deformational history of an archean fold belt eastern point lake area slave structural province n w t archean metasedimentary rocks in the eastern point lake area of the slave structural province preserve a sequence of archean structures consisting of two generations of folds f1 and f2 with littl

role of plutonism in low pressure metamorphic belt formation wickham and oxburgh1 recently proposed that low pressure high temperature low p high t metamorphism in the eastern pyrenees and possibly all low p high t metamorphic belts resulted from anomalously high mantle heat flow brought about by rifting their model is largely constrained by the presence of nearby synmetamorphic rift related sedimentary rocks and the interpretation that the migmatites and granites are the product of in situ melting in the presence of an anomalously steep geotherm here we present an alternative model in which low p high t metamorphism pro grade reactions at pressures near or below the al2sio5 triple point results from contact effects near sill like igneous intrusions at intermediate crustal levels low p high t conditions can be achieved through this process in regions of continent continent collision with normal mantle heat flux as well as in zones of extension our model is based on studies of the low p high t metamorphic terrane in the new england appalachians

ascent of a granitoid diapir in a temperature varying medium a relationship for the ascent velocity of a granitoid diapir is derived and used in conjunction with a crustal heat flow model which incorporates a depth dependent temperature to predict emplacement histories ascent rate is strongly dependent on the width of a deformation layer of variable viscosity that is formed by the transfer of heat to the country rock and on the buoyancy force which propels the diapir through it ascent velocity is described by the expression u 2 gd3z 0r where is the density contrast between diapir and country rock g is gravitational acceleration d is the deformation zone width z is a parameter which describes the increase in viscosity across the zone 0 is the country rock viscosity at the contact and r is the diapir radius the width of the deformation zone as dictated by the temperature distribution and rheological function is the point at which the viscosity increases by a factor f from the contact value although ascent rates vary with choice of this parameter ascent distances are not strongly dependent on f results of simulations which incorporate a spectrum of input parameters reveal that ascent distance is strongly dependent on both the rheology and ambient temperature of the encompassing rock but only weakly dependent on the initial diapir temperature ascent velocity varies with the diapir size with larger bodies moving more slowly and ascending for longer periods relative to smaller plutons as a result of the proportionately larger amount of thermal energy available for ascent larger bodies will rise greater distances than smaller diapirs however the additional ascent appears nominal relative to the contrast in available energy modeling diapirs using a no slip boundary condition decreases ascent velocity by a factor of about 3 relative to results incorporating a stress free boundary condition the time scale of granitoid diapirism over crustal distances cannot be less than 104 years due to the rate limiting effect of thermal conduction above the body and not greater than 105 years reflecting solidification times of kilometer sized plutons a consequence of ascent by a deformation zone mechanism is the generation following emplacement of a mechanically weakened crust which extends from beneath the diapir to near the source perhaps explaining the relatively common occurrence of synmagmatic to postmagmatic mafic dikes within granites believed to be derived from interaction of basalt with the lower crust

different impacts of various el nino events on the indian ocean dipole our early work wang and wang in j clim 26 1322 1338 2013 separates el nino modoki events into el nino modoki i and ii because they show different impacts on rainfall in southern china and typhoon landfall activity the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively el nino modoki i features a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modoki ii shows an asymmetric distribution with the warm sst anomalies extending from the northeastern pacific to the equatorial central pacific the present paper investigates the influence of the various groups of el nino events on the indian ocean dipole iod similar to canonical el nino el nino modoki i is associated with a weakening of the walker circulation in the indo pacific region which decreases precipitation in the eastern tropical indian ocean and maritime continent and thus results in the surface easterly wind anomalies off java sumatra under the bjerknes feedback the easterly wind anomalies induce cold sst anomalies off java sumatra and thus a positive iod tends to occur in the indian ocean during canonical el nino and el nino modoki i however el nino modoki ii has an opposite impact on the walker circulation resulting in more precipitation and surface westerly wind anomalies off java sumatra thus el nino modoki ii is favorable for the onset and development of a negative iod on the frame of the bjerknes feedback

a new paradigm for the predominance of standing central pacific warming after the late 1990s canonical el nino has a warming center in the eastern pacific ep but in recent decades el nino warming center tends to occur more frequently in the central pacific cp the definitions and names of this new type of el nino however have been notoriously diverse which makes it difficult to understand why the warming center shifts here we show that the new type of el nino events is characterized by 1 the maximum warming standing and persisting in the cp and 2 the warming extending to the ep only briefly during its peak phase for this reason we refer to it as standing cp warming cpw global warming has been blamed for the westward shift of maximum warming as well as more frequent occurrence of cpw however we find that since the late 1990s the standing cpw becomes a dominant mode in the pacific meanwhile the epochal mean trade winds have strengthened and the equatorial thermocline slope has increased contrary to the global warming induced weakening trades and flattening thermocline we propose that the recent predominance of standing cpw arises from a dramatic decadal change characterized by a grand la nina like background pattern and strong divergence in the cp atmospheric boundary layer after the late 1990s the anomalous mean cp wind divergence tends to weaken the anomalous convection and shift it westward from the underlying sst warming due to the suppressed low level convergence feedback this leads to a westward shift of anomalous westerly response and thus a zonally in phase sst tendency preventing eastward propagation of the sst anomaly we anticipate more cpw events will occur in the coming decade provided the grand la nina like background state persists

the slave province a distinct archean craton the slave province is a relatively small late archean craton that exhibits distinctive rock associations and structures by comparison with the much larger superior province differences are evident in i the abundance of sedimentary versus volcanic rocks and of felsic versus mafic volcanic rocks ii the greater evidence for sialic basement iii the higher proportion of more evolved potassium rich granite iv the type setting and timing of gold and base metal mineralization and v a regional zonation of gold deposits that seems to be a unique feature of the slave province contrasts in structure are also significant the large scale linear belts and boundaries sutures that characterize the superior province have no obvious counterpart in the slave province despite some similarities with other archean cratons the distinct features of the slave province are important for they imply that no single archean craton should be used to develop a universal paradigm for the genesis and tectonic evol

the diffusion behavior of hydrogen in plagioclase feldspar at 800 1000 c implications for re equilibration of hydroxyl in volcanic phenocrysts to use structural hydroxyl oh concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption it is first necessary to understand the diffusive behavior of hydrogen in plagioclase in this study diffusion coefficients for a natural oh bearing plagioclase feldspar ab 66 an 31 or 3 are determined from a series of integrated loss heating experiments performed at 800 1000 c and 1 atm under air nitrogen gas and a co 2 h 2 mixture at the fmq oxygen buffer hydrogen diffusion is found to be isotropic within analytical error using a one dimensional diffusive loss model for an infinite slab the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log d 0 1 62 0 31 m 2 s and e a 266 77 kj mol and log d 0 0 97 0 35 m 2 s and e a 278 90 kj mol for experiments only conducted under nitrogen gas nearly complete 83 97 loss of oh from the andesine was achieved in 900 and 1000 c heating series except for the 900 c fmq buffer experiment in which only 64 of the total oh was lost after 21 6 days of cumulative heating the diffusion rates of hydrogen in the plagioclase after 800 1000 c are similar to interpolated diffusion rates for sodium diffusion in an 30 feldspar implying that na and h both diffuse via frenkel defects involving the large cation sites and interstitial ions the diffusion coefficient d values for hydrogen in plagioclase are lower than most reported diffusion data for hydrogen in nominally anhydrous minerals and are most similar to d reported for pure forsterite unaffected by iron redox reactions based on the hydrogen diffusion parameters in this study a 1 mm spherical plagioclase phenocryst experiencing dehydration under lowered water activity during ascent and eruption at 800 c retains 50 of its initial oh concentration after 34 days at 900 and 1000 c a 1 mm phenocryst retains 50 of its initial oh concentration after only 1 3 days and 0 25 day respectively oh concentrations in plagioclase are therefore most indicative of magmatic water contents during the latest stages of ascent and eruption

garnet rotation and the development of axial plane crenulation cleavage rotated helicitic garnets syntectonically overgrowing axial plane crenulation cleavage on the limbs of folds show the opposite sense of rotation to that undergone by the folded foliation during the development of the fold the garnet rotation is inconsistent with simple minded shear models for the development of the crenulation cleavage and it is useful to consider this problem in order to understand the development of crenulation cleavage better various models are considered in an attempt to explain both garnet rotation and cleavage morphology earlier models were based on the assumption that garnet rotation is driven by shear parallel to s2 they were mostly unsatisfactory but one involving migration of the crenulation hinges is viable when combined with other models described here the new models proposed here are based on the assumption that garnet rotation is driven by shear on the crenulated surface s1 the new foliation s2 is considered to be a passive structure at least in the early stages of its development these models satisfactorily explain garnet rotation and development of the cleavage including differentiation and they can be used to predict the morphological evolution of the cleavage microstructure as it should be preserved in garnets comparison of observed and predicted helicitic structures strongly supports the proposed models evidence is presented to show that where a garnet has an se that is a schistosity and an si that is a crenulation cleavage the schistosity can have developed by unfolding of the crenulations

the role of hydrogen in promoting alsi interdiffusion in albite naalsi3o8 at high pressures the rate of al si disorder in dry low albite is greatly enhanced at high pressures this enhancement takes place in ap t regime where the presence of water would induce melting none was observed the experimental work was carried out in piston cylinder apparatus using nacl pressure medium modification of the experimental conditions to avoid production of hydrogen by dissociation of moisture in the pressure medium as well as to capture hydrogen with fe2o3 and zno indicates that hydrogen is the active agent in promoting al si diffusion at high pressures in naalsi3o8 a mechanism involving transient oh groups that stimulate coordinations greater than 4 simultaneously breaking alo and sio network bonds is proposed

a new look at the stratigraphy of the yellowknife supergroup at yellowknife n w t implications for the age of gold bearing shear zones and archean basin evolution based on recent detailed mapping a revised stratigraphic column is proposed for the rocks of the archean yellowknife supergroup in the yellowknife greenstone belt the mafic volcanic rocks of the kam formation previously thought to represent the oldest supracrustal rocks of the belt overlap remnants of an earlier volcanic sedimentary sequence here referred to as the octopus formation as its enormous thickness makes it too unwieldy to be described as a single formation the kam formation is raised to group status and subdivided into four formations it is proposed that the kam group should replace the beaulieu group in the yellowknife area the chan formation at the base of the kam group consists of multiple gabbroic intrusions that were emplaced into a carapace of pillowed flows the intrusions locally resemble sheeted mafic dyke complexes in phanerozoic ophiolites thought to represent evidence for sea floor spreading the crestaurum formation which overlies the chan formation is characterized b

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

development of a chevron cleavage pattern and porphyroblast rotation in graded metaturbidites slave structural province northwest territories canada abstract chevron cleavage pattern displays opposite cleavage vergence across a psammite pelite contact or within a single graded couplet in this example graded metaturbidites preserve an s2 cleavage with dextral vergence in their competent psammitic bases and an s3 crenulation cleavage with sinistral vergence in their less competent semi pelitic tops bedding parallel shear partitioned into tops of graded couplets resulted in buckle folding of s2 cleavage s3 is also a compositionally differentiated cleavage displaying alternating quartz rich microlithons q and muscovite rich cleavage domains m together q and m domains define s microfolds related to d3 biotite porphyroblasts developed during static metamorphism before d 2 s 2 contain quartz inclusion trails sii with three orientation patterns that are related to their location within graded beds porphyroblasts in psammitic bases of graded couplets are not affected by d 3 s 3 in comparison sii in porphyroblasts in semi pelitic tops of beds are on average about 5 clockwise in m domains and about 90 counter clockwise in q domains corresponding to flat and steep limbs of s shaped microfolds in s2 from these observations it is apparent that biotite porphyroblasts within q domains rotated about 90 counter clockwise during microfolding within m domains the sii data suggest that porphyroblasts rotated little relative to their orientation in the base of the beds

p t paths from garnet zoning a new technique for deciphering tectonic processes in crystalline terranes a procedure to calculate quantitative rock pressure temperature p t paths based on chemical zoning profiles in garnet combined with mineral chemistry from the other minerals in the assemblage has been applied to samples from diverse tectonic settings with the result that the calculated p t path is shown to be a sensitive monitor of tectonic processes terranes where metamorphic recrystallization paths are controlled by uplift and erosion show heating during decompression in the prograde p t path and cooling during decompression in the retrograde path in nappe terranes where hot rocks are emplaced over cool rocks the upper plate shows cooling during decompression whereas the lower plate shows heating during compression in nappe terranes where cool rocks are emplaced over hot the lower plate shows cooling during compression calculation of p t paths from mineral zoning should provide a powerful new tool for deciphering tectonic processes in crystalline terranes

multiple dikes in lower kam group yellowknife greenstone belt evidence for archean sea floor spreading a mafic intrusive extrusive complex at the base of the kam group in the archean yellowknife supergroup at yellowknife northwest territories canada grades from gabbros through a zone of multiple and sheeted dikes into massive and pillowed flows with thin beds of interflow sediments although rock types and primary structures resemble those in upper parts of phanerozoic ophiolites the kam group lacks an ultramafic base and is much thicker than typical ophiolites because similar mafic sections occur in certain atypical ophiolites and in plateau areas of modern ocean basins however the kam group is viewed as a remnant of archean oceanic crust rather than as a product of intracontinental rift volcanism the dikes are analogous to sheeted dikes of ophiolites and are suggestive of sea floor spreading in an archean marginal basin setting

molecular h2o as carrier for oxygen diffusion in hydrous silicate melts abstract dissolved water is known to dramatically enhance oxygen diffusion in silicate melts glasses and minerals a quantitative theory has been developed to explain this phenomenon by transport via molecular h2o diffusion y zhang e m stolper g j wasserburg diffusion of a multi species component and its role in the diffusion of water and oxygen in silicates earth planet sci lett 103 1991 228 240 here we report experimental confirmation of the theory for rhyolitic melts by measuring both h2o and 18o diffusion profiles in a single experiment in sorption experiments at 100 mpa and temperatures from 1041 to 1136 k isotopically enriched water diffused into doubly polished rhyolitic glass wafers h2o profiles were analyzed by infrared spectroscopy and 18o profiles by sims 18o diffusivities were found to be 1 2 orders of magnitude slower than bulk water diffusivities but 3 4 orders of magnitude faster than eyring diffusivities calculated from viscosity the data show that oxygen self diffusion under hydrothermal conditions is due to molecular h2o diffusion not due to the self diffusion of oxygen itself with this confirmation experimental data on h2o diffusion in silicate melts can be used to infer 18o diffusion under hydrothermal conditions and hydrothermal oxygen diffusion data in silicate minerals can be used to infer h2o diffusivity as long as the concentration or solubility of h2o in the given phase is known

the annual cycle modulation of meridional asymmetry in enso s atmospheric response and its dependence on enso zonal structure previous studies documented that a distinct southward shift of central pacific low level wind anomalies occurringduringtheensodecayingphaseiscausedbyaninteractionbetweenthewesternpacificannualcycleand el nino southern oscillation enso variability the present study finds that the meridional movement of the central pacificwindanomalies appears only duringtraditional eastern pacific el nino ep el nino eventsrather than in central pacific el nino cp el nino events in which sea surface temperature sst anomalies are confined to the central pacific the zonal structure of enso related sst anomalies therefore has an important effectonmeridionalasymmetryintheassociatedatmosphericresponseanditsmodulationbytheannualcycle in contrasttoepelninoevents thesstanomaliesofcpelninoeventsextendfartherwesttowardthewarmpool regionwithitsclimatological warmssts inthewarmpool region relativelysmallsstanomaliesarethusable to excite convection anomalies on both sides of the equator even with a meridionally asymmetric sst background state therefore almost meridionally symmetric precipitation and wind anomalies are observed over the central pacific during the decaying phase of cp el nino events the sst anomaly pattern of la nina events is similar to cp el nino events with a reversed sign accordingly no distinct southward displacement of the atmospheric response occurs over the central pacific during the la nina decaying phase these results have important implications for enso climate impacts over east asia since the anomalous low level anticyclone over the western north pacific is an integral part of the annual cycle modulated enso response

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

geothermometry and geobarometry in pelitic rocks of north central wopmay orogen early proterozoic northwest territories canada pressure and temperature estimates for the pelitic schists and gneisses along the east flank of the hepburn batholith early proterozoic have been determined by means of an electron microprobe study of coexisting garnet biotite plagioclase and cordierite garnet biotite geothermometry using recent calibrations yields results between 560 and 765 c consistent in spatial distribution with andalusite sillimanite and sillimanite k feldspar metamorphic zones calibrations of the garnet cordierite equilibrium give temperature estimates on average 23 c lower both sets of temperature estimates for the garnet cordierite bearing assemblages are consistent with the theoretical stability field of these rocks geobarometry based on the 3 caal 2 si 2 o 8 ca 3 al 2 si 3 o 12 2 al 2 sio 5 sio 2 equilibrium outlines a broad pressure culmination with variation from 2 6 to 5 2 kbar the p culmination coincides with a structural plunge culmination as outlined by the change in plunge azimuth of folds of bedding by a re entrant in the trace half window of a major premetamorphic thrust fault and by a narrowing of the synmetamorphic funnel shaped hepburn batholith garnet cordierite geobarometric calibrations generally give pressure determinations in the same range as the grossular anorthite results the spread in the garnet cordierite pressure estimates from various calibrations however points to the need for considering the role of water when using the garnet cordierite geobarometer

two distinct shortening events during late archean orogeny in the west central slave province northwest territories canada late archean structures in the west central part of the slave province formed during two separate orogenic events evidence for early folding and thrusting in an accretionary prism is confined to a narrow belt along the east margin of an older microcontinent the anton terrane in the west part of the province structures related to this event are overprinted by regional low pressure metamorphism subsequent shortening occurred in a continental arc setting in which folding and faulting was accompanied by calc alkaline magmatism and regional low pressure metamorphism although the entire region was affected the bulk of shortening during the second orogenic event occurred east of the early fold and thrust belt the first orogenic event produced a suture zone between old continental crust to the west and juvenile rocks to the east and during the second orogenic event rocks on either sides of the suture were tectonically underplated and intruded

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

a survey of hydrous species and concentrations in igneous feldspars the hydrous components in 85 feldspars from various igneous environments spanning the range of naturally occurring compositions were examined with infrared spectroscopy the feldspars contain structural oh 0 512 ppm h 2o h 2o 0 1350 ppm h 2o and nh 4 0 1500 ppm nh 4 groups as well as fluid inclusions and alteration products although composition and structure do influence the type of hydrous species that can be incorporated into a particular feldspar mineral the concentration of these species is not controlled by major element composition coarse perthitic microclines have a heterogeneous distribution of hydrous species and contain h 2o or nh 4 in k rich lamellae and fluid inclusions in na rich areas the structural oh in plagioclase feldspars is not associated with twin boundaries or exsolution lamellae all of the possible structural hydrous species are found in pegmatite feldspars whereas volcanic feldspars contain only structural oh the variation in oh concentration within a given feldspar composition suggests that fluids in the geologic environment play a role in determining the hydrogen concentration of each sample the vast majority of plutonic feldspars have undergone partial or total equilibration with meteoric fluids during low temperature 400 150 c hydrothermal exchange obliterating any structural hydrogen and creating substantial concentrations of fluid inclusions up to 4000 ppm h 2o in the exchanged regions the amount of water stored as fluid inclusions within feldspars in the upper crust 1 10 19 kg is small compared to the 1 35 10 21 kg of water in the oceans but is roughly equivalent to the reservoir of water stored in hydrous minerals in the upper crust

climatic and tectonic influences on fan deltas and wave to tide controlled shoreface deposits evidence from the archaean keskarrah formation slave province canada the 2 6 ga keskarrah formation located in the central slave province northwest territories canada is a late orogenic tectonically controlled sedimentary sequence that developed under unusual climatic and depositional conditions the formation is adjacent to the crustal scale north trending beniah lake fault and overlies the 3 15 ga augustus granite the 2 69 2 7 ga mafic volcanic peltier formation and the turbiditic contwoyto formation unconformably principal lithofacies in the keskarrah formation include conglomerate sandstone and siltstone sandstone the conglomerate lithofacies represents coalescing gravelly streamflow dominated fan deltas adjacent to topographic highs up section quartz rich arenites and quartz arenites of the sandstone lithofacies are interpreted to be shallow water shoreface deposits influenced by wave action and tides the overlying feldspathic litharenites of the siltstone sandstone lithofacies are consistent with a lower shoreface to proximal offshore environment dominated by wave and tide interaction tidal influence in both sandstone dominated lithofacies is inferred from the presence of mudstone laminae between bedforms and on foresets of cross beds as well as from abundant reactivation surfaces with local mudstone drapes intense chemical weathering during the archaean resulting from elevated atmospheric co2 levels higher temperatures and moist climatic conditions played an important role in the development of quartz rich arenites that appear to be first cycle deposits few lithic fragments and feldspar grains are preserved due to in situ host rock weathering chemical weathering during transport and wave and tide action hydraulic sorting and abrasion in the shoreface environment contributed to the continued breakdown and transport of labile minerals increased proportions of lithic fragments in sandstone beds of the conglomerate lithofacies are the result of shorter transport distances from source areas to the depositional environment abundant conglomerate with up to 4 m large granitic boulders derived from the adjacent augustus granite and mafic clasts from the peltier formation indicate high relief and fault related uplift and subsidence the intimate association of fan deltas and wave and tide influenced shallow marine deposits in association with quartz rich sandstones forming in a high relief area make the keskarrah formation remarkable in the rock record

impact of different el nino types on the el nino iod relationship previous studies reported that positive phases of the indian ocean dipole iod tend to accompany el nino during boreal autumn here we show that the el nino iod relationship can be better understood when considering two different el nino flavors eastern pacific el nino events exhibit a strong correlation with the iod dependent on their magnitude in contrast the relationship between central pacific cp el nino events and the iod depends mainly on the zonal location of the sea surface temperature anomalies rather than their magnitude cp el nino events lying farther west than normal are not accompanied by significant anomalous easterlies over the eastern indian ocean along the java sumatra coast which is unfavorable for the local bjerknes feedback and correspondingly for an iod development the el nino iod relationship has experienced substantial changes due to the recent decadal el nino regime shift which has important implications for seasonal prediction

a deformed polymictic conglomerate the influence of grain size and composition on the mechanism and rate of deformation abstract in a deformed polymictic conglomerate from the hill end area new south wales australia almost all the strain is confined to fine grained quartz rich rock fragments coarse quartz and feldspar clasts generally show little evidence of intracrystalline plasticity the most strongly elongated rock fragments are finer grained and richer in layer silicates relative to quartz and feldspar indicating that both grain size and composition have influenced finite strain and thus strain rate the relationship between grain size and strain rate is broadly consistent with a dominance of grain boundary deformation mechanisms over intracrystalline dislocation mechanisms at finer grain sizes however strong quartz c axis preferred orientations have been measured in the most highly strained clasts implying a significant component of dislocation glide close examination of the microfabric mineralogy and petrology of the fine grained clasts shows that other factors are likely to have influenced their mechanical behaviour and led to enhancement of strain rate these factors include the trace element chemistry of the phases especially quartz the role of a mobile fluid phase the presence of poorly bonded mica 001 interfaces and the evolutionary nature of microfabric and mineralogy all of which are relevant to the bulk of crustal metamorphic rocks and should be taken into account in developing mechanical models of metamorphic belts

cation diffusion in feldspars feldspars are among the most common minerals in the earth s crust and are found in a variety of rock types diffusion in feldspars has been studied for well over half a century with rosenqvist s 1949 measurements of ra and pb diffusion among the earliest published works major efforts in measuring diffusion in feldspars primarily of the alkali elements were undertaken in the early 1970s with the work of bailey 1971 lin and yund 1972 petrovic 1972 foland 1974 giletti et al 1974 and kasper 1975 many of these early studies used bulk exchange techniques rather than direct depth profiling or employed methods of limited depth resolution such as serial sectioning these methods while state of the art for their time impose several limitations including a range of measurement restricted to relatively fast diffusivities and the difficulty of distinguishing the effects on measured chemical or isotopic compositions that may be a result of diffusional fast paths surface reaction and or other artifacts from those contributions due solely to volume diffusion development of high resolution depth profiling techniques such as sims and rbs have permitted measurement of much smaller diffusivities for a broader range of elements and reduced some of the uncertainties characteristic of bulk exchange methods feldspar diffusion data have been previously summarized in yund 1983 and smith and brown 1988 and were included in brady s 1995 compilation of diffusion data for silicate minerals since the publication of these works there have been numerous diffusion studies of feldspars encompassing a range of compositions in alkali feldspars and across the plagioclase series these have included measurements of diffusion of major elements na k ca ba oxygen and silicon as well as na k and caal nasi interdiffusion diffusion of noble gases and diffusion of minor and trace elements including fe mg sr

structural patterns and tectonic evolution of supracrustal domains in the archean slave province canada a new plate tectonic model accounts for lithological relations and regional structural patterns in late archean supracrustal domains of the slave province multiple dykes and pillowed mafic flows most common in the western part of the province suggest sea floor spreading the mafic volcanics lying in narrow homoclinal belts stratigraphically below more extensive turbidites are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics the latter predominating over mafic volcanics in northeastern domains the felsic calc alkaline magmas may have risen from a shallow dipping subduction zone westerly verging folds westerly convex fold arcs and inclinations of later foliations particularly in lower level rocks of higher metamorphic grade are in accord with underthrusting to the east the zone of underthrusting shifted progressi

silicon self diffusion in single crystal natural quartz and feldspar abstract silicon diffusion was measured in natural quartz and anorthitic feldspar under dry low pressure 0 1 mpa conditions using a 30 si tracer sources of diffusant consisted of 30 si enriched silica powder for experiments on quartz and microcrystalline 30 si doped synthetic feldspar of composition comparable to the feldspar specimens distributions of 30 si were measured with rutherford backscattering spectrometry and nuclear reaction analysis using the reaction 30 si p 31 p the following arrhenius relations were obtained for anneals at 1 atm in air for quartz transport normal to c d qtz c 7 97 10 6 exp 447 31 kj mol 1 rt m 2 s 1 transport parallel to c d qtz c 6 40 10 6 exp 443 22 kj mol 1 rt m 2 s 1 for anorthitic feldspar an 93 d an 3 79 10 7 exp 465 50 kj mol 1 rt m 2 s 1 the few successful experiments on diffusion in plagioclase of more albitic compositions an 67 and an 23 reveal si diffusivities a few orders of magnitude faster than that in the anorthite the results for these feldspars bracket the determination of caal nasi interdiffusion under dry conditions by grove et al geochim cosmochim acta 48 1984 2113 2121 suggesting that the rate limiting process is indeed si diffusion si diffusion in quartz under more reducing conditions nno is slightly slower by about half an order of magnitude than diffusion in samples annealed in air this is consistent with observations made in studies of synthetic quartz bejina and jaoul phys earth planet inter 50 1988 240 250

late archean tectono magmatic evolution of the central slave province northwest territories an early tectono stratigraphic and late plutonic assemblage are distinguished in the central part of the archean slave province contwoyto lake area on the basis of their relationship to deformation and metamorphic episodes and by geochemical characteristics the older assemblage which predates the onset of intense deformation and the thermal peak of metamorphism comprises 2 68 2 65 ga calc alkaline volcanic and plutonic rocks as well as extensive turbidites the younger assemblage comprises ca 2 61 2 58 ga plutonic units that were emplaced during and after deformation d d3 and the thermal peak of metamorphism compositions of the late plutonic units vary systematically with time of intrusion from an early calc alkaline diorite tonalite suite to late peraluminous granites the early assemblage is interpreted to represent remnants of an island arc or arcs overlain by turbidites and accreted during d1 and d2 the later assemblage is interpreted as a product of late to post accretion suprasu

structural development of an archean orogen western point lake northwest territories the point lake orogen in the central archean slave province of northwestern canada preserves more than 10 km of structural relief through an eroded antiformal thrust stack and deeper anastomosing midcrustal mylonites fault restoration along a 25 km long transect requires a minimum of 69 km slip and 53 km horizontal shortening in the western part of the orogen the basal decollement places mafic plutonic volcanic rocks over an ancient tonalitic gneiss complex ten kilometers to the east in the keskarrah bay area slices of gneiss unroofed on brittle thrusts shed molasse into several submerged basins conglomerates and associated thinly bedded sedimentary rocks are interpreted as channel levee and overbank facies of this thrust related sedimentary fan system the synorogenic erosion surface at the base of the conglomerate truncates premetamorphic or early metamorphic thrust faults formed during foreland propagation while other thrusts related to hinterland progressing imbrication displace this unconformity tightening of synorogenic depositional troughs resulted in the conglomerates present localization in synclines to the west of associated thrust faults and steepening of structural dips eastern parts of the orogen consist of isoclinally folded graywackes composed largely of mutti and ricci lucchi turbidite facies b c and d interpreted as submarine fan deposits eroded from a distant volcanic arc thrust faults in the metasedimentary terrane include highly disrupted slate horizons with meter scale duplex structures and recrystallized calcmylonites exhibiting sheath folds and boudin trains with very large interboudin distances the sequence of fabric development and the overall geometry of this metasedimentary terrane strongly resembles younger forearc accretionary prisms conditions of deformation along the thrusts parallel the regional metamorphic zonation amphibolite facies in the basal decollement through greenschist facies shear zones to cataclastic crush zones in the region of emergent thrusts in keskarrah bay depth differences can account for only half of the metamorphic gradient thermal profiles which increased downwards in obducted greenstone belts and synthrusting plutonism explains other high metamorphic gradients a tectonic model involving the collision of an accretionary prism with a continental margin best explains the structural and sedimentological evolution of the orogen