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| Titel |
Microtectonic characterization of the deformation in fault zone: A key to understand the mechanical evolution of a thrust fault (Monte Perdido thrust fault, Spain) |
| VerfasserIn |
B. Lacroix, H. Leclère, M. Buatier |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068193
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| Zusammenfassung |
| In thrust-and-fold belts, the development of low angle thrust faults is highly related to the
presence of fluids. Although increasing of fluid pressure can be an important parameter in
fault reactivation, it could also be responsible for fluid-rock interaction and triggers the
apparition of weaker hydrous minerals facilitating fault reactivation.
In this study, we aim to decipher the mechanical processes and the mineralogical changes
accompanying the shear surfaces reactivation in thrust faults at various P-T conditions. The
current investigations focus on the Monte Perdido thrust fault (South Pyrenean orogenic
wedge). The fault zone is characterized by meter-thick shear zone with highly deformed
foliated clay bearing rocks and shear surfaces.
Petrographic, SEM and TEM observations coupled to geochemical and thermometric
analysis in the fault zone highlighted two principals stage of deformation:
The first stage corresponds to the development of calcite shear veins, opened by a
combination of incremental shear surface reactivation and extension vein opening. The spatial
relationships existing between shear veins and cleavage seams attest that pressure solution is
the major deformation process. Fluid inclusions microthermometry and oxygen isotopic
composition of cogenetic vein minerals suggest that this first stage of deformation occurs at
about 210Ë C and at burial depths of 6 km.
The second stage corresponding to the fault reactivation involves Fe-chlorite
(Si2.86Al1.14O10(Al1.67Fe2.31Mg1.71)(OH)8) crystallization. Syntectonic chlorites
precipitated along shear surface. Chlorite chemical compositions coupled with fluid
inclusions thermometry allows to estimate higher P-T conditions of fault reactivation (240Ë C
and 6.5 km).
These results allow to propose a model of fault evolution in which a competition between
fluid pressure and creep mechanisms are occuring. During the first step of deformation, the
Monte Perdido Thrust Fault activation is facilitated by a high pore fluid pressure conditions.
Pressure solution processes triggered a calcite departure from host sediments to
veins. As a consequence, an increase of the relative insoluble clay minerals content
occurs in the sediment matrix. During the second stage of deformation chlorite
precipitates along shear surfaces. Although such minerals are supposed to decrease the
frictional coefficient of fault zone, the contribution of fluid pressure still remains high. |
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