the character and reactivation history of the southern extension of the seismically active clarendon linden fault system western new york state abstract integration of 11 types of data sets enabled us to determine the location character and fault history of the southern extension of the clarendon linden fault system clf in southwestern new york state the data sets utilized include detailed stratigraphic and fracture measurements at more than 1000 sites soil gas anomalies seismic reflection profiles well logs and lineaments on air photos topographic maps landsat and slar images the seismically active clf consists of as many as 10 parallel segmented faults across the fault system the fault segments are truncated by nw striking cross strike discontinuities csds the faults of the clf and intersecting csds form fault blocks that have semi independent subsidence and uplift histories east dipping reflectors in the precambrian basement indicate the southward continuation of thrusts of the intra grenvillian elzevir frontenac boundary zone these thrusts were reactivated during iapetan rifting as normal listric growth faults in ordovician black river to trenton time the southern clf segments experienced a second phase of growth fault activity with faults displaying a cumulative stratigraphic throw of as much as 170 m thrusting on the same east dipping precambrian reflectors typified the clf in taconic post trenton times detailed comparisons among the fault segments show that the fault activity in silurian and devonian times generally alternated between the western and central main faults in late devonian time the fault motion reversed from down on the east to down on the west about the time the appalachian basin axis passed across the clf in its westward migration the deep precambrian faults of the clf were thus reactivated as the appalachian basin developed in acadian times finally the clf thrust fault imaged on seismic line clf 1 offsets all bedrock devonian units thus significant motion occurred along this fault during late acadian or more likely alleghanian time

silurian deformation in eastern notre dame bay newfoundland eastern notre dame bay newfoundland is divided into five fault bounded terranes they are from north to south the twillingate terrane the chanceport terrane the new world island terrane the dildo run terrane and the port albert terrane the new world island terrane is characterized by fault repeated sequences of middle ordovician to early silurian turbiditic sandstones sansom formation and conglomerates goldson formation the chanceport terrane has a lower volcanic unit and an upper sedimentary unit consisting of red and green siltstones shales overlain by turdiditic sandstones this sequence is structurally overlain by a mafic and felsic volcanic unit the clastic sedimentary rocks of the chanceport new world island and port albert terranes best record the silurian deformation in the area silurian deformation is divided into two deformation events an early silurian d1 thrusting event and a late silurian d2 dextral ductile faulting event the early silurian joey s cove melange constrains th

deformation processes in an accretionary prism a study from the torlesse terrane of new zealand abstract the style of deformation observed in rocks of the torlesse pahau terrane exposed in the aorangi range of the north island records accretion of thick trench fill by offscraping at the toe of a growing accretionary prism during the early cretaceous the relatively coherent nature of the aorangi range rocks enables detailed study of the deformation processes produced by offscraping and subsequently within the prism and many of the structures observed in these rocks are consistent with those described from both modern accreting margins and other ancient accretionary terranes overprinting relationships indicate three phases of folding and multiple faulting events early deformation involved large scale sheath like folding oblique to the overall trend of the margin and development of an anastomosing axial planar cleavage folding of the sediments promoted dewatering the subsequent disruption of strata by shearing parallel to bedding and low angle to bedding faulting records the transition to more brittle responses to the deformation the most widespread folding phase d 2 produced numerous upright typically isoclinal folds with local development of an axial planar s 2 cleavage in macroscopic and some mesascopic fold hinges the variable plunge of the fold axes to the nne and ssw within the axial surface indicates progressive rotation of the fold axes after formation mesozoic strike slip faulting most likely produced the open e w trending folds and warps of the third folding phase d 3 in bedding already rotated to moderate dips faults which overprint the mesozoic deformation were formed in response to renewed subduction along the eastern coast of the north island during the cenozoic

dynamics of coupled diffusive and decompressive bubble growth in magmatic systems bubble growth in an ascending parcel of magma is controlled both by diffusion of oversaturated volatiles and decompression as the magma rises we have developed a numerical model which explores the processes involved in water exsolution from basaltic and rhyolitic melts rising at a constant rate from magma chamber depths of 4 and 1 km while the model does not attempt to simulate natural eruptions it sheds light on the processes which control eruptive behavior under various conditions ascent rates are defined such that a constant rate of decompression dp dt is maintained a variety of initial ascent rates are considered in the model from 1 m s to 100 m s for basalts and from a few centimeters per second to 10 m s for rhyolite at the base of the conduit the model results indicate that for any reasonable ascent rate basaltic melt degasses at a rate sufficient to keep the dissolved volatile concentration at equilibrium with the decreasing ambient pressure rhyolitic melt reaches the surface at equilibrium if its ascent rate is less than 1 m s but it can erupt with high oversaturation at greater ascent rates the latter may lead to explosive eruptions if the ascent rate of rhyolite is 10 m s or more then melt barely degasses at all in the conduit and erupts with the highest oversaturation possible for the case of slow magma rise bubble growth is limited by decompression for the case of rapid magma rise bubble growth is limited by diffusion the results of our simple model do not accurately simulate natural volcanic eruptions but suggest that subsequent more complex models may be able to simulate eruptions using the insights regarding diffusive and decompressive bubble growth processes explored in this study numerical modeling of volcanic degassing may eventually lead to better prediction of eruption timing energetics and hazards of active volcanoes

fossil evidence for fault derived stratigraphic repetition in the northeastern newfoundland appalachians two types of bedding parallel faults are common in the dunnage zone of eastern notre dame bay they are i early thrusts which together with bedding were rotated by later folding into steep attitudes and ii postfolding transcurrent faults both types of faults occur at all scales and give rise to repetitions in the stratigraphic sequence a compilation of the ages of various rock types based on fossil evidence indicates a relatively simple stratigraphy for the dunnage zone this interpretation appears to be at variance with many reported stratigraphic successions until repetitions by bedding parallel faulting are taken into account examples are given of sequences in which the repetition of various rock types dated by means of fossils is due to bedding parallel faulting we believe that the simple lithostratigraphy is a reliable aid for structural interpretations in areas where fossils are scarce or absent

silurian deformation in eastern notre dame bay newfoundland discussion i southeast thrusting and ocean closure across the exploits subzone resembles that of pickering et al 1988 but lafrance and williams assume deposition in a single marine basin on the gondwanan side of iapetus and postdepositional thrusting i rather than deposition in several basins on the laurentian side i of iapetus and syndepositional thrusting arnott et al 1985 pickering et al 1988 we wish to comment on the terrane analysis offered by them and to point out a number of errors i 1 in their presentation of the five terranes defined in the paper two twillingate and chanceport are known ordovician suspect terranes the new world island and port albert terranes while suspect to north america during the early and middle ordovician share the same late ordovician to early silurian rocks and stratigraphy virtually all previous workers have also recognized late ordovician early silurian sedimentologic links between the new world island terrane exploits subzone and the twillingate chanceport terranes notre dame subzone indicating middle ordovician accretion to north america kay 1967 1969 helwig and sarpi 1969 nelson and casey 1979 nelson 1981 arnott 1983a 19836 arnott et al 1985 pickering et al 1988 williams et al 1988 and others these data imply that any silurian basin s in this region must have been on the laurentian margin of iapetus rather than the gondwanan margin the authors dildo run terrane coextensive with the dunnage mclange is interpreted as being faulted against the new world island terrane following kay 1970 and van der pluijm 1986 however this contact has also been interpreted as stratigraphic home 1969 hibbard and williams 1979 the authors present no evidence that any of their terranes were distinctive in the silurian time period of chief interest to their paper according to the authors the twillingate and dunnage terranes were affected by the earlier event however they conclude that these terranes evolved on opposite sides of an ordovician ocean hence there is no reason to suppose that pre silurian events can be correlated in any meaningful sense

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

a nd and o isotope study of the ree rich peralkaline strange lake granite implications for mesoproterozoic a type magmatism in the core zone ne canada it is well established that a type granites enriched in high field strength elements such as zr nb and the ree form in anorogenic tectonic settings the sources of these elements and the processes controlling their unusual enrichment however are still debated they are addressed here using neodymium and oxygen isotope analyses of samples from the 1 24 ga strange lake pluton in the paleoproterozoic core zone of quebec labrador an a type granitic body characterized by hyper enrichment in the ree zr and nb age corrected end values for bulk rock samples and sodic amphiboles mainly arfvedsonite from the pluton range from 0 6 to 5 7 and 0 3 to 5 3 respectively the end values for the napeu kainiut quartz monzonite which hosts the pluton range from 4 8 to 8 1 the 147sm 144nd ratios of the suite and the host quartz monzonite range from 0 0967 to 0 1659 large variations that can be explained by in situ fractionation of early lree minerals strange lake and late hydrothermal hree remobilization oxygen isotope analyses of quartz of both strange lake and the host yielded 18o values between 8 2 and 9 1 which are considerably higher than the mantle value of 5 7 0 2 bulk rock oxygen isotope analyses of biotite gneisses in the vicinity of the strange lake pluton yielded 18o values of 6 3 8 6 and 9 6 the negative end values and positive 18o values of the strange lake and napeu kainiut samples indicate that both magmas experienced considerable crustal contamination the extent of this contamination was estimated assuming that the contaminants were sedimentary derived rocks from the underlying archean mistinibi para gneiss complex which is characterized by low end and high 18o values mixing of 5 15 of a gneiss having an end value of 15 and a 18o value of 11 with a moderately enriched mantle source end 0 9 18o 6 3 would produce values similar to those obtained for the strange lake granites based on analogies between the nain plutonic suite and the gardar alkaline igneous province sw greenland we conclude that the strange lake pluton and associated ree mineralized anorogenic bodies formed from a combination of subduction induced fertilization of the sublithospheric mantle crustal extension and in situ magma evolution

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

southwest new world island stratigraphy new fossil data new implications for the history of the central mobile belt newfoundland the identification of fossils from 16 new localities on southwestern new world island has resulted in the refinement and simplification of local stratigraphy and in the correlation of rock units across an intensely deformed area complex stratigraphic classifications of earlier workers are replaced by a simpler scheme consisting of four formations the summerford formation oldest rogers cove formation sansom formation and goldson formation mclange units are fault related and cannot be included in the stratigraphy fossil and lithological data provided here confirm previous indications that the rocks of the summerford formation are the remains of a long lived volcanic island complex this complex is overlain by a markedly diachronous coarsening upwards sequence of marine clastic sediments now represented by the rogers cove sansom and goldson formations the new stratigraphic data combined with structural evidence indicate that the stratigraphy is repeated across several bedding parallel faults significant diachroneity of formation boundaries and the absence of syndepositional high angle faults suggest deposition in one large rnid paleozoic basin rather than in a number of small dynamic basins

ion microprobe studies of water in silicate melts concentration dependent water diffusion in obsidian abstract the temperature dependence of water diffusivity in rhyolite melts over the range 650 950 c and pt h2o 700 bars is evaluated from water concentration distance profiles measured in glass with an ion microprobe diffusivities are exponentially dependent on concentration over this temperature range and vary from about 10 8 cm2 s at 650 c to about 10 7 cm2 s at 950 c at 2 wt water water solubility also varies with temperature at a rate of 0 14 wt per 100 c increase the avtivation energy ea appears to be constant at 19 1kal mole for 1 2 and 3 wt h2o comparison of these data with results for cation diffusion indicates that this value is a minimum ea for diffusion of any species in a rhyolite melt compensation plots of log10d0 the frequency factor versus ea indicate that hydrous rhyolite melts follow the same trend as anhydrous basalts d0 increases for h2o and ca2 1 as ea decreases this suggests that these molecules may diffuse by different mechanisms than do monovalent cations and that hydration of the melt affects diffusion of ca2 and h2o differently than it does monovalent cation diffusion the results imply that dramatic increases in cation diffusivities by hydration 1 may occur with additions of less than 1 wt h2o

water contents temperatures and diversity of the magmas of the catastrophic eruption of nevado del ruiz colombia november 13 1985 abstract the petrology of the highly phyric two pyroxene andesitic to dacitic pyroclastic rocks of the november 13 1985 eruption of nevado del ruiz colombia reveals evidence of 1 increasingly fractionated bulk compositions with time 2 tapping of a small magma chamber marginally zoned in regard to h 2 o contents 1 to 4 temperature 960 1090 c and amount of residual melt 35 to 65 3 partial melting and assimilation of degassed zones in the hotter less dense interior of the magma chamber 4 probable heating thermal disruption and mineralogic and compositional contamination of the magma body by basaltic magma underplating and 5 crustal contamination of the magmas during ascent and within the magma chamber near crater fall back or spill over emitted in the middle of the eruptive sequence produced a small pyroclastic flow that became welded in its central and basal portions because of ponding and thus heat conservation on the flat glaciated summit near the arenas crater the heterogeneity of ruiz magmas may be related to the comparatively small volume 0 03 km 3 of the eruption nearly ten times less than the 0 2 km 3 of the plinian phase of mount st helens and probable steep thermal and p h 2 o gradients of a small source magma chamber estimated at 300 m long and 100 m wide for an assumed ellipsoidal shape

near laurentian paleogeography of the lawrence head volcanics of central newfoundland northern appalachians abstract paleomagnetic analyses were completed on two volcanic units of the exploits group in newfoundland s central mobile belt which are part of an ordovician arc back arc system the tea arm volcanics display scattered and unstable characteristic directions that cannot be interpreted however stable end points in six sites supported by great circle analysis of seven sites in the mid arenigian to llanvirnian lawrence head volcanics yield a tilt and strike corrected characteristic direction of d 56 i 23 95 19 k 14 n 6 the magnetization is carried by magnetite and passes a tilt test the corresponding paleolatitude of 12 10 is interpreted as southerly and is similar to the paleolatitude of 11 4 for arc volcanics of the nearby moreton s harbour group however this near laurentian paleolatitude is distinctly different from the paleolatitude of 31 8 reported for the robert s arm cottrell s cove chanceport summerford volcanic terrane the low paleolatitude of the lawrence head volcanics supports the location of a major ordovician subduction system near the laurentian margin of iapetus whereas the present day juxtaposition of latitudinally distinct elements in the area represents a complex accretionary history involving early silurian or older thrusting and younger strike slip faulting of several iapetan island arc terranes to laurentia

numerical study of nucleation and growth of bubbles in viscous magmas the nucleation and growth processes of bubbles in viscous magmas with a constant decompression rate have been numerically investigated based on a formation which accounts for effects of viscosity as well as diffusivity interfacial tension and decompression rate the numerical solutions show two regimes in the nucleation and growth process a diffusion controlled regime and a viscosity controlled regime mainly depending on the decompression rate initial saturation pressure and viscosity the basic mechanism common to both regimes is that growth governs nucleation through depletion of degassing components in basaltic eruptions the vesiculation is essentially controlled by diffusion and the viscosity controlled regime is limited to very high decompression rate and very small water content when andesitic magma saturated by water at 10 mpa is decompressed through the propagation of rarefraction wave induced by a landslide as took place in the mount st helens 1980 eruption the vesiculation is controlled by the viscosity up to 100 m depth on the other hand in a rhyolitic magma for the same situation vesiculation is controlled by the viscosity over the whole depth of the magma column in the viscosity controlled regime the vesicularity may be 90 or less as seen in silicic pumice whereas in the diffusion controlledmore regime the vesicularity equals or exceeds 98 such as in reticulite in hawaiian basalt an observed variation of the number density of bubbles by several orders of magnitude in plinian eruptions and the correlation with the sio2 content can be attributed approximately to the dependence of diffusivity of viscosity on sio2 content and temperature assuming the apparent correlation between sio2 content and temperature of magma less

distinct taconic salinic and acadian deformation along the iapetus suture zone newfoundland appalachians structural mapping in central newfoundland has identified seven distinct phases of deformation d 1 to d 7 the most significant of which are d 1 d 2 and d 4 d 1 involved the formation of a middle and late ordovician southsoutheast directed thrust belt and concomitant development of mylonite and phyllonite a late ordovician to early silurian d 2 thrust and fold belt overprints d 1 mylonitic deformation and is the most distinctive deformation event in the study area late silurian to devonian d 4 is responsible for folds and north northwest directed dextral thrust and reverse faults that overprint d 1 to d 3 structures d 4 structures in central newfoundland include the exploits gander boundary subsequent deformation is generally of local significance only the arc back arc complexes making up the various terranes in central newfoundland are predominantly juxtaposed along d 1 shear zones which include the red indian line our data indicate that terrane boundaries initiated during d 1 may have protracted deformation histories spanning several deformation events this has important implications for the interpretation of terrane boundaries in newfoundland as d 1 terrane boundaries may be interpreted as d 2 or d 4 shear zones depending on the intensity of overprinting or reactivation the deformation history proposed in this paper corresponds closely to that of established appalachian orogenic cycles d 1 is correlated with the ordovician taconic orogeny and involved accretion of arc back arc complexes to the laurentian margin d 2 and d 4 are correlated with the ordovician silurian salinic and silurian devonian acadian orogenies which involved the subsequent accretion of the ganderia and avalonia microcontinents to the laurentian margin respectively

paleomagnetism of the lawrenceton formation volcanic rocks silurian botwood group change islands newfoundland paleomagnetic sampling of the lawrenceton formation of the silurian botwood group in northeastern newfoundland was combined with detailed structural mapping of the area in order to determine the deformation history and make adequate structural corrections to the paleomagnetic data structural analysis indicates that the lawrenceton formation experienced at least two folding events i a regional northeast southwest trending siluro devonian folding episode that produced a well developed axial plane cleavage and ii an episode of local north trending folding bedding regional cleavage relationships indicate that the latter event is older than the regional folding thermal demagnetization of the lawrenceton formation yielded univectorial southerly and shallow directions in situ a fold test on an early mesoscale fold indicates that the magnetization of the botwood postdates this folding event however our results combined with an earlier paleomagnetic study of nearby lawrenceton formation rocks demo

synchroneity of folding and crosscutting cleavage in the newfoundland appalachians abstract cleavage that cuts obliquely across folds is relatively common in the appalachians caledonides and this has been interpreted as evidence for regional transpression an interpretation which is only valid if contemporaneity of folding and cleavage formation can be demonstrated crosscutting cleavages in folds of the early silurian and older exploits group of the northeastern newfoundland appalachians are axial planar to rare mesoscopic f 2 fold in the unconformably overlying botwood group on change islands as an alternative to transected folds it is argued that crosscutting cleavage relationships in the exploits units are composite d 1 d 2 structures that represent fold superimposition

collision along an irregular margin a regional plate tectonic interpretation of the canadian appalachians an idealized plate tectonic model for the pre carboniferous development of the canadian appalachians explains the 400 km dextral offset of tectonostratigraphic zones from quebec and northern new brunswick to newfoundland and the up to 600 km offset of oppositely verging belts of acadian deformation from the gaspe peninsula to eastern newfoundland it is proposed that these offsets which occur at the st lawrence promontory result from the collision of an irregular north american passive continental margin with island arc and continental crust to the east along an east dipping subduction zone the line of subduction is assumed to have been linear and the subducting slab to have maintained its mechanical integrity during collision a jigsaw fit of the opposite sides of the iapetus ocean is made unnecessary by invoking lithospheric delamination and tectonic wedging during the acadian orogeny in newfoundland the model is consistent with surface geology and recent deep seismic reflection observations fro

timing and spatial distribution of deformation in the newfoundland appalachians a multi stage collision history van der plmjm b a 1987 timing and spatial distribution of deformation in the newfoundland appalachians a multi stage collision history in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tectonophysics 135 15 24 the newfoundland appalachians have been interpreted as an area where lower paleozoic plate convergence culminated in collision between an ordovician volcanic chain and the north american craton in middle ordovician times closure of the intervening proto atlantic iapetus ocean was considered incomplete subsequent deformation gave rise to regional folding and faulting recent studies in the newfoundland dunnage zone have revealed that the deformation history is far more complex than previously recognized large scale thrusting folding and faulting occurred in silurian devonian times furthermore it has been suggested that the dunnage zone is an allochthonous terrane underlain by dominantly continental crust rather than representing remnants of a rooted ocean basin in view of these results a revision of tectonic scenarios and zonal subdivision is warranted and a multi stage collision history will be discussed with emphasis on the spatial distribution and significance of silurian devonian deformation in central newfoundland subduction in lower paleozoic times gave rise to the formation of a volcanic terrane concurrently to the southeast a marginal sea was formed mariana type subduction in middle ordovician times the volcanic terrane collided with the north american craton first stage collision and back arc spreading terminated continued crustal shortening resulted in the formation of a silurian accretionary terrane telescoped marginal sea and its subsequent deformation second stage collision devonian carboniferous strike slip faulting represents the third stage in the collision history the model is applicable to large tracts of the caledonian appalachian chain its main characteristics are a the revised zonal subdivision of the area is based on characteristics of silurian and older rocks rather than middle ordovician and older rocks only b the central part of the orogen represents a telescoped marginal sea that formed to the southeast of the ordovician volcanic chain rather than a remnant of the incompletely closed iapetus ocean c the earliest deformation is progressively younger toward the southeast d the appalachian collision history is a result of the activity of a single deformation regime over a long period of at least 75 ma

the development of folds and cleavages in slate belts by underplating in accretionary complexes a comparison of the kodiak formation alaska and the calaveras complex california the development of folds and cleavages in slate and graywacke belts is commonly attributed to arc continent or continent continent collisions however the kodiak formation of southern alaska and the calaveras complex of the western sierra nevada california are two slate and graywacke belts in which folds and slaty cleavages developed during simple underthrusting and underplating within accretionary wedges the maastrichtian kodiak formation is composed dominantly of coherent turbidites but includes lesser pebbly mudstone minor conglomerate and rare chert the kodiak formation is part of a large accretionary complex that youngs in age seaward but bedding tops generally show landward younging a progression of structures has been determined by crosscutting relationships and includes 1 syndeformational depositional features 2 broken formation 3 slaty cleavage folds and thrust faults 4 crenulations and crenulation cleavage 5 late brittle thrust faults and 6 right lateral strike slip faults broken formation slaty cleavage thrust faults and folds developed during underthrusting and underplating within an accretionary wedge crenulations and brittle thrust faults are related to subsequent intrawedge shortening based on peak metamorphism in the uppermost zeolite to prehnite pumpellyite facies underplating occurred at a minimum depth of 10 km the calaveras complex is composed of argillite chert graywacke pebbly mudstone limestone and volcanic rocks its age of deposition has a maximum range from permian to early jurassic overall the unit appears to young westward but local facing indicators show eastward younging of individual blocks the sequence of structures developed in the calaveras complex is 1 syn depositional olistostromes 2 broken formation 3 slaty cleavage folds and thrust faults and 4 younger jura triassic folds and crenulation cleavages broken formation and slaty cleavage developed during underthrusting and underplating in an accretionary wedge in an analogous fashion to the kodiak formation greenschist facies metemorphism during underplating suggests that the calaveras complex was accreted at deeper levels or in a wedge with a higher geothermal gradient than the kodiak formation some other probable examples of slate graywacke belts that became folded and well foliated during underplating include part of the dunnage zone newfoundland the southern uplands complex scotland the torlesse terrane new zealand part of the hamburg klippe pennsylvania and the taconic allochthons new york peak metamorphism in these belts indicates that they were accreted in accretionary wedges with geothermal gradients higher than usually assumed for such tectonic settings such wedges may have been fairly common features at convergent margins

geology of eastern new world island newfoundland an accretionary terrane in the northeastern appalachians eastern new world island is located in the northeastern part of the dunnage zone of the newfoundland appalachians contrary to previous interpretations deposition of the sedimentary sequences in this area took place in a single basin although styles of deposition varied laterally within this basin four generations of deformation have affected these rocks d 1 deformation was progressive and highly heterogeneous and it is associated with thrusting movement zones are present at the bases of thrusts locally with zone parallel cleavage s 1 these zones show a complex deformation history folds overprinted by cleavage folds with axial plane cleavage and folded cleavages all occur movement zones are locally associated with technically deformed olistostromes repetition of the general stratigraphic sequence occurs as a consequence of d 1 thrusting the thrusting direction on eastern new world island however cannot be unequivocally determined superimposed on d 1 deformation there is regional folding f 2 with a well developed regional s 2 axial plane cleavage two types of f 3 folds are present and these are associated with strike slip faulting f 4 deformation caused the formation of minor kinks d 1 deformation is lower silurian and younger in age and is included in the acadian orogeny of the appalachians evidence for earlier taconic deformation is absent the over all geometry of eastern new world island is that of a steeply dipping thrust pile with a complex internal geometry it strongly resembles parts of the imbricate fan complex of the southern uplands of scotland

structural evolution of a transpression zone in north central newfoundland abstract a dextral transpression zone in notre dame bay north central newfoundland was active in middle to late silurian times following the closure of a marginal basin the deformation in the transpression zone was complex and involved several generations of structures deformation was initially distributed over wide low strain zones through the formation of a penetrative regional cleavage with steepening and overturning of the strata the orientation of the sequence was favorable for strike slip bedding parallel movement and the deformation became more efficiently accommodated by shear within the incompetent lithologic horizons forming localized shear zones in high strain zones the sheared incompetent horizons define a belt of melange the boones point complex centered on the contact between a volcanic island arc terrane to the north and a marginal basin terrane to the south two cleavages with similar orientation and morphology were generated at different times during the structural evolution of the transpression zone one of the cleavages is regional in distribution and is transposed by the shear zones folds with no axial planar cleavage but a cleavage cutting obliquely across their hinges are reported they have the geometry of transected folds but are clearly the result of overprinting by a younger generation of cleavage

detrital modes of the riding island graywacke north central newfoundland evidence for deposition in a collisional successor basin in the dunnage zone the riding island graywacke late caradoc ashgill crops out in notre dame bay north central newfoundland previous tectonic interpretations suggest that this succession of turbidites and hemipelagic mudstone accumulated in a basin adjacent to an active volcanic arc the varied framework mineralogy of 29 riding island samples studied however records derivation from a complex source terrane composed of mafic and silicic volcanic rocks sedimentary and metamorphic successions and plutonic rocks assessment of the tectonic environment of deposition of the riding island graywacke by use of popular sandstone provenance ternary diagrams yields ambiguous results the mineralogy of the riding island samples reveals a change in tectonic scenario from one dominated by island arc volcanism in pre caradoc time to a setting marked by tectonic shortening transcurrent faulting and terrane accretion near the end of the ordovician the complex composition of these sandstones and the fact that they accumulated afte

silurian llandovery graptolites from the bay of exploits north central newfoundland and their geological significance only one specimen of a silurian graptolite has ever been recorded from newfoundland and it was not identifiable below generic level the graptolite assemblage discussed and figured here from a sequence of turbidites on upper black island north central newfoundland includes the first positively identified silurian taxa from the province and provides the first unequivocal evidence of silurian oceanic sedimentation in the dunnage zone the graptolite taxa include rastrites peregrinus barrande coronograptus sp cf c gregarius lapworth monograptus austerus sequens hutt orthograptus insectiformis nicholson monograptus spp indet climacograptus sp and glyptograptus sp this assemblage demonstrates that the strata previously assigned to the middle ordovician lawrence harbour formation are actually aeronian middle llandovery in age and that the turbidites considerably postdate both the lawrence harbour and point leamington formations of the exploits subzone furthermore the graptoli