kennetcook thrust system late paleozoic transpression near the southern margin of the maritimes basin nova scotia a major zone of deformation affects early carboniferous rocks in the southern part of the maritimes basin of nova scotia close to the boundary between the avalon and meguma terranes of the appalachians field relationships at cheverie indicate thrusting of tournaisian horton group clastics over visean windsor group carbonates evaporites and clastics a relationship confirmed by the cheverie 01 well mapped relationships to the south indicate that a system of thrusts here termed the kennetcook thrust system climbs upsection to the southeast becoming a decollement within windsor group evaporites industry seismic profiles clearly show deformed windsor group and include fold and fault structures indicative of evaporite flow and solution collapse below the windsor group half grabens filled with horton group are clearly imaged offsets at graben related faults show that these structures were inverted during later shortening above the windsor group less deformed rocks of the pennsylvanian scotch vil

mean stream coordinates structure of the subantarctic front temperature salinity and absolute velocity 1 the mean synoptic structure of the northern strongest branch of the antarctic circumpolar current southwest of tasmania at the subantarctic front saf is estimated by a stream coordinates analysis of data from overlapping arrays of inverted echo sounders iess and horizontal electric field recorders deployed during the 1995 1997 sub antarctic flux and dynamics experiment the stream coordinates are derived from a daily objective mapping of the temperature field obtained from combining the ies travel time measurements with an empirical look up table constructed from the extensive hydrography acquired during woce full water column stream coordinates sections of temperature salinity and absolute velocity are presented and compared with prior observations the along stream current has a single peak with surface velocities reaching about 50 cm s 1 the vertical structure of the along stream velocity is roughly consistent with a combined external and first internal normal mode description that is adapted to the buoyancy frequency as it varies across the front although there are some significant differences the cross stream structure of along stream velocity is very nearly symmetric about the jet axis but the lateral shear magnitude is slightly larger on the cold side of the saf separating the baroclinic and barotropic currents reveals that the saf currents are diffluent primarily baroclinically in the cross stream direction baroclinic cross stream diffluence of approximately 0 23 sv per km sv 106 m3 s 1 or about 16 sv per degree of longitude at 51 s the 2 year mean total saf transport is 75 sv for a 220 km width the barotropic contribution is small 8 sv but not negligible

alleghanian reactivation of the acadian fold belt meguma zone southwest nova scotia shear zones and northwest verging folds define a 30 km wide belt of deformation that overprints the acadian fold belt and telescopes isograds in the meguma zone in southwest nova scotia the shear zones appear to form a linked system that accommodated convergence dominated transpression of the meguma zone against an irregular avalon boundary available geochronological data indicate a mid carboniferous alleghanian variscan age for the overprinting deformation the mid carboniferous basement reactivation in southwest nova scotia is likely coeval with deformation of carboniferous strata and reactivation of basement structures meguma group in the northern meguma zone together these mid carboniferous structures may define a wide belt of alleghanian variscan deformation across the northwest cratonward margin of the meguma zone

structure of the gulf stream and its recirculations at 55 w abstract two years of direct current and temperature observations from an army of 13 current meter moorings deployed near 55 w as part of the synop synoptic ocean prediction experiment have been used to explore the spatial and temporal variability of the gulf stream from three points of view in the geographic reference frame mean eastward velocities were observed from the surface to 4000 m there was no evidence of westward flow south of the eastward jet suggesting that the worthington recirculation gyre was located south of the array during this time period westward flow was observed north of the jet only at 4000 m where it had a magnitude comparable to the mean gulf stream 5 10 em s 1 these data also indicate that the mean eastward jet is much more vertically aligned than was depicted in an earlier picture constructed from noncontemporaneous observations in the lagrangian or streamwise reference frame it was found that at the thermocline level the width of the average synoptic gulf str

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

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

progressive localization of deformation during exhumation of a major strike slip shear zone norumbega fault zone south central maine usa detailed structural studies along with 40ar 39ar thermochronology provide important constraints on the temporal spatial and structural evolution of a major orogen parallel strike slip shear zone the norumbega fault zone in maine detailed structural analysis in south central maine reveals two very different styles of dextral noncoaxial deformation a wide zone 25 km of heterogeneously distributed ductile shear structures and a relatively narrow zone 1 km of lower greenschist facies high strain mylonitization 40ar 39ar thermochronology indicates that these two zones of deformation developed during a prolonged period of regional exhumation following middle devonian amphibolite facies metamorphism the wide zone of dextral shear is interpreted to reflect a major episode of moderate temperature post amphibolite facies metamorphism but pre regional cooling below 320 c late devonian to early carboniferous transcurrent tectonism the narrow zone of dextral shear represents both a younger latest carboniferous and significantly cooler 320 c deformational event occurring at much higher structural levels a general model of increasingly narrow but more highly focused noncoaxial deformation during progressive regional exhumation is supported by the observations

a 6 year record of baroclinic transport variability of the antarctic circumpolar current at 140 e derived from expendable bathythermograph and altimeter measurements 1 repeat hydrographic sections across the antarctic circumpolar current are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 dbar from temperature measurements with an error of a few per cent the mean transport distribution derived from 31 austral summer expendable bathythermograph xbt sections over a 6 year period consists of westward flow immediately south of tasmania a broad band of strong eastward flow between 50 and 55 s and three cores of eastward flow south of 55 s by defining a second empirical relationship between surface dynamic height and cumulative transport a continuous time series of baroclinic transport is derived from altimeter measurements of sea surface height transports derived from altimetry in this way agree well with simultaneous in situ estimates root mean square error in net transport is 4 106 m3 s 1 suggesting sea level anomalies largely reflect baroclinic changes above 2500 dbar the 10 day sampling of the altimeter transport time series shows the irregular xbt sampling aliases variability at unresolved timescales the standard deviation of net transport above and relative to 2500 m is 4 3 106 m3 s 1 the variability in net transport is largest 2 7 106 m3 s 1 in the quasi annual band periods of 4 months to 1 5 years slightly smaller 2 3 106 m3 s 1 in the mesoscale band 1 5 years 1 5 106 m3 s 1 changes in transport are correlated with local changes in both wind stress and wind stress curl in the quasi annual and interannual bands but the transport time series is too short to draw significant conclusions

paleomagnetism of the triassic red beds of the lower fundy group and mesozoic tectonism of the nova scotia platform canada the lower fundy group red beds of the wolfville and lower blomidon formations in nova scotia and of wolfville equivalent units in new brunswick are exposed around the bay of fundy these red beds were sampled at twenty six shoreline sites for paleomagnetic analysis primarily by thermal step demagnetization methods samples from four sites proved too fragile to core however coating many of the rest of these poorly indurated samples and cores with waterglass enabled them to withstand the rigours of coring measurement and thermal cleaning a stable hematite remanence was found in all twenty one coherent sites with normal reversed and mixed polarities conglomerate and fold tests indicate the remanence is either primary or very early diagenetic its mean direction is d 196 5 i 3 8 95 7 2 which converts to a pole position of 45 3 n 97 1 e dp 3 6 dm 7 2 this pole indicates that the lower fundy group was likely deposited in the early triassic rather than in the middle and late triassic as currently thought it also indicates that the nova scotia platform was rotated about 8 clockwise after deposition of the lower fundy group and before extrusion of the north mountain basalts the consequences are briefly discussed for two alternative tectonic models of mesozoic motion on the minas geofracture that led to formation of the bay of fundy rift as the atlantic ocean basin started to open in early rather than middle triassic time the fundy group pole is similar to those from granitic plutons in maine thereby increasing the probability that there is a significant error in the mid triassic portion of the apparent polar wander path for north america finally magnetostratigraphic methods appear to be a promising way to subdivide and correlate between these red beds

the interplay of regional structure and emplacement mechanisms at the contact of the south mountain batholith nova scotia floor down or wall up in southern nova scotia the devonian south mountain batholith was emplaced into metasedimentary rocks of the cambro ordovician meguma group at ca 370 ma the contact of the eastern end of the south mountain batholith transects at a high angle the trace of subhorizontal upright acadian mid late devonian folds formed in the meguma group at two locations where the contact is well exposed there are contrasting structures in the country rocks adjacent to acadian anticlinoria and synclinoria respectively regional folds are affected by ductile deformation where anticlinoria abut the batholith but are undisturbed at the synclinoria at the anticlinorial contacts the metasedimentary bedding youngs towards the granite and granite side down shear resulted in a belt in which bedding is transposed to a new contact parallel fabric deflection of linear structures that were initially horizontal in the acadian folds e g intersection lineations illustrates the granite side down shear the reorientation of

anatomy and evolution of a pull apart basin stellarton nova scotia the stellarton basin is a late paleozoic pull apart basin located close to the meguma avalon terrane boundary in the canadian appalachians at the stepover between the cobequid and hollow strike slip faults the basin contains 3 km of rapidly deposited pennsylvanian clastic sedimentary rocks representing lacustrine and deltaic environments extensively documented through coal related mining and drilling coal seams and oil shales allow stratigraphic correlation within the basin permitting reconstruction of basin subsidence and structural evolution coal seams represent approximately paleo horizontal surfaces thickness variations corrected for tilt and compaction in the most coal rich part of the basin fill show that the south basin margin subsided rapidly during deposition acting as a trap for coarse sediment and allowing coal forming mires to develop in the north abundant soft sediment deformation structures reflect synsedimentary tectonic activity north striking normal faults dissected the basin fill during and soon after deposition early in the diagenetic history contouring of mine plans allows fault heaves to be identified and also shows that both coal seams and faults were folded by east to northeast trending folds consistent with 1 an environment of deformation involving dextral strike slip motion and 2 clockwise rotation of fault blocks during progressive strain later north northeast striking contractional structures within the basin and a positive flower structure at the northwest margin probably represent a transition from transtension to transpression the basin illustrates the role of rotational progressive strain in the reorientation of structures generated during transtension it displays evidence for changes in tectonic style through time from transtension to transpression that may typify basins developed on major strike slip faults

mylonitic mafic granulite in fault megabreccia at clarke head nova scotia a sample of avalonian lower crust the clarke head fault megabreccia was produced within a major late palaeozoic transcurrent structure the minas fault system which separates the displaced meguma terrane of southern nova scotia from rocks more typical of the avalon superterrane a large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy 2 pyroxene garnet plagioclase and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone whole rock geochemistry reveals the granulite protolith to have been a continental within plate mafic magma transitional between theoleiitic and alkaline the original geochemical signature has survived strong dynamic recrystallization at granulite grade well preserved ree abundances testify to a lack of metasomatic fractionation during high grade shearing under water absent conditions sm nd data indicate that the basic granulite has a t dm age of c 1 ga isotopic comparisons with adjacent areas reveal similar t dm ages both north and south of the minas fault system the high grade clast may be typical of the lower crust in nova scotia and is thought to offer a rare window into the deep crust of the avalon superterrane in north america

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

velocity and transport structure of the kuroshio extension at 35 n 152 e a current meter mooring maintained for 2 years at 35 n 152 e as part of the wespac array schmitz et al 1987 sampled the kuroshio extension during the last 390 days of deployment based on a method developed by hall and bryden 1985 for the gulf stream at 68 w velocity and temperature time series at five depths from 350 to 6000 m have been used to construct the representative horizontal velocity structure of the current cross stream position is quantified in terms of temperature at 350 dbar and an alongstream flow direction is defined on the basis of the current shear integrated transport of the kuroshio is 87 21 sv compared to 94 26 sv for the gulf stream at 68 w based on analogous data sets and analysis techniques the two currents are compared in terms of horizontal and vertical distributions of transport as well as relative strength of barotropic and baroclinic components the kuroshio has a larger relative barotropic component than the gulf stream while the latter has a stronger deeper thermocline expression the effects of rotating velocity measurements to a continuously changing alongstream direction are examined for both currents the major impact is to cut the apparent velocity variance in half demonstrating that much of the original variance is due to the meandering of a quasi fixed velocity profile rather than the passage of eddies results from these somewhat unconventional analysis methods are placed in broader geographical context and compare favorably with more traditional methods of determining these currents transports

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

paradoxical pseudotachylyte fault melt outside the seismogenic zone abstract fault generated melt pseudotachylyte is an established indicator of palaeoseismic faulting the existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime central to this issue is whether all pseudotachylyte originates as pressure dependent frictional melt along slip surfaces or if pressure independent processes have roles in its formation propagation of high velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone pseudotachylyte from the minas fault zone nova scotia canada is used to demonstrate the formation and preservation of fault related melt under lower crustal conditions microstructures retain evidence of intense dislocation glide with minimal climb and ductile disaggregation of the host the latter are consistent with intracrystalline deformation in the peierls stress controlled glide regime it remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high velocity slip or is itself responsible for both instability and the thermal transient there are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts tremor that emphasize the mechanistic complexity of deep faulting and the need to extend consideration beyond that of a simple brittle ductile response the occurrence of tremor bursts fall within the depth range of paradoxical pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination

a review of the mesothermal gold deposits of the meguma group nova scotia canada abstract the gold province of the meguma terrane in nova scotia contains several classic examples of turbidite hosted mesothermal gold deposits there are over 300 gold occurrences and deposits hosted by the cambro ordovician meguma group rocks in southern nova scotia canada the meguma group consists of two formations 1 a lower sand dominated flysch goldenville formation and 2 an upper shaley flysch halifax formation subdivision of the goldenville formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization although detailed stratigraphic investigations in all of the major gold producing areas is still ongoing it is evident that the steve s road beaverbank and the mt uniacke stratigraphic intervals contain most of the major past gold producers in the province the meguma group rocks are variably deformed into upright gently to moderately doubly plunging folds with multiple cleavages the strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca 370 ma peraluminous granites and minor mafic intrusions the gold deposits can be divided into three main types 1 high grade approximately 15 g t au narrow gold bearing quartz veins 2 low grade 0 5 4 g t au slate argillite hosted and 3 low grade meta sandstone hosted a combination of two or more of the above can also occur almost all of the historic production 47 million g au has come from the high grade veins within 200 m of surface a variety of vein types occur although most of the gold produced came from bedding concordant stockwork and fissure veins isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the acadian orogeny disseminated low grade gold with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in nova scotia the presence of disseminated gold in combination with high grade vein mineralization greatly enhances the economic viability of gold deposits in the meguma group the association of disseminated gold and narrow vein hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere

the net transport of the antarctic circumpolar current through drake passage abstract estimates of the net transport through drake passage are made for three periods during which the year long drake 79 current meter array spanning the passage was in operation relative geostrophic shears from hydrographic surveys in january 1979 april 1979 and january 1980 were referenced to directed speed measurements to give profiles of net speed direct measurements were averaged in time to make them more compatible with the spatially averaged baroclinic shears the agreement between directly measured and baroclinic shears is generally good except in regions of large bathymetric relief and during periods when current cores were shifting past or between moorings the presence of cold core rings during two of the drake 79 hydrogaphic surveys resulted in intensified flow and increased transport within fronts but did not affect the net transport through the passage the three latest estimates of net transport 117 144 and 134 106 m3 s 1 are in close agreement with a previous estimate of 124

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

shear band foliation as an indicator of sense of shear field observations in central spain the macizo de nevera a paleozoic basement inlier surrounded by essentially flat lying mesozoic cover rocks of central spain exhibits an extremely consistent system of steep dextral strike slip faults different faults have a variable amount of displacement but their en echelon arrangement and similar sense of displacement imply a cogenetic origin a maximum displacement of 1 0 km corresponding to an averaged angular shear strain of 1 5 and peak values of 6 6 occurs along the central part of the 6 km long truchas ductile shear zone an early axial plane cleavage is locally deflected into the truchas shear zone and superposed by coarse shear band foliation the consistent angular relationship between the new foliation and the shear zone boundary confirms the megascopic sense of shear

eddy variability and energetics from direct current measurements in the antarctic circumpolar current south of australia two year time series measurements of current velocity and temperature in the subantarctic front saf south of australia from 1993 to 1995 provide estimates of eddy fluxes of heat and momentum across the antarctic circumpolar current acc and further insight into the variability of the acc the saf was found to be an energetic meandering jet with vertically coherent fluctuations varying on a timescale of 20 days with typical amplitude 30 cm s21 at 1150 dbar a daily varying coordinate frame that follows the direction of flow allowed mesoscale variability of the saf to be isolated from variability due to meandering of the front and proved very successful for examining eddy fluxes vertically averaged cross stream eddy heat flux was 11 3 kw m 22 poleward and significantly different from zero at 95 for fluctuations in the 2 90 day band zonally integrated this eddy heat flux 50 9 pw is more than large enough to balance heat lost south of the polar front and is as large as cross saf fluxes found in drake passage cross stream eddy momentum fluxes were small not significantly different from zero and of indeterminate sign but tending to decelerate the mean flow a relationship between vertical motion and meander phase identified in the gulf stream was found to hold for the acc eddy kinetic energy levels were similar to those in drake passage and southeast of new zealand eddy potential energy was up to an order of magnitude larger than at other acc sites most likely because meandering of the front is more common here baroclinic conversion was found to be the dominant mechanism by which eddies grow south of australia typical eddy growth time is estimated to be 30 days approximately twice as fast as in drake passage consistent with eddy energy growing rapidly downstream

post taconian shortening inversion and strike slip in the stephenville area western newfoundland appalachians deformed terrigenous and carbonate sedimentary rocks representing the early paleozoic laurentian continental margin form a series of elongate fault bounded blocks that plunge north beneath the humber arm allochthon in the stephenville area west newfoundland appalachians the continental shelf succession was folded and thrust faulted after emplacement of the humber arm allochthon in the west of the area table mountain is cut by a pop up structure bounded by downward converging reverse faults structures at the east margin of table mountain indicate both dextral and reverse slip the phillips brook structure farther east contains multiple fault bounded carbonate slices one slice carried by the west blanche brook fault is thrust over the humber arm allochthon the western edge of the indian head massif consisting of grenville basement is also a thrust contact these reverse faults and thrusts which cut the carbonate succession and postdate emplacement of the humber arm allochthon are in turn

profiling the gulf stream with a current meter mooring a current meter mooring was deployed for one year at the mean position of the gulf stream at 68 w with instruments from 400 m to 4000 m it provides the first unambiguous evidence that the gulf stream extends from top to bottom of the water column using the strong cross stream temperature structure to derive a horizontal coordinate related to temperature we estimate the width and transport of the gulf stream for four individual events and we determine an average profile of the vertical and cross stream structure of the gulf stream a conservative estimate of transport for this average profile indicates that the gulf stream has a transport of 103 106 m s 1 at 68 w

shear criteria in the grenville province ontario canada abstract the grenville province of canada is a major proterozoic orogenic belt mapping and structural analysis shows that the central ontario segment of this belt is composed of a stack of imbricated thrust nappes separated by mylonite zones the mylonite zones were generated at high metamorphic grades and contain a distinctive assemblage of mesoscopic and microscopic asymmetric structures these structures include rotated tectonic inclusions rotated boudins and pinch and swell structures sheath folds rotated single crystal porphyroclasts single crystal fish and shear band foliation the shear asymmetry indicated by these structures is highly consistent between members of the assemblage and over a large area of the grenville province and shows that the thrust nappes were transported to the northwest the consistency of the structures is thought to be due to cyclical dynamic recrystallization leading to steady state foliations in the mylonites

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

progressive folding and foliation development in a sheared coticule bearing phyllite abstract an evolutionary sequence of fold and foliation development interpreted to be the result of a single progressive deformation is seen in exposures of strongly sheared phyllite and coticule 10 km south of the e w trending chedabucto fault in the meguma terrane of nova scotia canada transposition sensu sander at mesoscopic and microscopic scales is fundamental to this development as are fold hinge rotation and migration the transposition process is cyclic with folds of layering and foliation developing rotating and being refolded fold hinges and axial surfaces repeatedly tend towards stable end orientations but do not reach them due to the cyclic transposition process the foliation is a steady state feature continually reconstituted by microscale transposition and dynamic recrystallization several important consequences of these contemporaneous processes are 1 geometrical relationships between folds and foliation are variable in the same outcrop even though both developed synchronously and many folds have the geometrical relationships of cleavage transected folds 2 the foliation is transient in orientation and therefore cannot track the xy principal plane of total finite strain and 3 fold hinge migration may be a common process especially in deformations involving a large component of simple shearing the observed relationships may be applicable to study of fold and foliation development in orogenic belts in general

brittle faulting in the canadian appalachians and the interpretation of reflection seismic data abstract brittle faults in the canadian appalachians mostly late devonian or younger in age are divided into two groups on the basis of their movement vectors a strike slip group and a dip slip group the two groups are subdivided on the basis of orientation and sense of movement they are interpreted in terms of palaeozoic transpression and mesozoic extension during atlantic opening the palaeozoic faults comprise strike slip and reverse faults which were active in devono carboniferous times mesozoic strike slip faults are interpreted as transfer faults and they are coupled with normal faults many of which developed by reactivation of earlier reverse faults or steeply dipping surfaces including bedding and earlier foliations together these mesozoic faults comprise an adequate mechanism for crustal extension perpendicular to the orogen evidence for listric normal faults is rare in the older rocks of the orogen and it is suggested that this is due to the adequacy of the deformation mechanisms afforded by the pre existing planes of weakness the data presented demonstrate clearly that geological structures are commonly repeated at all scales from outcrop to regional following this principle prominent shallowly dipping reflectors imaged in the lithoprobe east seismic profiles are interpreted as large scale representatives of the palaeozoic reverse faults seen in outcrop that were reactivated as normal faults during atlantic opening it is suggested that reverse faulting is to be expected as a deformation mechanism in general in the late stages of a collisional orogen we draw attention to the importance of the mesozoic faults in modifying the attitude of earlier surfaces such a bedding foliations and faults

fabric development in experimentally sheared quartzites abstract a fine grained quartzite was deformed under a combination of simple shear and axial compression to varying amounts of shear strain 1 3 to 2 9 the experiments were conducted at 800 c 1500 mpa and an axial strain rate of 10 6 s in the dislocation creep regime shear zone boundaries were oriented at 45 or 30 to the compressior axis the progressive development of deformation microstructures including planar fabrics and c axis preferred orientations was studied as a function of increasing shear strain elongate original grains define a foliation s which rotates from 45 to 0 to the shear zone boundary with increasing strain producing a sigmoidal foliation in a single shear zone a second foliation invariant in orientation is defined by elongate recrystallized grains which lie at about 30 40 to the shear zone boundaries no c surfaces parallel to the shear zone boundaries were observed however extensional crenulation cleavages c defined by parallel zones of recrystallized grains as well as impurity and melt segregations were observed even at low strain lying at approximately 30 to the shear zone boundaries and these could easily be mistaken for c surfaces c axis preferred orientations of original grains define symmetric type i crossed circle girdles at low strain 2 with the greater concentration of c axes in the direction of shear these features are very similar to those observed in natural ductile shear zones

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence

a mean synoptic view of the subantarctic front south of australia abstract a mean synoptic view of the subantarctic front saf is obtained from current meter and hydrographic data by averaging absolute and baroclinic velocity measurements in bins defined by a cross stream coordinate that moves with the current the cross stream coordinate is derived from current meter measurements of vertical shear of the horizontal velocity and is expressed in terms of specific volume anomaly at 780 dbar 780 by averaging absolute and baroclinic velocity measurements in stream coordinates the spatial smoothing that results from eulerian averaging of measurements of a meandering current is avoided the mean saf velocity profile is composed of one central peak and several smaller peaks in the central peak the 2 yr mean absolute velocity from current meters reaches 52 cm s 1 at 420 dbar the mean baroclinic velocity from six ctd sections reaches 34 cm s 1 the saf flow is coherent at all levels reaches the seafloor and is at least 220 km wide the cross stream structure of barocl

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

absolute geostrophic velocity within the subantarctic front in the pacific ocean velocity measurements from a shipboard acoustic doppler current profiler adcp are used as a reference for geostrophic current calculations on six sections across the subantarctic front saf in the pacific ocean the resulting cross track velocity estimates near the bottom range from 4 to 10 cm s 1 to the east in the eastward jet at the saf in adjacent regions of westward surface flow the near bottom velocity is usually to the west on one section where simultaneous lowered adcp velocity profiles are available they confirm the results from the shipboard adcp annual mean velocity sections from the parallel ocean program numerical model also show near bottom velocities exceeding 5 cm s 1 with the same tendency for the zonal velocity component near the bottom to match the direction of the surface jets transport across the entire antarctic circumpolar current acc cannot be estimated accurately from adcp referenced geostrophic sections because even a very small cross track bias integrates to a large error a preliminary look at the 1992 model transport stream function shows that the effect of bottom referencing varies from section to section it can cause 40 sv recirculations to be missed and can cause net transport to be underestimated or overestimated by o 30 sv

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

baroclinic instability in drake passage abstract a linearized baroclinic instability model is applied to the drake passage area the predictions of the model are found to be in good agreement with observations temporal and spatial scales are predicted accurately and the vertical structure of the most unstable wave is consistent with observations results indicate that the observed release of potential energy from the mean state in this area is made possible by the presence of a negative gradient of mean potential vorticity at and near the lower boundary further it is found that the model results are stable with respect to variations of the mean velocity field which might be incurred by errors in the data explanations for this insensitivity are given

the port mouton shear zone intersection of a regional fault with a crystallizing granitoid pluton abstract the peraluminous tonalite monzogranite port mouton pluton is a petrological geochemical structural and geochronological anomaly among the many late devonian granitoid intrusions of the meguma lithotectonic zone of southern nova scotia the most remarkable structural feature of this pluton is a 4 km wide zone of strongly foliated 040 subvertical monzogranites culminating in a narrow 10 30 m straight zone of compositionally banded rocks that extends for at least 3 km along strike the banded monzogranites consist of alternating melanocratic and leucocratic compositions that are complementary to the overall composition of that part of the pluton suggesting an origin by mineral melt and mineral mineral sorting biotite and feldspar are strongly foliated in the plane of the compositional bands these compositional variations and foliations originated by a process of segregation flow during shearing of the main magma with a crystallinity of 55 75 subsequent minor brittle fracturing of feldspars twinning of microcline development of blocky sub grains in quartz and kinking of micas demonstrate overprinting by a high temperature deformation straddling the monzogranite solidus small folds and late sigmoidal dykes indicate dextral movement on the shear zone this port mouton shear zone pmsz is approximately co linear with the only outcrops of late devonian mafic intrusions in the area two of which are syn plutonic with well developed mingling textures in the marginal tonalite of the port mouton pluton also closely co linear with the mafic intrusions are a granitoid dyke that extends well beyond the outer contact of the port mouton pluton a swarm of large aligned angular xenolithic slabs a zone of thin wispy schlieren banding a large be bearing pegmatite and a breccia pipe with abundant garnetiferous metapelitic xenoliths in various ways the shear zone may control all of these features the port mouton shear zone is parallel to many other ne trending faults and shear zones in the northern appalachians probably related to the docking of the meguma zone along the cobequid chedabucto fault system

horizontal and vertical structure of the gulf stream velocity field at 68 w abstract a curent meter mooring instrumented from the bottom into the thermocline was deployed in the gulf stream at 68 w for a year data from the uppermost instrument indicate the gulf stream moved back and forth across the mooring site so that the horizontal as well as vertical structure of the stream may be deduced the two key points to the success of the analysis are 1 the well defined relationship between temperature and cross stream distance in the thermocline enabling the use of the former as a horizontal coordinate and 2 a daily changing definition of gulf stream flow direction based on the shear between the thermocline and 2000 m depth time series of daily rotated velocities may be used to calculate empirical orthogonal functions for the along and cross stream vertical structures which are decoupled and are respectively baroclinic and barotropic using the inferred horizontal coordinate one can estimate masss momentum and kinetic energy fluxes agree well with historical data bryden

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

geophysical and structural signatures of syntectonic batholith construction the south mountain batholith meguma terrane nova scotia summary the late devonian south mountain batholith is a very large 7000 km2 composite peraluminous granitoid complex situated within the meguma terrane of the northern appalachians it is made up of two suites of granodioritic to leucogranitic plutons emplaced at approximately 380 370 ma during the acadian orogeny i e during the collision of gondwana with the eastern margin of north america a significant geophysical and geological database makes the south mountain batholith a type example of a very large syntectonic batholith emplaced within a collisional orogen gravity models reveal the plutons have flat or gently dipping floors at approximately 7 0 km depth and aspect ratios 651 they are underlain by deeper 10 km elongate northeast southwest trending roots that may indicate magma feeder zones dyke transport of granitic magma and the progressive construction of plutons by sheet injections are supported by field observations and by mapping of the anisotropy of magnetic susceptibility at the pluton scale the very narrow deformation aureole within the country rocks suggests lateral spreading of the plutons was not the main space creation mechanism during emplacement space was mostly created by vertical displacements of country rocks the data are consistent with a laccolithic model for syntectonic batholith assembly the laccolithic plutons may have been emplaced at the base of the meguma supergroup metasedimentary rocks suggesting a maximum thickness of approximately 7 0 km for the supracrustal rocks in the meguma terrane

the acadian fold belt in the meguma terrane nova scotia cross sections fold mechanisms and tectonic implications 1 structural data and cross sections from the eastern part of the devonian carboniferous fold belt of the meguma terrane give insight into its structural development and crustal tectonics the sandy goldenville formation the active competent member during buckling formed a multilayer several kilometers thick that lay beneath the denser softer muds and silts of the halifax formation cross sections reveal 2 orders of folds 11 18 km wavelength folds are interpreted as resulting from buckling under the influence of gravity 4 6 km wavelength folds reflect the thickness of the multilayer with buckle shortening in the range 32 44 depth to detachment derived from the sections 11 13 5 km below present erosion surface is such that given the depth of the detachment below the paleosurface during the main phase pre devonian granite of folding it would likely have been a relatively soft and thick shear zone that would have influenced profile geometry of the main phase folds at this stage of fold belt development granite production that may have been triggered by mantle delamination during continuing convergence accompanying terminal pangean assembly and ocean basin closure was followed by rapid exhumation later localized deformation late devonian carboniferous in the fold belt took place as the meguma terrane was displaced along the terrane bounding cobequid chedabucto fault system the characteristic asymmetric cross sections of structures of this phase are attributed to cooling and strengthening of the detachment that was a consequence of the postgranite uplift and exhumation

sense of displacement on the cobequid chedabucto fault system nova scotia canada the cobequid chedabucto fault system of the canadian appalachians is a major anastomosing fault system over 300 km in length it separates the meguma terrane of southern nova scotia from the avalon terrane to the north these terranes are distinct tectonic and lithological entities in the appalachian orogen two areas at either end of this fault system have been examined in detail to determine the sense and history of offset along it both areas are situated on major component fault zones of the system and both exhibit structures due to early intense ductile shearing that are overprinted by semi brittle to brittle structures caused by later faulting along the eastern chedabucto fault zone area a ductile structures were examined this area is characterized by the progressive development of s c textures and shear bands rotated syntectonic porphyroblasts and asymmetric minor folds features indicative of and caused by ductile shearing along the western cobequid fault zone area b semi brittle and b

flexural slip folding in the meguma group nova scotia canada abstract flexural slip folding has been established for two anticlines in the meguma group nova scotia flexural slip postdates the main acadian episode of flexural flow fold growth and represents a late brittle ductile reactivation of the fold belt flexural slip structures are dominated by bedding parallel movement horizons but include a linked system of frontal and lateral ramps and conjugate movement horizons slip amount calculated from displacement of discordant quartz veins combined with vein spacing indicates an average local shear strain of approximately 0 5 however because flexural slip occurred when the fold limbs were steep the shear strain accounts for a small change in limb dip 4 8 variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons the presence of quartz veins along flexural slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent separated by periods of ductile deformation and build up of fluid pressure flexural slip veins in the ovens anticline are auriferous and a flexural slip model may be appropriate for other similar meguma gold deposits thrust sheets up to 10 m thick occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode thrusting may have assisted the transformation of a box fold into a chevron

monitoring the transport of the antarctic circumpolar current at drake passage abstract data from an extensive moored instrument array and three hydrographic cruises are used to calculate a time series of the net transport through the upper 2500 m of the drake passage the baroclinic geostrophic transport was monitored with heavily instrumented moorings at each side of the passage pressure gauge measurements at the northern and southern ends of the passage provided a reference speed at 500 m to adjust the relative transport the net transport of the upper 2500 m for the 370 day record ending in january 1980 averaged 121 106 m3 s 1 the total transport through the entire cross sectional area of drake passage is probably between 118 and 146 106 m3 s 1 fluctuations in the relative transport are related to changes in latitude of the northernmost front in the passage the subantarctic front variability of the net transport is coherent with the zonally averaged eastward wind stress

toward a unified conceptual framework for shear sense indicators abstract the growing lexicon for shear sense indicators has created a need for a unified conceptual system of classification many common shear structures can be described by linear combinations of two kinematic variables which quantify the relative importance of objects vs foliations in controlling the shear zone velocity field

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

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

geochronological evidence for multiple tectono thermal overprinting events in the east kemptville muscovite topaz leucogranite yarmouth county nova scotia canada the east kemptville muscovite topaz leucogranite located in yarmouth county nova scotia canada is host rock to the only producing primary tin deposit in north america 56 mt 0 165 sn previous geochronological studies include i rb sr whole rock analyses of the quartz topaz greisens which indicated a date of 337 5 ma and ii 40ar 39ar analyses of greisen muscovite which indicated apparent plateau dates of ca 300 ma however the pervasive development of deformational fabrics at east kemptville suggests that both the rb sr whole rock and 40ar 39ar muscovite ages are at best minimum estimates for the inferred time of mineralization in the present study rb sr whole rock and mineral muscovite plagioclase k feldspar analyses and 40ar 39ar incremental step heating of a muscovite separate indicate the following i diffusion of sr on the whole rock scale terminated at 344 5 ma 11 point isochron date coincident with closure of muscovite to intracrystalline diffusion of ar apparent plat

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

alleghanian paleostress reconstruction in the northern appalachians intraplate deformation between laurentia and gondwana a numerical paleostress tensor analysis using striated fault planes has been conducted in the quebec reentrant of the northern appalachians to characterize the stress field of late paleozoic deformations three directions of maximum compressional stress axes s1 have been found and correlated to 1 an early north northwest south southeast compression 2 a north northeast south southwest compression and 3 a late west northwest east southeast compression fault populations associated with these stress regimes are present in all tectonic zones of the quebec and northern new brunswick appalachians directions of 1 axes determined in the northern appalachians resemble in orientation and in relative chronology layer parallel shortening fabrics and joint patterns found in the appalachian foreland of the central appalachians the paleostress regimes are interpreted as the record of intraplate deformation related to the indentation of gondwana into laurentia during the late paleozoic alleghanian orogeny

generation and evolution of a cyclonic ring at drake passage in early 1979 abstract an equatorward meander in the antarctic polar front at drake passage was observed to amplify and pinch off during january and early february 1979 forming a cold core cyclonic current fins with a radius of 50 km this ring appeared to move directly across the passage parallel to a submarine ridge before turning northeastward upon reaching a gap between the ridge and the south american continental rise its net motion was across the polar frontal zone and the ring was last observed to be pushing through the subantarctic front geostrophic surface speeds of up to 90 cm s 1 relative to 3500 m wore observed where the northern sector of the ring and the subantarctic front were in proximity a stability analysis of the banded flow regime across drake passage suggests that necessary conditions for baroclinic instability exist everywhere within the zonal current and those for barotropic instability exist adjacent to the fronts the beat and salt anomalies of this ring relative to the polar frontal zone

petrogenesis and regional tectonic significance of late devonian mafic intrusions in the meguma zone nova scotia late devonian 377 368 ma 40ar 39ar 376 ma u pb mafic intrusions in the meguma zone crop out as dykes plugs and synplutonic bodies of gabbro diorite or lamprophyre all of the intrusions have similar lithologie characteristics and hydrous ferromagnesian mineral assemblages and they appear to represent a genetically related series of mafic bodies with similar petrogenetic histories in the crust of the meguma zone the intrusions show wide chemical variation of sio2 45 7 65 7 wt al2o3 8 9 26 5 wt mgo 2 8 26 5 wt cao 1 2 11 2 wt and k2o 0 1 4 4 wt and they have calc alkaline high k calc alkaline and shoshonitic characteristics large ion lithophile elements lile are present at variable but high concentrations e g ba 62 1920 ppm sr 176 2567 ppm relative to most high field strength element hfse abundances e g y 10 37 ppm zr 8 421 ppm and light rare earth elements lree have much higher concentrations than heavy rare earth elements hree la lu 24 3

volume transport of the antarctic circumpolar current from bottom pressure measurements abstract meausrements from bottom pressure gauges located at the north and south sides of drake passage are used to extend the one year time series of volume transport of the antarctic circumpolar current acc given previously by whitworth a small error in that paper is corrected and a revised transport time series is presented which shows the importance of including the transport in the northern and southern margins of drake passage direct measurements of vertical shear averaged across the passage are in good agreement with geostrophic shear and suggest that the acc is in geostrophic balance although most of the acc transport is in the baroclinic field transport fluctuations are mainly barotropic transport estimates based on pressure difference alone differ from the estimates of whitworth by less than 10 106 m3 s 1 fluctuations in transport of almost half of the mean value occur over periods as short as two weeks

influence of preexisting fault fabric on inversion related deformation a case study of the inverted fundy rift basin southeastern canada 1 preexisting zones of weakness significantly influenced the structural development of the fundy basin during rifting and subsequent basin inversion the preexisting fabric consisting of ne striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments formed during paleozoic and older orogenic activity during mesozoic rifting the preexisting fabric was reactivated creating a border fault system composed of linked ne and east striking extensional fault zones with anomalous dips gentle and steep compared to those of newly formed normal faults during inversion the preexisting fabric was again reactivated as the hanging wall of the composite border fault system moved nne relative to the footwall inversion was highly oblique on the ne striking fault zones producing gentle fault parallel buttress folds and fault perpendicular detachment folds above the low angle fault zones inversion was moderately oblique on the east striking fault zone producing relatively tight fault parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left lateral strike slip faults thus inversion related deformation on the east striking fault zone was partitioned at shallow levels i e partitioned updip our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion namely the type of inversion related faults the type and shape of inversion related folds and the distribution of deformation e g updip partitioning depend in part on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike

gulf stream structure transport and recirculation near 68 w an analysis of the structure and transport of the gulf stream is undertaken using direct current meter observations from a 13 mooring array deployed near 68 w from june 1988 to august 1990 the analysis is based on a stream coordinate approach in which velocities are rotated into a local downstream coordinate frame and averaged according to their relative cross stream location within the current the picture so obtained represents the average synoptic structure of the gulf stream rather than the eulerian averaged structure in which the current is weakened and broadened by lateral meandering of the current and adjacent recirculations many familiar features of the gulf stream are reproduced in the analysis including an asymmetric velocity profile with larger shear on the cyclonic shoreward side of the current an offshore displacement of the velocity core with depth and a subsurface velocity maximum on the offshore side of the current westward recirculations are also seen on both sides of the gulf stream maximum downstream speeds at the axis of the gulf stream reach approximately 2 0 m s at the surface and 0 7 m s at 1000 m roughly twice the corresponding eulerian averaged values the analysis also reveals a deep extension of the gulf stream at 3500 m depth with a width of 130 km and average speeds of 3 4 cm s the transport of the gulf stream in the stream coordinate frame is 113 8 sv approximately 30 larger than the eulerian averaged transport of 88 sv on the basis of these results and other recent studies the downstream transport increase of the gulf stream and the inflow structure to the gulf stream are reconsidered it is concluded that approximately 30 sv or over half of the transport increase between cape hatteras and 68 w is fed by inflow from the northern side of the gulf stream and that this inflow is concentrated near cape hatteras and 68 w where the gulf stream flows steeply across isobaths converging from the north