TY - JOUR
T1 - Fluid evolution at the Variscan front in the vicinity of the Aachen thrust
AU - Sindern, S.
AU - Meyer, F.M.
AU - Lögering, M.J.
AU - Kolb, J.
AU - Vennemann, T.
AU - Schwarzbauer, J.
N1 - Funding Information:
Acknowledgments This study was supported by grant ME 1425/9-1, 2 of the German Science Foundation DFG to F. M. Meyer. The authors would like to thank P. Muchez and Chr. Hilgers for helpful discussions. The allocation of cores at the Geological Survey Brussels, Belgium, by M. Dusar is much appreciated. We want to thank S. Becker for his help during core work. We would like to thank T. Derichs for the preparation of the thin and thick sections and R. Klinghardt for his patience during EMPA work, A. Kronimus for his suggestions and advice on technical questions for gas-chromatographic work. J. Koester and A. Dziggel critically improved a previous version of the manuscript. Constructive criticism by the reviewers P. Muchez and A. Willner is gratefully acknowledged.
PY - 2012/1
Y1 - 2012/1
N2 - Quartz-carbonate-chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate subsolvus unmixing of a homogenous H2O-CO2-CH 4-(N 2)-Na-(K)-Cl fluid into a H 2O-Na-(K)-Cl solution and a vapour-rich CO2-(H 2O, CH4, N2) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between 200 and 250°C and salinities of <5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite, and dolomite by decrepitation yielded δDH2O values from -89 to -113 ‰, δ13CCH4 from -26. 9 to -28. 9‰ (VPDB) and δ13CCO2 from -12. 8 to -23. 3‰ (VPDB). The low δD and δ13C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the Stavelot-Venn massif. The metamorphic fluid was focused along major thrust faults of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics.
AB - Quartz-carbonate-chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate subsolvus unmixing of a homogenous H2O-CO2-CH 4-(N 2)-Na-(K)-Cl fluid into a H 2O-Na-(K)-Cl solution and a vapour-rich CO2-(H 2O, CH4, N2) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between 200 and 250°C and salinities of <5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite, and dolomite by decrepitation yielded δDH2O values from -89 to -113 ‰, δ13CCH4 from -26. 9 to -28. 9‰ (VPDB) and δ13CCO2 from -12. 8 to -23. 3‰ (VPDB). The low δD and δ13C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the Stavelot-Venn massif. The metamorphic fluid was focused along major thrust faults of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics.
KW - Aachen
KW - Fluid inclusions
KW - H-C-O isotopes
KW - Palaeo-fluid flow
KW - Variscan front zone
UR - http://www.scopus.com/inward/record.url?scp=84855338460&partnerID=8YFLogxK
U2 - 10.1007/s00531-011-0662-2
DO - 10.1007/s00531-011-0662-2
M3 - Article
SN - 1437-3254
VL - 101
SP - 87
EP - 108
JO - International Journal of Earth Sciences
JF - International Journal of Earth Sciences
IS - 1
ER -