Experimental study of phase transformations in a thermal gradient: application to the Soultz-sous-Forets granite (France).

The circulation of an injected fluid in the deep granite of the Soultz-sous-Forets HDR ('Hot Dry Rock') site causes important textural and mineralogical modifications. In order to determine the potential crystallization sequences along the fluid pathway, several experiments under thermal gradient were conducted at 600 bar (between 300 and 200 degreesC). After 40 days, the observed sequences of the newly formed products along the thermal gradient are always as follows, from high to low temperatures: quartz, feldspars, and finally interstratified clays, this implying a significant mobility of aluminium in the solution. (C) 2003 Academie des sciences. Publie par Editions scientifiques et medicales Elsevier SAS. Tous droits reserves.