tectonic history of the lunksoos composite terrane in the maine appalachians several ordovician volcanic terranes are preserved between the paleozoic north american margin and the avalon terrane in the northern appalachians of maine they have been interpreted as remnants of an island arc on the basis of their current position in the appalachians or as ocean islands near the margin of avalon on the basis of paleontologic data a study of one of these terranes the lunksoos terrane in northern maine was undertaken through a combination of paleomagnetic and structural analyses in order to understand its tectonic evolution paleomagnetic study of the pre caradoeian pre late ordovician stacyville volcanics revealed three components of magnetization the final magnetization removed d 90 i 36 95 11 8 is interpreted to be primary and yields a paleolatitude of approximately 20 s however a late ordovician remagnetization cannot be excluded the stacyville volcanics now overlie a cambrian and lower ordovician sequence the grand pitch and shin brook formations that is believed to have been deposited at the southern side of iapetus possibly near the margin of avalon during the middle and late ordovieian avalon was at paleolatitude s higher than 40 s while the volcanics were either formed or remagnetized at a paleolatitude of 20 s the pre caradocian stacyville volcanics therefore could not have been deposited directly on the grand pitch shin brook sequence but must have been tectonically emplaced the rockabema diorite which intrudes the entire cambro ordovician sequence constrains the timing of this emplacement to be pre late early silurian these relationships indicate that the lunksoos area is a composite terrane within the maine appalachians the tectonic emplacement scenario is unnecessary if the grand pitch and shin brook formations were not located on the south side of iapetus during the ordovician this alternative however poses conflicts with the interpretation of faunal affinities

are we studying deformed rocks in the right sections best practices in the kinematic analysis of 3d deformation zones abstract a standard procedure in kinematic analyses of deformed rocks is studying samples only on the foliation perpendicular lineation parallel section based on the assumption that the rotational component of deformation is restricted to that plane the theoretical background for this procedure is that deformation is plane strain which is often useful but fails to account for all relevant features observed in many natural cases more general 3d kinematic models reproduce several of these features and help to better understand 3d deformation likely predominant in nature so they are a more appropriate starting point for deformation zone analysis theoretical and natural 3d deformation examples suggest that the section with highest degree of asymmetry the vorticity normal section vns and the corresponding vorticity vector are independent from the finite strain fabric and thus may present varied orientations with respect to the tectonic foliation and lineation the vns orientation depends on the kinematics resulting from boundary conditions whereas the strain fabric orientation also depends on accumulated strain the orientation of the vns is itself an essential element of shear zone kinematics hence it cannot be pre assumed but must be determined independently

applying a general triclinic transpression model to highly partitioned brittle ductile shear zones a case study from the torcal de antequera massif external betics southern spain abstract oblique convergence and subsequent transpression kinematics can be considered as the general situation in most convergent and strike slip tectonic boundaries to better understand such settings progressively more complex kinematic models have been proposed which need to be tested against natural shear zones using standardized procedures that minimise subjectivism in this work a protocol to test a general triclinic transpression model is applied to the torcal de antequera massif tam an essentially brittle shear zone our results given as kinematic parameters of the transpressive flow transpression obliquity extrusion obliquity and kinematic vorticity number wk suggest that the bulk triclinic transpressive flow imposed on the tam was partitioned into two different flow fields following a general partitioning type as such one flow field produced narrow structural domains located at the limits of the tam where mainly dextral strike slip simple shear dominated transpression took place outer domains ods in contrast the remaining part of the bulk flow produced pure shear dominated dextral triclinic transpression at the inner part of the tam inner domain id a graphical method relating internal wk to far field dip of the shear zone boundary angle of oblique convergence transpression parameters is proposed to obtain the theoretical horizontal velocity vector v which in the case of the tam ranges between 099 and 118 these results support the applicability of kinematic models of triclinic transpression to brittle ductile shear zones and the potential utility of the proposed protocol

variscan intra orogenic extensional tectonics in the ossa morena zone evora aracena lora del rio metamorphic belt sw iberian massif shrimp zircon u th pb geochronology

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

sequence stratigraphy and proveance on gondwana s margin the meguma zone cambrian to devonian of nova scotia canada the meguma zone is the second largest terrane in the canadian appalachians three thick sandstones cambrian upper ordovician and lower devonian alternate with two thick shales lower ordovician and silurian the succession is a marginal assemblage shoaling upward from deep sea fan complexes to coastal facies in terms of sequence stratigraphy the succession consists of a basal type 1 sequence the meguma supergroup and three overlying type 2 sequences collectively the annapolis supergroup interpretations of sedimentary environments and stratigraphic relations agree with those of classical systems tracts the meguma zone is a sedimentary sink for an enormous amount of well sorted fine grained sand and silt this quantity and its westward dispersal indicate a gondwanan derivation stratigraphic units of the west african craton mimic those of the meguma zone in lithology provenance dispersal succession and age during neoproterozoic time continental ice sheets rivers and wind moved sediment southeastward down a cratonic paleoslope from what is now morocco through mauritania and mali remnants of widespread sand sheets extend across southern mali this sand reservoir became the source rock for the meguma zone in the early cambrian the paleoslope reversed perhaps due to birth of iapetus these same agents eroded the malian sand sheets episodically during relative sea level lows in cambrian late ordovician and early devonian times remnants of the resulting northwestward moving cratonic sands and silts occur today as mesas and buttes in northern mali mauritania southern morocco and algeria the ultimate destination of this detritus was the continental margin of north gondwana this sediment now forms the meguma zone and other terranes of southern europe northern africa and the middle east

finite strains in transpression zones with no boundary slip abstract a mathematical model describing finite strains has been developed for transpression zones where no slip is allowed in any direction at the zone boundaries this has been adapted to model transpression zones where the boundaries are inclined the model can also be used to describe finite strain patterns where material is incorporated into the deforming zone from one or both sides after the initiation of deformation so that the deforming zone remains at a constant width thus allowing large transpressional strains to be accommodated without the deforming zone closing to zero thickness this model of steady state transpression can be used to explain some of the features of the south mayo trough a late silurian transpression zone in the west of ireland

mylonites from the towaliga fault zone central georgia products of heterogeneous non coaxial deformation abstract retrograde mylonitic rocks occur in the segment of the towaliga fault southeast of jackson georgia mylonite protoliths are heterogeneous quartz feldspathic gneisses upper amphibolite facies sillimanite zone from the pine mountain and piedmont terranes protoliths contain no distinctive lithological markers that can be used to determine fault displacement shear sense can only be determined using microstructural criteria and type porphyroclast systems shear bands asymmetric microfolded quartz ribbons subgrain fabrics in quartz ribbons the most common porphyroclast system developed in mylonites and ultramylonites is type type systems do not have readily identifiable tails but do produce distinctive asymmetrical pile ups in the matrix such that the angle of intersection between the perturbed zone and the mylonitic foliation points in the shear direction differences in morphology between and type systems can be related to differences in the recrystallization rate deformation rate ratio r reflecting changes in ductility contrast between matrix and porphyroclast that controls the amount of recrystallized material in a porphyroclast mantle that is potentially available to form tails in early stages of mylonitization with low ductility contrasts and large r ratios large mantles occur around porphyroclasts and tailed systems develop in advanced stages of mylonitization with large ductility contrasts and small r ratios either very small or partially or totally missing mantles occur and type systems develop microstructural criteria ubiquitously record a right lateral strike slip motion component to the deformation textural evidence e g unidirectional shear bands consistent vorticity recorded by porphyroclasts and asymmetrical microfolds suggest that the mylonites are the products of non coaxial deformation the local presence of fabrics with coaxial symmetry result from heterogeneity in the deformation the right lateral offset on the towaliga fault most likely occurred during the late paleozoic alleghanian orogeny

high pressure metamorphism in the early variscan subduction complex of the sw iberian massif abstract several units exposed in the boundary area of the ossa morena zone omz and the south portuguese zone spz preserve petrographic and thermobarometric evidence for an early metamorphic episode m1 developed under a high p low to intermediate t gradient related to early variscan subduction in the sw iberian massif in the omz these are the cubito moura unit p min 9 2 kbar and t 395 45 c blueschists from its basal melange p min 12 4 kbar and t 310 11 c and the underlying fuenteheridos group p 10 9 0 4 kbar and t 449 31 c the equivalent units in the spz are the la minilla formation p 8 7 0 4 kbar and t 388 16 c and the lawsonite pseudomorphs bearing pulo do lobo formation all these units formed part of an approximately ne verging orogenic wedge present coordinates developed by the accretion of subducted slabs of the outermost margin of gondwana and other elements of the rheic ocean realm from at least the middle devonian to the lowermost tournaisian high pressure rocks were subsequently emplaced on more internal zones of the omz that only experienced a younger high t low to intermediate p metamorphism m2 this high t event was coeval with magmatic activity from the uppermost devonian to the middle mississippian probably as a consequence of transtensional lithospheric thinning and or delamination of the lower crust and mantle lithosphere of the gondwana margin pre late devonian synorogenic sedimentation in forearc and back arc basins of the subduction complex evolved to a late devonian middle mississippian foreland basin system in early collisional stages finally a new middle late mississippian fold and thrust belt with opposite sw vergence and new foreland basins developed during late collisional stages

taconian orogeny in the new england appalachians collision between laurentia and the shelburne falls arc tectonic models of the ordovician taconian orogeny in western new england usually invoke a collision between the laurentian margin and a magmatic arc identified as the bronson hill arc however in central massachusetts and southern new hampshire rocks in the bronson hill arc are 454 to 442 ma and therefore younger than much of the taconian deformation and metamorphism in western new england and eastern new york which began by 470 ma u pb and single grain evaporation zircon ages combined with geochemical analyses reveal the presence of an older magmatic arc the shelburne falls arc that formed west of the bronson hill arc at 485 to 470 ma the shelburne falls arc formed above an east dipping subduction zone by the early ordovician the taconian orogeny was the result of the collision between laurentia and the shelburne falls arc beginning ca 475 to 470 ma the younger bronson hill arc formed above a west dipping subduction zone that developed along the eastern edge of the newly accreted terrane during the final stages of and subsequent to the taconian orogeny the taconian orogeny ended when plate convergence between laurentia and iapetus was accommodated by the newly developed west dipping subduction zone instead of by crustal shortening in the taconian thrust belt the tectonic history of the new england appalachians is inconsistent with a middle ordovician collision between laurentia and the proto andean margin of gondwana

bridging the gap between the foreland and hinterland i geochronology and plate tectonic geometry of ordovician magmatism and terrane accretion on the laurentian margin of new england

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

the southern iberian shear zone a major boundary in the hercynian folded belt a long ductile shear zone extending across the northern parts of sevilla and huelva provinces southwest spain and very probably stretching further west into portugal is characterized by a conspicuously developed l s fabric and the existence of various mylonitic textures the shear zone closely associated with amphibolites of tholeiitic affinity represents an important oceanic suture of the hercynian belt in europe the sense of displacement inferred from microstructures is consistent with southwest directed upthrusting evolving to a left lateral shearing movement

analogue modelling of inclined brittle ductile transpression testing analytical models through natural shear zones external betics abstract the combination of analytical and analogue models gives new opportunities to better understand the kinematic parameters controlling the evolution of transpression zones in this work we carried out a set of analogue models using the kinematic parameters of transpressional deformation obtained by applying a general triclinic transpression analytical model to a tabular shaped shear zone in the external betic chain torcal de antequera massif according to the results of the analytical model we used two oblique convergence angles to reproduce the main structural and kinematic features of structural domains observed within the torcal de antequera massif 15 for the outer domains and 30 for the inner domain two parallel inclined backstops one fixed and the other mobile reproduce the geometry of the shear zone walls of the natural case additionally we applied digital particle image velocimetry piv method to calculate the velocity field of the incremental deformation our results suggest that the spatial distribution of the main structures observed in the torcal de antequera massif reflects different modes of strain partitioning and strain localization between two domain types which are related to the variation in the oblique convergence angle and the presence of steep planar velocity and rheological discontinuities the shear zone walls in the natural case in the 15 model strain partitioning is simple and strain localization is high a single narrow shear zone is developed close and parallel to the fixed backstop bounded by strike slip faults and internally deformed by r and p shears in the 30 model strain partitioning is strong generating regularly spaced oblique to the backstops thrusts and strike slip faults at final stages of the 30 experiment deformation affects the entire model box our results show that the application of analytical modelling to natural transpressive zones related to upper crustal deformation facilitates to constrain the geometrical parameters of analogue models

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

development of lattice preferred orientation in clinoamphiboles deformed under low pressure metamorphic conditions a sem ebsd study of metabasites from the aracena metamorphic belt sw spain the mechanical properties of the lower continental crust are intimately related to the rheology of calcic clinoamphibole naturally deformed clinoamphibole typically shows brittle behaviour under a wide range of deformation conditions whereas crystal plasticity is rarely observed in this study the microfabric of clinoamphiboles from metabasites deformed under low pressure medium to high temperature metamorphic conditions is presented amphiboles from all samples have developed lpo that can be attributed to different deformation mechanisms depending on deformation temperature fluid content structure and phase strength contrasts rigid body rotation of amphibole prisms within a weaker plagioclase matrix corresponds to metabasites deformed under medium deformation temperatures that show a weak layer structure and a high phase strength contrast between plagioclase and clinoamphibole lower temperatures and the presence of fluids mean that one of the studied rocks was affected also by dissolution precipitation creep and cataclastic flow in the final sample dislocation creep was accommodated by recovery and subgrain rotation dynamic recrystallization in monominerallic hornblende layers at higher temperatures which could be representative of the rheology of amphiboles in a lower continental crust at high temperature conditions

geochemistry and u pb zircon age of comenditic metafelsites of the tibbit hill formation quebec appalachians metafelsites in waterloo area quebec represent the only known silicic volcanic rocks in the predominantly basaltic tibbit hill formation low grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite quartz albite schists the volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs the principal compositional type was a comendite a component of intermediate rocks is also present but its extent is undetermined and probably minor u pb zircon studies of the metafelsites have yielded a reliable age of this early cambrian age is probably representative of the age of the tibbit hill formation as a whole the tibbit hill formation accumulated at one of the clearest examples of a rrr rift rift rift triple junction the sutton mountains triple junction of the continental rift system formed as a prelude to the opening of the iapetus ocean its volcanic rocks are products of the youngest major episode of rift rela

characterization of tectono metamorphic events using crystal size distribution csd diagrams a case study from the acebuches metabasites sw spain crystal size is one of the main characteristics of a metamorphic rock since it is the result of several processes including prograde metamorphism as well as retrometamorphism and static and dynamic recrystallisation in this paper crystal size histograms mean crystal size crystal size distribution diagrams mean aspect ratio and proportion of prismatic sections of amphiboles have been used to describe two tectono metamorphic events that affected the acebuches metabasites in the southwestern part of the iberian massif the diagrams depicting the crystal size distribution csd of metamorphic rocks show typically a straight segment that reflects the kinetic conditions during prograde metamorphism as well as retrometamorphic and dynamic recrystallisation processes and a bell shaped curve formed during the last stages of growth the geometrical characteristics of the straight lines of csd diagrams from different samples of the acebuches metabasites vary consistently with the structural and metamorphic features indicative of the tectono metamorphic history suffered by these rocks this suggests that csd diagrams can be a useful tool of microstructural analysis in metamorphic rocks

comment on the late devonian variscan suture of the iberian massif a correlation of high pressure belts in nw and sw iberia tectonophysics 654 96 100 by r fernandez and r arenas abstract a vast variscan nappe spreading from the allochthonous complexes of nw iberia to the ossa morena zone in sw iberia has been proposed by diez fernandez and arenas 2015 based on the correlation of different outcrops of high pressure and morb type rocks this interpretation conflicts with well known geological and geophysical data regarding the sw iberian variscides which point to i major kinematic and geometric inconsistencies come up when interpreting the ossa morena zone as an allochthonous unit ii the outcrops of high pressure and morb type rocks belong to two different sutures rather than a single one and iii sw iberia is characterized by transpressional deformation related to a very oblique left lateral continental collision while nw iberia features a rather frontal collision

spatially averaged conservation equations for interacting rill interrill area overland flows the modeling of flows at hillslope scale over land surfaces that contain rills and interrill areas is presented the flow in rills is treated as one dimensional channel flow the flow at interrill areas is treated as two dimensional sheet flow sheet flow equations are averaged along the interrill area width local averaging to account for the interaction between interrill and rill sections the flow depth at the interrill area outlet section is derived by assuming that the flow profile of the interrill area section has the profile of a sine function to minimize computational efforts and economize on the number of model parameters locally averaged rill and sheet flow equations are then averaged over the transects of a hillsope large scale averaging the expectations of the terms containing more than one variable are obtained through the taylor series expansion around their mean values only the first two moments of the series expansion are considered the results of the model are in good agreemen

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

early paleozoic paleogeography and accretionary history of the newfoundland appalachians new paleomagnetic results were obtained from several units in the central mobile belt of the north central newfoundland appalachians combined with recently published data the results place important limits on interpretations of early paleozoic paleogeography and evolution of the appalachian caledonian orogen the ordovician appalachian margin of north america located at low paleolatitudes and facing roughly south was separated from the southern margin of iapetus avalon armorica by 3500 km primary directions in pillowed volcanic rocks of the moreton9s harbour group that are part of an early ordovician island arc show that these rocks were formed near the north american margin at a paleolatitude of 12 s early to middle ordovician volcanic rocks of the roberts arm chanceport and summerford groups on the other hand were extruded at paleolatitudes of 30 40 s unconformably overlying volcanics of the silurian botwood group were extruded subaerially at a paleolatitude of 24 s combined with tectonostratigraphic data these results suggest the following tectonic history in early ordovician time northerly subduction of the main iapetus basin was accompanied by the formation of a volcanic arc and a back arc basin near the north american margin middle ordovician emplacement of ophiolites on the north american margin reflects the closure of this back arc basin iapetus i and continued northerly subduction in silurian time closed the main basin iapetus ii

a model for the development of crenulations in shear zones with applications from the southern appalachian piedmont abstract two sets of crenulations are associated with a major alleghanian dextral shear zone which deformed stratigraphic and structural boundaries in the eastern piedmont of south carolina both sets of crenulation planes are oblique to the boundaries of the shear zone the morphologies and orientations of the crenulation sets and their spatial distributions indicate that they are related to slip along foliation planes and that they serve to compensate for displacement components of foliation slip normal to the overall movement direction in the shear zone the crenulations act to maintain the initial thickness of the shear zone our evaluation of the recent literature on shear zones suggests that crenulations related to foliation slip are abundant and constitute a reliable sense of shear indicator

triclinic transpression zones with inclined extrusion data from natural transpressional shear zones reveal a large range of lineation orientations that can spread along complete girdles one possible way to account for such a type of fabrics is variation in the extrusion direction this work presents a new theoretical model of oblique transpression with inclined extrusion the model is kinematic and the flow is considered as homogeneous and steady the angle between the simple shear direction and the extrusion direction is one of the main parameters controlling the final fabric low values of 40 can generate strain ellipsoids very close to the abscissa axis of the flinn plot depending on the vorticity of the flow the finite strain and the actual value of the angle the model predicts the generation of lineation fabrics ranging from point maxima to patterns with opposite plunge senses these patterns can display monoclinic nearly monoclinic or clearly triclinic symmetry lineation patterns spreading along complete girdles can be obtained by allowing the extrusion direction to deviate less than 30 about the vertical in either direction

modeling of conjunctive two dimensional surface three dimensional subsurface flows in the rainfall runoff process interaction between surface and subsurface flow components plays an important role especially in rainwater abstraction and overland flow initiation at the early stage of rainfall events coupling of surface and subsurface flow submodels therefore is necessary for advanced comprehensive and sophisticated rainfall runoff simulation this article presents a conjunctive two dimensional 2d surface and three dimensional 3d subsurface flow model which uses the noninertia approximation of the saint venant equations for 2d unsteady surface flow and a modified version of the richards equation for 3d unsteady unsaturated and saturated subsurface flows the equations are written in the form of 2d and 3d heat diffusion equations respectively and solved numerically the surface and subsurface flow components are coupled interactively using the common boundary condition of infiltration through the ground surface the conjunctive model is verified with smith and woolhiser s exper

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

structural analysis of an accretionary prism in a continental collisional setting the late paleozoic pulo do lobo zone southern iberia abstract models concerning the tectonic evolution of accretionary complexes typically relate outcrop scale to plate scale multiphase deformation as a smooth variation of strain on all scales however at oblique convergent margins regional scale brittle faults in the shallow crust are commonly parallel to the main orogenic grain these faults impose a strong structural anisotropy and can subsequently control deformation at subordinate scales as a result finite strain in each domain may not record local kinematics consistent with the overall orogenic scale motion implying that structural data must be analyzed selectively from a large area in order to relate outcrop scale kinematics to global plate scale dynamics field mapping and preliminary structural analysis of the late devonian pulo do lobo pdl formation and suspect exotic south portuguese zone spz in southern iberia indicate tectonic juxtaposition of diverse deposits such as foreland basin flysch sedimentary and tectonic melange and passive margin sediments showing an overall geometry consistent with an accretionary wedge setting variations in finite strain lithology and regional structure were used as proxies for defining tectonic domains for structural analysis numerous local kinematic indicators within the pdl suggest a complex regional deformation with several enigmatic features that can be explained by sequential compartmentalization of strain during the development of the imbricate stack followed by late stage bulk strain imposed across the entire complex structural data produced by local strain partitioning reveals kinematic indicators which contradict the overall regional structural style e g spatial juxtaposition of sinistral and dextral fabrics when viewed at larger scales i e regional scale however these data indicate that significant sinistral strike slip movement occurred in conjunction with both an extension and shortening outcrop scale deformation in polydeformed domains is controlled by local conditions resulting from brittle deformation coeval with orogenic scale bulk strain the entire pulo do lobo zone is dominated by a pervasive late stage vertical to sub vertical e w cleavage axial planar to chevron folds which overprint earlier deformation in the older passive margin units this overprinting suggests that in the late stages of the evolution of the accretionary complex bulk strain was imposed over the entire complex as a result of internal locking of the accretionary complex and reduced strain rates during the waning stages of collision between gondwana and laurussia stereographic analysis of fabric elements from each distinct tectonic domain together with regional geological constraints support this hypothesis and are indicative of progressive deformation imposed on the pdl during the variscan orogeny

radiometric discrimination of pre variscan amphibolites in the ediacaran serie negra ossa morena zone sw iberia new results on the geochronology of metabasites hosted by the neoproterozoic late ediacaran serie negra of the ossa morena zone iberian massif are presented these rocks record a protracted subduction at least since the latest cryogenian followed in a continuum by early cambrian rifting the serie negra country rocks are continental crust forearc segments of the thinned continental margin of gondwana the metabasite suite exhibits e and n morb as well as volcanic arc signatures and discloses the existence of a diverse late ediacaran early cambrian magmatism across the ossa morena zone protoliths of the e morb metabasites are clearly ediacaran they exhibit geochemical characteristics typical of younger island arcs notably of their forearc zones affected by extension soon after the initiation of subduction radiometric dating of n morb metabasites shows that these rocks are significatively younger than their country rocks whose age has been stratigraphically and paleontologically constrained as ediacaran they record early cambrian rifting developed in a continuum after a protracted subduction metabasite petrological zonation permits to reconstruct a single ediacaran subduction zone located to the s of the current omz and dipping towards the n in present day geographical coordinates

age constraints to the relationships between magmatism metamorphism and tectonism in the aracena metamorphic belt southern spain the aracena metamorphic belt amb southwest iberian peninsula is characterized by the following geological elements a a high temperature low pressure ht lp metamorphic belt a few kilometres wide and more than 200 km long b a linear belt of oceanic amphibolites with a low pressure inverted metamorphic gradient c crustal scale ductile shear zones and d mafic noritic intrusions of high mg andesite boninite composition the relationships between these elements led to the proposal of a model of ridge subduction for this sector of the hercynian belt of europe this interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously the results of a geochronological study ar ar rb sr and sm nd clearly support a late paleozoic tectonic evolution at an active continental margin the time evolution of the metamorphism in the oceanic domain ranging from 342 6 0 6 ma in the west to 328 4 1 2 ma in the east over a distance of 70 km along the metamorphic belt support a tectonic model of triple junction migration responsible for the creation at depth of a slab free window with decisive consequences for the thermal evolution of the region the origin of the linear metamorphic belt of ht lp regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple junction at the continental margin

how was the iapetus ocean infected with subduction because subduction in the iapetus ocean began only 35 m y after the end of rifting spontaneous foundering of mature passive margins is an unlikely subduction initiation mechanism subduction is more likely to have entered the iapetus from the boundary with the external paleo pacific similar to the incursion of the scotia caribbean and gibraltar arcs into the modern atlantic the subduction zone probably became sinuous entraining fragments of the gondwanan margin along its complex sinistral southern boundary where oblique collision caused monian penobscottian deformation following taconian grampian collision of part of the subduction system with laurentia remaining parts of the iapetus were progressively infected with subduction leading to silurian closure

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

tectonometamorphic evolution of the aracena metamorphic belt sw spain resulting from ridge trench interaction during variscan plate convergence 1 the aracena metamorphic belt is a high temperature low pressure ht lp band located at the southern end of the european variscan chain it marks a suture between armorica and avalonia this belt is characterized by 1 the presence of mid ocean ridge basalt derived metabasites that were affected by an inverted ht lp metamorphism related to sw verging thrusting whose thermal peak diachronously migrated eastward 2 the occurrence of a ht lp metamorphism related to an extensional event affecting continental rocks belonging to the ossa morena zone with peak temperatures that are 150 c higher than that recorded in the oceanic metabasites and 3 the presence of near trench magmatism with high mg andesite composition these and other characteristics can be interpreted in terms of a ridge trench trench triple junction that migrated along the armorican margin during variscan oblique convergence

relationships between kinematic indicators and strain during syn deformational exhumation of an oblique slip transpressive plate boundary shear zone the alpine fault new zealand abstract in order to assess how different elements of plate boundary scale shear zone tectonite fabrics reflect the boundary kinematics and strain history we have examined a range of such structures within the active alpine fault mylonite zone new zealand in this oblique slip zone we find that quartz cpo fabric symmetry and individual mica grain lineations reflect incremental stretches but develop stable orientations parallel to the finite stretching direction s 1 this s 1 trends oblique to the plate motion vector because the shear zone experiences some extrusion toward the free surface conversely asymmetric structures such as shear bands and mica fish reflect simple shear dominated deformation late in the shear zone history parallel to the imposed relative plate motion vector finally linear fabrics are a poor record of the mylonitic deformation in this zone because 1 they are dominantly inherited and have been only partially re oriented during mylonitisation and 2 macroscopically they become less visible at higher strains due to fabric homogenisation generally these results indicate that particularly in heterogeneous polyphase shear zones a full understanding of the movement history can only be obtained by considering kinematic information from as many different sources as possible

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

orogenic evolution of the new england appalachians of southwestern connecticut new u pb ages are presented that place constraints on the paleozoic orogenic evolution of the new england appalachians in southwestern connecticut beardsley and pumpkin ground orthogneisses yield concordant u pb zircon ages of 446 2 ma and 428 2 ma respectively these orthogneisses were considered conformable metavolcanic members of the harrison gneiss but are now recognized as structurally juxtaposed metaplutonic units pumpkin ground orthogneiss contains young inherited zircons and has k feldspars with elevated 207 pb 204 pb a characteristic of avalonian crust the ansonia leucogranite 406 13 ma discordant zircon and monazite marks the inception of abundant leucogranite magmatism that heralds the onset of the acadian orogeny the shelton muscovite granite previously interpreted as a metamorphosed siliceous tuff shelton white gneiss yields a concordant u pb garnet age of 380 3 ma in agreement with u pb monazite ages middle devonian granites have k feldspars with elevated 207 pb 204 pb and zircons with possible avalonian inheritance morphologically distinct monazites from staurolite kyanite grade pelitic schists of the trap falls formation display complicated u pb systematics that indicate acadian metamorphism was a prolonged event lasting from ca 395 to 376 ma a u pb sphene age of 362 1 5 ma from the pumpkin ground orthogneiss suggests that cooling through the 550 c isotherm was attained by 362 ma based on an assumed temperature of 700 c at 375 ma the cooling rate immediately following the acadian orogeny was 12 c ma constraints on deformation are provided by foliated syn metamorphic granites and cross cutting post tectonic intrusions deformed intrusions include the ansonia leucogranite 406 13 ma a transposed dike of muscovite granite 391 3 ma concordant garnets and the shelton muscovite granite 380 3 ma deformation accompanied or post dated emplacement late kinematic pegmatite and post kinematic granite yield u pb monazite ages of 375 1 ma and 376 2 ma respectively and show that kinematic deformation pre dated 375 ma the alleghenian orogeny in southwestern connecticut was associated with the growth of morphologically distinct metamorphic monazite in the ansonia leucogranite at 296 2 ma and emplacement of the pinewood adamellite at 291 4 ma during this orogeny temperatures approached but did not exceed 550 c at the present erosional surface combined field and laboratory studies provide a geologic link to the u pb geochronology and highlight necessary revisions to current tectonic models for the new england appalachians of southwestern connecticut plutonic rocks constitute a large proportion of exposed units and record nearly continuous magmatism from 446 ma to 375 ma this constrasts sharply with models advocating little to no magmatism in southwestern connecticut crustal scale imbrication of basement rocks with grenvillian and avalonian pb isotopic signatures occurred by early silurian time the acadian was a prolonged ca 395 to 376 ma middle crustal level orogenic event that generated considerable volumes of leucogranite

the structure of the temsamane fold and thrust stack eastern rif morocco evolution of a transpressional orogenic wedge abstract the structure of the temsamane fold and thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds this ductile stack was formed in an inclined left handed transpressional zone at the north african paleomargin during chattian to langhian times producing two main deformational events the first event d p produced a s p l p planar linear fabric generated in a non coaxial deformation with a top to the wsw sense of movement and was associated to metamorphic p t conditions varying from late diagenesis in the southernmost temsamane outcrops to epizone in the north according to the 40 ar 39 ar ages this deformation occurred at chattian aquitanian times the second deformational event d c event generated ene wsw trending folds with sse vergence and a set of anastomosing shear zones with s m l m planar linear fabric the latter units were generated at around 15 ma langhian and indicate a strong localization of the simple shear component of the transpression moreover this orientation is compatible with the kinematics of the temsamane detachment which can explain most of the uplift of the temsamane rocks from the middle to the uppermost crust the described evolution indicates that collision between the western mediterranean terranes and the north african paleomargin and the formation of the rifean orogenic wedge occurred at chattian to langhian times

testing the model of oblique transpression with oblique extrusion in two natural cases steps and consequences abstract kinematic models of various types of transpression have been used to explain fabric features and strain in many natural deformation studies here a mathematical model that encompasses all monoclinic and triclinic transpressional deformations including triclinic deformation with inclined simple shear and or inclined extrusion orientations can be tested using a step by step approach with available field evidence two cases are presented the first case from the wabigoon quetico boundary in the archean superior province utilizes both fabric orientation and quantified strain data the best fit of the field evidence to the model indicates that deformation likely took place along subvertical shear zones via transpression with subhorizontal simple shear 0 20 and variable inclined extrusion direction extrusion can be either east or west and typically indicates extrusion orientations between 0 and 50 from vertical the second case of the south iberian shear zone has fabric orientation data but no quantifiable strain possibilities the best fit of the field evidence to the model indicates that deformation likely took place along a moderately inclined shear zone via transpression with subhorizontal simple shear 0 20 and variable inclined extrusion direction values between 0 and 80 from the true dip of the shear zone using this protocol in other examples of natural deformation will allow further constraints to be applied to kinematic models

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

application of the analytic model of general triclinic transpression with oblique extrusion to an active deformation zone the alhama de murcia fault se iberian peninsula abstract we have applied the analytic model of general triclinic transpression with oblique extrusion to an active shear zone in southeastern spain this study opens a new methodological approach in the study of active fault zones we are able to constrain the triclinic transpression model with absolute measures of active deformation such as gps velocity gradients and have exhaustively explored the predictions of the model and compared them to the orientation data of field kinematic markers fault slip data and reorientation of fold hinges during progressive deformation gps data and the kinematic study of the fault gouge that is developed at the alhama de murcia fault the combined analysis allows the values of the kinematic vorticity number the orientation of the vorticity vector the orientation of the local and regional convergence vectors the angle of extrusion in the shear zone and the amount of extrusion to be constrained the results point to a highly partitioned heterogeneous shear zone with domains deforming in response to the same boundary conditions but are displaying different kinematic responses that reflect both their intrinsic properties and geometric effects related to competency contrasts we propose that the alhama de murcia fault is an incompletely coupled fault zone with two different domains a low competency domain comprising the fault gouge ductilely deformed with low vorticity values which probably experienced a steady state aseismic slip that reflects regional convergence vectors convergence eurasia nubia and a domain outside of the fault gouge with episodic brittle failure with higher vorticity values and showing convergence vectors which are parallel to the local convergence vectors calculated from the gps velocity field

distribution of ordovician and devonian metamorphism in mafic and pelitic schists from northern vermont 40 ar 39 ar range from 471 to 439 my and confirm that ordovician metamorphism is recorded from the canadian border south to the precambrian core of the green mountain anticlinorium gma medium high pressure p facies series metamorphism in the north and medium p metamorphism to the south similar metamorphic ages and compatible estimates of t and p indicate mafic and pelitic rocks were metamorphosed together medium p devonian metamorphism has overprinted the ordovician metamorphism in northern vermont east and probably west of the gma axis resulting in conventional k ar 40 ar 39 ar total fusion and plateau ages of 386 to 355 my on muscovite biotite and amphibole modified journal abstract

mathematical model of shallow water flow over porous media a conjunctive mathematical model for a surface subsurface flow system is developed the unsteady surface flow is explored by a set of one dimensional dynamic wave equations for shallow water which are solved by using a four point implicit finite difference scheme the transient subsurface flow is two dimensional with potential gradients in the vertical direction as well as the surface flow direction the porous medium may be saturated or unsaturated or both and it can be nonhomogeneous and anisotropic the subsurface flow equation is solved by employing a successive line over relaxation implicit finite difference scheme the surface and subsurface flow components are coupled at the ground surface considering the mass conservation and pressure relationships the model is verified by using existing experimental data and analytical solutions for special cases

mixing in flow perturbations a model for development of mantled porphyroclasts in mylonites abstract the presence of a rigid object such as a porphyroclast in simple shear flow induces a flow perturbation with a relatively simple geometry domains of closed and open flow lines are bounded by a separatrix that surrounds the porphyroclast the concept of a separatrix to describe heterogeneous flow gives rise to some new insights in the development of porphyroclasts with a mantle of recrystallized material in mylonites the final shape of the recrystallized mantle depends on separatrix shape but also on the degree of intersection of the mantle and the separatrix and therefore on relative mantle width this model can explain the coexistence of several types of mantled porphyroclast in a single mylonite sample the occurrence of porphyroclasts that lack wings at high strain values and the presence of symmetric winged mantled porphyroclasts in ductile shear zones

u pb zircon age of metafelsite from the pinney hollow formation implications for the development of the vermont appalachians the pinney hollow formation of central vermont is part of a rift clastic to drift stage sequence of cover rocks deposited on the laurentian margin during the development of the iapetan passive margin in late protero zoic to cambrian time conventional u pb zircon data indicate an age of 571 5 ma for a metafelsite from the pinney hollow formation geochemical data indicate that the protolith for the metafelsite now a quartz albite gneiss or granofels was rhyolite from a source that was transitional between a within plate granite and ocean ridge granite setting and probably came through partially distended continental crust the transitional setting is consistent with previous data from metabasalts in the pinney hollow formation and supports the idea that the source magma came through continental crust on the rifted margin of the laurentian craton the 571 5 ma age provides the first geochronologic age from the rift clastic cover sequence in new england and establishes a late proterozoic age for the pinney hollow formation the late proterozoic age of the pinney hollow confirms the presence of a significant mapped thrust fault between the autochthonous and para autochthonous rocks of the cover sequence these findings support the interpretation that the taconic root zone is located in the hinterland of the vermont appalachians on the eastern side of the green mountain massif introduction the pinney hollow formation of central vermont is part of a para autochthonous eugeoclinal rift clastic to drift stage sequence deposited on the laurentian margin during the development of the iapetan passive margin in late proterozoic to cambrian time the pinney hollow formation consists of metamorphosed pelitic and psammitic sedimentary rocks and lesser amounts of predominantly mafic volcanic rocks exposed east of middle proterozoic basement gneiss and schist in the green mountains of vermont fig 1 prior to plate tectonic models the cover rocks were considered to be an eastward dipping and younging homoclinal sequence of coherent stratigraphy doll and others 1961 in the past 15 years many faults have been identified in the eastern cover sequence throughout vermont as a result the pinney hollow formation is now considered part of a fault bounded lithotectonic belt with its own internal stratigraphy walsh and ratcliffe 1994a b walsh and falta 1996a b and in press and ratcliffe walsh and aleinikoff 1997 similarities between the metasedimentary rocks of the eastern cover sequence and metasedimentary rocks in the lower parts of the taconic allochthons have long been recognized these lithic similarities led early workers to suggest that the source of the taconic slices was in the eastern cover sequence on the east side of the green mountain massif in vermont and the berkshire massif in massachu setts keith 1932 prindle and knopf 1932 osberg 1952 more recently stanley and ratcliffe 1985 postulated that the taconic root zone was exposed at the western edge of the pinney hollow underhill and hazens notch formations at the latitude of the northern end of the taconic allochthons stanley and ratcliffe 1985 assigned these three formations to lithotectonic belts called the pinney hollow and underhill slices and interpreted the western limit of these slices as the root zone for the taconic allochthons the geochemistry of the mafic volcanic rocks in the eastern cover sequence from alkalic to transitional within plate basalts in the west to morb like basalts in the east has been linked to the relative original geometry of the ancient margin in this model west to east

the palaeogeography of early ordovician iapetus terranes an integration of faunal and palaeomagnetic constraints abstract new and existing fossil data from ireland britain newfoundland and scandinavia emphasize a significant degree of latitudinal variation in biogeographic patterns across the ordovician iapetus ocean platform provinces together with marginal belts and island complexes can be recognised with increasing clarity on the basis of palaeontological information statistical analysis of the distribution patterns of about 70 early ordovician brachiopod genera across some 25 sites using both cladistic and phenetic methods together with a critical analysis of their geological settings combined with current palaeogeographic and palaeomagnetic data reaffirm the existence of the celtic brachiopod province during the early ordovician the majority of sites assigned to the celtic province define a high latitude peri gondwanan belt shadowing the distribution of the low latitude circum laurentian toquima table head faunas rapidly changing ordovician faunal signals across the baltic province and exploits zone of central newfoundland track the cross latitude movement of these terranes from high temperate to near tropical belts during the period new fossil information together with continuing statistical appraisal of an expanding database are providing more accurate and sophisticated models for the dynamics of the iapetus ocean system

geometry classification and kinematics of s c and s c fabrics in the mushandike area zimbabwe planar fabrics in small dextral shear zones in the mushandike area of the zimbabwe archaean craton consist of a sigmoidal primary foliation s displaced by discrete shears c or c these planar fabrics can be divided into porphyroclastic megacrystic and banded types depending mainly on the values of the angles between s and c or c surfaces the structures that define s surfaces and the spacing of c or c surfaces the values of the angles between the foliations are proposed as the basis for a general classification of planar fabrics in shear zones the values of the angles depend on microstructures and strain microstructural evidence shows that slip did not occur on s surfaces but only on c or c surfaces a model for the development of the fabrics proposes that s surfaces lie parallel to the xy plane of the local finite strain ellipsoid in domains of simple shear between c or c surfaces c surfaces may form in the orientation of a coulomb failure surface the field evidence suggests that an increase in bulk strain is at least partly accommodated by an increase in local strain in domains between c or c surfaces as the s surfaces rotate with the local finite strain ellipsoid

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

inclined transpression in the neka valley eastern alborz iran three major nappes in the neka valley in the eastern alborz mountains of iran allow the cimmerian to present convergence following the oblique collision between iran and the southern margin of eurasia this work reports the identification of an inclined transpression zone recognized by field investigations and strain analyses of the geometries of formations and detailed mesoscopic structural analyses of multiple faults folds and a cleavage the main structures encountered include refolded recumbent asymmetric fold nappes highly curved fold hinges in a transpression zone that dips 37 to the nw between boundaries thrusts striking from n050 to n060 the angle the angle between the zone boundary and direction of horizontal far field shortening is about 80 the north west and south east boundaries of this zone coincide with the haji abad thrust and the shah kuh thrust respectively fold axes generally trend ne sw and step to both right and left as a result of strike slip components of fault displacements strain analyses using fry s method on macroscopic ooids and fusulina deformed into oblate ellipsoids indicate that the natural strain varies between 2 1 and 3 14 the estimated angle between the maximum instantaneous strain axis isamax and the transpression zone boundary is between 6 and 20 the estimated oblique convergence angle therefore ranges between 31 and 43 the average kinematic vorticity number wk is 0 6 in a zone of sinistral pure shear dominated inclined triclinic transpression these results support the applicability of kinematic models of triclinic transpression to natural brittle ductile shear zones

the elusive nature of the rheic ocean suture in sw iberia the rheic ocean suture resulted from pre carboniferous oceanic subduction followed by late devonian carboniferous variscan collision in sw iberia this suture has been classically located along the boundary between the ossa morena and south portuguese zones based on the presence of three units i a conspicuous metamafic unit beja acebuches that crops out along this boundary and has been interpreted as a pre carboniferous rheic ocean ophiolite ii a low grade metasedimentary unit with minor mid ocean ridge basalt like lithologies pulo do lobo unit thought to represent a rheic ocean subduction related accretionary prism and iii the allochthonous cubito moura unit that contains high pressure and ophiolitic like rocks we report new structural and geochronological data that allow us to reinterpret the origin and internal structure of the beja acebuches and the pulo do lobo units thus both the beja acebuches protoliths and the pulo do lobo metabasalts would have been formed in the context of an intracollisional extensional stage that interrupted the variscan collision at early carboniferous time after the rheic ocean consumption and the first continental collision later on collision was resumed in an oblique left lateral regime that gave way to coeval frontal folds and thrusts and lateral shear zones and strike slip faults structures with variable pressure temperature conditions and space distribution along time as a consequence of the superposition of transtension and complex transpression the rheic suture in sw iberia has an obscure nearly cryptic appearance

coupling of groundwater and open channel flow abstract the paper describes an approach to incorporating drainage and the interaction of groundwater and open channel flow in a physically based hydrologic response model two classes of exchange are distinguished the first is concerned with the influence of minor conduits which require too much refinement to be modelled on an individual basis but amalgamated make an important contribution to the water budget of a region on an areal basis the second class of exchange is direct seepage from or into the larger waterways in which the flow is significant and is modelled as a distinct hydrologic process in the first part of the paper a theory for treating the exchange phenomena is developed the basis is formed by the hooghoudt ernst formula of drainage design and the theory of additional seepage resistances the remainder of the paper is devoted to the technical implementation of this theory a number of practical steps to limit the data and organization required are outlined the main technical hurdle dealt with is the coupling of the two fundamentally incompatible numerical schemes for groundwater and open channel flow in such a way that a conservative water balance is maintained details of the complete hydrologic response model are presented as an appendix

structural evidence for slip partitioning and inclined dextral transpression along the se sanandaj sirjan zone iran the structural evolution of the sanandaj sirjan zone is the result of the convergence of the iranian microcontinent and the afro arabian continent the study area at khabr in the se sanandaj sirjan zone in the hinterland of the zagros orogen consists of paleozoic mesozoic and cenozoic rocks in this area deformation phases were distinguished in different rock units based on structural and stratigraphical evidence and the deformational events are divided into two stages 1 a late triassic event and 2 a late cretaceous to miocene event the late triassic deformation event caused regional metamorphism in the paleozoic units these units are overlain by unmetamorphosed jurassic clastic sequences fabrics and structural evidence confirm that the f1 folding recumbent and refolded folds were synchronous with the metamorphism of the paleozoic units and terminated in the early jurassic the time table of the orogenic phases shows that this deformation event is related to the cimmerian orogenic phase from a geodynamic point of view the early cimmerian deformation in the southeastern iranian margin suggests that the se sanandaj sirjan zone was an active margin at that time the early cimmerian discordance recorded the onset of a contractional component related to the oblique subduction of neo tethys beneath the central iranian microcontinent structures related to the late cretaceous to miocene deformation phase are observed in jurassic to oligocene units which contain moderately inclined and plunging folds comparing these folds with domains of deformation generated in models of transpression shows that the folding was caused by a combination of contractional and dip slip components of movement eventually resulting in the formation of a thrust system the khabr thrust systems consist of five sheets of oblique thrusts duplex structures and shear zones the shear zones generally strike e w and dip moderately n 30 40 the occurrence of asymmetric folds with hinges that are either parallel to strike or plunge down dip demonstrates an oblique slip component in these thrust shear zones the stretching lineation in the mylonites within the shear zones is defined by the long axes of ellipsoidal grains of quartz calcite plagioclase and garnet in general stretching lineations trend from n40 w to n80 w with an intermediate 35 plunge the geometry of foliation and lineation within these shear zones shows the effect of dip and oblique slip shearing deformation continued with strike slip faulting becoming important during the last stages of deformation from the miocene to the present day the results of this study demonstrate that the evolution of the se sanandaj sirjan zone from late triassic to miocene is compatible with an inclined dextral transpression along this zone

new insights into the appalachian orogen from geology and geochronology along the cape ray fault zone southwest newfoundland reverse oblique overthrusting of high grade port aux basques gneiss over the lower grade supracrustal windsor point group along the cape ray fault zone occurred during late silurian to early devonian time and is attributed to major oblique collision between gondwanan and laurentian continental blocks new u pb zircon 40 ar 39 ar and k ar data limit the timing of this orogenic event the megacrystic granitic phase of the cape ray igneous complex and the cape ray tonalite have been dated at 488 3 ma and 469 2 ma respectively a black rhyolite from the windsor point group yielded an ordovician age 453 5 4 ma a pretectonic gabbro sill within the windsor point group dated at 424 4 3 ma is cut by the windowglass hill granite dated at 424 2 ma synkinematic hornblende and biotite from the grand bay complex mylonites of the port aux basques gneiss have 40 ar 39 ar ages of 407 4 ma and 403 4 ma respectively which is indicative of a late silurian early devonian age for the amphibolite grade deformation these ages are compatible with a previously determined 415 ma monazite age interpreted as the time of peak metamorphism in the port aux basques gneiss and suggests rapid exhumation the east west flexure of the cape ray fault zone represents a tear fault accommodating differential shortening between the cape ray fault zone and the correlative fault system in central newfoundland mid devonian granites 386 3 384 2 ma intervene between the thrusting events and a younger sinistral transcurrent movement this deformation and magmatic history can be correlated throughout the northern appalachians along other major fault boundaries

palaeostress perturbations near the el castillo de las guardas fault sw iberian massif use of stress inversion methods on faults measured at 33 sites located at the northwestern part of the south portuguese zone variscan iberian massif and analysis of the basic dyke attitude at this same region has revealed a prominent perturbation of the stress trajectories around some large crustal scale faults like the el castillo de las guardas fault the results are compared with the predictions of theoretical models of palaeostress deviations near master faults according to this comparison the el castillo de las guardas fault an old structure that probably reversed several times its slip sense can be considered as a sinistral strike slip fault during the moscovian these results also point out the main shortcomings that still hinder a rigorous quantitative use of the theoretical models of stress perturbations around major faults the spatial variation in the parameters governing the brittle behaviour of the continental crust and the possibility of oblique slip along outcrop scale faults in regions subjected to general non plane strain

tectonic synthesis of the taconian orogeny in western new england a tectonic synthesis based on stratigraphic and structural analysis of western new england is proposed for the ordovician taconian orogeny it emphasizes arc continental collision in which ocean floor continental margin and ensialic rift rocks were imbricated westward in a repeatedly deformed accretionary wedge continued compression displaced segments of the north american sialic crust to the west and deformed the earlier emplaced slices of the taconic allochthons which were derived from the continental margin critical arguments for this synthesis are 1 the west to east stratigraphic relations among the basal rift clastic rocks of the dalton pinnacle and hoosac formations of late precambrian to early cambrian age 2 the stratigraphic and sedimentological similarities between the rocks of the lower taconic sequence and rocks in the pinney hollow and underhill slices to the east and north of the green mountain massif 3 the environmental similarities between the cambrian and lower ordovician section of the giddings brook slice and the age equivalent section in the st albans synclinorium 4 the presence of carbonate platform rocks as slivers between each of the successively higher and younger premetamorphic slices groups 1 and 2 of the taconic allochthons 5 the presence of synmetamorphic fault related structures in the youngest and highest slices group 3 of the taconic allochthons 6 the recognition of extensive thrust zones in the pre silurian eugeoclinal sequence east of the middle proterozoic basement of the housatonic berkshire green mountain and lincoln massifs 7 the location of the taconic root zone within the pre silurian eugeoclinal sequence 8 the recognition of numerous faults in the serpentinite belt 9 the similarity between the rocks of the moretown formation and modern fore arc basin sequences 10 the recognition that the volcanic arc continental complexes of the ascot weedon and bronson hill have been displaced westward over the moretown and or hawley formations along such faults as the bristol and coburn hill thrusts 11 the allochthonous and internally imbricated nature of the north american basement in the berkshire massif 12 the proposition that the housatonic green mountain and lincoln massifs as well as the middle proterozoic cored domes of southeastern vermont are also thick sialic slices of north american basement 13 the recognition of medium high to high pressure metamorphic mineral assemblages in the pre silurian eugeoclinal rocks of vermont and 14 the recent synthesis of isotopic age data by sutter and others 1985 on the basis of an analysis of the foregoing arguments and relationships a chronological sequence of seven structural sections between albany new york and the bronson hill anticlinorium in central massachusetts is used to depict the evolution of the taconian orogeny retrodeformed distances are based on structural overlap and restoration of the taconic slices to their depositional setting along the ancient north american continental margin these easterly younging diverticulated slices formed as a result of horizontal compression rather than gravity sliding this palinspastic analysis implies the following 1 approximately 1 000 km of shortening has occurred during the emplacement of the taconic allochthons and the subsequent imbrication of north american basement as thick sialic slices approximately 330 km of this shortening is attributed to multiple cleavage generations 2 repeated movement along such major surfaces as the cameron9s line whitcomb summit belvidere mountain thrust zone has buried the taconic root zone we suggest that the northern extension of this root zone is exposed to the east of the lincoln massif in vermont where the underhill pinney hollow and hazens notch formations are exposed these formations here considered thrust slices disappear along the belvidere mountain whitcomb summit thrust zone as it is traced southward into western massachusetts and western connecticut 3 taconian metamorphic rocks particularly the older medium high pressure rocks in northern vermont have been transported westward on such reactivated surfaces as the belvidere mountain thrust 4 the anticlinorial form of the middle proterozoic basement in the green mountain and lincoln massifs may have resulted from fault bend folding on deep mantle involved thrusts that developed late in the taconian orogeny

shear senses and viscous dissipation of layered ductile simple shear zones velocity profiles and shear heat profiles for inclined layered newtonian simple shear zones are considered reverse fault like simple shear of the boundaries and upward net pressure gradient act together in such shear zones as the velocity of the boundary increases the point of highest velocity shifts from the lower layer of less viscosity into the upper layer the shear heat profile shows a temperature peak inside the lower layer for a more viscous upper layer the point of highest velocity is located inside the upper layer and shifts towards the upper boundary of the shear zone the shear heat profile shows a maximum temperature within the upper layer depending on the flow parameters of the two layers the slip rate of the boundary and the dip and thickness of the shear zone a shear sense in reverse to the relative movement of the shear zone boundaries may develop these models can decipher thermo kinematics of layered shear zones in plate scale hot orogens

tectonic significance of basement cover relationships in the green mountain massif vermont middle proterozoic basement rocks of grenvillian age form the core of the green mountain massif in southern vermont and two distinctive cover rock sequences of late proterozoic to middle ordovician age flank the massif on the west and east the eastern cover sequence is dominated by metamorphosed graywacke silt stone shale and mafic volcanics and unconformably overlies the basement rocks along the eastern margin and in the northern interior of the massif the western boundary of the massif south of clarendon vermont is an unconformity between middle proterozoic basement and western cover sequence rocks composed of metamorphosed conglomerate quartz sandstone dolomite and limestone the western boundary north of clarendon however is a thrust which carried grenville basement and eastern cover rocks over the western cover sequence the structural interpretation of these basement cover contacts and the contrast in lithology and inferred depositional environment of the western and eastern cover seq

age and origin of the boil mountain ophiolite and chain lakes massif maine implications for the penobscottian orogeny the boil mountain ophiolite complex of west central maine is widely interpreted to mark the lower ordovician penobscottian suture between the dunnage chain lakes and gander terranes the ophiolite consists of two distinct volcanic groups including a lower island arc tholeiite sequence and an upper mid ocean ridge basalt sequence a new middle ordovician 477 1 ma u pb age on a tonalite sill that intrudes the lower volcanic gabbroic sequence is younger than other ca 500 ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the chain lakes massif a comparison of ages and paleogeography of the boil mountain ophiolite with ophiolitic sequences in quebec and newfoundland indicates that the taconian and penobscottian orogenies and ophiolite obduction occurred simultaneously although on different margins of the iapetus ocean the taconian ophiolite sequences were obducted onto the appalachian margin of laurentia during its col

determination of the fluid absent solidus and supersolidus phase relationships of morb derived amphibolites in the range 4 14 kbar experiments on a morb mid ocean ridge basalt derived amphibolite have been conducted in order to determine fluid absent solidus and supersolidus phase relationships the solidus has been determined in the range 4 14 kbar by using the incremental heating technique tested against classical procedures peritectic clinopyroxene was produced below 10 kbar and epidote was the stable peritectic phase at pressures greater than 10 kbar for temperatures near the solidus garnet was the peritectic phase for temperatures above 800 c and pressures of 10 to 14 kbar the shape of the solidus was similar to previous estimations but the temperature interval between the high and low pressure regions was strongly reduced with these new estimations the possibilities for melting of the oceanic crust at p below 10 kbar are increased and consequently the number of tectonic scenarios needed for magma generation from amphibolite sources is enlarged in the absence of free water the solidus in the pressure region above 10 kbar is at higher t than previous estimations

a newly identified gondwanan terrane in the northern appalachian mountains implications for the taconic orogeny and closure of the iapetus ocean the taconic and salinic orogenies in the northern appalachian mountains record the closure of the iapetus ocean which separated peri laurentian and peri gondwanan terranes in the early paleozoic the taconic orogeny in new england is commonly depicted as an ordovician collision between the peri laurentian shelburne falls arc and the laurentian margin followed by silurian accretion of peri gondwanan terranes during the salinic orogeny new u pb zircon geochronology demonstrates that the shelburne falls arc was instead constructed on a gondwanan derived terrane preserved in the moretown formation which we refer to here as the moretown terrane metasedimentary rocks of the moretown formation were deposited after 514 ma and contain abundant ca 535 650 ma detrital zircon that suggest a gondwanan source the moretown formation is bound to the west by the peri laurentian rowe belt which contains detrital zircon in early paleozoic metasedimentary rocks that is indistinguishable in age from zircon in laurentian margin rift drift successions these data reveal that the principal iapetan suture in new england is between the rowe belt and moretown terrane more than 50 km farther west than previously suspected the moretown terrane is structurally below and west of volcanic and metasedimentary rocks of the hawley formation which contains laurentian derived detrital zircon providing a link between peri laurentian and peri gondwanan terranes the moretown terrane and hawley formation were intruded by 475 ma plutons during peak activity in the shelburne falls arc we propose that the peri laurentian rowe belt was subducted under the moretown terrane just prior to 475 ma when the trench gap was narrow enough to deliver laurentian detritus to the hawley formation interaction between peri laurentian and peri gondwanan terranes by 475 ma is 20 m y earlier than documented elsewhere and accounts for structural relationships early ordovician metamorphism and deformation and the subsequent closure of the peri laurentian taconic seaway in this scenario a rifted arc system on the gondwanan margin resulted in the formation of multiple terranes including the moretown that independently crossed and closed the iapetus ocean in piecemeal fashion

late taconian and pre acadian history of the new england appalachians of southwestern connecticut new u pb age determinations and field observations combined with published field relations refine the late taconian and pre acadian history of the new england appalachians of southwestern connecticut foliation within the camerons line shear zone was developed after 514 11 ma but prior to 445 1 5 ma this structure probably experienced renewed movement in the early silurian 437 2 ma as suggested by new xenotime growth in protomylonite metasedimentary and metavolcanic rocks east of camerons line were deposited were isoclinally folded and reached temperatures in excess of about 550 c before emplacement of small dioritic plutons of the 453 3 ma brookfield plutonic series igneous titanites in brookfield plutons cooled below u and pb diffusion e g 525 25 c in the latest ordovician to earliest silurian and were not reset in the acadian the newtown gneiss is a composite magmatic complex composed of quartz diorite 446 2 ma granodiorite 436 2 ma and granite 438 2 ma low 207 pb 204 pb feldspar isotopic compositions and 1150 ma zircon inheritance in the newtown gneiss and brookfield plutonic series are consistent with interaction with grenvillian crust or crustally derived material we propose that the newtown and harrison gneisses and possibly the brookfield plutonic series make up the plutonic roots of a late ordovician to early silurian 454 438 ma magmatic arc complex generated during subduction along the eastern north american continental margin magmatic activity was coeval with that in the bronson hill anticlinorium to the east ca 454 442 ma

kinematic analysis of the southern iberian shear zone and tectonic evolution of the acebuches metabasites sw variscan iberian massif 1 the acebuches metabasites constitute a slice of oceanic crust located at the variscan suture between the ossa morena and the south portuguese zones iberian massif the emplacement of the metabasites onto the accretionary prism was associated with the activity of the southern iberian shear zone careful measurements of the fabrics and structures related to this shear zone show consistent kinematic criteria pointing to the presence of a simple shear component with an oblique predominantly left lateral sense of displacement the data are consistent with existing models of triclinic or oblique shear zones considering coeval simple shear and pure shear components these models provide a satisfactory explanation of the observed spatial variations in the foliation lineation and fold hinge data the kinematics of other shear deformations older and younger than the southern iberian shear zone have also been established these results offer new insights into the tectonic evolution of this suture of the variscan belt and show how complex transpressional strains can arise during oblique crustal deformation associated with the motions of tectonic plates

modeling of contaminants mobility in underground domains with multiple free porous interfaces 1 existing simulation techniques for subsurface water quality management remain inadequate despite the phenomenal progress made in the computing capabilities in the past 2 decades one major lacunas found in mathematical models for groundwater hydrodynamics in combined free flow zones zones that are devoid of porous materials and porous domains e g soil water regions in the subsurface is that these models impose continuity of all flow transport parameters to describe the flow behavior at the intermediate surfaces between the two zones prescription of such interfacial conditions cannot always be physically justified and in general result in ill posed mathematical formulations the present paper aims to remove the above limitations of the mathematical models by imposing well posed mathematical formulations of mass and momentum transfer across the boundaries between free and porous zones underground for simulating subsurface flow the possibility of the existence of a multiple number of pervious boundaries in the domain across which water may flow is considered in this work as it represents the most realistic scenario for the subsurface transport processes the hydrodynamics of coupled fluid flow and behavior of contaminants transport are described combined effects of darcy and reynolds numbers on the subsurface transport of contaminants are discussed sensitivity of the flow variables to a coefficient of the permeability and porosity of interfacial boundary which is determined by its structural properties is also considered

petrofabric of forsterite marbles and related rocks from a low pressure metamorphic terrain almaden de la plata massif ossa morena zone sw spain and its kinematic interpretation abstract a fabric study of forsterite marble and calc silicate rock paragenetic minerals is presented for samples collected in the almaden de la plata massif of sw spain that experienced variscan low pressure metamorphism related to the tectonic evolution of the suture between the ossa morena and south portuguese zones of the iberian massif two tectonically stacked metamorphic units contain marble metacarbonate and variably impure dolomitic rocks that record contrasting thermal conditions of the upper greenschist structuraly upper unit and the upper amphibolite granulite facies structuraly lower unit different reactional paths lead to formation of forsterite marbles in both units dolomite and calcite petrofabrics disclose their contrasting rheological behaviour during syn metamorphic ductile deformation under temperatures between 500 and 700 c dolomite formed harder porphyroclast systems and boudinaged bands whereas weaker calcite underwent dynamic recrystallization in both cases deformation was facilitated by activation of various intracrystalline slip systems complemented by other deformation mechanisms the fabrics of other paragenetic metamorphic minerals also denote crystal plasticity and exhibit close geometrical relationships with respect to the macroscopic foliation and mineral stretching lineation including a systematic asymmetry suggestive of non coaxial deformation components foliations and lineations are interpreted as solid state flow planes and directions bearing a kinematic significance in particular regional sinistral shear at mid deep crustal realms coeval with low pressure metamorphism explains the imbrication of metamorphic units and their exhumation concomitant with the overall wrench tectonic framework ruling the tectonic evolution of the ossa morena south portuguese suture between the late devonian 360 ma and the latest carboniferous 300 ma

experimental modelling of mantled porphyroclasts abstract mantled porphyroclasts are commonly used as sense of shear indicators in mylonites analogue experiments have been carried out to model the development of such objects rigid spheres mantled by a viscous plasticene putty mixture with power law behaviour were suspended in an optically transparent newtonian polymer matrix the samples were deformed between two cylinders one placed within the other and with coinciding axes this induces a non coaxial flow between the cylinders and allows the achievement of high finite strain the viscous mantle around the rigid sphere remained undeformed deformed into an ellipsoid or developed wings the final geometry depends mainly on the induced viscosity contrast between the mantle and the matrix which is a function of the flow induced stress on the surface of the mantle winged mantles only develop if the induced viscosity contrast between the mantle and the matrix polymer is sufficiently small if this critical induced viscosity contrast is exceeded the mantled sphere remains undeformed or obtains a stable ellipsoidal shape even at high finite strain shaped winged mantles only develop in simple shear flow if the mantle around a rigid sphere is thin

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

paleomagnetism of the moreton s harbour group northeastern newfoundland appalachians evidence for an early ordovician island arc near the laurentian margin of iapetus paleomagnetic results have been obtained from mafic volcanic units in the upper part of the moreton s harbour group which is part of an accreted island arc terrane that is preserved in the notre dame bay subzone of the central mobile belt of the newfoundland appalachians detailed thermal and alternating field demagnetization reveals a stable characteristic component of magnetization carried by magnetite at a large number of sites in pillow basalts and coeval basaltic dikes the intrusives contain both polarities and a primary age for the characteristic magnetization is indicated by a positive contact test for one of the dikes and by a positive structural test involving a correction for block rotations strike correction the overall mean direction for the characteristic component after tectonic tilt and strike correction flows and intrusives d 171 i 22 k 22 6 95 6 5 pole 29 n 135 e flows d 166 i 22 k 33 2 95 6 5 corresponds to an early ordovician paleolatitude for the arc of 11 s which is indistinguishable from the expected paleolatitude of the north american margin this implies that the arc formed at or near the margin of the craton in contrast the avalon block which formed the other margin of iapetus was widely separated from the arc and the craton at this time the early ordovician paleolatitude of the arc terrane supports a tectonic model in which coeval ophiolitic sequences inboard of the arc were formed in a narrow ocean basin between the arc and the craton subsequent convergence between the arc and laurentia in middle ordovician time resulted in closure of this narrow ocean basin and obduction of the back arc basin oceanic crust onto the ancient margin of the craton thus giving rise to the taconic orogenic pulse in the newfoundland appalachians

geology and paleobiology of islands in the ordovician iapetus ocean review and implications a history of islands in the iapetus ocean and their destruction is recorded by widespread occurrences of lower to upper ordovician volcanic and epiclastic rocks and some limestone through the axial parts of the appalachian caledonide orogen in north america and northwestern europe assemblages of arenigian and llanvirnian benthic shelly fossils chiefly brachiopods from these rocks constitute the celtic biogeographic province that is distinguished by its endemic genera and by some that are older than in other biogeographic provinces some that are younger than elsewhere and others that have not hitherto been found together evidence from these fossils and from the geology of the rocks pertaining to them suggests that north american terranes that included islands of arenigian llanvirnian age lay at middle to high latitudes both in mid ocean and within the armorican continental margin whereas coeval rocks in west central ireland and norway that have toquima table head shelly fossils were originally part of the laurentian continental margin eradication of the celtic assemblage and the reduction of ordovician faunal provinciality in the appalachian caledonide region coincide with llanvirnian obduction subduction of hundreds of kilometres of iapetus ocean crust late llanvirnian and younger ordovician rocks in the remnant basin including some of peri insular origin have brachiopods of scoto appalachian affinities no discrete islands of ashgillian age have been recognized although fossiliferous volcaniclastic and polymictic conglomerates indicate intermontane basins in some places shelly fossils in these rocks and those in the siltstones and limestones from the gaspe peninsula are like those of ashgillian age elsewhere

deformation mechanics in inclined brittle ductile transpression zones insights from 3d finite element modelling abstract most natural examples of transpression zones developed at oblique convergence regime are inherently 3d and have inclined boundaries a 3d finite element model with an elasto plastic rheology is used to investigate the structural and mechanical evolution of inclined transpression zones in a rock sequence above a frictional basal detachment inelastic constitutive relationships allow permanent strains to develop in response to the applied loads fe modelling results show that oblique convergence is accommodated by discrete deformation at the main pre existing inclined faults 70 and by distributed brittle and ductile deformation at active blocks oblique contraction at the active blocks resulted mainly in layer parallel shortening orthogonal to the model outer boundaries whereas thickening in the horizontal and vertical directions was accommodated via layer parallel fault strike parallel extension and up dip extrusion i e inclined extrusion lateral extrusion should have compensated the rest and or volume loss took place folding and thickening of the mobile backstop produced a non cylindrical asymmetric bi vergent anticline where permanent strains developed principally in the steep forelimb secondary conjugate fault zones also accommodate oblique slip and contribute to uplift displacement vectors within the transpression zone are rotated counter clockwise ca 20 30 with respect to vectors in the fixed backstop areas with higher rotation values seem to correlate with those showing higher ellipticity values the presence of pre existing faults favored strain partitioning from the onset of deformation fe modelling results compared with analytical natural example and analogue modelling results show that our mechanical modelling can overall match inclined transpression zones geometry that present different modes of strain partitioning and localisation

how do lineations reflect the strain history of transpressive shear zones the example of the active alpine fault zone new zealand abstract lineations within mylonites exhumed in the hanging wall of new zealand s active alpine fault zone have a complicated relationship to contemporary plate kinematics the shear zone is triclinic and macroscopic object lineations are not usually parallel to the simple shear direction despite high total simple shear strains 150 this is mostly because the lineations are inherited from pre mylonitic fabrics and have not been rotated into parallelism with the mylonitic stretching direction which pitches c 44 in the fault plane furthermore some lineations have been variably rotated depending on whether they are present in shear bands or microlithons which accommodated bulk strains with different vorticities total strains required to obtain parallelism between the finite maximum principal stretching direction calculated from transpression models and these mylonitic lineations are pure shear stretch s 1 3 5 simple shear 11 7