Stable isotope and Ar/Ar evidence of prolonged multiscale fluid flow during exhumation of orogenic crust: Example from the Mont Blanc and Aar Massifs (NW Alps)

Abstract

The spatial and temporal scales and the geometry of fluid pathways in a collisional orogen are investigated using stable isotope analysis (O, C, and H) C values that are buffered by the Helvetic metasediments, which suggests that these veins formed in a closed system from a locally derived CO 2 -rich fluid. The fluid in equilibrium with C-type veins has depleted δ 13 C values similar to mantle-CO 2 , while the intermediate δ

Th‐Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland

“…Age data available for the Grimsel area are compiled in Figure , which illustrates the timing of near peak and retrograde P‐T‐t evolution in the Grimsel area. Ages obtained for hydrothermal cleft adularia in the Grimsel area are between 11.51 ± 0.42 Ma and ~11.5–14.5 Ma ( 40 Ar‐ 39 Ar ages [ Rossi and Rolland , ; Rauchenstein‐Martinek , ]) and were interpreted as crystallization or cooling ages, which overlap with or slightly predate monazite crystallization dated in this study. The oldest monazite Th‐Pb domain age of 11.65 ± 0.40 Ma (horizontal cleft; sample PK2) indicates that monazite crystallization in the Grimsel zone is coeval with adularia crystallization.…”

“…The external massifs were strongly affected by thick‐skinned thrusting during the Alpine orogeny. For the Aar Massif as a whole, up to six phases of deformation can be distinguished [ Steck , ], with up to four phases of deformation recognizable in the Grimsel area [ Mullis , ; Hofmann et al ., ; Challandes et al ., ; Rolland et al ., ; Goncalves et al ., ; Rossi and Rolland , ; Wehrens , ; Diamond and Tarantola , ].…”

Interpretation of fluid inclusions in quartz deformed by weak ductile shearing: Reconstruction of differential stress magnitudes and pre-deformation fluid properties

“…12-10 Ma; continuous path in Fig. 2): By about 12 Ma (Dempster, 1986;Rolland et al, 2009;Rossi and Rolland, 2014;Bergemann et al, 2014) the NW-directed thrusting had rotated into dextral strike-slip shearing (Rolland et al, 2009). Many of the stage-1 shear zones were reactivated but also more localized ductile shear zones and mylonites developed.…”

“…This success has been facilitated by a clear theoretical and experimental framework in which the chemical composition, density and phase-state of the trapped paleofluids can be inferred (e.g., Samson et al, 2003). The framework has been extended to inclusions in quartz that has been deformed by hydrostatic loading or unloading, such as occurs during metamorphic burial and inclusions are often preserved, however, where the host quartz has experienced only weak ductile strain, but a theoretical basis to interpret any deformation-induced effects on the inclusions, such as changes in chemical composition and density, is lacking.…”

Laser‐cut Rb–Sr microsampling dating of deformational events in the Mont Blanc‐Aiguilles Rouges region (European Alps)

“…Continued deformation is recorded in mylonitic shear zones with Early to Middle Miocene ages (Rolland et al ., , ; Egli, ), and younger ages in neighbouring areas indicate long‐lasting Alpine ductile deformation and/or fluid circulation (e.g. Rossi and Rolland, ).…”