a middle cambrian trilobite faunule from the meguma group of nova scotia the meguma group of southern nova scotia is a thick succession of mostly deep water siliciclastic sedimentray rocks of uncertain age previous fossil finds have been in the halifax formation of the upper part of the sequence and have provided early ordovician ages a newly discovered trilobite bearing bed from the underlying goldenville formation yields middle cambrian taxa of acado baltic affinity specimens belonging to paradoxides s l agraulos dorypyge and ellipsocephalidae indicate that the meguma group is an exotic succession with faunal similarity to the adjacent avalon terrane and to middle cambrian successions in europe the middle east and west africa

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

xenoliths in a mafic dyke at popes harbour nova scotia implications for the basement to the meguma group a recently recognized series of northwest trending mafic dykes cuts the cambro ordovician meguma group along the eastern shore of nova scotia some of the dykes contain gneissic and meta plutonic xenoliths interpreted here as including fragments of the basement to the meguma group most of the gneissic xenoliths in the dyke exposed at popes harbour are sillimanite and or kyanite bearing quartz poor metapelites and garnet orthopyroxene bearing tonalitic rock other enclaves include amphibolite quartzite gabbro granite granodiorite and granitic pegmatite textural features suggest that the earliest paragneissic assemblage included poikiloblastic garnet xfe 0 55 0 65 xmg 0 05 0 30 xca 0 02 0 16 xmn 0 02 0 16 biotite kyanite and or sillimanite oligoclase and quartz subsequent recrystallization at higher temperature and or lower pressure conditions is suggested by the replacement of kyanite by sillimanite mineral core composition data indicate early metamorphic conditions of 45

middle miocene tectonic boundary conditions for use in climate models utilizing general circulation models gcms for paleoclimate study requires the construction of appropriate model boundary conditions we present a middle miocene paleotopographic and paleobathymetric reconstruction geographically constrained at 15 ma for use in gcms paleotopography and paleogeography are reconstructed using a published global plate rotation model and published geological data paleobathymetry is reconstructed through application of an age depth relationship to a middle miocene global digital isochron map followed by the overlay of reconstructed sediment thickness and large igneous provinces adjustments are subsequently made to ensure our reconstruction may be utilized in gcms

northwestern africa and the avalonian plate relations during late precambrian and late paleozoic time morocco and especially the moroccan meseta is compared to the eastern margin of the appalachians the structural history of these regions is discussed for two key periods and orogenic episodes 1 late precambrian and the avalonian pan african orogeny and 2 late paleozoic and the alleghanian hercynian orogeny the observed similarities suggest that morocco and the eastern margin of the appalachians belong to the same continental block the avalonian plate

integrated model for meguma group lode gold deposits nova scotia canada meguma group lode gold deposits represent concentrations of a variety of auriferous quartz veins in lower paleozoic metaturbidites of the meguma terrane of southern nova scotia our studies incorporating extensive field regional and detailed mapping and laboratory petrography fluid inclusions geochemistry isotopes studies of 30 of these deposits in the eastern meguma terrane suggest that mineralization occurred at ca 370 ma 40 ar 39 ar dating of hydrothermal vein minerals during widespread incursion of mafic and felsic magmatism into the crust concurrent with subvertical shear zone development thus postdating regional acadian deformation by some 30 40 m y isotopic data s c o sr indicate that vein forming fluids were not solely magmatic and were in part exotic to the meguma group thus earlier magmatic and metamorphogenic lateral secretion models that considered either late stage magmatic fluids or the enveloping meguma group metasedimentary rocks as the sole source of vein components are invalidated

sm nd isotopic investigation of the age and origin of the meguma zone metasedimentary rocks the meguma zone of southern nova scotia is a suspect terrane in the eastern appalachians sm nd isotopic data on six samples from the thick sequence of flyschoid metasediments of the meguma group show that these rocks have a mean crustal residence age of tdm 1773 95 ma considerably older than their cambro ordovician depositional age this information should be useful in locating the matching terrane for the meguma and ultimately in determining whether it was derived from one or more precambrian sources with different crustal residence times

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

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

silurian cover late precambrian early ordovician basement and the chronology of silurian orogenesis in the hermitage flexure newfoundland appalachians

pacific variability under present day and middle miocene boundary conditions we use the coupled climate model mpi esm to show that for higher co2 levels the el nino southern oscillation enso and the pacific decadal oscillation pdo merge into a single mode of pacific variability regardless of present day or middle miocene 15 ma topographic boundary conditions hence topographic differences determining the landscape of past climates play a smaller role for pacific variability than previously thought we attribute the single variability mode to resonance between these two oscillation patterns in order to estimate the strength of the resonance we compute the spectral power of the enso and pdo time series and their coherence we find that for both middle miocene and present day topographic conditions higher co2 forcing leads to stronger resonance between enso and pdo our results show that 1 stronger co2 forcing enhances pacific variability resulting in stronger atmospheric bridge and that 2 past climates are likely to exhibit pacific variability corresponding either to enso pdo or our proposed single mode

interaction among upper crustal lower crustal and mantle materials in the port mouton pluton meguma lithotectonic zone southwest nova scotia the port mouton pluton is unique among the late devonian peraluminous granitoid bodies in the meguma lithotectonic zone of southwestern nova scotia in its lithological heterogeneity extensive physical and chemical interac tion with the country rocks clear evidence for mingling and mixing with mafic magmas and highly abundant pegmatites new u pb age determinations on monazite establish an intrusion age of 373 1 ma similar to the ages of other meguma lithotectonic zone granitoid plutons and mafic intrusions field relations petrology and geochemistry define three stages of intrusion of the port mouton pluton i early stage discontinuously exposed around the outer margin of the pluton dominated by coarse grained tonalite granodiorite and with rb sr 0 40 and gdn lun 0 55 eu eu 2 and iii late stage consisting of abundant minor sheets throughout the pluton dominated by fine grained tonalite granodiorite and leucogranite that are similar to rocks of the early and middle stages the port mouton pluton shows a wider range of 87 sr 86 sri 0 7036 0 7154 and a wider range and generally higher endi 3 72 to 2 12 than other granitoid rocks in the meguma lithotectonic zone potentially reflecting a com plex partially equilibrated interaction among mantle lower crust and upper crust field petrological and chemical evi dence for the involvement of mantle derived magmas and melting of upper crust permit modelling of the port mouton pluton granitoid compositions by three simultaneous mixing equations these mixing model results suggest that the early stage granitoid rocks can form from simple three component mixing relationships when the bulk distribution coefficients between residuum and melt for sr and nd range from 1 05 to 1 18 or two component mixing combined with fraction ation of material like the known felsic lower crust the middle stage granitoid rocks only yield solutions involving two component mixing and fractionation of material unlike the known felsic lower crust we conclude that the late devonian mafic magmas played a major role in the formation of granitoid magmas in the meguma lithotectonic zone by supplying heat and material to cause partial fusion of the avalon lower crust

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

the impact of convection on enso from a delayed oscillator to a series of events abstract the ncar community climate system model version 3 ccsm3 exhibits persistent errors in its simulation of the el nino southern oscillation enso mode of coupled variability the amplitude of the oscillation is too strong the dominant 2 yr period too regular and the width of the sea surface temperature response in the pacific too narrow with positive anomalies extending too far into the western pacific two changes in the parameterization of deep convection result in a significant improvement to many aspects of the enso simulation the inclusion of convective momentum transport cmt and a dilution approximation for the calculation of convective available potential energy cape are used in development integrations and a striking improvement in enso characteristics is seen an increase in the periodicity of enso is achieved by a reduction in the strength of the existing short circuited delayed oscillator mode the off equatorial response is weaker and less tropically confined largely as a

origin of the late devonian weekend lamprophyre dykes meguma zone nova scotia the weekend dykes consist of 10 late devonian spessartite lamprophyres cropping out within the allochthonous meguma lithotectonic terrane of the northern appalachians the dykes have characteristic panidiomorphic textures with seriate phenocrysts of amphibole clinopyroxene and rare biotite set in a groundmass of intergrown plagioclase k feldspar and quartz with deuteric calcite and epidote all dykes intruded during one magmatic episode ca 370 ma following terrane accretion of the acadian orogeny the unaltered weekend dykes show restricted major element variation sio2 54 58 wt al2o3 14 16 wt mgo 7 11 wt and total alkalies 2 4 5 5 wt and have high mg 71 80 and moderate to high concentrations of ni 69 278 ppm and cr 390 992 ppm large ion lithophile element e g sr ba 294 1194 ppm and light rare earth element 13 67cn abundances are high relative to high field strength element e g nb ta y 0 45 26 ppm and heavy rare earth element 6 30cn abundances geochemical varia

the weekend dykes a newly recognized mafic dyke swarm on the eastern shore of nova scotia canada a group of related mafic dykes is present along the eastern shore of nova scotia from halifax to country harbour the dykes are generally vertical strike about 150 and have an abundance of carbo

middle miocene climate and vegetation models and their validation with proxy data abstract the miocene is a relatively recent epoch of the earth s history with warmer climate than today particularly during the middle miocene climatic optimum mmco approximately 17 15 ma although the cause of the warming is probably not only attributable to co2 but also to changes in orography and configuration of ocean gateways this time interval represents an ideal case study to test the ability of climate models to simulate warm climates comparable to those that the earth may experience in the near future however even with higher than present day co2 concentrations the mmco warming inferred from terrestrial proxy data has been difficult to reproduce in climate models since fossil flora do not provide direct information on climate but on flora and vegetation climate model results are generally compared to climate reconstructions obtained from the fossil flora in this study we apply an alternative method by simulating palaeovegetation from the outputs of the climate model using a dynamic vegetation model model vegetation reconstruction can then be compared to the vegetation cover indicated by the fossil flora record at the various localities provided that a common classification of plant functional types pfts is used for the data and the model here we reconstruct the vegetation of the middle miocene with the global dynamic vegetation model caraib using the climatologies derived from five atmospheric general circulation models the reliability of the simulations is examined on a presence absence basis of pfts by comparison of vegetation reconstructions to palaeoflora data recorded in the northern hemisphere and the tropics this comparison provides an overall agreement around 60 between model and data when all sites and tree types are considered three model simulations out of five show to be better at predicting the absence than the presence the presence of warm temperate mixed forests in the middle latitudes dominated by broadleaved deciduous warm temperate and subtropical trees is generally well reproduced in caraib simulations however poor agreement is obtained for the presence of tropical pfts out of the tropics and for warm pfts at latitudes northward of 50 n where climate models remain too cold to produce assemblages of trees consistent with the data nevertheless the model data comparison performed here highlights several mismatches that could result not only from missing feedbacks in the climate simulations but also from the data the results of the likelihood analysis on presence absence of pfts illustrate the uncertainties in the pft classification of the neogene floral records the coexistence of some pfts in the palaeovegetation data is impossible to reproduce in the vegetation model simulations because of the climatic definition of the modern pfts this result indicates either a bias in the identification of modern analogues for fossil plant taxa or a possible evolution of environmental requirements of certain plants

accounting for centennial scale variability when detecting changes in enso a study of the pliocene the el nino southern oscillation enso is the dominant mode of interannual climate variability however climate models are inconsistent in future predictions of enso and long term variations in enso cannot be quantified from the short instrumental records available here we analyse enso behaviour in millennial scale climate simulations of a warm climate of the past the mid pliocene warm period mpwp 3 3 3 0ma we consider centennial scale variability in enso for both the mpwp and the preindustrial and consider which changes between the two climates are detectable above this variability we find that el nino typically occurred 12 less frequently in the mpwp but with a 20 longer duration and with stronger amplitude in precipitation and temperature however low frequency variability in enso meant that pliocene preindustrial changes in el nino temperature amplitude in the nino3 4 region 5 n 5 s 170 w 120 w were not always detectable the pliocene preindustrial el nino temperature signal in the nino4 region 5 n 5 s 160 e 150 w and the el nino precipitation signal are usually larger than centennial scale variations of el nino amplitude and provide consistent indications of enso amplitude change the enhanced mpwp temperature signal in the nino4 region is associated with an increase in central pacific el nino events similar to those observed in recent decades and predicted for the future this study highlights the importance of considering centennial scale variability when comparing enso changes between two climate states if centennial scale variability in enso has not first been established results suggesting changes in enso behaviour may not be robust

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

u pb geochronological constraints on precambrian stratified units in the avalon composite terrane of nova scotia canada tectonic implications concordant u pb ages of detrital zircons in several proterozoic units in the avalon composite terrane of nova scotia along with previously published data indicate that deposition of low and high grade stratified units in the cobequid highlands gamble brook formation and central cape breton island variously assigned to the george river group or george river metamorphic suite and the bras d or gneiss started after 977 ma extended through a period of volcanic activity between 694 and 637 ma and ended before the 629 612 600 ma volcanic activity associated with deposition of the georgeville and jeffers groups in the antigonish and cobequid highlands and the east bay hills and coxheath groups in southern cape breton island these age data along with u pb analyses of metamorphic and igneous zircon and monazite also constrain three late proterozoic tectonothermal events i oblique sinistral ductile shear deformation and greenschist amphibolite facies metamorphism probably occurred between 694 an

sm nd isotopic geochemistry of precambrian to paleozoic granitoid suites and the deep crustal structure of the southeast margin of the newfoundland appalachians in the eastern central mobile belt of the newfoundland appalachians late precambrian basement inliers have end from 3 to 2 but cambro ordovician metasedimentary rocks have initial end below 7

a permanent el nino like state during the pliocene the pliocene may have been characterized by permanent el nino like conditions initial modeling studies suggest that this may have contributed to pliocene warmth the termination of this state may have influenced northern hemisphere glaciation nhg we use the hadley centre coupled model version 3 to examine the role of the oceans and ocean structure on pliocene warmth a permanent el nino like state is not predicted annual mean sea surface temperatures in the eastern equatorial pacific at ocean drilling program sites 847 and 851 increase by 1 71 c and 1 15 c respectively however el nino southern oscillation events are clearly expressed by the model sensitivity tests indicate that a prescribed permanent el nino like condition increases annual global mean surface temperatures by a maximum of 0 6 c if the pliocene was characterized by such a condition it is questionable that it provided a major contribution to global warmth and therefore unlikely that the termination of this state contributed significantly to the onset of nhg

precise u pb dating of meguma basement xenoliths new evidence for avalonian underthrusting u pb zircon and monazite dates for granulite facies basement xenoliths from the popes harbour dyke on the eastern shore of nova scotia provide strong evidence that the meguma terrane overlies avalo

crustal xenoliths in triassic lamprophyre dykes in western morocco tectonic implications for the rheic ocean suture dykes of calc alkaline lamprophyre cutting granite of the hercynian jebilet massif of the moroccan meseta western morocco contain crustal xenoliths the xenoliths range in composition from mafic cognate cumulates and upper crustal granitic rocks through gneisses to middle crustal felsic granulites shrimp u th pb zircon analyses of these rocks indicate that the dykes were likely intruded during middle triassic times similar 235 ma whereas the xenoliths contain zircons with concordant carboniferous early permian neoproterozoic and palaeoproterozoic ages 280 328 ma c 540 615 ma 700 ma and similar 2000 ma the 280 328 ma ages appear to record synchronous intrusive and high grade up to granulite facies variscan metamorphic events suggesting that high grade metamorphism may have facilitated the s type granitic magmatism on the other hand the similar 540 615 ma 700 ma and 2000 ma ages correspond with pan african and eburnian orogenic events recorded in the west african craton in a triassic reconstruction morocco is juxtaposed against nova scotia canada and some have proposed that the basement of the easternmost terrane meguma terrane is a piece of the west african craton however lower crustal xenoliths from devonian dykes similar 370 ma cutting the meguma terrane have yielded late devonian neo and mesoproterozoic ages 378 ma 575 629 ma similar 880 1050 ma and similar 1530 ma the presence of similar 1 ga ages suggests that the basement of the meguma terrane is avalonian rather than west african implying that in a pangean reconstruction the rheic ocean suture between nw africa and maritime canada coincides with the atlantic ocean

robust enso across a wide range of climates abstractel nino southern oscillation enso is a pronounced mode of climate variability that originates in the tropical pacific and affects weather patterns worldwide growing evidence suggests that despite extensive changes in tropical climate enso was active over vast geological epochs stretching millions of years from the late cretaceous to the holocene in particular enso persisted during the pliocene when a dramatic reduction occurred in the mean east west temperature gradient in the equatorial pacific the mechanisms for sustained enso in such climates are poorly understood here a comprehensive climate model is used to simulate enso for a broad range of tropical pacific mean climates characterized by different climatological sst gradients it is found that the simulated enso remains surprisingly robust when the east west gradient is reduced from 6 to 1 c the amplitude of enso decreases only by 30 40 its dominant period remains close to 3 4 yr and the spectral peak stays above red noise t

late proterozoic tectonic model for the avalon terrane in maritime canada the avalon terrane in maritime canada extends from cape breton island through northern nova scotia antigonish and cobequid highlands to southern new brunswick the terrane contains abundant late proterozoic volcanic rocks 570 680 m y old the geochemistry of the volcanic rocks of southern cape breton island and southern new brunswick indicates that they were erupted in a volcanic arc environment in both regions the mafic rocks display a remarkably similar compositional zonation which resembles the across arc variations observed in modern volcanic arcs the progressive compositional changes that include a transition from island arc tholeiites along the southeastern coasts to calc alkaline rocks inland to the northwest are probably due to a northwest dipping subduction zone with a trench located to the southeast in the antigonish and cobequid highlands continental tholeiites and calc alkaline volcanic rocks are interbedded and overlain by turbidites that have probably been deposited in a back arc or intra arc environment the superimposed positive gravity and magnetic anomalies that may be traced discontinuously from the grand banks through nova scotia collector anomaly and along the northern side of the gulf of maine to near boston probably represent late proterozoic ophiolitic remnants preserved by incomplete suturing along a late proterozoic plate boundary northeast trending segments are inferred to mark subduction zones and the e w portions could correspond to transform faults thus the present geographical distribution of the late proterozoic volcanic rocks is explained by a tectonic model involving a single subduction zone offset by two late proterozoic transform faults located approximately along the minas fault and the scatarie ridge

an empirical sapphirine spinel mgfe exchange thermometer and its application to high grade xenoliths in the popes harbour dyke nova scotia canada owen j v and greenough j d 1991 an empirical sapphirine spinel exchange thermometer and its application to high grade xenoliths in the popes harbour dyke nova scotia canada lithos 26 317 332 spinel sapphirine corundum rutile parageneses in metapelitic xenoliths from the lamprophyric popes harbour dyke are enclosed by feldspathic rare quartz haloes that embay aluminosilicates and biotite these feldspathic haloes contain plagioclase an2o 4o and or an alkali or ternary hypersolvus feldspar and show a variety of igneous and devitrification textures suggesting an anatectic origin the spinelbearing parageneses are interpreted as the refractory residue formed by the incongruent melting of biotite aluminosilicates and associated phases equilibration temperatures of these assemblages are estimated from an empirical sapphirine spinel mg fe exchange thermometer derived from literature data on both silica saturated and undersaturated sapphirine granulites linear regression r 0 81 of the calibrant data yields the expression t c 800 228 lnkd 273 where kd x x g x x g precision is estimated at 100 c but will likely be less for highly oxidized sapphirine granulites owing to 1 errors in the stoichiometric estimation of xfe3 from microprobe data and 2 the formation of magnetite at the expense of spinel or sapphirine leading to an increase in xmg in either or both phases during cooling application of this expression to the reduced graphite bearing popes harbour xenoliths yields t of 725 795 c anatexis is attributed to thermal metamorphism by the lamprophyric magma prior to and or during entrainment of xenolith material in the dyke high t assemblages were quenched before the xenoliths attained thermal equilibrium with the magma consequently prograde reaction textures and compositional zoning patterns are preserved

a silurian u pb age for the cape st mary s sills avalon peninsula newfoundland canada implications for silurian orogenesis in the avalon zone mafic sills from cape st mary s on the avalon peninsula of newfoundland give an u pb baddeleyite age of 441 2 ma this age corresponds with the earliest ages recorded for the climactic silurian orogenic event that dominantly affected rocks of the central mobile belt in newfoundland the age is consistent with but in no way necessitates that the avalon and gander zones were juxtaposed during the silurian because sills tend to form in poorly lithified and undeformed sedimentary rocks it is unlikely that cambrian sediments hosting the sills were affected by ordovician orogenic events that strongly affected central newfoundland negative nb and ti anomalies on mid ocean ridge basalt normalized diagrams show that the sill geochemistry is consistent with formation in a transpressional tectonic environment mafic magmas clearly associated with the silurian event share these chemical and tectonic affinities thus both the age and geochemical data are consistent with but do not require a link between the gand

eocene el nino evidence for robust tropical dynamics in the hothouse much uncertainty surrounds the interactions between the el nino southern oscillation enso and long term global change past periods of extreme global warmth exemplified by the eocene 55 to 35 million years ago provide a good testing ground for theories for this interaction here we compare eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments the simulations show pacific deep ocean and high latitude surface warming of approximately 10 degrees c but little change in the tropical thermocline structure atmosphere ocean dynamics and enso in agreement with proxies this result contrasts with theories linking past and future hothouse climates with a shift toward a permanent el nino like state

ocean mixed layer processes in the pacific decadal oscillation in coupled general circulation models it is investigated how the pacific decadal oscillation pdo is simulated differently among various coupled general circulation models cgcms and how it is related to the heat budget of the simulated ocean mixed layer which includes the surface heat flux and ocean heat transport for this purpose the dataset of the climate of the 20th century experiment 20c3m from nine cgcms reported to ipcc s ar4 are used while the mri and miroc models are examined in detail detailed analyses of these two cgcms reveal that the pdo is mainly affected by ocean heat transport rather than surface heat flux in particular in the mri model which has a larger contribution of ocean heat transport to the heat budget it is found that the ocean heat transport due to ekman advection versus geostrophic advection contributes differently to the pdo in the western and central north pacific specifically the strength of pdo tends to be larger for cgcms with a larger ocean heat transport in the region

quasi decadal variability in paleoclimate records sunspot cycles or intrinsic oscillations 1 paleoclimatic proxies for interannual variability reveal power within the 7 15 year quasi decadal qd band in earth s history despite the fact that the best established sources of qd variability in modern climate are internal this qd variability in paleoclimatic records is commonly attributed to the 11 year sunspot cycle of solar variability intrinsic qd variability has received little attention in paleoclimatology we apply two different modeling frameworks to assess the degree to which qd variability might have occurred in the past and question whether existing paleoclimate records no matter how well resolved distinguish between internally driven and solar driven variability we show that even a simple atmospheric general circulation model gcm driven by constant solar radiation produces climate oscillations with a period of 11 years then motivated by numerous studies arguing for the presence of sunspot cycles in eocene 50 ma paleoclimate records we demonstrate that a fully coupled gcm simulation with constant solar forcing reproduces the full spectrum of reconstructed eocene variability in the examples we consider there is no compelling reason to invoke solar cycles as a cause of interpreted variability we stress the importance of identifying internal modes of variability from paleoclimate records to increase understanding of the climate system

contrasting u pb ages from plutons in the bras d or and mira terranes of cape breton island nova scotia u pb dates from zircon titanite and monazite in plutons of the bras d or and mira terranes of southern cape breton island combined with 40ar 39ar and other radiometric age data indicate that th

wind stress curl and enso discharge recharge in the equatorial pacific discharge and recharge of the warm water volume wwv above the 20 c isotherm in an equatorial pacific ocean box extending across the pacific from 156 e to the eastern ocean boundary between latitudes 5 s and 5 n are key variables in enso dynamics a formula linking wwv anomalies zonally integrated wind stress curl anomalies along the northern and southern edges of the box and flow into the western end of the box is derived and tested using monthly data since 1993 consistent with previous work a wwv balance can only be achieved if the 20 c isotherm surface is not a material surface that is warm water can pass through it for example during el nino part of the wwv anomaly entering the box is cooled so that it is less than 20 c and therefore passes out of the bottom of the box the 20 c isotherm surface the observations suggest that the anomalous volume passing through the 20 c isotherm is approximately the same as t the anomalous wwv entering the western end of the box therefore the observed wwv anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box the curl anomaly changes the wwv both by divergent meridional flow at the edges of the box and vortex stretching that is the sverdrup balance does not hold in the upper ocean a typical amplitude for the rate of change of wwv for the 5 s 5 n box is 9 6 sv sv 10 6 m 3 s 1 the wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the el nino index nino 3 4 the average sea surface temperature anomaly ssta over the region 5 s 5 n 170 120 w and nino 3 4 leads minus the wwv anomaly by one quarter of a cycle based on the preceding results a simple discharge recharge coupled enso model is derived only water warmer than about 27 5 28 c can give rise to deep atmospheric convection so unlike past discharge recharge oscillator models the west central rather than eastern equatorial sstas are emphasized the model consists of two variables t the ssta averaged over the region of strong enso air sea interaction in the west central pacific equatorial strip 5 s 5 n 156 e 140 w and d the 20 c isotherm depth anomaly averaged over the

magma injection directions inferred from a fabric study of the popes harbour dike eastern shore nova scotia canada a 15 m wide dike at popes harbour on the eastern shore of nova scotia shows an increase in both the size up to 1 m and density up to 50 of predominantly pelitic xenoliths toward the dike center these features reflect flowage differentiation processes during dike emplacement flow direction is indicated by sillimanite xenocrysts that represent the unassimilated products of xenolith disaggregation the xenocrysts are highly aligned parallel to the dike margins northwest southeast with a mean plunge of 20 se suggesting that the magma last moved and may have been injected in a subhorizontal northwestward direction the available information indicates that lateral injection of magma in mafic dikes is more common than predominantly vertical movement this study shows that an analysis of fabrics in mafic dikes should be useful in further evaluating the role of lateral magma injection in dike formation

late devonian lamprophyric dykes in the meguma zone of nova scotia hornblende rich lamprophyric dykes from southeastern nova scotia are contemporaneous with the large peraluminous granitic batholiths ca 370 ma of the meguma zone and may be closely associated with their origin

evidence for active el nino southern oscillation variability in the late miocene greenhouse climate an evaporite varve thickness record from the late miocene mediterranean reveals significant signals of interannual variability the frequency and persistence of which are compared with climatic oscillations affecting the region today sustained variability in the 2 7 yr band resembles the modern spectrum of the el nino southern oscillation enso and contrasts with that of the north atlantic oscillation nao the cyclicity of which is less stationary in frequency and less sustained in duration fully coupled climate model simulations demonstrate not only that enso variability persisted during the late miocene but also that its teleconnections may have extended further than today as high latitude climate modes weakened due to a reduced meridional temperature gradient enso appears to have exerted a stronger influence on the evaporative balance of the mediterranean in the late miocene than it does today this evidence suggests that the pacific prior to the northern hemisphere glaciation was characterized by ongoing interannual variability

regional significance of new u pb age data for neoproterozoic igneous units in avalonian rocks of northern mainland nova scotia canada gondwanan neoproterozoic tectonothermal events pan african and brasiliano are represented in northern mainland of nova scotia by volcanic and sedimentary rocks assigned to the jeffers and georgeville groups and by gabbroic to granitoid plutons these rocks comprise part of avalonia an exotic terrane in the appalachian orogen that was deposited in an arc related environment along the periphery of gondwana prior to accretion to laurentia lavas sampled in the basal units of the jeffers and georgeville groups yielded slightly discordant u pb zircon and monazite data that fall on chords with upper intercept ages of 628 ma and 617 7 1 6 ma respectively syntectonic to late syntectonic plutons intruded into these groups yielded u pb zircon ages of 606 6 1 6 ma and 603 9 5 ma the former intrusion also yielded a concordant titanite age of 607 3 ma when combined with previously published ages these data indicate that the back arc deposition recorded in these groups lasted 10 15 million years 628 613 ma and was closely followed by c 613 595 ma metamorphism intrusion and heterogeneous strike slip related deformation assuming no significant shuffling of fault blocks the relative locations of the cobequid antigonish back arc basin and the southern cape breton island volcanic arc are consistent with their genesis above a north west dipping subduction zone the age range of arc related magmatism in nova scotia is similar to that of avalonian rocks in southeastern newfoundland and britain lending support to hypotheses of neoproterozoic linkages

an oxygen isotope study of two contrasting orogenic vein gold systems in the meguma terrane nova scotia canada with implications for fluid sources and genetic models sampling of quartz vein material from two gold deposits of similar geological setting but different ages the ovens 408 ma dufferin 380 ma in the meguma terrane of nova scotia has been done to compare and contrast their 18oquartz signatures despite different ages of formation quartz from all vein types in each of the deposits i e saddle reef bedding concordant leg reefs en echelon discordant shows limited intra deposit variation with similar average 18o values of 15 2 0 9 n 16 for the ovens and 15 7 0 6 n 12 for dufferin using an average 18o value of 15 4 for the two deposits the corresponding 18oh2o values calculated for 400 c and 350 c based on constraints from mineral assemblages and fluid inclusion studies indicate averages of 11 4 0 2 and 10 2 0 2 respectively the isotopic data indicate that 1 the vein forming fluids have a metamorphic signature 2 all vein types in the two deposits represent formation from a single isotopically homogeneous fluid and 3 a fluid of similar isotopic signature was generated by two contrasting tectono thermal events in the meguma terrane that were separated by 30 ma integration of these results with previously published data for 14 meguma gold deposits indicate a general stratigaphic dependence in 18oh2o values for deposits when arranged in their relative stratigraphic position such that 18oh2o values increase upwards in the stratigraphy this apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein forming fluids but instead is modelled using fluid rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy

petrochemistry tectonic history and sr nd systematics of the liscomb complex meguma lithotectonic zone nova scotia the liscomb complex area ca 240 km2 located in the meguma lithotectonic zone of the canadian appalachians consists of three main lithological components high grade gneisses mafic plutons and peraluminous granitoid bodies field relations and 40ar 39ar dating 369 377 ma embracing all three lithological groups show that the complex is post acadian the gneisses occur as a domal uplift and represent a mixed volcano sedimentary package that is structurally metamorphically and chemically distinct from the surrounding low grade metawackes and metapelites of the meguma group the mafic intrusions quartz gabbro to quartz diorite have major and trace element compositions e g ti zr y nb zr y th yb ta yb rare earth elements typical of within plate or volcanic arc materials the peraluminous granitoid rocks range from two mica granodiorites to leucomonzogranites and are mineralogically and chemically very similar to granitic rocks elsewhere in the meguma zone neodymium and strontium isotopic

discussion of geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf 11appears in canadian journal of earth sciences 2011 48 4 703 718 doi 10 1139 e10 092 the paper geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf romer et al published in 2011 describes six samples of which four are from the meguma supergroup of nova scotia previous work indicates that these samples are cambrian and that they were deposited in a deep water turbidite basin megumia not on the avalonian shelf the geochemical data support models for mn concentration involving oxidation and reduction in a sedimentary environment but do not constrain water depth likely correlatives are in the cambrian of north wales and not in the european localities sampled by the authors

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

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

age of detrital zircon and titanite in the meguma group southern nova scotia canada clues to the origin of the meguma terrane abstract precise u pb isotopic analysis of seventeen selected high quality laboratory abraded zircon single grains seven multigrain fractions of similar material and four paramagnetic titanite fractions record the ages of the various detrital grain types from two turbidite samples collected from the top and about 5 km below the top of the goldenville formation of the meguma group the results show that the source of both sediments contained 600 ma and 2000 ma old volcanic plutonic components whereas a third 3000 ma old component occurs exclusively in the upper sample and the youngest zircons and titanite are found in the lower sample lead lead ages of bulk fractions at 2300 ma and two nearly concordant single grains at 2040 ma and 2140 ma upper sample together with 2157 ma bulk fraction and 2060 ma and 2080 ma single grain fractions lower sample indicate that the 2000 ma component dominates the pink purple euhedral grain types detrital titanite gives ages of 605 ma upper sample and 552 ma lower sample with the latter sample containing a minor 1975 ma component colourless zircons record this same age difference the lower sample contained the youngest concordant single zircon grain 566 ma and 580 605 ma bulk grain fraction even though two concordant single grains have ages of 632 and 643 ma estimated bulk fraction ages for certain zircon grain types from the upper sample fall in the range of 605 to 675 ma these data suggest that while the youngest rocks in the source region were removed by erosion during the early stages of deposition of the goldenville formation the oldest source rocks were not unroofed until later in the depositional history the 566 8 ma age of the youngest concordant zircon from the stratigraphically lower sample provides a maximum age for the deposition of this grain with the base of the cambrian placed between 545 and 530 ma the goldenville formation may straddle the precambrian cambrian boundary graptolites from the immediately overlying halifax formation are of early ordovician tremadocian age the lower sample contains spherical zircons that may have been derived from mafic granulite with an estimated age of 2000 2200 ma with this one possible exception all of the zircons analyzed appear to be igneous in origin and all are relatively euhedral indicating that rocks of the ages referred to above probably outcrop in the source area anomalous discordance patterns imply that part of the 2960 ma area was metamorphosed by the 2000 ma event and that both the 2960 and 2000 ma regions were metamorphosed during the 600 ma event the complete lack of detritus with ages between 680 and 2040 ma virtually eliminates a northern north american or baltic shield provenance however the available data are not sufficient to distinguish between a west african or guyana shield source