Temperature of paleo- to modern self-sealing within a continental rift basin; the fluid inclusion data (Soultz-sous-Forets, Rhine Graben, France)

Detailed petrographic and microthermometric studies of fluid inclusions reveal a complex and long-lived fluid circulation in both the sedimentary cover and in the basement of the Rhine graben. The earliest fluid stage (probably late Hercynian) is seen in healed fissures (fluid inclusion planes) affecting quartz grains in the granite and in some intragranitic early quartz-carbonate veins; this records rare CO (sub 2) -(N (sub 2) )-H (sub 2) O fluids, a succession of fluids of moderate salinity (2-7 wt.% eq. NaCl) trapped under a large range of T (min. 180-340 degrees C). The second main stage of mineral crystallization corresponds with a more recent crystallization of quartz cement in sandstones, and quartz-baryte veins in granite or sandstone; these showed a large salinity range and T 130-160 degrees C. The T-depth profile from recent vein infillings is close to the profile measured after drilling, indicating a recent to active self-sealing process.