precambrian accretionary tectonics in the bou azzer el graara region anti atlas morocco ophiolites of the anti atlas of morocco occur as highly dismembered slivers of mafic and ultramafic rocks sandwiched between a precambrian craton and a magmatic arc tectonic slices of accretionary melange ophiolites and forearc basins have been juxtaposed by oblique subduction and transpression in the forearc region of a late proterozoic subduction zone synkinematic to postkinematic calc alkalic magmatism in these terranes indicates migration of the magmatic front over the deformed forearc terranes

the bristol mendip foreland thrust belt the thrusts and associated fold structures of the bristol mendip area are interpreted in terms of a thin skinned piggy back foreland thrust belt of variscan age with dominant northward transport strike normal balanced sections and compatible strike parallel sections have been constructed to illustrate the 3 d geometry of the linked thrust system north south shortening of c 20 km 40 is calculated from deformed and restored strike normal sections a thick and extensive thrust wedge of pre old red sandstone basement in the west of the area is responsible for culminations expressed at the surface as the mendip periclines uplifted culminations permit erosion to lower stratigraphic levels in the west and south of the area strike parallel sections and a hanging wall cut off map indicate that the majority of thrusts in the area are mainly oblique ramps rather than simple frontal and lateral ramps or flats the en echelon pattern of the mendip periclines may be related to the oblique ne climb of two of these thrusts the angle of frontal ramp climb through the dinantian stratigraphy is generally low and this explains the presence of numerous klippen of lower on upper carboniferous rocks whilst suggesting that certain thrust sheets were much more extensive than present outcrops indicate early pre thrusting movement on basement lineaments in the variscan foreland created uplifts angular unconformities and a predominance of n s structures in the north of the area

elevation changes of ice caps in the canadian arctic archipelago 1 precise repeat airborne laser surveys were conducted over the major ice caps in the canadian arctic archipelago in the spring of 1995 and 2000 in order to measure elevation changes in the region our measurements reveal thinning at lower elevations below 1600 m on most of the ice caps and glaciers but either very little change or thickening at higher elevations in the ice cap accumulation zones recent increases in precipitation in the area can account for the slight thickening where it was observed but not for the thinning at lower elevations for the northern ice caps on the queen elizabeth islands thinning was generally 0 5 m yr 1 which is consistent with what would be expected from the warm temperature anomalies in the region for the 5 year period between surveys and appears to be a continuation of a trend that began in the mid 1980s farther south however on the barnes and penny ice caps on baffin island this thinning was much more pronounced at over 1 m yr 1 in the lower elevations here temperature anomalies were very small and the thinning at low elevations far exceeds any associated enhanced ablation the observations on barnes and perhaps penny are consistent with the idea that the observed thinning is part of a much longer term deglaciation as has been previously suggested for barnes ice cap on the basis of the regional relationships between elevation and elevation change in our data the 1995 2000 mass balance for the archipelago is estimated to be 25 km3 yr 1 of ice which corresponds to a sea level increase of 0 064 mm yr 1 this places it among the more significant sources of eustatic sea level rise though not as substantial as the greenland ice sheet alaskan glaciers or the patagonian ice fields

sensitivity of simulated arctic sea ice to realistic ice thickness distributions and snow parameterizations 1 sea ice and snow on sea ice to a large extent determine the surface heat budget in the arctic ocean in spite of the advances in modeling sea ice thermodynamics a good number of models still rely on simple parameterizations of the thermodynamics of ice and snow based on simulations with an arctic sea ice model coupled to an ocean general circulation model we analyzed the impact of changing two sea ice parameterizations 1 the prescribed ice thickness distribution itd for surface heat budget calculations and 2 the description of the snow layer for the former we prescribed a realistic itd derived from airborne electromagnetic induction sounding measurements for the latter two different types of parameterizations were tested 1 snow thickness independent of the sea ice thickness below and 2 a distribution proportional to the prescribed itd our results show that changing the itd from seven uniform categories to fifteen nonuniform categories derived from field measurements and distributing the snow layer according to the itd leads to an increase in average arctic wide ice thickness by 0 56 m and an increase by 1 m in the canadian arctic archipelago and canadian basin this increase is found to be a direct consequence of 524 km3 extra thermodynamic growth during the months of ice formation january february and march our results emphasize that these parameterizations are a key factor in sea ice modeling to improve the representation of the sea ice energy balance

a record of holocene summer climate from a canadian high arctic ice core melt layers in ice cores are formed by melting on the snow pack surface which produces water that percolates down and refreezes in the colder snow layers below melt layers are distinguished by their bubble texture because more ice forms in the snow pack in warm summers than in cool summers the changing concentration with depth of melt layers in snow pits1 2 and ice cores3 5 is an indicator of past summer climate here we report on studies of melt layers in two canadian high arctic surface to bedrock ice cores although changes in elevation of the drill site owing to isostatic depression and uplift may contribute up to 40 of the total climatic signal recorded in the melt layers we interpret their varying concentrations in terms of changing summer temperatures over the past 10 000 years the warmest summers occurred 8 10 kyr ago and the coldest only 150 years ago the summers over the past 100 years have been the warmest for more than 1 000 years but are still not as warm as those of the early holocene the melt layer record is in broad agreement with geological records of glacier retreat during the holocene6 8 indicating that these data also contain information of regional significance

the mass balance of circum arctic glaciers and recent climate change the sum of winter accumulation and summer losses of mass from glaciers and ice sheets net surface mass balance varies with changing climate in the arctic glaciers and ice caps excluding the greenland ice sheet cover about 275 000 km2of both the widely glacierized archipelagos of the canadian norwegian and russian high arctic and the area north of about 60 n in alaska iceland and scandinavia since the 1940s surface mass balance time series of varying length have been acquired from more than 40 arctic ice caps and glaciers most arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades there is no uniform recent trend in mass balance for the entire arctic although some regional trends occur examples are the increasingly negative mass balances for northern alaska due to higher summer temperatures and increasingly positive mass balances for maritime scandinavia and iceland due to increased winter precipitation the negative mass balance of most arctic glaciers may be a response to a step like warming in the early twentieth century at the termination of the cold little ice age arctic ice masses outside greenland are at present contributing about 0 13 mm yr 1to global sea level rise

anti atlas morocco role in neoproterozoic western gondwana reconstruction abstract reconstruction of latest neoproterozoic gondwana hinges on the interpretation of the subduction and collision kinematics of pan african orogenic belts that rim the west african craton the anti atlas suture zone of southern morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known west african orogens to the west mauretanian bassaride and rokelide and transaharan orogens to the east ougarta tuareg gourma and dahomeyan contrary to previous interpretations new data from the anti atlas indicate a history of late neoproterozoic 750 600 north dipping subduction culminating in the 600 ma collision of the saghro magmatic arc to the north with the north facing rifted margin of the west african craton thus the anti atlas suture links a 6000 km long chain of pan african suture zones that essentially encircle the west african craton the suture zones demarcate the former position of subduction zones that in all cases dipped away from the west african craton the anti atlas suture links the western and eastern segments of the pan african orogenic belts associated with the amalgamation of western gondwana

fissure fills along faults variscan examples from gower south wales the extent to which persistent rather than transient fissures wide planar voids can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon bearing fluids variscan late carboniferous faults cutting dinantian lower carboniferous limestones on the gower peninsula south wales host clear evidence for fissures up to several metres wide evidence includes dendritic hematite growth and elongate calcite growth into open voids spar ball and cockade breccia formation laminated sediment infill and void collapse breccias detailed mapping reveals cross cutting geometries and brecciation of earlier fissure fills showing that fissures were formed during rather than after active faulting fissures therefore probably formed by geometric mismatch between displaced fault walls rather than by solution widening along inactive faults

evolution of fault zones in carbonates with mechanical stratigraphy insights from scale models using layered cohesive powder abstract we present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones using cohesive hemihydrate powder caso 4 h 2 o the evolution of these dilatant fault zones involves a range of processes such as fragmentation gravity driven breccia transport and the formation of dilatant jogs to allow scaling to natural prototypes extensive material characterisation was done this showed that tensile strength and cohesion depend on the state of compaction whereas the friction angle remains approximately constant in our models tensile strength of the hemihydrate increases with depth from 9 to 50 pa while cohesion increases from 40 to 250 pa we studied homogeneous and layered material sequences using sand as a relatively weak layer and hemihydrate graphite mixtures as a slightly stronger layer deformation was analyzed by time lapse photography and particle image velocimetry piv to calculate the evolution of the displacement field with piv the initial predominantly elastic deformation and progressive localization of deformation are observed in detail we observed near vertical opening mode fractures near the surface with increasing depth dilational shear faults were dominant with releasing jogs forming at fault dip variations a transition to non dilatant shear faults was observed near the bottom of the model in models with mechanical stratigraphy fault zones are more complex the inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation

persistent cold climatic episodes around greenland and baffin island links to decadal scale sea surface temperature anomalies two unusually persistent cold episodes around greenland and baffin island in 1971 1972 and 1982 1984 are described in terms of their severity atmospheric circulation variability and changes in sea surface conditions the episodes are significant due to the sizeable station temperature departures many exceeding one standard deviation and their persistence in both episodes unusually persistent cold pools of water developed in the northern atlantic and intensified near davis strait close to the onset of the cold climatic events and then migrated out of the region as the episodes came to a close anomalous northerly surface air flow occurs in most months during the two episodes

kinematic significance of sediment filled fissures in the north mountain basalt fundy rift basin nova scotia canada abstract numerous sediment filled fissures are present near the upper surface of the north mountain basalt 202 ma of the fundy basin which formed during triassic jurassic rifting the fissures are infilled with the same clastic material comprising the basal parts of the overlying earliest jurassic age sedimentary formations which accumulated less than 200 k y after the cooling of the basalt nearly all of the 1368 fissures measured in this study are planar to sub planar and are sub vertical after correcting the basalt flows to paleo horizontal the fissures typically formed along preexisting columnar joints within the basalt northeast striking fissures generally define a preferred orientation and commonly are wider than other fissures the sediment filled fissures therefore indicate earliest jurassic age nw se extension this extension direction is consistent with that indicated by the ne striking shelburne diabase dike the attitude of mesoscopic faults and the geometry of the fundy rift basin thus sediment filled fissures by themselves can serve as useful kinematic indicators and place tight constraints on the relative timing of extension

a scale independent approach to fracture intensity and average spacing measurement fracture intensity the number of fractures per unit length along a sample line is an important attribute of fracture systems that can be problematic to establish in the subsurface lack of adequate constraints on fracture intensity may limit the economic exploitation of fractured reservoirs because intensity describes the abundance of fractures potentially available for fluid flow and the probability of encountering fractures in a borehole traditional methods of fracture intensity measurement are inadequate because they ignore the wide spectrum of fracture sizes found in many fracture systems and the consequent scale dependence of fracture intensity an alternative approach makes use of fracture size distributions which allow more meaningful comparisons between different locations and allow microfractures in subsurface samples to be used for fracture intensity measurement comparisons are more meaningful because sampling artifacts can be recognized and avoided and because common thresholds of fracture size can be enforced for counting in different locations additionally quantification of the fracture size distribution provides a mechanism for evaluation of uncertainties estimates of fracture intensity using this approach for two carbonate beds in the sierra madre oriental mexico illustrate how size cognizant measurements cast new light on widely accepted interpretation of geologic controls of fracture intensity

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

injection clastic dykes in the lower oxford clay jurassic of central england relationship to compaction and concretion formation an injection dyke of fine grained sandstone derived from the kellaways sand formation intrudes overlying organic rich shales and shell beds of the lower oxford clay the dyke shows cross cutting relationships with early carbonate concretions and fills uncompacted kosmoceratid ammonite shells both within the concretions and surrounding shales internally the dyke displays flow like features and the walls show lobate flow structures clasts of uncompacted lower oxford clay and fragments of pyrite rich concretions occur within the sandstone intrusions the sandstone of the dyke was cemented by calcite identical to that precipitated in septarian cracks in the concretions this cementation took place prior to final compaction of the oxford clay the dyke has a sub parallel relationship to the nearby tinwell marholm fault suggesting that the dyke may be related to local tectonic events during the middle jurassic

timing and significance of crosscourse mineralization in sw england rb sr isotope analyses of inclusion fluids from quartz have demonstrated a triassic age 236 3 ma for n s trendmg pb zn f vein mineralization in the tamar valley district of the cornubian orefield consideration of the stratigaphy and structure of the permo triassic basins both onshore and in the english channel suggest that this mineralization results from the formation of fractures during regional extension driven subsidence and the subsequent ingress of basinal brines to the variscan basement

the sticklepath lustleigh fault zone tertiary sinistral reactivation of a variscan dextral strike slip fault dextral strike slip movement on the sticklepath lustleigh fault zone slfz is indicated by displacements of permian and older rocks previous authors have inferred that the main dextral movement which caused these displacements was post permian and noting the presence of small tertiary pull apart basins along the fault zone probably of tertiary age however the geometry of these early tertiary pull apart basins indicates sinistral rather than dextral strike slip movement we present an alternative model for the history of the sticklepath lustleigh fault zone summarized below 1 late variscan strike slip movement with a total displacement of up to 10 km produced the slfz and offset dextrally an earlier variscan thrust 2 extensional reactivation of this thrust led to rapid permo triassic subsidence in the crediton trough and a dextrally offset neighbour the hatherleigh outlier 3 approximately 6 km of early tertiary sinistral movement on the slfz produced small pull apart sedimentary basins and reduced the net dextral offset across the fault 4 in mid tertiary times minor dextral movements on the slfz may have produced reverse faulting on the margins of the tertiary basins

natural fracture propping and earthquake induced oil migration in fractured basement reservoirs the geological processes that create fluid storage capacity and connectivity in global fractured basement reservoirs are poorly understood compared to conventional hydrocarbon plays hosting potentially multibillion barrels of oil the upfaulted precambrian basement of the rona ridge offshore west of shetland uk gives key insights into how such reservoirs form oil presence is everywhere associated with sub millimeter to meterthickness mineralized fracture systems cutting both basement and local preseal cover sequences mineral textures and fluid inclusion geothermometry suggest a low temperature 90 220 c near surface hydrothermal system as does the preservation of clastic sediments in the same fractures these fills act as permanent props holding fractures open forming long term fissures in the basement that permit oil ingress and storage calcite fill u pb dating constrains the onset of mineralization and contemporaneous oil charge to the late cretaceous the additional preservation of oil stained injected sediment slurries and silica gels along basement faults suggests that rift related seismogenic faulting initiated lateral oil migration from jurassic source rocks into the adjacent upfaulted ridge subsidence below sea level in the latest cretaceous sealed the ridge with shales and buoyancy driven migration of oil into the preexisting propped fracture systems continued long after the cessation of rifting these new observations provide an explanation for the viability of sub unconformity fractured basement reservoirs worldwide and have wider implications for subsurface fluid migration processes generally

rapid thinning of parts of the southern greenland ice sheet aircraft laser altimeter surveys over southern greenland in 1993 and 1998 show three areas of thickening by more than 10 centimeters per year in the southern part of the region and large areas of thinning particularly in the east above 2000 meters elevation the ice sheet is in balance but thinning predominates at lower elevations with rates exceeding 1 meter per year on east coast outlet glaciers these high thinning rates occur at different latitudes and at elevations up to 1500 meters which suggests that they are caused by increased rates of creep thinning rather than by excessive melting taken as a whole the surveyed region is in negative balance

40ar 39ar dating and geochemistry of tholeiitic magmatism related to the early opening of the central atlantic rift tholeiitic effusive and intrusive magmatism from iberia morocco algeria and mali related to the early opening of the central atlantic rift was dated by the 40ar 39ar step heating method four plateau ages ranging from 203 7 2 7 to 197 1 1 8 ma were obtained on plagioclase from dykes from the taoudenni area mali and two lava flows from morocco the messejana dyke iberia which previously yielded discrepant conventional kar dates did not furnish any 40ar 39ar plateau dates however there is a clear inverse relationship between apparent age and k ca ratio for gas fractions from a plagioclase separate proportional to the alteration degree which combined with dates obtained on amphibole biotite and pyroxene allows us to determine an age of around 200 ma for this body these data and those obtained on the foum zguid morocco and the ksi ksou algeria dykes give evidence of a brief magmatic event between 206 and 195 ma ago which affected a large area ca 2500 km long trace element modelling shows that most of these formations originated from a homogeneous enriched source material such a brief magmatic episode related to the opening of a continental rift is in agreement with findings in other magmatic provinces e g the deccan traps and the red sea rift precisely dated by the 40ar 39ar method as well

on the nature of decadal anomalies in north atlantic sea surface temperature north atlantic sea surface temperature data from the comprehensive ocean atmosphere data set were used to investigate the behavior of temperature anomalies on multiple year timescales during the period 1948 1992 monthly anomaly time series for each 2 square from the equator to 70 n were low pass filtered at 4 years and normalized by the local standard deviation attention is focused on the extreme events the upper and lower deciles of the anomaly time series a 45 year sequence of january maps shows the already familiar phenomena of generally cold conditions prior to 1951 a long warm interval from 1951 through 1967 and again a cold period from 1968 through 1977 the years 1978 through 1982 were largely devoid of persistent strong anomalies but moderate cold conditions returned during 1983 1986 warm conditions dominated the north atlantic from 1987 onward within these thermal epochs however a total of five cold anomaly features and nine warm anomaly features have been identified these features have individual lifetimes of 3 to 10 years a typical size is 20 of latitude or longitude but they range from barely detectable to spanning the width of the basin the latter especially in lower latitudes most of the anomalies move long distances along certain preferred paths these paths generally follow the routes of the subarctic and subtropical gyres anomalies originating off north america along the boundary between the gyres move northeastward toward the norwegian sea along the approximate route of the north atlantic current midlatitude anomalies originating at the eastern boundary tend to spread both northward and southward along the coast the speed of these movements 1 3 km d 1 is generally less than the expected speed of the near surface ocean circulation simple ideas about the effects of beta dynamics and air sea heat exchanges are briefly considered but do not provide a satisfactory explanation for the movements of the anomalies the long timescale of these extreme events and the continuity of their movements suggest a useful degree of predictability of sea surface temperature based on persistence and propagation of features

growth of fissure ridge travertines from geothermal springs of denizli basin western turkey fissure ridge travertines grown from geothermal springs of denizli basin southwestern turkey are investigated through stratigraphic structural geochemical and geochronological methods with the aim of understanding the growth of these elongate mound shaped structures two main types of travertine deposits are recognized 1 bedded travertines which grew as flowstone on sloping surfaces and form the bulk of fissure ridges and 2 banded travertines which grew as veins within the bedded travertine chiefly along its central feeding conduit stratigraphic and structural observations shed light on the bedded banded travertine relationships where the banded features grew through successive accretion phases crosscutting the bedded travertine or forming sill like structures the bedded and banded travertines alternated their growth as demonstrated by complicated crosscutting relationships and by the upward suture in places of banded travertine by bedded travertine that was in turn crosscut by younger banded travertine the bedded travertine is often tilted away from the central axis of the fissure ridge thus leaving more room for the central banded travertine to form u series ages confirm the bedded banded travertine temporal relationships and show that the growth of the studied fissure ridges lasted up to several tens of thousands of years during quaternary time the banded travertine was deposited mainly during cold events possibly in coincidence with seismic events that might have triggered the outflow of deep geothermal fluids c and o stable isotope and rare earth element data indicate a shallow feeding circuit for the studied structures with a fluid component deriving from a deeper geothermal circuit a crack and seal mechanism of fissure ridge growth is proposed modulated by the interplay of local and regional influencing factors and mechanisms such as geothermal fluid discharge paleoclimate tectonics and the progressive tilting of bedded travertine limbs over a soft substratum creating the necessary space for the central veins to grow

the nature and age of basement host rocks and fissure fills in the lancaster field fractured reservoir west of shetland hosting up to 3 3 billion barrels of oil in place the upfaulted precambrian crystalline rocks of the lancaster field offshore west of shetland give key insights into how fractured hydrocarbon reservoirs can form in such old rocks the neoarchean c 2700 2740 ma charnockitic basement is cut by deeply penetrating oil mineral and sediment filled fissure systems seen in geophysical and production logs and thin sections of core mineral textures and fluid inclusion geothermometry suggest that a low temperature supplementary material analytical methods and isotopic compositions and ages are available at https doi org 10 6084 m9 figshare c 4763237 thematic collection this article is part of the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs

thrust tectonics of s devon the tectonics of the area from start point to chudleigh sw england are shown to be dominated by northward verging thrust nappes two major thrusts are postulated the dartmouth antiform is considered to be a major thrust structure not a fold structure as previously interpreted the torquay limestones are allochthonous and part of a klippe of a major thrust nappe with a minimum displacement of 13 km northwards a progressive and diachronous sequence of deformation has been established with deformation starting in the s and moving n many of the folds and cleavages are probably related to the strains developed locally in thrust tips and may have no regional correlation more intense and complex deformation is found in the s compared to the n the diachroneity is also reflected in the k ar mineral ages in the s at start point southward verging backfolding is the last significant hercynian deformation phase folding the thrust nappes

cockade breccia product of mineralisation along dilational faults cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement they occur particularly in low temperature near surface hydrothermal veins at least six mechanisms have been proposed for the formation of cockade breccia like textures but only two repeated rotation accretion and partial metasomatic replacement of clast minerals have been supported by detailed evidence a typical example of cockade breccia from the gower peninsula south wales shows clear evidence for the rotation accretion mechanism in particular overgrown breakage points in cement layers where cockades were previously touching each other and rotated geopetal infills of haematitic sediment based on the available evidence it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip seven criteria are given for the correct identification of cockade breccias

chaotic breccia zones on the pembroke peninsula south wales evidence for collapse into voids along dilational faults chaotic breccias and megabreccias locally called gash breccias hosted within the pembroke limestone group visean mississippian lower carboniferous of southwest wales are re mapped along with spatially related crackle and mosaic breccias of thirteen studied megabreccia bodies seven lie along steep nnw or nne striking strike slip faults originating during north south variscan late carboniferous shortening though reactivated during later extension four bodies are conformable with e w striking steeply dipping bedding and two have irregular or indeterminate margins the bedding parallel zones are interpreted as the dilational tips of listric normal faults and the cross strike faults as transtensional transfer zones sub horizontal clast fabrics suggest brecciation by gravitational collapse into opening fissures rather than by cataclasis along the faults most fissures have geometrically matched margins produced by this dilational faulting and only locally have the indented margins indicating solutional processes the most likely age for the main fissure extension and fill is late triassic based on analogous dated fills at the eastern end of the bristol channel basin the pembroke megabreccias blur the distinction between fault rocks formed by deformation and those formed by redeposition along fault zones

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

a 750 yr record of autumn snowfall and temperature variability and winter storminess recorded in the varved sediments of bear lake devon island arctic canada abstract the varve record from high arctic proglacial bear lake reveals a regionally coherent hydroclimatic signal as well as complexities due to changing hydroclimatic and limnologic conditions varve formation is strongly dependent on underflows that exhibit variability in strength during the past 750 yr periods with reduced underflow sedimentation and accumulation rates fail to produce varves in the distal part of the lake isolated coarse silt and sand grains occur in 80 of the varves and are interpreted to be niveo aeolian in origin coarse 500 m sand grains deposited on the lake ice by strong winter winds are notably less common since a d 1850 likely due to reduced storminess regression of the varve thickness record with meteorological records indicates high correlations with autumn september and october temperatures and total monthly snowfall these correlations are best at times when underflow activity is sufficiently strong to produce varves throughout the lake the close association with warmer temperatures and snow bearing synoptic systems moving north in baffin bay suggests that the primary climate signal in the varves is varying autumn snow pack that controls nival discharge in the following year the similarity between the other records of melt season temperature and sea ice cover and the bear lake record suggests that summer and autumn conditions were generally similar across the baffin bay region through much of the last millennium

palladium bearing gold deposit hosted by proterozoic lake superior type iron formation at the caue iron mine itabira district southern sao francisco craton brazil geologic and structural controls the caue iron mine is located in the itabira district in the southern sao francisco craton three geologic units metamorphosed to amphibolite facies have been identified 1 an archean volcano sedimentary sequence 2 a proterozoic iron formation unit and 3 a proterozoic quartzite unit the iron formation unit is cut by amphibolite dikes and tectonically imbricated with talc schists and amphibolites of the volcano sedimentary sequence all the rocks were affected by three phases of folding and associated thrusting and boudinage in the iron formation unit the d 1 and d 2 structures have been generated by a progressive simple shear regime with a transport direction consistently east over west d 3 structures are characterized by open folds with an associated crenulation cleavage the caue palladium bearing deposit comprises five orebodies hosted by jacutinga in the iron formation unit jacutinga is a highly sheared metamorphosed hydrothermally altered lake superior type iron formation composed of hematite quartz talc phlogopite with minor amounts of tourmaline apatite and monazite in the corpo y orebody the highest gold concentrations occur in quartz veins whereas in the corpo x central aba leste and aba notre orebodies the highest gold grades occur in hematite veins with local concentrations of quartz the gold rich veins are parallel to s 1 foliation in all orebodies except aba norte in the aba norte the gold rich boudinaged hematite vein is parallel to s 2 the ore minerals are palladian gold gold palladium palladium oxide and palladseite the main mineralizating event was synchronous with the peak of thermal metamorphism t 600 degrees c and with d 1 shearing and thrusting the hydrothermal alteration associated with this event is characterized by the formation of tale phlogopite and tourmaline and hematite and quartz veins generating the jacutinga rock type weathering of the jacutinga resulted in the alteration of silicates to kaolin and oxides to goethite

fracpaq a matlab toolbox for the quantification of fracture patterns abstract the patterns of fractures in deformed rocks are rarely uniform or random fracture orientations sizes and spatial distributions often exhibit some kind of order in detail relationships may exist among the different fracture attributes e g small fractures dominated by one orientation larger fractures by another these relationships are important because the mechanical e g strength anisotropy and transport e g fluids heat properties of rock depend on these fracture attributes and patterns this paper describes fracpaq a new open source cross platform toolbox to quantify fracture patterns including distributions in fracture attributes and their spatial variation software has been developed to quantify fracture patterns from 2 d digital images such as thin section micrographs geological maps outcrop or aerial photographs or satellite images the toolbox comprises a suite of matlab scripts based on previously published quantitative methods for the analysis of fracture attributes orientations lengths intensity density and connectivity an estimate of permeability in 2 d is made using a parallel plate model the software provides an objective and consistent methodology for quantifying fracture patterns and their variations in 2 d across a wide range of length scales rock types and tectonic settings the implemented methods presented are inherently scale independent and a key task where applicable is analysing and integrating quantitative fracture pattern data from micro to macro scales the toolbox was developed in matlab and the source code is publicly available on github and the mathworks fileexchange the code runs on any computer with matlab installed including pcs with microsoft windows apple macs with mac os x and machines running different flavours of linux the application source code and sample input files are available in open repositories in the hope that other developers and researchers will optimise and extend the functionality for the benefit of the wider community

zoned and recurrent deposition of na mg fe si exhalites and cu fe sulfides along synsedimentary faults bleida morocco in the upper proterozoic marginal basin of bleida morocco several horizons of copper mineralization are present in the main orebody a hydrothermal synsedimentary system has been reconstructed with evidence from thickness and facies variations it includes two sulfide rich basins on both sides of a half horst along a synsedimentary normal fault trending orthogonally to the continental margin three successions of ferruginous jasper sulfide bearing felsic tuffs and turbidites occur in adjacent basins whereas only chloritite and albitite beds are present on the axial half horst toward the fault zone the ferruginous jasper becomes apatite and chlorite rich then grades laterally to a chlorite and k feldspar rich albitite whereas in the same direction sulfide bearing layers show a mineral zoning pyrite chalcopyrite bornite then grade to a bornite and chlorite rich albitite chlorite is more magnesian toward the axial half horst it crystallized around 250 degrees c the axial zone is characterized by high b ba and zr contents zircon crystals and tourmaline needles are present toward the axial zone there is also a strong ree enrichment up to a hundred times and a marked light ree fractionation the ree patterns correspond to hydrothermal fluids linked to felsic volcanism the synsedimentary faults channeled first k na mg rich fluids which deposited chemical sediments on the sea floor then cu fe bearing fluids migrated through the more permeable laminations of the overlying felsic tuffs resulting in syndiagenetic crystallization of sulfides the lateral mineral zoning results mostly from decreasing temperature and increasing f sub o 2 away from the axial zone these long lived hydrothermal flows were muffled by the deposition of turbidite material although recurrent volcanic and hydrothermal activity occurred during stages of stagnating turbidite sedimentation these complex relationships between synsedimentary faulting felsic volcanism turbidite deposition and fluid expulsion from compressed sediments were controlled by the rapid and episodic subsidence of the marginal basin of bleida

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

the nature and significance of rift related near surface fissure fill networks in fractured carbonates below regional unconformities fissure fill networks are a widely recognized but relatively little described near surface phenomenon supplementary material appendix a is available at https doi org 10 6084 m9 figshare c 5023103

canada and the world glacier inventory this paper reviews the origins of the world glacier inventory program and canada s participation it tracks the program of the canadian federal government from its initiation to its demise today progress is geared towards the international glims and globglacier programs to which scientists from several canadian universities are making contributions achievements during the past decade towards providing data on canada s glacierized areas in the arctic and in western canada are documented

changes in late neoglacial climate inferred from former equilibrium line altitudes in the queen elizabeth islands arctic canada regional scale spatial variation in the change in equilibrium line altitude ela trend surface in the queen elizabeth islands qei arctic canada between the little ice age lia and 1960 corresponds to empirical orthogonal functions eofs representing specific patterns of summer climate variability found in the modern record extreme warm 1953 1962 and cold 1965 1974 decades in the modern record were used as modern analogues of climatic conditions during the early twentieth century and the lia respectively because of the minimal influence of precipitation during both extreme decades temperature is the variable upon which the fluctuation of the ela is dependent hence the ela h pattern describes the spatial pattern of change in sat across the qei between the lia and 1960 this pattern is consistent with the primary mode of variability of mean summer surface air temperature sat in the modern record ie eof 1 1949 2002 the positive negative phase of which is strongly in place during th

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

the age origin and tectonic significance of mesozoic sediment filled fissures in the mendip hills sw england implications for extension models and jurassic sea level curves in the eastern mendip hills on the northern margin of the wessex basin sw england the carboniferous limestone is cut by numerous fissures that are filled with mesozoic sediments sedimentary dykes neptunian dykes the fissures contain a record of triassic lower jurassic sediments that are only sparingly preserved in their normal stratigraphical position between the carboniferous limestone and the unconformably overlying upper inferior oolite of bajocian age detailed analysis of cross cutting relationships facies analysis biostratigraphy lithostratigraphy and strontium isotope ages of relevant mesozoic sediments has allowed the construction of an upper triassic lower jurassic fissure fill stratigraphy for the eastern mendip area most fissures were clearly formed by rapid influx of unlithified sediment from the land surface or sea floor some smaller cavities or larger cavities with restricted access to the unconformity were apparently filled by sediment that trickled down into the fissure system the vast majority of the mendip fissures are interpreted as having formed as a response of the carboniferous limestone north of major basin bounding faults to pulses of tectonic extension during ladinian norian rhaetian late hettangian early sinemurian late sinemurian early pliensbachian late pliensbachian and bajocian times triassic earliest jurassic fissures have a broad spread of strike from e w to nw se to n s accommodating extension in a roughly ne sw direction younger jurassic fissures show well defined e w and n s trends with the former becoming dominant through time total extension of 4 7 n s and 0 6 e w was produced by the formation of triassic jurassic fissures within the carboniferous limestone such patterns of extension are thought likely to be characteristic of the subsurface geology in much of southern england and wales major implications of this study are that 1 the presence of seismically unresolvable sediment filled fissures in supposedly rigid fault blocks can lead to a significant underestimate of regional extension based on the restoration of motion on normal faults on seismic reflection profiles and 2 the isolation of pulses of tectonic activity with a temporal resolution of 10 5 10 6 years may provide a means of identifying a tectonic signal in relative sea level curves derived from the jurassic sedimentary record

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

a varve record of increased little ice age rainfall associated with volcanic activity arctic archipelago canada varved sediments from nicolay lake canadian high arctic record major summer rainfall events over the last five centuries increased incidences of summer rainfall occurred during the coldest periods of the little ice age and were strongly clustered in the years immediately following major volcanic events compari son of the summer rainfall and proxy air temperature records thus provides a fuller understanding of the nature and causes of natural climate variability in the arctic study of the synoptic conditions associated with the two most recent large summer rainfall events suggests that they are associated with the incursion of cold low pressure systems from the arctic ocean basin volcanic activity may produce atmospheric conditions more conducive to the formation of such low pressure systems which generate rainfall at low elevations and summer snowfall at higher elevations thus explaining the correlation between rainfall and summer snow accumulation recorded in ice cores from high elevation ice caps

changes in late neoglacial perennial snow ice extent and equilibrium line altitudes in the queen elizabeth islands arctic canada changes in late neoglaical climate resulted in extensive modification of arctic terrestrial ice cover a substantial reduction in terrestrial ice cover in the queen elizabeth islands qei following the little ice age lia ad 1250 1900 is indicated by widespread light toned patches of poorly vegetated terrain extending back to the modern ice mass these patches display abrupt outer margins trimlines which record the former position and maximum extent of perennial snow ice and in many cases mark the former equilibrium line altitude ela trimlines surrounding terrain formerly covered by lia perennial snow ice were mapped using multispectral clas sification approaches applied to high resolution satellite imagery elas were reconstructed from trimlines associ ated with former perennial snow ice produced by long term snowline lowering between the end of the lia and 1960 the area of terrestrial ice in the qei decreased by 37 62 387 km 2 most of this reduction 94 occurred in the eastern qei where the majority of the ice exists today however a 100 reduction in ice cover occurred on many of the western islands by 1960 an effect largely controlled by the subtle topography of these islands the reconstructed lia ela trend surface was used with the 1960 mapped elas to calculate spatial variations in the change in height h of the ela trend surface throughout the qei during the first half of the twentieth century ela h between the lia and 1960 reveal a high degree of local variability in the mountainous regions ranging from 0 to 600 m however a strong regional scale pattern of change is shown over the qei as a whole

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

the process of ghost rock karstification and its role in the formation of cave systems abstract this paper presents an extensive review of the process of ghost rock karstification and highlights its role in the formation of cave systems the process integrates chemical weathering and mechanical erosion and extends a number of existing theories pertaining to continental landscape development it is a two stage process that differs in many respects from the traditional single stage process of karstification by total removal the first stage is characterised by chemical dissolution and removal of the soluble species it requires low hydrodynamic energy and creates a ghost rock feature filled with residual alterite the second stage is characterised by mechanical erosion of the undissolved particles it requires high hydrodynamic energy and it is only then that open galleries are created the transition from the first stage to the second is driven by the amount of energy within the thermodynamic system the process is illustrated by detailed field observations and the results of the laboratory analyses of samples taken from the karstotype area around soignies in southern belgium thereafter a series of case studies provide a synthesis of field observations and laboratory analyses from across western europe these studies come from geologically distinct parts of belgium france italy and the united kingdom the process of ghost rock karstification challenges a number of axioms associated with the process of karstification by total removal on the basis of the evidence presented it is argued that it is no longer acceptable to use karst morphologies as a basis with which to infer specific karstogenetic processes and it is no longer necessary for a karst system to relate to base level as ghost rock karstification proceeds along transmissive pathways in the rock there is also some evidence to suggest that ghost rock karstification may be superseded by karstification by total removal and vice versa according to the amount of energy within the thermodynamic system the proposed chemical weathering and subsequent mechanical erosion of limestone suggest that the development of karst terrain is related far more closely to the geomorphological development of aluminosilicate and siliceous terrains than is generally supposed it is now necessary to reconsider the origin of many karst systems in light of the outlined process of ghost rock karstification

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

neoglacial ice expansion and late holocene cold based ice cap dynamics on cumberland peninsula baffin island arctic canada abstract radiocarbon dating of fossil flora and fauna collected along receding cold based ice caps and cold based sections of polythermal glaciers on cumberland peninsula reveal insights into neoglacial ice expansion and late holocene ice dynamics the taphonomic advantages of subfossilized moss were exploited to precisely document regional expansions of ice caps through the late holocene when compared with climate proxies and records of volcanic eruptions the moss radiocarbon age distributions indicate i onset of neoglaciation shortly after 5 ka concomitant with increased sea ice cover ii intensification of ice expansion between 1 9 and 1 1 ka followed by halt of ice growth or ice recession during the medieval warm period and iii renewed ice expansion after 0 8 ka in response to cooling related to a combination of large volcanic eruptions and low solar activity overall the observations support a model of near instantaneous glacial response to regional climate controls and that these responses were synchronous throughout eastern canadian arctic and possibly eastern greenland

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

glacier change from the early little ice age to 2005 in the torngat mountains northern labrador canada abstract the glaciers of the torngat mountains of northern labrador are the southernmost of the canadian arctic and the easternmost of continental north america currently 195 small mountain glaciers cover an area in excess of 24 km2 confined mostly to small cirques and upland depressions using a combination of field and remote sensing methods this study reconstructs and dates the areal extent of torngat glaciers at their neoglacial maximums enabling the first assessment of regional glacier change over the past several centuries mapped glacier paleomargins n 165 are compared to current 2005 glaciers and ice masses showing a 52 5 reduction in glacier area with at least 11 former glaciers altogether disappearing glacier change is spatially homogenous and independent of most geographic and topographic factors however glacier elevation and glacier size mitigated total change previously established lichen growth stations were revisited and growth rates recalculated based on 30 year long records enabling the construction of locally derived low and high altitude lichen growth curves using growth rates and in situ lichen measurements the retreat from maximum neoglacial moraine extents are suggested to have occurred between a d 1581 and 1673 these findings indicate a similar magnitude of post lia retreat to mountain glaciers elsewhere yet a much earlier timing 200 years of retreat than other glaciers in the eastern canadian arctic though no definitive answer explaining this discrepancy is presented evidence suggests that regional climate dynamics and the importance of solar radiation for torngat glaciers may play an important role in local glacierization

breccia formation by particle fluidization in fault zones implications for transitory rupture controlled fluid flow regimes in hydrothermal systems breccias in the rusey fault cornwall uk and the roamane fault porgera gold deposit papua new guinea provide insights about the dynamics of fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid these faults contain cockade like breccias in which rock fragments are mantled by spheroidal overgrowths of hydrothermal minerals at rusey the overgrowths are quartz dominant whereas in the roamane fault overgrowths are composed of calcite quartz or gold rich pyrite although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours the spheroidal overgrowths do contact each other and are at least partially cemented together the hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core rock fragment or finer grained inequigranular to mesh like intergrowths concentric textural banding and oscillatory growth zones are present in some hydrothermal mantles the breccias occur as fault parallel layers and lenses each up to several tens of centimeters thick adjacent layers are characterized by texturally distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths in the rusey fault many texturally distinct breccia layers are present within a 3m wide fault core some layers truncate others and many breccia layers exhibit grainsize grading or banding clasts in the breccias include fragments of wall rock veins and various fault damage products including fragments of earlier generations of cemented breccia brecciation was episodic and separated by periods of cementation the distinctive textures of the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime hydrothermal coatings developed while clasts were in a suspended state during fluid ascent through dilatant fault segments layered breccias record multiple episodes of particle fluidization and indicate that the faults provided conduits for repeated transitory fluid upflow particle size distributions indicate that fluid velocities during fluidization were in the range 0 1 ms 1 to 1 ms 1 the maximum flow rates correspond to fluid fluxes of 10 to 100 l s 1 per meter strike length of fault through dilatant fault apertures up to several tens of centimeters wide such high flow rates characteristically induce intense swarm seismicity rather than mainshock aftershock seismicity and have implications for the dynamics and rates of formation of fault related hydrothermal ore deposits