geology and tectonic development of the bras d or suspect terrane cape breton island nova scotia the bras d or terrane is defined in cape breton island and consists of four distinctive components i low pressure regionally metamorphosed aluminous and calcareous gneiss of the proterozoic bra

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

the estimation of global sea level change a problem of uniqueness an objective method of estimating regional averages of coherent sea level sl change is developed the technique is applied to a large set of sl data representative of most of the world s continental margins the results show highly coherent sl changes over many of the regions studied the method is then applied to the regional averages themselves to develop an overall estimate of the coherent pattern of sl variations existing in the historical sl data set the pattern is characterized by a coherent rise of sl in all regions except alaska scandinavia both areas of notorious crustal uplift and southeast asia where sl appears to be falling the analysis suggests little or no change in sl prior to the early 1900 s the period since that time has seen an increase in sl that is optimally fit by a linear trend of 23 cm century the study results suggest that it is not possible to uniquely determine either a global rate of change of sl or even the average rate of change associated with the existing inadequate data set indeed different analysis methods by themselves can cause 50 variations in the estimates of sl trend in the existing data set a signal noise analysis suggests it should be easy to detect small future changes in the sl trends estimated for the period 1930 1980 however detection of theoretically predicted low frequency signals e g caused by co2 warming will be difficult in view of the huge low frequency natural variability associated with glacial tectonic processes

tectonic implications of 40ar 39ar hornblende ages from late proterozoic cambrian plutons in the avalon composite terrane nova scotia canada the avalon composite terrane in nova scotia mainly represents a late proterozoic rifted cratonic magmatic arc complex the geo chemistry of the volcanic rocks indicates that most of southeastern cape breton island is underlain by a volcanic arc whereas the antigonish and cobequid highlands expose intra arc rift sequences in cape breton island late proterozoic rocks are both volcanic and plutonic south of the macintosh brook fault transecting the boisdale hills whereas they are mainly plutonic rocks north of the fault these igneous units are unconformably overlain by subaerial to shallow marine cambrian ordovician sedimentary sequences containing an atlantic fauna that are interbedded with early to middle cambrian within plate continental rift volcanic rocks 4o ar 39 ar plateau ages recorded by hornblende from plutons spatially associated with these volcanic rocks correspond to three groupings 1 ca 600 635 ma in cape breton island south of the macintosh brook fault 2 ca 525 555 ma in cape breton island north of the macintosh brook fault boisdale hills north mountain and creignish hills 3 ca 600 625 ma in the antigonish and cobequid highlands based upon the low metamorphic grade of the late proterozoic and early paleozoic rocks and the low pressures recorded in contact aureoles and plutons it is inferred that these plutons were emplaced at relatively shallow crustal levels and therefore the 40 ar 39 ar plateau ages probably closely date their emplacement interpretation of the age data suggests that plutonism in nova scotia associated with the rifted magmatic arc lasted from ca 635 600 ma igneous activity continued between ca 555 525 ma and may have been related to the cambrian within plate rift volcanism

devonian extension in northwestern newfoundland 40ar 39ar and u pb data from the ming s bight area baie verte peninsula abstract the ming s bight group of northwestern newfoundland an outlier of humber zone continental margin rocks is entirely surrounded by ophiolitic rocks of the dunnage zone structures in the ming s bight group and adjacent units record three main phases of deformation the earliest structures relate to silurian sinistral transpression previously documented in the region two later phases of extensional deformation produced a series of dextral oblique normal shear zones and faults that now separate the ming s bight group in the footwall from ophiolitic and granitoid rocks in the hangingwall 40ar 39ar and u pb data constrain the times of oblique normal shear and cooling metagabbro in the point rousse ophiolite complex which lies in the hangingwall preserves disturbed ordovician hornblende 40ar 39ar ages whereas adjacent shear zones record devonian ages hornblendes in pacquet harbour group amphibolites within extensional shear zones mainly record 40ar 39ar ages of 390 380 ma synkinematic titanite

late pleistocene and halocene sea level changes in japan implications for tectonic histories and mantle rheology abstract it is very important to separate the tectonic and glacial isostatic components in the observed holocene and late pleistocene sea level changes in tectonically active areas such as japan for studying tectonic processes and for constraining mantle rheology the separation can be achieved by considering the spatial dependence of the relative sea level on the geometry of the coastline around the site where sea level is evaluated in fact the relative sea level caused by the last deglaciation at sites in the embayment such as tokyo and osaka has a sea level curve with a high stand at mid holocene and that site situated on the tip of peninsula has a sea level curve culminating towards the present the geometric effect also causes the regional difference of the sea level variations in the late glacial phase in the japanese islands the regional difference of the predicted relative sea level is about 5 m at 6000 years ago 20 m at 10 000 years ago and 30 m at 18 000 years ago comparison between observations and predictions indicates that the observations at several sites in japan are consistent with the predicted sea level variations more systematic data is required for the period 18 000 years ago to the present in order to examine tectonic processes and mantle rheology

tectonic setting of the tetagouche group in northern new brunswick implications for plate tectonic models of the northern appalachians a regional compilation and reinterpretation of geochemical analyses of mafic igneous rocks from the ordovician tetagouche group in northern new brunswick indicates the presence of at least three mafic assemblages two groups of basalts and gabbros and one group of gabbros only the three groups can be separated on the basis of tio2 and trace element content group a basalts generally have mid ocean ridge basalt morb like compositions whereas group b basalts indicate a within plate setting wpb group c gabbros intrude into silicic volcanics that underlie the basalts but are rare or absent in the areas underlain by group a and b basalts the group c gabbros probably represent the earliest stages of mafic igneous activity and have morb like compositions or represent a transition between morb and arc basalts the association of group a and b basalts with abundant marine sediments such as thinly bedded turbidites and black and red shales and the fact that they erupted locally on top of continental crus

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

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

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

intracrystalline vorticity record of flow kinematics during shear zone reactivation abstract the vorticity axis of deformation of a shear zone is a rotational axis controlled by the relative movement of its boundaries when characterized it is a reliable tool to determine the ductile flow geometry monoclinic general monoclinic transpressive or triclinic and an asset to identify the kinematics of complex oblique collisions advancements in analysis of electron backscattered diffraction ebsd maps now permit inference of vorticity axes known as crystallographic vorticity axes cvas from the intragranular lattice orientation dispersion of strain bearing minerals however natural shear zones may preserve a record of multiple shear events with contrasting kinematics and it is not understood to which extent the quartz lattice may preserve a kinematic record through multiple deformation events herein we characterize the finite flow kinematic record produced during reactivation of the eastern highlands shear zone ehsz in an oblique collision within the canadian appalachians we integrate field and thin section observations quartz lattice preferred orientations ebsd maps and grain classification leading to a new method to determine and compare cva within relict and recrystallized quartz grains using this method we were able to conclude that the ehsz was reactivated in an heterogenous monoclinic flow environment

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

episodic reactivation of a late precambrian mylonite zone on the gondwanan margin of the appalachians southern newfoundland the grand bruit fault zone of southern newfoundland is a fundamental structure within late precambrian basement on the gondwanan margin of the appalachian orogen within the fault zone a sequence of structures documents changes in the sense of ductile displacement from 1 reverse dip slip to 2 dextral strike slip to 3 sinistral oblique slip and finally to 4 dextral lateral offsets fault movements along this structure were punctuated by emplacement of a variety of plutons and minor intrusions which when precisely dated allow these movements to be bracketed at between 571 ma and 564 ma 497 ma and 427 ma 424 ma and 420 ma and 421 ma and 387 ma respectively the tectonic evolution of the gondwanan inlier of southern newfoundland is mirrored in large part by the record of mylonite development within the grand bruit fault zone these tectonic events are attributable to well constrained regional orogenic events of both the pan african and appalachian cycles newly formed shear zones in the fault zone reactivate parts of much older faults of similar regional orientation and are in some cases kinematically indistinguishable from the ancestral structures integration of precise geochronological data with the sequence of overprinted fault structures demonstrates that although the role of progressive deformation in shear zone development was important the observed disposition of structures and rock units is primarily a function of polyorogenic accretion as a multiple reactivated structural lineament in a gondwanan basement inlier the fault zone exerted fundamental control over the tectonic development of the leading edge of the convergent southeast margin of the orogen

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

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

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

early paleozoic paleogeography and accretionary history of the newfoundland appalachians new paleomagnetic results were obtained from several units in the central mobile belt of the north central newfoundland appalachians combined with recently published data the results place important limits on interpretations of early paleozoic paleogeography and evolution of the appalachian caledonian orogen the ordovician appalachian margin of north america located at low paleolatitudes and facing roughly south was separated from the southern margin of iapetus avalon armorica by 3500 km primary directions in pillowed volcanic rocks of the moreton9s harbour group that are part of an early ordovician island arc show that these rocks were formed near the north american margin at a paleolatitude of 12 s early to middle ordovician volcanic rocks of the roberts arm chanceport and summerford groups on the other hand were extruded at paleolatitudes of 30 40 s unconformably overlying volcanics of the silurian botwood group were extruded subaerially at a paleolatitude of 24 s combined with tectonostratigraphic data these results suggest the following tectonic history in early ordovician time northerly subduction of the main iapetus basin was accompanied by the formation of a volcanic arc and a back arc basin near the north american margin middle ordovician emplacement of ophiolites on the north american margin reflects the closure of this back arc basin iapetus i and continued northerly subduction in silurian time closed the main basin iapetus ii

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

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

geological interpretation of a high resolution reflection seismic survey at the buchans mine newfoundland sixteen kilometres of high resolution vibroseis reflection seismic data have been acquired in the vicinity of the former buchans mine direct identification of the cause of several reflectors is possible because the geology is tightly constrained by underground workings and drill holes both of which locally exceed 1 km depth many of the mine scale thrust faults are imaged as reflectors but conformable and intrusive contacts generally responded poorly a significant shallow dipping thrust the powerline fault is recognized below the orebodies and traced throughout the buchans area primarily as a result of the seismic survey it truncates ore stratigraphy and forms the floor thrust of a large duplex stack which hosts all the orebodies its presence has negative implications for exploration in the immediate mine area several lines of evidence suggest that this fault has a significant component of out of sequence movement a strong reflector 4 5 km below buchans is correlated with the surface expression

tectonic burial thrust emplacement and extensional exhumation of the cabot nappe in the appalachian hinterland of cape breton island canada silurian imbricate thrusting early devonian high grade metamorphic nappe emplacement and devonian carboniferous extensional denudation characterize deformation in the appalachian hinterland of cape breton island compressional deformation following early silurian arc volcanism features imbrication of cambrian precambrian basement rocks of gondwana derivation with ordovician silurian cover sequences across thick zones of mylonite during south directed transport high grade metamorphism and gneissic rocks of late silurian age in the region indicate that significant tectonic burial and crustal thickening occurred as a result of the thrusting partial denudation of the high grade assemblages occurred during early devonian thrust emplacement of the cabot nappe toward the northwest along the highlands shear zone the nappe is characterized by an amphibolitic gneiss and high grade schist complex defining a large folded klippe above silurian units kyanite is widespread within the nappe and a distinctive feature of the thrust sheet is the dynamothermal metamorphism of cooler greenschist grade footwall rocks producing inverted isograds staurolite is regionally distributed and occurs in pelitic units in the immediate footwall of the highlands shear zone forming a discontinuous halo around the klippe greenschist grade footwall rocks are exposed in structural windows as a result of folding and faulting shear sense indicators along the margins of the cabot nappe have been rotated into their present positions due to superposed folding providing apparent movement directions for the nappe complete exhumation to surface occurred during late devonian extension along the low angle margaree shear zone

detrital zircon geochronology of a conglomerate in the northeastern cape breton highlands implications for the relationships between terranes in cape breton island the canadian appalachians cape breton island has been interpreted as consisting of four zones of pre carboniferous rocks but the relationships among them are controversial to help resolve the controversy we have dated detrital zircons from a conglomerate part of the cheticamp lake gneiss in the aspy terrane in the northeastern cape breton highlands using the u pb method the following ages were obtained 462 2 ma middle ordovician 492 488 ma 6 ages early ordovician 552 3 ma latest precambrian early cambrian 620 13 and 687 4 ma cadomian and 809 17 1423 10 1462 12 1605 14 1644 4 and 1911 5 ma proterozoic the middle ordovician age sets a maximum age limit for deposition of the conglomerate and supports an ordovician silurian age for the cheticamp lake gneiss the early ordovician latest precambrian early cambrian and cadomian ages match published ages from the bras d or terrane and its correlatives and the mira terrane and its correlatives and indicate provenance of the conglomer

post taconic blueschist suture in the northern appalachians of northern new brunswick canada a narrow belt of late ordovician early silurian blueschist at least 70 km long separates an allochthonous fragment of back arc oceanic crust of the middle ordovician fournier group from underlying rift related volcanic rocks of the middle ordovician tetagouche group in northern new brunswick canada the basalts on both sides of the blueschist belt are predominantly metamorphosed to greenschist facies conditions the blueschist belt is interpreted to be an out of sequence thrust zone that accommodated tectonic transport of higher pressure rocks on top of lower pressure rocks during post peak blueschist facies metamorphism the blueschists have higher fe sub 2 o sub 3 feo ratios and total iron contents in comparison to otherwise chemically equivalent basalts of the fournier and tetagouche groups that have been metamorphosed into greenschists the blueschist belt was probably the site of channelized flow of oxidizing fluids during active deformation ina subduction complex formed during the closure of a wide taconic back arac basin in late ordovician silurian time

secular and earthquake related vertical crustal movements in japan as deduced from tidal records 1951 1981 abstract monthly tidal records for the last 31 years from about 100 tidal stations are used to delineate vertical crustal movements in japan a new computer aided processing system was created for this purpose its principle is differential use of tidal records in a region so that the oceanographic disturbances of common causes may be eliminated from the sea level data this method enables us to observe nearly absolute vertical land movement at tidal stations with a precision of a few centimeters the japanese islands are divided into nine regions taking oceanographic conditions into account general discussion on recent vertical movements has yielded several notable features and trends as follows 1 1 rapid and stationary subsidence in the northeastern part of japan presumably of tectonic origin 2 2 a complex pattern of uplift and subsidence in the southwestern part of japan which seems to reflect subduction of the philippine sea plate against the honshu block 3 3 relatively stable land on the japan sea side of honshu movements related to the earthquakes during the period 1951 1981 are also discussed although few of the cases show clear cut premonitory movements if abnormal movements in a coastal area appeared with an amplitude exceeding 2 or 3 cm we could detect them by the present system

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

glacial rebound and relative sea level variations a new appraisal summary late pleistocene and holocene changes in sea level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the earth to changes in surface loads on time scales of 104yr some separation of parameters defining the ice loads and the earth s response can be achieved by examining sea level change at different sites around the world and at different epochs this paper examines the mathematical requirements for obtaining satisfactory solutions for the sea level equation rather than emphasizing results for the earth s response to the surface loads an examination of the equation expressing the sea level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant earth response parameters are to be deduced from observations of relative sea level the spectrum of the 5 x 5 area mean description of the ice load widely used in glacial rebound studies contains significant power at high degrees n 30 and can result in substantial spatial variations in sea level unless a thick lithosphere is introduced in the earth s response function a smoothed 1 1 description of the ice model avoids these high degree oscillations in relative sea level and produces satisfactory sea level results without requiring a thick lithosphere at far field sites the holocene sea levels are sensitive to the earth s response to the meltwater loading in the vicinity of the site and a high degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site at some sites convergence of the solution to the sea level equation is not obtained even when the solution is expanded to degree 180 convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere if high resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere estimates of mantle viscosity are also of questionable value if these high resolution models are not used a preliminary examination of sea levels at sites in both the near and far field places an upper limit of about 50 80 km on the effective lithospheric thickness these sea level observations are also consistent with an upper mantle viscosity of about 1021 pas with a lower mantle viscosity in the range of 1021 1023pa s

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

lithoprobe onshore seismic reflection transects across the newfoundland appalachians vibroseis seismic reflection data have been recorded to 18 s two way traveltime along three transects across the island of newfoundland the upper crust has both steep and subhorizontal reflectors consistent with a ramp flat style of deformation whereas the middle and lower crust are largely free of regional flats reflectors descend through ca 20 km of vertical section in the middle and lower crust to flatten into the moho or perhaps cut through it in places the moho is interpreted to be no younger than the dipping reflectors reflection fabrics interpreted to be indicators of dominantly mid ordovician to mid silurian strain show consistent orientations among the transects and divide the crust into two blocks a northwestern block is characterized by upper and middle crustal reflectors dipping mostly southeast at variable angles this block is underlain to the southeast by supposedly younger and dominantly northwesterly dipping reflectors that define a northwest tapering wedge shaped block floored

promontory promontory collision in the canadian appalachians in cape breton island and southwestern newfoundland the appalachian orogen is extremely narrow the rocks were strongly deformed and underwent high grade barrovian type metamorphism in silurian time and the orogen parallel silurian thrusts are dominantly west vergent antithetic to the westward subduction this area is bounded by two transverse dextral wrench faults the canso fault to the southwest and the gunflap hills fault to the northeast these tectono stratigraphic structural and metamorphic features are explained by silurian collision between the st lawrence promontory on the laurentian margin and the cabot promontory on the avalon margin during the final closure of the iapetus ocean the west vergent antithetic thrusting is interpreted to be related to tectonic wedging while the two transverse wrench faults accommodated differential movement from promontories to reentrants during the collision promontory promontory collision should be a common process and probably played a significant role in shaping the tectonic framework of many orogenic belts

a reevaluation of the position of the baie verte brompton line in the quebec appalachians the influence of middle devonian strike slip faulting in gaspe peninsula the baie verte brompton line bbl the surface expression of the taconian suture in the canadian appalachian orogen extends from southern quebec to the northeast end of newfoundland in the que

transgressive sand sheet covering the shelf and upper slope off sendai northeast japan abstract a thin sand sheet deposited during the last major transgression from 14 000 to 6000 yrs b p covers the shelf and upper slope off sendai northeast japan the sand sheet overlies the sediments deposited during the last low sea level stand and is partly overlain by modern offshore muds this sheet is regarded as palimpsest sediment formed during the transgression in water depths of 50 m the sand sheet is 50 150 cm thick and consists of alternations of poorly sorted thin sand layers and mud layers that are several millimeters to a few centimeters thick it bears mixed environment molluscan shells and small amounts of glauconite scour and fill structures are frequently found gravel with shell fragments is common near the base of the sheet

structural evolution and tectonic significance of the eastern highlands shear zone in cape breton island the canadian appalachians the eastern highlands shear zone in cape breton island of the canadian appalachians is characterized by an amphibolite facies deformation zone over 5 km wide overprinted by a greenschist facies mylonite zone about 1 km wide deformation zones in both metamorphic grades dip steeply to the southeast with movement direction pitching steeply to the southwest and shear sense indicators indicate the same sense of shear that is an east over west dip slip movement with minor sinistral strike slip component deformation in both conditions is constrained to the late silurian to early devonian mainly late silurian it is suggested that the greenschist facies deformation represents the last stage of a single episode of deformation that occurred initially under amphibolite facies conditions the west vergent shearing along the shear zone is antithetic to the westward subduction that led to the silurian continent continent collision which is interpreted by tectonic wedging in this part of the canadian appalachians

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

fluid flow pathways in actively deforming sediments the role of pore fluid pressures and volume change abstract the manner in which sediments respond to burial and shear depends largely on the ease with which fluids can escape rapid increase of overburden pressure or shear prevents efficient dewatering and can lead to the generation of excess pore fluid pressures a principal control on the development of overpressure and hence mechanical strength is the sediments permeability observations from modern plate margin accretionary prisms indicate that many faults are associated with both overpressuring and efficient fluid flow that operates in pulses indicative of permeability that is constantly changing we present the results of laboratory experiments exploring how the permeability of sediment retrieved from the barbados accretionary prism and laboratory analogues varies with progressive strain volume changes are linked to permeability fluctuations and the drainage capacity of the material we investigate the importance of the previous stress history imparted on the sediment and quantify the extent to which different deformation structures can acts as conduits for fluid flow under conditions of fluctuating effective stress material that has been initially consolidated and then subjected to reduction of effective stress either by raised fluid pressure or reduction of load inducing overconsolidation dilates during shear zone formation and displays an increase in permeability during strain shear fabrics can localise flow further where the principal mode of deformation is intensely localised and brittle and effective stress approaches zero conversely normally consolidated sediments deform by bulk volume loss without generating discrete fabrics and hence do not enhance flow under reduced effective stress conditions permeability can increase during strain by up to one order of magnitude when deformation results in sudden porosity collapse and pore water expulsion microstructural analysis and permeability testing before during and after shear have helped constrain the principal factors that control the evolution of flow conduits in fine grained low permeability sediments

holocene sea level highstand and its implications for the vertical stability of panglao island southwest bohol philippines abstract emerged tidal notches in panglao island southwest bohol central philippines were used to investigate relative sea level changes during the holocene the elevation and profile of a laterally continuous notch were surveyed at 22 sites around panglao island the tidal notch documents higher than present mean sea level pmsl consistent with regional field observations and predictions for mid holocene time the reconstructed paleo shoreline elevations range from 0 to 1 6 m above pmsl exhibiting a general increase to the northeast the more protected part of the coast this lateral variation in the holocene paleo mean sea level msl along with changes in notch depth and profile suggests tilting of the island best explained by differential land movement last interglacial msl estimates by previous workers also show tilting to the southwest moreover the holocene notch data suggest segmentation of the island into several blocks that tilt consistently to the southwest suggesting the presence of faults lineations in aerial photographs trending northeast southwest confirm the presence of these faults these data indicate differential land movements during the holocene and late pleistocene calculated rates of uplift are 0 3 and 0 06 mm yr for the holocene and for the late pleistocene respectively these values relative to the high uplift rates from tectonically active regions imply that panglao is relatively vertically stable after accounting for tectonic tilting mid holocene sea level is estimated at approximately 0 3 0 6 m

40ar 39ar age pattern associated with differential uplift along the eastern highlands shear zone cape breton island canadian appalachians abstract the eastern highlands shear zone in cape breton island is a crustal scale thrust it is characterized by an amphibolite facies deformation zone 5 km wide formed deep in the crust that is overprinted by a greenschist facies mylonite zone 1 km wide that formed at a more shallow level hornblende 40ar 39ar plateau ages on the hanging wall decrease towards the centre of the shear zone in the older zone over 7 8 km from the centre the ages are between 565 and 545 ma in the younger zone within 4 5 km of the centre they are between 425 and 415 ma and in the transitional zone in between they decrease abruptly from 545 to 425 ma pressures of crystallization of plutons in the hanging wall based on the al in hornblende barometer and corresponding to depth of emplacement increase towards the centre of the shear zone and indicate a differential uplift of up to 28 km associated with movement along the shear zone the age pattern is interpreted to have resulted from the differential uplift the pressure data show that rocks exposed in the younger zone were buried deep in the crust and did not cool through the hornblende ar blocking temperature 500 c until differential uplift occurred the 40ar 39ar ages in the zone 425 415 ma thus date shear zone movement or the last stage of it in contrast rocks in the older zone were more shallowly buried before differential uplift and cooled through the blocking temperature soon after the emplacement of 565 555 ma plutons in the area long before shear zone movement the transitional zone corresponds to the ar partial retention zone before differential uplift the 40ar 39ar age pattern thus reflects a neoproterozoic to silurian cooling profile that was exposed as a result of differential uplift related to movement along the shear zone a similar k ar age pattern has been reported for the alpine fault in new zealand it is suggested that such isotopic age patterns can be used to help constrain the ages kinematics displacements and depth of penetration of shear zones

40 ar 39 ar mineral ages from the southern cape breton highlands and creignish hills cape breton island canada evidence for a polyphase tectonothermal evolution 40 ar 39 ar ages for hornblende and muscovite from plutons and metamorphic country rocks in the southern cape breton highlands and creignish hills together with previously published u pb rb sr and 40 ar 39 ar ages document a complex tectonothermal history that included 1 episodes of plutonic activity at ca 600 565 560 555 500 490 470 and 410 395 ma all of which cooled through 500 400 c within ca 20 m y and 2 deformation in the late precambrian 550 ma and the late silurian middle devonian 415 380 ma the latter was associated with evelopment of a positive flower like structure during maintenance of medium pressure greenschist amphibolite facies regional metamorphic conditions that may be traced northward along the length of the cape breton highlands it may be correlated with the kingston complex and associated mylonite zone exposed in the avalon composite terrane of southern new brunswick northward it merges with a major high grade poly deformed belt within the gan

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

age and tectonic setting of granitoid plutons in the cheticamp belt western cape breton island nova scotia canada geological mapping in the cheticamp granitoid belt in combination with petrographic and geochemical studies and u pb zircon dating by laser ablation inductively coupled plasma mass spectrometry have resulted in major reinterpretation of the geology in the western part of the ganderian aspy terrane of cape breton island nine new u pb zircon ages show that the former cheticamp pluton consists of 10 separate plutons of five different ages late neoproterozoic ca 567 ma cambrian ordovician 490 482 ma ordovician silurian 442 440 ma mid silurian ca 428 ma and late devonian 366 ma the three late neoproterozoic granodioritic to monzogranitic plutons are older than the adjacent metavolcanic and metasedimentary rocks of the jumping brook metamorphic suite whereas the tonalitic to quartz dioritic cambrian ordovician plutons intruded those metamorphic rocks petrographic characteristics and approximately 100 whole rock chemical analyses show that with the exception of the mid silurian grand falaise alkali feldspar granite which has a type within plate characteristics the plutonic units have calc alkaline affinity and were emplaced in a volcanic arc tectonic setting these results are evidence that fragments of a long history of episodic subduction related magmatism and terrane collision are preserved in this small part of ganderia eight new sm nd isotopic analyses are consistent with the ganderian affinity of the cheticamp plutonic belt the ca 490 482 ma plutons are the first direct evidence in cape breton island for the penobscottian event recognized in the exploits subzone of central newfoundland and in new brunswick however the structural relationship of the cheticamp plutonic belt to the rest of the aspy and bras d or terranes remains enigmatic as is the apparent absence of effects of devonian deformation and metamorphism in the older plutonic units

holocene sea levels in oceanic islands implications for the rheological structure of the earth s mantle abstract relative sea levels in oceanic islands that are situated sufficiently far from glaciated regions were studied in relation to the rheological structure of the earth s mantle the local hydro isostatic adjustment associated with the mantle flow from the oceanic side to an inland side depends on the size of the island the effective upper mantle viscosity and the elastic plate thickness the relative sea level has a significant dependence on the upper mantle rheology for islands with a radius larger than 10 km but it is almost independent of the upper mantle rheology for islands with a radius less than 10 km in other words the observed sea level changes in such small islands follow the global isostatic adjustment which depends strongly on the lower mantle viscosity in fact the relative sea levels in small oceanic islands impose important constraints on the lower mantle viscosity on the other hand the effective upper mantle viscosity and the elastic plate thickness are determined by analyzing the relative sea levels for islands greater than 10 km the observed sea level curves in japan and new zealand are consistent with the effective viscosity of the upper mantle equal to 2 to 6 10 21 poises the effective elastic plate thickness for japan and new zealand is estimated to be less than 50 km and greater than 100 km respectively the thickness of the lithosphere obtained by sea level curves in japan and new zealand is compatible with the results obtained by seismological studies

relationship between the aspy and bras d or terranes in the northeastern cape breton highlands nova scotia according to previous interpretations the eastern highlands shear zone separates ordovician silurian volcano sedimentary rocks to the west cheticamp lake gneiss of the aspy terrane from late precambrian sedimentary rocks and dioritic tonalitic plutons and early ordovician granite to the east bras d or terrane new mapping discovered a basal conglomerate of the cheticamp lake gneiss that rests on deformed diorite of the bras d or terrane and contains clasts similar or identical to rocks of the bras d or terrane the late precambrian rocks of the bras d or terrane are also overlain by a volcano sedimentary sequence of silurian age clyburn brook formation these observations suggest that rocks of the aspy terrane lie unconformably on those of the bras d or terrane the eastern highlands shear zone is therefore not a terrane boundary the ordovician silurian rocks of the aspy terrane are interpreted to have formed in an arc back arc basin system the back arc basin is interpreted to h

grenvillian basement in the northern cape breton highlands nova scotia the northernmost cape breton highlands are underlain by the blair river complex a distinctive assemblage of basement rocks including felsic and mafic gneisses foliated gabbroic to granitic rocks

the dog bay line a major silurian tectonic boundary in northeast newfoundland the dog bay line separates different silurian rock groups in northeast newfoundland west of the line terrestrial volcanic rocks and sandstones botwood group overlie marine greywackes and conglomerates badger group east of the line red sandstones overlie shallow marine shales and limestones indian islands group throughout dog bay the line is marked by a disrupted zone of dark grey to black shales volcanic rocks and gabbros pervasive dextral transpressive ductile deformation followed by successively more brittle extension with renewed dextral movements mark the northwest side of the line on the coast the dog bay line is traceable for 100 km and it is open ended dextral offset is deduced to be many tens of kilometres the line trends northeast parallel to outcrop belts and both the line and outcrop belts are curved eastward at the coast the mount peyton batholith dated at 420 8 ma apparently cuts the line the dog bay line occurs within the dunnage zone whose cambrian ordovician rocks

quaternary paleoenvironmental variation and its impact on initial human dispersals into the japanese archipelago abstract to understand the late pleistocene human dispersals to the japanese archipelago we examine the paleobathymetric changes in and around the archipelago based on the results of recent paleoclimatological study of the japan sea that has provided millennium scale sea level changes the pleistocene mammalian faunal record e g extinct proboscideans and the paleolithic archaeological record proboscideans likely migrated from continental east asia to paleo honshu consisting of the present day honshu shikoku and kyushu islands and the ryukyu islands via land bridges across the tsushima strait and yonaguni strait during the coldest periods of the middle pleistocene mis 6 12 16 and probably 35 however no clear evidence of hominin arrival in the archipelago has been dated to the middle pleistocene further land bridges connecting continental east asia and paleo honshu were not present during the period of initial major human dispersals to the japanese archipelago i e marine isotope stage mis 3 and 2 thus initial dispersals to paleo honshu and the ryukyus were achieved by watercraft and would have involved advanced seafaring skills the paucity of archaeological sites before the onset of late mis 3 prior to 40 ka and the significant increase of archaeological sites since late mis 3 suggests that increasing population density on the east asian mainland may have been a factor for humans to disperse into the japanese archipelago