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

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

generation and obduction of ophiolites constraints from the bay of islands complex western newfoundland constraints provided by the bay of islands ophiolite complex boic western newfoundland suggest that its generation as well as its obduction is related to collision of the dunnage zone island arc system with the irregular continental margin of eastern north america the constraints include the supra subduction zone setting of the boic its extensional environment of generation the synchronous occurrence of ophiolite generation with initiation of drowning and deformation of the north american continental margin and the restriction of the boic as well as other appalachian ophiolites and associated taconian allochthons to reentrants in the north american margin during the early phases of collision of the dunnage arc with the north american margin subduction of old oceanic lithosphere trapped in reentrants will continue and allow the development of two potential sites of ophiolite generation the first develops through trench rollback leading to ophiolite generation in the overriding arc plate outboard of the reentrant whereas the second develops in a transtensional environment with spreading centers offset by strike slip faults which propagate through the overriding plate away from the indenter promontory the configuration of the boic spreading ridge normal to the continental margin and the direction of initial obduction parallel to the margin favor generation of the ophiolite in an overall strike slip regime with complete subduction of the oceanic remnant extension in the overriding plate ceases and the buoyant newly formed oceanic lithosphere is obducted onto the continental margin diachronous collision of the arc with the irregular continental margin accounts for the range of ages for ophiolite generation and obduction observed within the dunnage zone and for termination of arc volcanism along the north american margin

a u pb age for the sulitjelma gabbro north norway further evidence for the development of a caledonian marginal basin in ashgill llandovery time the sulitjelma gabbro in the central norwegian caledonides has been dated with the u pb zircon sphene method to 437 2 ma geological relationships as well as trace element geochemistry and nd and sr isotopic compositions suggest that the gabbro and associated dyke swarms and pillow lava formed during the initial stages of back arc spreading the age constrains the timing of juxtaposition of an older island arc terrane and continental margin lithologies exposed within the caledonian nappes the age of the gabbro is similar to that of the solund stavfjord ophiolite in west norway and confirms that spreading related magmatism and marginal basin development took place along the margin of iapetus in late ordovician early silurian times

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

early silurian palaeolatitude of the springdale group redbeds of central newfoundland a palaeomagnetic determination with a remanence anisotropy test for inclination error we studied the palaeomagnetism of red fine grained sandstones and coarse siltstones of the early silurian springdale group of central newfoundland at 10 sites a high blocking temperature characteristic remanence carried by haematite was isolated this remanence is shown to predate probable early devonian folding anti parallel north and south directed remanences through a 100 m section of redbeds and a positive conglomerate test on haematite bearing volcanic clasts suggest absence of remagnetization inverting the south directed sites and unfolding yields a characteristic remanence with a mean declination of 23 6 and a mean inclination of 14 2 myg5 7 3 k 45 4 the inclination corresponds to a probable early silurian palaeolatitude of 7 s f 4 we find no significant difference between early silurian palaeolatitudes for central newfoundland north and south of the red indian line suture and conclude that the part of the iapetus ocean across the suture had narrowed to less than about 5 by the early silurian this is consistent with palaeomagnetic results from britain and ireland that suggest no more than a narrow iapetus at low palaeolatitude by the early silurian we also tested whether we have underestimated palaeolatitude because of sediment compaction reducing remanence inclination from that of the early silurian field we measured anisotropy of the isothermal remanence irm acquisition for one specimen from each stable site finding that a field of 200 to 800 rnt applied at 45 to bedding produced an isothermal remanence oriented on average at 42 to bedding theory then predicts that sediment compaction caused less than 2 average inclination shallowing in the springdale group redbeds and less than a 1 underestimation of palaeolatitude

lithostratigraphic hydrothermal and tectonic setting of the boundary volcanogenic massive sulfide deposit newfoundland appalachians canada formation by subseafloor replacement in a cambrian rifted arc the boundary volcanogenic massive sulfide vms deposit 0 5 mt 3 5 cu 4 zn 1 pb 34 0 g t ag in the tally pond group central newfoundland represents one of the best preserved subseafloor replacement style vms deposits in the northern appalachian orogen the deposit is hosted within a late cambrian 510 ma volcanic sequence consisting predominantly of rhyolitic flows and associated volcaniclastic rocks footwall strata are dominated by rhyolitic lapilli tuff tuffs lesser rhyolite flows and in situ rhyolite breccias the hanging wall consists of massive quartz bearing flow banded lobe and breccia facies rhyolite the deposit occurs at and below the contact between these two units and comprises pyrite chalcopyrite and lesser sphalerite and other minerals massive mineralization contains abundant clasts of the surrounding host rocks including chlorite sericite quartz altered rhyolite lapilli and ash hydrothermally altered rocks consist of variably intense chlorite with lesser sericite and quartz chlorite alteration occurs in a discordant geometry likely representing hydrothermal upflow zones and chlorite sericite quartz occur as blankets that are parallel to the volcanic stratigraphy likely representing alteration associated with replacement the hanging wall rhyolite flows also contain moderate to intense pervasive quartz and sericite alteration both the hanging wall and footwall are characterized by strong na2o sr depletions k2o mgo fe2o3 ba enrichments high alteration index values e g ba sr chlorite carbonate pyrite index ccpi alteration index ai and enrichments in base metals and volatile metals e g cu zn pb hg the presence of abundant remnant wall rock and host rock clasts within the ore intricate sulfide replacement of laminated porous tuff and sand dikes replacement fronts in host lithofacies and intense alteration in both the footwall and hanging wall where the hanging wall is preserved are all features consistent with formation of the bulk of the boundary deposit via subseafloor replacement the deposit likely formed as a result of cooling of metal bearing hydrothermal fluids mixing with ambient seawater and pore water entrained seawater within the volcanic rocks at a permeability interface between young unlithified highly permeable footwall volcaniclastic rocks and relatively impermeable hanging wall rhyolitic flows in our model this permeability boundary was an important feature that promoted subseafloor replacement within the deposit immobile element systematics of rhyolitic rocks from the boundary deposit lack major differences in primary petrochemistry between hanging wall and footwall strata all rocks from the deposit area are subalkalic with transitional zr y ratios 2 8 4 5 la sm ratios 1 normalized to upper crust and primitive mantle normalized signatures with slightly light rare earth element lree enriched patterns with flat heavy ree hree and negative nb ti and eu anomalies these geochemical features coupled with existing nd pb isotope data zircon inheritance patterns and geologic information are consistent with rhyolitic rocks at the boundary deposit having formed by re melting of arc basement with continental crust or recycled continental crust present in the source region it is likely that the deposit and its associated rhyolitic host rocks formed within a cambrian continental or pericontinental rifted arc along the margin of ganderia within the iapetus ocean

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

the topsails igneous suite western newfoundland an early silurian subduction related magmatic suite the topsails igneous suite contains several late ordovician to early silurian volcanic and intrusive sequences which overlie and intrude early to middle ordovician oceanic and arc rocks the oldest components of this suite may represent calc alkaline continental arc magmatism the younger components are bimodal with felsic compositions vastly predominating and include a major 2200 km2 alkaline a type granite complex these felsic components have similarities to peralkaline suites formed in unusual subduction related settings younger mafic components resemble within plate basalts emplaced in a continental setting silurian magmatic activity in the canadian appalachians is widespread includes diverse magmatic types and has contrasting metamorphic and tectonic overprinting even in contiguous areas these features and the probability of major post silurian displacements in the orogen render correlation and interpretation difficult tectonic models that consider basin closure and major plate movem

crystallization and emplacement chronology of the fournier oceanic fragment canadian appalachians collision zones between the plates that form the earth s surface are commonly delineated by displaced fragments of oceanic crust and mantle these fragments are important because they can be used to constrain the timing of the generation and destruction of former oceans by means of radiometrie and fossil studies in the northern appalachian caledonian orogen of canada the united kingdom and scandinavia the majority of the oceanic fragments crystallized between 480 and 500 myr ago in basins marginal to the lapetus ocean and were emplaced onto continental margins at least 10 myr later here we report a significant exception u pb geochronology of zircons extracted from a plagiogranite in the fournier oceanic fragment of the canadian appalachians reveals a much younger crystallization age of 461 3 2 myr whereas fossil evidence indicates continental incorporation in the silurian some lapetan marginal basins therefore continued to develop or were created after the early ordovician

petrogenesis and paleotectonic history of the wild bight group an ordovician rifted island arc in central newfoundland the wild bight group wbg is a sequence of early and middle ordovician volcanic subvolcanic and epiclastic rocks part of the dunnage tectonostratigraphic zone of the newfoundland appalachians a detailed geochemical and nd isotopic study of the volcanic and subvolcanic rocks has been carried out to determine the geochemical characteristics of the rocks interpret their palcotectonic environments and constrain their petrogenetic history the lower and central stratigraphic levels of the wbg contain mafic volcanic rocks with island arc geochemical signatures including lree enriched are tholeiites with e nd t 0 1 to 2 2 type a i lree depleted arc tholeiites with e nd t 5 6 to 7 1 type a ii and an unusual suite of strongly incompatible element depleted tholeiites in which e nd t ranges from 0 9 to 4 6 and is negatively correlated with147sm 144nd type a iii high silica low k rhyolites occur locally in the central part of the stratigraphy associated with mafic rocks of arc affinity and have e nd t 4 7 to 5 4 the upper stratigraphic levels of the wbg dominantly contain rocks with non arc geochemical signatures including alkalic basalts with e nd t 4 6 to 5 5 type n i strongly lree and incompatible element enriched tholeiites that are transitional between alkalic and non alkalic rocks with e nd t 4 4 to 7 0 type n ii and rocks with flat to slightly lree enriched patterns and e nd t 5 1 to 7 4 type n iii rocks with non arc and arc signatures are locally interbedded near the stratigraphic type of the wbg nd isotopic data in the type a i and a ii rocks are generally compatible with mixing partial melting models involving depleted mantle variably contaminated by a subducted crustally derived sediment the petrogenesis of type a iii rocks must involve source mixing and multi stage partial melting but the details are not clear the geochemistry and nd isotope data for types n i n ii and n iii rocks are compatible with petrogenetic models involving variable partial melting of a source similar to that postulated for modern oceanic island basalts comparison of the wbg with modern analogues suggests a 3 stage developmental model stage 1 island arc volcanism eruption of type mafic volcancs stage 2 arc rifting continued eruption of type a i a i eruption of types a ii and a iii mafic volcanics and high silica low k rhyolites and stage 3 back arc basin volcanism continued minor eruption of type a i basalts eruption of types n i n ii n iii basalts stages 1 and 2 volcanism involved partial melting of subduction contaminated mantle while stage 3 volcanism utilized depleted mantle sources not affected by the subducting slab this model provides a basis for interpreting coeval sequences in central newfoundland and a comparative framework for some early paleozoic oceanic volcanic sequences elsewhere in the appalachian orogen

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

u pb ages and tectono magmatic evolution of middle ordovician volcanic rocks of the wild bight group newfoundland appalachians the wild bight group and spatially associated south lake igneous complex form one of the ordovician oceanic terranes of the central mobile belt of the newfoundland appalachians an integrated study of these rocks involving detailed mapping geochemistry sm nd isotopic analyses and u pb geochronology has shown that there are two temporally and genetically distinct volcanic sequences within the wild bight group the younger sequence comprises a lower volcanic succession associated with coarse volcaniclastic rocks and an upper volcanic succession interbedded with argillite chert and minor greywacke the lower volcanic succession has calc alkaline affinties and isotopic evidence for minor crustal contamination it is interpreted to represent a volcanic arc formed in proximity to the gondwanan margin above an east dipping subduction zone the age of this volcanic sequence is confined to 472 3 ma by felsic tuffs which occur stratigraphically above and below it the upper volcanic unit has predominantly enriched tholeiitic to alkaline geochemical characteristics with isotopic signatures indicative of little or no crustal contamination and is interpreted to represent arc rifting the age of this sequence was determined indirectly by dating two geochemically related gabbro sills 472 9 ma and 471 4 ma this work shows that despite different lithologies and stratigraphic and structural relationships between early and middle ordovician sequences in the northern and southern exploits subzone they have undergone essentially the same tectono magmatic events the age constraints on the magmatic events in the wild bight group provide evidence for the timing of obduction of early ordovician oceanic sequences and the reversal of subduction polarity along the gondwanan margin suggested by previous workers resume le groupe de wild bight et le complexe de south lake des terrains associes constituent un des terranes oceaniques ordoviciens de la ceinture mobile centrale des appalaches de terre neuve une etude pluridisciplinaire de ces roches incluant la cartographie detaillee la geochimie les analyses isotopiques sm nd et la geochronologie u pb a demontre que le groupe de wild bight est forme de deux sequences volcaniques qui sont genetiquement et

lithostratigraphy and geochemistry of the cottrells cove group buchans roberts arm volcanic belt new constraints for the paleotectonic setting of the notre dame subzone newfoundland appalachians new sedimentological geochemical and geochronological data from the cottrells cove group in central newfoundland provide important constraints on the nature of the notre dame subzone its tectonic setting and the history of the laurentian margin during the early ordovician the cottrells cove group forms the eastern extension of the roberts arm group and correlates with the chanceport group on new world island it is represented by two volcano sedimentary formations that occur in a complex thrust stack the fortune harbour formation consists of calc alkalic island arc lavas followed by a 1250 m thick succession of volcaniclastic deposits radiolarian cherts and calc alkalic mafic flows which were deposited in a back arc basin plain setting the volcaniclastic deposits include felsic tuff which has a u pb zircon age of 484 f 2 ma and an inheritance component of 2517 f 26 ma these new u pb and nd isotope data suggest that the island arc back arc volcanism and sedimentation in the notre dame subzone developed in the vicinity of continental margin and approximately 10 ma earlier than has previously been established the moores cove formation is undated but contains boulders of calc alkalic basalt and is presumed to be at least in part younger than the fortune harbour formation tholeiitic lavas together with associated radiolarian cherts and volcaniclastic deposits constitute the basal part of the moores cove formation and may have been deposited in a back arc environment synchronously with some parts of the fortune harbour formation they are conformably followed by an over 1200 m thick coarsening upward succession of lower slope and submarine fan deposits the polymictic flysch containing clasts of island arc basalt accompanied by other volcanic plutonic ultramafic and sedimentary detritus may record middle or upper ordovician uplift and erosion of obducted arc back arc volcano sedimentary sequences and their ophiolitic substrate

neoproterozoic and cambrian arc magmatism along the eastern margin of the victoria lake supergroup a remnant of ganderian basement in central newfoundland abstract the eastern margin of the composite and structurally complex victoria lake supergroup has previously been mapped where the silurian rogerson lake conglomeratic rocks unconformably overlie cambrian tally pond volcanic rocks however the recognition that the form of this contact changes between an unconformity and a brittle ductile fault in conjunction with the neoproterozoic age of the crippleback intrusive suite dictate that the above interpretation of the nature of this margin requires revision these discrepancies are resolved by the recognition of a neoproterozoic largely bimodal volcanic sequence sandy brook group which is unconformably overlain by rogerson lake rocks to the east with these combined units in fault contact with the tally pond group to the west the sandy brook group and crippleback intrusive suite form a terrane of ca 563 ma rocks with continental arc like geochemical signatures the distinctly negative nd 563 values for the felsic rocks mean 3 of this terrane imply derivation from a crystalline basement older than the largely pan african crust that underlies contemporaneous volcanic rocks in west avalonia but similar to that inferred for the gander zone thus this terrane is likely to be the leading edge of the peri gondwanan microcontinent ganderia the ca 511 ma tally pond group arc magmatism represent some of the oldest products of iapetean subduction in newfoundland although the tally pond group are only observed to be in fault contact with the ca 50 million year older sandy brook group the high proportion of felsic volcanic rocks sandy brook crippleback age inherited zircons and pb isotopic data all support the inference that the tally pond group was formed on sandy brook crippleback continental crust

u pb ages and tectonomagmatic relationships of early ordovician low ti tholeiites boninites and related plutonic rocks in central newfoundland canada the wild bight group wbg and south lake igneous complex slic together comprise one of the ordovician accreted oceanic terranes of the central mobile belt of the newfoundland appalachians combined detailed mapping geochemistry sm nd isotopic studies and u pb geochronology have shown that sheeted dykes and hornblende diorite and tonalite plutons of the slic are genetically related to a discrete package of volcanic rocks in the wbg these igneous rocks are geochemically isotopically and temporally distinct from volcanic rocks in the rest of the wbg plutonic rocks of the slic range in age from 486 3 ma to 489 3 ma and a cross cutting gabbro dyke gives a minimum age of 486 4 ma for the related volcanic sequence volcanic rocks in the rest of the wbg sequence are predominantly younger than 472 3 ma the older volcanic sequence of the wbg and the slic occur as fault bounded packages interleaved within the younger wbg sequence a conformable stratigraphic relationship between the older and younger sequences of the wbg has not been demonstrated the mafic rocks of the older package include boninites and low ti high mg tholeiitic island arc basalts which are interpreted to be genetically related and normal island arc tholeiites iat the high mg mafic rocks are interpreted to have formed in an extensional setting during subduction zone initiation and the normal iat are thought to represent stabilisation of the volcanic front the associated high si low k rhyolite and tonalite are interpreted to be the products of secondary melting at the base of thickened early arc crust sm nd isotopic compositions indicate that the characteristic trace element signature of the boninites developed at or near their time of generation and was not a long lived characteristic of the source region the boninites and low ti tholeiites are interpreted to have originated from a similar source which was metasomatized by different subduction related components apparent decoupling of sm nd geochemical and isotopic compositions suggests that these very depleted rocks may be recording the effect of subduction zone processes not yet fully understood

geochronology of the buchans roberts arm and victoria lake groups and mansfield cove complex newfoundland volcanic groups of the central mobile belt of the newfoundland appalachians have previously been subdivided into early and late arc sequences separated in time by a quiescent caradocian stage defined in some areas by fossil bearing black shales new u pb zircon ages of and 473 2 ma for rhyolites of the buchans and roberts arm groups respectively show them to be correlative early ordovician sequences these ages serve to refute both the previous rb sr whole rock isochron ages of 447 ma and the idea that these groups were late arc sequences these new ages corroborate evidence from late arenig early llanvirn conodonts in the buchans group and calibrate this fossil occurrence a new u pb zircon age of 479 3 ma from plagiogranite of the mansfield cove complex immediately west of the roberts arm group shows that this plutonic body is only slightly older than the adjacent volcanic rocks and not hadrynian as previously supposed local field relationships suggest this body may represent part of a dis

geochemical constraints on the origin of the annieopsquotch ophiolite belt newfoundland appalachians the early ordovician annieopsquotch ophiolite belt occurs immediately west of the main iapetus suture zone and imposes important constraints on the tectonic processes associated with closure of the peri laurentian portion of iapetus the annieopsquotch ophiolite the most prominent ophiolite within the annieopsquotch ophiolite belt exposes a 5 5 km thick section of gabbros sheeted dikes and pillow basalts in which three magmatic episodes have been recognized based on field and geochemical data the first phase is composed of layered troctolites which are preserved as enclaves within the gabbro zone trace element modeling suggests the troctolites crystallized from boninitic melts the troctolite substrate was intruded by the dominant second tholeiitic magmatic phase which formed a gabbro sheeted dike basalt sequence all tholeiites have suprasubduction zone chemical characteristics but the suprasubduction zone signature decreases toward the top of the basalt sequence the third magmatic episode is composed of primitive dikes which are interpreted as off axis intrusions other ophiolites within the annieopsquotch ophiolite belt have comparable geochemical signatures suggesting they may have constituted a single piece of oceanic lithosphere based on geochemical and regional tectonic constraints the annieopsquotch ophiolite belt is interpreted to have formed during initiation of west directed subduction fast rollback of the subducting slab would have induced volatile fluxed decompression melting of previously depleted mantle yielding boninitic melts the suprasubduction zone tholeiite sequence would have formed from ascending fertile mantle fluxed with sub duction related fluids as rollback continued this suggests that the annieopsquotch ophiolite belt does not represent the remnants of normal oceanic crust or backarc basin crust as previously thought our model constrains the initiation and early evolution of a west dipping peri laurentian subduction zone that was responsible for formation of several arc backarc complexes currently preserved in the annieopsquotch accretionary tract

tectono stratigraphic setting of the moreton s harbour group and its implications for the evolution of the laurentian margin notre dame bay newfoundland1this article is one of a series of papers published in this cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology the moreton s harbour group lies along the red indian line the fundamental iapetus suture that separates rocks of peri laurentian affinity with rocks of peri gondwanan affinity in the newfoundland appalachians characterization of age and environment of formation of the moreton s harbour group is an important constraint on evolution of the laurentian margin during ordovician closure of iapetus ocean and associated marginal basins the moreton s harbour group comprises a fault bounded ophiolitic sequence of layered gabbro sheeted diabase pillow basalt and felsic intrusive rocks it is offset by high angle shear zones that were contemporaneous with a 477 4 0 4 ma syn tectonic and syn magmatic suite of trondhjemite and tonalite trace element data from the felsic suite indicate formation in a supra subduction zone setting although isotopic data from the felsic intrusive rocks end 5 02 to 10 53 tdm 1200 1800 ma indicate a significant amount of contamination from mesoproterozoic or older contin

u pb ages of ophiolites and arc related plutons of the norwegian caledonides implications for the development of iapetus u pb zircon ages are reported for four ophiolites and three crosscutting arc related plutons from the norwegian caledonides plagiogranite differentiated from gabbro of the karmoy ophiolite is dated at 493 7 4 ma whereas arc related trondhjemite cutting this ophiolite crystallized at 485 2 ma a crosscutting clinopyroxene phyric gabbro intrusion is dated at 470 9 5 ma by near concordant magmatic titanite sphene and discordant u rich 2903 6677 ppm zircon lower intercepts of 247 68 and 191 70 ma defined by the plagiogranite and clinopyroxene phyric gabbro best fit lines may reflect a real low t alteration rift related event

assembly of the annieopsquotch accretionary tract newfoundland appalachians age and geodynamic constraints from syn kinematic intrusions abstract the annieopsquotch accretionary tract aat comprises several ophiolites and arc back arc igneous complexes that were accreted to the dashwoods microcontinent during the ordovician taconic orogeny the lloyds river fault zone which separates the aat from the dashwoods microcontinent yielded 40ar 39ar hornblende ages of ca 470 ma the fault zone was intruded syn kinematically by the shoshonitic portage lake monzogabbro and the pierre s pond suite which gave u pb zircon ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document lan

characteristics of gold mineralization in volcanogenic massive sulphide deposits of the notre dame bay area central newfoundland a reconnaissance study of 19 volcanogenic massive sulphide deposits in the notre dame bay area indicates au concentrations of up to 30 ppm betts cove and elevated gold contents 1 ppm au have been found in samples from 10 additional past producers and developed prospects systematic trends in the occurrence of gold are observed in two principal sulphide assemblages polymetallic pyrite sphalerite chalcopyrite galena arsenopyrite assemblages type i and pyrite chalcopyrite sphalerite pyrrhotite assemblages type ii type i assemblages occur in deposits with dominantly felsic host rocks whereas type ii assemblages are restricted to deposits in mafic dominated ophiolite sequences free gold grains were observed in samples from eight different deposits in both type i and type ii assemblages x ray emission spectra and electron microprobe analyses of the gold indicate that most grains are electrum although a au bearing telluride occurs at point leamington ion microprobe analyses indicate that

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

geology mineralogy and lithogeochemistry of metalliferous mudstones associated with the lemarchant volcanogenic massive sulfide deposit tally pond belt central newfoundland the cambrian lemarchant zn pb cu au ag bimodal felsic volcanogenic massive sulfide vms deposit tally pond group central newfoundland canada contains metalliferous mudstones that occur either immediately on top or laterally along strike from massive sulfide mineralization or as interflow mudstones within hanging wall basaltic rocks the mudstones are brown to black graphite rich and locally have intercalations of siliciclastic volcaniclastic and or amorphous chert layers and in some cases fine lamina of organic matter the main sulfide phases are pyrite framboidal and euhedral and pyrrhotite with minor chalcopyrite sphalerite arsenopyrite and galena barite is a common sulfate the metalliferous mudstones occur at various stratigraphic levels and have variable inputs of hydrothermal high fe al and base metal values and detrital components lower fe al and base metal values with positive shale normalized eu anomalies eu eu 1 negative ce anomalies ce ce 1 and an average y ho ratio of 28 3 these signatures suggest precipitation from reduced high temperature hydrothermal vent fluids in an oxygenated water column coupled with the hydrothermal particles having a short residence time within the hydrothermal plume i e a vent proximal setting deposition from an oxygenated water column is also supported by the presence of abundant barite in both the lemarchant massive sulfides and the metalliferous mudstones as well as locally preserved marcasite in the mudstones redox sensitive trace elements as u v mo cr ni and co were scavenged as oxyanions onto fe oxyhydroxides during mudstone formation and these elevated levels of scavenged redox sensitive trace elements cause apparent anoxic signatures immobile element systematics la th zr 10 and th la sc indicate that the detrital components of the lemarchant mudstones were mixtures of both continental and mafic sources most likely deposited within a pericontinental rifted arc environment our research illustrates that the lithogeochemistry of metalliferous mudstones can identify vent proximity and provides insights into the physiochemical conditions of the deposit formation and the ambient environment these results have implications for similar precious metal bearing vms deposits globally

a high precision u pb age for the ben vuirich granite implications for the evolution of the scottish dalradian supergroup high precision high accuracy u pb analyses of zircons from the ben vuirich granite in the scottish dalradian succession were performed on carefully picked high integrity abraded fractions of specific morphologies zircon needles which grew during crystallization give an age of 590 2 ma stubby prisms show inheritance with an upper concordia intercept of 1448 7 ma the age of intrusion at 590 ma contrasts strongly with a previous u pb zircon age of 514 6 7 ma determined on bulk fraction unabraded grains which it is argued must have suffered significant pb loss as the ben vuirich granite was emplaced between the regional d2 and d3 deformation events in the dalradian block the new data imply that all dalradian sedimentation was precambrian supposed lower cambrian fauna1 links between the dalradian succession and laurentia are thus discounted and the possibility that the dalradian supergroup has non laurentian affinities must be considered the early d1 d2 nappe forming grampian structures are also precambrian and may be associated with terrane docking along a tectonically active ocean margin later d3 structures and associated peak barrovian metamorphism suggest a subsequent thickening event possibly c 520 ma ago

tectonic setting and regional significance of the port aux basques gneiss sw newfoundland the port aux basques gneiss of southwest newfoundland comprises three paragneiss and schist assemblages the grand bay and port aux basques complexes and the harbour le cou group they are intruded by large volumes of basic sheets and coeval middle ordovician granitoids the margaree and kelby cove orthogneiss which also cut a tectonic slice of earlier ultrabasic to basic rocks within the grand bay complex the big barachois assemblage the grand bay and port aux basques complexes are juxtaposed by the late silurian isle aux morts fault zone against the harbour le cou group to the east which dominantly comprises sillimanite and garnet bearing pyritiferous metasediments with amphibolitic intrusions and meta pillow basalts in its lower stratigraphic units geochemical studies have shown that metabasites of the grand bay complex port aux basques complex margaree and kelby cove orthogneiss comprise fractionated and crustally contaminated morb like and within plate tholeiites suggestive of an ensialic okinawa type back arc basin these have comparable characteristics to metabasites in the harbour le cou group and suggest that these units comprise remnants of an extensive mid ordovician marginal basin developed within a promontory on the peri gondwanan continental margin in contrast the big barachois assemblage in part comprises a distinct suite of pre mid ordovician island arc tholeiites

mid late ordovician magmatism and metamorphism along the gander margin in central newfoundland fieldwork coupled with u pb dating has clarified the relationships between the exploits and gander derived rocks in central newfoundland during the mid ordovician opening of the exploits back arc basin reinforcing correlation across the peri gondwanan segments of the appalachian caledonian orogen we have separated a new back arc related unit the red cross group from the arc related victoria lake supergroup this group includes 466 3 ma felsic volcanic rock interlayered with alkali basalt enriched mid ocean ridge basalt 457 6 ma gabbro llanvirn caradoc normal mid ocean ridge basalt island arc tholeite limestone black shale and melange locally the red cross group is in parautochthonous contact with low grade gander psammite this contact was overrun by the meelpaeg metamorphic nappe during the devonian the nappe contains gander metapsammite meelpaeg subzone and the coticule bearing howley waters complex exploits which hosts 467 3 ma felsic porphyry the gander and exploits metasediments in the nappe are stitched by arenig llanvirn granite 467 6 ma and 468 3 5 3 ma and caradoc intrusions 458 3 ma and 454 2 ma metamorphic monazite 462 1 ma and titanite 460 3 ma from the nearby mount cormack subzone gander indicate the coeval formation of a low pressure high temperature metamorphic dome the widespread presence of caradoc magmatism suggests that the width of the back arc basin remained relatively narrow

lower to middle ordovician evolution of peri laurentian arc and backarc complexes in iapetus constraints from the annieopsquotch accretionary tract central newfoundland the annieopsquotch accretionary tract in newfoundland is composed of a series of west dipping structural panels each containing remnants of ophiolitic and arc backarc complexes of laurentian affinity formed during the ordovician closure of iapetus panels were transferred from an upper plate to a lower plate setting during their middle to late ordovician accretion to the laurentian margin and become progressively younger eastward geochronological data indicate a complex and rapid history of generation and accretion of peri laurentian suprasubduction zone rocks the rapid changes in tectonic environments and the complexity of the relationships are analogous to the complex arc backarc relationships observed in the western pacific today the recognition of the peri laurentian provenance of these units based on stratigraphy geochronology isotopes and geochemistry defines the position of the red indian line the fundamental suture zone in the northern appalachians but more importantly enables the development of a realistic tectonic model for the annieopsquotch accretionary tract involving both thrust and sinistral transcurrent displacements the oldest and most inboard unit in the annieopsquotch accretionary tract is the annieopsquotch ophiolite belt ca 480 ma which marks the initiation of subduction outboard of the laurentian margin the lloyds river ophiolite complex ca 473 ma preserves a fragment of younger more mid ocean ridge like backarc oceanic crust than the adjacent structurally overlying annieopsquotch ophiolite belt the lloyds river ophiolite complex originated as a backarc to the buchans group ca 473 ma ensialic bimodal calc alkaline arc the panels containing the annieopsquotch ophiolite belt and lloyds river ophiolite complex were stitched and overlain by ensialic arc rocks of the otter pond complex ca 468 ma immediately after their accretion to composite laurentia together with the structurally underlying buchans group the youngest structurally lowest two panels comprise the elements of the red indian lake group 465 460 ma which record the opening of a backarc basin and the subsequent establishment of a bimodal ensialic calc alkaline arc sequence the observed relationships indicate that the annieopsquotch accretionary tract was generated above a single west dipping subduction zone outboard of the laurentian margin over 20 m y accretion mainly took place in two stages at ca 468 and 450 ma which correspond with the collision between laurentia and the dashwoods ribbon continent and the collision with the peri gondwanan victoria arc along the red indian line respectively both collisions form part of the taconic orogeny the latter late ordovician collision terminated the relatively rapid closure of the main iapetan tract the proposed model is similar to the correlative tracts in the british and irish caledonides and may encourage a new look at the new england appalachians

provenance of exhalites associated with the lemarchant volcanogenic massive sulphide vms deposit central newfoundland canada insights from nd isotopes and lithogeochemistry neodymium isotope data on exhalites and tuffs from the cambrian lemarchant volcanogenic massive sulphide vms deposit provide insights into the tectonic environment of the tally pond group canada new data from exhalites from the lemarchant area show evolved values of end 513 6 0 to 1 8 whereas the associated volcanic rocks have end 513 of 0 4 to 1 4 the lemarchant exhalite end compositions overlap the underlying ganderian neoproterozoic sandy brook group end t 6 5 to 1 9 and crippleback intrusive suite end t 5 9 to 5 2 the evolved nd isotopic signatures suggest that the volcanic rocks of the tally pond group were formed upon ganderian arc basement which itself was possibly built upon or proximal to the gondwanan amazonian margin erosion of older crustal material and tally pond group volcanic rocks together with coeval eruption of the volcanic rocks released nd rich detritus into the water column uptake of eroded detrital and scavenged nd resulted in mixed nd sources juvenile and evolved which are archived in the exhalites the results of this study are not only of significance for occurrences of exhalites within the tally pond group but also have exploration implications for vms districts globally

geology and lithogeochemistry of hydrothermal mudstones from the upper block near the duck pond volcanogenic massive sulfide vms deposit newfoundland canada evidence for low temperature venting into oxygenated mid cambrian seawater pyrite and pyrrhotite rich mudstones are spatially associated with cambrian 512 509 ma volcanogenic massive sulfide vms deposits throughout the tally pond group central newfoundland canada at the duck pond mine sulfide rich mudstones are hosted within a weakly mineralized upper block that structurally overlies the deposit but is older 513 versus 509 ma the mudstones are laminated 10 30 cm thick and pyrite and pyrrhotite rich and occur along pillow lava selvages or in between pillow lavas rhyolite flows and volcaniclastic rocks the mudstones are laterally extensive and proximal to the mudstone host rocks are hydrothermally altered to epidote quartz chlorite basalt host and sericite quartz rhyolite host lithogeochemical data for the sulfide rich mudstones reflect the varying contributions of elements from sedimentary detritus hydrothermal discharge and hydrogenous scavenging from middle cambrian seawater the mudstones have minor detrital element abundances and significant hydrothermal element enrichments i e elevated fe2o3 s pb zn cu and ba concentrations high fe al ratios the hydrothermal mudstones are also enriched in oxyanions i e p2o5 u v cr ni co and hg interpreted to have been enriched via oxidative scavenging from seawater by fe oxide oxyhydroxide particles the mudstones also have ree y signatures similar to modern oxygenated seawater with high y ho and negative ce anomalies ce ce 0 40 0 86 average 0 58 which correlate with adsorbed oxyanion concentrations the low eu eu 1 02 1 86 average 1 22 in the mudstones suggest that they were deposited from low temperature 250 c fe rich hydrothermal fluids that likely formed a buoyant plume into an oxygenated water column the ree y oxyanion signatures suggest that the particles within the hydrothermal plume had sufficient residence time to scavenge oxyanions from seawater and inherit a middle cambrian seawater signature the predominant seawater ree y oxyanion signature in the duck pond upper block sulfide rich mudstones suggests that they are distal hydrothermal sedimentary rocks that could have formed up to 10 km from their original vent sources correspondingly to utilize hydrothermal mudstones as vectors to mineralization in the tally pond belt and similar belts globally it is critical to identify vent proximal samples that have hydrothermal signatures i e high fe al base metals ba s with subdued seawater and adsorption signatures i e chondritic y ho low p2o5 ni u co cr v and hg indicating minimal residence time in the water column and deposition proximal to the vent

discordant silurian paleolatitudes for central newfoundland new paleomagnetic evidence from the springdale group ancient remanences are retained by the early silurian 429 6 5 ma mafic volcamcs of the sprmgdale caldera five sites and the overlying red beds seven sites dual polarity magnetizations are obtained by thermal demagnehzation of samples from the red beds whereas single polarity d rectlons are observed m the volcamcs high unblockmg temperatures indicate hematite as the remanence carrier m both the volcamcs and sedxments these h gh temperature characteristic remanences are easily solated and pass both the tilt and conglomerate tests they are likely to be of primary silurian age characteristic dechnatlons are predominantly northerly and northeasterly and md cate s gmficant structural rotahons on a local scale when the results of the red beds and the voleamcs are combined they show characteristic mchnatlons that are shallower than those of the correlative botwood group ca 36 vs 43 but not nearly as shallow as those reported from the king george iv lake area 0 5 mean mchnatlons obtained from the sprmgdale red beds are however slgmficantly shallower than those of the sprmgdale volcanlcs the same difference can be seen m other previous silurmn paleomagnehc studies of central newfoundland we infer that an mcllnat on error affects the red bed magnetizations of the sprmgdale group botwood group wigwam formation and rocks of the king george iv lake area therefore the results from sdurlan red beds should not be used to determine paleolahtudes for central newfoundland the mean paleolatltude of the sprlngdale group volcamcs is 30 the mean paleolatltudes for both the sprlngdale volcanlcs and botwood volcamcs lawrenceton formation are md stmgmshable w thm paleomagnetlc error hm ts from the predicted paleolatltude of newfoundland on the northeast trendi ng north american margin thus no detectable post silurian displacement ts shown by the volcamcs of the sprmgdale group with respect to cratomc north america

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

upper cambrian to upper ordovician peri gondwanan island arc activity in the victoria lake supergroup central newfoundland tectonic development of the northern ganderian margin the exploits subzone of the newfoundland appalachians comprises remnants of cambro ordovician peri gondwanan arc and back arc complexes that formed within the iapetus ocean the exploits subzone experienced at least two accretionary events as a result of the rapid closure of the main portion of the iapetus tract the penobscot orogeny c 480 ma which juxtaposed the penobscot arc c 513 486 ma with the gander margin and c 450 ma collision of the victoria arc c 473 454 ma with the annieopsquotch accretionary tract that juxtaposed the peri laurentian and peri gondwanan elements along the red indian line the newly recognized pats pond group forms a temporal equivalent to other lower ordovician intra oceanic complexes of the penobscot arc the pats pond group c 487 ma has a geochemical stratigraphy that is consistent with rifting of a volcanic arc an ensialic setting is indicated by low end values end 0 3 to 0 5 near the stratigraphic base and its abundant zircon inheritance c 560 ma and 0 9 1 2 ga the spatial distribution of tremadocian arc back arc complexes indicates that the penobscot arc is best explained in terms of a single east dipping subduction zone this model is favored over west dipping models in that it explains the distribution of the penobscot arc elements continental arc magmatism and the obduction of back arc penobscot ophiolites without requiring subduction of the gander margin or subduction reversal the newly recognized wigwam brook group c 454 ma disconformably overlies the pats pond group and records the youngest known phase of ensialic arc volcanism end 4 1 in the victoria arc which is also related to east dipping subduction thus the penobscot and the overlying victoria arc are reinterpreted in terms of a single relatively long lived east dipping subduction zone beneath the peri gondwanan microcontinent of ganderia the cessation of arc volcanism towards the top of the wigwam brook group and the subsequent syn tectonic sedimentation in the badger group constrain the arrival of the leading edge of ganderia with the ensialic arc complexes to the laurentian margin to c 454 ma

the origin and significance of the delaney dome formation connemara ireland dalradian meta sediments of the laurentian margin and mafic intrusions thereof in sw connemara ireland tectonically overlie meta rhyolites of the delaney dome formation the two units are separated by the mannin thrust a new u pb age of 474 6 5 5 ma shows that the delaney dome formation is a temporal equivalent of arc volcanic rocks preserved in the adjacent south mayo trough the tourmakeady volcanic group erupted during the collision of an oceanic island arc with the laurentian margin in the grampian orogeny new rare earth and high field strength element data show that the delaney dome formation and tourmakeady volcanic group are chemically similar and arc like in character this suggests that the delaney dome formation is an along strike equivalent of the tourmakeady group strike slip faulted south of the south mayo trough during or after the grampian orogeny further correlation of these units with northern appalachian rhyolites is also possible the delaney dome formation is an extrusive temporal equivalent of intrusions that penetrate the connemara dalradian thus movement along the mannin thrust brought mid crustal plutons and dalradian country rocks tectonically above the extrusive volcanic sequence the mannin thrust is identified as a major imbricating structure within a continental arc but not a terrane boundary

geochemistry u pb geochronology and genesis of granitoid clasts in transported volcanogenic massive sulfide ore deposits buchans newfoundland1 the buchans group central newfoundland represents an ordovician continental bimodal calc alkaline arc sequence that hosts numerous volcanogenic massive sulfide vms occurrences including both i

stream response to repeated coseismic folding tiptonville dome new madrid seismic zone abstract fluvial response to tectonic deformation is dependent on the amount and style of surface deformation and the relative size of the stream active folding in the new madrid seismic zone nmsz forms the tiptonville dome a 15 km long and 5 km wide surface fold with up to 11 m of late holocene structural relief the fold is crossed by streams of varying size from the mississippi river to small flood plain streams fluvial response of these streams to repeated coseismic folding has only been preserved for the past 2 3 ka since the tiptonville meander of the mississippi river migrated across the area forming the present flood plain this surface comprises a sandy point bar deposit locally overlain by clayey overbank and silty sand crevasse splay deposits an abandoned chute channel infilled with laminated sandy silt and silty clay and an abandoned neck cutoff filled with a sandy cutoff bar and silty clay oxbow lake deposits dating various stream responses to coseismic folding has more tightly constrained the timing of earthquake events in the central nmsz and provides a means of partitioning the deformation amount into individual seismic events three earthquakes have been dated in the reelfoot lake area ca a d 900 1470 and 1812 the latter two earthquakes had large local coseismic deformation both of these events were responsible for numerous stream responses such as shifting depocenters modification of mississippi river channel geometry and derangement of small streams overbank sedimentation ceased on the dome as it was uplifted above the normal flood stage and sedimentation of crevasse splay deposits from the mississippi river colluvium from the scarp and lacustrine sediment accumulated in the adjacent reelfoot basin the much larger mississippi river channel responded to uplift by increasing its sinuosity across the uplift relative to both upstream and downstream increasing its width depth ratio across and downstream of the uplift and decreasing the width depth ratio upstream of the uplift despite the size of the mississippi river it has not yet attained equilibrium since the latest uplift 190 years ago small channels that could not downcut through the uplift were filled locally reversed flow direction or formed a lake where they were dammed uplift and stream response to folding along the tiptonville dome is less dramatic between 2 3 and 0 53 ka during this interval abandoned channel fill and overbank deposition across the dome suggests that it was not a high relief feature one earthquake event occurred during this interval ca a d 900 but coseismic stream response was probably limited to a slight aggradation of a small flood plain stream