 |
| Titel |
Using vein fabric and fluid inclusion characteristics as an integrated proxy to constrain the relative timing of non cross-cutting, syn- to late-orogenic quartz vein generations |
| VerfasserIn |
Dominique Jacques, Philippe Muchez, Manuel Sintubin |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089358
|
| Publikation (Nr.) |
 EGU/EGU2014-3558.pdf |
|
|
|
|
|
| Zusammenfassung |
| Research on ancient fluid systems mainly focuses on veins, because they offer the
opportunity to combine macro- and microstructural data with geochemical data to gain
insight into the P-T-X conditions present during veining. By applying such an integrated
petrographic and microthermometric methodology to syn- to late-orogenic quartz veins in the
Palaeozoic High-Ardenne slate belt (Belgium), we were able to define the relative
timing and related P-T-X conditions of different quartz vein generations, despite of
the absence of any mutual cross-cutting relationships in the field (Jacques et al.,
2014).
The different quartz vein generations represent the meso-scale brittle accommodation
during fold initiation, amplification and locking. The presence of free polycrystal
growth in cavities at a midcrustal depth, and fluid-assisted brecciation indicate
that veining occurred under overpressured fluid conditions during the orogeny.
Significant differences in crystal-plastic deformation microstructures and P-T trapping
conditions indicate that the different processes accommodating folding occurred in a
progressive manner along a retrograde deformation path. While vein quartz in an extrados
vein and in the peripheral part of a lenticular, fault-accommodating vein shows
moderate crystal-plastic deformation (e.g. bulging recrystallisation, deformation
lamellae, shear bands), crystal-plastic deformation is relatively absent in the vein
quartz of a saddle reef and the core of the lenticular vein (i.e. no to minor undulose
extinction).
Successive veining occurred from peak metamorphic conditions (ca. 300 °C and 190
MPa), measured in the extrados vein, to lower P-T conditions in the periphery of the
lenticular vein (ca. 275 °C and 180 MPa), the late-orogenic saddle reef (ca. 245 °C and 160
MPa) and the core of the lenticular vein (ca. 220 °C and 150 MPa). The relative timing and
accompanying decrease in P-T conditions of the different quartz vein generations reflect the
gradual exhumation of the slate belt from ca. 7.5 to 6 km depth along a retrograde
deformation path.
A comparison of these results with a former study of syn- to late-orogenic calcite veins at
the Variscan front zone (Kenis et al., 2000), indicates that exhumation processes throughout
the Rhenohercynian fold-and-thrust belt were diachronous. While exhumation and related
quartz veining in the High-Ardenne slate belt occurred during the Sudetic stage of the
Variscan orogeny (ca. 325-310 Ma), the exhumation and related calcite veining at the
Variscan front zone occurred during the Asturian stage of the Variscan orogeny (ca. 300
Ma).
With this study we demonstrate that a relative timing for different vein generations,
lacking any cross-cutting relationship, can still be attained through an integration of
petrographic and microthermometric arguments. Moreover, this particular approach, enables
to further delineate the P-T history of an orogenic system from its pre-, to its syn-, late- and
finally postkinematic stages.
References
Jacques, D., Derez, T., Muchez, P., Sintubin, M., 2014. Syn- to late-orogenic quartz veins
marking a retrograde deformation path in a slate belt: Examples from the High-Ardenne slate
belt (Belgium). Journal of Structural Geology, 58, 43-58.
Kenis, I., Muchez, P., Sintubin, M., Mansy, J.-L., Lacquement, F., 2000. The use of a
combined structural, stable isotope and fluid inclusion study to constrain the kinematic
history at the northern Variscan front zone (Bettrechies, northern France). Journal of
Structural Geology, 22, 589-602. |
|
|
|
|
|
|