Research Interests

Mass tranfer, mineral evolution and pororsity  generation during fluid-rock interaction in crysalline basement rock

Research Collaboratores:
Prof. Dr. Kurt Bucher, Institute for Geosciences Freiburg University, Germany


Low-grade mineral assemblages are the key to the appreciation of water-rock interaction in hydrothermal and geothermal systems located in granites and gneisses. Zeolite formation is an important process in rocks of the continental crust. It takes place at temperatures below 250°C under hydrothermal conditions. A detailed study of the mineralogical, chemical and petrological evolution of crystalline basement rocks in Arvigo was performed to assess information about the evolution of fluid-rock interaction during uplift of the Alpine orogen. The Arvigo fissures contain the assemblage epidote, prehnite, chlorite and various species of zeolites.
Fluid rock interaction takes place along a retrograde exhumation path which is characterized with decreasing temperature by: (1) coexisting prehnite/epidote, that reveals temperature conditions of 330 - 380°C, (2) chlorite formation at temperature of 333 ± 32°C and (3) formation of zeolites <250°C. The formation of secondary minerals is related to the hydrothermal replacement reaction during albitization and chloritization that releases components for the formation of Ca-Al silicates and form a distinct reaction front. The fluid-rock interaction is associated with a depletion of Al2O3, SiO2, CaO, Fe2O3 and K2O in the altered wall rock. The reaction is associated with an increase in porosity up to 14.2 ± 2.2 %, caused by the volume decrease during albitization and the removal of chlorite. The propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution-reprecipitation mechanism. Zeolite formation is tied to the plagioclase alteration reaction in the rock matrix, which releases components for zeolite formation to a CO2-poor, alkaline aqueous fluid.

Reference:
Weisenberger T. & Bucher K. (2011) Mass transfer and porosity evolution during low temperature water-rock interaction in gneisses of the Simano nappe: Arvigo, Val Calanca, Swiss Alps. Contributions to Mineralogy and Petrology. 162 (1), 61-81. doi: 10.1007/s00410-010-0583-2 (pdf)