structural setting and age of the partridge island block southern new brunswick canada a link to the cobequid highlands of northern mainland nova scotia the partridge island block is a newly identified tectonic element in the saint john area of southern new brunswick located south of and in faulted contact with proterozoic and cambrian rocks of the ganderian brookville and avalonian caledonia terranes it includes the lorneville group and tiner point complex the lorneville group consists of interbedded volcanic and sedimentary rocks subdivided into the taylors island formation west of saint john harbour and west beach formation east of saint john harbour a sample from thin rhyolite layers interbedded with basaltic flows of the taylors island formation at sheldon point yielded a late devonian early carboniferous u pb zircon age of 358 9 6 5 ma petrological similarities indicate that all of the basaltic rocks of the taylors island and west beach formations are of similar age and formed in a continental within plate tectonic setting west of saint john harbour basaltic and sedimentary rocks of the taylors island formation are increasingly deformed and mylonitic to the south and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the tiner point complex based on magnetic signatures the deformed rocks of the tiner point complex can be traced through partridge island to the eastern side of saint john harbour where together with the west beach formation they occupy a thrust sheet above a redbed sequence of the mid carboniferous balls lake formation the tiner point complex includes leucotonalite and aegirine bearing alkali feldspar granite with a type chemical affinity and early carboniferous u pb zircon ages of 353 6 5 7 and 346 4 0 7 ma respectively based on similarities in age petrological characteristics alteration iron oxide copper gold iocg type mineralization and deformation style the partridge island block is correlated with late devonian early carboniferous volcanic sedimentary plutonic rocks of the cobequid highlands in northern mainland nova scotia deformation was likely a result of dextral transpression along the cobequid chedabucto fault zone during juxtaposition of the meguma terrane

granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

the jeffers brook diorite granodiorite pluton style of emplacement and role of volatiles at various crustal levels in avalonian appinites canadian appalachians small appinite plutons ca 610 ma outcrop in the peri gondwanan avalon terrane of northern nova scotia with different structural levels exposed field mapping shows that the jeffers brook pluton is a laccolith emplaced along an upper crustal thrust zone likely in a dilational jog in a regional dextral strike slip system the oldest rocks are probably mafic sills which heated the area facilitating emplacement of intermediate magmas cross cutting relationships show that both mafic and intermediate magmas were supplied throughout the history of pluton emplacement the modal composition mineral chemistry and bulk chemistry of gabbro diorite tonalite granodiorite and granite have been studied in the main plutonic phases dykes and sills and mafic microgranular enclaves as with the type appinites in the scottish caledonides the pluton shows evidence of high water content the dominance of hornblende locally within pegmatitic texture vesicles and irregular felsic patches in enclaves and late aplite dykes analyzed mafic microgranular enclaves are geochemically similar to larger diorite bodies in the pluton tonalite granodiorite is distinct from the diorite in trace element geochemistry and radiogenic isotopes elsewhere to the east similar rocks of the same age form vertically sheeted complexes in major shear zones hornblende chemistry shows that they were emplaced at a deeper upper crustal level this implies that little of the observed geochemical variability in the jeffers brook pluton was developed within the pluton the general requirements to form appinites are proposed to be small magma volumes of subduction related magmas that reach the upper crust because of continual heating by mafic magmas moving through strike slip fault pathways and trapping of aqueous fluids rather than venting through volcanic activity

minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

strike slip tectonics and granite petrogenesis transpression is a process that thickens the crust and therefore in obliquely convergent orogens as in normally convergent orogens there is the potential to generate granitic melts individual transcurrent shear zones may not only control the ascent paths siting and emplacement mechanisms of plutons but they may also cause the genesis of the granitoids themselves two contrasting situations are examined in the hercynian shear zones of iberia thickening together with hydrous fluxing along shear zones created intracrustal wet melting of fertile gondwanan sediments to produce syntectonic granites in the northern part of the british caledonides the association of compositionally expanded granitoids with a major mantle component and transcurrent shear zones may be explained by melting of continental crust at the lower limits of crustal transpressional faults detaching into the moho

petrology chronology and sequence of vein systems systematic magmatic and hydrothermal history of a major intracontinental shear zone canadian appalachians abstract intra continental shear zones developed during continental collision may experience prolonged magmatism and mineralization the cobequid shear zone formed part of a ne sw trending orogen parallel shear system in the late devonian early carboniferous where syn tectonic granite gabbro plutons and volcanic rocks 4 km thick were progressively deformed in late carboniferous to permian alleghanian collision of africa with laurentia formed the e w trending minas fault zone reactivating parts of the cobequid shear zone the 50 ma history of hydrothermal mineralization following pluton emplacement is difficult to resolve from field relationships of veins but sem study of thin sections provides clear detail on the sequence of mineralization the general paragenesis is albite quartz chlorite monazite biotite calcite allanite pyrite fe carbonates fe oxides minor sulfides calcite and synchysite chronology was determined from literature reports and new u pb la icpms dating of monazite and allanite in veins vein mineralization was closely linked to magmatic events vein emplacement occurred preferentially during fault movement recognised from basin margin inversion as a result of fractures opening in the damage zone of master faults the sequence of mineralization from ca 355 ma riebeckite and albite veins to ca 327 305 ma siderite magnetite and sulfide mineralization resembles precambrian iron oxide copper gold iocg systems in the literature the abundant magmatic na halogens and co2 in veins and some magmatic bodies characteristic of iocg systems were derived from the deeply subducted rheic ocean slab with little terrigenous sediment regional extension of the magdalen basin caused asthenospheric upwelling and melting of the previously metasomatized sub continental lithospheric mantle crustal scale strike slip faulting facilitated the rise of magmas resulting in high heat flow driving an active hydrothermal system

temporal variation of titanite morphology and chemistry in a long lived shear zone the clarke head syenite in the minas fault zone nova scotia abstract the mineral chemistry of titanite has been studied in hydrothermally altered syenite preserved as blocks in a salt wall within a regional intracontinental shear zone the study focusses on the controls on temporal variation in rees zr nb u and th several generations of titanite are recognised on the basis of morphology chemistry and relationship to other secondary minerals magmatic euhedral to subhedral titanite has ti and zr contents characteristic of magmatic titanite in other studies but does not have a magmatic abundance of ree rather it is 102 104 times depleted in lree and only slightly depleted in hree the leaching of lree began during a regionally recognised phase of potassic alteration as amphibole and biotite in gabbro and diorite recrystallized along shear zones and released k ca and f later some 15 ma after emplacement the alkali feldspar in the syenite was largely altered to scapolite and analcime by interaction with adjacent halite and gypsum deposits titanite formed at that time from dissolution reprecipitation reactions in large rutile crystals is less depleted in lree as a result of the dominance of cl in hydrothermal waters following that event f dominated hydrothermal waters prevailed again resulting in more lree depletion in previously formed titanite and in neoformed hydrothermal titanite at that time there was also depletion in zr and u the trace elements in hydrothermal titanite are thus very informative on the hydrothermal history of the rocks a combination of morphology and trace element signature allows different hydrothermal stages to be distinguished

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

the gem lake shear zone cretaceous dextral transpression in the northern ritter range pendant eastern sierra nevada california the gem lake shear zone is a northwest striking steeply dipping dextral transpressional shear zone that provides the first direct evidence for dextral deformation in wall rock pendants in the central part of the sierra nevada batholith the gem lake shear zone is a minimum of 30 km in length and extends at least from the north end of the northern ritter range pendant to the southeast edge of the ritter range pendant the amount of displacement on the zone is uncertain but matching fault slivers of pennsylvanian marble in the northern ritter range pendant to similar exposures north of the mount morrison pendant suggests a minimum dextral offset of 20 km the gem lake shear zone was active in early late cretaceous time from before 91 ma the age of the syntectonic granodiorite of kuna crest to at least 80 ma 40ar 39ar age of syndeformational mica from the shear zone in the ritter range pendant deformation in the gem lake shear zone is characterized by combined dextral simple shear and subvertical stretching which are variably partitioned in anastomosing high strain zones in the shear zone at gem lake predominantly dextral deformation is indicated by porphyroclast asymmetries s c fabric and asymmetric crenulations a component of subvertical stretching is indicated by a moderately to steeply plunging stretching lineation in a segment of the shear zone at kuna crest a strongly developed stretching lineation indicates predominantly subvertical stretching with a lesser component of dextral strike slip the gem lake shear zone is considered to be part of a proposed regional system of shear zones in the eastern sierra nevada the sierra crest shear zone system this dextral transpressional system was active prior to and synchronous with intrusion of the late cretaceous sierra nevada batholiths deformation ceased shortly after pluton emplacement the sierra crest shear zone system includes possibly related shear zones as far north as saddlebag lake pendant and at least as far south as oak creek pendant and the owens valley indicating a possible strike length greater than 150 km

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

influence of relative sea level change and tidal inlet development on barrier spit stratigraphy sandy neck massachusetts abstract sandy neck is a 10 km long sheltered mesotidal barrier spit along the southeastern new england coast bordering cape cod bay its stratigraphy contains evidence of relative sea level rsl rise and tidal inlet development and enables reconstruction of accretion and progradation of this barrier through time core trench and ground penetrating radar gpr data show that the lower boundary of the uppermost eolian facies climbs about 9 m from the proximal to the distal part of the spit away from the mainland anchor point this change is thought to be related primarily to a comparable rise in rsl the same boundary also shows a shallowing trend in a seaward direction indicating net spit progradation through time the absence of inlet channel facies in the stratigraphy of the proxima part of the barrier spit in contrast to the presence of inlet facies in more distal parts of the spit indicates that some time elapsed after barrier initiation before an inlet thalweg developed in its earliest stages this thalweg was poorly defined wide and shallow but its characteristics changed as the barrier spit lengthened in the central part of sandy neck the assemblage of inlet channel facies becomes markedly thicker reflecting thalweg deepening in response to paleotopographic and substrate lithologic factors the stratigraphy of the distal part of the spit shows the effects of continued but more gradual inlet deepening that may be tied directly to increasing barrier length the process controlled stratigraphy presented here differs from current facies models because i accounts for temporal changes in coastal environmental processes and parameters it suggests a high preservation potential for proximal eolian facies in the spit sequence underneath a cover of fine grained and organic back barrier sediment once reliably dated the new stratigraphic data will help to improve the regional rsl curve for the southern cape cod bay area

the relationship between length and width of plutons within the crustal scale cobequid shear zone northern appalachians canada the lengths and widths have been measured for 69 component bodies of composite plutons along the cobequid shear zone plutons on major fault strands those with mylonite zones 0 1 km wide exhibit evidence of multiple intrusion of magma batches small plutons along short faults in stepover zones appear related to rapid emplacement of magma in bodies 1 5 4 km long by 0 1 2 km wide such small plutons show low enrichment in incompatible elements in older component bodies but increasing amounts in younger bodies as a result of progressive magma expulsion from crystal mush during crystallization and shear enhanced compaction in fault zones wider plutons generally occur along longer fault strands accommodating more strain and penetrating deeper into the crust and show enrichment in incompatible elements the width of the mylonitic fault zone is about 15 of the width of these plutons the length to width ratio of component bodies and composite plutons varies between 2 and 11 the best fit line describing these data has a slope of 1 056 which implies scaling behavior between plutonism and tectonic processes scalar properties of plutonic bodies are similar to those of faults but scalar relationships observed in component bodies do not apply to composite plutons

structure and development of shell cheniers in essex southeast england investigated using high frequency ground penetrating radar abstract the stratigraphy and internal structure of contemporary shell cheniers on the southern essex coast england were investigated using a high frequency 900 mhz ground penetrating radar gpr system the cheniers lie on the seaward edge of laterally eroding saltmarshes at the junction with the tidal flats four main types of chenier are recognised each with a characteristic morphology and dynamic status migrated radar reflection profiles obtained from each of the chenier types achieved a sub decimetre vertical resolution ground truthing data demonstrate that the radar profiles accurately delineate the subsurface stratigraphy and sedimentary structure of the cheniers interpretation of the radar stratigraphy derived from the radar reflection profiles allows various deposits to be identified these have resulted from overwashing overtopping sedimentation across the whole of a seaward dipping beachface or berm ridge welding onto the upper beachface each chenier is characterised by a different spatial arrangement of these four basic depositional units the results from the gpr surveys support the hypothesis that each of the chenier types represents a distinct phase in the development of these contemporary coastal landforms however a simple model involving a linear progression through chenier types 1 4 with time appears inappropriate instead two main evolutionary pathways are proposed with the sequence of development being principally controlled by the nature of the cheniers longer term sediment budgets

transpressional shearing and strike slip partitioning in the late cretaceous sierra nevada magmatic arc california the rosy finch shear zone rfsz represents an example of synmagmatic strike slip tectonics in the east central sierra nevada and provides information on transpressional tectonics within magmatic arcs the rfsz 1 4 km wide and 80 km long is contained in late cretaceous granitoids 92 83 ma of the mono pass intrusive suite dextral strike slip deformation is indicated by a continuous band of orthogneiss mylonitic and cataclastic deformation characterized by subvertical foliations with subhorizontal lineations the style of dextral shearing in the rosy finch shear varies along strike from wide zones of ductile deformation in the youngest plutons to narrow zones of cataclastic deformation in the older plutons deformation of the youngest granitoids is synmagmatic as constrained by both field observations and isotopic studies dextral shearing occurs concurrently in contemporaneous intrusive suites to the north and south tuolumne and mount whitney suggesting strike slip movement along the axis of active plutonism field studies also suggest that contraction across the arc acted concurrently with strike slip movement consistent with a transpressional setting for the late cretaceous sierra nevada magmatic arc comparison of the field data with strain models of oblique plate convergence suggests that the rfsz is a preserved ductile signature of transcurrent motion of strike slip partitioning within a transpressional orogenic system recent plate reconstructions indicate a switch from sinistral to dextral oblique convergence at 95 ma which is consistent with the timing constraints on the dextral movement on the rfsz

the west indian road pit central nova scotia key to the early cretaceous chaswood formation the west indian road pit is the only large outcrop in nova scotia of the chaswood formation the terrestrial equivalent of the offshore missisauga and logan canyon formations it provides outcrop information on sedimentology gravel petrology and structures for a formation that is otherwise known from a few small overgrown pits and from boreholes the chaswood formation in the pit is 60 m thick and consists principally of sorted sand and gravel with three thinner clay units successions of sedimentary structures indicate deposition from a coarse bedload river flowing to the east southeast gravel consists principally of vein quartz quartz arenite and subarkose together with minor igneous lithologies that can be matched to sources in the cobequid highlands to the north quartz arenite and subarkose appear derived from carboniferous horton group single crystal 40 ar 39 ar dates of detrital muscovite are a little older than the muscovite ages for the south mountain batholith interpreted to mean that the muscovite is second cycle from the horton group which records the earliest unroofing of the batholith the chaswood formation accumulated during progressive tectonic deformation along nne trending strike slip faults in basement rocks resulting in syn sedimentary faulting and local unconformities sedimentation kept pace with the creation of accommodation unrelated younger deformation folded the chaswood formation at the pit into an east west trending syncline the early cretaceous paleogeography of the maritime provinces is interpreted to have consisted of fault bound horsts shedding coarse detritus surrounded by an interconnected series of basins that accumulated fluvial sands and gravels and overbank muds with well developed paleosols

early carboniferous deformation and mineralization in the cobequid shear zone nova scotia an 40ar 39ar geochronology study latest devonian to early carboniferous igneous rocks along the cobequid shear zone of central nova scotia record a complex history of intrusion volcanism deformation and hydrothermal alteration twenty new 40ar 39ar age determinations have been made on biotite and hornblende separates from rocks that constrain these events the mafic plutons of the cobequid shear zone are synchronous with the previously dated granitoid plutons 363 355 4 ma with the exception of the younger folly lake gabbro 355 350 4 ma high temperature shear deformation continued along the cobequid shear zone during this entire period of pluton emplacement several samples from mylonitic and hydrothermally altered rocks with dates ca 340 ma indicate renewed movement along the cobequid shear zone at this time accompanied by minor magmatism younger 330 320 ma ages reflect final movement along the rockland brook fault resulting in mid namurian uplift of the cobequid highlands following this regional alleghenian event ther

evolution of late palaeozoic shearing in the cobequid highlands constraints on the fragmentation of the appalachian orogen in nova scotia along intra continental shear zones

late pleistocene barrier island development reconstructed from genetic classification and timing of erosional surfaces paleo tokyo bay japan abstract formative processes of a retrogradational barrier island system and associated transgressive erosional surfaces are reconstructed from the upper pleistocene kioroshi formation developed in paleo tokyo bay japan the kioroshi formation provides high quality sedimentary records of a preserved barrier island system three volcanic ash beds intercalated in the formation provide a high resolution chronostratigraphic framework the barrier island system of the kioroshi formation developed in a glacio eustatically forced sea level cycle during oxygen isotope stages 6 to 5e in the early stage of the transgression paleo tokyo bay was non barred and was exposed to the pacific ocean affected by open ocean wave processes shoreface erosion in such a non barred environment developed a wave ravinement surface rs1 rs1 overlies incised valley fill deposits formed in the earliest stage of the transgression and is overlain by shoreface deposits that are further overlain by embayment deposits such as lagoonal and flood tidal delta deposits formed during succeeding barrier development during the later stage of the same transgression associated with the formation and landward migration of the barrier chain tidal currents in tidal inlet and flood tidal deltas became active and a tidal ravinement surface trs was formed trs is developed on the base of tidal inlet and flood tidal delta deposits furthermore shoreface erosion on the open ocean side of the barrier chain eroded underlying embayment deposits and formed a secondary wave ravinement surface rs2 a chronostratigraphic surface in embayment deposits defined by a volcanic ash bed intersects trs and is eroded by rs2 this relationship together with associated facies architecture indicates diachroneity of the formation of these marine erosional surfaces associated with the retrogradational barrier island system

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

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

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

structure of late variscan millevaches leucogranite massif in the french massif central ams and gravity modelling results in the limousin area variscan leucogranitic plutons are spatially associated with normal faults and major strike slip shear zones that are a continuation of the south armorican shear zone our study focuses on the large n s trending millevaches granitic massif massif central france and intends to highlight through gravity modelling structural and anisotropy of magnetic susceptibility ams the massif structure at depth and to discuss the mode of emplacement of granites within a strike slip tectonic context the mica subfabric suggests that the magnetic foliations display a general nw se sub horizontal pattern on both sides of the n s pradines dextral wrench fault zone that deforms the core of the massif on 5 km width the magnetic lineation trend exhibits a sigmoidal pattern n s in the pradines fault zone and nw se on both sides of it which are consistent with a dextral wrench component the horizontal magnetic foliations and lineations are consistent with the thin granite laccolith model there is no significant imprint of the extensional variscan belt collapse on the internal fabric of millevaches granites than the tectonic dextral transcurrent movement prevailing in this area

the transition from magmatic to high temperature solid state deformation implications from the mount stuart batholith washington criteria for syntectonic emplacement of plutons are commonly ambiguous the strongest single criterion is probably the preservation of a continuous transition from submagmatic to high temperature solidstate deformation this transition is not commonly documented an exception is the mount stuart batholith which displays a variety of syntectonic structures within its sheared northeastern margin including the following 1 s c fabrics that range from submagmatic to high temperature solid state 2 solid state foliation and lineation defined by amphibolite facies assemblages that overprint and are parallel to magmatic foliation and lineation 3 folds of magmatic and solid state foliation that have hinge lines parallel to magmatic and solid state lineation and to equivalent structures in wall rocks 4 dikes that were folded and boudinaged over a wide range of rheological states with boudin necks locally filled by tonalite 5 pegmatite dikes and mineralized joints that are sub perpendicular to magmatic and solid state lineation and 6 submagmatic and high temperature solidstate ductile shear zones we suggest that many plutons emplaced during regional deformation do not preserve evidence for syntectonic deformation because of the transitory nature of the submagmatic state and the obscuring effects of postemplacement deformation syntectonic features are most likely preserved in plutons cooled at slow to moderate rates or in plutons deformed at high strain rates during emplacement the optimum conditions for preservation may occur in plutons emplaced along fault zones in the mid crust such as the mount stuart batholith and in intrusions at deeper levels that were rapidly exhumed and or intruded during the waning stages of regional deformation

record of late mississippian tectonics in the new perce group visean of eastern gaspesie quebec visean clastic units and structures at the northwest margin of the upper paleozoic maritimes basin provide information on tectonic events that are only poorly recorded in more central parts of the basin these continental units are time equivalent to marine sediments of the windsor group of nova scotia they are herein assigned to the new perce group which includes the la coulee and bonaventure formations as well as a new unit the cap d espoir for mation the latter unit unconformably underlies the bonaventure formation in a small but thick sub basin of the ristigouche basin in eastern quebec it is characterized by a succession of sandstone and mudstone rhythmites that contrast with the coarse alluvial fan deposits of the overlying bonaventure formation the cap d espoir formation was sourced from a broad area of subdued topography occupied by the visean la coulee formation and underlying units erosional remnants of the la coulee formation are unconformably overlain by the bonaventure formation in marginal parts of the ristigouche basin whereas these units are separated by the cap d espoir formation in more central areas of the basin the la coulee and cap d espoir formations underwent tilting and erosion during a normal faulting event that preceded deposition of the fault controlled bonaventure formation this series of events is interpreted to represent different steps in the reactivation of a pre carboniferous dextral strike slip system in response to northwest southeast compression during the visean in gaspesie resume des unites clastiques viseennes et leurs structures intrinseques dans la marge nord ouest du bassin des mari times paleozoique superieur illustrent des evenements tectoniques qui ne sont que pauvrement enregistres dans les parties plus centrales du bassin ces unites continentales sont chronologiquement equivalentes aux sediments marins du groupe de windsor en nouvelle ecosse elles sont ici assignees au nouveau groupe de perce lequel inclut les forma tions de la coulee et de bonaventure ainsi qu une nouvelle unite la formation de cap d espoir cette derniere est re couverte en discordance par la formation de bonaventure a l interieur d un petit mais relativement epais sous bassin du bassin de ristigouche dans l est du quebec elle est caracterisee par une succession de depots rythmiques de gres et de mudstone qui contraste avec les depots grossiers de cones alluviaux de la formation de bonaventure sus jacente la formation de cap d espoir est le produit de l erosion d une region source de grande etendue et a faible gradient topo graphique laquelle etait occupee par la formation de la coulee et les unites qui lui sont sous jacentes les reliques d erosion de la formation de la coulee sont recouvertes de facon discordante par la formation de bonaventure dans les parties marginales du bassin de ristigouche alors que ces unites sont separees par la formation de cap d espoir dans les parties plus centrales du bassin les formations de la coulee et de cap d espoir ont ete basculees et partiel lement erodees a l interieur d un evenement de fracturation ayant precede le depot de la formation de bonaventure dont les facies ont ete controles par des escarpements de failles cette serie d evenements est consideree comme etant le resultat de differentes etapes dans la reactivation d un systeme de coulissage dextre pre carbonifere en reponse a des contraintes orientees nw se durant le viseen en gaspesie

geochemical variation of amphiboles in a type granites as an indicator of complex magmatic systems wentworth pluton nova scotia canada abstract the wentworth pluton is the most complex intrusion among a series of a type granitic plutons emplaced along an active shear zone in the cobequid highlands of nova scotia during the latest devonian earliest carboniferous this pluton consists of a type granites of different generations and a large gabbroic body among all late paleozoic plutons in the cobequid highlands only the wentworth granites contain both primary calcic edenite hornblende and sodic amphiboles arfvedsonite whole rock and mineral chemical data were examined along with estimated magmatic parameters such as temperature emplacement pressure oxygen fugacity and volatile contents in order to understand the geological factors responsible for this mineralogical variation the granites with calcic amphiboles show systematically lower e nd values magmatic temperatures and f in melt contents and appear geochemically less evolved compared to the granites with the sodic amphiboles all granites however appear geochemically homogeneous with limited evidence of fractionation specific chemical differences between these two types of granites indicate the presence of two coeval but distinct granitic systems in the wentworth pluton the granites with the calcic amphiboles were formed from a geochemically less evolved hydrous relatively calcic melt whereas the granites with sodic amphiboles were emplaced at structurally deeper levels and were derived from a relatively drier sodic melt which had a larger mantle component and was enriched in fluorine coexistence of these two magmas is indicated by the presence of interstitial sodic calcic amphiboles in a late granitic dyke this study provides evidence that in a type granites where fractional crystallization is limited extreme variation in the type of amphibole can be the result of a very complex magmatic history

magma assisted strain localization in an orogen parallel transcurrent shear zone of southern brazil in a lithospheric scale orogen parallel transcurrent shear zone of the pan african dom feliciano belt of southern brazil two successive generations of magmas an early calc alkaline and a late peraluminous have been emplaced during deformation microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions magmatic deformation is indicated by the coexistence of aligned k feldspar plagioclase micas and or tourmaline with undeformed quartz submagmatic deformation is characterized by strain features such as fractures lattice bending or replacement reactions affecting only the early crystallized phases high temperature solid state deformation is characterized by extensive grain boundary migration in quartz myrmekitic k feldspar replacement and dynamic recrystallization of both k feldspar and plagioclase decreasing temperature during solid state deformation is inferred from changes in quartz crystallographic fabrics decrease in grain size of recrystallized feldspars and lower ti amount in recrystallized biotites final low temperature deformation is characterized by feldspar replacement by micas the geochemical evolution of the synkinematic magmatism from calc alkaline metaluminous granodiorites with intermediate 87sr 86sr initial ratio to peraluminous granites with very high 87sr 86sr initial ratio suggests an early lower crustal source or a mixed mantle crustal source followed by a middle to upper crustal source for the melts shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle but whatever the process initiating partial melting lithospheric transcurrent shear zones may collect melt at different depths because they enhance the vertical permeability of the crust these zones may then act as heat conductors by advection promoting an upward propagation of partial melting in the crust synkinematic granitoids localize most if not all deformation in the studied shear zone the regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies consistently displaying similar plane and direction of flow argue for accommodation of large amounts of orogen parallel movement by viscous deformation of these magmas moreover activation of high temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and consequently contributed significantly to the localization of deformation finally the small extent of the low temperature deformation suggests that the strike slip deformation ended approximately synchronously with the final cooling of the peraluminous granites the evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone magma intrusion in an orogen scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust it triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments

petrochemistry and tectonic significance of carboniferous volcanic rocks in new brunswick carboniferous volcanic rocks from the new brunswick platform in the maritimes basin are divided into three age groups late tournaisian to early visean volcanic rocks are tholeiitic basalts and andesites that in southern new brunswick are inter bedded with abundant calc alkalic rhyolite late visean to namurian volcanic rocks consist of an interbedded sequence of alkalic basalts and trachyandesites late westphalian volcanic rocks change in composition up section from trachyte to peralkalic rhyolite all three age groups display petrochemical features indicative of an intraplate tectonic setting the volcanic geochemistry is consistent with the development of the maritimes basin either as a failed rift formed along the margin of a late paleozoic ocean or as a rhomb graben formed within a transcurrent zone the former model is preferred the change in basaltic composition from tholeiitic to alkalic apparently coincided with a decrease in rate of extension between the tournaisian and namurian local peral

stratigraphic significance of upper devonian and lower carboniferous miospores from the type area of the horton group nova scotia late devonian late famennian miospores have been found in the lowermost 7 3 m of the horton group on harding brook in the type area windsor subbasin nova scotia below tournaisian miospores of the emphanisporites rotatus indotriradites explanatus zone extending the age of the horton group in the type area down into the latest devonian shows that the lowest beds of the 1000 m thick group are coeval with latest devonian rocks elsewhere in the maritimes basin that have been excluded from the horton group by some authors evidence presented here favours the argument that late devonian rocks lithologically similar to the horton group deposited on the acadian unconformity should be included in that group miospore evidence indicates a minimum age of about 355 ma for exhumation of the northeastern part of the south mountain batholith

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

progressive deformation of a zone of magma transfer in a transpressional regime the variscan merens shear zone pyrenees france the ew striking variscan merens shear zone msz located on the southern border of the aston dome pyrenees corresponds to variously mylonitized gneisses and plutonic rocks that are studied using the anisotropy of magnetic susceptibility ams technique the plutonic rocks form ew striking bands with from south to north gabbro diorites quartz diorites and granodiorites the msz underwent a mylonitic deformation with an intensity progressively increasing from the mafic to the more differentiated rocks the foliations are ew to nw se striking and subvertical a first set of lineations shows a moderate wnw plunge with a dextral reverse kinematics more recent subvertical lineations correspond to an uplift of the northern compartment to the east the msz was cut by a n120 e striking late shear band separating the msz from the querigut pluton the different stages of mylonitization relate to late variscan dextral transpression this regime allowed the ascent of magmas along tension gashes in the middle crust we interpret the msz as a zone of magma transfer which fed a pluton now eroded that was similar to the querigut and millas plutons located to the east we propose a model of emplacement of these plutons by successive pulses of magmas along en echelon transfer zones similar to the msz

the age and significance of carboniferous plutons of the western cobequid highlands nova scotia a series of granite plutons with minor gabbro diorite phases outcrops immediately north of the cobequid fault in the western cobequid highlands nova scotia the plutons were cut by numerous dykes and parts of some plutons and some dykes subsequently underwent ductile deformation four rb sr whole rock k feldspar isochron dates ranging from 338 to 356 ma have been obtained from these plutons and the dykes that cut them the ages of these plutons are indistinguishable from an age of 341 ma obtained for the nearby fountain lake group volcanic rocks within estimated uncertainties measured carboniferous granite ages are uncommon in the appalachian orogen of eastern canada the geochemical character of these plutons indicates that they result from crustal extension this extension and the compression observed in the granites with ductile deformation are related to transcurrent motion between the avalon and meguma terranes along the minas fault zone preliminary rb sr whole rock data from poorly exposed pluto

sea level variation during the holocene deduced from the morphologic and stratigraphic evolution of morgan peninsula alabama u s a abstract recent gulf of mexico shoreline studies interpret middle to late holocene sea level as falling from a level above present elevation or stable at present elevation however the architecture of morgan peninsula alabama does not support this morgan peninsula is a beach ridge strandplain composed of two obliquely aligned holocene beach ridge sets ground penetrating radar profiles discriminate between parallel even to wavy reflectors of the eolian dune environment and the underlying seaward dipping complex sigmoidal oblique reflectors of the foreshore and upper shoreface environment the contact between foreshore and eolian facies in beach ridges can be used as a sea level indicator the average elevation of this contact in morgan peninsula rises throughout shoreline accretion which occurred throughout the last 5 4 ka suggesting that there was continual sea level rise during this time morgan peninsula is a useful modern analog to ancient shoreface shelf parasequences and demonstrates the significant internal complexities that can exist in these deposits erosional discontinuities imaged in the holocene foreshore upper shoreface environment are laterally continuous extend to elevations above mean sea level and correlate to beach ridges and the transition between beach ridge sets an increase in the wave regime or fluctuations in sediment supply appear to be likely mechanisms for forming erosional discontinuities below beach ridges the erosional surface separating beach ridge sets may have formed by increased storm activity and associated barrier breaching or a reconfiguration of the mobile bay tidal delta complex superimposed on a gradual rate of sea level rise this boundary is recognized by a change in beach ridge orientation at the surface and an increase in the aggradational component of shoreline accretion

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

microgranitic enclave shapes and magmatic strain histories constraints from drop deformation theory microgranitic mafic enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas these enclaves are often ellipsoidal or elongate in shape in order to constrain the conditions under which such enclaves were generated and deformed by their host pluton we apply drop deformation theory to model their distortion our model takes into account the change in viscosity of both the host and enclave with temperature composition and the amount of suspended solids in enclave host systems and it assumes that simple shear flow predominates in the plutonic system we focus on the deformational history of enclaves over the time period in which they remain liquid and are either more or less viscous than their granitic host we find that the most stable enclaves with respect to being broken up by their entraining flow are generally the most mafic enclaves those with silica contents near those of the host granite are highly unstable this is in reasonable accord with field observations of the abundance of enclaves of different chemistry most deformation of microgranitic enclaves is likely to occur at relatively high temperatures probably between 950 c and 1050 c and therefore the enclaves record magmatic strain of the host over only a limited temperature time range in the host s cooling history furthermore the observation of apparent deformation of these enclaves in a liquid regime coupled with our calculated dependences of enclave deformation on flow velocity implies that magmatic flow velocities are likely to be below 10 m yr in enclave bearing plutonic systems

variations in deformation fields during development of a large volume magmatic arc central sierra nevada california mid to late cretaceous plutons in the central sierra nevada magmatic arc show widely preserved magmatic foliation whereas regionally developed solid state foliation is absent relatively slow cooling of these plutons and expected strain rates 10 14 suggest that the plutons were emplaced in a neutral or weakly extensional deformation regime domains of solid state ductile shear of only slightly younger age than the plutons on the other hand indicate a contractional regime timing of pluton emplacement and movement on the shear zones have been constrained using pb u zircon and 40 ar 39 ar hornblende and biotite geochronology both plutons and ductile shear zones become younger toward the east the four more westerly shear zones which were active between ca 100 and 90 ma show steeply plunging stretching lineations whereas the most easterly and or youngest zones active between ca 88 and 78 ma show mostly oblique and or subhorizontal stretching lineations indicating a change in kinematics at ca 90 ma the above events define a complex deformation pattern in which strain regimes fluctuated in time and space between neutral or weak extensional and contractional we propose a tectonic model in which thenospheric mantle corner flow produced eddy pairs in the mantle corner that transmitted a neutral or weak extensional regime to the overlying crust and facilitated the movement of granitic magma to mid and upper levels probably as dikes via fractures slab flattening caused the neutral or weak extensional regime to move eastward away from the trench increased coupling between upper and lower plates induced by the slab flattening promoted contractional strain in the cooling plutons and domains of ductile shear formed in progressively younger plutons to the east the above events were accompanied by an oblique convergence vector between north america and farallon plates engebretson et al 1985 which imposed a relatively small component of right lateral shear onto the arc that increased with time we estimate that at ca 100 ma the convergence vector made an angle obl 20 to the arc normal and we suggest that around ca 90 ma obl passed through a critical value conceivably 20 oblcrit 30 at this juncture the component of right lateral shear became sufficiently large to induce significant arc parallel strike slip movement on the most easterly shear zones these kinematics continued as the dominant scheme possibly as late as ca 78 ma

crustal scale en echelon p shear tensional bridges a possible solution to the batholithic room problem the apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic are has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc parallel strike slip fault systems as an alternative hypothesis we propose that an en echelon p shear array provides a continuous batholith scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics in the sierra nevada california the late cretaceous granitoids of the cathedral range intrusive epoch are consistent with emplacement into bridges between p shears because 1 they are elongated oblique to the magmatic trend consistent with p shear orientation within a dextral system 2 they were all emplaced within 5 10 m y along a 300 km trend resulting in a displacement rate of 1 cm yr across the arc and 3 syn to late magmatic dextral shear zones bound and crosscut the plutons as in a p shear tensional bridge

numerical simulation of thermally induced gyres in lake biwa the formation process of three gyres in lake biwa as observed using an acoustic doppler current profiler is simulated using three different sgs models smagorinsky model dynamic mixed model dmm and mixed scaling formulation model msfm based on very large eddy simulation vles the driving force of gyre formation is assumed to be differential heating due to heat volume differences between the middle lake and shoreline areas this condition is created in the simulation by setting the initial temperature distribution in the lake based on field observation data the significant patterns of gyre formation are calculated both by dnm and msfm owing to the huge disproportion of horizontal and vertical grid spacing the isotropic subgrid scale sgs model such as the smagorinsky model does not perform well when using normal grid spacing according to the comparison between field observation data and numerical simulation it is concluded that the surface heat transfer process is one of the main driving forces for gyre formation in lake biwa copyright 2003 john wiley sons ltd

persistent mafic igneous activity in an a type granite pluton cobequid highlands nova scotia the west moose river pluton is one of a series of latest devonian early carboniferous plutons of granite and gabbro diorite in the cobequid highlands southern edge of avalon zone intrusion of minor gabbro preceded emplacement of the granite which is fractured and cut by later mafic dykes of which some predate and others postdate a namurian compressive deformation minor hybrid phases reflect mixing of mafic and felsic magmas which are also represented by basalt and rhyolite in the synchronous fountain lake group the mafic rocks are continental tholeiites reflecting regional early carboniferous extension later dykes are more fractionated with high p2o5 tio2 and other high field strength elements the dykes are pervasively altered probably by residual fluids from the granite hydrothermally circulated by the hot mafic rocks higher ga al hf and zn content in basalts than dykes suggests upward increase in halogen complexing in the mafic plumbing system late stage fluids concentrated k rb an

late neoproterozoic to carboniferous genesis of a type magmas in avalonia of northern nova scotia repeated partial melting of anhydrous lower crust in contrasting tectonic environments avalonian rocks in northern mainland nova scotia are characterized by voluminous 640 600 ma calc alkalic to tholeiitic mafic to felsic magmas produced in a volcanic arc however after the cessation of arc activity repeated episodes of felsic magmatism between ca 580 ma and 350 ma are dominated by a type geochemical characteristics sm nd isotopic data combined with zircon saturation temperature estimates indicate that these magmas were formed by high temperature 800 1050 c melting of the same anhydrous crustal source regional tectonic considerations indicate that a type felsic magmatism was produced 1 at 580 ma in a san andreas type strike slip setting 2 at 495 ma as avalonia rifted off gondwana 3 at 465 and 455 in an ensialic island arc environment and 4 at 360 350 ma during post collisional intra continental strike slip activity as avalonia was translated dextrally along the laurentian margin these results attest to the importance of crustal source rather than tectonic setting in the generation of these a type magmas and are an example of how additional insights are provided by comparing the geochemical and isotopic characteristics of igneous suites of different ages within the same terrane they also suggest that the shallow crustal rocks in northern mainland nova scotia were not significantly detached from their lower crustal source between ca 620 ma and 350 ma a time interval that includes the separation of avalonia from gondwana its drift and accretion to laurentia as well as post accretionary strike slip displacement

stoped blocks in plutons paleo plumb bobs viscometers or chronometers abstract stoped blocks potentially provide information about paleohorizontal during emplacement of plutons and about the timing of and viscosities and kinematics during magmatic fabric formation in the mount stuart batholith washington we have examined magmatic fabrics patterns around stoped blocks in tonalite located near the pluton roof and completed 1 1 scale three dimensional mapping of fabric patterns around stoped blocks in diorite located 1000 m below the roof in both settings no structural record of magma ascent early emplacement or settling of the blocks is preserved instead fabric formation largely post dates the settling and trapping of stoped blocks two dimensional finite difference thermal modeling and calculations of sinking rates support short

late devonian palinspastic reconstruction of the avalon meguma terrane boundary implications for terrane accretion and basin development in the appalachian orogen abstract a late devonian early carboniferous palinspastic reconstruction of atlantic canada restoring subsequent motion along the avalon meguma terrane boundary and other major faults facilitates re examination of the spatial distribution of important accretionary and post accretionary events in the northern appalachian orogen the reconstruction suggests a genetic relationship between 415 and 360 ma tectonothermal activity in both these terranes and the collision between laurentia and gondwana in a zone of anomalously intense shortening opposite the st lawrence promontory in the appalachian orogen erosional products of this collision are an order of magnitude greater than the thin ca 1 km veneer of latest devonian early carboniferous clastic rocks that were deposited in intermontane basins across the orogen this missing detritus may be found in the thick deposits of the catskill clastic wedge in the central appalachians

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

authigenesis of titania minerals and the mobility of ti new evidence from pro deltaic sandstones cretaceous scotian basin canada titania tio2 minerals are minor diagenetic phases in many sandstone shale successions but the conditions of ti mobility and titania authigenesis are poorly known here new modes of occurrence of authigenic titania minerals filling pores and replacing phytodetritus are documented from lower cretaceous prodeltaic sandstones in the offshore scotian basin of southeastern canada textural relationships suggest that titania minerals formed at the same time as kaolinite most commonly below lowstand sequence boundaries related to flux of meteoric water such authigenic titania is most abundant in thin bedded sandstones interbedded with thick prodeltaic mudstone in which fine grained detrital ti rich minerals are concentrated textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near surface eodiagenesis eogenetic titania is enriched in phosphorus 0 6 p2o5 and may co occur with authigenic fluorapatite and crandallite crystals such titania resulted from prolonged flow of meteoric water that dissolved p from apatite and feldspar thereby enhancing ti solubility in basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water the assumption that ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid probable mesodiagenetic titania has low p content suggesting that ti mobility under these conditions was facilitated by some other agent probably organic acids the results of this study illustrate that even in cases where titania minerals are volumetrically insignificant their microtextures and trace element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks

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

interglacial glacial climatic signatures preserved in a regressive coastal barrier southeastern australia abstract regressive barriers persisting in the landscape over interglacial glacial cycles are important repositories of paleoclimatic signatures such as past sea level and regional aridity the gippsland region of victoria contains a multi barrier system formed during past interglacial glacial cycles and the late holocene an extensive series of parallel foredune ridges forming the elongate inner barrier was sampled for luminescence dating with ages indicating deposition ca 125 000 108 000 years ago coinciding with the later phase of the last interglacial lig marine isotope stage mis 5e and the transition to mis 5d ground penetrating radar gpr imaged beach face reflectors within the lig barrier indicate that sea level was within 2 to 3 m of present level during mis 5e in this far field location significant reworking of the barrier system through blowout and parabolic dune activity occurred between 23 000 18 000 years ago corresponding to the last glacial maximum lgm with an estimated 160 000 000 m3 of coastal sediments eroded and redistributed the morphological changes to this coastal barrier over the most recent interglacial glacial cycle mis 5e to present also imply significant landscape instability during the lgm in southeastern australia and are further evidence for extension of the geographical range and intensity of aridity at this time

emplacement of the miocene west naxos pluton aegean sea greece a structural study synmagmatic and solid state structures within the naxos pluton and its rim may provide insight into the interplay between plutonism and regional deformation at upper crustal level within the hornblende biotite granite of western naxos synmagmatic foliations display two distinct patterns onion skin in the north and tangential to the rim in the south the two areas are separated by the ne trending glinadon fault deformed mafic enclaves in the pluton are prolate with their long axes parallel to the synmagmatic lineation in contrast phenocryst distribution analysis using the fry method defines an apparent oblate strain with a horizontal stretching lineation planar markers within the pluton progressively steepen through the vertical at the east pluton border several lines of evidence such as dykes intruding axial areas of rim parallel folds foliated or folded aplite veins folds and spaced cleavage in the mollase and inverted stratigraphy suggest pluton emplacement and deformation during transpressional deformation a northward divergent flow regime with magma spreading out mainly from the naxos fault and the deflection of both the synmagmatic foliation pattern and the flow lines at the glinadon fault suggest that the ne sw and n s trending faults were active during pluton formation in the south the pluton has grown by the expansion of dykes occupying p shear positions with respect with the naxos fault in the north a piecemeal block down drop complements this process and favours voluminous magma concentration during the late evolutionary stages of pluton construction the magma chamber was compartmentalized into ne trending sectors affected by block rotation in an anticlockwise manner understanding the role of faults in the emplacement of the naxos pluton is important for understanding emplacement of other plutons in the aegean sea region since most of them are controlled by n s ikaria pluton or ne tinos serifos and delos plutons trending faults

the mortagne granite pluton france emplaced by pull apart along a shear zone structural and gravimetric arguments and regional implication the emplacement mechanism and kinematics and the 3 d geometry of the variscan granite pluton of mortagne are interpreted using systematic measurements of the granite structure allied with micro structural observations from a detailed gravimetric study it is proposed that magma infilled a pull apart structure which formed along a jog of a northwest southeast trending sinistral zone of shear a second episode of shearing under a dextral regime and independent of emplacement was responsible for perigranitic tectonites these successive transcurrent opposite movements already documented for variscan times in western france are discussed concerning the age of the mortagne pluton 313 15 m y

alleghanian deformation in the eastern gaspe peninsula of quebec canada juxtaposition of the mississippian risti gouche and cannes de roches basins which are subbasins of the composite late paleozoic maritimes basin occurred through dextral movement along the north west striking percefault system in the east ern gaspepeninsula of quebec the north west striking faults are truncated by small north northwest striking dextral strike slip faults which probably developed as region al stress gradually rotated clockwise from north northwest south southeast to north east southwest this study provides the first evidence in eastern quebec for significant post acadian block displacement other than normal faulting and indicates that al leghanian deformation extended much far ther north than previously thought iden tification of these structures formed during the alleghanian orogeny but more than 1000 km away from areas of peak allegh anian metamorphism in the southeastern united states underlines the far reaching effects of continental collisions it also casts doubt on the age attribution of brittle strike slip faults elsewhere in the gaspe peninsula away from mississippian expo sures such brittle faults were previously associated with late stages of the acadian orogeny but could in fact be considerably younger

depositional controls on a hypertidal barrier spit system architecture and evolution pointe du banc spit north western france physical stratigraphy architecture and evolution of barrier systems in hypertidal environments tidal range above 6 m are understudied and depositional controls are poorly understood compared with wave dominated barrier systems and barrier spits in microtidal mesotidal and macrotidal settings based on vibracores ground penetrating radar radiocarbon and optically stimulated luminescence age data the formation and evolution of the hypertidal barrier system of pointe du banc north western france has been reconstructed the study shows that the barrier spit has a complex composite sedimentary architecture consisting of wave dominated and tide dominated sedimentary bodies a morpho sedimentary model is presented that demonstrates how barrier spit progradation resulting from littoral drift was the main manner of spit elongation whereas sediment convergence caused by landward migration of swash bars and seaward migration of tidal dunes caused the spit terminus to grow in height and width these results suggest that long term accretion rates varied considerably in response to changes in sediment supply variations in storminess together with the large scale topography of the coast controlled the sediment supply and thus the evolution of the barrier system during latest holocene despite architectural complexity hypertidal barrier systems preserve records of past climate changes

sea level rise and coastal marsh sustainability geological and ecological factors in the mississippi delta plain chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea level positions continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea level rise rslr rates of past accumulation estimated using dating techniques are then used to hindcast the rate of sea level rise in that area estimates of contemporary sea level rise rates are often derived from tide gauge records this approach allows identification of subdecadal variations in mean water level accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition the frequency and spacing of these events does not necessarily coincide with periods of increased local sea level in addition short term increases in sea level could result in marsh deterioration as soils become excessively waterlogged a conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the holocene has been developed for the mississippi delta plain mdp the survival of some marshes in this area despite high rates of subsidence indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea level rise

internal structure of a trough blowout determined from migrated ground penetrating radar profiles ground penetrating radar gpr was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits although analogous many of the data processing techniques routinely applied in seismic reflection are very rarely applied in gpr studies in this study a simple migration program was used that significantly enhanced the quality of gpr images from a large trough blowout at raven meols on the sefton coast northwest england these improvements aided subsequent data interpretation which was achieved through application of the principles of radar stratigraphy gpr shows the pre blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover subsequent to stabilization of these dunes a thin soil developed this dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout the internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition as derived from contemporary process studies reported in the literature instead the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high angle cross strata which often display a spatially variable radial dip pattern that is only very poorly or partially developed in addition a soil or other surface representing a significant hiatus in dune deposition is likely to underlie the blowout deposits the topography of which will show a clear relationship to the dip and orientation of the overlying cross strata

the relationship between ree y nb th minerals and the evolution of an a type granite wentworth pluton nova scotia the wentworth pluton in the eastern cobequid highlands consists principally of metaluminous to peralkaline a type granite 362 ma a large part of which was remelted by a major gabbro intrusion 357 ma magmatic minerals like allanite ce chevkinite ce zircon and hingganite y and post magmatic mineral phases such as ree bearing epidote samarskite y aeschynite y fersmite thorite like phases and hydroxylbastnasite ce were identified the presence of fluorine in the parental magma indicated by whole rock geochemical data and the presence of fluorite increased the solubility of monazite and xenotime and thus facilitated retainment of rare metals in the magmatic system fractionation of allanite ce and chevkinite ce led to a melt enriched in heavy rare earth elements hree from which hingganite y crystallized during late magmatic stages the remelting of the early granite led to fluorine and sulfur release in volatile phases which circulated with hydrothermal fluids thus mobilizing the ree and other rare metals reduction of fluorine activity during the late to post solidus crystallization resulted in the precipitation of hree and rare metals in samarskite y thereby enriching the residual hydrothermal fluids in light rare earth elements lree post magmatic lree minerals such as hydroxylbastnasite ce either replaced earlier minerals or precipitated from these hydrothermal fluids carbonate fluids involved in a late regional hydrothermal circulation event along the cobequid chedabucto fault 320 315 ma promoted ti mobility and the formation of tio 2 minerals and probably of aeschynite y this mineralogical diversity in addition to the complex geological history of the pluton provides a unique opportunity to correlate the formation of individual rare metal minerals to different stages of pluton evolution and thus provide an insight to the formation conditions of these minerals

the great tonalite sill emplacement into a contractional shear zone and implications for late cretaceous to early eocene tectonics in southeastern alaska and british columbia the late cretaceous to early tertiary great tonalite sill of southeast alaska and british columbia is a very long 1 000 km and thin 25 km orogen parallel composite batholith which lies between the insular superter rane including the alexander and wrangellia terranes and the intermontane superterrane including the stikine and cache creek terranes the batholith is delineated by many steep sheet like plutons which are dominated by northwest southeast striking concordant fabrics with steep lineations that formed during deformation in a country rock shear zone prior to the complete crystallization of the magmas deformation in this shear zone is dominated by northeast southwest directed contraction orthogonal to the orogenic strike associated with a component of northeast over southwest high angle shear the steep multiple dike like nature of the body and its emplacement during orogenic contraction imply that ascent and emplacement have been achieved by dike wedging mechanisms along the deep reaching shear zone the remarkable narrowness of the great tonalite sill is probably the result of melting at the base of a very localized zone of thickened crust produced by the associated narrow contractional shear zone extending along the orogen length such a shear zone of late cretaceous to early tertiary age lying along 800 km of the possible boundary between the insular and intermontane superterranes implies that it may represent the actual boundary between them if this hypothesis is correct it implies that the large scale tectonic regime during emplacement of the great tonalite sill was predominantly orthogonal and not obliquely dextral as has been indicated from paleomagnetic data

the geomorphology and evolution of a large barrier spit farewell spit new zealand farewell spit is a 25 km long barrier spit that marks the end of a littoral drift system almost 1000 km in length that runs along south island new zealand the spit is composed of barchan dunes over 20 m high sand sheets over 1 km wide and vegetated linear dunes analysis of aerial photography indicates a rapid colonization of the spit by vegetation which has expanded in area by 75 since 1950 vegetation colonization preferentially occurs on the southern side of the spit with its northern margin characterized by barchan dunes which migrate at rates of up to 64 m yr sand sourced from longshore drift appears to be the primary source of beach sediment which is then transported into the dune field by the persistent westerly winds of the roaring 40s while there has been significant dune roll over on the surface of the spit its overall area has remained much the same for the past 54 years occasional cyclone events cause erosion but this is balanced by aeolian sediment transport it would appear that extension of the subaerial portion of the spit is related to the development of shells banks at its downdrift end which are periodically welded to the main spit by dune extension farewell spit therefore provides an ideal example of a barrier environment where longshore sediment supply and aeolian transport dominates geomorphic evolution this differentiates the study site from other barrier environments where overwash or tidal inlet development often characterizes recent landform evolution copyright 2010 john wiley sons ltd

relationships between syn tectonic granite fabrics and regional pttd paths an example from the gander avalon boundary of ne newfoundland abstract syn tectonic granitic plutons and their host rocks not only provide a potential wealth of information about the timing and nature of regional kinematics but also record information about thermal conditions successive syn tectonic plutons emplaced into the gander zone of ne newfoundland preserve fabric overprinting formed during cooling to regional ambient thermal conditions ambient conditions have been approximated for each pluton by careful analysis of microstructures and consideration of potential cooling histories and have illustrated regional exhumation during a tectonic reversal from silurian devonian sinistral transpression to devonian dextral transpression because the time period of emplacement is relatively short by comparison to orogenic events typically by more than an order of magnitude individual plutons may record a snap shot of the regional history by combining information from a number of plutons emplaced sequentially during a period of regional orogenesis a picture may be built up defining time temperature deformation ttd paths such information may compliment regional metamorphic pt studies in helping to establish orogenic pttd paths

the ground penetrating radar facies and architecture of a paleo spit from huangqihai lake north china implications for genesis and evolution abstract a paleo spit is identified from huangqihai lake in north china and proposed as a classic example for investigating the influence of lake level changes and storms on the construction of these bodies ground penetrating radar gpr data collected with a 400 mhz antenna are used together with sedimentologic observations from trenches to define the facies and sedimentary architecture of the spit six types of radar surface both depositional and erosional were identified radar facies bounded by radar surfaces were interpreted from reflection characteristics and termination patterns eight different radar facies were identified in the profiles and we assign these to three groups inclined horizontal and irregular the whole barrier spit system comprises spit bar and salt marsh units distinguished using gpr profiles linked radar and sedimentologic data are used to develop a model for spit bar evolution the spit was formed during a cycle of lake level change spanning 200 years the characteristics of the different building blocks washover lobes sheets and swash laminated sands within the spit bar unit and their depositional regimes are defined and interpreted based on the known lake evolution during the holocene a relative chronological framework is presented two storms in the 1880s and 1960s may have played an important role in building the spit bar

fractured latest devonian granites of the west moose river pluton along the cobequid shear zone nova scotia implications for regional mineralization latest devonian 365 358 ma a type granites in the cobequid highlands host complex sequences of rare earth element ree and other hydrothermal minerals the west moose river pluton is the only pluton truncated and brittly deformed by the mid carboniferous 327 ma strike slip minas fault zone during the alleghanian orogeny fractures in the granite provide a record of several deformational and hydrothermal events with distinct mineral assemblages early sodic alteration produced albitisation of feldspar and riebeckite and tourmaline veins the 18 o of albite and albitised granite 5 6 is similar to other regional granites suggesting a mantle source of albitising fluids nearby halite deposits are younger and thus not a source of na early chlorite veins were followed by potassic alteration and hydrothermal biotite and by diabase and lamprophyre dyke emplacement euhedral magnetite occupies new cross cutting fractures and vugs correlated with regional iron oxide carbonate sulphide

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

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

optical dating of dune sand for the study of sea level change a new widely applicable method to obtain well constrained relative sea level records presented here relies on optical dating of inorganic coastal landforms and sediments eighteen optical ages of basal dune sand from a barrier in massachusetts united states indicate that local relative sea level rose 8 m during the past 5 5 k y a sea level curve drawn from these optical ages shows good agreement with independent evidence from salt marsh peat sampled behind the barrier demonstrating the reliability of the method optical dating will be particularly useful in analyzing coastal records that contain too few organic indicators to allow high resolution 14 c based analyses

middle to late paleozoic acadian orogeny in the northern appalachians a laramide style plume modified orogeny the laramide orogeny of the western united states is proposed as a modern analogue for the silurian devonian acadian orogeny and subsequent diachronous voluminous short lived magmatism and basin formation in the northern appalachians shallowing of the benioff zone accounts for several enigmatic features associated with plate convergence in the northern appalachians including 1 wenlockian ludlovian termination of arc related magmatism in the avalon terrane followed by a period of relative magmatic quiescence from 395 to 380 ma and 2 diachronous migration of the acadian deformation front from ca 415 ma in the southeast to ca 370 ma in the northwest extending more than 600 km into the continental interior the flattening of the subduction zone is attributed to overriding of a plume by the convergent margin which may explain 1 the abrupt termination of magmatic quiescence by 380 370 ma and voluminous felsic magmatism and production of plume related lamprophyres in the southeast meguma terrane as the plume thermally eroded the oceanic lithosphere causing melting of the lower crust 2 late devonian regional high temperature low pressure metamorphism in the meguma terrane related to the thermal anomalies above a plume 3 synchronous devonian emplacement of meguma gold deposits and associated siderophile elements possibly derived from fluid circulation above an ascending plume 4 rapid late devonian uplift and erosion of as much as 10 km due to dynamic uplift over a plume 5 migration of magmatism to the north avalon terrane cobequid highlands so that plume related carboniferous magmatism occurred in and around the carboniferous permian maritimes basin 6 the high density lens at the base of the crust beneath the maritimes basin the product of plume derived underplated mafic rocks and 7 a subsidence mechanism for formation of the maritimes basin by cooling of a decapitated plume head

systematic mineralogical diversity in a type granitic intrusions control of magmatic source and geological processes the origin and causes of mineralogical diversity of a type granites are debated the series of a type granite plutons with distinct mineralogical differences emplaced along an upper paleozoic crustal scale shear zone in the cobequid highlands nova scotia provide an opportunity to examine the origin of different a type plutons in a similar tectonic setting based on the ferromagnesian minerals present the plutons are classified into sodic granites with sodic amphibole calcic granites with calcic amphibole and biotite granites sodic and calcic granites occur exclusively in complex intrusions with subequal amounts of gabbro in the eastern shear zone whereas plutons in the western shear zone with lesser gabbro are solely biotite granites trace elements and radiogenic isotopes show that the three granite types have different sources intensive parameters including temperature pressure and water in melt contents were estimated from mineralogical and geochemical data modeling of these geochemical data suggests that the biotite and calcic granites were derived by 20 40 partial melting of intracrustal feldspathic rocks whereas the sodic granites are extreme fractionates 90 of coeval mafic magma we propose that supply of upper paleozoic mafic magma probably related to regional extension and decompression melting beneath the magdalen basin created a deep crustal hot zone in the eastern cobequid highlands and extreme fractionation of underplated mafic sills produced the sodic granites heat transfer from crystallizing mafic magma induced partial melting of the surrounding crust creating batches of biotite and calcic granitic melts in different depths fractionated and crustally derived melts segregated along crustal scale faults constructing the complex plutons in the east melting of the crust was further facilitated by the release of water from the crustal rocks upon heating in the eastern shear zone water was released predominantly by magmatic rocks and in lesser amounts compared to the west where neoproterozoic sedimentary and volcaniclastic rocks are more abundant the volatile rich granitic melts in the western part of the shear zone were crystallized rapidly stabilizing only biotite this study demonstrates that the mineralogical variations in a type granites arise from rather similar magma compositions but they are important petrogenetic indicators of varying sources specific magmatic processes and emplacement conditions

synkinematic granite emplacement in a shear zone the pleasant hills pluton canadian appalachians the 361 356 ma late devonian pleasant hills pluton comprises a series of sheets of mafic felsic and hybrid intermediate plutonic rocks that were emplaced along a positive flower structure associated with the crustal scale cobequid fault zone this dextral strike slip fault zone forms the boundary of the meguma and avalon terranes the sequence of emplacement is inferred from crosscutting structures radiometric dating shows that the pluton was crystallized within a few million years gabbroic magma was probably derived from partial melting of the mantle beneath the extensional magdalen basin and successive batches of mafic magma were progressively richer in h 2 o ti zr and nb felsic magmas were probably derived by partial melting of the lower crust small batches of felsic magma show differing trace element evolution that reflects changes in magma temperature and type of volatiles younger magmas being generally richer in high field strength elements and fluorine rapakivi textured granite is common heat transfer and mass transfer along the fault zone resulted in thermal softening and lubrication of all branches of the flower structure so that there was repeated magma flow through each branch the presence of magma controlled the localization of strain which is expressed as synmagmatic deformational structures and deformation continued under solid state conditions to produce mylonitic fabrics each branch of the flower structure acted as a pathway for many magma batches and only small volumes of magma reached the highest structural levels the pluton was emplaced by progressive widening of and magma emplacement along branches of the flower structure as a result of country rock translation this translation involved both lateral and upward movement of blocks within the cobequid fault zone dextral slip is recognized on the southern margin of the escaping block and reverse oblique sinistral slip on its northern margin the pleasant hills pluton shows progressive creation of space for magma along branches of the flower structure and gradual expansion of the pluton from a series of dike like bodies to a larger composite pluton through the emplacement of numerous small geochemically distinct magma batches

the emplacement of the rieserferner pluton eastern alps tyrol constraints from field observations magnetic fabrics and microstructures abstract within the alpine chain several tertiary intrusions e g bergell adamello intruded along the periadriatic lineament this study attempts to show how the rieserferner pluton vedrette di ries is related to the defereggen antholz vals dav line for a survey of the fabric pattern over the pluton the anisotropy of the magnetic susceptibility ams was determined on nearly 170 samples low bulk susceptibilities of k vol 6 si and a total degree of anisotropy p

deep seismic reflection data from the bay of fundy and gulf of maine tectonic implications for the northern appalachians three deep penetration seismic reflection profiles were collected off southwest nova scotia to determine the crustal structure and geometry beneath the avalon and meguma zones of the appalachian orogen in canada onshore geological features have been traced seawards using new gravity and magnetic anomaly maps the seismic data can also be correlated with the previous united states geological survey profile in the central gulf of maine two seismically distinct lower crustal blocks are identified the avalon and sable lower crustal blocks separated by a major north dipping reflection zone that cuts the entire crust the recognition of the sable block adds a fourth block to the three already identified in the canadian appalachians the sable block is overlain by the meguma zone the avalon zone overlies at least the northern part of the avalon lower crustal block although offshore extension of geological features is not unequivocal it appears that a north dipping reflection zone southwest of nova scotia m

observations from the floor of a granitoid pluton inferences on the driving force of final emplacement an east west profile across the tilted bergell pluton exposes a 10 km thick interval in terms of crustal depth consequently the floor as well as the root and side of the main intrusive body of the pluton crop out at the surface and a tentative three dimensional geometry is constructed at the highest crustal level the geometry and deformation features at the margin of the pluton indicate ballooning whereas the folded floor of the main intrusive body indicates synmagmatic shortening related to regional deformation these contrasting features are best explained by shortening of the base of the pluton which caused an expansion at a higher crustal level final emplacement of the pluton into higher crustal levels was therefore not driven primarily by buoyancy but rather by regional deformation within deeper levels of the crust

facies architecture and depositional processes of the holocene recent accretionary forced regressive skagen spit system denmark spit systems are seldom recognized in the pre quaternary sedimentary record compared to their common occurrence along present day coasts and in quaternary successions this lack of recognition may partly be due to the lack of widely accepted depositional models describing the facies characteristics of spit systems and their subaqueous platforms in particular the skagen spit system is a large active system that began to form 7150 yr bp and from 5500 bp to recent times it has prograded 4 m year 1 and accumulated 3 5 109 m3 of sand the spit system provides a unique opportunity for establishing a well constrained depositional model because uplift and erosion have made large windows into the preserved facies while active spit forming processes can be examined at the young prograding end of the same system the depositional model presented here thus builds on excellent outcrops surface morphology a well defined palaeogeography and detailed c14 age control supplemented with observations from continuous well cores and profiles obtained by ground penetrating radar and transient electromagnetic surveys the factors that have governed the development of the spit system such as relative sea level change wave and current climate tidal range sediment transport and depositional rates are also well understood the sedimentary facies of the spit system are grouped into four principal units consisting from below of thick storm sand beds dune and bar trough deposits beach deposits and peat beds these four units form a coarsening and shallowing upward sand dominated succession up to 32 m thick which overlies offshore silt with a transition zone and is topped by a diastem overlain by young aeolian dune sand the sedimentary structures and depositional processes are described in detail and integrated into a depositional model which is compared to other spit systems and linear shoreface models