.New Frontiers in Integrated Solid Earth Sciences Phần 5 pptx

9 Thickness of the European lithosphere as determined by a seismic tomography; b surface wave tomography; c geothermics; d magnetotellurics after Artemieva et al., 2006 deeper crust and

60 30–10 0

Electromagnetic data (d)

Thermal data (c)

–10

Surface waves (b)

Body waves (a)

Fig 9 Thickness of the

European lithosphere as

determined by (a) seismic

tomography; (b) surface wave

tomography; (c) geothermics;

(d) magnetotellurics (after

Artemieva et al., 2006)

deeper crust and mantle rocks depends on their

chem-ical composition, temperature and pressure conditions

(combination of burial and regional heat flow) and their

water content Furthermore, the crust and lithospheric

mantle may be locally weakened by the occurrence of

pre-existing discontinuities related to earlier

deforma-tion phases (Ziegler et al., 1998; Ziegler and Cloetingh

2004) Such inherited weakness zones, represented by

e.g., crustal scale faults or eclogitized continental crust

inserted into the sub-crustal mantle, may be

character-ized by considerably reduced strengths as compared to

surrounding crustal and mantle domains

Analogue modelling techniques were first

devel-oped, and are now routinely used by many

lab-oratories to simulate thin-skinned deformation of

sedimentary rocks (see Colletta et al., 1991, and

references therein), but also of the lithosphere as a

whole (Sokoutis et al., 2005, 2007, and references

therein), using specific analogue materials for elling either brittle or ductile sediments, the crust

mod-or the mantle Further numerical developments are,however, required when investigating the effects ofother parameters during basin evolution, such as pore-fluid pressure, temperature and mineralogical phasetransitions

In the following paragraphs, we shall summarizesome recent advances achieved in documenting andunderstanding the rheology and long term behaviour

of the European lithosphere, as well as a few dedicatedcase studies outlining (1) the incidence of deep activedécollements on surface topography, (2) the respec-tive effects of coupling and strain partitioning betweenthe foreland and hinterland during the development

of selected intramontane basins, as well as the all dynamics of (3) intracratonic basins and (4) passivemargins

over-Lithosphere Strength and Deformation

Mode

The strength of continental lithosphere is controlled by

its depth-dependent rheological structure in which the

thickness and composition of the crust, the thickness

of the lithospheric mantle, the potential temperature of

the asthenosphere, and the presence or absence of

flu-ids, as well as strain rates play a dominant role By

con-trast, the strength of oceanic lithosphere depends on

its thermal regime, which controls its essentially

age-dependent thickness (Kuznir and Park, 1987;

Cloet-ingh and Burov, 1996; Watts, 2001; see also Burov,

2007)

Figure 10 gives synthetic strength envelops for

three different types of continental lithosphere and for

oceanic lithosphere at a range of geothermal gradients

(Ziegler and Cloetingh, 2004) These theoretical

rheo-logical models indicate that thermally stabilized

conti-nental lithosphere consists of the mechanically strong

upper crust, which is separated by a weak lower

crustal layer from the strong upper part of the

lithosphere that in turn overlies the weak lower

mantle-lithosphere By contrast, oceanic lithosphere has a

more homogeneous composition and is characterized

by a much simpler rheological structure In terms

of rheology, thermally stabilized oceanic lithosphere

is considerably stronger than all types of continental

lithosphere However, the strength of oceanic

litho-sphere can be seriously weakened by transform faults

and by the thermal blanketing effect of thick

sedimen-tary prisms prograding onto it (e.g., Gulf of Mexico,

Niger Delta, Bengal Fan; Ziegler et al., 1998)

The strength of continental crust depends largely

on its composition, thermal regime and the presence

of fluids, and also on the availability of pre-existing

crustal discontinuities (see also Burov, 2007)

Deep-reaching crustal discontinuities, such as thrust- and

wrench-faults, cause significant weakening of the

oth-erwise mechanically strong upper parts of the crust

Such discontinuities are apparently characterized by a

reduced frictional angle, particularly in the presence

of fluids (Van Wees, 1994) These discontinuities are

prone to reactivation at stress levels that are well below

those required for the development of new faults Deep

reflection-seismic profiles show that the crust of Late

Proterozoic and Paleozoic orogenic belts is generally

characterized by a monoclinal fabric that extends from

upper crustal levels down to the layered lower crustand Moho at which it either soles out or by which it

is truncated (Figs 2, 3, 4; see Bois, 1992; Ziegler andCloetingh, 2004) This fabric reflects the presence ofdeep-reaching lithological inhomogeneities and shearzones

The strength of the continental upper lithosphericmantle depends to a large extent on the thickness ofthe crust but also on its age and thermal regime (seeJaupart and Mareschal, 2006) Thermally stabilizedstretched continental lithosphere with a 20 km thickcrust and a lithospheric mantle thickness of 50 km

is mechanically stronger than unstretched lithospherewith a 30 km thick crust and a 70 km thick lithosphericmantle (compare Fig 10b, d) Extension of stabilizedcontinental crustal segments precludes ductile flow ofthe lower crust and faults will be steep to listric andpropagate towards the hanging wall, i.e., towards thebasin centre (Bertotti et al., 2000) Under these con-ditions, the lower crust will deform by distributingductile shear in the brittle-ductile transition domain.This is compatible with the occurrence of earthquakeswithin the lower crust and even close to the Moho (e.g.,southern Rhine Graben: Bonjer, 1997; East Africanrifts: Shudofsky et al., 1987)

On the other hand, in young orogenic belts, whichare characterized by crustal thicknesses of up to 60 kmand an elevated heat flow, the mechanically strongpart of the crust is thin and the lithospheric mantle isalso weak (Fig 10c) Extension of this type of litho-sphere, involving ductile flow of the lower and middlecrust along pressure gradients away from areas lack-ing upper crustal extension into zones of major uppercrustal extensional unroofing, can cause crustal thin-ning and thickening, respectively This deformationmode gives rise to the development of core complexeswith faults propagating towards the hanging wall (e.g.,Basin and Range Province: Wernicke, 1990; Buck,1991; Bertotti et al., 2000) However, crustal flow willcease after major crustal thinning has been achieved,mainly due to extensional decompression of the lowercrust (Bertotti et al., 2000)

Generally, the upper mantle of thermally stabilized,old cratonic lithosphere is considerably stronger thanthe strong part of its upper crust (Fig 10a) (Moisio

et al., 2000) However, the occurrence of upper tle reflectors, which generally dip in the same direc-tion as the crustal fabric and probably are related tosubducted oceanic and/or continental crustal material,

man-Fig 10 Depth-dependent rheological models for various

litho-sphere types and a range of geothermal gradients, assuming a

dry quartz/diorite/olivine mineralogy for continental lithosphere

(Ziegler, et al., 1995; Ziegler et al., 2001) (a) Unextended,

thick-shield-type lithosphere with a crustal thickness of 45 km and a

lithospheric mantle thickness of 155 km (b) Unextended,

“nor-mal” cratonic lithosphere with a crustal thickness of 30 km and

a lithospheric mantle thickness of 70 km (c) Unextended, young

orogenic lithosphere with a crustal thickness of 60 km and a

lithospheric mantle thickness of 140 km (d) Extended, cratonic

lithosphere with a crustal thickness of 20 km and a lithospheric

mantle thickness of 50 km (e) Oceanic lithosphere Modified

from Ziegler et al (2001)

suggests that the continental lithospheric mantle is not

necessarily homogenous but can contain lithological

discontinuities that enhance its mechanical anisotropy

(Vauchez et al., 1998; Ziegler et al., 1998) Such

dis-continuities, consisting of eclogitized crustal material,

can potentially weaken the strong upper part of the

lithospheric mantle Moreover, even in the face of

similar crustal thicknesses, the heat flow of deeply

degraded Late Proterozoic and Phanerozoic orogenic

belts is still elevated as compared to adjacent old

cratons (e.g., Panafrican belts of Africa and Arabia;

Janssen, 1996) This is probably due to the younger

age of their lithospheric mantle and possibly also to

a higher radiogenic heat generation potential of their

crust These factors contribute to weakening of

for-mer mobile zones to the end that they present

rhe-ologically weak zones within a craton, as evidenced

by their preferential reactivation during the break-up

of Pangea (Ziegler, 1989; Janssen et al., 1995; Ziegler

et al., 2001)

Concerning rheology, the thermally destabilized

lithosphere of tectonically active rifts, as well as of

rifts and passive margins that have undergone only

a relatively short post-rift evolution (e.g., 25 Ma), is

considerably weaker than that of thermally stabilized

rifts and of unstretched lithosphere (Figs 10 and 11,

Ziegler et al., 1998) In this respect, it must be realized

that during rifting, progressive mechanical and

ther-mal thinning of the lithospheric mantle and its

substi-tution by the upwelling asthenosphere is accompanied

by a rise in geotherms causing progressive weakening

of the extended lithosphere In addition, its permeation

by fluids causes its further weakening (Fig 11) Upon

decay of the rift-induced thermal anomaly, rift zones

are rheologically speaking considerably stronger than

unstretched lithosphere (Fig 10) However,

accumula-tion of thick syn- and post-rift sedimentary sequences

can cause by thermal blanketing a weakening of

the strong parts of the upper crust and lithospheric

mantle of rifted basins (Stephenson, 1989)

More-over, as faults permanently weaken the crust of rifted

basins, they are prone to tensional as well as

com-pressional reactivation and tectonic inversion (Roure

et al., 1994, 1997; Ziegler et al., 1995, 1998, 2001,

2002; Brun and Nalpas, 1996; Roure and Colletta,

1996)

In view of its rheological structure, the

continen-tal lithosphere can be regarded under certain

condi-tions as a two-layered visco-elastic beam (Fig 12;

Reston, 1990, Ter Voorde et al., 1998) The response ofsuch a system to the build-up of extensional and com-pressional stresses depends on the thickness, strengthand spacing of the two competent layers, on stressmagnitudes and strain rates and the thermal regime(Zeyen et al., 1997; Watts and Burov, 2003) As thestructure of continental lithosphere is also regionallyheterogeneous, its weakest parts start to yield firstonce tensional as well as compressional intraplatestress levels equate their strength (Ziegler et al.,2001)

The flow properties of mantle rocks control thethickness and strength of the lithospheric plates, thedegree of coupling between moving lithospheric platesand the pattern and rate of asthenospheric convection,and the rate of melt extraction at mid-ocean ridges To

be able to understand the dynamic behaviour of theouter parts of the solid Earth, notably the dynamics oflithospheric extension and associated rifting and sed-imentary basin development, a detailed knowledge ofthe rheology and evolution of the upper mantle (30–

410 km depth) and between the 410 and 670 tion zones is essential At present, these flow proper-ties are surprisingly poorly known Experimental workhas yielded constitutive equations describing varioustypes of flow in mantle rocks, but it is not clearlyestablished to what extent the experimentally observedflow mechanisms are relevant for natural crust andmantle conditions A second problem is that traceamounts of water and melt can cause drastic weaken-ing of mantle rocks and may cause the development

transi-of upper mantel convective instabilities (Lustrino andWilson, 2007) Such fluid-related weakening effectsare widely recognized as, for example, controlling thestrength of trans-lithospheric faults in the substratum

of active basins However, only limited data are able on such effects, and a quantitative, mechanicalunderstanding suitable for extrapolation to nature islacking

avail-These problems can be addressed by means

of experimental studies, scanning and transmissionelectron microscopy (SEM, TEM) and field stud-ies on exposed upper mantle rocks Integration ofthese approaches aims at arriving at quantitative,mechanism-based descriptions of mantle rheologiessuitable for use in modelling the dynamics of the uppermantle and transition zone Field-based studies involv-ing structural geological and EM work on upper mantlerocks deformed in a variety of geological environments

normal continental lithosphere

extended, thermally rejuvenated lithosphere strength (MPa)

wet

dry

0 250 500 750 1000 1250 1500 temperature (°C)

0 250 500 750 1000 1250 1500 temperature (°C)

tension compression

wet dry tension compression

Fig 11 Depth-dependent rheological models for dry and wet,

unextended ‘normal’ cratonic lithosphere and stretched,

ther-mally attenuated lithosphere, assuming a quartz/diorite/olivine

mineralogy (a) Unextended, cratonic lithosphere with a crustal

thickness of 30 km and a lithospheric mantle thickness of 70 km.

(b) Extended, thermally destabilized cratonic lithosphere with a

crustal thickness of, 20 km and a lithospheric mantle thickness

of 38 km Modified from Ziegler et al (2001)

upper crust

lower crust

asthenosphere mantle lithosphere MSC

MSL

Fig 12 Kinematic model for

extension of rheologically

stratified lithosphere See

strength profile on left side of

diagram MSC and MSL

indicate the base of the

mechanically strong crust and

mechanically strong

lithosphere, respectively.

From Reston (1990)

may provide information on flow mechanisms

occur-ring in the upper mantle Therefore, special attention

has to be paid to upper mantle rocks showing possible

asthenospheric flow structures, which developed when

the rocks contained some fluid or partial melts In

addi-tion, attention has to be paid to upper mantle shear zone

rocks as such shears probably control the extensional

strength of the lithosphere

Lithospheric Folding: An Important Mode

of Intraplate Basin Formation

Folding of the lithosphere, involving its positive aswell as negative deflection (see Figs 13 and 14),appears to play a more important role in the large-scale neotectonic deformation of Europe’s intraplate

weak

Moho

Fig 13 Schematic diagram illustrating decoupled lithospheric

mantle and crustal folding, and consequences of vertical motions

and sedimentation at the Earth’s surface V is horizontal

short-ening velocity; upper crust, lower crust, and mantle layers are

defined by corresponding rheologies and physical properties A

typical brittle-ductile strength profile (in black) for decoupled

crust and upper mantle- lithosphere, adopting a

quartz-diorite-olivine rheology, is shown for reference

domain than hitherto realized (after Cloetingh et al.,

1999) The large wavelength of vertical motions

asso-ciated with lithospheric folding necessitates integration

of available data from relatively large areas (Elfrink,2001), often going beyond the scope of regional struc-tural and geophysical studies that target specific struc-tural provinces Recent studies on the North GermanBasin have revealed the importance of its neotectonicstructural reactivation by lithospheric folding (Marotta

et al., 2000) Similarly, the Plio-Pleistocene subsidenceacceleration of the North Sea Basin is attributed tostress-induced buckling of its lithosphere (Van Weesand Cloetingh, 1996; Unternehr and van den Driess-che, 2004) Moreover, folding of the Variscan litho-sphere has been documented for Brittany (Bonnet

et al., 2000), the adjacent Paris Basin (Lefort and wal, 1996) and the Vosges-Black Forest arch (Ziegler

Agar-et al., 2002; Dèzes Agar-et al., 2004; Bourgeois Agar-et al., 2007;Ziegler and Dèzes, 2007) Lithospheric folding is avery effective mechanism for the propagation of tec-tonic deformation from active plate boundaries far intointraplate domains (e.g., Stephenson and Cloetingh,1991; Burov et al., 1993; Ziegler et al., 1995, 1998,2002)

Type-1 model simulating the collision between two different lithospheric blocks

Type-2 model representing a cold lithosphere with a strong upper mantle

Σ belt

34%

26%

Upper Crust Lower Crust

Upper Mantle

Asthenosphere

Pre-cut sutu re

Fig 14 Analogue tectonic modelling for continental lithosphere folding Top: uniform lithosphere Bottom: lithosphere blocks

separated by suture zone (after Sokoutis et al., 2005)

At the scale of a micro-continent that was affected

by a succession of collisional events, Iberia provides

a well-documented natural laboratory for lithospheric

folding and the quantification of the interplay between

neotectonics and surface processes (Fig 15;

Cloet-ingh et al., 2002) An important factor in favor of a

lithosphere-folding scenario for Iberia is the

compati-bility of the thermo-tectonic age of its lithosphere and

the wavelength of observed deformations

Well-documented examples of continental

litho-spheric folding come also from other cratonic areas

A prominent example of lithospheric folding occurs

in the Western Goby area of Central Asia, involving

a lithosphere with a thermo-tectonic age of 400 Ma

In this area, mantle and crustal wavelengths are 360

and 50 km, respectively, with a shortening rate of

∼10 mm/year and a total amount of shortening of 200–

250 km during 10–15 Myr (Burov et al., 1993; Burov

and Molnar, 1998)

Quaternary folding of the Variscan lithosphere in

the area of the Armorican Massif (Bonnet et al., 2000)

resulted in the development of folds with a

wave-length of 250 km, pointing to a mantle-lithosphericcontrol on deformation As the timing and spatial pat-tern of uplift inferred from river incision studies inBrittany is incompatible with a glacio-eustatic ori-gin, Bonnet et al (2000) relate the observed verti-cal motions to deflection of the lithosphere under thepresent-day NW–SE directed compressional intraplatestress field of NW Europe (Fig 16) Stress-induceduplift of the area appears to control fluvial incisionrates and the position of the main drainage divides.The area located at the western margin of the ParisBasin and along the rifted Atlantic margin of Francehas been subject to thermal rejuvenation during Meso-zoic extension related to North Atlantic rifting (Robin

et al., 2003; Ziegler and Dèzes, 2006) and quent compressional intraplate deformation (Ziegler

subse-et al., 1995), also affecting the Paris Basin (Lefortand Agarwal, 1996) Levelling studies in this area(Lenotre et al., 1999) also point towards its ongoingdeformation

The inferred wavelength of these neotectonic sphere folds is consistent with the general relationship

–750 –749 –748 –747 –746 –745 –744 –743 –742 Topography (mm)

–750 –749 –748 –747 –746 –745 –744 –743 –742 Topography (mm)

-743

Fig 15 Analogue modelling of intraplate continental

litho-sphere folding of Iberia (Fernández-Lozano et al., 2008) Left:

incremental shortening and topographic evolution Top right: 2D

section of the final stage Bottom right: 3D view of the final

stage Notice the pop-up structures in the upper crust (layered), the ductile flow of the lower crust (orange), and the folded man- tle lithosphere (light grey)

0 11 22 33

64 72

Fig 16 Present-day stress map of Europe showing orientation

of maximum horizontal stress axes (SHmax) Different symbols

stand for different stress indicators; their length reflects the data

quality, “A” being highest Background shading indicates

topo-graphic elevation (brown high, green low) This map was derived

from the World Stress Map database

(http://www.world-stress-map.org)

that was established between the wavelength of

spheric folds and the thermo-tectonic age of the

litho-sphere on the base of a global inventory of lithospheric

folds (Fig 17; see also Cloetingh and Burov, 1996;

Cloetingh et al., 2005) In a number of other areas

of continental lithosphere folding, also smaller

wave-length crustal folds have been detected, for example in

Central Asia (Burov et al., 1993; Nikishin et al., 1993)

Thermal thinning of the mantle-lithosphere, often

associated with volcanism and doming, enhances

litho-spheric folding and appears to control the wavelength

of folds Substantial thermal weakening of the

litho-spheric mantle is consistent with higher folding rates in

the European foreland as compared to folding in

Cen-tral Asia (Nikishin et al., 1993), which is marked by

pronounced mantle strength (Cloetingh et al., 1999)

Linking the Sedimentary Record

to Processes in the Lithosphere

Over the last decades basin analysis has been in the

forefront of integrating sedimentary and lithosphere

components of previously separated fields of ogy and geophysics (Fig 18) Integrating neotecton-ics, surface processes and lithospheric dynamics in thereconstruction of the paleo-topography of sedimen-tary basins and their flanking areas is a key objective

geol-of integrated Solid-Earth science A fully integratedapproach, combining dynamic topography and sedi-mentary basin dynamics, is also important consideringthe societal importance of these basins on account oftheir resource potential At the same time, most of thehuman population resides on sedimentary basins, oftenclose to coastal zones and deltas that are vulnerable togeological hazards inherent to the active Earth system.One major task of on-going research is to bridge thegap between historic and geological time scales in ana-lyzing lithospheric deformation rates Major progresshas been made in reconstructing the evolution of sed-imentary basins on geological time scales, incorporat-ing faulting and sedimentary phenomena From this,

we have considerably increased our insights into thedynamics of the lithosphere at large time slices (mil-lions of years) On the other hand, knowledge onpresent-day dynamics is rapidly growing thanks tothe high spatial resolution in quantification of earth-quake hypocenters and focal mechanisms, and ver-tical motions of the land surface Unification, cou-pling and fully 3-D application of different modellingapproaches to present-day observations and the geo-logical record will permit to strengthen the recon-structive and predictive capabilities of process quan-tification Particularly an intrinsically time-integratedapproach will permit to assess in greater detail theimportance of the geological memory of lithosphericproperties on present-day dynamics This is one of thekey parameters for predicting future vertical motions

Mechanical Controls on Basin Evolution: Europe’s Continental Lithosphere

Studies on the mechanical properties of the pean lithosphere revealed a direct link between itsthermo-tectonic age and bulk strength (Cloetingh et al.,

Euro-2005, Cloetingh and Burov, 1996; Pérez-Gussinyé andWatts, 2005) On the other hand, inferences from Pand S wave tomography (Goes et al., 2000a, b; Rit-ter et al., 2000, 2001) and thermo-mechanical mod-elling (Garcia-Castellanos et al., 2000) point to a

Iberia

Iberia (south)

Iberia (north) Brittany

Arctic Canada

Central Australia

Trans Continental Arch

of North America Central Asia

Central Asia

mantle folding

whole lithosphere folding

upper crustal folding

0 100 200 300 400 500 600 700 800

Arctic Canada

Central Australia

Trans Continental Arch

of North America Central Asia

Central Asia

mantle folding

whole lithosphere folding

upper crustal folding

0 100 200 300 400 500 600 700 800

Fig 17 Comparison of observed (solid squares) and modelled

(open circles) wavelengths of crustal, lithospheric mantle and

whole lithospheric folding in Iberia (Cloetingh et al., 2002c)

with theoretical predictions (Cloetingh et al., 1999) and other

estimates (open squares) for wavelengths documented from

geological and geophysical studies (Stephenson and Cloetingh,

1991; Nikishin et al., 1993; Ziegler et al., 1995; Bonnet et

al., 2000) Wavelength is given as a function of the

thermo-tectonic age at the time of folding Thermo-thermo-tectonic age sponds to the time elapsed since the last major perturbation of the lithosphere prior to folding Note that neotectonic folding

corre-of Variscan lithosphere has recently also been documented for Brittany (Bonnet et al., 2000) Both Iberia and Central Asia are characterized by separate dominant wavelengths for crust and mantle folds, reflecting decoupled modes of lithosphere folding (Cloetingh et al., 2005) Modified from Cloetingh et al (2002)

Methods for studying uplift and erosion

Geomorphology

Maximum burial

Sedimentology

Fission tracks + He-dating

al geology

Fig 18 Role of constraints from structural geology,

geo-chronology, geomorphology and sedimentology in linking the

sedimentary record to lithospheric processes (cartoon for coastal

Norway by Japsen)

pronounced weakening of the lithosphere in the Lower

Rhine area owing to high upper mantle temperatures

However, the Late Neogene and Quaternary

tecton-ics of the Ardennes-Lower Rhine area appear to form

part of a much wider neotectonic deformation

sys-tem that overprints the Late Paleozoic and Mesozoicbasins of NW Europe This is supported by geomor-phologic evidence and the results of seismicity studies

in Brittany (Bonnet et al., 1998, 2000) and Normandy(Lagarde et al., 2000; Van Vliet-Lanoë et al., 2000), bydata from the Ardennes-Eifel region (Meyer and Stets,1998; Van Balen et al., 2000), the southern parts ofthe Upper Rhine Graben (Nivière and Winter, 2000),the Bohemian Massif (Ziegler and Dèzes, 2005, 2007)and the North German Basin (Bayer et al., 1999; Littke

et al., 2008)

Lithosphere-scale folding and buckling, in response

to the build up of compressional intraplate stresses, cancause uplift or subsidence of relatively large areas attime scales of a few My and thus can be an impor-tant driving mechanism of neotectonic processes Forinstance, the Plio-Pleistocene accelerated subsidence

of the North Sea Basin is attributed to down buckling

of the lithosphere in response to the build-up of thepresent day stress field (Van Wees and Cloetingh,1996; Unternehr and van den Driessche, 2004) Sim-ilarly, the Vosges-Black Forest arch, which at thelevel of the crust-mantle boundary extends from theMassif Central into the Bohemian Massif, was rapidlyuplifted during the Burdigalian (±18 Ma) and since

then has been maintained as a major topographic

fea-ture (Ziegler and Fraefel, 2009) Uplift of this arch is

attributed to lithospheric folding controlled by

com-pressional stresses originating at the Alpine collision

zone (Ziegler et al., 2002; Dèzes et al., 2004; Ziegler

and Dèzes, 2005, 2007; Bourgeois et al., 2007)

An understanding of the temporal and spatial

strength distribution in the NW European lithosphere

may offer quantitative insights into the patterns of its

intraplate deformation (basin inversion, up thrusting of

basement blocks), and particularly into the pattern of

lithosphere-scale folding and buckling

Owing to the large amount of high quality

geophys-ical data acquired during the last 20 years in Europe,

its crustal configuration is rather well known (Dèzes

and Ziegler, 2004; Tesauro et al., 2008) though

signifi-cant uncertainties remain in many areas about the

seis-mic and thermal thickness of the lithosphere (Babuska

and Plomerova, 1992; Artemieva and Mooney, 2001;

Artemieva, 2006) Nevertheless, available data helps

to constrain the rheology of the European lithosphere,

thus enhancing our understanding of its strength

So far, strength envelopes and the effective elastic

thickness of the lithosphere have been calculated for

a number of locations in Europe (Fig 19, Cloetingh

and Burov, 1996) However, as such calculations were

made for scattered points only, or along transects, they

provide limited information on lateral strength

varia-tions of the lithosphere Although lithospheric

thick-ness and strength maps have already been constructed

for the Pannonian Basin (Lankreijer et al., 1999) and

the Baltic Shield (Kaikkonen et al., 2000), such maps

were until recently not yet available for all of Europe

As evaluation and modelling of the response of the

lithosphere to vertical and horizontal loads requires

an understanding of its strength distribution, dedicated

efforts were made to map the strength of the European

foreland lithosphere by implementing 3D strength

cal-culations (Cloetingh et al., 2005)

Strength calculations of the lithosphere depend

pri-marily on its thermal and compositional structure

and are particularly sensitive to thermal uncertainties

(Ranalli and Murphy, 1987; Vilotte et al., 1993;

Ranalli, 1995; Burov and Diament, 1995) For this

rea-son, the workflow aimed at the development of a 3D

strength model for Europe was two-fold: (1)

construc-tion of a 3D composiconstruc-tional model and (2)

calculat-ing a 3D thermal cube The final 3D strength cube

was obtained by calculating 1D strength envelopes for

each lattice point (x, y) of a regularized raster ering NW-Europe (Fig 20a) For each lattice-pointthe appropriate input values were obtained from a 3Dcompositional and thermal cube A geological and geo-physical geographic database was used as reference forthe construction of the input models

cov-For continental realms, a 3D multi-layer sitional model was constructed, consisting of onemantle-lithosphere layer, 2–3 crustal layers and anoverlying sedimentary cover layer, whereas for oceanicareas a one-layer model was adopted For the depth tothe different interfaces several regional or European-scale compilations were available that are based ondeep seismic reflection and refraction or surface wavedispersion studies (e.g., Panza, 1983; Calcagnile andPanza, 1987; Suhadolc and Panza, 1989; Blundell

compo-et al., 1992; Du compo-et al., 1998; Artemieva compo-et al., 2006).For the base of the lower crust, we strongly relied onthe European Moho map of Dèzes and Ziegler (2004)(Fig 2.1a) Regional compilation maps of the seismo-genic lithosphere thickness were used in subsequentthermal modelling as reference to the base of the ther-mal lithosphere (Babuska and Plomerova, 1993, 2001;Plomerova et al., 2002) (see Fig 20b)

Figure 21a shows the integrated strength undercompression of the entire lithosphere of Western andCentral Europe, whereas Fig 21b displays the inte-grated strength of the crustal part of the lithosphere

As evident from Fig 21, Europe’s lithosphere is acterized by major spatial mechanical strength varia-tions, with a pronounced contrast between the strongProterozoic lithosphere of the East-European Platform

char-to the northeast of the Teisseyre-Tornquist Zone (TTZ)and the relatively weak Phanerozoic lithosphere ofWestern Europe

A similar strength contrast occurs at the sition from strong Atlantic oceanic lithosphere tothe relatively weak continental lithosphere of West-ern Europe Within the Alpine foreland, pronouncednorthwest-southeast trending weak zones are recog-nized that coincide with such major geologic struc-tures as the Rhine Graben System and the NorthDanish-Polish Trough, that are separated by the high-strength North German Basin and the Bohemian Mas-sif Moreover, a broad zone of weak lithospherecharacterizes the Massif Central and surroundingareas

tran-In the area of the Trans-European Suture Zone,which corresponds to a zone of terranes that were

Fig 19 Compilation of observed and predicted values of

effec-tive elastic thickness (EET), depth to bottom of mechanically

strong crust (MSC), and depth to bottom of mechanically strong

lithospheric mantle (MSL) plotted against the age of the

conti-nental lithosphere at the time of loading and comparison with

predictions from thermal models of the lithosphere Labeled

contours are isotherms Isotherms marked by solid lines are

for models that account for additional radiogenic heat

produc-tion in the upper crust Dashed lines correspond to pure

cool-ing models for continental lithosphere The equilibrium

ther-mal thickness of the continental lithosphere is 250 km Shaded

bands correspond to depth intervals marking the base of the

mechanical crust (MSC) and the mantle portion of the

litho-sphere (MSL) Squares correspond to EET estimates, circles

indicate MSL estimates, and diamonds correspond to estimates

of MSC Bold letters correspond to directly estimated EET

values derived from flexural studies on, for example, foreland

basins, Thinner letters indicate indirect rheological estimates

derived from extrapolation of rock-mechanics studies The data set includes (I): Old thermo-mechanical ages (1,000–2,500 Ma): northernmost (N.B.S.), central (C.B.S.), and southernmost Baltic Shield (S.B.S.); Fennoscandia (FE); Verkhoyansk plate (VE); Urals (UR); Carpathians; Caucasus, (II): Intermediate thermo- mechanical ages (500–1,000 Ma): North Baikal (NB); Tarim and Dzungaria (TA-DZ); Variscan of Europe: URA, NHD, EIFEL; and (III): Younger thermo-mechanical ages (0–500 Ma): Alpine belt: JURA, MOLL (Molasse), AAR; southern Alps (SA) and eastern Alps (EA); Ebro Basin; Betic rifted mar- gin; Betic Cordilleras Modified from Cloetingh and Burov (1996)

amalgamated during the Early Paleozoic, the debated

occurrence of thickened crust adjacent to the Tornquist

Zone (Fig 5) was refuted by large-scale deep

seis-mic experiments (POLONAISE, DEKORPBASIN96

and CELEBRATION; Guterch et al., 1999, 2003;

BASIN Research Group, 1999) The process of

ter-rane amalgamation was assumed to give rise to

pro-nounced mechanical weakening of the lithosphere,

particularly of its mantle part Recent studies

indi-cate, however, a rather steep crustal thickness

gra-dient across the Tornquist Zone (Scheck-Wenderoth

and Lamarche, 2005), which does not fit the expectedconfiguration of an intracratonic suture zone TheTeisseyre-Tornquist Zone is now better described asthe boundary zone that separates the Precambrian crust

of the East European Craton from the Phanerozoiccrust of Western and Central Europe, which was con-solidated during the Caledonian and Variscan oro-genies (Ziegler, 1990b; Berthelsen, 1998; Erlström

et al., 1997; Grad et al., 2002; Guterch et al., 1999;Guterch and Grad, 2006) The northwestern prolon-gation of the Teisseyre-Tornquist Zone into Denmark,

a

base thermal lithosphere (in km)

c) Depth thermal lithosphere

Strength Modelsgeothermlocal base thermal lithosphere

1300°C isotherm

local geotherm hot

cold

Thermal Models Compositional Models

Fig 20 a) From crustal thickness (top left) and thermal

struc-ture (top right) to lithospheric strength (bottom): conceptual

configuration of the thermal structure and composition of the

lithosphere, adopted for the calculation of 3-D strength

mod-els Modified from Cloetingh et al., 2005 b) Heterogeneity in

compressional and thermal structure in Europe’s lithosphere and

upper mantle (a) Heterogeneity in crustal controls on spheric strength (from Dèzes and Ziegler, 2004) (b) Heterogene- ity in surface heat flow (c) Heterogeneity in depth (km) to the

litho-base of the lithosphere inferred from constraints from seismic tomography

where it is referred as the Sorgenfrei-Tornquist Zone

(STZ), separates the stable part of the East

Euro-pean Craton from its weaker southwestern margin

(Berthelsen, 1998; Erlström et al., 1997; Pharaoh

et al., 2006)

Whereas the lithosphere of Fennoscandia is

char-acterized by a relatively high strength, the North Sea

rift system corresponds to a zone of weakened

litho-sphere Other areas of high lithospheric strength are

the Bohemian Massif and the London-Brabant Massif

both of which exhibit low seismicity (Fig 22)

A pronounced contrast in strength can also be

noticed between the strong Adriatic indenter and the

weak Pannonian Basin area (see also Fig 21)

Comparing Fig 12 with Fig 13 reveals that

the lateral strength variations of Europe’s intraplate

lithosphere are primarily caused by variations in

the mechanical strength of the lithospheric

man-tle, whereas variations in crustal strength appear to

be more modest Variations in lithospheric mantlestrength are primarily related to variations in the ther-mal structure of the lithosphere that can be related

to thermal perturbations of the sub-lithospheric uppermantle imaged by seismic tomography (Goes et al.,2000a); lateral variations in crustal thickness play asecondary role, apart from Alpine domains which arecharacterized by deep crustal roots High strength inthe East-European Platform, the Bohemian Massif,the London-Brabant Massif and the FennoscandianShield reflects the presence of old, cold and thick litho-sphere, whereas the European Cenozoic Rift Systemcoincides with a major axis of thermally weakenedlithosphere within the Northwest European Platform.Similarly, weakening of the lithosphere of southernFrance can be attributed to the presence of tomo-graphically imaged upper mantle convective insta-

Fault Normal fault Thrust fault

10°0'0''E

20°0'0''E

30°0'0''E 20°0'0''E

Integrated strength (10**10N/m

Fig 21 Integrated strength

maps for intraplate Europe.

Contours represent integrated

strength in compression for

(a) total lithosphere and (b)

crust Adopted composition

for upper crust, lower crust,

and mantle is based on a wet

quartzite, diorite, and dry

olivine composition,

respectively Rheological rock

parameters are based on

Carter and Tsenn (1987) The

adopted bulk strain-rate is

10–16s–1, compatible with

constraints from GPS

measurements (see text) The

main structural features of

Europe are superimposed on

the strength maps Modified

from Cloetingh et al (2005)

bilities rising up under the Massif Central (Granet

et al., 1995; Wilson and Patterson, 2001; Lustrino and

Wilson, 2007)

The major lateral strength variations that ize the lithosphere of extra-Alpine Phanerozoic Europeare largely related to its Late Cenozoic thermal per-

integrated strength for the

European crust (see Fig 21).

Earthquake epicenters from

the NEIC data center (NEIC,

2004), queried for magnitude

>2 and focal depths <35 km

turbation as well as to Mesozoic and Cenozoic rift

systems and intervening stable blocks, and not so

much to the Caledonian and Variscan orogens and

their accreted terranes (Dèzes et al., 2004, Ziegler

and Dèzes, 2006) These lithospheric strength

varia-tions (Fig 21) are primarily related to variavaria-tions in

the thermal structure of the lithosphere, and therefore,

are compatible with inferred variations in the

effec-tive elastic thickness (EET) of the lithosphere (see

Cloetingh and Burov, 1996; Pérez-Gussinyé and Watts,

2005)

The most important strong domains within the

lithosphere of the Alpine foreland correspond to the

London-Brabant, Armorican, Bohemian and

West-Iberian Massifs The strong Proterozoic

Fennoscan-dian – East-European Craton flanks the weak

Phanero-zoic European lithosphere to the northeast whereas

the strong Adriatic indenter contrasts with the weak

lithosphere of the Alpine-Mediterranean collision zone

(Cavazza et al., 2004)

Figure 22 displays on the background of the crustalstrength map the distribution of seismic activity,derived from the NEIC global earthquake catalogue(USGS) As obvious from Fig 16, crustal seismicity islargely concentrated on the presently still active Alpineplate boundaries, and particularly on the margins ofthe Adriatic indenter In the Alpine foreland, seismic-ity is largely concentrated on zones of low lithosphericstrength, such as the European Cenozoic rift system,and areas where pre-existing crustal discontinuities arereactivated under the presently prevailing NW-directedstress field, such as the South Armorican shear zone(Dèzes et al., 2004; Ziegler and Dèzes, 2007) and therifted margin of Norway (Mosar, 2003)

It should be noted that the strength maps presented

in Fig 15 do not incorporate the effects of spatial ations in the composition of crustal and mantle layers.Future work will have to address the effects of suchsecond order strength perturbations, adopting con-straints on the composition of several crustal and man-

vari-tle layers provided by seismic velocities (Guggisberg

et al., 1991; Aichroth et al., 1992) and crustal and

upper mantle xenolith studies (Mengel et al., 1991;

Wittenberg et al., 2000)

Dynamics of Sedimentary Systems

and Deformation Patterns

The largest water mass outside the ocean resides not

in ice caps nor in lakes and rivers but in the pore

space of the Earth’s crust By far the largest proportion

of this pore space is contained in sedimentary rocks

Owing to their high porosity, sedimentary rocks are

the only significant reservoirs for oil, gas and water

and the most significant conduits for subsurface

pollu-tion Therefore, predicting the architecture and

proper-ties of sedimentary rocks in the subsurface is one of the

great challenges of Solid-Earth science Progress will

critically depend on successful integration of remote

imaging of the subsurface and forward modelling from

first principles of sedimentation, erosion and chemical

reactions Prediction includes both prediction in space

(“ahead of the drill”) and forecasting system behaviour

in time (based on 4-D-monitoring)

Quantitative analysis of the geometries and facies

patterns resulting from erosion and sediment

deposi-tion provides a key step in linking the dynamics of

hin-terland uplift and basin subsidence and the associated

mass flux The prospect of increasingly higher

resolu-tion in space and time will provide a better

understand-ing of factors controllunderstand-ing the topographic evolution on

continents and the subsidence of sedimentary basins

along their margins

During the last few years it has become increasingly

evident that recent deformation has strongly affected

the structure and fill of sedimentary basins Similarly,

the long-lasting memory of the lithosphere appears to

play a much more important role in basin reactivation

than hitherto assumed Therefore, a better

understand-ing of the 3-D fine structure of the linkage between

basin formation and basin deformation is essential for

linking lithospheric forcing and upper mantle

dynam-ics to the dynamdynam-ics of crustal uplift and erosion, and

the dynamics of sedimentary systems Structural

anal-ysis of the architecture of sedimentary basins,

includ-ing paleo-stress assessment, provides important

con-straints on the transient nature of intra-plate stress

fields

Reconstruction of the history of sedimentary basins

is a prerequisite for identifying transient processescontrolling basin (de)formation Full 3-D reconstruc-tions, including the use of sophisticated 3-D visualiza-tion and geometric construction techniques for faultedbasin architectures 3-D back-stripping, including theeffects of flexural isostasy and faulting, permits a thor-ough assessment of sedimentation and faulting ratesand changing facies and geometries through time Theestablished architecture of the preserved sedimentaryrecord serves as key input for the identification andquantification of transient processes

Compressional Basins: Lateral Variations

in Flexural Behaviour and Implications for Paleotopography

Deep seismic profiles across the Alps, the Pyrenees,the Apennines and the Carpathians have recently pro-vided a completely new understanding on the maindecoupling horizons acting during continental colli-sion, roll-back of the subducted slab and coeval open-ing of back-arc basins In many cases, the mantlelithosphere of the upper plate (Adria in the WesternAlps, Europe in the Pyrenees) progressively indentsthe lower plate (European lithosphere in the WesternAlps, Iberian lithosphere in the Pyrenees) and detachesits upper crust (Fig 4; Roure et al., 1989, 1996) Both

in the Alps and the Pyrenees, this process results inthe development of foreland-propagating thrusts in thelower plate and crustal-scale antithetic back-thrusts

in the upper plate, which account for the famous

“crocodile” tectonics of Meissner (1989) As dicted by Laubscher with his lithophere “Verschluck-ung” (Laubscher, 1970, 1988, 1990), only the mantlelithosphere is proved to be recycled in the astheno-sphere Most, if not all the lower crust, whichactually forms the main decoupling horizon, is pro-gressively stacked in deeply buried duplexes and, thus,contributes to the growth of crustal roots at the base

pre-of orogens Nevertheless lower crustal material can besubducted to depths of 55–60 km at which it entersthe eclogite stability field, acquiring P-wave velocitiestypical for the mantle, therefore crossing the geophys-ically defined Moho discontinuity, and thus limits theseismically resolvable depth of crustal roots (Bousquet

et al., 1997; Stampfli et al., 1998; Ziegler et al., 2001).Roure et al (1994, 1996) and Ziegler and Roure (1996)

give a detailed discussion on constraints provided by

deep seismic data on the bulk geometry of Alpine belts

Modelling of compressional basins followed

essen-tially the same philosophy as modelling of extensional

basins Initial lithosphere-scale models focused on the

role of flexural behaviour of the lithosphere during

foreland basin development (e.g., Zoetemeijer et al.,

1990; Van der Beek and Cloetingh, 1992) These

stud-ies drew on data sets consisting of wells, gravity data,

and deep seismic profiling, such as the ECORS

pro-file through the Pyrenees (Fig 4), completed in the

1980s Flexural modelling was backed up by

large-scale studies on the rheological evolution of

conti-nental lithosphere (Cloetingh and Burov, 1996) that

demonstrated in compressional settings a direct link

between the mechanical properties of the lithosphere,

its thermal structure and the level of regional intraplate

stresses

Inferences drawn from large-scale flexural

mod-elling provided feedback for subsequent analysis on

sub-basin scales For example, modelling

predic-tions for the presence of weak lithosphere in the

Alpine belt invoke steep downward deflection of

the lithosphere, favouring the development of upper

crustal flexure-induced synthetic and antithetic

ten-sional faults (Ziegler et al., 2002) Such fault systems

are observed on reflection-seismic profiles in the

Apen-nine and Sicilian foredeeps (Casero et al., 1991; Roure

et al., 1991; Hippolyte et al., 1994, 1996; Casero,

2004), in the Alpine Molasse Basin of Germany and

Austria (Ziegler, 1990a) and in the Carpathian

fore-land basin of Pofore-land (Roca et al., 1995; Oszczypko,

2006), the Ukraine (Roure and Sassi, 1995; Izotova and

Popadyuk, 1996) and Romania (Ellouz et al., 1996;

Matenco et al., 1997) Such flexure-induced upper

crustal normal faulting caused weakening of the

litho-sphere Integrated flexural analysis of a set of profiles

across the Ukrainian Carpathians and their foreland

demonstrates an extreme deflection of the lithosphere,

almost to the point of its failure, and very large

off-sets on upper crustal normal faults (Zoetemeijer et al.,

1999)

Following studies on the paleo-rheology of the

lithosphere, constrained by high-quality

thermo-chronology in the Central Alps (Okaya et al., 1996)

and Eastern Alps (Genser et al., 1996), the importance

of large lateral variations in the mechanical strength

of mountain belts became evident This pertains

par-ticularly to a pronounced strength reduction from the

external part of an orogen towards its internal parts As

a result, flexural foreland basins develop on the stronglithosphere of external zones of orogens, whereas onlow strength lithosphere of their internal zones pull-apart basins can develop (Nemes et al., 1997, Cloet-ingh et al., 1992; Roure, 2008) The effects of lateralflexural strength variations of the lithosphere of fore-land basins were explored by a modelling study thatwas carried out along a transect through the NE Pyre-nees that is well constrained by crustal-scale seismiccontrol and an extensive field-derived database (Verges

et al., 1995) Apart from investigating the presentconfiguration of foreland basins and quantifying thepresent-day mechanical structure of the lithosphereunderlying the southern Pyrenees fold-and-thrust belt,the relationship between paleo-topography and flexu-ral evolution of the orogen was analyzed (Millan et al.,1995) This novel approach led to a set of testable pre-dictions on paleotopography and sediment supply tothe foreland basin

Topographic Expression of Compressional and Extensional Flat-Ramp Systems

In contrast to lithospheric scale folding or bending,accounting for the development of large wavelengtharches and basins, and strongly asymmetric foredeepbasins, reverse and normal faults control the develop-ment of narrow anticlines and steep grabens or halfgrabens, respectively Such isolate structures occur-ring in the foreland of thrust belts or adjacent to

an extensional system may be linked to them viadeep seated detachment horizons, as evidenced byreflection-seismic data in the case studies presentedbelow

Northern Apennines Case Study

In the frontal parts of the Northern Apennines,industry-type reflection-seismic profiles documenttheir thrusted architecture and the configuration ofPliocene synkinematic sedimentary series that weredeposited in piggyback basins during the growth ofanticlines and rapid subsidence of the foreland litho-sphere (Fig 23a; Pieri, 1983; Zoetemeijer et al., 1992;Doglioni and Prosser, 1997; Roure, 2008) As in

piggy-back basin in the

Northern Apennines (after

Zoetemeijer et al., 1992;

Roure, 2008) b) La Clappe

roll-over anticline at the

northern margin of the Gulf of

Lions (Languedoc,

Southeastern France, after

Roure, 2008)

the southern parts of this profile Pliocene structures

are unconformably overlain by thick, little deformed

Quaternary sediments contained in a gentle synclinal

basin, it was assumed that all tectonic contraction had

stopped by the end of the Pliocene

Earthquake focal mechanisms and GPS

measure-ments attest, however, for a still ongoing compression

and growth of structures in the vicinity of the

Apen-nine thrust front (Picotti et al., 2007; Scrocca et al.,

2007)

Since the available seismic profiles were recorded

to 5 sec TwT only they do not image beneath the

Qua-ternary basin the basal décollement of the orogenic

wedge However, by extrapolation from the northern,

shallower parts of the seismic profiles and by

apply-ing cross-section balancapply-ing techniques, it is evident

that the basal décollement is located within Triassic

evaporites Moreover, it is evident that the Quaternary

basin takes in a piggyback position with respect to

the frontal thrusted structures and is apparently located

above a flat segment of the sole thrust In the process

of continued northward displacement of the orogenic

wedge above ramp segments stepping up from older

horizons in the south (i.e., either Paleozoic strata or

crystalline basement) to progressively shallower

strati-graphic horizons in thinner Mesozoic series in the

north, the southern and northern flanks of the

Quater-nary piggy-back basin became increasingly tilted

Further validation by coupled forward kinematic

and sedimentation modelling helped to quantify the

various parameters controlling the present architecture

of the orogenic wedge and the accommodation spaceavailable for synkinematic trapping of Quaternary sed-iments This required quantification of the overallamount of shortening, its partitioning from the basaldeformation into the individual thrusts which ramp upfrom it, their respective velocity and timing, and therates of bending of the lithosphere (Zoetemeijer et al.1992)

La Clappe Case Study (Northern Margin of the Gulf

of Lions)The structural cross-section across the northernonshore segment of the Gulf of Lions margin, given

in Fig 23b, is constrained by industry-type seismic profiles This cross-section extends from theSt-Chinian fold and thrust belt in the north, repre-senting the lateral equivalent of the North Pyreneanthrust front, across the La Clappe antiform in thesouth, an isolated Mesozoic carbonate massif that isflanked by tilted Oligocene and Miocene series (Roure,2008) This cross-section, which was not investigated

reflection-by ECORS deep seismic profiling, documents two nomena, namely a negative inversion and a roll-overstructure above an extensional detachment

phe-From the north to the south, this cross-sectionoutlines (1) an erosional remnant of the former LateCretaceous to Eocene Pyrenean flexural basin, (2) the

thin-skinned Eocene structures of St-Chinian

fold-and-thrust belt, representing a segment of the external

part of the Pyrenean Orogen, and (3) a number of

post-Eocene half grabens, which are controlled by

arcu-ate listric normal faults, such as the Quarante Fault

At depth these faults sole out into the basal

detach-ment thrust of the Pyrenean orogenic wedge The

ten-sional (negative) reactivation of former thrust faults

can be accurately dated by the late Oligocene and

early Miocene sedimentary fill of the footwall grabens,

and thus coincided with the opening of the Gulf of

Lions Basin (Roure et al., 1988; Séranne et al., 1995;

Séranne, 1999)

The La Clappe anticline is interpreted as a textbook

example of a roll-over or accomodation fold above

an extensional detachment (McClay, 1989) Although

seismic data evidence in the area of the La Clappe

structure a vertical offset of the basement beneath

the basal décollement, it is not yet clear whether

this fault developed during Mesozoic rifting,

control-ling the development of a flat-ramp décollement

dur-ing the Pyrenean orogeny, or whether it is related

to the Oligo-Miocene rifting event (in a similar way

as analogue models of Vendeville et al., 1987, and

the infra-salt tilted blocks imaged beneath the Bresse

Graben by ECORS; Bergerat et al., 1989, 1990)

Both solutions can be accurately balanced, but imply

very different kinematic scenarios during forward

modelling

Coupling versus Decoupling between Forelands

and Orogenic Wedges and Development

of Thrust-Top Pull-Apart Basins

Ziegler et al (2002) have documented at a plate

tectonic scale successive episodes of mechanical

cou-pling and decoucou-pling of orogenic wedges and

fore-lands, with far-field foreland inversions reflecting

peri-ods of strong coupling between the orogen and the

adjacent foreland lithosphere

Paleostress measurements and paleomagnetic

stud-ies help to trace the coupling versus decoupling

his-tory of tectonic wedges with respect to their

adja-cent forelands The inversion of microtectonic

mea-surements in well-dated strata provides a direct control

on the main horizontal stress direction at a given time,

whereas paleomagnetic data are required to

demon-strate whether a given tectonic unit has been rotated

or not between the considered time interval and thePresent This methodology has been applied to theSouthern Apennines by Hippolyte et al (1994, 1996),documenting the successive pattern of paleostressdirections in both the allochthon and the autochthon,for different stages including the Tortonian, Messinian,Lower, Middle and Upper Pliocene and Pleistocene.Surprisingly, results show periods during which pale-ostress directions were identical in the allochthonand the foreland, reflecting their mechanical coupling,and periods during which stress directions differedbetween the allochthon and the foreland, reflectingtheir mechanical decoupling Similar objectives werealso addressed by Malavieille (1984), Martinez et al.(2002), and McClay et al (2004) by means of ana-logue models, exploring the effects of oblique conver-gence on strain partitioning and coupling/decouplingprocesses in foreland fold-and-thrust belts Moreover,Nieuwland et al (1999, 2000; Fig 24) carried out aseries of experiments with a sand box containing pres-sure sensors which showed cycles of pressure build-

up and relaxation in the foreland that are directlyrelated to cycles of thrust activation At the onset ofeach cycle, a good coupling is observed between theallochthon and the autochthon, with no fault activitybut with a progressive increase of the maximum hori-zontal compressional stress Once this horizontal stressreaches a sufficient value, a new thrust fault nucle-ates, resulting in renewed decoupling of the autochthonfrom the allochthon and in a pressure decrease in theautochthon

At the reservoir level, this rapid increase of the imum compressional stress before the nucleation of anew frontal thrust is likely to account for the devel-opment of Layer Parallel Shortening (LPS) and coevalpressure-solution and quartz-cementation in sandstonereservoirs, as observed in the Sub-Andean basins ofVenezuela and Colombia (Roure et al., 2003, 2005),and for the re-crystallisation and re-magnetisation

max-of mesodolomites observed in the Alberta foreland(Robion et al., 2004; Roure et al., 2005) Deformation

is thus alternatively plastic (accounting for solution and LPS in the autochthon during periods ofcoupling), and brittle (accounting for nucleation of anew frontal thrust and thrust propagation during theperiods of decoupling)

pressure-Decoupling and strain partitioning near plateboundaries account also for the development of thrust-

85 173 261 349 437 525 613 701 789 877 965 1053 1141 1229 1317 1405

seconds –5

0 5

1 2 3

sensor positions

sensor positions

Fig 24 Analogue experiment

of thrust propagation, with

pressure sensors recording the

cyclic evolution of the main

principal stress in the foreland

autochthon, as a result of its

successive coupling and

decoupling with the tectonic

wedge (after Nieuwland et al.,

1999, 2000)

top pull-apart basins in a dominantly compressional

regime The Vienna Basin is probably the most famous

and archetype of this type of basins It developed on

top of the Alpine allochthon after emplacement of its

nappe systems on the foreland, in response to lateral

eastward escape of the Alpine-Carpathian Block into

the Carpathian embayment (Royden, 1985; Sauer et

al., 1992; Seifert, 1996; Decker and Peresson, 1996;

Schmid et al 2008)

Complex piggyback basins and thrust-top pull-apart

basins developed also in the internal parts of

Circum-Mediterranean thrust belts in response to local and

temporal changes in paleostress regime, and related

strain partitioning and lateral block escape Examples

are the Sant’Arcangelo Basin in the Southern

Apen-nines (Hippolyte et al., 1991, 1994; Di Stefano et al.,

2002; Sabato et al., 2005; Monaco et al., 2007) and

the Chelif Basin in North Algeria (Neurdin-Trescartes,

1995; Roure, 2008) In a very similar geodynamic

set-ting the Gulf of Paria developed between Venezuela

and Trinidad (Lingrey, 2007)

The physiography and lozenge shape of the lif Basin in North Algeria is clearly evident on geo-logical maps and landsat imagery (Fig 25; Roure,2008) This basin is located north of the Tellian thrustfront, which reached its current position during theLanghian (Frizon de Lamotte et al., 2000; Roca et al.,2004; Benaouali et al., 2006) To the north the ChelifBasin is delimited by a major east-trending lineament,known as the “Dorsale Calcaire”, which separates theKabylides crystalline basement in the north from theTellian nappes in the south, and most likely behaved as

Che-a mChe-ajor strike-slip fChe-ault during the development of theChelif Basin

The Neogene sedimentary fill of the Chelif Basincomprises Burdigalian to Langhian syn-kinematicseries, which were deposited in a piggyback positionduring the main southward transport of the Telliannappes involving oblique convergence, transpressionand strain-partitioning Post-kinematic Tortonian toPliocene series, contained in normal fault controlleddepressions, overlay these syn-kinematic deposits

Fig 25 Satellite image

outlining the location of the

Chelif thrust top pull-apart

basin (North Algeria)

These normal faults, locally exposed at the surface, can

be traced on seismic profiles downward into the

deep-est part of the basin, and trend oblique (en échelon)

with respect to the Dorsale Calcaire lineament, being

thus indicative of its Late Miocene-Pliocene

transten-sional reactivation Comparable to the El Pilar Fault

of Venezuela, the Dorsale Calcaire lineament

accom-modated during the Tortonian to Pliocene post-nappes

transtensional episode a lateral displacement of the

Kabylides relative to the Tell allochthon and the

under-lying African foreland crust

Plio-Quaternary inversion of the Chelif depocentre,

involving folding and erosion of Pliocene series along

basin bounding faults, accounts for renewed

transpres-sion along this segment of the Dorsale Calcaire

Intracratonic Basins

Intracratonic basins developed in the interior of

con-tinents, generally far from active plate boundaries In

cross-section they are generally saucer shaped, are

characterized by a protracted subsidence history often

exceeding 100 My during which there is hardly

evi-dence for extensional faulting As such they reflect

long-term progressive crustal down warping and are

generally characterized by low topographies

through-out their history The dimensions and depth of such

sag basins vary considerably Intracratonic basins are

of considerable economic interest as a number of them

host outstanding hydrocarbon provinces such as the

West Siberian, North Sea, Williston and Michigan

Three end members of intracratonic sag basinsare recognized, namely rift-, hot-spot- and cold-spot-driven basins (Ziegler, 1989) During the evolution

of such sag basins compressional intraplate stressescan interfere with their subsidence, controlling bylithospheric folding subsidence accelerations and byreactivation of pre-existing basement discontinuitiestheir partial inversion Furthermore, intraplate com-pressional deformation can cause by disruption ofsedimentary platforms the isolation of basins Sucherosional remnants of larger shelves and platforms dif-fer from sag basins in so far as their axes do not

necessarily coincide with depocentres (e.g., Paleozoic

Tindouf Basin; Mesozoic Paris Basin: Ziegler, 1989,

1990)

The proto-type of a rift-driven intracratonic sag

basin is the Late Cretaceous and Cenozoic North Sea

Basin, which is superimposed on the Mesozoic Viking

and Central grabens that transect Caledonian basement

and the Northern and Southern Permian Basin The

rifting stage of the North Sea commenced in the Early

Triassic and persisted intermittently into the Early

Cre-taceous During the Late Cretaceous and Cenozoic

post-rift thermal subsidence stage an over 4 km deep,

up to 500 km wide and 1,000 km long thermal sag

basin developed, widely overstepping the axial rift

sys-tem (Ziegler, 1990; Kuznir et al., 1995) This type of

basin essentially conforms to the lithospheric

stretch-ing model of McKenzie (1978), though its Paleocene

and Plio-Quaternary subsidence accelerations can be

related to deflection of the lithosphere in response

to the build-up of intraplate compressional stresses

(Ziegler, 1990; Van Wees and Cloetingh, 1996)

The West Siberian Basin, which extends into the

Kara Sea, is up to 1,500 km wide and almost 3,000 km

long and, though still debated, can be regarded as a

hot-spot-driven sag basin It evolved on a complex

pat-tern of arc terranes and continental blocks that were

assembled during the Late Paleozoic Uralian Orogeny

Following Early Permian consolidation of the Urals,

their back-arc domain was affected by Late

Permian-Early Triassic extension that were punctuated by major

plume activity at the Permo-Triassic boundary, as

evidenced by the extrusion of thick and widespread

basalts Evidence for limited crustal extension is

essen-tially limited to the Kara Sea and the northern parts of

the West Siberian Basin Post-magmatic regional

ther-mal subsidence of the West Siberian Basin by as much

as 6,500 m is interpreted as reflecting strong

ther-mal attenuation of the lithospheric mantle and

mag-matic destabilization of the crust-mantle boundary

dur-ing plume impdur-ingement Corresponddur-ingly the West

Siberian Basin is interpreted as a “hot-spot” basin that,

owing to limited crustal extension, does not conform

to the classical stretching model of McKenzie (1978)

The post-rift subsidence of the West Siberian Basin

was repeatedly overprinted by the build-up of

compres-sional stresses related to the Middle and Late Triassic

folding of the northernmost Urals and Novaya

Zem-blya, Early Cretaceous south-verging thrusting of the

South Taimyr fold belt and during the Oligocene

India-Asia collision (Rudkewich, 1988, 1994; Ziegler, 1989;Peterson and Clarke, 1991; Zonenshain et al., 1993;Nikishin et al., 2002; Vyssotski et al., 2006)

Potential “cold spot” basins are the sub-circularPaleozoic Williston, Hudson Bay, Michigan and Illi-nois basins of North America, which have diameters

of 500–750 km, vary in depth between 2 and 4.7 kmand evolved on stabilized Precambrian crust All ofthem lack a distinct precursor rifting or magmatic stageand are characterized by a thick crust Subsidence ofthese basins began variably during the Late Cambrian

to Late Ordovician and persisted into Early erous times, though subsidence rates varied throughtime and were not synchronous between the differentbasins (Quinlan, 1987; Bally 1989) As such they defythe principle of the classical thermal sag basins whichdevelop in response to lithospheric cooling and con-traction during the post-rift stage of extensional basins(McKenzie, 1978; Quinlan, 1987) During the LateCarboniferous and Permian these basins were region-ally uplifted and subjected to erosion Significantly,these intracratonic basins evolved during a periodwhen Laurentia underwent only relatively minor lat-itudinal drift and was flanked by the Ordovician-Silurian Taconic-Caledonian and during the Devo-nian and Early Carboniferous by the Appalachian andthe Antler-Inuitian subduction systems (Ziegler, 1989,1990) It has therefore been postulated that develop-ment of these intracratonic basins was controlled by adecrease in ambient mantle temperatures related to thedevelopment of down-welling cells in the upper man-tle (cold-spots), and that subsequent recovery of ambi-ent mantle temperatures resulted in their slow upliftand erosion, unless they were incorporated into anothersubsidence regime, such as flexural foreland basins(Williston Basin) Subsidence of these North Americanintracratonic basins ceased once Laurentia started todrift northward, thus decoupling them from their cold-spots (Ziegler 1989)

Carbonif-The invoked cold-spot model conforms essentially

to the model advanced by Heine et al (2008), whoadvocates that vertical displacement of the lithosphere,controlling the development of intracratonic basins,

is induced by mantle convection and related globalplate kinematics According to this model, the long-lasting subsidence of intracratonic basins and theirtopographic position close to sea level throughout theirevolution, results from negative dynamic topography

of the lithosphere that is controlled by down-welling