quantitative finite strain and kinematic flow analyses along the zagros transpression zone iran abstract the ghouri area in southwest iran exposes a cross section through the zagros orogenic belt the area provides an opportunity to investigate quantitative finite strain rs kinematic vorticity number wk proportions of pure shear and simple shear components sense of shear indicators steeply plunging lineations and other moderate to steeply plunging stretching lineations in a transpressional zone based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape the zagros orogenic belt is classified as a pure shear dominated zone of transpression but asymmetry of shear sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries the long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone the stretching lineations have a steep to moderate plunge but a constant strain magnitude characteristics of dextral inclined transpressional kinematics in the zagros continental collision zone were quantified and indicate an estimated k value

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

the origin of the upper palaeozoic chanaral melange of n chile the fragmented and mixed strata of the chanaral melange extend for some 220 km from n to s in the coastal ranges of n chile 26 20 to 28 20 s the melange was produced in an accretionary wedge resulting from the ne subduction of the ancestral pacific oceanic plate beneath the gondwana land margin during carboniferous times the melange consists essentially of blocks of sandstone in a pelitic matrix these sediments were deposited as deep sea basin plain turbidites prior to their fragmentation other blocks in the melange include mafic volcanic rocks with the geochemical characteristics of oceanic island basalts and rare shallow marine limestones structures in the melange suggest an origin by two distinct deformation processes involving unlithified sediments initial boudinage and break up of the strata was apparently accomplished by intrastratal movement resulting from imbricate thrusting within the accretionary wedge the second process produced cross cutting zones of breccia which are interpreted as fluid escape conduits resulting from the high pore pressures produced during underthrusting

debris flow olistostromes and slumping on a distal passive continental margin the palombini limestone shale sequence of the northern apennines an olistostrome accumulation up to 530 m thick occurs in the casanova area of the northern apennines it lies within or above the calciturbiditic palombini limestone shale sequence and is part of the allochthonous vara complex sediments originally deposited on oceanic crust the olistostromes are poorly sorted monomict matrix supported submarine debris flow deposits with rigid plugs they have a compactional foliation and a compaction modified planar clast fabric created during flow although diachronous in the main part of the area the olistostromes have a vertical gradational contact with the overlying slumped palombini in which recumbent asymmetric fold hinges and trains and slump boudins are present many criteria indicate soft sediment deformation fold asymmetry indicates a uniformly sw dipping palaeoslope the textural gradation from slumps to olistostrome beds plus slump folds and boudins as olistostrome clasts show that the olistostromes are dismembered slumps in vertical sections variations in limestone petrography volume percentage and size of clasts confirm that the olistostromes were derived from the palombini as a series of bed by bed slumps keeping pace with sedimentation of the palombini from olistostrome clast sizes and bed thicknesses a depositional slope of 4 is estimated the olistostromes are not precursor sediments shed from advancing nappes as in the bracco ridge model of some authors rather they were formed at the foot of a distal block faulted passive continental margin long before nappe emplacement

slump sheets as a record of regional tectonics and paleogeographic changes in south china abstract slumps of various scales are recognized in the late katian late ordovician mixed carbonate and siliciclastic slope successions in the changshan area western zhejiang province south china in order to understand their deformational processes triggering mechanisms paleo slope orientation and geological implications a detailed sedimentological study was carried out on four outcrop sections in the southern changshan the putangkou zhoutang and shikeng sections we recognized three slumping episodes ca 3 5 m 11 m and 73 m in thickness in stratigraphically ascending order and co occurred debris flows at the sanqushan section 11 5 km north of changshan thirteen slump units each being tens of cm to 6 m in thickness are recognized facies analyses and diagenetic characteristics of these slumps and their internal deformation structures suggest that they formed as a result of plastic and brittle deformation and liquefaction and fluidization during slumping the rip up blocks cracks and ruptured beds in the slumps of southern changshan indicate extensional features whereas recumbent and disharmonic folds in the slumps of northern changshan represent compressional features these spatially different features suggest that the slumps may have been generated on a paleo slope dipping generally to the north the case study of slumps and debris flows from the putangkou section indicates a significant mass flow transition from a slumped mass into debris flow deposits autogenic triggering mechanisms of these slumps e g rapid deposition storm wave loading and tidal shear are ruled out by the results of facies analysis instead the slumps might have been triggered by relative sea level changes or tectonically induced progressively steepening of the slope which is likely related to the contemporaneous kwangsian orogeny

zabyat formation semail nappe oman sedimentation on to an emplacing ophiolite the pelagic sediments of the semail ophiolite are depositionally overlain by ophiolite derived sediments of the zabyat formation dominated by matrix supported rudites with subordinate arenites and lutites the detritus was locally derived from the ophiolite in a deep marine environment indicated by both underlying and overlying pelagic carbonates the zabyat rocks are restricted to fault zones in the ophiolite which were active during emplacement they are interpreted as debris shed from the sub vertical fault zones during the initial disruption of the semail ocean floor prior to the final emplacement on to the arabian continental margin this interpretation places constraints on possible mechanisms of ophiolite emplacement

spectral analysis of quikscat surface winds and two dimensional turbulence a spectral decomposition of quikscat surface wind vectors reveals different levels of variance and different values of the spectral slope in various regions of the world ocean for the 12 months investigated the traditional considerations on the factors affecting the shape of the spectra are reviewed and compared to the results in particular the influence of large scale synoptic systems is shown by comparing the steeper and more energetic spectra of the midlatitudes to the shallower spectra of the tropics similarly the signature of convection is investigated by comparing spectra in the tropical convectively active and dry zones of the pacific ocean spectra of vorticity and divergence are calculated along with spectral vorticity to divergence ratios their spatial and temporal variations are discussed it is hypothesized that when convection is enhanced in the tropics the spectral analysis captures the mesoscale synoptic structures in which convection is embedded and that the spectra exhibit some of the characteristics of their midlatitude counterparts i e steeper and more energetic

topography and palaeogeographic evolution of a middle miocene foredeep basin plain northern apennines italy abstract the marnoso arenacea basin was a narrow northwest southeast trending foredeep of middle late miocene age bounded to the southwest by the apennine thrust front the basin configuration and evolution were strongly controlled by tectonics geometrical and sedimentological analysis of serravallian turbidites deposited within the marnoso arenacea foredeep combined with palaeocurrent data turbidite flow provenance reflection and deflection identify topographic irregularities in a basin plain setting in the form of confined troughs the more internal mandrioli sub basin and the external s sofia sub basin separated by an intrabasinal structural high this basin configuration was generated by the propagation of a blind thrust striking northwest to southeast parallel to the main trend of the apennines thrust belt ongoing thrust induced sea bed deformation marked by the emplacement of large submarine landslides drove the evolution of the two sub basins in an early stage the growth and lateral propagation of a fault related anticline promoted the development of open foredeep sub basins that were replaced progressively by wedge top or piggy back basins partially or completely isolated from the main foredeep meanwhile the depocenter shifted to a more external position and the sub basins were incorporated within an accretionary thrust belt

experimental decipherment of the soft sediment deformation observed in the upper part of the talchir formation lower permian jharia basin india abstract four types of soft sediment folds of distinct geometry can be recognized in the upper part of the talchir formation lower permian of jharia basin india these folds on systematic examination indicate some events of progressive deformation experimental study reveals that if a layered stack of clay and overlying sand is allowed to flow slowly down a slope differential velocity due to viscosity contrast leads to the deformation of the rheologic interface the sharp planar contact gradually becomes wavy leading to the development of round hinged folds involving sediments adjacent to it with the advancement of the flow these folds gradually become overturned with the rotation of the axial plane in the direction of flow computer simulation suggests that progressive deformation of these folds by simple shearing may lead to the formation of tight isoclinal folds which on dislocation along intrastratal normal faults may lead to the development of rootless isoclinal folds the sheath folds observed in the studied section also indicate accentuation of the curved hinge due to simple shearing the spatial distribution of these fold types in conjunction with the inferred direction of progressive deformation indicate basinward translation of the slump slice if the same stack of sediments rapidly flows down the slope the waveform generated at the interface quickly breaks in the form of roll up recumbent fold due to kelvin helmholtz instability

testing the utility of the porphyroclast hyperbolic distribution method of kinematic vorticity analysis kinematic vorticity wk is a dimensionless measure of rotation relative to finite stretching and is essential for complete understanding of flow in ductile shear zones the porphyroclast hyperbolic distribution phd method is a widely used technique for estimating wk based on the acute angle between the flow eigenvectors determined from the orientations of back rotated s porphyroclasts the utility of the phd was tested with tertiary ultramylonites from the santa catalina mountains arizona proterozoic ultramylonites from the virgin mountains nevada and a paleozoic ultramylonite from the hylas zone in the virginia piedmont bootstrapping statistics and a computational sieving process were used to analyze the phd data set average standard deviations of the bootstrapped data sets yield a 1s standard error of 9 for a wk value measured as a simple shear sieving results imply that back rotated porphyroclasts may not orient parallel to the extensional eigenvector the phd method is useful for discerning between deformations that are pure shear dominated general shear or simple shear dominated but is not accurate enough to report precise wk values when performed on multiple sections the phd method can identify zones of monoclinic versus triclinic shear 2007 elsevier ltd all rights reserved

implications of strain and vorticity of flow analyses to interpret the kinematics of an oblique convergence event zagros mountains iran abstract finite strain and vorticity of flow analyses were carried out within the deh vazir deformed conglomerates in the sanandaj sirjan metamorphic belt zagros mountains iran this belt is in a sequence of tectono metamorphic complexes made of low to high grade metamorphic rocks affected by a polyphase deformation history using rf technique for two dimensional strain analysis showed that the finite strain of xz plane is rs 3 7 0 70 the calculation of the harmonic mean from the axial ratios of the extracted pebbles and plotting these data in the flinn diagram resulted in k 0 7 0 38 i e oblate strain ellipsoid kinematic vorticity analysis of deformed pebbles showed that wk parameter is 0 59 0 10 i e pure shear dominated non coaxial flow the results quantitatively support the recognition of a partitioned dextral inclined transpressive regime with bulk triclinic symmetry along the sanandaj sirjan metamorphic belt resulted from the oblique collision between the african arabian continent and the iranian microcontinents

seismic imaging of melanges pieniny klippen belt case study the authors present results of the first high resolution deep seismic reflection survey in the pieniny klippen belt pkb in poland this survey sheds new light on the matter of olistostromes and the melange character of the pkb the sedimentary mass transport deposits represented by olistoliths and olistostromes manifest themselves by different petrophysical parameters of rocks velocity density and resistivity and seismic attributes seismic attributes are very effective in the interpretation of the geology of complex melanges the authors used selected attributes low pass filter energy energy gradient dip steered median filter prewitt filter laplacian edge enhancing filter and square root of the energy gradient these attributes emphasize changes of the seismic image inside melange zones the distinguished olistoliths are now inside imbricated thrust structures and they are tectonically rearranged polygenetic melanges in the pkb originated as a result of sedimentary and tectonic processes the pkb in the investigated area forms several north vergent thrust sheets belonging to the zlatne and hulina nappes both nappes contain large chaotic non reflective olistoliths as well as the smaller mainly high reflective olistoliths olistoliths are arranged parallel to the flysch layering and thrusts the results presented confirm the postulated two olistostrome belts within the pkb structure

the giant ruatoria debris avalanche on the northern hikurangi margin new zealand result of oblique seamount subduction despite convergent margins being unstable systems most reports of huge submarine slope failure have come from oceanic volcanoes and passive margins swath bathymetry and seismic profiles of the northern hikurangi subduction system new zealand show a tapering 65 30 km wide by 65 km deep margin indentation with a giant 3150 630 km3 blocky debris avalanche deposit projecting 40 km out across horizontal trench fill and a debris flow deposit projecting over 100 km slide blocks are well bedded up to 18 km across and 1 2 km high the largest being at the avalanche deposit s leading edge samples dredged from them are mainly miocene shelf calc mudstones similar to those outcropping around the indentation cores from cover beds suggest that failure occurred 170 40 ka possibly synchronously with a major extension collapse in the upper indentation however the northern part of the indentation is much older the steep straight northern wall is close to the direction of plate convergence and probably formed around 2 0 0 16 ma as a large seamount subducted leaving in its wake a deep groove obliquely across the margin and an unstable triangle of fractured rock in the 60 angle between groove and oversteepened margin front the triangle collapsed as a blocky avalanche leaving a scalloped southern wall and probably causing a large tsunami tentative calculations of compacted volumes suggest that the indentation is over 600 km3 larger than the avalanche supporting a two stage origin that includes subduction erosion since failure convergence has carried the deposits 9 km back toward the margin causing internal compression the eventual subduction accretion of the ruatoria avalanche explains the scarcity of such features on active margins and perhaps the nature of olistostromes in fold belts

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

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

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

role of the olistostromes and olistoliths in tectonostratigraphic evolution of the silesian basin in the outer west carpathians abstract the silesian series deposited in the proto silesian and silesian basins and preserved within the silesian nappe represents most complete continuous basinal sedimentary succession late jurassic early miocene within the outer carpathians it contains intercalations of numerous olistostromes that occurred during every stage of flysch basin evolution from rift and post rift through orogenic to postorogenic stage the olistostromes represent sediments of sub marine debris flows and avalanches they are of different size and composition and were derived from ridges and their slopes bordering proto silesian and silesian basins 0however the main source was the tectonically active southern slope and adjacent ridges the silesian and bukowiec ridges composition of olistostromes is an important source of knowledge about the geological structure and history of ridges and basin slopes which now are not preserved some large olistoliths and olistoplaques have been incorrectly interpreted as thrust sheets so detail studies of their true origin allowed correct interpretation of local tectonics

fabric attractors in general triclinic flow systems and their application to high strain shear zones a dynamical system approach high strain zones may deform by flow with a triclinic symmetry this paper describes triclinic flow in a reference frame where instantaneous stretching axes isa are fixed the operation of triclinic flow is described in two ways first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain in monoclinic flow at least one of the eigenvectors of the flow coincides with one of the isa and one or two of the eigenvectors act as attractors of foliation or lineation elements in triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues controlling the flow are imaginary imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20 from one of the isa strong deviation from monoclinic flow is therefore possible but this will not produce permanent foliations or lineations for triclinic flow that does produce permanent fabrics the angle between isa and the fabric is so small that it is unlikely that it can be recognised in nature a discussion of the potential application of such results within real shear zones is presented

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

strain partitioning in transpression zones abstract transprcssional strain acting upon structurally anisotropic rocks can be partitioned into separate deformational domains of pure shear and simple shear this contrasts with homogeneous transpression in which both the pure shear and the simple shear strain components are uniformly distributed across the zone of deformation structural weaknesses capable of partially or fully accommodating one component of deformation include lithological contacts rheological heterogeneities and faults or shear zones situated within the deformation zone or lying along its boundaries partitioning of transprcssional strain can occur when stress is applied oblique to pre existing structural weaknesses or can occur during later stages of progressive strain when the early deformation of isotropic rocks imparts sufficient anisotropy to allow subsequent strain to be partitioned partitioning of transpressional strain into domains lying parallel to the deformation zone boundaries can be distinguished from fault stepped transpression in which strain is partitioned along the length of a segmented fault zone mesofracture analysis of rocks affected by mid devonian deformation on both sides of the highland boundary fault zone hbfz in central scotland shows that strain was not homogeneous the mesofracture data suggest that regional north south compression orientated oblique to the pre existing ne sw trending hbfz was partitioned into separate deformational domains the hbfz accommodated most of the simple shear component whilst the rocks flanking the zone were deformed predominantly by pure shear a contemporary example is the san andreas fault in central california where analyses of neo tectonic stresses show that the direction of principal compression is perpendicular to the fault zone many examples of the partitioning of transpressional strain have also been recognised at destructive plate margins where the direction of plate motion is oblique to the edge of the over riding plate

vitrinite reflectance illite crystallinity and tectonics results from the northern apennines italy abstract vitrinite reflectance measurements were used in the ligurian apennines to identify 14 tectonic units nappes these are arranged in 5 tectonic supergroups with different degrees of coalification relative dating of 2 orogenetic processes and heating events in the eocene and late miocene was possible maximum paleotemperatures around 300 c and burial depths of up to 5 km are estimated enormous masses are thought to have accumulated and to have been removed within a very short time span the development of the sedimentary organic matter from diagenetic very low grade up to initial low grade metamorphic stages is investigated the joint occurrence of vitrinite and transitional matter between vitrinite and graphite is significant of the initial graphitization process diessel et al 1978 and occurs between 4 and 7 r max vitrinite reflectance r m and illite crystallinity are closely correlated in a similar way as in other areas of a similar tectonic history the relationship between the quantity of mixed layer minerals and vitrinite reflectance suggests a connection with the degree of diagenesis

kinematics of rock flow in a crustal scale shear zone implication for the orogenic evolution of the southwestern hellenides combined shear sense criteria finite strain data and vorticity analyses were used to study the deformation path in a curved crustal scale shear zone phyllite quartzite series of the southwestern hellenides the results are combined with data on the structural evolution of a cover nappe pindos thrust belt to provide new insights into the orogenic evolution of this region ductile deformation within the phyllite quartzite series was associated with a top to the west southwest shearing and was partitioned into two structural domains a root zone and a frontal domain the root zone is characterized by vertical coaxial stretching high strain and upward movement of the material while the frontal domain comprises simple shear deformation at the base and pure shear at the top this pattern suggests superposition of pure shear on simple shear deformation and implies tectonic extrusion of the material from the root zone the initiation of brittle deformation in the pindos thrust belt was associated with westward translation above the sub horizontal pindos thrust later as the mountain range elevated normal faulting at high altitudes and migration of thrusting to the west occurred while east directed folding and thrusting in the belt started to the east according to the proposed model crustal thickening was taking place throughout the oligocene and early miocene including the subduction of the apulian beneath the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite series during the lower miocene vertical buoyancy forces led to the successive steepening of the shear zone and the simultaneous duplexing of its basement facilitating tectonic extrusion of the material from its root zone finally an indentation process caused vertical expulsion of the orogenic wedge and gravity collapse in the brittle crust

detachment folding related miocene submarine slope instability in the romagna apennines italy 1 the relationships between slope failure and growing thrust related structures have been explored in the miocene marnoso arenacea foredeep basin romagna apennines impressive fossil slump layers are distributed along the footwall of the regional mount nero thrust which evolved from detachment fold to breakthrough thrust during the detachment fold stage development of growth strata on the rotating forelimb was preceded by the emplacement of slump layers that are currently part of the mount nero thrust footwall in this process sliding is assumed to nucleate along the contacts between different lithologies in the semiconsolidated rock mass the conditions of sliding specifically the critical angle of sliding crit are quantified by adding the influence of cohesion of sediments to the equilibrium analysis reported in hubbert and rubey s 1959 classical work the resulting angles crit are discussed with respect to the depth of the basal surface of sliding and pore fluid pressure states on the basis of such an analysis and field work results an evolutionary model is proposed in which slide sheets come from the crest and upper forelimb of growing detachment folds and attain a deeper detachment depth as the forelimb rotates and steepens pore fluid pressure is found to play a major role by radically decreasing the critical angle of sliding likewise localization of overpressures may also control the depth of sliding during progressive forelimb rotation to allow sliding along gently dipping bedding surfaces slope failure is interpreted as being related to the reactivation of anisotropies represented by lithological discontinuities

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

scatterometer and ecmwf derived wind vorticity over the mediterranean basin this article investigates the spatial and temporal structures of the monthly mean vorticity fields and over the mediterranean basin derived respectively from satellite scatterometers and ecmwf global atmospheric model t799 wind fields from february 2006 to january 2010 statistics show a mean difference between and over the whole mediterranean sea relative bias of 0 108 10 5 s 1 furthermore both the cyclonic and the anticyclonic components of are stronger than those of the analysis of the spatial features of and shows that the greatest discrepancies occur along coasts and in the adriatic sea due to the ability of to describe vorticity features smaller than about 6 9 103 km2 roughly corresponding to square areas of side 83 km or circular areas of radius 46 km that are not present in given the effective spatial resolution of the model the temporal features of and have shown a substantially similar trend in anticyclonic and a deep difference in cyclonic circulations again related to the limited ability of to describe small scale vorticity patches as the main source of the differences local characterization of and along six transects across areas where the wind vorticity features are well known has confirmed the results of substantial similarity of and at spatial scales larger than 100 km or so and remarkable differences in those regions such as the adriatic and crete seas affected by vorticity variability at smaller scales copyright 2012 royal meteorological society

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

climatology of cyclogenesis mechanisms in the mediterranean abstract a general climatology of the main mechanisms involved in mediterranean cyclogenesis is presented a diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons and in different cyclogenetic regions within the same season it is shown that cyclones that developed over the three most active areas in winter the gulf of genoa the aegean sea and the black sea are essentially subsynoptic lows triggered by the major north atlantic synoptic systems being affected by local orography and or low level baroclinicity over the northern mediterranean coast it is also suggested that cyclones in two or all three of these regions often occur consecutively linked to the same synoptic system in spring and summer thermally induced lows become progressively more important despite the existence of other factors such as the atlas mountains contributing to lee cyclogenesis in northern africa or the extension of the asian monsoon into the eastern

thin bedded diamictites in the glaciomarine hoyada verde formation carboniferous calingasta uspallata basin western argentina a discussion on the emplacement condition of subaqueous cohesive debris flows abstract thin bedded 0 5 20 cm diamictites are present in the glaciomarine sequence of the hoyoda verde formation carboniferous of the calingasta uspallata basin the sharp non erosive contacts the high mud content and the wide range in clast size suggest that the thin bedded diamictites have been deposited as subaqueous debris flows bed thickness bth versus maximum clast size mcs plots show a strong positive correlation 0 95 proving that the flows had a close balance between capacity and competence and were laminar the cohesive factor also deduced from the bth mcs plots indicates that the flows can be interpreted as cohesive debris flows the widespread presence of inversely graded or massive beds and low bth mcs values mean bth mcs 2 71 standard deviation 0 33 suggest relatively concentrated competent debris flows with minor water intake in contrast to other more frequent examples of more dilute water rich subaqueous debris flows with lower competence relative to flow thickness

deformation path in high strain zones with reference to slip partitioning in transpressional plate boundary regions abstract the current status of the kinematics and strain geometry of high strain zone studies is briefly summarized a general high strain zone has a triclinic deformation path and monoclinic shear zones are special end member cases fabrics observed in natural shear zones and theoretical considerations based on continuum mechanics are compatible with this conclusion non steady deformation paths remain difficult to deal with and may ultimately rely on a realistic mechanical treatment of high strain zones which may be possible when our knowledge of the mechanical behavior of rocks under natural deformation conditions is improved an examination of the phenomenon of slip partitioning in transpressional plate boundary regions shows that the bulk deformation path in the forearc area trench parallel high strain zone is generally triclinic the alpine fault in the south island of new zealand provides an example of a currently active triclinic shear zone the southern knee lake shear zone of manitoba canada provides an archean example of a triclinic shear zone

cementation hydrothermal alteration and zn pb mineralization of carbonate breccias in the irish midlands textural evidence from the cooleen zone near silvermines county tipperary a reply sir we are delighted to respond to the comments of reed and wallace on our paper on the origin of breccia hosted base metal mineralization in the irish ore field lee and wilkinson 2002 reed and wallace s thesis is that the mineralized breccias we have described within the mississippian waulsortian limestone formation at cooleen are not of sedimentary origin and therefore by extension that synsedimen tary breccias do not exist elsewhere in the ore field if correct one of a number of lines of evidence that have been used to infer a near sea floor origin for at least a component of sulfide mineralization in ireland that of reworked clasts of sulfide within sedimentary breccias would be invalidated contrary to the suggestion of reed and wallace the existence of sedimentary breccias spatially associated with mineralization in the waulsortian is universally accepted in the literature mine based investigations that include underground observations as well as drill core data and sedimentological studies have concluded that the stratiform wedge shaped breccia bodies commonly developed within the waulsortian limestone facies are sedimentary debris flows of courceyan age boyce et al 1983 taylor 1984 andrew 1986 clifford et al 1986 somerville et al 1992 submarine fault scarp sedimentary breccias are common in sediment hosted zn pb deposits e g goodfellow et al 1993 and display the same characteristics as the breccias at cooleen hitzman and beaty 1996 p 125 also recognized that synsedimentary breccias are present within the waulsortian at both silvermines and lisheen but went on to state that textural and field relationships clearly show that the principal episode of brecciation postdated regional burial dolomiti zation inferring a hydrothermal origin for the ore hosting breccias while we would not agree with this conclusion particularly in relation to the silvermines area we accept that the ore hosting breccias at lisheen galmoy and silvermines have been

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

extensional tectonics and gravitational collapse in an ordovician passive margin the western argentine precordillera abstract the paper describes ubiquitous extensional structures developed in a passive margin of ordovician age in the argentine precordillera these extensional structures include normal faults and boudinaged sequences in some places the boudinage reaches very high extension values giving rise to block in matrix formations most of these extensional structures developed when sediments were not well lithified as recorded by hydroplastic fractures slump folds and pinch and swell structures the presence of slump folds coeval with the extensional deformation the variable extension directions obtained from the kinematic analysis and a weak cleavage recording layer perpendicular shortening support the interpretation that gravitational collapse related to submarine sliding was the cause for extensional deformation well consolidated rocks located at the lower part of the stratigraphic sequence also display scarce extensional faults these extensional faults predate folding because they were breached by flexural slip faults and as a result of their passive rotation in fold limbs these initial normal faults may now appear as reverse faults particularly in steep and overturned limbs the truncation of extensional faults by flexural slip faults produces typical bed thickness changes across the extensional faults giving rise to apparent synsedimentary faults these normal faults can be attributed to the crustal extension that generated the passive continental margin or may represent deep parts of faults related to gravitational collapse

physical experiments of vertical transpression with localized nonvertical extrusion abstract previously proposed models of vertical walled transpression implicitly assume that material extrudes upwards during deformation this assumption is not necessarily valid at all scales given that a in areas of diverse lithologies local zones of relatively rigid materials may cause extruding material to deflect around those zones and b ductile strain often forms anastomosing geometries of shear zones therefore it is possible that a local extension direction in otherwise classic transpression may be nonvertical for rocks deforming at depth using an analogue experiment we have modeled a transpression zone with localized nonvertical extrusion this extrusion is accomplished by the addition of a side leak that allows sideways extrusion in addition to vertical extrusion the net extension direction depends on the material s position within the deforming zone resulting in a significant range of lineation orientations with deformation the strain patterns produced by transpression with localized nonvertical extrusion may explain the wide array of lineation orientations found in some natural ductile transpression zones

strain partitioning in ductile shear zones an example from a lower pennine nappe of switzerland abstract the rocks of the maggia nappe a lower pennine nappe of the swiss alps were deformed in at least three phases during alpine orogeny hercynian granites in the core of the nappe developed ductile shear zones during the early phases of deformation but between shear zones they remained almost undeformed both heterogeneous simple shear and heterogeneous volume change played an important role in the formation of the ductile shear zones partitioning of different strain components indicates a volume loss of nearly 80 90 towards the centres of some of the shear zones such a large amount of volume loss is also corroborated by strain analysis of deformed xenoliths in other shear zones of the same region a comparative study of theoretical strain paths and the natural results indicates constant shear strain rate but changing dilation rate during deformation

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

the relevance of the sedimentary history of the grand conglomerat formation central africa to the interpretation of the climate during a major cryogenian glacial event the cryogenian grand conglomerat formation 735 ma in age and with considerable thickness variations up to a maximum thickness of about 950 m is an association of interbedded glaciogenic clastic periglacial and non glacial deposits topped by the kakontwe limestone cap carbonate these units occur within the nguba group of the katanga supergroup which was deposited in a rift basin and subsequently deformed as part of the pan african lufilian orogenic belt that separates the congo and kalahari cratons both correlation of regional unconformities and facies distribution suggest that the grand conglomerat sediments were deposited during and after eruption of flood basalts in an asymmetrical rift with a strongly uplifted southern shoulder and a graded shelf defining the northern margin glaciomarine sedimentary rocks along the southern margin of the katangan rift are preserved within fan delta conglomerates supplied from an elevated rift shoulder by contrast the northern margin of the rift was the site of continental glaciation with cross bedded glaciofluvial and marginal marine sandstones and conglomerates associated with massive tills glaciogenic diamictites that pass laterally towards the south into glaciomarine mixtite interlayered with wedges of dolomitic sandstone the kakontwe limestone cap carbonate is present only in the distal parts of the basin its absence in proximal regions is considered to reflect very high rates of sedimentation of fine grained glaciogenic debris derived from deglaciated source areas palaeomagnetic data indicates that the grand conglomerat glaciogenic sediments were deposited close to the equator during the cryogenian this low latitude setting coupled with the absence of a topographical trigger would suggest that glaciation was related to global atmospheric cooling however the presence of water borne glaciogenic on shore sediments and offshore sediments derived from floating glaciers suggests that the ocean during this part of the cryogenian was not completely frozen associations of glaciogenic facies with non glaciogenic sedimentary rocks imply glaciation with interglacial periods and gradual deglaciation instead of severe conditions of permanent sea ice cover and rapid change to the greenhouse environment

sediment creep on slopes in pelagic limestones upper jurassic of northern calcareous alps austria abstract slump structures in upper jurassic pelagic limestones of the northern calcareous alps were studied using methods of ductile structural geology the early deformation observed cannot be explained by conventional models for slumping commonly describing slump complexes with an extending upper and contracting lower part instead the structures suggest distributed bedding parallel surficial stretching and folding localized by roll over normal faulting the initially isoclinal and recumbent folds are pervasively overprinted by stretching causing reorientation of fold axes into the downslope direction transport of folds separates antiformal and synformal hinges and the resulting isolated hinges resemble intrafolial folds in metamorphic terranes only folds formed late in the process of lithification allow insight in the early stages of fold evolution we suggest that this type of early deformation represents sediment creep that may be characteristic for slump structures in pelagic carbonates

constraints on deformation path from finite strain gradients we present a methodology for analyzing finite strain gradients in high strain zones in order to place constraints on the zone s possible deformation path to accomplish this the high strain zone is divided into several sub zones within each of which finite strain is described by a single ellipsoid based on knowledge of the spatial and temporal evolution of deformation strain observed in less deformed sub zones is then mathematically removed from more deformed sub zones to calculate incremental finite strains the mean kinematic vorticity number of each of these increments must be constant if deformation was steady state we use the methodology to analyze two natural examples of high strain zones at different scales both natural examples have non steady state likely deformation paths which may be a common characteristic of high strain zones although results of the methodology are not unique identification of likely paths considerably narrows the range of possible deformation paths consequently useful kinematic information can be extracted from finite strain data even in instances where the detailed spatial and temporal evolution of a high strain zone cannot be determined conclusively

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

pebbly mudstones in the cretaceous pigeon point formation western california a study in the transitional stages from submarine slumps to cohesive debris flows abstract the pebbly mudstones in the late cretaceous pigeon point formation originated by slumping and related debris flow processes in a submarine canyon slope depositional system the sedimentary characteristics of the pebbly mudstones pm enable the distinction of two main varieties a heterogeneous or patchy pebbly mudstones ppm exhibiting irregular bed geometries and diffuse to irregular bed contacts with maximum clast sizes in intraformational boulder sized population including abundant rip up mudstone and sandstone clasts with common soft sediment deformations b homogeneous pebbly mudstones hpm with tabular bed geometries non erosive and almost flat bed contacts maximum clast sizes in extraformational pebble sized fraction and scarce to absent soft sediment deformations the two varieties of pebbly mudstone represent the mechanical transition from slumps to cohesive debris flows the presence of abundant intraformational clasts and disrupted yet preserved slump fold features in the ppm suggest that this facies represents a stage closer to the slump end member as the shear strain progressed and a fully remolded cohesive debris flow developed an almost complete disaggregation of the poorly consolidated sand and mud clasts and the incorporation into the remolded matrix phase took place

using ascat scatterometer winds to evaluate relative biases in the quikscat derived wind vorticity relative wind vorticity hereafter vorticity is a crucial parameter to understand the spatial features of the wind field in the mediterranean sea which is the area where this study is focused these are particularly interesting because they are often the effects of the interaction between the airflow and the orography wind vorticity has been derived from both quick scatterometer quikscat and advanced scatterometer ascat 12 5 km scatterometer data downloaded from the national aeronautics and space administration physical oceanography distributed active archive center data archive and compared in the period from march to november 2009 the monthly mean fields of the vorticity show discrepancies which need to be understood this paper thus aims to understand the nature of these differences to make the two vorticity data sets compatible and usable as a common data set results have been provided in terms of the relative bias in vorticity which is the mean difference between the ascat a and quikscat q monthly mean vorticities averaged over the entire mediterranean basin and the entire study period this difference 0 093 10 5 0 05 10 5s 1 is mainly due to a relative vorticity bias in the cyclonic component of rather than in the anticyclonic component whose bias is four times smaller this bias does not depend significantly on the variable accuracy of the wind speed and direction across the quikscat swath this study led us to define and analyze the so called vorticity noise which is present particularly in the quikscat derived vorticity to understand if and how it can contribute to the relative bias in vorticity the contribution of this kind of noise on has been found relevant only for the cyclonic vorticity of q by applying a cyclonic denoising to each swath of quikscat 0 016 10 5 0 05 10 5s 1 is obtained drastically reduced with respect to the initial value this may be considered the typical bias over the mediterranean sea between a and q derived from the 12 5 km data after applying the cyclonic denoising to quikscat vorticity fields

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

strain in ductile shear zones in the caledonides of northern sweden a three dimensional puzzle small scale ductile shear zones are well developed in amphibolites of caledonian nappes of the swedish lapland strain in the shear zones is recorded by the shapes of originally sub equant aggregates of plagioclase feldspar classical strain analysis on two dimensional xz profiles across the shear zones leads to results that indicate large volume losses associated with the shear strain large volume losses are however incompatible with geochemical analysis which shows little chemical variation across the shear zones by including data from xy and yz sections information on the three dimensional state of strain can be obtained these data indicate that deformation is not confined to a two dimensional plane particle extension within the shear zone parallel to the shear plane and perpendicular to the shear direction has also occurred the state of strain and strain path in the shear zone can be modeled in a general way by combining stretches in x y and z with simple shearing and volume loss end member models correspond to plane strain with volume loss kx ky 1 kz 1 transpression kx 1 ky 1 kz and pure shear kx 1 kz ky 1 these models produce identical strain ratios and orientations on the xz section but differ in stretch in y and in area of the strain ellipse on the xz section extension in y or x allows for reconciliation of the geometrical and geochemical data for part of an individual shear zone but poses a problem of strain compatibility at the edges and terminations of the shear zones the shear zones show a complex anastomosing pattern in three dimensions and their connectivity provides a way in which strain compatibility is maintained

glacial or non glacial origin for the bigganjargga tillite finnmark northern norway bigganjargga is the classic locality for the varangian ice age in northern scandinavia the presence of two sets of striations on the underlying quartzite basement has been taken as evidence for a glacial origin of the bigganjargga diamictite however soft sediment surface structures on the underlying sandstone indicate that it was not consolidated when the diamictite was emplaced together with structures in the diamictite this shows that the deposit formed as a debris flow moving northwestwards over an unconsolidated substrate there is no evidence for glacial origin or contribution for the diamictite material

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

the use of structure functions and spectra from numerical model output to determine effective model resolution abstract the effective model resolution of three numerical weather prediction nwp models is determined from analyses of spatial structure functions and spatial spectra in this paper the effective resolution is defined as the dimensions of the rectangular spatial filter that describes the net effect of all of the nwp model s numerical filtering and smoothing effects these effects are determined by comparison of spatial statistics of the nwp model output with statistical climatologies derived from aircraft data for the upper troposphere and lower stratosphere the comparisons are based on both spatial structure functions and spatial spectra the structure function approach has fewer assumptions and fewer numerical artifacts accurate estimates of nwp effective model resolution require a robust climatology of the spatial statistics which are a function of latitude and location such as over mountainous regions an artifact in the climatology of the velocity statistics resulting from mountain waves is i

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

tectono metamorphic evolution of the neyriz metamorphic complex quri kor e sefid area sanandaj sirjan zone sw iran abstract the neyriz region includes outcrops of metamorphic rocks that are thrust over the neotethyan ophiolites these rocks are affected by a major deformational event the result of which includes a shearing polyphase foliation present in gneissic core domes overprinted by a crenulation cleavage these fundamental structures developed contemporaneously with a medium pressure metamorphism which is characterized by the syn kinematic crystallization of kyanite and the beginning of anatexis followed by the development of retrometamorphic mineral parageneses the major deformation phase in the area occurred during the early cimmerian orogeny in the late triassic following the orogeny the gneiss domes started to rise into the upper levels of the crust from the geodynamic point of view after the mid permian the studied area was situated at southern passive margin of the iranian plate the central iranian microcontinent at that time was separated by the neotethys ocean from the gondwanian supercontinent after the late triassic the region became an active margin associated with an accretionary prism the margin was finally involved in an orogenic wedge after the closure of the neotethyan oceanic basin in the late mesozoic closure of the basin resulted in a major thrusting of the metamorphic rocks of the southern iranian margin over the neotethyan ophiolites

general shear deformation in the pinaleno mountains metamorphic core complex arizona abstract granitic mylonites from the pinaleno mountains metamorphic core complex in southeastern arizona record general shear deformation the mean kinematic vorticity number w m was estimated using 1 the strain ratio r s and the angle between the long axis of the strain ellipsoid with respect to the high strain zone boundary and 2 the porphyroclast hyperbolic distribution method w m for protomylonites and mylonites ranged from 0 6 to 0 9 ultramylonites record lower w m values 0 1 0 3 suggesting that the incremental vorticity changed during deformation three dimensional strain analysis indicates that deformation in protomylonites and mylonites approximates plane strain and has a monoclinic symmetry the vorticity path followed by rocks tectonically exhumed in the footwall of major extensional fault systems may evolve from a significant pure shear component early in the deformation towards simple shear as overburden load decreases during uplift

3d evolution of fold and thrust belts formed by oblique convergence abstract this paper presents the results of a series of scaled analogue models designed to simulate thrust belt development formed by orthogonal and oblique convergence the models were constructed to produce doubly vergent orogenic wedges with a pro wedge and a retro wedge separated by an uplifted orogenic core models were constructed from homogeneous layered sandpacks in a 3 m 1 3 m deformation rig the progressive evolution of the models was recorded using digital photography and the photographs were animated for analysis the experiments investigated convergence obliquities from orthogonal 90 to as low as 15 obliquity orthogonal models produced long linear critically tapered pro wedge fold and thrust belts parallel to the convergence margin together with a narrow uplifted core and a steep retro wedge thrust system the taper angle of the pro wedge was typically 11 12 whereas the retro wedge maintained a steeper taper of 38 42 models where the convergence vector was oblique at angles of 60 and 45 to the margin produced doubly vergent thrust wedges with thrust faults trending parallel to the margin there was little evidence of linked penetrative strike slip faulting but en echelon riedel like shear systems developed in the 45 oblique model subordinate oblique slip motion was observed on some thrust faults in contrast for 30 and 15 oblique convergence models strong deformation partitioning developed with steeply sloping pro wedges that did not have critical tapers through going linked strike slip faulting was developed that cut the uplifted axial zones of these models analysis of the models by animation of the digital photographs shows how the thrust systems initiated and propagated in particular it is clear that at any one time several thrusts were moving simultaneously serial cross sections through the moderately oblique convergence models 60 45 are almost indistinguishable from the orthogonal model cross sections the results of orthogonal convergence experiments compare well to the map patterns of faults and folds in the salt range pakistan 60 and 45 oblique convergence models compare well to the zagros where some strain partitioning on strike slip faults occurs the highly oblique models show very strong strain partitioning with penetrative margin parallel strike slip faulting similar to that found in ne venezuela

possible significance of early paleozoic fluctuations in bottom current intensity northwest iapetus ocean sedimentologic and geochemical characteristics of red and green deep water mudstone exposed in the central appalachian orogen define climatically induced fluctuations in bottom current intensity along the northwest flank of the iapetus ocean in early and middle ordovician time red mudstone accumulated under the influence of moderate to vigorous bottom current velocities in oxygenated bottom water produced during climatically cool periods interbedded green mudstone accumulated at greater sedimentation rates probably from turbidity currents under the influence of reduced thermohaline circulation during global warming periods the close association of green mudstone and carbonate turbidites of early ordovician late tremadocian to early arenigian age suggests that a major warming phase occurred at this time increasing temperatures reduced bottom current velocities and resulted in increased production of carbonate sediment and organic carbon on the carbonate platform of eastern north america much of the excess carbonate sediment and organic carbon was transported into deep water by turbidity currents although conclusive evidence is lacking this eustatic event may reflect a climatic warming phase that followed the postulated glacio eustatic black mountain event subsequent middle ordovician fluctuations in bottom current intensity recorded by thin red green mudstone couplets probably reflect periodic growth and shrinkage of an ice cap rather than major glacial episodes

submarine debris flow deposits from the upper carboniferous dwyka tillite formation in the kalahari basin south africa four types of sediment gravity flow deposits occur interbedded with rhythmite shale siltsone mudstone and minor diamictite in a 230 m thick carboniferous glacial sequence shear and plug zones are present in the cohesive debris flow deposits which have a diamictic texture the high density turbidity flow deposits which consist of coarse to medium grained clastics are characterized by both normal and reverse grading the medium to fine grained low density turbidity flow deposits show normal grading and consist of bouma units a b d and e deposition occurred by gravity flow suspension settling and minor basal melt out during ice retreat along the southern margin of the kalahari basin immediately basinwards of the ice grounding line a proximal diamictite facies consisting predominantly of cohesive and high density turbidity flow deposits and minor melt out tills formed a distal sedimentary facies of graded sandstone and siltstone units deposited by low density turbidity flows and suspension settling of muds with ice rafted debris is located basinwards

generalized hydraulic solutions pertaining to severe downslope winds abstract nonlinear steady state solutions for stratified two layer flow over a ridge are found in parameter space these solutions lie between the interfacial case of long and the constant stratification case of smith the solutions predict the depth of the layer which will descend and accelerate qualitative agreement with bora and boulder observations is found

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

progressive development of block in matrix fabric in a shale dominated shear zone insights from the bobbio tectonic window northern apennines italy 1 block in matrix is a common fabric characterizing highly deformed to apparently chaotic rocks originated by sedimentary tectonic and mud diapiric processes in many exposed orogenic belts a true melange originates when this fabric is associated with mixing of rocks of different ages and provenance as that characterizing the main decollement shear zone developed between the highly allochthonous ligurian nappe and its substratum of foredeep deposits at the margins of the bobbio tectonic window trebbia valley northern apennines mixing of rocks by both mass transport processes and synsedimentary thrusting occurs at the front and tectonic erosion at the base of the nappe during its emplacement evidence of polyphased deformations spanning from liquefaction related and hydroplastic structures to pseudo hydrofracturing features and mineralized veining have been recognized within the marginal portions and along the sheared contacts of blocks encased within a scaly matrix crosscutting relationships testify a progressive deformation involving a transition from mesoscopic ductile to brittle conditions with the significant contribution of fluid overpressure a novel evolutionary scheme for block in matrix fabric development is here proposed involving the progressive dismembering of already highly deformed units originally developed in non to poorly lithified conditions through a generalized simple shearing achieved during the evolution of the shear zone coupled with strain hardening due to tectonic compaction synkinematic diagenesis and fluid expulsion

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

deformation path partitioning within the transpressional white mountain shear zone california and nevada most numerical simulations of transpression zones predict a change in finite stretching direction from subhorizontal to subvertical for simple shear dominated zones we provide a detailed description of a dextral transpression zone the white mountain shear zone wmsz with a range of lineation orientations and compare these natural data to numerical models the wmsz is characterized by steeply dipping foliations with dominant shallowly plunging lineations and coeval subordinate domains of steeply plunging lineations within shallowly lineated domains foliation geometry shear sense indicators and quartz c axis fabrics indicate a large component of simple shear while microstructural and quartz c axis fabric data from steeply lineated domains indicate a large component of pure shear geometric relationships between foliations and lineations and quartz c axis fabrics demonstrate that lineation orientation has remained constant during much of the deformation history comparison of numerical models with the data collected from wmsz shows that the shear zone geometry and the observed strain path partitioning do not match any of these models we propose a conceptual kinematic model for the wmsz involving stable segregated coeval kinematic domains of simple shear dominated fabrics and pure shear dominated fabrics that accommodate the transcurrent and contractional components of deformation respectively

testing models for obliquely plunging lineations in transpression a natural example and theoretical discussion theory predicts that stretching lineations in an ideal vertical transpressional zone should be either vertical or horizontal many field descriptions of transpressional zones however indicate a range of lineation orientations between these extremes several theoretical models have been developed to explain such departures from expected lineation orientation and we discuss these in the context of a field example from the archean superior province in the north american craton existing models are insufficient to explain obliquely plunging lineations in this example because 1 obliquely plunging lineations cannot be accounted for by shear zone boundary effects imposed by a no slip condition 2 foliations and lineations vary independently 3 the vorticity normal section is subhorizontal limiting possibilities for inclined simple shear 4 high vorticity is needed for finite strains and lineations to match previously proposed triclinic models but vorticity is relatively low and 5 juxtaposed east and west plunging lineations are unlikely in the previously proposed triclinic models because existing theoretical models are not applicable to our field example we contemplate a new model to explain obliquely plunging lineations within quasi homogeneous transpression

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

slip partitioning and inclined dextral transpression along the zagros thrust system iran abstract flexural duplex structures and shear zones are well developed in the heneshk area in southwestern iran the zagros thrust system in this area consists of eight sheets of nw striking ne dipping dextral strike slip duplexes that are linked with imbricate fans and oblique slip thrusts the zagros thrust system is a portion of the internal zone of the zagros orogenic belt this internal zone is characterized by penetrative plastic deformation and metamorphism based on the kinematic vorticity number w k 0 73 0 02 calculated from quartz porphyroclasts of the goshti shear zones along the zagros thrust system the estimated angle between the maximum instantaneous strain axis isa and the transpressional zone boundary is 33 the estimated angle of the plate convergence or the flow apophysis of the displacement field is 25 the presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence the mean estimated finite deformation w m value indicates relative contributions of 47 pure shear and 53 simple shear for the deformation which involved both strike slip and oblique slip displacements in this inclined transpression about 40 strike slip partitioning was required to accommodate the finite strain and re orientation of instantaneous strain

the casanova complex of the northern apennines a melange formed on a distal passive continental margin abstract the cretaceous palaeocene casanova complex occurs in two thrust sheets of the eugeosynclinal ligurids of the northern apennines it is a sedimentary melange with ophiolitic and quartzose turbidites or limestone shale olistostrome submarine debris flows as matrix exotic blocks of ophiolite and granite serpentinite breccias and lenticular ophiolitic breccias and olistostromes contribute to the melange character of the complex deformational structures include soft sediment slump folds indicating a sw dipping palaeoslope and boudins a gradational slumped top to the melange small scale faults in chert blocks and deformation associated with the emplacement of the exotic slide blocks the blocks were shed as rotational slides from submarine fault scarps and are surrounded by haloes of debris created by submarine weathering the stacking pattern of the blocks with the originally stratigraphically highest ophiolite lithologies lowest in the pile of blocks is explained by a diverticulation model with progressively deeper erosion mechanical analysis shows that the blocks were stable when partly exposed resting on a soft sediment substratum criteria which distinguish the casanova complex from a tectonic melange and which may be of value in other melanges are discussed previous interpretations of the complex as a precursor olistostrome to northeastward nappe emplacement the bracco ridge model are rejected the melange is believed to have formed on ocean crust as a result of turbidite and debris flow sedimentation soft sediment deformation block faulting gravity sliding and submarine erosion at the distal edge of a uniformly sw dipping continental margin

strain and possible volume loss in a high grade ductile shear zone small scale ductile shear zones in high grade metagabbros from the caledonides of northern sweden provide a good opportunity for examining the development of fabric and strain in rocks undergoing progressive non coaxial deformation the rocks contain strain markers in the form of aggregates of plagioclase feldspar a selected shear zone is analyzed assuming monoclinic symmetry which requires for the zone as a whole variable simple shear variable volume change or variable simple shear and volume change plus a homogeneous deformation both size of the feldspar aggregates and aspect ratio of the aggregates plotted against orientation indicate significant volume decrease in excess of 50 and perhaps as much as 80 towards the centers of the zones the data are broadly consistent with a deformation path involving constant shear strain across the zone followed by variable volume change or by a path of progressive loss of volume with increasing shear strain followed by a homogeneous strain they are not consistent with a single path involving rates of shear strain and volume loss that are in constant proportions there is little difference in chemical composition between the shear zone and the surrounding rock an analysis of the concentrations of elements in the shear zone and wall rock suggests that volume changes were slight 15 the discrepancy between the values of volume change estimated from strain analysis and geochemical analysis may be resolved either by geochemical equilibration being attained after deformation or by a departure from the geometric constraints of the monoclinic band model for shear zones modification of marker particle size and shape during dynamic recrystallization may also partly account for the apparent volume loss