collapse of the thickened variscan crust in the french massif central mont pilat extensional shear zone and st etienne late carboniferous basin abstract a large scale extensional shear zone is described from the mont pilat area in the northeastern part of the french massif central this shear zone is about 2 km thick and is characterized by well developed n dipping foliation and stretching lineations deformation occurred under conditions of retrograde metamorphism from high temperature conditions to greenschist facies it is superimposed on a composite foliation related to the earlier variscan 380 350 ma compressional events associated with southward emplacement of nappes and hp mt metamorphism regional n s lineations and shear criteria observed at a regional scale indicate a northward displacement of the hanging wall during extension large strains locally recorded in thick mylonitic zones suggest that displacement was substantial some tens of kilometres late superimposed extensional brittle deformation and pseudotachylites show that northward displacement on normal faults continued at a shallower depth a large granitic pluton granite du velay intruded late in the the variscan orogeny was associated with extension some small leucogranitic syntectonic melts were emplaced within the shear zone and are strongly deformed geochronological rb sr data on these leucogranite bodies give an age of 320 ma and 40 ar 39 ar dating of synkinematic biotites from gneissose rocks in the shear zone yields a plateau age of 313 ma these data show that extensional ductile deformation and magmatism were still active during the latest late carboniferous thus extension occurred immediately after the well known late palaeozoic collision type compressional tectonics which had significantly thickened the crust we propose that the extensional tectonism described here is due to the gravitational collapse of the initially thick variscan crust the stephanian intracontinental sedimentary basin of st etienne was formed along the hanging wall of the normal shear zone during the late stages of this post orogenic crustal extension

crustal structure and surface zonation of the canadian appalachians implications of deep seismic reflection data in 1986 1181 km of marine seismic reflection data was collected to 18 20 s of two way traveltime in the gulf of st lawrence area the seismic profiles sample all major surface tectono stratigraphic zones of the canadian appalachians they complement the 1984 deep reflection survey northeast of newfoundland together the seismic profiles reveal the regional three dimensional geometry of the orogen three lower crustal blocks are distinguished on the seismic data they are referred to as the grenville central and avalon blocks from west to east the grenville block is wedge shaped in section and its subsurface edge follows the form of the appalachian structural front the grenville block abuts the central block at mid crustal to mantle depths the avalon block meets the central block at a steep junction that penetrates the entire crust consistent differences in the seismic character of the moho help identify boundaries of the deep crustal blocks the moho signature varies from uniform over extended di

late devonian early carboniferous volcanism in western cape breton island nova scotia the fisset brook formation of western cape breton island and its equivalents at macmillan mountain and the north baddeck river are examples of late devonian and early carboniferous volcanic sequences associated with the formation of post acadian successor basins in the northeastern appalachians they consist of bimodal basalt rhyolite suites interbedded with alluvial fan lacustrine and rare fluvial sediments the earliest volcanic products are rhyolites and somewhat evolved basalts associated with coarse sediments followed by tholeiitic to transitional basalt flows interlayered with lacustrine type deposits geochemical studies on the fisset brook formation indicate extensive remobilization of alkalies ca rb and sr making these elements inappropriate for determining tectonic setting or magmatic affinity use of less mobile elements ti nb y and zr suggests that the basalts are tholeiitic and that the apparent alkalinity of the type section lavas is a result of alteration we conclude that volca

alleghanian reactivation of the acadian fold belt meguma zone southwest nova scotia shear zones and northwest verging folds define a 30 km wide belt of deformation that overprints the acadian fold belt and telescopes isograds in the meguma zone in southwest nova scotia the shear zones appear to form a linked system that accommodated convergence dominated transpression of the meguma zone against an irregular avalon boundary available geochronological data indicate a mid carboniferous alleghanian variscan age for the overprinting deformation the mid carboniferous basement reactivation in southwest nova scotia is likely coeval with deformation of carboniferous strata and reactivation of basement structures meguma group in the northern meguma zone together these mid carboniferous structures may define a wide belt of alleghanian variscan deformation across the northwest cratonward margin of the meguma zone

geochemistry of oil inclusions in sulfide related calcites fingerprinting the source of the sulfate reducing hydrocarbons of the pb zn carbonate hosted jubilee deposit of nova scotia canada abstract sulfide precipitation in the context of carbonate hosted base metal deposits has been previously explained by numerous processes including so 4 reduction in the presence of hydrocarbons this model has been suggested for numerous deposits although clear criteria to support the model have not been systematically provided numerous oil inclusions are encompassed by fibrous calcite crystals in finely laminated carboniferous limestone at the base of the windsor group a unit that hosts numerous base metal occurrences in nova scotia particularly the hydrocarbon rich jubilee pb zn deposit in cape breton island oil from two inclusion rich samples from this deposit have been characterised by gas chromatography gas chromatography mass spectrometry gas chromatography isotope ratio mass spectrometry and bulk stable c isotopes as established in the authors former publications the jubilee deposit is a clear metallogenic case for which the ground preparation and mineralisation stages involved reduction of so 4 by hydrocarbons here the question of potential sources of these hydrocarbons is addressed it is postulated that the hydrocarbons that were trapped in the sulfide related calcites at the deposit correlate with previously characterised oil seeps and it is demonstrated that their source is not the marine host carbonates but stratigraphically deeper lacustrine formations of the horton group

structural geology of the penobsquis salt structure late bashkirian inversion tectonics in the moncton basin new brunswick eastern canada this study uses new information acquired from field mapping mineral exploration boreholes and seismic reflection profiles to constrain the structural geology deformation mechanisms and timing of the penobsquis salt structure this information is used to place the development of the salt structure into the context of the tectonic evolution of the moncton basin the penobsquis salt structure is an elongate salt wall separated from underlying rocks by a mylonitic detachment horizon it may be divided into two segments a southwestern asymmetric southeast verging structure and a northeastern strongly asymmetric to overturned southeast verging structure associated with the penobsquis fault an initial low amplitude salt anticline formed during deposition of the mabou group serpukhovian time the salt anticline was modified into a high amplitude salt wall after deposition of cumberland group sediments early bashkirian or later the sense of asymmetry of the penobsquis salt structure the presence of thrust faults within the structure the spatial association of the structure with a major reverse fault in the salt cover and the temporal association of salt movement and compressional tectonic events suggest that the salt structure developed in response to tectonic contraction during inversion of the moncton basin

acadian remobilization of a taconian ophiolite hare bay allochthon northwestern newfoundland the hare bay fault is a major subhorizontal detachment at the base of the ophiolitic st anthony complex in the hare bay allochthon northwestern newfounland the fault is a postmetamorphic brittle detachment that truncates footwall structures related to both initial ordovician taconian assembly of the allochthon and subsequent silurian devonian acadian deformation although previously mapped as a thrust the fault has an extensional rather than a contractional geometry it cuts downsection to the west in the direction of transport and it juxtaposes a hanging wall sequence that contains little or no acadian deformation against a footwall sequence that was pervasively deformed during the acadian orogeny the st anthony complex lies on the western margin of the acadian deformed zone its final emplacement through movement on the hare bay fault probably occurred through extensional faulting during gravitational collapse of the acadian mountain front

spring bloom dynamics in a subarctic fjord influenced by tidewater outlet glaciers godthabsfjord sw greenland in high latitude fjord ecosystems the spring bloom accounts for a major part of the annual primary production and thus provides a crucial energy supply to the marine food web however the environmental factors that control the timing and intensity of these spring blooms remain uncertain in 2013 we studied the spring bloom dynamics in godthabsfjord a large fjord system adjacent to the greenland ice sheet our surveys revealed that the spring bloom did not initiate in the inner stratified part of the fjord system but only started farther away from tidewater outlet glaciers a combination of out fjord winds and coastal inflows drove an upwelling in the inner part of the fjord during spring april may which supplied nutrient rich water to the surface layer this surface water was subsequently transported out fjord and due to this circulation regime the biomass accumulation of phytoplankton was displaced away from the glaciers in late may the upwelling weakened and the dominant wind direction changed thus reversing the direction of the surface water transport warmer water was now transported toward the inner fjord and a bloom was observed close to the glacier terminus overall our findings imply that the timing intensity and location of the spring blooms in godthabsfjord are controlled by a combination of upwelling strength and wind forcing together with sea ice cover the hydrodynamic regime hence plays a crucial role in structuring food web dynamics of the fjord ecosystem

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

tectonic stacking of metamorphic zones in cheticamp river area cape breton highlands nova scotia metabasic and quartzo feldspathic schists and gneisses of the cheticamp river area can be subdivided into three north south trending metamorphic belts the westernmost belt the low grade belt has been metamorphosed to transitional greenschist amphibolite facies with development of one penetrative foliation the central medium grade belt has been metamorphosed to amphibolite facies with development of two penetrative foliations the eastern high grade belt has been metamorphosed to amphibolite facies accompanied by development of strong gneissic segregation and nonanatectic migmatite leucosomes during formation of two penetrative foliations deformation has been inhomogeneous in each of these belts most rocks in each belt show evidence of post tectonic porphyroblast growth however deformation continued after the metamorphic peak in localized zones very high strain occurred in many of these zones during and after the metamorphic peak so that early formed fold axes were rotated towards the stretching d

calculated mineral equilibria in the pelite system kfmash k 2 o feo mgo al 2 o 3 sio 2 h 2 o

granodiorites of the south mountain batholith nova scotia canada derived by partial melting of avalonia granulite rocks beneath the meguma terrane implications for the heat source of the late devonian granites of the northern appalachians abstract the late devonian south mountain batholith smb of nova scotia is the largest batholith of the northern appalachians the peraluminous granitic rocks range from biotite granodiorite to leucogranite samples collected from a drill core of the scrag lake granodioritic pluton of the western smb are chemically homogeneous from the surface to a depth of 1425 m the homogeneous composition implies that the granodiorite was derived from a relatively homogeneous source and that country rock assimilation was not an important source for the parental magma equilibrium partial melt modeling of underlying sub meguma granulite rocks indicates that they are the primary source rocks of the granodiorites we suggest that mantle derived magmas intruded the lower crust and induce large scale melting of the granulite basement rocks to produce the granodiorites fractional crystallization of the granodiorites plus assimilation of meguma supergroup metasediments likely produces the silica rich rocks of the smb the cause of mantle melting is uncertain however it may be related to the transitioning of the northern appalachians from a position above the deep mantle pacific large low shear velocity province llsvp to a higher shear velocity region of the mantle

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

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

late devonian carboniferous detachment faulting and extensional tectonics in western cape breton island nova scotia canada abstract shallow dipping detachment faults have played a key role in the evolution of the late devonian to carboniferous maritimes basin of western cape breton island the faults are responsible for large scale post orogenic crustal thinning and denudation of mid crustal levels tournaisian and westphalian clastic sedimentation can be related to detachment faulting along the margaree shear zone msz and the ainslie detachment ad respectively the msz consists of thick shallow dipping retrogressive mylonite overprinted by cataclastic horizons brittle detachment faults and chloritic breccia the shear zone crosscuts and transports low grade late devonian bimodal volcanic rocks and redbeds of the fisset brook formation in its hanging wall towards the west and juxtaposes them against exhumed medium to high grade metamorphic rocks and basement in its footwall locally the mylonite is 200 700 m thick and outcrops along strike from north to south for approximately 60 km tournaisian coarse clastic units and debris flow deposits of the horton group unconformably overlie ductile mylonite of the msz due to incision of brittle faults into the msz regional transgression and marine flooding of the extensional complex and exhumed units are marked by the thick visean carbonate and evaporite deposits of the windsor group the carbonates reflect a relatively quiescent tectonic regime and widespread subsidence was likely due to the cessation of extension related thermally induced buoyancy in a tectonically thinned crust the ainslie detachment nucleated as a regional flat lying fault along the carbonate evaporite contact at the top of the macumber formation forming calc mylonite near the base of the windsor group significant stratigraphic omissions in the windsor group above the detachment provide clear evidence of an extensional regime during faulting clastic deposits of the westphalian cumberland group are bounded by the detachment and sedimentation is related to listric normal faults which cut down section towards the west southwest the documentation of detachment faults has widespread implications for the interpretation of the post orogenic evolution of the northern appalachians an extensional regime can now be recognized deep reflection seismic data are interpreted in light of the new findings and can be related to late devonian carboniferous basin formation

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

an 40ar 39ar study of the cape breton highlands nova scotia thermal histories and tectonic implications forty new 40ar 39ar age spectra on micas and amphiboles from both granitic and metamorphic rocks show that two geologically distinct terranes in the cape breton highlands nova scotia have had contrasting thermal histories some plutons in the bras d or terrane in the southeastern highlands apparently cooled through the hornblende or muscovite closure temperature immediately following precambrian to cambrian intrusion other rock units in this terrane particularly in the west have been variably overprinted by a silurian tectonothermal event probably associated with juxtaposition of the bras d or terrane with the aspy terrane to the northwest gneisses at kellys mountain in the southeastern bras d or terrane apparently were not overprinted by this event argon data from the aspy terrane suggest that silurian deposition deformation and metamorphism were followed by rapid cooling through hornblende and biotite closure temperatures in the middle devonian this probably resulted from uplift and exhumati

the record of changing hematite and goethite accumulation over the last 22 ma on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy

u pb zircon titanite and monazite ages in the bras d or and aspy terranes of cape breton island nova scotia implications for igneous and metamorphic history new u pb ages from zircon titanite or monazite separates from 12 units in the aspy and bras d or terranes nova scotia range from late precambrian to devonian and generally support the interpretation that the 2 terranes had differing histories until juxtaposition in the devonian five plutons of dioritic tonalitic and granodioritic compositions in the northern bras d or terrane yielded zircon ages between 575 maximum and 556 4 m y younger titanite ages of 548 2 and 521 2 m y from two of these plutons may indicate younger metamorphism previously undocumented early ordovician plutonism 493 2 ma zircon and metamorphism 496 5 ma titanite also occurred in the bras d or terrane in the aspy terrane a zircon age of 433 7 4 m y was obtained for a rhyolite unit in the upper part of a widespread metavolcanic metasedimentary sequence which together with higher grade probably correlative units is characteristic of the terrane the age is interpreted to indicate that most metamorphic rocks in the terrane are ordovician to early silurian in age in contrast to precambrian ages in the bras d or terrane devonian plutonism was widespread in the aspy terrane whereas devonian plutonism in the bras d or terrane appears restricted to the vicinity of the boundary with the aspy terrane zircon titanite or monazite ages from 4 plutonic and orthogneissic units in the aspy terrane and in the bras d or terrane adjacent to the terrane boundary range from 403 3 to 375 5 4 m y

40ar 39ar muscovite dates from the nappe region of southwestern norway dating extensional deformation in the scandinavian caledonides abstract the caledonian thrust nappes and basal decollement zone above the baltic shield record penetrative caledonian deformation related to ese directed nappe transport and subsequent wnw directed ductile shearing during extensional collapse of the orogen muscovite within proterozoic quartzite conglomerates in the lower bergsdalen nappe that record only ese vergent caledonian deformation display internally concordant 40ar 39ar age spectra which yield plateau ages of 403 ma and 398 ma similar plateau ages 402 and 399 ma were obtained from muscovite from mica schists which record additional penetrative wnw directed shearing suggesting that muscovite intracrystalline argon systems did not cool below appropriate closure temperatures until during or after extensional wnw vergent movements quartz microfabrics indicate that temperatures were higher than those required for argon retention in muscovite until the end of the wnw directed nappe translation extension and that lower temperatures were maintained during subsequent movements along w and nw dipping extensional ductile shear zones the 40ar 39ar muscovite ages are therefore interpreted to post date the extensional wnw directed shearing along the decollement zone and closely date the initiation of w and nw dipping extensional shear zones when compared to the age of contractional deformation the results confirm that extension followed orogenic contraction very shortly after the main scandian orogenic phase

upper paleozoic mafic and intermediate volcanic rocks of the mount pleasant caldera associated with the sn w deposit in southwestern new brunswick canada petrogenesis and metallogenic implications abstract upper paleozoic 365 ma mafic and intermediate volcanic rocks of the piskahegan group constitute a subordinate part of the mount pleasant caldera which is associated with a significant polymetallic deposit tungsten molybdenum bismuth zones 33 mt ore with 0 21 w 0 1 mo and 0 08 bi and tin indium zones 4 8 mt with 0 82 sn and 129 g t in in southwestern new brunswick canada the epicontinental caldera complex formed during the opening of the late paleozoic maritimes basin in the northern appalachians the mafic and intermediate rocks make up two compositionally distinct associations the first association includes evolved rift related continental tholeiitic basalts and the second association comprises calc alkaline andesites although both associations were emplaced penecontemporaneously the basalts have low mg 0 34 0 40 smooth chondrite normalized ree patterns with la yb n 5 6 primitive mantle normalized trace element patterns without noticeable negative nb ta anomalies and their nd t ranges from 2 5 to 2 2 the basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of 70 90 km the calc alkaline andesites of the second association have chondrite normalized ree patterns that are more fractionated with la yb n 7 8 5 but without significant negative eu anomalies compared to the basaltic rocks they have lower nd t values ranging from 0 5 to 1 9 and their mantle normalized trace element plots show negative nb ta anomalies the nd t values display negative correlations with indicators of crustal contamination such as th la th nb and sio2 the andesitic rocks are interpreted to have formed by assimilation fractional crystallization processes which resulted in the contamination of a precursor basaltic magma with crustal material the parent basaltic magma for both suites underwent a different evolution the tholeiitic basalts experienced shallow seated fractional crystallization and evolved along a tholeiitic trend of early iron enrichment non oxic conditions the contaminated magma of the second association followed a calc alkaline fractionation trend of no iron enrichment oxidizing conditions characterized by a high ph2o and po2 environment at the mid crust levels the piskahegan group which is associated with an important polymetallic mineral deposit differs from the numerous non mineralized rift related volcanic suites of the regional upper devonian to lower carboniferous successions in the maritimes basin by the presence of a significant amount of coeval calc alkaline andesite which may be an indicator of potential mineralization

u pb and 40ar 39ar mineral ages from cape north northern cape breton island implications for accretion of the avalon composite terrane isotopic studies have been used to determine protolith and tectonothermal ages in rocks of the cape north and money point groups and two plutons that form part of the avalon composite terrane colourless euhedral zircon crystals from low grade metarhyolite in the money point group record a concordant u pb age of 427 5 4 ma which is interpreted to date the time of extrusion this provides a maximum age of middle silurian for polyphase deformation and concomitant greenschist amphibolite facies metamorphism that affected the cape north area in the eastern half of a major sinistral positive flower structure monazite from the cape north granite intruded during peak metamorphic conditions yielded nearly concordant data with a 207pb 235u age of 414 3 ma this dates the time of crystallization of the cape north granite metamorphic hornblende from the cape north and money point groups records variably discordant 40ar 39ar age spectra that define plateau and or isotope correlation ages of ca 380 390

chronology of devonian to early carboniferous rifting and igneous activity in southern magdalen basin based on u pb zircon dating fifteen u pb zircon radiometric age determinations have been made on igneous rocks of middle devonian to early carboniferous age from the southern margin of the magdalen basin in cape breton island and northern mainland nova scotia volcanic rocks interbed with early rift basin sedimentary rocks with some palynological biostratigraphy dated intrusive rocks cut these sedimentary units our biostratigraphically constrained ages are in close agreement with the current devonian time scale combined with previously published data the age determinations show that igneous activity occurred in four pulses middle devonian 390 385 ma early late devonian 375 370 ma latest devonian to early tournaisian 365 354 ma and late tournaisian to early visean ca 339 ma middle devonian 385 389 ma volcanic rocks are confined to the guysborough group the fisset brook formation basalt and minor rhyolite in the type area and elsewhere in cape breton island and northern mainland nova scotia is late devonian c

tectonic setting and regional correlation of ordovician silurian rocks of the aspy terrane cape breton island nova scotia interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of ordovician to silurian age are characteristic of the aspy terrane of northwestern cape breton island these rocks were affected by medium to high grade metamorphism and were intruded by synkinematic granitoid orthogneisses during late silurian to early devonian times they were intruded by posttectonic devonian granitic plutons and experienced rapid devonian decompression and cooling the chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic arc setting the volcanic rocks of the aspy terrane differ from many other silurian and silurian devonian successions in atlantic canada which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within plate settings and are somewhat younger than the aspy terrane sequences aspy terrane units are most similar to ordovician silurian volcanic and metamorphic units in southwestern newfoundland incl

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

pluton emplacement by wall rock thrusting hanging wall translation and extensional collapse latest devonian plutons of the cobequid fault zone nova scotia canada

geological correlations between cape breton island and newfoundland northern appalachian orogen geological correlations between cape breton island and newfoundland are apparent both in surface geology and at deeper crustal levels based on similarities in sm nd isotopic signatures the mira terrane of southeastern cape breton island is part of the avalon terrane sensu stricto and is composed of neoproterozoic volcanic sedimentary plutonic belts and overlying cambrian rocks directly comparable to those in the western part of the newfoundland avalon terrane the bras d or terrane is also mainly of neoproterozoic age but shows lithological and isotopic contrasts with the mira terrane small areas of similar neoproterozoic rocks occur in southern newfoundland and to the north as inliers in the exploits terrane the bras d or terrane and similar rocks in newfoundland are interpreted to represent a peri gondwanan terrane where rocks of the gander terrane were later formed hence this area is part of the central mobile belt and distinct from avalon terrane sensu stricto the aspy terrane is a complex area

crustal thickness under the gulf of st lawrence northern appalachians from gravity and deep seismic data we have determined crustal thickness in the gulf of st lawrence an area that corresponds to an offset of the main northern appalachians units a complete bouguer anomaly was calculated from recent depth to basement compilations and sediment densities from well data the moho surface was obtained by inverting the bouguer anomaly assuming a single density contrast at depth and using an average depth provided by deep reflection seismic data the resulting crustal model shows a moho depth of 42 44 km beneath the grenville craton north of the appalachian deformation front south of this front the depth to moho displays a pronounced thinning of the crust beneath the carboniferous magdalen basin this is in striking contrast to the deep seismic data which give a moho depth of about 43 km the modelling of the bouguer anomaly in the magdalen basin taking into account the seismic reflection and refraction data reconciles these different results and suggests that a 43 km deep moho beneath the basin is as

the ainslie detachment a regional flat lying extensional fault in the carboniferous evaporitic maritimes basin of nova scotia canada the ainslie detachment occurs near the base of the carboniferous windsor group forming a regional flat lying extensional fault distributed across 10 000 km 2 new mapping has delineated the structure through southwestern cape breton island and into central nova scotia shearing is concentrated at the top of the basal macumber limestone along its contact with overlying evaporites and younger allochthonous units the highly contrasting rheologies of the formations created an anisotropic zone of weakness which acted as an upper crustal stress guide stratigraphically controlling the trajectory of the detachment through the basin the detachment is characterized by an approximately 3 10 m thick calc mylonite zone with an intense planar fabric featuring alternating very fine grained shear planes and coarser annealed layers coarser layers are boudinaged into pinch and swell structures locally producing segmented augen highly strained intraclasts ooids and peloids recrystallized carbonate boudins and carbonate vein segments are included in the calc mylonite as semirigid inclusions and rotated porphyroclasts thick zones of fault breccia straddle portions of the detachment and overprint the mylonite demonstrating an evolution to brittle conditions during progressive shear listric faults in the hanging wall of the detachment feature a ramp and flat geometry with an upper detachment occurring along the upper contact of the windsor group with the overlying namurian mabou group locally up to 2 km of the stratigraphic succession has been removed with faults cutting downsection in a westerly direction producing rollover in the hanging wall

reply to comment on tectonic burial thrust emplacement and extensional exhumation of the cabot nappe in the appalachian hinterland of cape breton island canada

tectono stratigraphic terranes in cape breton island nova scotia implications for the configuration of the northern appalachian orogen cape breton island is divided into four terranes on the basis of contrasts in pre carboniferous geology the blair river complex in the north is an exposure of north american grenvillian basement analogous to the humber zone basement in newfoundland ordovician to devonian metavolcanic metasedimentary gneissic and granitic rocks of the aspy terrane are correlative with parts of the gander terrane of newfoundland and new brunswick the bras d9or terrane characterized by low pressure gneisses a carbonate clastic platform sequence and late precambrian early cambrian plutons may be correlative with units previously included in the gander terrane in southern newfoundland and the avalon terrane in southern new brunswick the mira terrane in southeastern cape breton island including late precambrian to early cambrian volcanic and sedimentary sequences and fossiliferous cambrian ordovician units is clearly part of the avalon terrane therefore with the exception of the dunnage terrane which is not represented in cape breton island the terranes of newfoundland continue through cape breton island they are offset to the northwest to the mainland part of the appalachian orogen in new brunswick

the role of dextral transpressional faulting in the evolution of an early carboniferous mafic felsic plutonic and volcanic complex cobequid highlands nova scotia canada abstract the wentworth plutonic complex consisting of gabbro and granite was emplaced in the earliest carboniferous in the cobequid shear zone of the northern appalachians the plutonic complex is coeval with a 5 km thick pile of volcanic rocks early alkalic a type granite correlates with thick felsic pyroclastics and minor basalt which are overlain by 1 5 km thick basalts that correlate with a large gabbro pluton that is intruded in turn by late granites the basalt and gabbro are fe rich tholeiites the geochemistry of the late granites suggests that they formed by differentiation of a granodioritic magma resulting from assimilation of early granite by the gabbroic magma the wentworth plutonic complex lies on the north side of the dextral rockland brook fault near the western tip of wedge shaped basement block of the avalon terrane field observations of mesoscopic structures and map contacts show that the plutonic bodies at all structural levels are related to transpressive strike slip faults dykes parallel to the mylonitic foliation in the rockland brook fault zone and at the contacts between igneous phases suggest that the plutons developed largely through dyke to pluton construction the plutonism was initiated by dyking related to major faults under transpression that was partitioned into shear zone bounded blocks while the sinking of those blocks finally provided the space for mafic magma emplacement dyking was active over at least a 10 ma time period the overall location of plutonism in the cobequid shear zone appears related to its position at the intersection of the shear zone bounding the southwestern margin of the magdalen basin and the e w transpressional contact of the avalon and meguma terranes magmatism enabled thermomechanical softening of the crust and the vertical and lateral extrusion of the wedge shaped basement blocks whose movement controlled the localisation of the voluminous magmatic activity

low angle faulting in strike slip dominated settings seismic evidence from the maritimes basin canada abstract the maritimes basin is an upper paleozoic sedimentary basin centered in the gulf of st lawrence canada early phases of basin formation included the development of partly connected sub basins bounded by high angle faults in an overall strike slip setting interpretation of reprocessed seismic reflection data indicates that a low angle detachment contributed to the formation of a highly asymmetric sub basin this detachment was rotated toward a lower angle and succeeded by high angle faults that sole into the detachment or cut it this model bears similarities to other highly extended terranes and appears to be applicable to strike slip and or transtensional settings

deposition of a saline giant in the mississippian windsor group nova scotia and the nascent late paleozoic ice age abstract saline giants are vast marine evaporite deposits that currently have no modern analogues and remain one of the most enigmatic of chemical sedimentary rocks the mississippian windsor group ca 345 ma maritimes basin atlantic canada is a saline giant that consists of two evaporite rich sedimentary sequences that are subdivided into five subzones sequence 1 is composed almost entirely of thick halite belonging to subzone a osagean sequence 2 is in unconformable contact and comprised of stacked carbonate evaporite peritidal cycles of subzones b through e meramecian subzone b the focus of research herein documents the transition from wholly evaporitic to open marine conditions and thus preserves an exceptional window into the processes forming saline giants lithofacies stacking patterns in subzone b reveal that higher order fluctuations in relative sea level produced nine stacked parasequences interpreted to reflect high frequency glacioeustatic oscillations during the onset of the late paleozoic ice age each parasequence reflects progradation of intertidal and sabkha sediments over subtidal carbonate and evaporite deposits dissimilarities in cycle composition between sub basins imply the development of contrasting brine chemistries from differing recharge rates with the open ocean what the windsor group shows is that evaporite type is ostensibly linked to the amplitude and frequency of sea level rise and fall during deposition true saline giants like the basinwide evaporites of sequence 1 apparently require low amplitude long frequency changes in sea level to promote the development of stable brine pools that are only periodically recharged with seawater by contrast the high amplitude short frequency glacioeustatic variability in sea level that controlled the accumulation of peritidal evaporites in subzone b produce smaller subeconomic deposits with more complex facies relationships

evidence for extension at the willimantic dome connecticut implications for the late paleozoic tectonic evolution of the new england appalachians

exhumation of high pressure pelitic schist lake murray spillway south carolina evidence for crustal extension during alleghanian strike slip faulting

tectonic deformation and magmatism along the southern flank of the maritimes basin the northeastern cobequid highlands nova scotia distributed crustal scale faulting in the cobequid highlands in the middle devonian to carboniferous resulted from the oblique convergence of the meguma and avalon terranes in the northeastern cobequid highlands seismic reflection profiles show neoproterozoic and lower paleozoic rocks together with enigmatic foliated rocks overlying the early carboniferous fountain lake group the foliated rocks form the hanging wall of a north vergent thrust fault their protolith is inferred from petrography and geochemistry to be principally neoproterozoic rhyodacitic tuff and late paleozoic hypabyssal intrusions the age of thrusting is stratigraphically constrained to the late tournaisian mid visean and sericite from mylonite yielded a tournaisian k ar age of 352 8 ma the thrusting occurs at the base of a tectonic escape sheet and resulted from a restraining bend in the rockland brook master fault farther west where the rockland brook fault trends almost east west tournaisian extensional features include

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

textural and rb sr isotopic evidence for late paleozoic mylonitization within the honey hill fault zone southeastern connecticut a petrographic and rb sr isotopic study of rocks within and near the honey hill fault zone places important constraints on its history of movement rb sr apparent ages for micas and plagioclase from these rocks have been reset and range from permian to triassic considerably younger than the minimum stratigraphic age ordovician of the rocks studied or of acadian devonian regional metamorphism permian rb sr ages of dynamically recrystallized muscovite date the development of mylonite fabric an older age is precluded by the excellent preservation of unrecovered quartz which indicates that these rocks did not experience temperatures high enough to anneal quartz or thermally reset rb sr isotopic systems in muscovite since the time of mylonitization metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist lower amphibolite grade conditions during permian to triassic time collectively these results indicate that the honey hill fault zone was active during the late paleozoic and that ductile deformation and metamorphism associated with the alleghanian orogeny extend well into southern connecticut an alleghanian age for mylonitization within the honey hill fault zone suggests it should be considered as a possible site for the major late paleozoic strike slip displacementsmore inferred from paleomagnetic studies for parts of coastal new england and maritime canada less

early carboniferous extension in east avalonia 350 my record of lithospheric memory abstract despite reactivations during variscan and alpine orogenies and the opening of the northern atlantic avalonia is one of the few regions where the initial mid paleozoic basin structure is still recognisable largely intact and well studied its kinematics and dynamics remain however largely unknown in particular in view of the successive late paleozoic to recent evolution of the basin consequently the importance of the mid palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies in this paper we reassess the importance of mid palaeozoic tectonics on subsequent sedimentary basin evolution of north western europe to this end we analyse the dynamics of early variscan extension in avalonia based on the integration and re evaluation of available geophysical and geological data from lithosphere to basin scales based on a revised crustal map of the thor suture zone we present a new paleo tectonic reconstruction and tectonic scenario for the devonian carboniferous rifting these findings are key for a better understanding of long lived tectonic segmentation and post rifting deformation phases our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the north sea central graben were created in the early carboniferous consequently the main basement structuration of northwest europe was completed before the variscan orogeny and successive post variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups incorporation of the paleozoic structural grain allows for a consistent tectonic framework for the mesozoic contributing to fundamental understanding of basin evolution from our tectonic framework analysis avalonia therefore stands out as a fine example of long lived lithosphere memory spanning over 350 my of structural control in geodynamic evolution

geochemical evolution of earliest carboniferous continental tholeiitic basalts along a crustal scale shear zone southwestern maritimes basin eastern canada abstract continental tholeiites were extruded locally within the extensional wrench maritimes basin from about 375 to 330 ma late devonian early carboniferous basalts of the early carboniferous diamond brook formation are up to 1 5 km thick and overlie a succession of predominantly felsic volcanic rocks reaching several kilometres in thickness the volcanic rocks and co genetic plutons occur along a crustal scale strike slip fault that facilitated the transport of relatively primitive magma resulting in basalts with high mg number ni and cr end 4 and relatively low tio2 v y and zr fractional crystallization of plagioclase and lesser clinopyroxene in the absence of iron oxide fractionation resulted in repetitive extrusion cycles hundreds of metres in thickness that show an upward increase in plagioclase phenocrysts or megacrysts and in tio2 and other high field strength elements hfses rare andesites are interpreted as products of partial melting of underplated gabbro the relatively primitive basalts resemble low ti basalts found in other continental flood basalt provinces and have trace element and isotopic characteristics that have been ascribed in the literature either to partial melting of or contamination of asthenospheric melts by subcontinental lithospheric mantle in the maritimes basin similar continental tholeiites were extruded intermittently over a 45 ma period high feot 12 normalised to 8 mgo suggests high potential temperature in the source mantle presumably within a mantle plume the youngest eruption products geochemically and isotopically resemble himu oib plume activity may have gradually migrated eastward from late devonian to permian from the maritimes basin through scotland to norway and north germany

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

contrasting metamorphic terranes near cheticamp cape breton highlands nova scotia two contrasting metamorphic terranes can be recognized in northwestern cape breton island one terrane pleasant bay complex consists of biotite gneiss and quartzite with minor calc silicate lenses that were metamorphosed in late precambrian time about 550 ma and were subsequently intruded by silurian salic and mafic plutons that were in turn deformed and intruded by granite in devonian time the other terrane jumping brook complex consists of volcanogenic and sedimentary schists of probable silurian age that were metamorphosed in devonian time p t estimates indicate that the older parts of the pleasant bay complex were metamorphosed at about 790 c and 7 kbar 1 kbar 100 mpa at low to moderate water fugacities during a major intrusive episode the jumping brook complex exhibits a single progressive metamorphic sequence now disrupted by faulting p t conditions during this devonian 370 390 ma metamorphism varied from greenschist 300 c at 3 kbar to amphibolite 650 c at 4 kbar facies me

microstructure metamorphism and tectonics of the western cape breton highlands nova scotia microstructural and petrological data from the jumping brook metamorphic suite western cape breton highlands suggest that a single episode of syntectonic prograde metamorphism followed by uplift cooling and associated retrogression affected these rocks during mid palaeozoic times microstructures indicative of progressive crenulation foliation development can be traced from low grade chlorite zone through high grade kyanite zone rocks allowing a clear sequence of porphyroblast growth to be established metamorphic reactions and p t calculations suggest metamorphic conditions of 700 750 c at 8 10 kbar were achieved in kyanite zone rocks although a complete p t t path was not defined combined petrological and geochronological data can be used to constrain computed p t t models these models suggest that a component of post metamorphic tectonic exhumation is required to explain the observed times of cooling and uplift the microstructural and petrological data to not support the interpretation that the high grade rocks represent pre existing crystalline basement indeed the metamorphic history geochronology and computed tectonic models all point to a single short lived episode of silurian devonian volcanism intrusion convergence regional metamorphism and uplift probably resulting from collision tectonics at an irregular continental margin