the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

influence of the great lakes on the dynamics of the southern laurentide ice sheet numerical experiments a time dependent flow line ice sheet model is used to explore interactions between last glacial climate the laurentide ice sheet and the great lakes we seek to understand perturbations in the ice flow field that caused three neighboring lobes to leave different geomorphic and sedimentary records driven by reconstructed air temperature variations from 65 to 18 ka the simulated lobe dynamics are consistent with constraints from loess and till chronologies till stratigraphy and ice surface profiles contrasts in lobe dynamics are best explained by the geometry of lakes along each flow line as ice entered these lakes calving influenced glacier mass balance in particular deep water in lake superior likely delayed ice advance into northern wisconsin by promoting large calving losses whereas lobes to the east that encountered shallower water were less affected by calving the driftless area of wisconsin may thus owe its existence at least in part to the presence of lake superior our results suggest that morainal bank evolution should be treated in ice sheet models in lacustrine and shallow marine settings determining the sediment flux to the morainal bank remains a difficult task for example ice advance across central lake superior was probably sediment flux limited otherwise the driftless area would have been glaciated

the use of palaeomagnetism and rock magnetism to understand volcanic processes introduction this special publication provides a snapshot of our understanding of volcanic processes through the use of palaeomagnetic and rock magnetic techniques here we provide a context for the book placing individual chapters within the milieu of previous work including some magnetic techniques that were not used in the particular studies described herein thermoremanent magnetization is a powerful tool to understand processes related to heating and cooling of rocks including estimating the temperature of emplacement of pyroclastic deposits which may allow us to better understand the rates of cooling during eruption and transport anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics and allow the interpretation of flow dynamics in dykes lava flows and pyroclastic deposits as well as the location of the eruptive vents rock magnetic characteristics can help in the correlation of volcanic deposits but also provide means to date volcanic deposits and to better understand the processes of cooling of the deposits as the magnetic minerals can change with temperature in addition volcanic rocks may be key recorders of past magnetic fields allowing a better understanding of changes in field intensity and perhaps providing clues of how the magnetic field is formed over the past several decades palaeomagnetic and rock magnetic techniques have been applied to numerous problems in volcanology since aramaki akimoto s pioneering study in 1957 which used natural remanent magnetization nrm data to qualitatively estimate the temperature of emplacement of selected pyroclastic deposits in japan aramaki akimoto 1957 many studies have utilized and refined the approach of using progressive thermal demagnetization data to estimate emplacement temperatures of pyroclastic deposits and have demonstrated the utility of this approach in many settings another extensively utilized technique is that of anisotropy of magnetic susceptibility ams which was first applied to pyroclastic volcanic rocks by ellwood 1982 on ignimbrites in the san juan mountains sw colorado usa to estimate flow fabrics and in that study to infer source locations through triangulation it is staggering to think of the number and diversity of ams studies on volcanic rocks that have been undertaken since that time in a bit more than three decades remanent magnetization characteristics have long been used to correlate volcanic rocks and such data together with rock magnetic properties have been employed to study crystallization and cooling processes e g schlinger et al 1988 wells hillhouse 1989 as techniques have been refined and the sensitivity precision reliability and or speed of measurements for an array of modern instrumentation all have improved workers have been able to study volcanic problems in more detail pulling out details of the processes that have not previously been considered in addition the types of problems addressed have diversified considerably we intend this special publication to provide a representative suite of contributions that help to summarize the current array of studies that apply palaeomagnetism and rock magnetism to volcanic processes and to stimulate further research in this exciting science this book is a result of two sessions on volcanic processes and palaeomagnetism held at the international union of geodesy and geophysics congress in melbourne australia in july 2011 and at the american geophysical union annual meeting in san francisco usa in december 2011 from ort m h porreca m geissman j w eds 2015 the use of palaeomagnetism and rock magnetism to understand volcanic processes geological society london special publications 396 1 11 first published online january 20 2015 http dx doi org 10 1144 sp396 17 2015 the geological society of london for permissions http www geolsoc org uk permissions publishing disclaimer www geolsoc org uk pub ethics angharad hills at the geological society of london graciously and tactfully guided this book and the editors through the entire process from chapter solicitation to publication thermoremanent magnetization in volcanic rocks and emplacement temperature

the succession of ice flow patterns in north central quebec labrador canada abstract quebec labrador canada is one of the postulated dispersal centres of the late wisconsinan laurentide ice sheet and also contains an unusually complex and rich glacial geological record a reliable reconstruction of glaciation history represented by this record would improve our comprehension of the dynamics of the eastern sector of the laurentide ice sheet such as the evolution of the basal thermal regime and the timing of enhanced ice flow into ungava bay we mapped glacial landforms over a 200 000 km2 area using aerial photographs and conducted a detailed field based survey of the central part of the area to establish the relative age of crosscutting glacial geological features the position of the last ice remnant was south of ungava bay well north of what has commonly been perceived as the location for this dispersal centre southward radial flow from a northward migrating and predominantly cold based dispersal centre was the last glacial event in north central quebec labrador a widespread occurrence of older ice flow traces towards the southwest was detected in some areas large drumlins formed during this ice flow event occur in alignment with landforms formed during the last deglaciation this older southwestward flow is however overprinted by and therefore predates traces of northward convergent flow into ungava bay ungava bay flow traces of a northeastward flow event and in some areas traces of the deglacial flow event flutes and glacial striae indicating ice flow towards northeast are superimposed on the ungava bay flow the northeastward ice flow system has been recognised across the mapped area and because of its direction and regional significance we infer formation approximately during the last glacial maximum

a dynamic interpretation of tristan da cunha volcano south atlantic ocean abstract new observations on the morphostructure eruptive characteristics and intrusive system of tristan da cunha an active intraplate volcano of predominantly trachybasaltic composition are combined with previously published data to arrive at a model of its internal structure volcanic activity on the island of tristan da cunha is characterized by a dual central and lateral feeding system the central activity occurred at the summit presumably on top of an axial magma column the eruptions produced small flows as well as a high percentage of pyroclastic deposits partly of hydrovolcanic origin the basaltic magma probably encountered a shallow water table or ephemeral crater lakes these pyroclastic products contributed in large part to the building up of a well developed central cone from the column a dense swarm of radial dykes were generated by hydraulic fracturing in contrast the lateral activity occurred on a much lower level on the flanks of the volcano the style of eruption was strombolian resulting in scoria cones and flows there is a concentration of strombolian vents around the base of the central cone this concentric pattern is ascribed to conical shear planes in depth created by uplift of the roof of the magma chamber the uplift may have contributed to the elevation of the central cone in addition a number of lateral vents occur along radial fractures that appear to be concentrated along two tectonic axes oriented n170 e and n80 e these directions are parallel to the compressive axes of the stress field in the ocean floor the most prominent axis n170 e connects the two most recent eruptions of rather unusual trachyandesitic entirely effusive character segmented en echelon dykes and fissures observed in plan and in vertical cliffs are related to slope instability when a dyke propagates to the surface it enters a zone of bimodal stress extension and shearing as a result of downslope movement under such conditions en echelon segmentation of the dyke takes place

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

emplacement dynamics of alkaline volcanic and subvolcanic rocks in trindade island brazil abstract anisotropy of magnetic susceptibility ams and anhysteretic remanent magnetization aarm are tools to characterize flow structures and emplacement conditions of volcanic and subvolcanic bodies directly related to magnetic fabrics an ams and aarm study was performed to contribute to the understanding of the processes involved in magma transportation and emplacement dynamics of the volcanic and subvolcanic rocks of trindade island and their implications on the evolution of the volcanic field trindade island is located in the south atlantic ocean at 1260 km to the east of the espirito santo state coast in brazil the island is composed of lava flows intrusions and pyroclastic rocks of alkaline sio2 undersaturated nature forming five geological units aged 3 9 0 25 ma during fieldwork 17 sampling sites were established in the phonolitic necks and melanephelinitic dyke of the oldest unit trindade complex and in the melanephelinitic a a flows of the youngest units morro vermelho valado and paredao volcano formations totaling 160 oriented mini cores and 504 rock specimens the analysis of petrofabric magnetic mineralogy ams and aarm diagrams suggests the dominance of a low coercivity magnetic mineral phase represented by low ti titanomagnetite titanomagnetite in the phonolitic necks and melanephelinitic dyke these bodies display normal fabric multi domain and vortex grains and sub vertical high angle magnetic foliation and lineation the melanephelinitic a a lavas present at least two magnetic mineral phases of high and low coercivity titanomagnetite maghemite and hematite with normal intermediate or inverse fabrics vortex or single domain grains mean magnetic foliation and lineation suggest that lavas flowed to ne data interpretation indicates that the subvolcanic bodies were emplaced vertically during the initial stages of island formation followed by lavas flowing to the northeast the orientation of the dyke and lava feeders along nnw sse leads to the conclusion that the tensional field during the evolution of volcanism remained the same with nw direction for during approximately 4 my this study is an example for the understanding of physical processes in the evolution of world oceanic islands

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

refining the ice flow chronology and subglacial dynamics across the migrating labrador divide of the laurentide ice sheet with age constraints on deglaciation geological survey of canada s geo mapping for energy and minerals ii gem2 program 2013 2020

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

till geochemistry in west central manitoba interpretation of provenance and mineralization based on glacial history and multivariate data analysis till geochemical datasets from archived samples in west central manitoba are interpreted using multivariate data analytical techniques such as principal component analysis and pathfinder element index methods combined with a spatial representation of the data in a geographic information system gis results show that carbonate till derived from hudson bay as expressed by the ca mg na ratio is found predominantly east of leaf rapids and extends south into the northeastern kisseynew domain a 30 to 70 km wide zone is documented beyond the limit of dissolvable carbonate dispersal that contains till of labradorean provenance with low ca mg mn te concentrations noncalcareous till of keewatin provenance and silty calcareous till at depth the variation in till provenance together with the predominance of southwesterly ice flow indicators suggests that carbonate dispersal occurred prior to deglaciation and that surface tills in the zone of confluence between labradorean and keewatin ice are likely the result of recycling of calcareous tills and or carbonate leached sandy tills mainly by keewatin ice the newly defined limits of carbonate and ca rich till typically used to assess provenance and glacial transport provide a new framework for evaluating the significance of till geochemical patterns when drift prospecting over the trans hudson orogen several regional to local scale dispersal trains from geochemically distinct bedrock sources are discussed in terms of elemental association glacial transport characteristics and potential bedrock sources the multivariate statistical approach combined with gis mapping also highlights new areas with small multi or single element enrichments that may be of further interest for volcanogenic massive sulfide exploration or for potentially more detailed drift sampling

les ecoulements et le transport glaciaires dans la partie septentrionale du nunavik quebec in northern nunavik orientation of ice flow features and dispersal patterns of lithologic indicators suggest three major regional ice flow phases the oldest ice flow phase is related to the buildup of an outflow centre the ungava centre over the high plateaux located north of the povungnituk hills during that event probably of early wisconsinan age ice flows towards the south and southeast carried cape smith belt rock fragments over a maximum distance of 65 km the second phase is characterized by ice flow mainly towards the north from an outflow ice centre located south of the studied area payne centre the most recent ice flow phase is related to the presence of the northern extension of the new quebec ice divide from that northwest trending ice divide extending between ivujivik and lake nantais ice was flowing outward on the peninsula the orientation of most of the ice flow features and dispersal patterns is associated with that last ice flow north of the cape smith belt glacial transport was at least 70 km in hudson strait ice flow and glacial transport data support the existence of an eastward flowing ice stream

constraining the late pleistocene history of the laurentide ice sheet by dating the missinaibi formation hudson bay lowlands canada abstract well dated paleorecords from periods prior to the last glacial maximum lgm are important for validating models of ice sheet build up and growth however owing to glacial erosion most late pleistocene records lie outside of the previously glaciated region which limits their ability to inform about the dynamics of paleo ice sheets here we evaluate new and previously published chronology data from the missinaibi formation a pleistocene aged deposit in the hudson bay lowlands hbl canada located near the geographic center of the laurentide ice sheet lis available radiocarbon ams 44 conventional 36 amino acid n 13 uranium thorium u th n 14 thermoluminescence tl n 15 and optically stimulated luminescence osl n 5 data suggest that an ice free hbl may have been possible during parts of marine isotope stage 7 mis 7 ca 243 000 to ca 190 000 yr bp mis 5 ca 130 000 to ca 71 000 yr bp and mis 3 ca 29 000 to ca 57 000 while mis 7 and mis 5 are well documented interglacial periods the development of peat forest bed and fluvial deposits dating to mis 3 n 20 radiocarbon dates 4 tl dates 3 osl dates suggests that the lis retreated and remained beyond or somewhere within the boundaries of the hbl during this interstadial ice sheet models approximate the margin of the lis to southern ontario during this time which is 700 km south of the hbl therefore if correct our data help constrain a significantly different configuration and dynamicity for the lis than previously modelled we can find no chronological basis to discount the mis 3 age assignments however since most data originate from radiocarbon dates lying close to the reliable limit of this geochronometer future work on dating the missinaibi formation using other geochronological methods e g u th osl is necessary in order to confirm the age estimates and strengthen the boundaries of the lis during this period

organic matter biomarker analysis as a potential chemostratigraphic tool for late pleistocene tills from the hudson bay lowlands canada abstract during the last glacial maximum approximately 22 000 years ago the hudson bay lowlands hbl lay at the center of the 3 km thick laurentide ice sheet during the course of the last glacial cycle hbl was crossed by ice from the west the keewatin sector and from the east labrador sector but the relative influence of the outflow centers is debateable because of continuing uncertainty surrounding the age and stratigraphic position of lithologically similar tills in different areas this study examines the use of organic matter om biomarkers to analyze om sources in hbl tills these tills are believed to be of late wisconsin age sachigo severn and an older possibly early wisconsin deposit rocksand till and biomarkers may provide insights into source materials and degree of diagenesis solvent extraction base hydrolysis and cupric oxide oxidation were performed to isolate and quantify free lipids bound lipids and lignin derived phenols respectively lipid biomarker patterns indicate higher sphagnum derived om to the severn and rocksand tills relative to the sachigo till consistent with subglacial reworking and incorporation of peat om within the severn till is dominated by om derived from non woody gymnosperms and non woody angiosperms whereas sachigo and rocksand tills have both woody and non woody gymnosperms and angiosperms derived om furthermore the severn till contained the most suberin derived om while the sachigo till had the least acid to aldehyde ratios of lignin derived phenols suggest that the severn till has undergone less diagenesis in comparison to sachigo and rocksand confirming that it is likely the youngest of the three tills this study highlights that biomarker analysis is an important chemostratigraphic tool that may distinguish till deposits and provides insight into paleovegetation and paleoclimate in the hbl prior to glacial incorporation of om into till this information facilitates paleoenvironmental analyses to be extended into preglacial and interstadial episodes where no stratigraphic record exists

early holocene deglaciation of the eastern coast of hudson bay abstract the final stage of deglaciation of hudson bay was a major holocene catastrophic event marked by the drainage of lake agassiz ojibway at 8 47 ka cal bp and the rapid collapse of the laurentide ice sheet previous work undertaken in the nastapoka river area eastern hudson bay demonstrated that during the relative sea level highstand that shortly followed the drainage of the lake the western margin of the quebec labrador ice sector rapidly retreated eastward to reach a stillstand position in a coastal hill range in this study an analysis of landsat 7tm images has allowed a mapping of large scale glacial landforms outwash deposits eskers flutings and de geer and rogen moraines between kuujjuaraapik se hudson bay and puvirnituq ne hudson bay the key results from this mapping are i ice contact outwash deposits mapped along the entire arc shaped coastline of the eastern hudson bay outline a major ice stillstand phase in the coastal hills that extended at least from kuujjuaraapik to inukjuak the presence of these hills allowed a stabilisation of the ice margin that led to the accumulation of thick and extensive ice contact submarine fans ii the position of these deposits on the down ice side west of large sets of flutings indicates an important phase of sediment delivery by a rapid ice flow phase toward a marine based ice margin iii a second system of outwash deposits observed farther inland indicates a subsequent phase of stabilisation of the ice margin during its retreat toward central quebec labrador

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

plate kinematics of the south atlantic chron c34 to present a high resolution seafloor spreading history of the south atlantic since chron c34 is constrained by a combination of seasat altimeter data and underway marine geophysical data a set of 45 finite rotation poles defines the relative position of africa and south america at roughly 2 m y intervals a set of 12 stage poles constrain the relative motion of these two plates at 5 to 10 m y intervals the position of the stage poles continuously migrates reflecting the continuously changing azimuths of the fracture zones major changes in spreading direction are observed in the late cretaceous and early cenozoic as the fracture zones sweep out broad s shaped curves similar to the pattern seen on the kane fracture zone in the central atlantic small offset fracture zones were found to be the most accurate recorders of changes in plate motion large offset fracture zones such as the agulhas falkland fracture zone were the least reliable recorders at 30 s spreading rates decrease throughout the late cretaceous from a high of 75 mm yr at the end of chron c34 to a low of 30 mm yr around chron c27 a period of slow spreading between chron c30 and chron c20 corresponds to a zone of fracture zone proliferation an increase in the amplitude of geoid anomalies over fracture zones greater relief on topographic profiles and locally evidence of intraplate crustal deformation spreading rates increase at chron c20 to about 50 mm yr and then gradually decrease during the late paleogene and neogene a comparison of synthetic fracture zones based on the south atlantic stage poles to the observed trends of fracture zones in the equatorial atlantic indicates that the vema and marathon fracture zones were generated by south atlantic spreading as opposed to central atlantic spreading at least as far back as 35 m y ago and possibly 50 m y ago

glacial and nonglacial events in the eastern james bay lowlands canada marine and continental records indicate that the laurentide ice sheet lis was highly dynamic throughout the last glacial cycle with significant reorganizations of its ice divide system the extensive depositional record of the hudson bay lowlands hbl is particularly important for the study of ice sheet dynamics because this region was once located near two important ice domes of the lis however important stratigraphic issues remain in the hbl notably regarding the chronology of nonglacial units and the direction and extent of the ice flow events recognized here we focus on the northeastern sector of the lis by documenting the provenance of tills and dating nonglacial deposits in sedimentary sequences east of james bay our investigations indicate that the regional stratigraphy comprises at least five distinct tills and an important unit of glaciolacustrine rhythmites this glacial sequence lies on massive lacustrine clay and fluvial sand containing abundant organic debris and wood fragments the

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

the subglacial mosaic of the laurentide ice sheet a study of the interior region of southwestern hudson bay abstract reconstructions of past ice flow provide useful insights into the long term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped here we present reconstruction of a 10 phase ice flow history from southwestern hudson bay in northeastern manitoba canada a dynamic region situated between two major ice dispersal centres of the laurentide ice sheet we utilize a diverse geologic dataset including 1900 field based erosional indicators 12 streamlined landform flowsets esker and meltwater corridor orientations 103 till fabrics analyses and 1344 till clast lithology counts our reconstruction suggests that both pre mis 2 and mis 2 glaciations followed similar growth patterns where ice advanced into study area from ice centered to the east probably in northern quebec followed by a switch in ice flow direction indicating flow from the keewatin ice centre to the northwest and north the cause for this switch in ice flow orientation is uncertain but the youngest switch may relate to retreat of ice during mis 3 that then left space for keewatin sourced ice to advance over the study area while modelling experiments indicate widespread cold based conditions in the study area during the last glacial cycle uniformly relict landscapes are not common instead the glaciated landscape is palimpsest and commonly fragmented forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice flow direction through time and shifting subglacial conditions each assemblage formed or modified during times of dynamic warm based ice and later preserved under conditions below or close to the pressure melting point slow and sluggish or cold based

sedimentary record of ice divide migration and ice streams in the keewatin core region of the laurentide ice sheet abstract the aberdeen lake region of central mainland nunavut is a former core region of the laurentide ice sheet that is characterized by streamlined glacial landforms classified into multiple crosscutting flow sets and near continuous till blanket the presence of widespread till near the centre of the keewatin ice dome raises questions about its origin detailed drillcore logging revealed a complex stratigraphy consisting of at least 6 till units variably preserved across the study area till provenance analysis indicates deposition by near opposite trending ice flow phases interpreted as evidence of reconfiguration of the keewatin ice divide at the surface large north northwesterly aligned landforms are present across the study area the till stratigraphy within these landforms indicates the same nnw ice flow phase is responsible for considerable till production this ice flow phase is also correlated to a long regional dispersal train of erratics toward the gulf of boothia the production of an extensive thick 12 m till sheet during the nnw trending ice flow phase occurred far from the ice margin at a time of extensive ice cover of mainland nunavut likely from an east west oriented ice divide a deglacial westerly trending ice flow phase formed small drumlins atop the larger nnw streamlined till ridges and deposited a surficial till unit that is too thin to mask the nnw flow set across the study area it is proposed that the boothia paleo ice stream catchment area propagated deep into the laurentide ice sheet and contributed to significant till production in this core region of the keewatin sector prior to the westerly ice flow shift the apparent relationship between till thickness and the size of the associated or correlated drumlins flow sets and dispersal trains indicates complex erosion deposition interplay is involved in the formation of streamlined subglacial landforms

geochemical evidence for the trindade hotspot trace columbia seamount ankaramite abstract the columbia seamount 825 km offshore from brazil at 20 s lies on the east west trace of the trindade hotspot continental and oceanic magmatism believed to have originated with this hotspot is alkalic and sio2 undersaturated and dates from 85 ma in southern brazil to

overview of the spirit mars exploration rover mission to gusev crater landing site to backstay rock in the columbia hills spirit landed on the floor of gusev crater and conducted initial operations on soil covered rock strewn cratered plains underlain by olivine bearing basalts plains surface rocks are covered by wind blown dust and show evidence for surface enrichment of soluble species as vein and void filling materials and coatings the surface enrichment is the result of a minor amount of transport and deposition by aqueous processes layered granular deposits were discovered in the columbia hills with outcrops that tend to dip conformably with the topography the granular rocks are interpreted to be volcanic ash and or impact ejecta deposits that have been modified by aqueous fluids during and or after emplacement soils consist of basaltic deposits that are weakly cohesive relatively poorly sorted and covered by a veneer of wind blown dust the soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover mobilization of soluble species has occurred within at least two soil deposits examined the presence of monolayers of coarse sand on wind blown bedforms together with even spacing of granule sized surface clasts suggests that some of the soil surfaces encountered by spirit have not been modified by wind for some time on the other hand dust deposits on the surface and rover deck have changed during the course of the mission detection of dust devils monitoring of the dust opacity and lower boundary layer and coordinated experiments with orbiters provided new insights into atmosphere surface dynamics

anisotropy of magnetic susceptibility in relation to source vents of ignimbrites empirical observations the anisotropy of magnetic susceptibility ams of young undeformed ashflow deposits e g bishop tuff california bandlier tuff new mexico show alignment of the maximum axis of magnetic susceptibility kmax with inferred flow lines the sense of flow is deduced from the predominant plunge bias of kmax axes these principles are discussed in relation to four deformed settings of ashflow deposits in the great basin of the western united states the magnetic susceptibility data provide valuable but not always unambiguous insight into probable source areas various complications arise in interpreting the ams data in terms of flow directions but these can be reduced by integration with geologic observations

major end moraines of younger dryas age on wollaston peninsula victoria island canadian arctic implications for paleoclimate and for formation of hummocky moraine some of the most extensive and massive end moraines of younger dryas age 11 10 14c ka bp yet recognized in north america occur on wollaston peninsula of victoria island on the western part of the peninsula numerous closely spaced end moraines formed in the interval starting 11 100 100 radiocarbon years ago and ending about 10 500 10 200 years ago net recession was generally slow throughout and was punctuated by moraine building and at least two readvances recession is mapped with a resolution that is approximately decadal the moraines form an orderly nested succession and are consistently associated with westward shedding of meltwater which formed a sequence of marine limit deltas we lack firm independent proxy climate evidence needed to assess whether these moraines formed because of cold younger dryas climate rather than because of controls such as topographic setting and water depth but climatic control seems probable the moraines evidently retain glacier ice cores as do most similarly

anisotropy of magnetic remanence a brief review of mineralogical sources physical origins and geological applications and comparison with susceptibility anisotropy the magnetic fabric of rocks and sediments is most commonly characterized in terms of the anisotropy of low field magnetic susceptibility ams however alternative methods based on remanent magnetization measured in the absence of a magnetic field rather than induced magnetization measured in the applied field have distinct advantages for certain geological applications this is particularly true for 1 adjunct studies in paleomagnetism in order to assess the fidelity with which a natural remanence records the paleofield orientation 2 studies of weakly magnetic or weakly deformed rocks for which susceptibility anisotropy is very difficult to measure precisely and 3 quantitative applications such as strain estimation the fundamental differences between susceptibility and remanence and their respective anisotropies are due to several factors 1 susceptibility arises from all of the minerals present in a sample whereas remanence is carried exclusively by a relatively small number of ferromagnetic minerals 2 ferromagnetic minerals are generally more anisotropic than para and diamagnetic minerals 3 for ferromagnetic minerals remanence is inevitably more anisotropic than susceptibility and 4 a number of common minerals including single domain magnetites possess an inverse anisotropy of susceptibility i e they tend to have minimum susceptibility parallel to the long axis of an individual particle remanence is immune to this phenomenon as a consequence of all these factors remanence anisotropy may generally provide a better quantitative estimate of the actual distribution of particle orientations in a rock sample

comment on catastrophic ice shelf breakup as the source of heinrich event icebergs by c l hulbe et al hulbe et al 2004 argue that the original binge purge model of their coauthor macayeal 1993a 1993b is not appropriate for heinrich events but that a new ice shelf collapse mechanism may work we believe that thenew collapse mechanism disagrees with important dataand that macayeal s original model remains viable afterappropriate modifications we have enjoyed a fascinatingdiscussion with hulbe et al on this topic which isstimulating our thinking and research and we presentsome of the arguments here for a wider audience

temporal and spatial variability of seafloor spreading processes in the northern south atlantic the paper reports the results of an aeromagnetic study of the mid atlantic ridge in the northern south atlantic the study consists of 38 000 km of low altitude magnetics tracks centered on the ridge covering nearly 700 000 km2 south of ascension island most tracks extend out to crust of anomaly 5b age large areal coverage coupled with high resolution allows comparison of crustal generation processes over space along ridge strike and time across strike temporal heterogeneities revealed in the data include a pattern of change in spreading rate and direction of plate motion the total spreading rate increased sharply at 10 ma and then decreased between 6 ma and the present the time variation of spreading rate is similar to that seen in other areas such as the north atlantic and the southern and eastern pacific the plate boundary has evolved over time in response to the shift in plate motion direction through fragmentation and rotation of ridge segments between fracture zones in several cases the location of the spreading axis has shifted through jumps or propagation across fracture zones the periods of plate boundary modification correlate with the increase and decrease in spreading rate spatial heterogeneities are caused by the influence of the ascension hotspot on the mid atlantic ridge in the northern portion of the study area and include two apparent seamount chains formed by the hotspot ascension island and several of the seamounts appear to have been produced some distance away from the hotspot location presently about 225 km southeast of ascension island by channeled subaxial magma flow beneath the spreading center the seamount chains therefore do not mark hotspot tracks large local variations in spreading rate and degree of asymmetry along strike are also found

the timing of the gold cove glacial event a comment on signature of the gold cove event 10 2 ka in the labrador sea abstract the recent paper in quaternary international rashid et al 2014 signature of the gold cove event 10 2 ka in the labrador sea attributes sediment layers rich in detrital carbonate dc in several marine sediment cores in the labrador sea to the so called gold cove gc glacial advance of the early holocene the age estimate for the gc event as well as the correlations between sediment cores in this study are based on radiocarbon dates mostly from previously published studies although this work provides a good overview of an apparently widespread dc layer in the early holocene the reported age of 10 2 cal ka bp for the actual gold cove event is too young due to a mistake made during re calibration of the original radiocarbon dates used to describe the event the 14c dates have been corrected to compensate for the marine reservoir effect two times leading to an unrealistically large total reservoir age of more than thousand years by applying such a large marine reservoir offset the final calibrated age becomes too young originally the gc event was described to consist of an advance and retreat phase in total spanning several centuries the gold cove event should therefore more accurately be reported as an age range and it occurred most likely ca 500 years earlier than 10 2 ka bp the age reported by rashid et al 2014

alteration induced changes of magnetic fabric as exemplified by dykes of the koolau volcanic range abstract we studied 93 samples from 8 basaltic dykes of the koolau volcanic range on the island of oahu hawaii usa to determine the influence of hydrothermal alteration on the magnetic fabric as determined by anisotropy of magnetic susceptibility ams measurements rock magnetic as well as microscopic investigations show that only 25 of the samples have retained their original magnetomineralogical composition of unaltered ti poor titanomagnetite the remaining samples have undergone hydrothermal alteration which transformed the primary magnetic phase into a granular intergrowth of titanomagnetite titanomaghemite and hematite in both sample groups this magnetic phase occurs in coarse tens of microns irregularly shaped particles as well as interstitial clusters of smaller

rapid holocene deglaciation of the labrador sector of the laurentide ice sheet abstract retreat of the laurentide ice sheet lis following the last glacial maximum 21 000 yr bp affected regional to global climate and accounted for the largest proportion of sea level rise although the late pleistocene lis retreat chronology is relatively well constrained its holocene chronology remains poorly dated limiting our understanding of its role in holocene climate change and sea level rise here new 10be cosmogenic exposure ages on glacially deposited boulders are used to date the final disappearance of the labrador sector of the lis ls lis these data suggest that following the deglaciation of the southeastern hudson bay coastline at 8 0 0 2 cal ka bp the southwestern margin of the ls lis rapidly retreated 600 km in 140 yr and most likely in 600 yr at a rate of 900 m yr 1 with final deglaciation by 6 8 0 2 10be ka the disappearance of the ls lis 6 8 10be ka and attendant reduction in freshwater runoff may have induced the formation of labrador deep seawater while the loss

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

uncovering the hidden part of a large ice stream of the laurentide ice sheet northern ontario canada abstract this investigation was prompted by an enigmatic ice flow anomaly area a on the glacial map of canada which covers about 10 000 km 2 in the hearst kapuskasing area of northeastern ontario it consists of streamlined landforms and striations indicative of a major ice flow toward 130 oriented at right angle to another toward 220 both are late glacial flows but long lasting disagreement exists regarding their relative age the analysis of aerial photographs and satellite images in conjunction with a detailed survey of bedrock cross striated surfaces over an area of about 30 000 km 2 within and around area a clearly indicate that the 130 flow preceded the 220 flow the earlier conflicting interpretations within area a are attributed mainly to the sporadic occurrence of relict striated surfaces formed by older southwestward 220 240 wisconsinan ice flows that have locally escaped destruction by late glacial flows with the result that the southwestward flows are older wisconsinan at some sites and younger late glacial 220 at others relative to the 130 flow when considered with other factors such as the maximum elevation reached by the youngest late glacial flow these ice flow relationships indicate that area a is the outcropping southern part of a much larger ese ice flow system which is probably related to a large fluted belt located to the north and that was identified as the winisk ice stream the distal part of the ice stream except for area a escaped detection by remote sensing mapping methods because depositional and erosional features associated with it are masked by deposits laid down by the younger 220 cochrane ice flow and or by postglacial marine and organic deposits or were destroyed by the younger ice flow the only reliable indicators of the passage of the ice stream in this buried section are ese relict striations crossed by sw striations the advancing ice stream toward the ese not only preceded the late cochrane 220 flow but probably outlasted it as suggested by the mapping of several thousand iceberg furrows in quebec and ontario also directed toward the ese and overprinted on flutes formed by the last glacial flow if this interpretation is correct this makes the winisk ice stream the largest terrestrial ice stream in the hudson bay basin an alternative interpretation associates this fluted belt to the exposed western fringe of streamlined bedforms from a late hudson lobe buried by younger sediments

review paper exploration geophysics for intrusion hosted rare metals igneous intrusions notably carbonatitic alkalic intrusions peralkaline intrusions and pegmatites represent significant sources of rare earth metals geophysical exploration for and of such intrusions has met with considerable success examples of the application of the gravity magnetic and radiometric methods in the search for rare metals are presented and described ground gravity surveys defining small positive gravity anomalies helped outline the shape and depth of the nechalacho formerly lake deposit within the blatchford lake alkaline complex northwest territories and of spodumene rich mineralization associated with the tanco deposit manitoba within the hosting tanco pegmatite based on density considerations the bastnaesite bearing main ore body within the mountain pass carbonatite california should produce a gravity high similar in amplitude to those associated with the nechalacho and tanco deposits gravity also has utility in modelling hosting carbonatite intrusions such as the mount weld intrusion western australia and elk creek intrusion nebraska the magnetic method is probably the most successful geophysical technique for locating carbonatitic alkalic host intrusions which are typically characterized by intense positive circular to sub circular crescentic or annular anomalies intrusions found by this technique include the mount weld carbonatite and the misery lake alkali complex quebec two potential carbonatitic alkalic intrusions are proposed in the grenville province of eastern quebec where application of an automatic technique to locate circular magnetic anomalies identified several examples two in particular displayed strong similarities in magnetic pattern to anomalies accompanying known carbonatitic or alkalic intrusions hosting rare metal mineralization and are proposed to have a similar origin discovery of carbonatitic alkalic hosts of rare metals has also been achieved by the radiometric method the thor lake group of rare earth metal deposits which includes the nechalacho deposit were found by follow up investigations of strong equivalent thorium and uranium peaks defined by an airborne survey prominent linear radiometric anomalies associated with glacial till in the canadian shield have provided vectors based on ice flow directions to source intrusions the allan lake carbonatite in the grenville province of ontario is one such intrusion found by this method although not discovered by its radiometric characteristics the strange lake alkali intrusion on the quebec labrador border is associated with prominent linear thorium and uranium anomalies extending at least 50 km down ice from the intrusion radiometric exploration of rare metals hosted by pegmatites is evaluated through examination of radiometric signatures of peraluminous pegmatitic granites in the area of the tanco pegmatite

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

the internal structure of lava flows insights from ams measurements ii hawaiian pahoehoe toothpaste lava and a ā abstract we studied the anisotropy of magnetic susceptibility ams of 22 basaltic flow units including s type pahoehoe p type pahoehoe toothpaste lava and a emplaced over different slopes in two hawaiian islands systematic differences occur in several aspects of ams mean susceptibility degree of anisotropy magnetic fabric and orientation of the principal susceptibilities among the morphological types that can be related to different modes of lava emplacement ams also detects systematic changes in the rate of shear with position in a unit allowing us to infer local flow direction and some other aspects of the velocity field of each unit a flows are subject to stronger deformation than pahoehoe and also their internal parts behave more like a unit according to ams the central part of pahoehoe commonly reveals a different deformation history than the upper and lower extremes probably resulting from endogenous growth

ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec abstract outcrops bearing stained striated facets indicative of north northeastward moving ice truncated by unstained striated facets indicative of various younger flows occur in the caniapiscau area of north central quebec this is the first report of differential staining of striated facets in the region we propose that the staining occurred in an ice free interval of probable interglacial age this early ice flow probably occurred during ice retreat toward the quebec highlands ice flow and glacial transport data from the southern hudson bay and james bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an early wisconsinan glacier in the quebec highlands the northern part of this flow was diverted northwestward through hudson bay and the southern part southwestward across james bay following a progressive counterclockwise rotation of flow a zone of intersection zi of two major glacier bedform systems often referred to as the horseshoe shaped labrador ice divide represents the head of a large northward convergent ice flow system that extended to ungava bay and beyond the ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of caniaspiscau reservoir we propose that this capture event correlates with the gold cove advance in ungava bay and on baffin island at about 9900 14c yr bp it is the largest advance of quebec labrador ice yet proposed for the region this correlation is based on the relative ice flow chronology accommodation of glacial lakes naskaupi and mclean in the deglaciation sequence the constraints placed on last glacial maximum lgm ice configuration by the postglacial uplift pattern and events in the deep sea record therefore the ungava ice flow pattern is not a relict pre wisconsinan glacial landscape as recently proposed

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

sediment sources of northern quebec and labrador glacial deposits and the northeastern sector of the laurentide ice sheet during ice rafting events of the last glacial cycle provenance studies of anomalously high flux layers of ice rafted detritus ird in north atlantic sedi ments of the last glacial cycle show evidence for massive iceberg discharges coming from the hudson strait region of the laurentide ice sheet lis although these so called heinrich events h events are commonly thought to be associated with abrupt drawdown of the lis interior uncertainties remain regarding the sector s of this multi domed ice sheet that conveyed ice through hudson strait in northern quebec and labrador nql large scale patterns of glacial lineations indicate massive ice flows towards ungava bay and hudson strait that could reflect the participation of the labrador quebec ice dome in h events here we evaluate this hypothesis by constraining the source of nql glacial deposits which provide an estimate of the provenance characteristics of ird originating from this sector specifically we use 40 ar 39 ar ages of detrital hornblende grains in 25 till samples distributed along a latitudinal transect lat 58 extending east and west of ungava bay the data show that tills located west and southwest of the ungava bay region are largely dominated by hornblende grains with archean ages 2 6 ga while tills located east of ungava bay are characterized by grains with early paleo proterozoic ages 2 0 1 8 ga although most samples contain a few archean age grains ird derived from the nql region should thus be characterized by a large proportion of archean age detrital grains which contrasts significantly with the predominant paleoproterozoic 40 ar 39 ar ages 1 8 1 6 ga typically reported for the dominant age population of hornblende grains in h layers comparisons with ird through the last glacial cycle from a western north atlantic core off newfoundland do not show evidence for any prominent ice rafted event with the provenance characteristics of nql glacial deposits thereby suggesting that significant ice calving event s from the labrador quebec sector may have been limited throughout that interval although these results tend to point towards a relative stability of this ice dome during h events our study also indicates that further provenance work is required on ird proximal to the hudson strait mouth in order to constrain with a greater confidence the sector s of the lis that fed ice into hudson strait during h events alternatively these results and other paleogeographic considerations tend to support models suggesting that part of the ungava bay glacial lineations could be associated with a late glacial ice flow across hudson strait

north american ice sheet build up during the last glacial cycle 115 21 kyr the last glacial maximum lgm outline and subsequent retreat pattern 21e7 kyr of north americanice sheets are reasonably well established however the evolution of the ice sheets during their build upphase towards the lgm between 115 and 21 kyr has remained elusive making it difficult to verifynumerical ice sheet models for this important time interval in this paper we outline the pre lgm icesheet evolution of the laurentide and cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first order reconstruction of ice sheet extent and flow pattern we mappedthe entire area covered by the laurentide and cordilleran ice sheets in landsat mss images andapproximately 40 of this area in higher resolution landsat etm images mapping in aerial photographsadded further detail primarily in quebec labrador the cordilleran region and on baffin island our analysis includes the recognition of approximately 500 relative age relationships from crosscuttinglineations together with previously published striae and till fabric data these are used as the basis forrelative age assignments of regional flow patterns for the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms reflecting flow direction and configuration and linking these topreviously published constraints on relative and absolute chronology our results reveal that icedispersalcentres in keewatin and quebec were dynamically independent for most of pre lgm time andthat a massive quebec dispersal centre rivalling the lgm in extent existed at times when the sw sectorof the ice sheet had not yet developed the oldest flow system in eastern quebec labrador atlanticswarm had an ice divide closer to the labrador coast than later configurations a northern keewatin central arctic ice sheet existed prior to the lgm but is poorly chronologically constrained there is alsoevidence for older and more easterly cordilleran ice sheet divide locations than those that prevailedduring the late wisconsinan in terms of ice sheet build up dynamics it appears that residual ice capsafter warming phases may have played an important role in particular the location and size of remnantice masses at the end of major interstadials i e ois 5c and 5a must have been critical for subsequentbuild up patterns because such remnant uplands may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain the ice sheet configuration duringstadials would also be governed largely by the additional topography that such residual ice constitutesbecause of inherent mass balance topography feedbacks

final laurentide ice sheet deglaciation and holocene climate sea level change abstract despite elevated summer insolation forcing during the early holocene global ice sheets retained nearly half of their volume from the last glacial maximum as indicated by deglacial records of global mean sea level gmsl partitioning the gmsl rise among potential sources requires accurate dating of ice sheet extent to estimate ice sheet volume here we date the final retreat of the laurentide ice sheet with 10 be surface exposure ages for the labrador dome the largest of the remnant laurentide ice domes during the holocene we show that the labrador dome deposited moraines during north atlantic cold events at 10 3 ka 9 3 ka and 8 2 ka suggesting that these regional climate events helped stabilize the retreating labrador dome in the early holocene after hudson bay became seasonally ice free at 8 2 ka the majority of laurentide ice sheet melted abruptly within a few centuries we demonstrate through high resolution regional climate model simulations that the thermal properties of a seasonally ice free hudson bay would have increased laurentide ice sheet ablation and thus contributed to the subsequent rapid labrador dome retreat finally our new 10 be chronology indicates full laurentide ice sheet had completely deglaciated by 6 7 0 4 ka which re quires that antarctic ice sheets contributed 3 6 6 5 m to gmsl rise since 6 3 7 1 ka

time perspectives on glacial landscape formation glacial flow chronology at lac aux goelands northeastern quebec canada we used mapping from aerial photographs and field investigations around lac aux goelands whitegull lake northeastern quebec to establish a glacial flow chronology that involves three different glacial landform systems we interpret the youngest of these systems as related to the late wisconsinan deglaciation this system has an up glacier discontinuity that marks a temporal shift from warm based subglacial conditions to non erosive cold based subglacial conditions whereby older glacial landscapes are preserved in the interior of quebec labrador furthermore our results support theories suggesting a northward migrating ice divide to a final position south of ungava bay during the final deglaciation the recognition that a glacial landscape is fragmented and consists of smaller temporally unrelated units is of considerable significance in understanding ice sheet dynamics and patterns of subglacial preservation and destruction this is because a fragmented landscape implies a fragmented formation history where formation of subglacial landforms occurred in restricted subglacial zones during restricted time periods periods of formation must have been separated by periods of preservation and inhibited subglacial reshaping based on estimates of the ice margin retreat velocity and the velocity of the warm based inward migrating zone we suggest that periods of preservation were orders of magnitude longer than periods of subglacial landform formation copyright 2003 john wiley sons ltd

rapid laurentide ice sheet advance towards southern last glacial maximum limit during marine isotope stage 3 abstract marine isotope stage mis 3 58 28 ka is a period of intermediate global ice volume between mis 4 and the last glacial maximum of mis 2 here we report geologic evidence for southern laurentide ice sheet rapid growth to near its last glacial maximum extent after a period with limited ice in the southernmost hudson bay lowland a14c age on wood in lacustrine sediments interbedded with glacial tills in central eastern wisconsin dates a laurentide ice sheet advance southwards to an extent at least equivalent to at least its 17 ka deglacial limit by 39 1 0 4 ka this advance ended before 30 4 0 9 ka based on another 14c date on wood in lacustrine sediment overlying the till layers this advance is consistent with 14c ages from michigan and iowa and gulf of mexico runoff records that support a concurrent southern laurentide ice sheet advance we infer changes in north american ice volume using ice sheet model simulations from a large ensemble that are consistent with 14c data and gulf of mexico discharge constraints the simulations show the laurentide ice sheet growing from a volume equivalent to 25 30 m of global mean sea level gmsl before 40 ka to 40 45 m of gmsl at 40 ka and reaching 65 70 m gmsl by 30 ka consistent with glacial isostatic adjustment assessments of near to intermediate field sea level data we thus show from our terrestrial field data and ice sheet model simulations that an individual ice sheet can grow rapidly which has only been inferred previously for global ice volume from gsml records

vertical and lateral propagation of radial dikes inferred from the flow direction analysis of the radial dike swarm in komochi volcano central japan dikes with lateral and outward intrusion directions named l type dike and dikes with vertical and upward intrusion directions v type dike are recognized in a radial dike swarm of komochi volcano japan by the combined analysis of the preferred orientations of deformed vesicles and anisotropy of magnetic susceptibility ams intrusion directions of magmas were examined for 41 dike outcrops among them 19 dikes were classified as l type dike and 15 dikes were as v type the l type dikes distribute over the area of the dike swarm radiating from the central conduit which is named daikokuiwa stock and the v type dikes occur mainly in the peripheral portion of the volcano the l type dikes are characterized with evolved whole rock compositions similar to those of rocks consisting of the central conduit whereas the v type dikes have less fractionated composition and are enrich in mafic phenocryst as compared to the l type dikes the outward intrusion directions of the l type dikes and their petrological similarity to the rock of the central conduit indicate that these dikes intruded from the shallow part of the central conduit where the magmas underwent fractional crystallization and degassing the petrological characteristics of the v type dikes suggest that the less fractionated magma intruded directly from a magma chamber in which mafic phenocryst crystals accumulated the larger dike thickness and higher magnetic foliation of the v type dike as compared to the l type dike indicate higher magmatic overpressure which was possibly result of the direct connection to the pressurized magma chamber and vertical growth of the dikes with buoyant magma solidification of the central conduit is favorable for the accumulation of internal excess pressure in the magma chamber to break the wall rock fissure eruptions independent of the central conduit have occurred in many volcanoes and these fissure eruptions might be fed by the dikes directly propagated from the deeper magma chamber

late wisconsinan glacial history in the bonaparte lake map area south central british columbia implications for glacial transport and mineral exploration1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2earth sciences sector contribution number 20100093 this study is centred on the bonaparte lake map area located in the southern interior plateau of south central british columbia the reconstruction of the late wisconsinan glacial history of this part of the southern sector of the cordilleran ice sheet incorporates i the analysis and interpretation of landforms of various scales ii the sedimentology and stratigraphy of glacial sediments and iii the geochemical and mineralogical composition of till and analysis of regional glacial dispersal of these components the onset of the last glacial event was initiated by ice advancing westerly and southwesterly into the study area from an alpine source region located in the cariboo mountains as glaciation intensified ice from the coast mountains coalesced with the cariboo mountain ice over the interior plateau and developed into an ice divide around 52 north latitude which resulted in ice flow to be diverted to a southerly direction over the study area the two dominant ice flow directions produced pal

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

on the interpretation of normal and inverse magnetic fabric in dikes examples from the eger graben nw bohemian massif abstract recent studies of igneous rocks indicate that the predominant occurrence of normal inverse fabric in dikes may either reflect the presence of multi domain md single domain sd grains or it may result from different orientation mechanisms of magnetic minerals in magmas of different viscosities the ambiguity in physical vs geological cause of normal inverse magnetic fabric must be answered before any successful geological interpretation of magnetic fabric can be made in order to address this problem we studied magnetic fabric of selected dikes associated with the sw ne trending eger graben nw bohemian massif the studied area offered very extensive collection of rock types basanite bostonite camptonite tinguaite and trachybasalt magnetic susceptibility varies according to rock type and reflects the relative contents of magnetic minerals in most cases titanomagnetite with variable ti content was identified as main magnetic carrier the degree of anisotropy is relatively low in most cases less than 10 the shape of anisotropy ellipsoid ranges from slightly prolate to neutral and oblate several different types of magnetic fabric using anisotropy of low field magnetic susceptibility ams were observed in studied dikes so called normal and inverse magnetic fabrics and anomalous magnetic fabric comparing all studied sites it seems that the type of magnetic fabric is lithology dependent normal magnetic fabric with magnetic foliations and subhorizontal magnetic lineations both parallel to the dike margins was found in bostonite and trachybasalt dikes inverse magnetic fabric with magnetic lineations and magnetic foliations perpendicular to the dike margins was found in camptonite dikes anisotropy of anhysteretic remanent magnetization amr indicate that the observed inverse magnetic fabric may be caused by the presence of sd magnetic grains amr fabric being normal with respect to dike margins in contrast to that no single domain particles were revealed using frequency dependence and anhysteretic susceptibility measurements the ams measured in variable weak magnetic fields is field dependent for camptonite dike and field independent for other rock types i e bostonite basanite tinguaite and trachybasalt for further flow direction and tectonic interpretations of magnetic fabric in dikes it is suggested to use preferably the amr fabric at least for dikes which demonstrate significant field dependence of ams as it reflects the true rock fabric more accurately than ams fabric

magnetic petrofabric of igneous rocks lessons from pyroclastic density current deposits and obsidians abstract measurement of the anisotropy of magnetic susceptibility ams of igneous rocks can provide clues concerning their mechanism of formation and in particular are very helpful as flow direction indicators unlike other igneous rocks however pyroclastic density current deposits pdcds present a challenge in the interpretation of ams measurements due to the complexity of their mechanism of emplacement in this paper we review the most common assumptions made in the interpretation of the ams of pdcd taking advantage of key lessons obtained from obsidians despite the complexities on the mechanism of formation of pdcds it is shown that a key element for the fruitful interpretation of ams is to give proper attention to the various components likely to be involved in controlling their general petrofabric the anisotropies of ferromagnetic crystals whether as free phases or embedded within clasts or shards and those of paramagnetic minerals mainly ferrosilicates need to be taken into consideration when interpreting the ams measurements of pdcds variations of the deposition regime both as a function of position and of time also need to be considered on the interpretations nevertheless if a suitable sampling strategy is adopted the potential of the ams method as a petrofabric indicator is maximized

insights into the late cenozoic configuration of the laurentide ice sheet from 40ar 39ar dating of glacially transported minerals in midcontinent tills glacial sedimentary sequences in the north central united states record multiple advances of the laurentide ice sheet lis since 2 ma although the tills found in these sequences were deposited by southward flowing glacial lobes little information is available on the geometry of flow lines in the interior of the lis during any one glaciation and the provenance of glacial deposits older than the last ice advance is largely unknown systematic changes in the composition of midcontinent tills and other paleogeographic considerations however raise the possibility of significant shifts in the trajectory of flow lines feeding the lobes of the southwestern lis margin here we constrain till provenance using 40ar 39ar ages of individual hornblende and feldspar grains retrieved from tills representing several glaciations since 2 ma hornblende grains show 40ar 39ar ages that indicate erosion of paleoproterozoic 1 7 2 0 ga and late archean 2 5 ga rock sources whereas feldspar grains show a broad range of paleoproterozoic ages 1 4 2 4 ga dating of hornblende and feldspar minerals in single pebbles suggests that this latter distribution of ages is related to the greater sensitivity of feldspars to thermal resetting during minor tectonic events accordingly the range of 40ar 39ar ages for the predominant population of paleoproterozoic hornblende and feldspar grains in our samples is consistent with a source from terrains forming the churchill province of the canadian shield while the small population of archean age grains likely reflects a source from the southwestern tip of the archean superior province that crops out near the study area these results indicate that midcontinent tills were deposited by ice derived from the northwestern keewatin sector of the lis the nearly identical distribution of hornblende and feldspar ages in the till samples identifies the keewatin ice dome and the related ice flow to the midcontinent as long standing features of the lis throughout the late pliocene pleistocene glaciations

dynamics of the north american ice sheet complex during its inception and build up to the last glacial maximum the north american ice sheet complex played a major role in global sea level fluctuations during the late quaternary but our knowledge of its dynamics is based mostly on its demise from the last glacial maximum lgm a period characterised by non linear behaviour in the form of punctuated ice margin recession episodic ice streaming and major shifts in the location of ice divides in comparison knowledge of the pre lgm ice complex is poorly constrained largely because of the fragmentary nature of the evidence relating to ice sheet build up in this paper we explore the inception and growth of ice 120 20 ka using a glacial systems model which has been calibrated against a large and diverse set of data relating to the deglacial interval we make use of calibration data prior to the lgm but its scarcity introduces greater uncertainty which is partly alleviated by our large ensemble analysis results suggest that following the last interglaciation oxygen isotope stage ois 5e the ice complex initiated over the north eastern canadian arctic and in the cordillera within a few thousand years it then underwent rapid growth to an ois 5 maximum at 110 ka 5d and covered 70 of the area occupied by the lgm ice cover although only 30 by volume an ois 5 minimum is modelled at 80 ka 5a before a second phase of rapid growth at the start of ois 4 which culminated in a large ice complex at 65 ka almost as large as at the lgm subsequent deglaciation was rapid maximum modelled sea level contribution of 16 cm per century and resulted in an ois 3 minimum between ca 55 60 ka thereafter the ice complex grew towards its lgm configuration interrupted by several phases of successively less significant mass loss our results support and extend previous inferences based on geological evidence and reinforce the notion of a highly dynamic pre lgm ice complex e g with episodes of 10 s m of eustatic sea level equivalent in 50 but even the thin ois 5 ice sheets exhibit fast flow features several 1000 m a 1 in major topographic troughs notwithstanding the severe limitations imposed by the use of the shallow ice approximation we note that most fast flow features generated prior to the lgm correspond to the location of known ice streams during deglaciation i e in major topographic troughs and over soft sediments at the southern and western margins moreover the modelled flux of these ice streams sensu lato appears to be non linearly scaled to ice sheet volume i e there is no evidence that decay phases were associated with significantly increased ice stream activity this hypothesis requires testing using a model with higher order physics and future modelling would also benefit from additional pre lgm constraints e g dated ice free margin positions to help reduce and quantify uncertainties

subtill nonglacial deposits and their climatic implications for the last interglacial mis 5e hudson bay lowlands canada abstract in hudson bay lowlands hbl the wisconsinan tills are often underlain by organic bearing nonglacial deposits formed during episodes of significant reduction of ice volumes or complete ice free conditions in this region the subtill nonglacial deposits often correlated with the missinaibi formation are beyond the method limit of radiocarbon dating in general as such they have been a subject of debates for their stratigraphy and associated climatic conditions owing to poor age constraints extensive studies were undertaken on a subtill argillaceous lacustrine deposit uncovered recently on the winisk river this 9 m thick organic rich deposit referred to as the webequie beds was dated at 121 9 ka 126 24 ka and 105 11 ka using optically stimulated luminescence osl dating method and correlated with the last interglacial lig or marine isotope stage mis 5e pollen and plant macrofossils suggest spruce boreal forests along with extensive wetlands not unlike what exists in the hbl today of particular note is the sporadic rise of birch in the upper part of the pollen sequence interpreted as a response to the availability of frequent forest clearance by fires under a warmer climate the birch zone is noteworthy because it corresponds to the development of conspicuous s rich ferromagnetic nodules 0 125 1 5 mm diameter in the lake sediment the nodules comprise native sulphur and greigite fe3s4 along with iron oxyhydroxide goethite and lepidocrocite they likely resulted from significant warming during this interval that enhanced microbial sulphate reduction and increased the release of h2s an essential component for the formation of the s minerals in the lake besides the strengthened microbial metabolization a prolonged summer lake stratification and development of an anoxic bottom water also likely promoted the sulphate reduction although confirmation is needed the warming probably linked to the lig thermal maximum 120 ka when a climate with a higher summer temperature than today prevailed a similar subtill nonglacial deposit on the little current a tributary of the albany river was also examined for comparison apart from a similar pollen flora s rich nodules were also recovered near a horizon osl dated at 118 13 ka comparable to the lig thermal maximum results of this study provide new insights into the stratigraphy and climatic conditions of the lig in the hbl but also help better understand the behavior and dynamics of the laurentide ice sheet during the late pleistocene

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

sedimentology of an ice contact glaciomarine fan complex nastapoka hills eastern hudson bay northern quebec abstract emerged holocene coalescing glaciomarine fans are exposed along the nastapoka hills eastern hudson bay the fans form part of a regional stratified drift belt associated with terrestrial and submarine frontal moraines and other grounding lines deposits these thick extensive and in many cases coalescent sediment bodies were deposited during a stillstand of the quebec labrador sector qls of the laurentide ice sheet lis that pinned on the hills during eastward retreat from hudson bay the fans are composed of basal interbedded and interlaminated sand silt and silty clay facies association i fa i deposited by suspension settling from overflow plumes sediment gravity flows and ice rafting towards the ice contact zone fa i interfingers with diamict layers fa ii deposited by gravity flows and ice rafting these two sedimentary units are overlain by interbedded sand and gravel fa iii formed by reworking during subsequent emergence parts of fa i and fa ii were remobilized by submarine gravity flows which prevailed long after ice retreat the sedimentology of the nastapoka hills provides information on the processes operating near the grounding line of a temperate ice sheet reaching tidewater

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

clinker formation in basaltic and trachybasaltic lava flows clinker is a term used to describe massive or scoriaceous fragments commonly associated with a lava flows clinker is generally considered to form by fragmentation of an upper vesiculated crust due to an increase in apparent viscosity and or to an increase in shear strain rate surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion clinker that we have observed on a variety of lava flows has very variable textures which suggests several different mechanisms of formation in order to study clinker formation we examined several lava flows from the chaine des puys central france where good sections surface morphology and surface textures are widespread and clearly visible we observed basal and surface a clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions in two p hoehoe flows we have observed basal clinker that formed in situ two other flows display clinker features identical to those commonly observed in phreatomagmatic ash such as adhering particles blocky shapes spherical glass and attached microphenocrysts another p hoehoe flow has a flakey angular basal breccia with microfaulted and abraded clasts these were probably formed at a cooled lava base by large amounts of simple shear and consequent intra lava brittle faulting using these observations we propose three different ways of fragmentation 1 clinker can form at the surface and eventually produce roll over basal breccia 2 water lava interactions can form basal clinker by phreatomagmatic fragmentation water lava ratio variations may produce different clinker structures in a manner similar to observed textural changes in phreatomagmatic eruptions 3 clinker can be formed by brittle brecciation during basal simple shear the different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement

cosmogenic 10 be dating of raised shorelines constrains the timing of lake levels in the eastern lake agassiz ojibway basin

early holocene glacial lakes and ice marginal retreat pattern in labrador ungava canada abstract the existence of glacial lakes naskaupi mclean minto melezes and wapussakatoo during the deglaciation of labrador ungava canada was recognized at the end of 1950s however glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in labrador ungava reconstruction of the ice flow succession in labrador ungava has often primarily focused on till lineation systems these reconstructions often depict a late glacial ice dispersal center situated over central labrador ungava more recent studies on glacial geomorphology including meltwater features however suggest that north central labrador ungava exhibited cold based conditions at least during the latest deglaciation cold based conditions inhibit basal sliding and formation of landforms except for meltwater traces such as meltwater channels glacial lake shorelines and deltas this situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold based deglaciation evidence presented in this study such as glacial lake shorelines fossil deltas and spillway and drainage channels in north central labrador ungava indicates the existence of numerous previously unmapped glacial lakes the mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which in turn are used to constrain the late glacial ice margin retreat pattern over the inferred cold based areas of north central labrador ungava a total of 26 glacial lakes 65 sub stages existed during the deglaciation of labrador ungava these lakes were impounded along the southern margin of the shrinking ice sheet the required damming ice margins indicate that the last ice remnant of the laurentide ice sheet in labrador ungava was situated over the southern ungava bay and the adjacent southern shore

shallow plumbing systems for small volume basaltic volcanoes eruptive dynamics in basaltic volcanoes are controlled in part by the conduit geometry however uncertainties in conduit shape and dike to conduit transition geometry have limited our predictive capability for hazards assessments we characterize the subvolcanic geometry of small volume basaltic volcanoes magmatic volatile driven eruptions 0 1 to 0 5 km3 based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes conduits and vent areas 250 m depth study areas include east grants ridge new mexico usa basalt ridge east basalt ridge paiute ridge and southeast crater flat nevada usa basaltic feeder dikes 250 to 100 m deep have typical widths of 4 12 m with smooth host rock contacts rhyolite tuff at depths less than 100 m heterogeneities in the host rock form preferential pathways for small dike splays and sills resulting in a 30 m effective width at 50 m depth the development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock the overall zone of effect at depths less than 50 m is 110 m wide 220 m elongated along the feeder dike based on comparisons with theoretical conduit flow models the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1 2 m at depths greater than 500 m the flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure balanced flow conditions sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface 50 m depth but at depths greater than 100 m the difference is a factor of 2 to 4 this difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events while theoretical model results define dimensions necessary for a single steady eruption phase the complex details of magma host rock interactions observed at the study areas contact welding brecciation bifurcating dikes and sills and stoping represent the mechanisms by which the lithostatic pressure balanced geometry is attained the similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure balanced modeling approach consistent with the conclusions of wilson and head j geophys res 86 2971 3001 1981 for this type of volcano

geomorphological reconstruction of the labrador sector of the laurentide ice sheet abstract the labrador sector formed one of three major domes of the laurentide ice sheet during the last wisconsinan glaciation reconstruction of its evolution is important because it modulated atmospheric and oceanic circulation over 1 100 ka time scales this paper reports new geomorphological evidence of ice flow which is used to reconstruct glimpses of the behaviour of the labrador sector during its evolution flow evidence indicates a southern position 51 n of the labrador ice divide presumed to be the usual location when the ice sheet was close to its maximum extent a previously inferred dramatic surge of labrador ice across hudson strait and onto baffin island at 9 9 9 4 ka is verified seemingly contradictory evidence regarding deglaciation in northern quebec has been analysed and a reconstruction developed that solves this problem deglacial retreat of the labrador ice sheet was highly asymmetric with rapid retreat of the southern margin northwards migration of the centre of mass by 500 km and slow retreat along the northern margin as it shrank its thermal regime changed from cold centred to entirely cold based and it finally fragmented into many residual ice caps and glaciers this dynamic and asymmetric behaviour may be due to destabilisation of the labrador ice sheet triggered by heinrich event ice streaming through hudson strait