kinematics of active deformation in the sulaiman lobe and range pakistan the western margin of the indian plate is highly oblique to the direction of convergence between india and asia and represents an excellent example of large scale oblique continent continent collision determining the strain field in western pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general through the inversion of regional and teleseismic body waves we have determined the source parameters of 10 moderate sized earthquakes that occurred between 1964 and 1985 in and around the sulaiman range pakistan the earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate sulaiman mountain front slip vector orientations rotate 60 70 from a n s to a wnw ese direction of compression consistent with the geometries of the complex festoon shaped mountain belts of this margin we have estimated the spatial variation of the horizontal strain rate and velocity fields within sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer the most important factors determining the style of strain rotation in the sulaiman lobe and range are the presence of pure strike slip motion along the chaman fault and the relatively rigid and undeformed katawaz basin that is therefore allowed to translate obliquely relative to india this same conclusion is obtained using either a three dimensional frictional analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions thrusting in a predominantly nw se direction in the sulaiman range accommodates 5 14 mm yr of n s motion between india eurasia and 3 6 mm yr of e w shortening seismic moment release this century within the india eurasia plate boundary zone west of the western himalayan syntaxis constitutes roughly 40 of the expected total seismic moment release for this time period particularly significant moment rate deficits exist within the sulaiman range and along the chaman fault

interseismic strain accumulation along the western boundary of the indian subcontinent 1 despite an overall sinistral slip rate of 3 cm yr few major earthquakes have occurred in the past 200 years along the chaman fault system the western boundary of the india plate with the eurasia plate gps and insar data reported here indicate sinistral shear velocities of 8 17 mm yr across the westernmost branches of the fault system suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east at its southernmost on land segment 26 n near the triple junction between the arabia eurasia and india plates we find the velocity across the ornach nal fault is 15 1 13 4 16 9 mm yr with a locking depth probably less than 3 km at latitude 30 n near the town of chaman pakistan where a m6 5 earthquake occurred in 1892 the velocity is 8 5 6 8 10 3mm yr and the fault is locked at approximately 3 4 km depth at latitude 33 n and further north insar data indicate a velocity across the chaman fault of 16 8 2 7 mm yr the width of the plate boundary varies from several km in the south where we observe 2 mm yr of convergence near the westernmost strike slip faults to a few hundreds of km in the north where we observe 6 9 mm yr of convergence and where the faulting becomes distinctly transpressional the shallow locking depth along much of the transform system suggests that earthquakes larger than those that have occurred in the historical record would be unexpected and that the recurrence interval of those earthquakes that have occurred is of the order of one or two centuries similar in length to the known historical record

balanced cross sections and their implications for the deep structure of the northwest alps reply abstract the structure of the northwest external french alps around the internal belledonne and mont blanc massifs in the beaufortain area can be explained by foreland wnw propagating thrust tectonics the internal belledonne massif is interpreted as having developed by imbrication of an originally thin skin of basement with a mesozoic cover above this massif all thrusts tend to climb lateral sections to the south to converge with the frontal pennine thrust the southern termination of the mont blanc massif is merely a spectacular example of such a lateral ramp

tectonic implications and seismicity triggering during the 2008 baluchistan pakistan earthquake sequence abstract a damaging and widely felt moderate earthquake mw 6 4 hit the rural mountainous region of southwestern pakistan on october 28 2008 the main shock was followed by another earthquake of identical magnitude mw 6 4 on the next day the spatial distribution of aftershocks and focal mechanism revealed a nw se striking rupture with right lateral strike slip motion which is sympathetic to the nnw sse striking active mapped urghargai fault the occurrence of strike slip earthquakes suggests that along with the thrust faults strike slip faults too are present beneath the fold and thrust belt of sulaiman kirthar ranges and accommodates some of the relative motion of the indian and eurasian plates to assess the characteristics of this sequence the statistical parameters like aftershocks temporal decay b value of g r relationship partitioning of radiated seismic energy due to aftershocks and spatial fractal dimension d value have been examined the b value is estimated as 1 03 0 42 and suggests the tectonic genesis of the sequence and crustal heterogeneity within rock mass the low p value of 0 89 0 07 implies slow decay of aftershocks activity which is probably an evidence for low surface heat flow a value of spatial fractal dimension of 2 08 0 02 indicates random spatial distribution and that the source is a two dimensional plane filled up by fractures the static coseismic coulomb stress changes due to the foreshock mw 5 3 were found to increase stress by more than 0 04 bars at the hypocenter of the main shock thus promoting the failure the cumulative coseismic coulomb stress changes due to the foreshock and mainshocks suggest that most of the aftershocks occurred in the region of increased coulomb stress and to the se to the mainshock rupture

thrusting and wedge growth southern alps of lombardia italy abstract a south vergent fold thrust belt of miocene recent age accompanies the south slope of the lombardian alps and is partly buried beneath plio pleistocene po valley basin fill the belt is probably detached along a trans crustal thrust named main south alpine thrust msat with an estimated dip slip of 70 100 km transport on this thrust piggybacks the adamello pluton of late eocene age pre adamello folds and oligocene miocene insubric strike slip structures by ramping up through 12 15 km of austro alpine adria crust and through 8 10 km of triassic to eocene sediments folds in the front ranges are ascribed to msat ramping not to pre adamello compression the msat soles upward in a blind thrust beneath 3 4 km of oligocene pliocene foredeep fill initial regional failure along the msat implies substantial and pre existing topographic relief near the insubric line an average of 25 wedge thickening during msat transport is consistent with the requirement of coulomb critical taper progression of the south alpine detachment from the msat to the base of the foreland sediments has added a thickness of 6 12 km in footwall imbrications to the base and the toe of the thrust wedge this addition in wedge volume is consistent with wedge dynamics only if a mid miocene or younger spike of excess alpine topography is admitted

a model for the deep structure of the moine thrust zone seismic refraction and electrical conductivity profiles across northern scotland together with geological and other geophysical data are interpreted in terms of the deep structure of this part of the orthotectonic caledonides our preferred interpretation is that the moine thrust zone extends to the base of the crust and the caledonian front is steep this contrasts with recently proposed ultra thin skinned solutions the results of the recently completed moist deep seismic reflection experiment should inter alia test our hypothesis in order to test the geometrical feasibility of our interpretation balanced sections have been constructed to illustrate the crustal evolution of the region during the caledonian orogeny these sections permit estimates to be made of crustal shortening thickening and erosion our model requires that the n highlands were once overlain by major exotic nappes which by analogy with nw newfoundland may have been ophiolitic the proposed regional structural pattern comprises a duplex of crustal dimensions we suggest that crustal duplex development is an important mechanism in the orogenic deformation of previously thinned and extended passive continental margins

influence of deformation partitioning and metamorphic re equilibration on p t path reconstruction in the pre alpine basement of central southern alps northern italy the dominant foliation s2 in the metapelites of the southalpine basement near the western side of the tertiary adamello intrusive stock is a variscan greenschist facies planar fabric slightly reworked during thick skin alpine tectonics s2 is defined by muscovite and chlorite and was formed by decrenulation of pre existing foliations which are confined to metre size less deformed domains and defined by biotite and white mica the pre s2 fabric is composite d1a d1b and defined by contrasting amphibolite facies metamorphic assemblages in diverent residual sites cld bt i grt ms i pl qtz and st bt ii grt ms ii pl qtz assemblages mark d1a and d1b fabrics respectively these developed during successive steps of a single temperature prograde polyphase event rather than during separate tectonometamorphic imprints avecting diverent tectonic units later coupled during a d2 greenschist facies stage thermobarometric estimates of assemblages formed during d1a d1b and d2 show a transition from t 480 540 c during d1a to t 570 660 c during d1b corresponding to a slight pressure increase from 0 75 0 95 gpa to 0 85 1 15 gpa d2 greenschist retrogression corresponds to a pressure and temperature decrease t 400 550 c and p 0 3 0 4 gpa this p t deformation time path is inferred to be the result of uplift from a depth of c 35 km after palaeozoic subduction and continental collision it is consistent with models postulated for other metamorphic units of the variscan belt in europe this is the first documented example in the southern alps of temperature prograde metamorphism before palaeozoic collision

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

porphyroblast inclusion trails the key to orogenesis detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral shaped inclusion trails are common indicates that spiral shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates they formed instead by progressive growth by porphyroblasts over several sets of near orthogonal foliations that successively overprint one another the orientations of these near orthogonal foliations are alternately near vertical and near horizontal in all porphyroblasts examined this provides very strong evidence for lack of porphyroblast rotation the deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two stage cycle of 1 crustal shortening and thickening with the development of a near vertical foliation with a steep stretching lineation followed by 2 gravitational instability and collapse of this uplifted pile with the development of a near horizontal foliation gravitational spreading near coaxial vertical shortening and consequent thrusting on the orogen margins correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen this information combined with information about chemical zoning in porphyroblasts provides details about the structural metamorphic p t t paths the rocks have followed the ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical ductile tear transcurrent faults across which there is no component of bulk shortening or transpression

tectonics of the dolomites southern alps northern italy abstract in post variscan times the dolomites underwent a number of tectonic events which may be summarized as follows permian and triassic rifting phases broke the area into n s trending basins with different degrees of subsidence a middle triassic transpressive event then deformed the region along a n70 e axis generating flower structures within the basement volcano tectonic domal uplift and subsequent caldera formation occurred at the same time as the late ladinian magmatism early jurassic rifting also controlled the subsidence which increased eastward this long period of deformation was followed by a pre neogene late cretaceous palaeogene e w ene wsw compression which generated a w vergent belt possibly equivalent to the folded foreland of the dinaric chain a 70 km e w section of the dolomites indicates shortening of at least 10 km during the neogene the dolomites as far north as the insubric lineament were the innermost part of a s vergent thrust belt the basement of the dolomites was thrust southwards along the valsugana line onto the sedimentary cover of the venetian prealps for at least 10 km this caused a regional uplift of 3 5 km the valsugana line and its backthrusts on the northern side of the central dolomites generated a 60 km wide pop up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural slip often forming triangle zones the shortening linked to this folding is about 5 km with neogene thrusts faulting and folding pre existing thrust planes on the north eastern side of the dolomites neogene deformation is apparently more strictly controlled by the transpressive effects of the insubric lineament and shortening of the sedimentary cover may be greater than in the central dolomites minor deformation linked to the giudicarie belt is present in the western dolomites the present structure of the dolomites is thus the result of a number of tectonic events of different significance and different strike only a 3 dimensional restoration can unravel the true structure of the dolomites

shortening of the axial zone pyrenees shortening sequence upper crustal mylonites and crustal strength abstract the strength of the lithosphere may be constrained qualitatively by field observations on localized vs distributed modes of deformation and by the mineral assemblages formed during deformation the internal deformation of the bielsa basement unit of the pyrenean axial zone is investigated through structural microstructural and thermometric data in this area shortening is widely distributed as attested by the folded attitude of the interface between the basement and its sedimentary triassic cover shortening is estimated around 1 7 km 13 from a regional balanced cross section and should be considered in pre pyrenean reconstructions shortening probably occurred before strain localization on crustal ramps as suggested by zircon fission track analysis distributed shortening is characterized at small scale by low temperature mylonites and cataclasites in thin section feldspar originally present in the magmatic protolith is partially to totally sericitized this transformation led to significant weakening of the rock and took place in the 250 350 c temperature range sericitization is ubiquitous even in un deformed granodiorites this shows that the weakening effect of sericitization not only occurs in ultra mylonites ultra cataclasites and phyllonites but also more generally in the upper crust early during the shortening history with implications for the shortening style estimates of the geothermal gradient suggest that inherited thermicity may also have influenced the style of shortening we propose that the upper crust was very weak before or at the onset of its shortening due to high thermal gradients and fluid circulation that induced large scale sericitization in greenschist facies conditions this has strong implications on the rheological evolution of the upper crust submitted to metamorphic alteration in the greenschist facies and below

incremental strain analysis using two generations of syntectonic coaxial fibres an example from the monte marguareis brianconnais cover nappe ligurian alps italy abstract composite calcite quartz fibres developed in strain fringes on pyrites in the monte marguareis cover nappe ligurian brianconnais northern italy are utilised for an incremental strain analysis classical methods require non coaxial fibres to reconstruct incremental strain histories as an innovation this contribution shows that two generations of coaxial fibres grew independently on different pyrite sites during the two major deformation phases d1 and d2 which affected the monte marguareis structural unit rare curved fibres are shown by meso and microstructural analyses to have grown during d1 and been deformed by d2 folds this peculiarity provides a way to estimate quantitatively the strain associated with these deformation phases without the uncertainties related to classical methods d1 strain shows a marked strain partitioning among different lithologies and within the same lithology the measured elongations ranging between 1 84 and 8 45 measurements of d2 incremental elongation are available only for one lithology and indicate that d2 stretching is approximately half that of d1 and its contribution to the finite strain ellipsoid cannot be neglected this finding is consistent with qualitative inferences on strain partitioning between d1 and d2 phases measured d2 elongations display higher homogeneity throughout the area both l1 fibre orientation generally ne sw and d1 fold asymmetry suggest d1 deformation occurred in a ductile shear zone possibly induced by the south westward motion of nappes consistently with regional tectonics the l2 lineation orientation approximately ne sw and the d2 folds asymmetry suggest that the d2 phase is likely to be the product of a regionally recognised backthrusting event

thrust kinematics and internal deformation in basement involved fold and thrust belts the eastern orobic alps case central southern alps northern italy a new model which integrates original detailed structural data and published geological data is proposed for the alpine cretaceous to present convergent evolution of the northern portion of the central southern alps the central southern alps are believed to have developed from the very beginning of their convergent evolution as a critical wedge characterized by plastic deformation at depth clear evidence for the existence of a brittle plastic transition at depth within the central southern alps wedge during pre oligocene evolutionary stages comes from detailed structural data original 1 10000 form surface mapping a regionally verified fabric sequence manifests the superposition of brittle to plastic to brittle structures developed during the path followed by the same volume of rocks within the wedge on the other side no direct evidence exists in the rear part of the wedge for the occurrence of plastic deformation at depth during post oligocene stages however considerations driven by the comparison of timing and amount of deformations in the central southern alps and brittle wedge theory predictions strongly support this hypothesis different deformation mechanisms operating at different structural levels have been controlling a crustal scale strain partitioning between deep plastic and shallow brittle portions of the central southern alps wedge plastic deformations have strongly controlled the overall mechanical behavior of the central southern alps wedge reducing sensitively the amount of internal deformation required in order to attain criticality of the wedge

deformation of the western indian plate boundary insights from differential and multi aperture insar data inversion for the 2008 baluchistan western pakistan seismic sequence

area balancing as a test of models for the deep structure of mountain belts with specific reference to the alps abstract basic concepts of structural restoration are applied to crustal cross sections through mountain belts to explore large scale tectonic models and deep structure however restored sections should account for variations in pre orogenic crustal thicknesses crustal balancing approaches are reviewed and applied to two alpine sections coinciding with deep seismic experiments nrp 20 east central alps and ecors crop western alps existing studies assume large 300 km orogenic contraction and only moderately thinned pre orogenic crust the resulting restored sections contain more crust than is imaged beneath the present day alps the missing crust generally assumed to be subducted two kinematic modifications reduce the requirement for subduction thinning and buoyancy driven return flow of ultra high pressure metamorphic rocks during orogenesis and pre orogenic hyperextension using large stretching factors for the pre orogenic crust negates crustal subduction on both alpine transects if the lower crust was approximately rigid restorations of the central alps require strongly depth heterogeneous stretching of upper and lower crust during mesozoic rifting relaxing this requirement allows uniform lithospheric stretching a corollary consistent with published subsidence estimates restorations make implicit statements on the form of pre orogenic basins and the structure of continental margins incorporated into mountain belts that can in turn provide tests of tectonic models

emplacement related deformation of granitoid magmas southern adamello massif italy the lago della vacca suite in the tertiary adamello massif italian alps is a small 10 km 2 crudely zoned granitoid pluton emplaced at a pressure of 3 5 kbar into folded mesozoic sediments and precursor intrusive rocks field relations and detailed mapping reveal a temporal evolution in the style of emplacement from early passive stoping by the mafic to intermediate composition marginal units to later forceful emplacement of the more silicic core marginal units of the pluton have highly discordant stoped outer contacts against folded triassic carbonates and precursor mafic ultramafic rocks in contrast the core units have steeply inward dipping contacts against these marginal units magmatic foliations defined by the planar alignment of plagioclase amphibole and biotite and by mafic enclaves are well developed in all units they describe steeply inward dipping concentric trajectories that approximately parallel unit contacts and in general increase in intensity toward the pluton margin lineations are rarely present the most intensely foliated rocks occur in the marginal units as anastomosing sinuous bands that wrap around lenses of less intensely foliated granitoid three dimensional strain analysis using mafic enclaves from throughout the pluton indicates that these bands represent zones of very high strain strain ellipsoids are weakly prolate within the core of the pluton becoming increasingly oblate as strain increases toward the pluton margin the short axis z of the strain ellipsoid is uniformly subnormal to the foliation suggestive of radial flattening textures of the marginal rocks which record high strain coupled with amphibole plagioclase thermometry indicate that deformation occurred in the magmatic or submagmatic state 650 780 c and was accompanied by significant migration of interstitial melt the documented transition from passive to forceful emplacement and final geometry of the suite resulted from temporal changes in the rheology of both the magma and adjacent country rocks pulses of low density hydrous magma were initially emplaced by stoping denser country rocks on cooling and solidification these magmas contracted by 15 20 creating an unpressured volume which allowed subsequent magma pulses to be emplaced into the pluton core these pulses distended and flattened their partially molten carapace and those parts of the aureole that had been thermally softened by intrusion of earlier magmas emplacement of the lago della vacca suite was therefore the product of several internal or magma related processes an interaction between stoping radial expansion and volume contraction on solidification of the hydrous magmas the heterogeneous distribution of strain in the marginal units reflects local variations in temperature and most importantly in the distribution of interstitial melt during emplacement

systematic insar tropospheric phase delay corrections from global meteorological reanalysis data 1 despite remarkable successes achieved by differential insar estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated mainly because of the topography related atmospheric phase screen aps in areas of high relief empirical removal of the stratified component of the aps may lead to biased estimations of tectonic deformation rates here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with sar acquisitions using the era interim global meteorological model the modeled phase delay is integrated along vertical profiles at the era i grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel this approach is validated on unwrapped interferograms we show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography

the restoration of thrust systems and displacement continuity around the mont blanc massif nw external alpine thrust belt abstract foreland propagating external thrust belts may be considered as essentially plane strain phenomena so that displacements can be correlated throughout their linked three dimensional fault geometry this approach has been applied to part of the northwest external french swiss alps around the mont blanc basement massif imbricates of basement and cover sequences on the sw margin of this massif restore to a width in excess of 77 km with an implicit shortening of at least 67 km these displacements can be correlated with those in the neighbouring helvetic nappes by transferring movements via lateral branch lines onto the mont blanc thrust by reappraising thrust geometries the helvetic ultrahelvetic nappe complex has been restored to a width of 114 km to the ese of the aiguilles rouges basement massif displacements on the internal se margin of the mont blanc massif estimated by balanced sections and a restoration of the ultrahelvetic klippen in the sub alps exceed 59 km thrust continuity incorporating the restorations of nappes and imbricate geometries around the mont blanc massif is illustrated on a crude restored branch line map which also serves as a preliminary palaeogeographic reconstruction external thrust systems to the east of the external belledonne aiguilles rouges massif restore to a width of at least 140 km in the footwall to the frontal pennine thrust

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

fold and thrust partitioning in a contracting fold belt insights from the 1931 mach earthquake in baluchistan 1 surface deformation associated with the 27 august 1931 earthquake near mach in baluchistan is quantified from spirit leveling data and from detailed structural sections of the region interpreted from seismic reflection data constrained by numerous well logs mean slip on the west dipping dezghat bannh fault system amounted to 1 2 m on a 42 km 72 km thrust plane with slip locally attaining 3 2 m up dip of an inferred locking line at 9 km depth slip also occurred at depths below the interseismic locking line in contrast negligible slip occurred in the 4 km near the interseismic locking line the absence of slip here in the 4 years following the earthquake suggests that elastic energy there must either dissipate slowly in the interseismic cycle or that a slip deficit remains pending its release in a large future earthquake elastic models of the earthquake cycle in this fold and thrust belt suggest that slip on the frontal thrust fault is reduced by a factor of 2 to 8 compared to that anticipated from convergence of the hinterland a partitioning process that is presumably responsible for thickening of the fold and thrust belt at the expense of slip on the frontal thrust near the latitude of quetta gps measurements indicate that convergence is 5 mm yr hence the minimum renewal time between earthquakes with 1 2 m mean displacement should be as little as 240 years however when the partitioning of fold belt convergence to frontal thrust slip is taken into account the minimum renewal time may exceed 2000 years

the effects of brittle plastic transitions in basement involved foreland belts the central southern alps case n italy abstract the central southern alps csa a 100 km wide basement involved fold and thrust belt formed during the europe africa convergence from the cretaceous onward two main phases of deformation have been recognized in the central southern alps the first is a pre late oligocene thrusting of pre alpine basement units upon triassic cover sequences which is sealed by the adamello intrusion 42 30 ma in the northern sector of the belt the folds and thrust faults of this phase are locally overprinted by a post adamello deformation phase possibly corresponding to the middle late miocene 16 6 ma milano phase recorded by the oligo miocene sediments buried under the plio pleistocene padane plain several lines of evidence indicate that compressive deformations originating from the current relative convergence between eurasian and adriatic plates are still occurring within the southalpine wedge which can therefore be modelled as a critical wedge a simple brittle rheology is not adequate to explain the slope and plateau topographic features of the belt which compare more favourably with those predicted by a critical taper model including the effects of temperature dependent deformations low angle surface slopes typical of frontal sectors of wedges deforming with a purely brittle behaviour are interrupted by relatively steeper slopes where the wedge base crosses the brittle plastic b p transition and starts creeping while the basal decollement deforming at higher strain rates still behaves frictionally further to the rear where both the wedge base and the decollement are plastic the surface slope flattens plateau calculated brittle plastic transition depths along the basal decollement fit well with observed topographic changes the location of slope to plateau topographic changes in the csa is strongly influenced by surface heat flow distribution and the occurrence within the wedge and in particular at the wedge base of rock types characterised by different plastic rheological parameters is responsible for repeated topographic changes each related to a different b p transition the transition from brittle to plastic behaviour at the base of the wedge is responsible for a significant weakening within the basal decollement which in turn has dramatic consequences on the dynamics and hence on the kinematics of the foreland fold and thrust belt the maintenance of the critical state of a wedge with a weak plastic basal decollement necessitates a lower amount of internal deformation than that required by completely brittle wedges moreover these deformations are strongly localised in the lower weak portions of the wedge and do not pervasively affect the upper brittle portions these characteristics have been ascertained in the rear part of the csa b p transitions commonly develop not only within wide mountain belts e g the andes but also in narrow ones e g csa this means that b p transitions must be taken into account when modelling the mechanics of foreland fold and thrust belts at all scales the occurrence of b p transitions must be tested particularly when topographic features suggest their existence since only an appropriate rheological behaviour can account for the structural evolution and kinematics derived from field studies

basement balancing of rocky mountain foreland uplifts restorable cross sections of foreland basement uplifts must contain faults whose curvatures are consistent with the relative slip and tilt between adjacent basement blocks cylindrical fault surfaces can explain the uniform dip of strata on the back side of foreland uplifts local zones of shortening and extension occur in hinge zones above transitions in fault curvature high curvature fault splays form fault wedges of basement which ease the transition from thrust and reverse faulting of basement blocks to folding in the sedimentary cover 20 references 4 figures

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

morphological features of miocene submarine coherent lavas from the green tuff basins examples from basaltic and andesitic rocks from the shimokita peninsula northern japan basaltic and andesitic volcanic rocks of miocene age exposed in the shimokita peninsula northern japan illustrate morphological features of typical submarine coherent lavas of the green tuff basins in japan they are pillow lobes with surface structures such as ropey wrinkles corrugations spreading cracks and tensional cracks and lava lobes composed of a lithic core and glassy border zone or rim with an in situ breccia zone grading outward into surrounding hyaloclastite in addition they include massive lavas with columnar joints and jointed dykes the submarine coherent lavas and dykes are commonly associated with hyaloclastic breccias such as pillow fragment breccia and angular fragment breccia the descriptions of the miocene volcanic rocks in the shimokita peninsula provide good criteria for recognition of submarine coherent lavas of basalt and andesite

polyphase deformation in the western mount isa inlier australia episodic or continuous deformation abstract the polyphase deformation history of the mount novit ranges western mount isa inlier australia involved the development of four generations of n s to nw plunging folds development of which alternated with movement on n s striking faults shear zones with west over east displacement the spatial relationships between successive structures and the distinct similarities in the kinematics style and asymmetry are all consistent with continuous deformation during e w to ne sw shortening additional support for this hypothesis is based on the development of the three major fold generations and the intervening faults and shear zones during low p high t metamorphism although the duration of this metamorphic event cannot be constrained recent studies have linked low p metamorphism to heat advection by migrating melts thermal modelling indicates that such metamorphic events will be short lived in comparison to those associated with thermal relaxation of over thickened crust low p metamorphism is unlikely to persist through two or more separate tectonic events therefore syn metamorphic polyphase deformation in the mount novit ranges apparently formed during a single continuous tectonic episode this structural history differs from both the regional scheme and that of previous workers in this area the main differences are i no evidence was found for early thrust faulting prior to n s folding ii there are four generations of n s to nw se folds as opposed to two and iii this study favors a single consistent tectonic regime in contrast to the interpretation of three discrete isolated tectonic events

kinematics and strain distribution of a thrust related fold system in the lewis thrust plate northwestern montana u s a abstract in order to understand interactions between motion along thrusts and the associated style of deformation and strain distribution in their hangingwalls geologic mapping and strain measurements were conducted in an excellently exposed thrust related fold system in the lewis thrust plate northwestern montana this system consists of 1 an e directed basal thrust the gunsight thrust that has a flat ramp geometry and a slip of about 3 6 km 2 an e verging asymmetric anticline with its nearly vertical forelimb truncated by the basal thrust from below 3 a 4 km wide fold belt the frontal fold complex that lies directly in front of the e verging anticline 4 a w directed bedding parallel fault the mount thompson fault that bounds the top of the frontal fold belt and separates it from the undeformed to broadly folded strata above and 5 regionally developed w dipping spaced cleavage although the overall geometry of the thrust related fold system differs from any previously documented fault related folds the e verging anticline itself resembles geometrically a rich type fault bend fold the observed initial cut off and fold interlimb angles of this anticline however cannot be explained by cross section balancing models for the development of either a fault bend fold or a fault propagation fold possible origins for the e verging anticline include 1 the fold initiated as an open fault bend fold and tightened only later during its emplacement along the basal thrust and 2 the fold started as either a fault bend or a fault propagation fold but simultaneous or subsequent volume change incompatible with any balanced cross section models altered its shape strain in the thrust related fold system was determined by the preferred orientation of mica and chlorite grains the direction and magnitude of the post compaction strain varies from place to place strains in the foreclimb of the hangingwall anticline imply bedding parallel thinning at some localities and thickening at others this inhomogeneity may be caused by the development of thrusts and folds strain in the backlimb of the hangingwall anticline implies bedding parallel stretching in the thrust transport direction this could be the effect of bending as the e verging anticline was tightened and transported across the basal thrust ramp strain measured next to the gunsight thrust again indicates locally varying shortening and extension in the transport direction perhaps in response to inhomogeneous friction on the fault or else to a history of alternating strain hardening and softening in the basal thrust zone

neglected basement ductile deformation in balanced section restoration an example from the central southern alps northern italy abstract in the construction of balanced sections through thick skinned belts basement bodies are frequently assumed to be rigid and internally undeformed with the exception of regional scale fault bend folding and only backstripping of thrust faults is performed during their retrodeformation possibly leading to underestimations of the regional shortening this simplifying assumption is generally made because reliable information on internal strain in basement is lacking and the sedimentary cover of the internal parts of thrust belts has been removed by erosion in a basement exposure in the eastern orobic alps alpine age ductile structures mainly chevron to sub isoclinal folds rarely associated with cleavage formation were recognized on the basis of overprinting criteria folding style and fabric orientation and their areal distribution was determined by foliation trace mapping although unevenly distributed in different lithologies ductile deformation is considerable average shortening is 47 neglecting such internal strain during construction of balanced sections leads for this area to an underestimation of at least 10 but could be more than 40 if the observed basement shortening is extrapolated to other basement involved thrust bodies across the entire width of the deformed belt it is concluded that detailed structural studies of the basement for example those using a foliation trace mapping technique are necessary to define the internal strain of basement bodies so that the shortening of thick skinned belts can be more accurately calculated

balancing cross sections with kinematic constraints the dolomites northern italy balancing of structural cross sections is often hindered by a limited database or tectonic complications in such cases kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth the kinematic implications of a known structure generally at the surface have to be considered for the unknown structure and for the internal consistency of a cross section a key point is the quantification of shortening of the known structure the extrapolation of this parameter allows balancing in an approximate way emphasizing major structures while minor structures are either neglected or treated in a simplified way with this approach a quick overview can be achieved on how much leeway for interpretation exists critical points for testing various working hypotheses become more evident and the trial and error effort during the construction of a balanced section is considerably shortened still the implications the observed structures have on the deeper crustal levels can be assessed this concept is applied to a section across the italian dolomites a brittle fold and thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure still active south vergent alpine thrusting is oriented approximately perpendicular to previous dinaric thrusting the ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence thanks to kinematic balancing based on surface data three alpine thrust systems could be identified each defining a thrust sheet with its particular basement unit and its sedimentary part superposition of the two more external basement units led to the presently observed high elevation of the triassic sequence in the dolomites shortening since late miocene times amounts to more than 50 km retrodeformation of alpine thrusting is a key for better understanding the previous dinaric structures and kinematics

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex