures and orientation relations observed by transmission electron microscopy. Normalizing the chlorite to 1.00 mole, the overall chemical change that took place during the retrograde metamorphism of the Stollberg rocks can be written as: 0.84Ged+0.14Bio+0.65Mg+4.76H2O+0.42H=1.00Chl+0.57Alb+0.72Fe+0.01Na+0.12K+0.01Ti+0.05Mn+0.95H4SiO4 The reaction results in ca 9% increase in volume for the solid phases. Thus, a slightly acidic Mg-rich fluid started the reaction and, upon leaving the system, the metasomatic fluid was enriched in Na, Fe, K, and Si. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|