constraints on the deep structure and dynamic processes beneath the alps and adjacent regions from an analysis of gravity anomalies summary gravity anomalies including terrain corrections over the western alps and the molasse basin are within 30 mgal of those calculated assuming local airy isostatic equilibrium but isostatic anomalies over regions nw and se of the alps exceed 50 mgal therefore mass excesses and deficits that must be supported by the strength of the lithosphere or by dynamically induced stress in the asthenosphere appear to be greater beneath the areas surrounding the alps than beneath the alpine chain itself attempts to account for the gravity gradient over the molasse basin and sub alpine chains and the small bouguer anomalies measured over the elevated areas of the vosges and black forest by the flexure of an elastic plate require an absurd set of parameters the high elevations of the vosges and the black forest are presumably due to high temperature in the underlying uppermost mantle but the deviations from isostatic equilibrium as well as the high temperature probably result from active upwelling in the asthenosphere beneath this area the absence of large isostatic anomalies over the alps and the failure of an elastic model to account for the gravity anomalies over the molasse basin suggest that the dynamic processes that flexed the european plate down to form the molasse basin and that built the alpine chain have waned the late cenozoic uplift of the molasse basin and the alps might be a consequence of a diminution or termination of downwelling of mantle material beneath the alps

the tertiary structural and thermal evolution of the central alps compressional and extensional structures in an orogenic belt the western alpine arc has been created during the cretaceous and the tertiary orogenies the interference patterns of the tertiary structures suggest their formation during continental collision of the european and the adriatic plates with an accompanying anticlockwise rotation of the adriatic indenter extensional structures are mainly related to ductile deformation by simple shear these structures developed at a deep tectonic level in granitic crustal rocks at depths in excess of 10 km in the early palaeogene period of the tertiary orogeny the main tertiary nappe emplacement resulted from a nw thrusting of the austroalpine penninic and helvetic nappes heating of the deep zone of the upper cretaceous and tertiary nappe stack by geothermal heat flow is responsible for the tertiary regional metamorphism reaching amphibolite facies conditions in the lepontine gneiss dome geothermal gradient 25 c km the tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative nw se oriented stretching lineation xi finite extension parallel to the direction of simple shear earliest cooling after the culmination of the tertiary metamorphism some 38 ma ago is recorded by the cooling curves of the monte rosa and mischabel nappes to the west and the suretta nappe to the east of the lepontine gneiss dome the onset of dextral transpression with a strong extension parallel to the mountain belt and the oldest s vergent backfolding took place some 35 to 30 ma ago during retrograde amphibolite facies conditions and before the intrusion of the oligocene dikes north of the periadriatic line the main updoming of the lepontine gneiss dome started some 32 30 ma ago with the intrusion of the bergell tonalites and granodiorites concomitant with s vergent backfolding and backthrusting and dextral strike slip movements along the tonale and canavese lines argand s insubric phase subsequently the center of main updoming migrated slowly to the west reaching the simplon region some 20 ma ago this was contemporaneous with the westward migration of the adriatic indenter between 20 ma and the present the western aar massif toce culmination was the center of strong uplift the youngest s vergent backfolds the glishorn anticline and the berisal syncline fold the 12 ma rb sr biotite isochron and are cut by the 11 ma old rhone simplon line the discrete rhone simplon line represents a late retrograde manifestation in the preexisting ductile simplon shear zone this fault zone is still active today the oligocene neogene dextral transpression and extension in the simplon area were concurrent with thrusting to the northwest of the helvetic nappes the prealpes 35 15 ma and with the jura thin skinned thrust 11 3 ma it was also contemporaneous with thrusting to the south of the bergamasc 35 5 ma and milan thrusts 16 5 ma the oligocene neogene dextral transpression in the central alps is of the same age as the thrusting to the west and southwest in the external french part and to the east in the internal italian part of the alpine arc of the western alps

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

flexural eustatic numerical model for drowning of the eocene perialpine carbonate ramp and implications for alpine geodynamics the paleocene2eocene nummulitic limestone formation of the alpine periphery occupies the lowermost part of a stratigraphic trinity above a major basal unconformity it is thought to have accumulated as a foraminiferal carbonate ramp at the distal featheredge of the underfilled north alpine and southwest alpine foreland basin we present the results of a numerical model that links carbonate sedimentation at the distal featheredge of a peripheral foreland basin to the flexural subsidence of an elastic plate subjected to a distributed load with a superimposed eustatic sea level history carbonate accumulation is treated as depth dependent model parameters are constrained by geological and geophysical observations of the alpine orogen and its peripheral foreland basin and from literature on the ecology of benthic foraminifers the generic alpine model shows that the carbonate ramp accumulates as a number of sedimentary cycles before rapid drowning giving rise to a retrogradational stratigraphic package terminated by a surface of accelerated transgression and backstepping running the model with sets of parameter values appropriate to the paleocene to middle eocene nummulitic limestone in central eastern switzerland and the late eocene nummulitic limestone

late miocene pleistocene evolution of india eurasia convergence partitioning between the bhutan himalaya and the shillong plateau new evidences from foreland basin deposits along the dungsam chu section eastern bhutan the shillong plateau is a unique basement cored uplift in the foreland of the eastern himalaya that accommodates part of the india eurasia convergence since the late miocene it was uplifted in the late pliocene to 1600 m potentially inducing regional climatic perturbations by orographically condensing part of the indian summer monsoon ism precipitations along its southern flank as such the eastern himalaya shillong plateau ism is suited to investigate effects of tectonics climate and erosion in a mountain range broken foreland system this study focuses on a 2200 m thick sedimentary section of the siwalik group strategically located in the lee of the shillong plateau along the dungsam chu at the front of the eastern bhutan himalaya we have performed magnetostratigraphy constrained by vitrinite reflectance and detrital apatite fission track dating combined with sedimentological and palynological analyses we show that 1 the section was deposited between 7 and 1 ma in a marginal marine deltaic transitioning into continental environment after 5 ma 2 depositional environments and paleoclimate were humid with no major change during the depositional period indicating that the orographic effect of the shillong plateau had an unexpected limited impact on the paleoclimate of the bhutanese foothills and 3 the diminution of the flexural subsidence in the basin and or of the detrital input from the range is attributable to a slowdown of the displacement rates along the main boundary thrust in eastern bhutan during the latest miocene pleistocene in response to increasing partitioning of the india eurasia convergence into the active faults bounding the shillong plateau

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

numerical modelling of drainage basin evolution and three dimensional alluvial fan stratigraphy abstract a forward numerical model is presented to study the effects of bedrock erodability thrust displacement rate pulsating tectonic activity and sea level fluctuations on drainage basin morphology and stratigraphy of large alluvial fan systems a low value of the bedrock erodability coefficient k b 0 5 10 4 year 2 3 vs thrust rate 2 0 m ky is associated with a time lag between cessation of tectonic activity and maximum sedimentation rates observed on the alluvial fans applying higher k b values ranging between 1 0 and 8 0 10 4 year 2 3 results in higher sediment yields due to more rapid headward catchment erosion and elaborate sideways branching of drainage networks pulsating tectonic activity is reflected in a stratigraphic alternation of prograding and retrograding alluvial fan gravels during tectonic activity fan gravel fronts and coastlines retreat because catchment yields are insufficient to fill the accommodation space created by the flexural response due to thrust loading phases of tectonic quiescence and cessation of flexural subsidence are indicated by progradation of the gravel front depending on the position in the basin the lag time for arrival of the gravel associated with tectonic cessation is several tens to hundred thousands of years a combination of pulsed tectonic activity with sinuous sea level fluctuation leads to a more complex stratigraphic pattern in that case stratigraphic response to tectonic pulses is masked by a similar but higher order frequency stacking pattern especially in the more distal parts

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

uplift and cooling pathways derived from fission track analysis and mica dating a review definition of time and temperature pathways for episodes of lithospheric movement provides not simply a chronological framework for crustal dynamism but also permits estimation of rates of crustal cooling and uplift important aspects of such pathways are the constraints provided for timing of both plate collision and lithospheric extension classically rb sr and k ar mica ages have been used to delineate rates of cooling and exhumation in the central alps by comparison of the measured ages with estimates of temperatures for the retention of daughter isotopes similar use of fission track apatite and zircon ages has provided data for lower temperature intervals 100 and 200 c respectively recent detailed studies of the annealing kinetics of fission tracks in apatite yield more precise estimates of cooling rate and permit predictive modelling of age and length parameters for given t t pathways in continental collision zones fast episodic uplift in the western alps can be contrasted with contemporaneous monotonic uplift in the central alps additional examples may be seen in the tibet himalayan orogenic belt in the southern alps of new zealand and in the bolivian andes in divergent teceonic regimes the record of uplift associated with rifting has been recorded by fission track ages in the southeastern australian margin and around the red sea in an intra plate tectonic setting our current fission track reconnaissance study in the british isles is revealing a hitherto unrecognised thermal history for crystalline and sediment alike

hornblende k ar ages and the climax of tertiary metamorphism in the lepontine alps south central switzerland an old problem reassessed abstract twenty five new k ar ages for amphiboles from the tertiary barrovian type metamorphic terrain of the central alps were determined these results lead to the conclusion that the meso alpine metamorphism reached its peak condition and maximum expanse about 26 3 m y ago along a profile of increasing grade of alpine metamorphism in both basement and cover rocks the following observations can be made 1 pre alpine hornblendes in the zone of greenschist facies show ages ranging from 639 to 152 m y the implied open system behavior may be related to the observed mineralogical instability of these hornblendes during the alpine overprint in contrast two greenschist facies hornblendes which grew in pennine mesozoic rocks during the alpine metamorphism yield ages of 23 2 and 29 3 m y 2 on both sides of the boundary marking the first occurrence of alpine staurolite pre or early alpine hornblende k ar ages are not fully reset unless the rocks were completely recrystallized for one rock specimen which clearly exhibits two generations of hornblende an age two times greater was obtained for the smaller crystals oriented parallel to the foliation than for the structurally younger hornblende porphyroblasts which overgrew the preexisting texture 3 in the high grade area of alpine metamorphism only young alpine ages between 23 and 28 m y were found for hornblendes which grew syn to postkinematically with respect to the last penetrative deformation one amphibolitic inclusion not affected by this deformation yielded a significantly older hornblende age of 32 1 m y these results suggest that temperature controlled ar diffusion is not the main factor governing the k ar system of metamorphic hornblendes we conclude that these hornblende ages should not be interpreted as cooling ages from a structurally ill defined earlier event instead they indicate that the high grade metamorphism responsible for the well known isograd pattern in the lepontine area persisted until some 23 m y ago

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

more reducing bottom water redox conditions during the last glacial maximum in the southern challenger deep mariana trench western pacific driven by enhanced productivity abstract the modern southern mariana trench is characterized by oligotrophic surface waters resulting in low primary productivity and well oxygenated bottom waters this study investigates changes in the redox conditions of bottom waters in the southern mariana trench during the last glacial maximum lgm and their potential causes we measured major trace and rare earth elements ree in three gravity cores gc03 gc04 and gc05 and one box core bc11 retrieved from the southern challenger deep at water depths from 5289 to 7118 m the upper sediment layers of both gc05 and bc11 are dominated by valve fragments of the giant diatom ethmodiscus rex forming laminated diatom mats ldms 14c ams dates of bulk organic matter show that the ldms accumulated between 18 4 and 21 8 kyr b p corresponding to the lgm modest enrichments of u and mo along with weak or absent ce anomalies in the ldm point to suboxic conditions during the lgm in contrast non ldm samples exhibit little to no enrichment of redox sensitive elements as well as negative ce anomalies indicating deposition under oxic bottom water conditions the ce anomalies are considered valid proxies for bottom water redox conditions because ree signatures were acquired in the early diagenetic environment as indicated by strong p ree correlations and middle ree enrichment associated with early diagenetic cycling of fe mn oxyhydroxides in the sediment column followed by capture of the ree signal by biogenic and or authigenic apatite we postulate that the more reducing bottom water conditions during the lgm were linked to increased primary productivity induced by enhanced asian dust input as shown in earlier studies the increased primary productivity associated with ethmodiscus rex blooms in the eastern philippine sea played a significant role in capturing atmospheric co2 during the lgm consequently the magnitude of atmospheric co2 sequestration by giant diatom blooms during the lgm may have been greater than previously envisaged

recognition of forebulge unconformities associated with early stage foreland basin development example from the north alpine foreland basin the peripheral upwarp forebulge associated with early foreland basin evolution may be recorded as an unconformity at the base of the foreland basin fill a forebulge unconformity represents a distinctive type of megasequence boundary forward modeling of foreland flexure illustrates the expected geometry of an unconformity cut by erosion of the forebulge during the early stages of foreland basin development internal conformity a zone of rapid increase in the depth of erosion and an external zone of steady state stratigraphic gap this geometry is modified by the preexisting bathymetry and by eustatic sea level changes which result in the formation of a composite unconformity however the geometry of the unconformity and the onlap of the overlying sediments are fund mentally different from those associated with a major eustatic sea level fall and represent a distinctive assemblage of petroleum play components producing hydrocarbon accumulations are associated with both forebulge arching and truncational unconformity traps modeling achieves an accurate simulation of the geometry and stratigraphic gap of the basal unconformity of the north alpine foreland basin switzerland further support for the flexural forebulge interpretation is provided by facies patterns in the overlying sediments suppression and smothering of forebulges during the late molasse stage of foreland basin development coupled with the cannibalization of the early flysch stage stratigraphy by the advancing orogenic wedge may limit the formation and recognition of forebulge unconformities model results may be helpful in predicting the timing duration and amount of uplift associated with flexural forebulges and thereby aid in assessing petroleum play potential particularly the formation of traps and the development of enhanced porosity

dating the northern deposits of the ebro foreland basin implications for the kinematics of the sw pyrenean front abstract dating the sedimentary infill of the northern margin of the ebro foreland basin informs about the orogen basin evolution a magnetostratigraphic section of 5 km thick combines new magnetostratigraphic results from the syntectonic alluvial uncastillo fm upper oligocene lower miocene 1 km thick the fuencalderas section with previous 3 3 km thick and new 0 7 km thick magnetostratigraphic data from the underlying fluvial campodarbe fm luesia and san marzal sections eocene oligocene this composite section allows dating the entire basin infill in this sector therefore bracketing the timing of the deformation in the southern margin of the pyrenees after considering previous kinematic studies deformation recorded by the continental deposits spans from syn gavarnie nappe activity broto and fiscal basement thrust sheets from 31 3 to 24 55 ma rupelian chattian oligocene to the syn guarga thrust activity from 24 55 to 21 2 ma chattian aquitanian oligocene miocene the accumulation rates vary from ca 22 to ca 39 cm kyr between the genetic stratigraphic units in the uncastillo fm through the section these rates are close to those of the underlying deposits of the campodarbe fm average of ca 36 cm kyr deformation for the latest pyrenean front syn guarga thrust is younger than previously assigned in 5 4 1 5 and 1 1 myr of the beginning of the punta comun thrust sheet from 29 4 ma to 24 ma lower riglos thrust sheet system from 24 to 22 5 ma and the upper riglos thrust system 22 5 to 21 4 ma respectively other significant changes in accumulation rate and its derivative also indicate variations in the tectonic activity ca 33 and 28 ma

a lithospheric cross section through the swiss alps ii constraints on the mechanical structure of a continent continent collision zone summary the calculation of strength profiles along the european geotraverse egt through the swiss alps yields constraints on the large scale vertical and lateral mechanical structure through the alpine continent continent collision zone strength profiles are evaluated for different assumptions on petrological stratification and strain rate and are based on temperature depth profiles derived from transient thermo kinematic modelling of the neoalpine orogeny the main contribution to the total strength results from the mantle lithosphere which is strongly controlled by temperature in contrast the crustal contribution is mainly determined by variations in petrological stratification a direct correlation between surface heat flow and the total strength of the crust the mantle lithosphere and the entire lithosphere crust and mantle lithosphere is not observed our results demonstrate that in tectonically active areas a transient thermal model along with detailed knowledge of the deep structure and petrology is necessary to evaluate lithospheric strength envelopes inside the collision zone strain rate has a strong control on the bottom of the mechanically strong crust whereas outside the collision zone the effect is less significant the cut off depth of seismicity along the profile which correlates largely with the bottom of the mechanically strong crust deviates from the 300 400 c isotherm the inferred effective elastic thickness for the molasse basin north of the alps is in agreement with flexural modelling results whereas for the southern alps the predictions deviate

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

stratigraphic modeling of foreland basins interpreting thrust deformation and lithosphere rheology the authors incorporate the processes of erosion and deposition in a numerical model to predict the stratal geometries and facies patterns produced during episodic thrusting in a nonmarine foreland basin the resultant stratigraphic record is characterized by a stairstepped facies package in which each retrogradation of facies toward the thrust marks the onset of a thrusting event the retrogradation of facies coincides with the migration of the forebulge toward the thrust and the generation of an erosional unconformity in the past changes in basin wavelength during basin evolution have been interpreted to record viscoelastic relaxation of the lithosphere this model suggests that changes in basin wavelength are a natural consequence of the interplay between thrust and sediment loading on an elastic lithosphere

a late archean foreland fold and thrust belt in the north china craton implications for early collisional tectonics abstract the archean north china craton is divided into the western and eastern blocks along the central orogenic belt a 1600 km long archean foreland basin and thrust belt fringes the eastern side of the central orogenic belt rocks in the orogen form tectonically stacked east vergent fold and thrust sheets including foreland basin sediments 2 50 ga ophiolitic melange and an island arc complex foreland basin sediments overlie a passive margin sequence and include a 2 50 ga deep water turbidite sequence that grades upward and westward into shallow water molasse now disposed in structurally imbricated east verging thrusts and asymmetric folds that gradually migrated craton ward with deformation uplift and erosion of the orogen there is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the north china craton along the central orogenic belt at 2 50 ga the qinglong foreland basin and central orogenic belt of the north china craton represents one of the best preserved archean orogen to craton transitions in the world its classic internal to external zonation and flexural response to loading demonstrate that convergent tectonics in the archean were broadly similar to phanerozoic convergent margin processes

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

the lower marine to lower freshwater molasse transition in the northern alpine foreland basin oligocene central switzerland south germany age and geodynamic implications the wilhelmine alpe section near immenstadt allgau south germany which represents one of the best continuously exposed outcrops within the northern alpine foreland basin has been analyzed for magnetostratigraphic and palynostratigraphic signals the section comprises the marine to terrestrial transition from lower marine umm to lower freshwater molasse usm sediments based on the correlation of the local magnetic pattern with the geomagnetic polarity timescale gpts and palynostratigraphic data an age of about 31 ma is suggested for the umm usm transition in the wilhelmine alpe section a comparison with coeval magnetostratigraphic sections from central and eastern switzerland indicates that the regression of the umm sea along the southern margin of the molasse basin occurred strongly heterochronously between 31 5 and 30 ma the heterochroneity is attributed to the deposition of fan delta and alluvial fan sediments which document that the overall marine conditions during the umm were accompanied by strong clastic input derived from the rising alps this clastic contribution had a much stronger influence on the depositional pattern than previously thought

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

magnetostratigraphic constraints on relationships between evolution of the central swiss molasse basin and alpine orogenic events magnetostratigraphic chronologies together with lithostratigraphic sedimentological and petrological data enable detailed reconstruction of the oligocene to miocene history of the north alpine foreland basin in relation to specific orogenic events and exhumation of the alps the molasse of the study area was deposited by three major dispersal systems rigi hohronen napf distinguished by characteristic heavy mineral suites conglomerate clast populations and the presence of key clasts these systems record three major phases of denudation of the alpine edifice the rigi system eroded the austroalpine and penninic nappes of eastern switzerland from 30 to 25 5 ma as a result of backthrusting and uplift of these units along the insubric line subsequent uplift of the aar massif some 40 km to the north appears to have controlled the duration of the hohronen and napf dispersal systems spanning 24 22 ma and 21 5 15 ma respectively they record downcutting into the crystalline cores of the penninic and austroalpine nappes of eastern hohronen and western napf switzerland high resolution reconstruction of the structural and geometrical evolution of the proximal molasse reveals in sequence and out of sequence thrusting events at the alpine front and incorporation of the molasse into the orogenic wedge by in sequence thrusting and underplating furthermore it reveals close relationships between periods of rapid denudation in the central alps and phases of increased sediment accumulation rates at the proximal basin border an initial increase in molasse accumulation rates to 1 km m y occurred between 30 and 25 5 ma and coincides with the insubric phase of backthrusting along the eastern insubric line where 10 km of vertical displacement is interpreted during the same time span the alpine wedge propagated forward along the basal alpine thrust as indicated by the coarsening and thickening upward megasequence and by occurrence of bajada fans derived from the alpine border the end of this tectonic event is marked by a basinwide unconformity interpreted to have resulted from crustal rebound after initial loading a subsequent increase in accumulation rates to 1 km m y between 23 and 21 5 ma coincides with initial uplift of the eastern aar massif by at least 4 km this phase of high accumulation rates is associated with incorporation of early chattian conglomerates into the orogenic wedge the third advance of the alpine wedge between 21 and 15 5 ma caused underplating of molasse deposits resulting in synsedimentary backthrusting of previously deposited molasse sequences and in the development of a progressive unconformity a rapid increase in accumulation rates from 0 35 to 1 km m y between 15 5 and 15 ma marks the final loading event in the wedge which may be caused by further major displacement and loading of the aar massif this deformation is coeval with out of sequence thrusting of the helvetic border chain and of the piggyback stack of north penninic and ultrahelvetic flysch nappes along the basal alpine thrust

post collisional deposits in the zagros foreland basin implications for diachronous underthrusting detailed sedimentology of the neogene foreland basin deposits is investigated and classified into 11 lithofacies associations with respect to their paleo sedimentary environments the foreland deposits reveal a single coarsening upward mega sequence with continuous passage from back bulge to forebulge foredeep and wedge top sedimentary environments the gachsaran deposits form the base of the foreland strata and consist mainly of three different lithofacies associations including fluvial marine and sabkha deposits in the eastern zagros in fars and are typically dominated with evaporites toward the west in the dezful and kirkuk embayments the mishan formation has three different shallow marine lithofacies associations in a vertical succession representing foredeep deposits in the eastern zagros which tapers toward the dezful embayment and disappears in iraq the agha jari distal wedge top deposits also contain three different lithofacies associations including delta deposits mostly in the fars tidal flat deposits in dezful and mesopotamia basin and continental fluvial deposits across the entire zagros the uppermost synorogenic bakhtiari formation represents proximal wedge top deposits and consists mainly of two main lithofacies associations including shallow marine and fluvial deposits within which the fluvial succession is divided into three sub lithofacies associations with respect to distance from the mountain front and hydraulic power of the river networks synthetizing sedimentary facies association with age constraints of the old foreland deposits near the zagros suture in the high zagros area suggests that a considerable part of the arabian plate has been removed at the northern edge by underthrusting and erosion moreover preservation of the young distal foreland deposits near the suture in the western zagros implies that the magnitude and rate of removal of the proximal foreland deposits have been inconstant along strike the belt and decreases toward the east

large scale stratigraphic architecture eustatic variation and unsteady tectonism a theoretical evaluation we incorporate a process based depositional model with basin subsidence models to predict stratigraphic records this allows us to investigate the importance of subsidence geometry on coastal stratigraphy and thus to characterize and compare the stratigraphic architecture of two categories of tectonic basins the models demonstrate that the correlation of stratigraphic sequences to eustatic cycles is not the same in passive margin basins as in foreland basins and that in a foreland basin the record of episodic tectonism is distinct from that of eustatic sea level change in the model sediment transport is approximated by slope controlled diffusion nonmarine transport is treated as more efficient diffusion than marine transport three different subsidence and sediment supply models are examined a simple passive margin basin a simple foreland basin and then a foreland basin for which vertical motions are driven by thrust shortening that is compensated flexurally and for which sediment supply is related to relief predicted passive margin stratigraphies for cases of varying eustatic sea level are similar to those of natural basins and include progradational packages and subaerial unconformities which are used to define sequence boundaries that form during sea level fall we explore the timing relationships between stratigraphic features and a sinusoidal sea level history showing that the phase relationship depends on subsidence sediment flux efficiency of sediment transport and period and amplitude of sea level when the basic geometry of the basin is inverted placing the sediment supply on the side with maximum subsidence as is the case in foreland basins the sequence character changes markedly subaerial erosion does not generate unconformities in the models of a dynamic foreland basin sediment supply and subsidence are linked to the structure of the flanking thrust belt and are not necessarily constant for steady thrusting and variable sea level unconformities that define sequence boundaries form only on the distal or forebulge side of the basin and the ages of the sequence boundaries correlate to limes of rising sea level in cases of constant sea level but variable thrusting subaerial unconformities are cut locally on both the proximal margin of the basin and the distal margin of the basin yet the ages of the proximal margin and distal margin unconformities are out of phase in the tectonic cycle erosion is most pronounced during quiescence on the proximal side and during thrusting on the distal side

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

preliminary correlations of magsat anomalies with tectonic features of africa an overview of the magsat scalar anomaly map for africa has suggested a correlation of magsat anomalies with major crustal blocks of uplift or depression and different degrees of regional metamorphism the strongest magsat anomalies in africa are closely correlated spatially with major tectonic features although a magnetic anomaly caused by a rectangular crustal block would be offset from the block s center by the effects of magnetic inclination an anomaly caused by real crustal blocks of varying uplift depression and degree of regional metamorphism would be located nearer to the locus of greatest vertical movement and highest grade of metamorphism thus the bangui anomaly may be caused by a central old precambrian shield flanked to the north and south by two relatively young sedimentary basins

differentiating the effect of episodic tectonism and eustatic sea level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems insights from a three dimensional stratigraphic forward model many studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial deltaic and alluvial fan systems the hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis yet this is difficult because of the lack of independent stratigraphic evidence in this study a three dimensional numerical model is presented which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems under conditions of variable tectonism and eustatic sea level change the tectono sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing and is of higher resolution than previous models of foreland basin filling numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments syntectonic fluvial patterns on the axial deltaic plain are dominated by bifurcating channels swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence the resulting surface morphology of the axial delta is convex upwards syntectonic eustatic sea level fluctuations result in parasequence scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level suites of amalgamating axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities coarse grained incised channel fills are found in the zone between the alluvial fan fringes and the convex upward body of the axial delta as the axial streams tend to migrate towards this zone of maximum accommodation

controls of erosional denudation in the orogen on foreland basin evolution the oligocene central swiss molasse basin as an example a high resolution three dimensional reconstruction of the 25 m y old central swiss molasse basin reveals two sedimentary domains separated by a 5 km wide flood plain the proximal domain of the basin attained a width of 20 km and its basement is steeply flexed 6 7 dip petrographic data indicate that it was filled by sediment from the rigi dispersal system derived from the central alps of eastern switzerland and by locally sourced bajadas in contrast the distal sedimentary domain located farther north was gently dipping 2 and was filled by the meandering lac leman and honegg dispersal systems chronological data reveal that sedimentation in the northern proximal part of the basin started at 27 ma when sediment supply to the basin started to increase deflection of the foreland plate at 25 ma is successfully simulated by flexural modeling of the thrust load and the sediment load the model reveals that the lac leman and honegg dispersal systems are located on a buried flexural bulge furthermore it shows that burial and suppression of the flexural bulge at 27 ma as well as an increase of the basin wavelength were controlled by the contemporaneous increase in the sediment supply rate of the rigi system the model presented suggests that the tectonic subsidence of the molasse basin was mainly controlled by tectonic events in the northern part of the orogen within 70 km distance from the tip of the orogenic wedge crustal thickening in this part of the orogen is reflected in the proximal molasse by sedimentary cycles characterized by an increase in the sediment accumulation rates up section and by the presence of locally sourced bajada fans at the top of each cycle although south vergent back thrusting along the insubric line 150 km south of the foreland basin contributed little to flexure it resulted in an increase of the sediment supply to the foreland basin this is reflected in the molasse by coarsening and thickening upward trends an increase of the basin wavelength basinward shifts of the depocenters of the dispersal systems and uplift and erosion of the proximal basin border

isotope systematics in minerals biotite rejuvenation and exchange during alpine metamorphism abstract the hercynian schists and granites of the helvetic basement aar massif in the central swiss alps are overprinted by low grade alpine metamorphism and associated deformation rb sr and k ar ages of biotites are systematically reset by the later greenschist facies event this rejuvenation is apparently controlled by temperature mineral chemistry and grain size and independent of deformation and exsolution thermally activated volume diffusion best explains this behaviour with ar and sr having similar activation energies and diffusion rates for sr showing a greater dependence on biotite composition feldspars and apatite also show increasing equilibration to the alpine event and together with alpine equilibria in the micas reveal important changes in the isotopic compositions of exchanging reservoirs these spatial and temporal variations must be assessed before true mineral ages can be calculated generally the higher grade equilibria show less radiogenic exchange reflecting increased dilution by external fluids of radiogenic components released at the main front of isotopic resetting rb sr ages of alpine muscovites in the granites suggest a maximum possible age of metamorphism of 25 ma in this low grade area this implies significant diachroneity in the timing of peak metamorphism in the central alps with the relatively delayed metamorphism in this area a reflection of the later initial thickening and delayed uplift of the helvetic basement

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

present day deformations of the jura arc inferred by gps surveying and earthquake focal mechanisms this study presents a compilation of more than 40 years of seismotectonic data including 54 computed focal mechanisms combined with 15 years of gps data coming from a dense network of 35 permanent gps stations within the jura arc and its vicinity these data are compared to previous available geomorphological geophysical and structural studies in order to discuss the 3d distribution of the deformation within the jura arc gps data show coherent schemes in terms of velocities and allowed to discriminate between two provinces ne of the belt and in its front foreland they also constrain a low but significant overall strain tensor with a nnw sse shortening of 2 16 nanostrain year associated with an ene wsw extension of 0 44 nanostrain year the seismotectonic approach is based on a data set of 2 400 events and 54 focal mechanisms inversions of the focal mechanisms both globally and in homogeneous sectors highlight a general strike slip deformation regime with sigma1 oriented nw se and sigma3 oriented ne sw we discriminate two different sectors in terms of basement cover un coupling 1 potentially decoupled deformation between the basement and the sedimentary cover in the ne part and 2 coupled deformation in the sedimentary cover and its basement in the jura foreland

tectonics controls on fluvial landscapes and drainage development in the westernmost part of switzerland insights from dem derived geomorphic indices abstract this work focuses particularly on the geomorphological evidence for the tectonic controls on the development of the present day fluvial landscapes in the westernmost part of switzerland the tectonic deformation was evaluated on the basis of a combined analysis of several classical geomorphic indices hypsometric curves and integrals transverse topographic symmetry index and channel s bottom gradients through high precision dem processing a new optimization strategy was applied for defining geomorphic anomalies related to tectonic activity along the channels of three rivers based on a combined investigation of topographic swath longitudinal profiles geological and geophysical observations the results show that the abnormally high values of hypsometric integral are spatially occurred on the hanging walls of thrust faults while abnormally low ones are spatially observed in the same locations of paleo ice stream pathways observations obtained from transverse topographic symmetry index display asymmetries in the most of the studied drainage basins with a predominant se direction of lateral migration this direction is in agreement with the dominant dip direction of the bedding planes within the study area abnormal changes in the channel s bottom gradients which almost coincide in space with pronounced change in the depth of the subsurface geologic layers and in the geophysical properties are marked by distinct topographic relief in areas where rivers flow above blind and emergent faults our analysis not only confirms that there is a significant tectonic control on the evolution of drainage systems but also revealed a possible evidence for the reactivation of some inherited faults