 |
| Titel |
Low grade metamorphism fluid circulation in a sedimentary environment thrust fault zone: properties and modeling |
| VerfasserIn |
Vincent Trincal, Brice Lacroix, Martine D. Buatier, Delphine Charpentier, Pierre Labaume, Abdeltif Lahfid |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096568
|
| Publikation (Nr.) |
 EGU/EGU2014-12078.pdf |
|
|
|
|
|
| Zusammenfassung |
| In fold-and-thrust belts, shortening is mainly accommodated by thrust faults that can
constitute preferential pathways for fluid circulation. The present study focuses
on the Pic de Port Vieux thrust, a second-order thrust related to major Gavarnie
thrust in the Axial Zone of the Pyrenees. The fault juxtaposes lower Triassic red
siltstones and sandstones in the hanging-wall and Upper Cretaceous limestone in
the footwall. A dense network of synkinematic quartz-chlorite veins is present in
outcrop and allows to unravel the nature of the fluid that circulated in the fault
zone.
The hanging wall part of fault zone comprises a core which consists of intensely foliated
phyllonite; the green color of this shear zone is related to the presence of abundant
newly-formed chlorite. Above, the damage zone consists of red pelites and sandstones. Both
domains feature kinematic markers like S-C type shear structures associated with shear and
extension quartz-chlorite veins and indicate a top to the south displacement. In the footwall,
the limestone display increasing mylonitization and marmorization when getting close to the
contact.
In order to investigate the mineralogical and geochemical changes induced by
deformation and subsequent fluid flow, sampling was conducted along a complete
transect of the fault zone, from the footwall limestone to the red pelites of the hanging
wall.
In the footwall limestone, stable isotope and Raman spectroscopy analyzes were
performed. The strain gradient is strongly correlated with a high decrease in δ18OV PDB
values (from -5.5 to -14) when approaching the thrust (i.e. passing from limestone to
marble) while the deformation temperatures estimated with Raman spectroscopy on
carbon remain constant around 300°C. These results suggest that deformation
is associated to a dynamic calcite recrystallization of carbonate in a fluid-open
system.
In the hanging wall, SEM observations, bulk chemical XRF analyses and mineral
quantification from XRD analyses were conducted in order to compare the green phyllonites
from the fault core zone with the red pelites from the damage zone. Quartz, muscovite 2M1,
chlorite (clinochlore), calcite and rutile are present in all samples. Hematite occurs in the
damage zone but is absent in the core zone.
Synkinematic chlorites are abundant in the core and damage zones and are
mainly located in veins, sometimes in association with quartz. The temperature of
formation of these newly-formed chlorites is 300-350°C according to Inoue (2009)
geothermometer.
Mössbauer spectroscopic analyses were performed on bulk rock samples. In the damage
zone, Fe3+/Fetotal vary between 0.7 and 0.8, whereas in the core zone Fe3+/Fetotal is
about 0.35. This decrease in Fe3+ from the damage zone to the core zone can be
related to the dissolution of hematite. In contrast, Fe3+/Fetotal in phyllosilicates is
clearly related to the chlorite content relative to mica, as Fe2+ increases with chlorite
content.
All these data allow us to propose a model of fluid circulation in relation with the Pic de
Port Vieux thrust activity. The origin of the fluid, its interactions with host-rock and the
consequences on fault zone mineralizations will be discussed.
Inoue, A., Meunier, A., Patrier-Mas, P., Rigault, C., Beaufort, D., Vieillard, P., 2009.
Application of chemical geothermometry to low-temperature trioctahedral chlorites. Clay
Clay Min. 57, 371–382. |
|
|
|
|
|
|