strain partitioning and progressive deformation history in a transpressive belt northern appalachians abstract syntectonic fibres within rocks of the gaspetrough a mid paleozoic slate belt within part of the acadian orogen of the canadian appalachians record the complex structural evolution of a transpressive belt the fibres occur around pyrite framboids and can be divided into five segments which record four distinct structural stages all four structural stages are related to a single progressive deformation since fibre segments can be traced continuously from the first segments to the last fibre growth patterns within the gaspetrough clearly indicate that folding occurred during coaxial deformation during the first three structural stages these structural stages are 1 layer parallel shortening 2 combined flattening and rigid body rotation and 3 cleavage development strain associated with vertical extension during these three stages accounts for approximately 50 shortening within the slate belt during the last structural stage deformation resulting from regional simple shear continued to affect the entire slate belt as local flattening within cleavage planes produced horizontal extension and brought about further tightening of folds strain recorded by the horizontal fibre increments produced during simple shear accounts for 25 shortening in this part of the appalachians oblique convergence during the acadian orogeny was partitioned in time between strike slip and reverse faulting convergence was accommodated by folding flattening and reverse faulting during the first part of the deformation and later on by flattening and dextral transcurrent faulting

base metal skarns and au occurrences in the southern gaspe appalachians distal products of a faulted and displaced magmatic hydrothermal system along the grand pabos restigouche fault system in the southern gaspe appalachians base metal and au occurrences are spatially associated with the acadian dextral strike slip grand pabos and restigouche faults mineralization occurs as veins replacement zones and disseminations along the main structures and subsidiary faults with orientations compatible with the dextral strike slip kinematics along the main faults limestone of the upper ordovician lower silurian white head formation hosts numerous base metal skarns and au occurrences that are surrounded by halos of argillaceous alteration the reboul prospect is a type example of base metal skarns and consists of three types of mineralization 1 early strata bound disseminated cu zn ag associated with marble hornfels and skarn 2 northeast and northwest trending cu zn pb ag au and ag cu zn pb au sb veins parallel and perpendicular to the regional folding and 3 late ag au zn pb mineralized zones in quartz breccia veins parallel to the grand pabos fault crosscutting relationships fluid inclusion microthermometry mineralogy of the three types of mineralization and alteration patterns were used to define the timing of mineralizing processes which are 1 prograde metamorphism 2 metasomatism and hydrothermal alteration with high temperature skarn formation and cu zn ag mineralization 3 retrograde alteration with cu zn pb ag au and ag cu zn pb au sb veins and 4 late au precipitation at low temperature the saint andre de ristigouche prospect is the best example of au mineralization spatially associated with a base metal skarn in the area it consists of au sb as extensional veins and stockwork hosted by limestones felsic dikes associated with base metal skarns and a magmatic hydrothermal breccia at the reboul prospect are evidence for magmatic activity coincident with the mineralizing events argillaceous alteration high temperature and high salinity fluid inclusions and the pb isotope compositions of galena are compatible with a model linking the skarns and au occurrence to early to middle devonian magmatic activity at depth along the grand pabos and restigouche faults a palinspastic pre acadian strike slip reconstruction of the southern gaspe appalachians shows that all mineral occurrences hosted by the white head formation belong to the same mineralized area that might represent distal components of a magmatic hydrothermal system at depth

reconstruction of taconian and acadian paleostress regimes in the quebec and northern new brunswick appalachians a numerical analysis of fault populations was applied in the quebec and northern new brunswick appalachians to characterize paleostress fields attributed to the taconian and acadian orogenies the first brittle deformation documented in the external domain of the humber zone is associated with the thin skinned tectonics of the taconian orogen the taconian brittle deformation characterized by north south to ne sw reverse conjugated brittle faults evolved under a pure shear compressional regime vertical 3 axes with 1 axes oriented ese wnw the ene wsw dextral and nw se sinistral faults that are observed in the st lawrence lowlands are also attributed to taconian compression the first brittle deformation recognized in the dunnage zone and the gaspe belt is attributed to an ese wnw compression during the acadian orogeny in the dunnage zone of southern quebec the acadian paleostress axes are similar to the directions of 1 axes and to the pure shear compressional regime computed for the silurian and devonian rocks of the gaspe belt in the gaspe peninsula the acadian stresses are oriented ese wnw and are mechanically compatible with transpressional regimes reverse brittle faults and pure shear stress are identified along regional and secondary sets of ne sw brittle faults whereas a strike slip stress regime is reconstructed along major east west faults in the humber zone of the quebec appalachians a second compression is identified it is characterized by conjugate ene wsw dextral and nw se sinistral strike slip faults that crosscut taconian thrust faults this late deformation event is attributed to a distal expression of the acadian orogeny

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

carlin type gold mineralization at saint andre de ristigouche gaspe peninsula quebec canadian appalachians the gaspe peninsula in the canadian appalachians hosts a variety of mineral occurrences that are spatially associated with the grand pabos and restigouche faults among these occurrences the saint andre de ristigouche gold sar au showing has peculiar features comparable with carlin type gold deposits at the regional district and prospect scales the most striking ones are 1 the calcareous nature of the host rocks 2 the au as sb hg metallic signature with absence of base metals and ag 3 the association with a crustal scale fault zone 4 the hydrothermal alteration characterized by silicification calcite and quartz veinlets at the margin of the au bearing zones and the occurrence of kaolinite in large halos of argillic alteration 5 numerous felsic dikes 6 the occurrence of au in as rich pyrite forming overgrowths on premineralization as free pyrite and in arsenopyrite 7 hydrothermal fluids equilibrated with host rocks at high temperature 200 which cooled to precipitate arsenopyrite and then mixed with evolved meteoric water to precipitate stibnite in veins although the sar au showing is relatively small analogies with carlin type mineralization encourage exploration in the gaspe peninsula and in similar settings elsewhere in the appalachians

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

the cenozoic thrusting sequence of the longmen shan fold and thrust belt eastern margin of the tibetan plateau insights from low temperature thermochronology abstract the 2008 mw 7 8 wenchuan earthquake in china led to intensive studies on the development and dynamic mechanisms of the longmen shan fold and thrust belt to construct the uplift history of the longmen shan previous works had undertaken numerous low temperature thermochronological studies in mountainous area in particular apatite and zircon u th he dating which provided valuable evidence for understanding phases of uplift in the longmen shan during the cenozoic however few u th he ages have been obtained from the sichuan basin which leaves a blank in our understanding of the link between the wenchuan earthquake and the out of sequence longmen shan in this study we carried out u th he dating on apatite and zircon separated from samples collected in the sichuan basin and the frontal southern longmen shan together with previous low temperature thermochronological studies we reconstructed the thrusting sequence of the longmen shan the results of dating of apatite suggest that thrusting in the longmen shan is temporally and spatially variable after continuous thrust propagation into the sichuan basin over several to tens of myr deformation migrated back into the mountain range which in this case termed out of sequence style of deformation

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

gaspe belt subsurface geometry in the northern quebec appalachians as revealed by an integrated geophysical and geological study 1 potential field mapping abstract together recent gravity and high resolution aeromagnetic datasets are used to qualitatively investigate the upper and middle crustal geometry of the middle paleozoic gaspe belt in the northern appalachians long wavelength potential field anomalies define two sub basins that are divided by northeast trending gravity highs for each sub basins gravity lows correlate with the youngest rock units maps that highlight anomalies associated with near surface features at the expense of those related to deeper sources provide an important supplement to the spatially discrete observations derived from bedrock mapping analysis of such maps indicates that the sub basins are characterized by different structural patterns and that faults trending obliquely compared to the main structural grain have been previously underestimated the geometry of the gaspe belt as revealed by this integrated geophysical and geological study bears similarities with orogens exhibiting lateral extrusion this geometry is interpreted as the result of a heterogeneous strain regime in front of an indenter corresponding to the early paleozoic gander dunnage crustal block the indentation tectonic model is supported by 1 the various strike and kinematic of faults that suggest a strongly heterogeneous strain regime 2 the greater geological complexity and the occurrence of faults with a significant thrust component in front of the indenter 3 the predominance of dextral strike slip faults in the eastern gaspe peninsula that result in lateral material transport away from the indenter 4 the location of abundant devonian magmatic dykes sills and stocks in a fault bounded zone that experienced local extension 5 the occurrence of block rotation

vertical and fold axis parallel extension within a slate belt in a transpressive setting northern appalachians abstract an incremental and finite strain study of a mid paleozoic slate belt in a transpressive setting in gaspe canadian appalachians has been undertaken using syntectonic fibers from pyrite type pressure shadows regionally strain estimates are quite consistent and reflect only slightly higher strain in the central part of the anticlinorial structure defining the slate belt extensions of up to 160 vertically and 110 parallel to the fold axis were recorded in the slate belt combined with an estimated overall regional shortening of 80 the fibers first rotated toward the final position of the cleavage within a vertical section normal to the cleavage and then rotated from a vertical to a horizontal orientation this change in fiber orientation observed in cleavage parallel sections indicates an abrupt change in the incremental stretching direction from sub vertical to sub horizontal fold axis parallel the vertical extension is related to folding and cleavage development during coaxial flattening the horizontal extension reflects the strain imposed on the rocks during regional simple shear which produced strike slip faulting and further tightening of the folds folding cleavage development fold axis parallel extension and faulting are all related to oblique convergence during the middle devonian acadian orogeny in this part of the canadian appalachians and clearly indicate an overall transition from a pure shortening deformation to a simple shear dominant deformation in an overall transpressive setting

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

role of grain size in phyllonitisation insights from mineralogy microstructures strain analyses and numerical modeling abstract brittle y and p planes exist in an exposure of greywacke in the garhwal lesser himalaya india although y planes are well developed throughout the p planes are prominent only in some parts domain a and not elsewhere domain b to investigate why the p planes developed selectively the following studies were undertaken 1 clay separated xrd analyses clinochlore and illite are present in both the domains 2 strain analyses by rf method it deduces strain magnitudes of 1 8 for the ductile deformed quartz grains from both the domains a and b 3 grain size analyses of quartz clasts domain a is mostly composed of finer grains area up to 40 000 m2 whereas domain b consists of a population of coarser grains area 45 000 m2 a 2d finite element modeling of linear elastic material was performed using comsol software to investigate the control of grain size variation on the generation brittle shear planes the results of numerical modeling corroborate the known fact that an increase in grain size reduces the elastic strain energy density a broader grain size distribution increases the effects of diffusion creep and resists the onset of dislocation creep thus rocks with coarser grain population domain b tend to resist the generation of shear fractures unlike their fine grained counterpart domain a

reflection and transmission characteristics at the edge of shore fast sea ice the reflection and transmission of ocean waves at a sea ice boundary is reconsidered the sea ice is modelled as a continuous thin elastic plate of uniform thickness floating on water of arbitrary constant depth unlike earlier solutions matching of potentials between the free surface domain and the ice covered domain is done at all depths previous solutions were incompletely matched as the potentials in each domain were deficient in the present solution a number of the infinity of evanescent modes which were hitherto ignored are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor reflection and transmission are found to be markedly influenced by the inclusion of these modes suggesting that conclusions based on the incomplete potentials may be substantially in error

paleostress analysis of atlantic crustal extension in the quebec appalachians abstract a paleostress analysis using normal fault slip data and jurassic dike trends has been conducted in the quebec and new england appalachians stress tensor analysis of fault slip by a numerical inversion method has distinguished homogeneous and directionally consistent e w and nw se oriented extensional stress regimes in the quebec appalachians and st lawrence lowlands the directions of extension compare well with the mean direction of extensional stress inferred from the jurassic dolerite dike trend in new england both extensions are interpreted as the result of rift related stress associated with the separation of north america and africa early in the late triassic early jurassic fragmentation of pangea the paleostress field configuration is assumed to be related to the direction of divergent plate motion the n s and ne sw late proterozoic faults that bordered the quebec reentrant and taconian acadian structures of the quebec appalachians appear to have played a significant role in the dis

the thickness distribution of sea ice and snow cover during late winter in the bellingshausen and amundsen seas antarctica data collected from a voyage of rv nathaniel b palmer to the bellingshausen and amundsen seas during august september 1993 are used to investigate the thickness distribution of sea ice and snow cover and the processes that influence the development of the first year pack ice the data are a combination of in situ and ship based measurements and show that the process of floe thickening is highly dependent on ice deformation in particular rafting and ridging play important roles at different stages of floe development rafting is the major mechanism in the early stages of development and core structure data show the mean thickness of individual layers of crystals to be only 0 12 m most ice 0 6 m having some surface deformation blocks within ridge sails are typically in the range 0 3 0 6 m thick and ship based observations estimate approximately 25 of the pack exhibits surface ridging when corrected for biases in the observational methods the data show that the dominant ice and snow thickness categories are 0 7 m and 0 2 0 5 m respectively and account for 40 and 36 of the surface area of the pack ice approximately 8 of the pack is open water an estimate of the effects of ridging on the distribution of ice mass within the pack suggests that between 50 and 75 of the total mass is contained within the 25 of the pack that exhibits surface ridging

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

across strike geometry of the grand pabos fault zone evidence for devonian dextral transpression in the quebec appalachians the principal faults of southeastern gaspe peninsula in quebec consist of a central high strain zone that is characterized by mainly ductile deformation structures and bordered by low strain zones each dominated by brittle deformation structures the overall geometry of shear fractures within the low strain zones is quite similar to the expected geometry of riedel shear fractures the brittle structures overprint the dominant c s type fabric of the high strain zone which implies that brittle deformation outlasted ductile deformation the asymmetry of local micro to meso scale deformation features along the fault zones reflects the non coaxiality of the shear other features described within the fault zone stylolitic cleavage shear bands and reverse faults are evidence for a component of shortening perpendicular or oblique to the fault zone the geometry of the grand pabos fault zone gpfz a major fault of southern gaspe indicates that deeper seated fault rocks high strain zone have been brought

paleomagnetic constraints on siluro devonian laurentian margin tectonics from northern appalachian volcanics abstract paleomagnetic analyses of silurian mafic volcanics from the overstep sequence of sedimentary and volcanic rocks deposited over the central mobile belt of the northern appalachians provide insight into the mid paleozoic tectonic history of the laurentian margin stepwise thermal demagnetization of the subaerial mafic volcanics of the ludlovian fivemile brook formation of northwestern maine reveals two ancient high temperature dual polarity remanences a tilt corrected mean direction yields an inclination of 41 i 3 9 n 4 sites and the magnetization is interpreted as a near primary magnetization acquired well before the end of early devonian deformation an in situ mean direction d 165 i 35 95 6 k 65 n 10 entries from 8 sites is interpreted as a secondary overprint with a pole 22 s 306 e near the early carboniferous segment of the north american apparent polar wander path apwp conglomerate and fold tests of the high temperature characteristic remanence preserved in wenlockian subaerial mafic volcanics of the bryant point formation and a red bed of the south charlo formation both of the chaleur group of northeastern new brunswick constrain paleolatitude and deformational age the inclination only fold test peaks at 50 unfolding with a mean inclination of 35 i 8 5 n 148 synfolding acquisition of magnetization is wenlockian based on a negative conglomerate test at the base of the section and a positive conglomerate test at the top of the section clockwise streaking of site mean directions away from a predominantly northerly declination is consistent with post middle wenlockian dextral shear in the chaleur bay region comparison of a locus of paleomagnetic pole positions with the north american apwp supports a silurian age of the magnetization of the chaleur group the age and synfolding nature of this remanence furthermore requires that deformation associated with the acadian orogeny in new brunswick began by mid silurian times moreover inclinations from these units indicate that within paleomagnetic resolution there has been no significant latitudinal displacement with respect to stable north america since the silurian

taconian and acadian transpression between the internal humber zone and the gaspe belt in the gaspe peninsula tectonic history of the shickshock sud fault zone the shickshock sud fault has a history of ordovician taconian silurian salinic and devonian acadian movements taconian deformation involving ductile dextral oblique slip faulting is recorded in cambrian rocks in the footwall of the shickshock sud fault metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist shear bands asymmetric garnet porphyroclasts c s fabrics and mica fish textures indicate dextral shearing the regional sense of shear is top to west and southwest on generally southeast dipping shear zones hornblende of metabasalt yielded an 40ar 39ar age of 455 9 2 ma and muscovite from the mylonitic schist yielded an 40ar 39ar age of 454 3 0 9 ma which indicate metamorphism and deformation during the taconian orogeny evidence for silurian activity is indicated by the salinic unconformity to the south related to normal block faulting deformation features in the ordovician and silurian devonian rocks in the hanging wall were predominantl

along strike acadian structural variations in the quebec appalachians consequence of a collision along an irregular margin the quebec appalachians have been shaped by two major orogenies the middle to late ordovician taconian and the middle devonian acadian thrust faults and nappe structures characterized the taconian deformation throughout the quebec appalachians whereas structural styles pertaining to the acadian orogeny differ from southern quebec to the gaspe peninsula structural analysis of late ordovician to middle devonian supracrustal rocks shows two different acadian deformational regimes strike slip tectonics in the gaspe peninsula and thrust or dip slip tectonics in southern quebec in southern quebec acadian regional deformation produced folds which vary from upright to overturned and tight to isoclinal from the nw to the se major faults e g la guadeloupe are northwestward directed thrust faults marked by highly ductile shear zones outlined by mylonite in the gaspe peninsula structural trend is ne and major e w dextral strike slip faults transect this trend folds are open and upright inclined and tighter near the major faults where they have a clockwise rotation like the regional cleavage major faults e g grand pabos follow corridors delimiting high strain zones where the fabrics developed are indicative of a ductilebrittle regime of deformation in the temiscouata region major structural features of both southern quebec and the gaspe peninsula are recognized structures of this region consist of ene trending dextral strike slip faults and high angle wnw verging reverse faults parallel to major nne folds these structures reflect the transition from purely horizontal movement along major strike slip faults of the gaspe peninsula to vertical movement along thrust faults in southern quebec acadian structural variations within the quebec appalachians are interpreted in terms of a continental collision of gondwana along the irregular margin of laurentian and its taconian accreted terranes