Late Neogene extension in the vicinity of the Simplon fault zone (central Alps, Switzerland)

Grosjean, Grégory; Sue, Christian; Burkhard, Martin

doi:10.1007/s00015-004-1114-9

Cited by 30 publications

(32 citation statements)

References 42 publications

(34 reference statements)

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“…Figure 13 presents examples of such normal faults, and related meso-scale and large-scale structures. Numerous other examples of such extensional and transcurrent late Alpine structures have been published in the Western and Central Alps (e.g., Tricart 2002, 2003;Champagnac et al 2003Champagnac et al , 2004Grosjean et al 2004). At first sight, the overall pattern of the r3 axes (Fig.…”

Section: Orogen-parallel Versus Orogen-perpendicular Extensionmentioning

confidence: 88%

“…Regardless of this somewhat semantic issue, we deal with the reconstruction of the stress state acting within the belt since Early Miocene times. A series of regional analyses has been incorporated into our large-scale synthesis (Champagnac et al 2003Grosjean et al 2004). This provides a large and rather homogenous database (312 paleostress tensors) covering the entire arc of the inner Western and Central Alps, corresponding to a surface of some 10,000 km 2 (average density of 3 tensors/100 km 2 ).…”

Section: Orogen-parallel Versus Orogen-perpendicular Extensionmentioning

confidence: 99%

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Extensional neotectonics around the bend of the Western/Central Alps: an overview

Sue

Delacou

Champagnac

et al. 2007

Int J Earth Sci (Geol Rundsch)

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The Western Alps' active tectonics is characterized by ongoing widespread extension in the highest parts of the belt and transpressive/compressive tectonics along its borders. We examine these contrasting tectonic regimes using a multidisciplinary approach including seismotectonics, numerical modeling, GPS, morphotectonics, fieldwork, and brittle deformation analysis. Extension appears to be the dominant process in the present-day tectonic activity in the Western Alps, affecting its internal areas all along the arc. Shortening, in contrast, is limited to small areas located along at the outer borders of the chain. Strike-slip is observed throughout the Alpine realm and in the foreland. The stress-orientation pattern is radial for r3 in the inner, extensional zones, and for r1 in the outer, transcurrent/tranpressional ones. Extensional areas can be correlated with the parts of the belt with the thickest crust. Quantification of seismic strain in tectonically homogeneous areas shows that only 10-20% of the geodesy-documented deformation can be explained by the Alpine seismicity. We propose that, Alpine active tectonics are ruled by isostasy/buoyancy forces rather than the ongoing shortening along the Alpine Europe/Adria collision zone. This interpretation is corroborated by numerical modeling. The Neogene extensional structures in the Alps formed under increasingly brittle conditions. A synthesis of paleostress tensors for the internal parts of the West-Alpine Arc documents major orogen-parallel extension with a continuous change in r3 directions from ENE-WSW in the Simplon area, to N-S in the Vanoise area and to NNW-SSE in the Briançon area. Minor orogen-perpendicular extension increases from N to S. This second signal correlates with the present-day geodynamics as revealed by focal-plane mechanisms analysis. The orogen-parallel extension could be related to the opening of the Ligurian Sea during the Early-Middle Miocene and to compression/ rotation of the Adriatic indenter inducing lateral extrusion.

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Section: Orogen-parallel Versus Orogen-perpendicular Extensionmentioning

confidence: 88%

Section: Orogen-parallel Versus Orogen-perpendicular Extensionmentioning

confidence: 99%

Extensional neotectonics around the bend of the Western/Central Alps: an overview

Sue

Delacou

Champagnac

et al. 2007

Int J Earth Sci (Geol Rundsch)

Self Cite

128

150

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“…In its central section, it is marked by a zone of foliated clay gouge that can be up to a few meters wide. Kinematic indicators from both the ductile and brittle components consistently show a top down to the SW shear sense [Mancktelow, 1985[Mancktelow, , 1987[Mancktelow, , 1990Grosjean et al, 2004]. In contrast, older structures are generally well preserved in the hanging wall, showing overprinting relationships between several deformation phases that correspond well in their orientation and style to the four regional phases, D1 to D4 [Milnes et al, 1981].…”

Section: Simplon Fault Zonementioning

confidence: 99%

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

et al. 2010

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[1] Major low-angle normal faults juxtapose different structural levels of the crust that record both brittle and ductile deformation. Field relationships alone cannot establish whether these different responses to deformation represent (1) parts of a single process of exhumation along the detachment or (2) two separate events, with the later, more discrete brittle detachment exhuming a fossil ductile shear zone from depth. These two general models are critically assessed for the lowangle normal Simplon Fault Zone (SFZ) in the central Alps. The SFZ shows a spatial transition from a broad ductile mylonitic shear zone to a discrete brittle detachment with identical kinematics. The age of the ductile shear zone and ductile-brittle transition is controversial. We present a detailed geochronological study based on fission track, 40 Ar/ 39 Ar, and Rb/Sr microsampling dating, coupled with structural, petrological, and chemical analyses that provides tight constraints on SFZ timing. Discontinuous mineral cooling ages over a broad range of temperatures across the fault zone argue for fault activity between 20 and 3 Ma. On the basis of synkinematic white mica in low-temperature shear zones and necks of foliation boudinage, the brittle-ductile transition in the footwall could be dated at ∼14.5-10 Ma. Overall, the data presented here are consistent with a continuous transition from ductile shearing to a more localized zone of brittle deformation within the same geological framework, over a period of ∼15 Ma. The SFZ is therefore an example of a telescoped crustal section within a single major lowangle fault, involving a continuous period of exhumation rather than a two-stage structure.

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“…Grosjean et al 2004;Champagnac et al 2004). These studies have shown that, south of the Rhone Valley, a first phase of orogen-parallel (NE-SW) extension, including normal faulting along the Simplon fault and dextral strike-slip faulting along the Rhone fault, was succeeded by a second phase of orogenperpendicular (NW-SE) extension, the latter also recorded by the present-day stress field (Maurer et al 1997;Delacou et al 2004).…”

Section: Discussionmentioning

confidence: 99%

Brittle faulting in the Rawil depression: field observations from the Rezli fault zones, Helvetic nappes, Western Switzerland

Gasser

Mancktelow

2010

Swiss J Geosci

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The Helvetic nappes in the Swiss Alps form a classic fold-and-thrust belt related to overall NNW-directed transport. In western Switzerland, the plunge of nappe fold axes and the regional distribution of units define a broad depression, the Rawil depression, between the culminations of Aiguilles Rouge massif to the SW and Aar massif to the NE. A compilation of data from the literature shows that, in addition to thrusts related to nappe stacking, the Rawil depression is cross-cut by four sets of brittle faults: (1) NE-SW striking normal faults, (2) NW-SE striking normal faults and joints, (3) ENE-WSW striking and (4) WNW-ESE striking normal plus dextral obliqueslip faults. Fault set 1 was probably initiated during sedimentation and reactivated during nappe stacking, whereas the other fault sets formed after emplacement of the Helvetic nappes. We studied in detail two well-exposed parallel fault zones from set 4, the Rezli fault zones (RFZ) in the Wildhorn Nappe. They are SW-dipping oblique-slip faults with a total displacement across the two fault zones of *200 m vertically and *680 m horizontally. The fault zones crosscut four different lithologies: limestone, intercalated marl and limestone, marl and sandstone. The internal architecture of the RFZ strongly depends on the lithology in which they developed. In the limestones, they consist of extension veins, stylolites, cataclasites and cemented gouge, in the intercalated marls and limestones of shear zones, brittle fractures and chaotic folds, in the marls of anastomosing shear zones, pressure solution seams and veins and in the sandstones of coarse breccia, brittle faults and extension veins. Sharp, discrete fault planes within the broader fault zones cross-cut all lithologies. Fossil fault zones in the Rezli area can act as a model for studying processes still occurring at deeper levels in this seismically active region.

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Late Neogene extension in the vicinity of the Simplon fault zone (central Alps, Switzerland)

Cited by 30 publications

References 42 publications

Extensional neotectonics around the bend of the Western/Central Alps: an overview

Extensional neotectonics around the bend of the Western/Central Alps: an overview

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

Brittle faulting in the Rawil depression: field observations from the Rezli fault zones, Helvetic nappes, Western Switzerland

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