Evolution and geometry of the Jura mountains

Transcription

The Geometry and Evolution of
the Jura Mountains: Fernschub
mechanics
Tabea Kleineberg
03.10.2013
Paper for the excursion “Geländeseminar Alpen” led by Prof. Dr. Janos Urai, Institute of Structural Geology, Tectonics and Geomechanics and Prof. Dr. Ralf Littke, Institute of Geology and Geochemistry of Petroleum and Coal at the RWTH Aachen University. 2 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 ABSTRACT .......................................................................................................................................3 1. GEOLOGICAL SETTING..................................................................................................................4 2. STRATIGRAPHY AND EVOLUTION OF THE JURA MOUNTAINS.......................................................5 2.1 BASEMENT .......................................................................................................................................5 2.2 THE SEDIMENT COVER ........................................................................................................................5 2.2.1 The basal décollement within the Triassic evaporites ...........................................................7 2.3 EVOLUTION OF THE JURA MOUNTAINS ..................................................................................................7 2.4 PALINSPASTIC RECONSTRUCTION ..........................................................................................................8 3. STRUCTURES................................................................................................................................9 3.1 EVAPORITE-‐RELATED FOLDS .................................................................................................................9 3.2 THRUST-‐RELATED FOLDS .....................................................................................................................9 3.3 TEAR FAULTS ..................................................................................................................................10 4. FERNSCHUB HYPOTHESIS........................................................................................................... 11 4.1 MECHANICS ...................................................................................................................................11 4.1.1 Kinematics ...........................................................................................................................12 4.1.2 Critical taper ........................................................................................................................13 4.2 LABORATORY EXPERIMENTS ...............................................................................................................14 5. CONCLUSION ............................................................................................................................. 15 6. LITERATURE............................................................................................................................... 16 3 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 Abstract The Jura Mountains, representing the most external part of the Alpine chain at its North-‐western front, are divided into three parts, all featuring different structural styles, ranging from plain plateaux in the external and Tabular Jura to a well developed fold-‐train in the internal Jura. The Jura Mountains formed in the latest stage of the Alpine orogeny in Upper Miocene/ Lower Pliocene times and are closely linked to the Molasse Basin. Its basement is comprised of metamorphic rocks and is decoupled from the sediment cover by a basal décollement. Folding and thrusting is restricted to the sedimentary cover rocks, pointing to a thin-‐skinned fold-‐and-‐thrust tectonics, which require very low basal friction. When shortening in the subalpine Molasse reached the Jura, the décollement in the Triassic Evaporites sheared off into the foreland generating the thrusts and folds of the Jura Mountains. This process is called the Fernschub hypothesis by BUXTORF (1916) and it is, at the present day, the most broadly-‐acknowledged theory for the formation of the Jura Mountains. Its essence and mechanics will be discussed in this paper. 4 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 1. Geological Setting
The Jura Mountains are located in Central Europe, in the Northwest of Switzerland and in the East of France in front of the Western Alpine arc. Their length amounts to 370 km with a maximum width of 75 km (BECKER, 2000). Figure 1 shows the structural map of the Jura arc, with its division into the internal, external and Tabular Jura highlighted in different shades of grey. In the south, the Jura Mountains are linked with the Alpine front of the Prealps, however, in the northeast they are separated from the Alpine chain by the tertiary Molasse Basin which is up to 50 km wide close to the eastern termination of the Jura Mountains northwest of Zurich. The Molasse Basin correlates to an Oligo-‐ Miocene foredeep, that developed in front of the Alpine orogen (SOMMARUGA, 1998). The crucial features along the western and northern border are the Tertiary rifts of the Bresse Depression and the Upper Rhine Graben (BECKER, 2000). The Rhine and Bresse Graben are associated with the Eocene and younger, West-‐European rift system. The Jura overthrusts the Bresse Graben in the west, and the Tabular Jura in the north (SOMMARUGA, 1998). Both rifts were active during the Eocene to Miocene, before Jura folding commenced (AFFOLTER ET AL., 2004). The remaining areas along the northern margin of the Jura folds belong to the Tabular Jura; the more or less unfolded, locally block faulted and non-‐decoupled sedimentary analogue of the folded Jura cover (BECKER, 2000). 001
A[ Sommaru`a:Marine and Petroleum Geolo`y 05 "0888# 000 023
Figure 1: Structural sketch of the Jura Mountains (SOMMARUGA, 1998). Fig[ 1[ Tectonic sketch of the Jura arc showing main structural units[ Legend] PHS Plateau de Haute!Saone^ IC
Monts^ Fe Ferrette^ AR Aiguilles Rouges^ MB Mont Blanc[ Modi_ed from Sommaruga "0884#[
Ile Cre⇣ mieu^ AM
Avants!
5 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 2. Stratigraphy and Evolution of the Jura Mountains The Jura Mountains are a foreland fold-‐thrust belt, where the structural components involve a relatively thin sediment cover; approximately 2 km thick in the Internal Jura, deformed above a basal décollement within the Middle and Upper Triassic evaporites (Figure 3) (AFFOLTER ET AL., 2004). The Mesozoic and Cenozoic rocks are folded at variable degrees and detached from the gently 1-‐5° SE dipping pre-‐Triassic basement, illustrated by Figure 3 (SOMMARUGA, 1998 and BECKER, 2000). By contrast with the deformed Jura cover, the molasse fill of the foreland basin was left virtually un-‐
deformed by Alpine deformations (Figure 3) (AFFOLTER ET AL., 2004). 2.1 Basement The crystalline basement is composed of medium-‐to-‐high grade metamorphic and plutonic rocks, which were deformed during the Hercynian orogeny. The surface of the basement, including some Permo-‐Carboniferous troughs, is not strongly accentuated. Nowhere is it exposed in the Jura and Molasse Basin (BECKER, 2000). It is characterized by two major unconformities, one below the Carboniferous and the second below the Triassic (SOMMARUGA, 1998). Its tectonic style, the depth and geometry and its internal deformation are still uncertain (BURKHARD, 1990). Some moderate basement elevations, however, are proven along the Vuache fault system, the eastern border zone of the Bresse Depression, the southern rim of the Permo-‐Carboniferous Trough of northern Switzerland and in the Oyonnax region of the southern Jura Mountains. The depth of the basement varies from more than 7 km below sea level in front of the Aar massif to more than 4 km above sea level 20 km further to the southeast (Figure 3) (BECKER, 2000). 2.2 The sediment cover The sediment cover of the Jura Mountains reaches maximum thicknesses of 1.5 km in the north, approximately 2 km in the centre and more than 3 km in the south (BECKER, 2000). It is separated from the basement by an evaporite layer (Figure 2 and 3, compare to 2.2.1). The Jura is divided into an external and an internal part, based on different tectonic styles (Figure 1). The external Jura consists of flat areas, plateaux, separated from Figure 2: Stratigraphy of the Jura and adjacent Molasse Basin (modified after SOMMARUGA, 1998). Figure 3: Cross section through the Jura Mountains (SOMMARUGA, 1998). Fig[ 2[ "a# Large!scale balanced cross!section across the Molasse Basin from the external Jura to the Alps "external crystalline massifs#[ For location\ see Fig[ 1[ Modi_ed from Burkhard and
Sommaruga "0887#^ "b# Enlargement of the Jura Haute Cha(ne*Molasse Basin region from the above large scale cross!section[
6 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 A[ Sommaru`a:Marine and Petroleum Geolo`y 05 "0888# 000 023
002
7 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 each other by Faisceaux, narrow stripes comprising numerous small-‐scale imbrications and tear faults. The internal Jura consists of a well-‐developed fold train. At a large scale, deformation is characterized by major folds, the trend of which swings through 90° from east to south. Major tear faults, oriented at a high angle to fold axes, cut the internal Jura at regular intervals (SOMMARUGA , 1998). The crucial rock types of the sediment cover are Triassic evaporites (compare 2.2.1) and shales, Jurassic and Cretaceous limestones (compare 2.3) and molasse sediments from Oligoene and Miocene times (BECKER , 2000). 2.2.1 The basal décollement within the Triassic evaporites In order to shear off the sediment cover and to accomplish folding of the Jura Mountains, a basal décollement with a low basal friction is required. These properties are given by the Triassic evaporitic sequences of the Muschelkalk and the Keuper formations. The most important lithologies for generating décollement horizons are halite, anhydrite and, at depths of less than approximately 500m, gypsum (BECKER, 2000). The distribution of halite in the Triassic (Figure 4) correlates with the location of the Jura Mountains, most obviously at their southern and eastern end. Southwards, the halite Figure 4: Distribution of Halite of the Keuper and Muschelkalk in the Jura Mountains (BECKER, 2000). disappears before reaching the Alpine front, and anhydrite is replaced increasingly by dolomite and marl. The thickness of the Triassic decreases from more than 1000m in the southern and central Jura Mountains to less than 50m in the North Helvetic domain, 60 km to the south (SOMMARUGA, 1998). 2.3 Evolution of the Jura Mountains After the end of the Hercynian Orogeny, the Alpine cycle started with peneplanation and a subsequent transgression in the Early Triassic. After the Jurassic, the Jura and Molasse Basin realm became part of the Alpine Tethys passive margin. During the Triassic, up to 1 km of evaporites and shales accumulated in an elliptical depocenter in the area of the future Jura arc (Figure 2 and 3). Limestones were sedimented in Dogger and Malm, as well as in the Carboniferous. During the Oligocene and Miocene, fluvial, lacustrine and marine clastic molasse sediments were deposited in the Alpine foredeep as a sedimentary wedge, the Molasse Basin. Its thickness decreases from up to 3 km in the south to a few hundred meters in the north (SOMMARUGA, 1998). In upper Miocene and lower Pliocene times, the latest stage of the Alpine orogeny, the Jura belt formed, at the front of the Alpine foredeep. Originally, the Molasse Basin extended further north-‐ 8 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 and westwards into the region of the present Jura Mountains and is preserved in the Jura Mountains as relicts. In the Oligocene, this region experienced normal faulting synchronous with formation of the Bresse Graben. Later, the upper Miocene to early lower Pliocene the Jura deformation reactivated these extensional structures which probably played a role in the distribution of thrusts. At that time, the frontal Jura was thrust above the eastern border of the Bresse Graben (AFFOLTER ET AL., 2004). 2.4 Palinspastic reconstruction Palinspastic reconstructions are used for a clearer understanding of the pattern of strain of a heterogeneous deformation. They are achieved by dividing the area into homogeneous domains with a subsequent restoring and best-‐fitting of the individual domains to realize the initial undeformed state. The structure of the Weissenstein Anticline (upper section of Figure 5) exhibits two geometrically distinguishable tectonic generations. The shortening of the wedge system decreases, which is apparent from the decreasing height of the Weissenstein anticline. In contrast, the Ausserberg-‐thrust shows no Figure 5: Restored cross-‐section of the change (BITTERLI, 1990). region "Volgelsberg" (BITTERLI, 1990). 9 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 3. Structures Two different types of folds appear in the Jura Mountains: evaporite-‐related and thrust-‐ related folds. The Molasse Basin and the external Plateaux Jura feature folds of the first mentioned type. The second type is present in the internal Jura (SOMMARUGA, 1998). Strike-‐slip faults disrupt the lateral continuity of the folds, but no clear crosscutting relationships exist between both on geological maps (AFFOLTER ET AL., 2004) 3.1 Evaporite-‐related folds Evaporite-‐related folds are broad, long-‐wavelength, low-‐
amplitude folds that are cored by Triassic evaporites (Figure 6). They are difficult to recognize in the field or on geological maps, therefore an interpretation by seismic lines is required. Seismic sections prove that the folds are controlled by evaporite, salt and clay stacks within a ductile unit of the Triassic layer. Within the Plateaux Jura the folds have two long asymmetric limbs dipping with a very low angle towards the north and the south, respectively. The geometry of the folds is highlighted by a well-‐layered series of reflectors representing Cretaceous, Jurassic and Upper Triassic strata (Figure 6). Due to the scarcity and thinness of pure rock salt layers in the Triassic series and the lack of early extension or Figure 6: Seismic section of an Evaporite-‐
related anticline in the Plateau Jura (SOMMARUGA, 1998). differential sedimentary loading, no salt diapir occurs in the Jura belt and the Molasse Basin (SOMMARUGA, 1998). 3.2 Thrust-‐related folds Thrust-‐related folds are characterized by high-‐amplitude folds. These folds formed above thrust faults stepping up from the basal Triassic décollement zone. These anticlines duplicate the entire Jurassic sequence (Figure 7) (SOMMARUGA, 1998). The short wavelength of these folds is thought to be due to the reduced Figure 7: Geological profile through the thrust-‐related folds around thickness of sediments involved in Grenchenberg (PFIFFNER, 2010). deformation in this external area. This reduced thickness is due to a period of peneplanation 10 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 (compare to 2.3), thought to have lasted from Late Cretaceous times to the onset of Jura deformation in upper Miocene (AFFOLTER ET AL., 2004). Thrust-‐related anticlines are separated by broad or tight synclines. Many thrust faults are NW (NNW)-‐verging, for example the main thrust system (foreland-‐vergent thrust), and have at least kilometric dip slip. SE (SSE)-‐vergent thrust faults are considered as backthrusts (hinterland-‐vergent thrusts), and have few tens or hundreds of meters of displacements. Thrust faults include both flats and ramps. All mapped foreland-‐vergent thrust faults reach the surface, breaking through the structures in the steep frontal limbs (SOMMARUGA, 1998). 3.3 Tear faults Tear faults are small strike-‐slip faults which affect the whole Mesozoic and Cenozoic cover but do not show any offset of the basement top within the seismic resolution. (TWISS ET AL., 2007 and SOMMARUGA, 1998). These faults are defined here as belonging to an allochthonous cover with a transcurrent movement, and terminating into a décollement zone that can be well recognized on geological maps (Figure 8 right). They are sinistral and occur mainly in the Internal Jura; oriented NW-‐SE in the southern Jura, NNW-‐SSE to N-‐S in the central Jura and NNE-‐SSW in the eastern Jura (Figure 8 right). In Figure 8 the left part shows different types of tear faults. A mixture of A and B would represent the most common type in the Jura Mountains, where shortening is accommodated by trust-‐
related folds on both sides of Figure 8: Left: thrust sheets segmented by tear faults (Twiss et al., 2007). Right: location of tear faults on the Jura anticline map after Heim 1916 (SOMMARUGA, 1998). the tear fault. 11 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 4. Fernschub hypothesis The Fernschub hypothesis was conceived by Buxtorf in 1907. It states that the process begins with the subduction of the European plate accompanied by the rise of the Aar massif (Figure 3). The resulting push affected the sedimentary wedge of the Molasse Basin and the linked Jura Mountains, resulting in deformation of the sediment cover and shear of décollement nappe. The shear was enhanced by the basal detachment, consisting of a Triassic salt layer with low friction. Beneath this detachment, the rocks remain mostly undeformed (Figure 3) (DAHLEN, 1990). 4.1 Mechanics Mechanically, a fold-‐and-‐thrust belt is similar to a wedge of snow in front of a moving snow plough (DAHLEN, 1990). The snow deforms until it develops a constant critical taper, after which it slides stea-‐
dily, continuing to grow at constant taper as additional material is accreted at the toe (DAVIS, 1983). The mechanical possibilities of thrusting an extensive thin sheet of sediments are controlled by the amount of friction at its base (LAUBSCHER, 1961), therefore an increase in the sliding resistance increases the critical taper. In contrast, an increase in the wedge strength decreases the critical taper, since a stronger wedge can be thinner, not deforming while sliding constantly over a rough base (DAHLEN, 1990). A computed specific friction value is 30 kg/cm2 for the base of the Plateaux Jura, and three times this value for the Molasse Basin. Those low values are due to plastic yielding of salt within the Triassic evaporite series (LAUBSCHER, 1961). DAVIS (1983) emphasized that fold-‐and-‐thrust belts features two further characteristics besides the above-‐mentioned basal décollement. First, large horizontal compression in the strata that overlie the décollement (see chapter 2.2 and 3) and second, a distinctive wedge shape of the deformed strata tapering toward the margin of the mountain belt (compare to Figure 3). The Jura Mountains exhibit all three characteristics. Annu. Rev. Earth Planet. Sci. 1990.18:55-99. Downloaded from www.annualreviews.org
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13 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 4.1.2 Critical taper 1158
DAVIS ET AL.' MECHANICSOF FOLD-AND-THRUST
BELTS
The critical taper for the compressive wedge in Figure A
9 is governed by the balance of four forces in moving direction. First, a gravitational body force; second (in a submarine regime), the pressure of water overburden; third the frictional resistance of sliding over a basal décollement; and fourth, the compressive push of the normal tractions acting on the two side walls of the wedge (DAVIS, 1983). =7¬
!%
S $
!S S
(4) . =¬
=7¬
!%
S $
!S S
N{j{¬
Equation (4) shows that the increase of the critical dMȒ
Ȓ
ȒȒ%Ȓ
ȒäřȒȒ
Ȓ ȒĹȒȒȒ
Ȓ
@Ȓ@ȒȒȒȒ
taper correlates with the increase of the coefficient of Ȓ
Ȓ
ƤȒ
%Ȓ
Ȓ
ȒȒ
ȒȒ>
Ȓ
>Ȓ4
ȒØ¨
Ȓ
ţ>ȒØȒ
Ȓ@
Ȓ
'
Ȓ>Ȓ
>@Ȓ
T
the basal friction μ , as it was already mentioned in Ȓ
dMȒ
Ȓ
Ȓ
Ȓby Ȓ
Ȓ%Ȓ
Ȓ©uåùřof ȒĹȒ
Ȓthe ȒȒ
Ȓ
@Ȓ@ȒÅȒ
ȒȒȒ
ȒȒ
ȒȒ4'Ȓ2@Ȓ
~
ȒýȒ
4Ȓ
4.1, while it decreases an internal Ȓ
Ȓ
ƤȒ
%Ȓ
Ȓ
%Ȓ
äincrease řȒ
Ȓ
Ȓ
'Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
4Ȓ
ȒȒ
%ȒȒ
ȒȒ>
Ȓ
>Ȓ4
ȒØ¨
Ȓ
ţ>ȒØȒ
Ȓ@
Ȓ
'
Ȓ>Ȓ
>@Ȓ
T
Ȓ
Ȓ
4
Ȓ
%Ȓ
Ȓ
ŁȒ
Ȓ
Ȓ
%
Ȓ
Ȓ
Ȓ
%Ȓ
Ȓ
Ȓ
%Ȓ
friction angle ϕ. For the typical value for dry sand of Ȓ
Ȓ
ȒȒ
Ȓ
@Ȓ
õȒ
<
Ȓ%Ȓ
ȒȒ
ȒȒ4'Ȓ2@Ȓ
©uåùř
~
ȒýȒ
4Ȓ
'Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
4Ȓ
Ȓ
dMȒ
ȒȒMOƺȒ2
Ȓ%Ȓ%ȒȒ@ȒČ
%ȒȒ
ÅȒ
ϕ=30°, the critical surface slope is given by α≈⅓(μ -‐2β) Ȓ
Ȓ
4
Ȓ
%Ȓ
Ȓ
ŁȒ
Ȓ
Ȓ
%
Ȓ
Ȓ
Ȓ
%Ȓ
Ȓ
Ȓ
%Ȓ
X
Ȓ³4Ȓ4Ȓ
ȒȒȒ%
Ȓ
<
Ȓ
8Ȓ
XȒȒ%ȒȒ
(D :ȒȒ
, 1990). Ȓ
Ȓ
``²Ȓ
Ȓ Ȓ ȒȒ%Ȓ%ȒȒ@ȒČ
ȒȒȒ
@Ȓ
Ȓ@Ȓ
õ<
ȒȒÅ
'ȒȒ
Ȓ
`>Ȓ
Ȓ̀
Ȓ̀
Ȓ
`Ȓ
ǻ>2>
:
æȒ

Ȓ
²
>`²@Ȓ̀

>
Ȓ
dMȒ
ȒȒMOƺȒ2
In a Ȓ critically tapered wedge, the Ȓ
horizontal 4T
Ȓ
Ȓ
Ȓ
@Ȓ
Ȓk
2Ȓ%
ŐȒ XȒȒ%ȒȒ
X
Ȓ³4Ȓ4Ȓ
ȒȒȒ%
Ȓ
<
Ȓ8Ȓ
Ȓ
:
Ȓ
ȒȒ
@Ȓ
Ȓ
ȒȒÅ
Ȓ
'ȒȒ
Ȓstress σ ≈ -‐ρgz by the Coulomb compressive &K
stress σȒ is related with the lithostatic overburden Ń
8
řȒ
`>Ȓ
Ȓ̀
Ȓ̀
Ȓ
`Ȓ
``²Ȓ
ǻ>2>
:
Ȓ
æȒ

Ȓ
²
>`²@Ȓ̀

>
Ȓ
11ř
failure 4T
Ȓ law ȒłȒ
ȒȒ @ȒȒk2Ȓ%ȒŐȒ
Ȓ-
&K}ŕ`ě8řYȒ
ŃȒqȒ
4Ȓ4Ȓ
ȒȒȒ ȒȒȒř
ĬąÐř ȒȒ
4ȒȒ
ȒȒȒȒȒȒ
11ř
4ȒȒ
łȒ
O
.
Ȓ
y
Ȓ
cȒXȒ-
q
Ȓ
4ȒȒ
ȒȒ
Ŗŗ ĺīôř
ǭȒ
t
Ȓ
ÃȒȒ2Ȓ }ŕ`ěa ȒȒ
Ã(subcritical) Ȓt
tȒtćÃȒ
%
ȒȒȒ
%Ȓ
ćt
Ȓ-
qȒ
4Ȓ4Ȓ
ȒȒȒ
Ȓ
řσ Ȓ would fail, and increase its Therefore, thinner wedge with t4Ȓt%Ȓ
a greater σȒȒ
than YĬąÐř
4ȒȒ
ȒȒ
4Ȓ
Ȓ
ȒȒȒȒ
ȒȒ
Ȓ
Ȓ
<
Ȓ
~Ȓ
4Ȓ
Ȓ
Ȓ
:
'Ȓ
'Ȓ
Ȓ
Ȓ
Oĺīôř with a lower σ than σ
taper until it gets critical. In contrast, a Ȓ
thicker (supercritical) Ȓ
y
Ȓ
cȒXȒ-
q
Ȓ
4ȒȒ
ȒȒ
Ŗŗwedge Ȓ
@Ȓ
Ĝ
Ȓ
Ȓ
Ȓ
Ȓ
4Ȓ
R
Ȓ
Ȓ
Ȓ
4Ȓ
2:
ȒȒ
ȒȒ
Ȓ
ȒtȒtćÃȒ
%
Ȓ4Ȓ
ȒȒ%ȒȒ
Ȓ<
Ȓc@Ȓ
4Ȓ
ȒȒ
%ćt
'
Ȓ
Ȓ
ȒȒ
ǭȒ
t
Ȓ
ÃȒȒ2Ȓ
ÃȒt
t4Ȓt%Ȓ
ȒȒȒȒ
%Ȓ
would not deform if no fresh material would be encountered at the toe (D
, 1990). @Ȓ4Ȓ
Ȓ
Ȓ
4'Ȓ%
Ȓ
Ȓ
<
Ȓ
~Ȓ
Ȓ
:
Ȓ
'Ȓ
Ȓ
O
`aY Ĝ
ȑ
Ȓ
>depicting Ȓ
Ȓ
Ȓin ȒyȒsuch a wedge, where (A) 'Ȓ
Ȓ
4Ȓ
@Ȓ
ƮȒ
Ȓdiagram ȒȒ
ȒȒȒ
4Ȓ
<ȒȒ%Ȓ
Ȓ
RȒ
Ȓ
ȒȒ
Ȓ
|ł
ř 0, In Figure 1
MȒ
ohr is shown the state of stress 1ÒÓ
2
:
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
c@Ȓ
4Ȓ
%
illustrates the stress at an arbitrary pȒ%ȒȒ
oint and (B) at the base of the wȒedge. ψ and ψ are the angles @Ȓ4Ȓ
Ȓ
Ȓ
4'Ȓ%
Ȓ
ȒȒ
OY
`
ȒȒȒ> Ȓ%ȒȒȒȒ y@ȒȒ
'Ȓ
|ł1ÒÓřσȑ and tƮȒ
between he x axis within the wedge and base of the wedge, while ϕ and ϕ represent the 8Ȓ
Ȓƚ
Ȓ
4Ȓ%ȒXȒȒȒȒȒȒ4¶¹

Ȓ2@ȒȒ>Ȓ%Ȓ>Ȓ
Ȓ`>Ȓ>
Ȓ>Ȓ
¨4ȒȒ
Ȓ8Ȓ failure law |τ| = μ σ * with angles of the internal and basal friction. The intersection of the frictional 8Ȓ
>Ȓ>
Ȓ
@
Ȓ2@Ȓ>O
Ȓ>>ȒȒǼ>>`Ȓ%
the Mohr stress circle corresponding to the basal depth H gives @Ȓ
the @bȒasal shear traction τ . σ * and öȒƻ³ȒȒȒȒ
Ȓ
Ȓ
ȒȒ%ȒªȒ
Ȓƚ
Ȓ4Ȓ%ȒXȒȒȒȒȒȒ4¶¹
8Ȓ
Ȓ
Ȓ
C
@
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
4Ȓ
'Ȓ

Ȓ2@ȒȒ>Ȓ%Ȓ>Ȓ
Ȓ`>Ȓ>
Ȓ
>Ȓ
¨
Ȓ
8ȒȒ respectively (D , 1983). σ>Ȓ>
* denote the m
aximum a
Ȓ
nd m
inimum effective %
compressive s4
tresses, @Ȓ
<
Ȓ
¬Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
'@Ȓ
4Ȓ
Ȓ
öȒƻ³ȒȒȒȒ
Ȓ
@
Ȓ2@Ȓ>O
Ȓ>>ȒȒǼ>>`Ȓ%
4ȒȒ
ȒȒ>Ȓ
ȒȒ
Ȓ
C
Ȓ%ȒȒ%ȒĊ>
Ȓ@ȒȒȒƩ
ȒȒȒ
ȒȒ%ȒªȒ
@Ȓ
>Ȓ
Ȓ
é2>Ȓ
s>Ȓ
Ť
22>Ȓ
2@Ȓ
8Ȓ
Ȓ
@
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
4Ȓ
'Ȓ
8ȒȒȒ2
ȒȒȒȒ2Ȓ'
X
ȒȒ'Ȓ
ȒȒȒ
@Ȓ
<
Ȓ
¬Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
Ȓ
'@Ȓ
%
4Ȓ
Ȓ
4
@
:
Ȓ
ȒȒ
ȒȒȒ
Ȓ
Ȓ
<
Ȓ
ȒȒ>Ȓ
Ȓ%ȒȒ%ȒĊ>
Ȓ@ȒȒȒƩ
ȒȒȒ
>Ȓ
Ȓ-é2>Ȓ
s>Ȓ X
ȒȒ'Ȓ
Ť22>Ȓ 2@Ȓ ȒȒ
8ȒȒȒ2
ȒȒȒȒ2Ȓ'
@:Ȓ
ȒȒ
ȒȒȒȒ
Ȓ<Ȓ
/=¬
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N{j{¬
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Annu. Rev.Annu.
Earth Rev.
Planet.
Sci.Planet.
1990.18:55-99.
Downloaded
from www.annualreviews.org
Earth
Sci. 1990.18:55-99.
Downloaded
from www.annualreviews.org
by WIB6264
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HochschuleHochschule
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09/24/13.
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•b
. =¬
7$«¬
(2¬
²ƨ
AHLEN
ĚõīĵźŜĕƨ
ŘЋ
ĚõīĵźŜĕƨ
(2¬
•*
E¨¨ο
#
$
E¨¨ο
h
GƘƙƨ Ƨƨ g AʽήĿο
GƘƙƨ Ƨƨ g AʽήĿο
gg}
be written
h
as
•'0 = /XbO'z
*= ,U,b(1- Ko)pgH
(8)
where/x0= tan (b0is thebasalcoefficient
offrictionand)tois
the generalizedHubbert-Rubeyratio (6) on the base. In
gg}
introducing
thebasalvaluesgoand)towe allowexplicitly
zzfor
ÊЋ
weakness,either becauseof a lower intrinsic strengthor
because of elevated fluid pressures.For a wedge with
uniforminternalproperties/x and X, we must necessarily
have(1 - •.b)ld,
b • (1 - X)/xfor the baseof the wedgeto be a
throughgoingdecollement.
To determinethe remainingunknown quantity tr; in the
/?¬
hh}
/?¬
#
$
|}
|}
Fig. 6. Mohrdiagram
illustrating
thestateof stress
(a) at somepointwithinthewedge
and(b)at thebaseof the
wedge.
Thequantities
4•and4•,aretheangles
ofinternal
andbasal
friction,
and½and%,aretheangles
between
o-•and
thex axiswithinthewedge
andat thebaseof thewedge.
Thebasalsheartraction
r/,isgivenbytheintersection
of the
frictional
failurelaw Irl = •,rr,* withtheMohrstress
circlecorresponding
to thebasaldepthH.
Figure 10: Mohr diagram depicting the state of stress (A) at some point within the wedge and ÊaЋt frictional
the bsliding
ase o
the edge (Dthat
AVIS
, basal
1983). the fact
the
decollementwill usually be a zone of
The traction•'0(B) resisting
onf the
basew
will
b
7$«¬
xx
|}
|}
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;]f QʀF\Ћ
;]
'ο 8$ª¬
ôƨ ¬ƨ
f QʀF\Ћ
;]
C
ôƨ ¬ƨ
²ƨ
E¦¦ο
0
ÊЋƍƎƨ
ŘЋ
xx
xx
failure
hh}
xx
ÊЋƍƎƨ
xx
AHLEN
F
śĔä
( ( ( ( ( "( "(
F
1
b
śĔä
b
( ( ( ( ( "( "(
Ī
/C:C¬
3
/C:C¬
. D>&¬
. D>&¬
. D> . ¬
. D> . ¬
ο
ο
b n
b
7$¬
Ī
. D>& . D>7$¬
. !¬
. D>& . D> . !¬
AVIS
1
failure
between wedge taper (α, β), thickness H, and strength parameters is the
elegant general weak-base theory of Dahlen (1990), which we take as
our starting point, using the special case of a mechanically homogeneous
wedge
1990,
equation
99): of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 The (Dahlen,
Geometry and Evolution xceedingly weak
questions.
thrust belt, Niger
14 α+β =
)
(
β 1 − ρf ρ  + µ b (1 − λ b ) + Sb ρgH
,
 sin φ 
1 − ρ f ρ  + 2 (1 − λ ) 
 + C ρgH


 1 − sin φ 
(1a)
aults within it has
eorge Airy recog- 4.2 Laboratory experiments an the strength of
The theory mentioned in 4.1 states that the covariation of surface slope α with décollement dip β is remain difficult to where Sb and C are the non-pressure-dependent parts of the fault and wedge
and theories con- used strength.
equations contain
a number of
fault
to Such
determine the strengths of average
active regional-scale
thrust-‐belt wedges and their basal décollement. It was observe. Available and crustal strength parameters about which we would like to know much
significant fraction tested more, butwith unfortunately
have little
direct constraint
in actively
deforming
a sandbox deformational model in the laboratory by SUPPE (2007), among others. The 1978), suggesting regions. Therefore we simplify Equation 1a to something more manageable
conducted mechanics into a very simple form, to 997; Townend and experiments by collecting the were fault-strength
terms asto F =recast µb (1 − critical-‐taper λ b) + Sb /ρgH andwedge the
st sheets, some of wedge-strength terms as W = 2(1 − λ)[sinφ/(1 − sinφ)] + C/ρgH, obtaining
determine absolute regional strength achments relative
sion and probably fluid pressure. Mechanically heterogeneous wedges
1 − ρ f ρ  + F
β

lem addressedαby
(1b) require more observational constraints
+β = 
.
are beyond the geometries scope of this
from andobserved in 1 − ρ f ρ  + W
ges and fold-andsion
and
fluid pressure.
Mechanically
Dry-sand
wedge
short paper
(seeprobably
Fletcher, 1989;
Dahlen, 1990,
equations heterogeneous
98 and 103). wedges

β 1 − ρ f ρ  + F
al strength within α + β =
(1b) Carena
.
α
require et
more
observational
constraints
aremeasurements
beyondconditions. the scope
al. (2002)
presented
a set of and
taper
acrossof this
appropriate geologic The Mylar
 − ρf ρ  + W
tence, cause, and
short
paper
Fletcher,
1989;
Dahlen,
1990, equations
98 andslope,
103).
(Fig.
simplified equation 8°
raises a1hope
that we might constrain the Taiwan
2A)(see
that
shows
a
quasi-linear
relationship
of
negative
base
β
oversial. Much of
mechanical in Shaw
the (2005)
laboratory Carena
et al. (2002)wedges.
presented
a setmodel ofBilotti
taperand
measurements
across
wedge strengths (F, W ) from appropriate observations of wedge as predicted
for homogeneous
Similarly,
faults such as the
Taiwan
(Fig. 2A)
This
simplifi
equationbecause
raises athehope
we might
thatkm)
shows
a quasi-linear
negative slope,
β).
This
seemsedplausible
onlythat
remaining
termconstrain
in the the
presented
regional
(~100
measurements
of relationship
taper in theofdeep-water
Take-up
spool
enbruch and Sass,
consists of a bottomless box containing t[1and
wedge
strengthsthe
(F,ratio
W ) of
from
observations
predicted
for of
homogeneous
wedges.
Similarly,
Bilotti andrelationShaw (2005)
− (ρ
thrustasbelt
of the toe
the Niger
delta
that show
a quasi-linear
the appropriate
density of the
overlying flof
uidwedge
f /ρ)], contains
Scholz and
Hanks,
ship with
a negative
slope(~100
(Fig. km)
2B).measurements
We compute the
air)β).toThis
the seems
mean density
rock and
thusremaining
1 for subaerial
peor(α,
plausibleofbecause
theisonly
term in the
presented
regional
of normalized
taper in thewedge
deep-water
sand with transparent side walls, which xen, 2004).
–
s
strength
W
=
(σ
nd ~0.6
wedges.
Furthermore,
it
can
be
shown
that
−
σ
)/ρgH
based
on
the
regression
slopes
and
obtain
ation,
[1for
− (ρsubmarine
thrust
belt
of
the
toe
of
the
Niger
delta
that
show
a
quasi-linear
relation/ρ)],
contains
the
ratio
of
the
density
of
the
overlying
fl
uid
f
1
3
cast critical-taper
4° shear
egional
traction
F =and
στ /ρgH,
similar
results
both wedges.
Taiwan
gives
W
=
0.6
and
the
Niger
delta
ship
withfor
a negative
slopesits (Fig.upon 2B).
We
compute
the
normalized
wedge
water ornormalized
air) to the basal
mean
density
of rock
is thusdetermined
1 for subaerial
a sheet of Mylar. The base very simple form
gives strength
ure on
detachment,
and W
is the normalized
differential
W = 0.7,Wwhich
moderately
wedges, as
discussed
= (σ1indicate
ges
andthe
~0.6
for submarine
wedges.
Furthermore,
it can be stress
shown that
− σ3)/ρgH
based onstrong
the regression
slopes
and obtain
absolute regionalsection.
The
normalized
basal
shear
F =flat στ /ρgH,
σ
)/ρgH at failure
(see Dahlen,
1990, traction
equations
91, 97). In in thesimilar
the
normalized
basal shear
F 88,
= σ90,
results for
both
wedges.
gives
Wlies = 0.6is and
the
Niger
upon Taiwan
which it traction
and delta
rigid τ /ρgH, determined
βnext
2 regional
ctive
critical-taper
α=be
0° considered an effective coefficient of friction, is F = 0.08
wefailure
show on
twothe
ways
to apply this
simplifi
ednormalized
Equation 1b.
whichgives
can
he
detachment,
and
W
is
the
differential
stress
W
=
0.7,
which
indicate
moderately
strong
wedges,
as
discussed
apply this theory,
(Figure 11, basal
top right) (D
AVIS
1983). critical
α (see
of a Dahlen,
mechanically
homogeneous
wedge
= 0.04 for
Niger delta.
The shear
observed
ratio
(σ1 −wedges.
in the and
nextF section.
Thethe
normalized
traction
Fof, =fault
στ /ρgH,By σ2surface
)/ρgH atslope
failure
1990, equations
88, 90,
91, 97). for
In Taiwan
rong
related
the dip
the detachment
as shown
by rearranging
strength
to wedge
F/Wan=effective
στ /(σ1 −coeffi
σ3) is
0.13offor
Taiwan
paper
wetoshow
twoofways
to apply thisβ,simplifi
ed Equation
1b.
which
can be strength
considered
cient
friction,
is and
F = 0.08
0°
the Mylar sheet, the will 1b:
Nigerand
delta.
results
that
the The
basal
detachments
are
forthe
Taiwan
F =These
0.04 pulling for theshow
Niger
delta.
observed
ratiosand of fault
0°of a mechanically
4°homogeneous wedge
8° 0.06 for
SThe critical surface slope α
β
exceedingly
weak
absolutely
and
relative
to
the
wedge
strengths.
nearly
related
to the dip of the detachment β, as shown by rearranging strength to wedge strength F/W = στ /(σ1 − σ3) is 0.13 for Taiwan and
cs
is that
actively
F
W
get pressed against the back wall, Dry-sand
(2a)
=
βtapers
,
−
ation
1b:
0.06 for the Niger delta. These results show that the basal detachments are
es
areα
simultane1 − ρ f ρ  + W 1 − ρ f ρ  + W
COMPARISON
DEEP BOREHOLE
DATA
exceedingly WITH
weak absolutely
and relative
to
the wedge




which is plausible
miming tfrom
he pTaiwan
rocess of the
pstrengths.
late subduction. Figure Schematic W
model of critical taper laboratory measurements. F 11.1: Critical-taper
We
compare
the
wedge
strengths
W
and
Niger delta
Figure
measurements
of
dry-sand
wedges
on
Mylar
(2a)
α
=
β
,
−
e by deformation Linear regression gives a slope to compute the fault and wedge detachment
(Davis
1983). Linear regression
gives a slope
1 − ρ fetρ al.,
+W
with stress
measurements
from two
scientifi
c boreholes
(Fig. 3). In the Gerhe equation of a1line
off negative
ρ
ρ  + W slope
COMPARISON
WITH
DEEP
BOREHOLE
DATA
To minimize inhomogeneities, the sand  − strengths  , and

UPPE
2007). s = 0.66
±(S0.14
an intercept
βα= 0° = 5.6°man
± 0.2°,
which
we σ
use
to
KTB
borehole
is
vertical
(Brudy
et
al.,
1997),
whereas
in compresWe
compare
2 the wedge strengths W from Taiwan and the Niger delta
Taiwan University,
compute the fault and wedge strengths (F, W ) using Equations 3
σ3is ismeasurements
vertical; therefore
we scientifi
represent
the KTB
stress
data
as Ger= α4βof
,e packed t−negative
o sβbtext).
side wsive
all wedges
fwith
riction reduced by from
a graphite coating (DAVIS
, 13).
983). =0
stress
two
c boreholes
(Fig.
In the
ch is the equation of αneeds a line
slope evenly and (2b)
and
(see
W* =man
(σ1 −KTB
σ3)/σborehole
, which σ
is directly
comparable
to
W.1997),
W* iswhereas
relatively
con3
is
vertical
(Brudy
et
al.,
in
compres2
compute the regression
fault and (2b)
wedge equations are necessary to draw a linear stant as
astrengths, function
indicating
that the
regionthe
is KTB
dominated
andorder intercept
obtained
by linear
= 0 and s are the slopeIn sive
wedges of
σ3depth,
istwo vertical;
therefore
weKTB
represent
stressby
data
as
α = α βto =0 − sβ,
strength,
with
W*
=
1.0
±
0.2
to
a
depth
of
8
km.
data contact
(α, β) from
an active
mechanically
wedge pressure-dependent
oe copy,
Copyright
Permissions,
GSA, orhomogeneous
editing@geosociety.org.
W* = (σ1 − σ3)/σ3, which is directly comparable to W. W* is relatively conregression left). Both Inresult from the rearranging of equation (99) from 0.1130/G24053A.1;
5 fifi
gures.
contrast,
W in1127
thedepth,
California
SAFOD
pilot
hole
(Hickman
andDAHLEN
From
2 we
nd that wedge(Figure strength 11 W isbottom a very simple
re αβ Equation
stant
as a function
of
indicating
that the
KTB
region
is dominated
by
= 0 and s are the slope and intercept obtained by linear regression
Zoback,
2004) shows a strong
decrease
3),a suggesting
that
of
the slope
pressure-dependent
strength,
with with
W* =depth
1.0 ±(Fig.
0.2 to
depth of 8 km.
uitable
data of
(α,the
β)regression
from
an active mechanically homogeneous wedge
(1990). The wedge strength W is a simple function of the slope of the regression (equation (4)) and the measurements,
which
a depth
of 1–2SAFOD
km in granite,
are still
within and
In contrast,
Ware
in atthe
California
pilot hole
(Hickman
. 1). From Equation 2 swe find that wedge strength W is a very simple
1 − ρ f ρ  ,
the near-surface
boundary
in which
cohesion
dominates
(cf.suggesting
(3)strength Zoback,
2004)
showslayer
a strong
decrease
withtimes depth
(Fig.
3),
that
ction of the slopeWof=the
equation (5) shows that the fault F is the regression intercept βα=0 wedge sDahlen
trength. 1 −regression
s
et al., the
1984).
The
cohesive
strength
C
=
~46
MPa
given
by
linear
regression
measurements, which are at a depth of 1–2 km in granite, are still within
s
strength F is simply the regression
β
(Fig. 1) times of the data is a factor of four less than the borehole-scale cohesion estimated
1 − intercept
(3) the near-surface boundary layer in which cohesion dominates (cf. Dahlen
W=
ρ f ρ  , α=0
for the SAFOD pilot hole at 197–212 MPa (Hickman and Zoback, 2004).
ength
1− s 
(4) et al., 1984). The cohesive strength C = ~46 MPa given by linear regression
Knowing C, we obtain the pressure-dependent component of the stress of
fault strength F is simply the regression intercept βα=0 (Fig. 1) times of the data is a factor of four less than the borehole-scale cohesion estimated
(4)
F = β α = 0W .
for the SAFOD pilot hole at 197–212 MPa (Hickman and Zoback, 2004).
ge strength
(5) Knowing C, we obtain the pressure-dependent component of the stress of
s is the , we should be ablewhere to determine
theslope. wedge and detachment
(4)4° A)
F = β α = 0W .
(W, F) simply from the linear covariation of surface slope α
Taiwan tapers
Based on this linear wedges,
regression, t is possible to determine the wedge and décollement strength. chment dip β in mechanically
homogeneous
based ion
refore, we should be able to determine the wedge and detachment
ression.
4° A)
ngths (W, F) simply from the linear covariation of surface slope α2°
Taiwan tapers
β
= 7.7°
h detachment dip β in mechanically homogeneous wedges, based on
α
α
=
0°
ATION TO ACTIVE WEDGES
β
0° 2°
fiarrstregression.
consider laboratory experiments with dry-sand wedges on a
5°
10°
15°
20°
β
=
7.7°
se, looking at the response of critical surface slope α to changes
α
α = 0°
PLICATION
TO1).
ACTIVE
WEDGESof the data of Davis et al.
ment dip β (Fig.
Linear regression
–s = –0.37
β
Weafibasal
rst consider
laboratory
experiments
dry-sand wedges on a-2° 0°
elds
coefficient
of friction
of F = µwith
5°
10°
15°
20°
b = 0.27 and a wedge
ar
base,
looking
at
the
response
of
critical
surface
slope
α
to
changes
W = 1.9, which corresponds to a cohesionless internal friction of
etachment
dip βvalues
(Fig. are
1). Linear
of the
of Davis
–s = –0.37
= 0.57. These
similarregression
to the basal
anddata
internal
fric- et al.
-4° -2°
83)
yields
a
basal
coeffi
cient
of
friction
of
F
=
µ
=
0.27
and
a
wedge
b et al. (1983),
= 0.3, µ = 0.58) measured independently by Davis
ngth
= 1.9, which
corresponds
to and
a cohesionless
internal
g theWviability
of estimating
wedge
fault strengths
fromfriction
the of2° B)
tanφ = 0.57.
These
values
arefisimilar
to the
basal and
internal fricNiger delta tapers
variation
of α and
β, if
we can
nd suitable
geological
examples
-4°
–s = –0.55
s (µbdetachment
= 0.3, µ = 0.58)
independently
Davis et al. (1983),
α
able
dip β measured
and plausible
mechanicalby
homogeneity.
gesting the
of estimating
wedge
andand
fault
from the
2° B)
consider
twoviability
active geologic
wedges,
Taiwan
thestrengths
Niger delta,
1°
Niger delta tapers
ar
covariation
of
α
and
β,
if
we
can
fi
nd
suitable
geological
examples
approximate the assumption of large-scale homogeneity because
–s = –0.55
α
h
variable
detachment
dip
β
and
plausible
mechanical
homogeneity.
β
w approximate linear covariation of α and β, and because they are
α = 0° = 3.35°
geologic
andlikely
the Niger
ckWe
(Hconsider
= 5–12 two
km);active
therefore
theirwedges,
strengthsTaiwan
are less
to be delta,
may approximate
assumption
of large-scale
homogeneity
because0° 1°
hanging
laterally. Inthe
contrast,
the thin
toes (H < ~1
km) of active
β
βα = 0° = 3.35°
show
approximate
linear
covariation
of αBarbados
and β, and
because
they are 0°
1°
2°
3°
4°
ary
wedges
such as the
Nankai
trough and
show
surface
+α (
(
)
)( )
( )
(
) −α
(
)
(
)
(
)
)
(
(
)
(
)
15 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 5. Conclusion The Jura Mountains and the Molasse Basin are closely linked and share a mutual evolution. Figure 12 depicts a simplified sketch of their evolution and the accompanied formation into an foreland fold-‐ and thrust belt. In the buckling stage, folds evolve to low-‐amplitude buckle folds in response to compression induced by the rise of the Aar-‐massif. The weak Triassic evaporites infill the space generated by rising anticlines at the space of the sedimentary cover. After thickening of the basal zone, fault ramps nucleate and prograde upwards, doubling the sediment cover (SOMMARUGA, 1998). This evolutionary stage resulted in the present day structural units of the Jura Mountains. Evaporite-‐ and thrust-‐related folds, as well as tear faults are its major tectonic features. In contrast, the Molasse Basin stayed relatively undeformed. The paper by Eva Görke elaborates in more detail on the sedimentary wedge, as well as further features of the Molasse Basin and the paper by Simon Freitag concentrates on the Hydrocarbon-‐
system within the Jura-‐arc-‐Molasse-‐Basin-‐system. The underlying mechanics of fold-‐and-‐thrust belts can be described by the wedge forming in front of a snow plough/bulldozer. Various papers (both older and more recent) give accurate descriptions of these processes, so that fold-‐and-‐thrust belts and accretionary wedges are one of the best understood deformational features of the Earth’s upper crust (DAHLEN, 1990). Figure 12: Conceptual evolutionary stages of the Jura foreland between 20-‐15 Ma. This sketch is without scale (SOMMARUGA, 1998). 16 The Geometry and Evolution of the Jura Mountains: Fernschub mechanics Tabea Kleineberg 319001 6. Literature LAUBSCHER, H. (1961): Die Ferschubhypothese der Jurafaltung. Eclog. Geol. Helvet., 54, 221-‐281. AFFOLTER, T., GRATIER, J.-‐P. (2004): Map view retrodeformation of an arcuate fold-‐and-‐thrust belt: The Jura case; J. Geophys. Res. 109, B03404 BECKER, A. (2000): The Jura Mountains -‐ an active foreland fold-‐and-‐thrust belt; Tectonophysics 321, 381-‐406 SOMMARUGA, A. (1999): Décollement tectonics in the Jura foreland fold-‐and-‐thrust belt; Marine and Petroleum Geochemistry 16, 111-‐134 BITTERLI, T (1990): The kinematic evolution of a classical Jura fold : a reinterpretation based on 3-‐
dimensional balancing techniques (Weissenstein Anticline, Jura Mountains, Switzerland) ; Eclog. Geol. Helvet., 83, 493-‐511 PFIFFNER, O.A. (2010): Geologie der Alpen; Haupt: Bern, Stuttgart, Wien. TWISS, R. J., MOORES, E. M. (2007): Structural Geology; Freeman and Company: New York. BURKHARD (1990): Aspects of the large-‐scale Miocene deformation in the most external part of the Swiss Alps (Subalpine Molasse to Jura fold belt). Eclog. Geol. Helvet., 83, 559-‐583. DAHLEN, F.A. (1990): Critical taper model of fold-‐and-‐thrust belts and accretionary wedges: Annual Review of Earth and Planetary Sciences, v. 18, p. 55–99. DAVIS, D., SUPPE, J., AND DAHLEN, F.A., 1983, Mechanics of fold-‐and-‐thrust belts and accretionary wedges: Journal of Geophysical Research, v. 88, p. 1153–1172. SUPPE, J. (2007): Absolute fault and crustal strength from wedge tapers. The Geological Society of America, v. 35, no. 12, p. 1127-‐1130.