Cordierite formation during the experimental reaction of plagioclase with Mg-rich aqueous solutions
MetadataShow full item record
The reaction between plagioclase (labradorite and oligoclase) and Mg-rich aqueous solutions was studied experimentally at hydrothermal conditions (600–700 °C, 2 kbar). During the experiments, plagioclase grains were readily converted to cordierite and quartz within 4 days. The cordierite crystals had well-developed polyhedral shapes, but showed skeletal internal morphologies suggestingthat the initial growth occurred fast under high-driving-force conditions. In pure MgCl2 solutions (0.5–5 M), plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that Al was to some extent mobile in the fluid. Cordierite crystals formed at 700 °C showed orthorhombic symmetry, whereas those formed at 600 °C dominantly persisted in the metastable hexagonal form suggesting a strong increase in Al, Si ordering speed between 600 and 700 °C. The thermodynamic evolution of the fluid–solid system ultimately resulted in stabilization of Ca-rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains. Cordierite was also observed to form when Mg was added to a potentially albitizing Na-silicate-bearing solution. In that case, cordieriteprecipitation appeared to be more closely coupled to plagioclase dissolution, and secondary alteration of remnant plagioclase grains did not occur most likely due to armouring of the plagioclase by the cordierite overgrowth. The fast reaction rates observed in our experimental study have potential implications for Mg-metasomatism as a rockforming process.
Showing items related by title, author, creator and subject.
P-T-t evolution of pelitic gneiss from the basement underlying the Northwestern Ordos Basin, North China Craton, and the tectonic implicationsGou, Long-Long; Zhang, C.; Brown, M.; Piccoli, P.; Lin, H.; Wei, X. (2016)© 2016 Elsevier B.V.. Using petrography, phase equilibria modeling and in situ (U-Th)-Pb monazite geochronology, we show that pelitic gneiss from close to the bottom of the Qitan1 borehole in the northwest of the Ordos ...
Walsh, A.; Kelsey, D.; Kirkland, Chris; Hand, M.; Smithies, R.; Clark, Chris; Howard, H. (2015)The ~ 120,000 km2 Musgrave Province forms part of a continuous Musgrave–Albany–Fraser mid-late Mesoproterozoic orogenic system that transects central and southern Australia, and continues into formerly contiguous Antarctica. ...
Osumilite–melt interactions in ultrahigh temperature granulites: Phase equilibria modelling and implications for the P–T–t evolution of the Eastern Ghats Province, IndiaKorhonen, Fawna; Brown, M.; Clark, Christopher; Bhattacharya, S. (2013)The exposed residual crust in the Eastern Ghats Province records ultrahigh temperature (UHT) metamorphic conditions involving extensive crustal anatexis and melt loss. However, there is disagreement about the tectonic ...