detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

the role of hydrothermal processes in concentrating high field strength elements in the strange lake peralkaline complex northeastern canada abstract the middle proterozoic peralkaline pluton at strange lake quebec labrador comprises hypersolvus to subsolvus phases which are unusually enriched in zr y rees nb be and f as exotic alkali and alkaline earth silicate minerals the highest concentrations of these elements are in subsolvus granite which underwent intense low temperature 200 c hydrothermal alteration involving hematization and the replacement of alkali high field strength element hfse minerals by calcic equivalents this alteration is interpreted to have been caused by meteoric or formational waters high temperature 350 c alteration attributed to orthomagmatic fluids is evident in other parts of the subsolvus granite by the replacement of arfvedsonite by aegirine comparisons of the chemical compositions of fresh and altered rocks indicate that rocks subjected to high temperature alteration were chemically unaffected except for depletion in zr y and hrees these elements were appreciably enriched in rocks that underwent low temperature alteration other elements affected by low temperature alteration include ca and mg which were added and na which was removed available data on hfse speciation in aqueous fluids and the chemistry of the pluton suggest that the hfses were transported as fluoride complexes if this was the case the low temperature fluid could not have been responsible for hfse transport because the high concentration of ca and low solubility of fluorite would have buffered f activity to levels too low to permit significant complexation we propose that hfse mineralization and accompanying alteration were the result of mixing in the apical parts of the pluton of a f rich essentially ca free orthomagmatic fluid containing significant concentrations of hfses with an externally derived meteoric dominated fluid enriched in ca as a result of interaction with calc silicate gneisses and gabbros according to this interpretation the latter fluid was responsible for the exchange of ca for alkalis mainly na in hfse rich minerals and by sharply reducing f activity in the mixed fluid through fluorite precipitation and or increasing ph destabilised the hfse fluoride complexes causing deposition of hfse bearing minerals an important implication of this study is that major hfse enrichment may be restricted to those rare cases where f rich ca free metal leaching environments and ca rich depositional environments are juxtaposed

spatiotemporal evolution of paludification associated with autogenic and allogenic factors in the black spruce moss boreal forest of quebec canada paludification is the most common process of peatland formation in boreal regions in this study we investigated the autogenic e g topography and allogenic fire and climate factors triggering paludification in different geomorphological contexts glaciolacustrine silty clayey and fluvioglacial deposits within the quebec black spruce picea mariana moss boreal forest paleoecological analyses were conducted along three toposequences varying from a forest on mineral soil to forested and semi open peatlands plant macrofossil and charcoal analyses were performed on basal peat sections 50 cm and thick forest humus sphagnum in microdepressions paludification resulted in the decline of some coniferous species such as abies balsamea and pinus banksiana the paleoecological approach along toposequences allowed us to understand the spatiotemporal dynamics of paludification and its impacts on the vegetation dynamics over the holocene

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

evidence of a strong paleoearthquake in 9 1 ka cal bp interpreted from mass transport deposits western quebec northeastern ontario canada this paper reviews and expands upon stratigraphic and chronologic evidence supporting the interpretation of a strong early postglacial paleoearthquake in western quebec northeastern ontario canada event horizon mapping at dasserat dufresnoy and duparquet lakes quebec coring at chassignolle and malartic lakes quebec analysis of varve exposures near both the twin falls and frederick house dams ontario and review of published and unpublished logs of varve exposures reveal that mass transport deposits formed in or are inferred to have formed in varve year vyr 1483 relative to the timiskaming varve series and about 9 1 ka cal bp are present at numerous locations within the study area the spatial extent of the vyr 1483 mass transport deposit signature covers at least 14 600 km2 and is best explained by shaking from a paleoearthquake the magnitude of the event is estimated to be a minimum of m 7 3 which is indicative of a strong paleoearthquake the vyr 1483 paleoearthquake is one of 11 events of m 5 occurring within a 425 varve year period between 9 4 and 8 95 ka cal bp and is likely part of a period of elevated early postglacial seismicity associated with rapid crustal unloading the absence of an equivalent signature within the younger portion of the glaciolacustrine or lacustrine deposits in local lakes implies that this paleoearthquake is the strongest to occur within the study area since about 9 1 ka cal bp the highly precise correlation of widely spaced mass transport and disturbed deposits provided by varves is essential to the paleoearthquake interpretation

experimental studies on the mobility of lanthanides accompanying alteration of andesite by acidic hot spring water abstract the mobility of lanthanides lns accompanying interactions of powdered andesitic rocks with acidic hot spring water and acidic hot spring water vapor steam was studied in the experiments set up in the field at the early stage of rock alteration light lns were slightly easier to be leached out by acidic hot spring waters from andesitic rocks than heavy lns this result qualitatively agreed with the result obtained in the previous experiments carried out in the laboratory it was also found that the ln abundance patterns ln patterns obtained by normalization with ln contents of the original rock showed slightly positive eu anomalies at the early stage of rock alteration and turned to show negative eu anomalies and the extent of negative anomaly monotonously increased as rock alteration proceeded this trend in the direction of eu anomaly was correlated to the degrees of decompositions of major rock forming minerals and interstitial materials in the rock at the earliest stage of rock alteration in acidic environments the interstitial materials with relatively low eu contents were decomposed which resulted in the positive eu anomaly in the following stage feldspar that had a relatively high eu content was decomposed which led to the negative eu anomaly

indialite from unazuki pelitic schist japan and its transition texture to cordierite indialite hexagonal cordierite has been found in a cordierite vein of polymetamorphosed pelitic rock a member of the unazuki schists in hida terrane central japan most of the indialite grains show intergrowth textures with cordierite of orthorhombic symmetry this is the second identification of indialite since the first one from a fused sediment in india

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

10be dating of former glacial lake naskaupi quebec labrador and timing of its discharges during the last deglaciation abstract the last deglaciation of the laurentide ice sheet in northern quebec and labrador led to the formation of several glacial lakes that drained into ungava bay and the nearby labrador sea assessing the potential impact of their drainage on ocean surface conditions and climate however is limited by the few existing age constraints on ice retreat and associated evolution of these lakes here we report 21 10be ages from shorelines and an outburst flood landform formed by lake naskaupi one of the largest glacial lakes in this region the results indicate that the lake drained from its full extent at 8300 300 a suggesting that it may have contributed to the freshwater forcing initiated by the drainage of lake agassiz ojibway that caused the 8 2 ka cold event additionally the results provide important constraints on the position of the ice margin of the labrador sector during its retreat across this region

evidence of late glacial paleoseismicity from submarine landslide deposits within lac dasserat northwestern quebec canada abstract an integrated seismo and chronostratigraphic investigation at lac dasserat northwestern quebec identified 74 separate failures within eight event horizons horizons e and b and h and g have strong or moderately strong multi landslide signatures respectively composed of 11 23 failures while horizons f d c and a have minor landslide signatures consisting of a single or pair of deposit s cores collected at six sites recovered glacial lake ojibway varve deposits that are interbedded with the event horizons the correlation of the varves to the regional timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons horizons h g e and b are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence based on the relative strength of the multi landslide signatures the correlation to other disturbed deposits of similar age in the region and the lack or possibility of alternative aseismic mechanisms the four interpreted paleoearthquakes occurred between 9770 200 and 8470 200 cal yr bp when glacial lake ojibway was impounded behind the laurentide ice sheet during deglaciation they probably represent an elevated period of seismicity at deglaciation that was driven by crustal unloading

a review and analysis of varve thickness records from glacial lake ojibway ontario and quebec canada abstract varve thickness records from glacial lake ojibway provide a detailed picture of ice margin dynamics and paleohydrology for the laurentide ice sheet during the early holocene the demise of lake ojibway occurred when an ice dam of the shrinking laurentide ice sheet failed perhaps releasing enough freshwater to impede atlantic meridional overturning circulation and precipitate the 8200 cal bp climatic cooling event previously published records and new information from lacustrine sediment cores are combined to reconstruct a varve record over 2100 years long between varves numbered 1 to 1500 average rates of ice margin retreat increased from 140 m y to as high as 400 m y beginning prior to varve year 1800 and lasting to around year 2000 ice readvanced along a front at least 300 km wide during an episode called the cochrane the total distance of the advance was at least 75 km and averaged around 200 m y during the advance a series of 50 anomalously thick varves were deposited the cause of which is uncertain a widespread unconformity occurred during the end of the cochrane advance which was followed at around varve year 2060 by the return of varves which thicken abruptly unlike previous varves these varves include ice rafted pellets of lake ojibway sediment these varves may have resulted from rapid melting and calving rather than a second advance and may relate to basin re filling following a lowstand there are no direct dates on the lake ojibway varves but a sudden increase in varve thickness at year 1528 is a regional stratigraphic marker that may have resulted from glacial sediment and meltwater including lake agassiz overflow diverted from routes to the lake superior basin into the lake ojibway basin dates from the lake superior basin suggest that the diversion of this water occurred at around 9040 cal bp applying this date to varve 1528 constrains the age of the lake ojibway varves numbered 1 to 2100 to between 10 570 and 8470 200 cal bp

origin of high silica liquids at stromboli volcano aeolian islands italy inferred from crustal xenoliths high silica igneous xenoliths granophyre and obsidian fragments with sio2 ca 75 wt and high silica glass sio2 between ca 64 and 75 wt within glass bearing tonalitic and dioritic xenoliths have been discovered at stromboli they are well beyond the silica range of the volcanic rocks erupted during the subaerial activity of the volcano the granophyre and the obsidian fragments occur within the petrazza pyroclastics high k andesite pumiceous scoriae of the paleostromboli i period 61 ka whereas the glass bearing tonalites and diorites are hosted in the omo basaltic andesite lava flows of the paleostromboli ii period 64 55 ka the obsidian represents an extremely evolved liquid derived from low pressure fractional crystallization of high k calc alkaline magmas of stromboli coupled with minor assimilation of upper crust or terrigenous sediments the other studied high silica products have an anatectic origin the granophyre composition is compatible with a genesis by low degree melting of leucotonalites similar to some calabrian arc lithotypes partial melting of crustal rocks from the stromboli basement is also demonstrated by interstitial glass in the tonalite and diorite xenoliths textural evidence and the presence of variable glass compositions suggest that in these plutonic xenoliths the melt chemistry was controlled by dehydration melting of biotite and non modal melting of local mineralogy high degree undercooling of granophyre melt and of the partially melted xenoliths is consistent with rapid rise of the host magmas leading to eruption whether partial melting was initiated during stoping and transport of xenoliths within the rising magma or in situ during magma storage within the crust has not been unequivocally established

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

elusive isotopic properties of deglacial meltwater spikes into the north atlantic example of the final drainage of lake agassizthis article is one of a series of papers published in the special issue on the theme polar climate stability network the impact of the final drainage of lake agassiz some 8 4 ka ago on the atlantic meridional overturning circulation is still debated the lack of isotopic response in planktic foraminifer records at the outlet of the drainage channel constitutes a puzzling element in this debate to estimate the response of the 18o salinity relationship in ocean surface waters to drainage we use a core raised from southeast hudson bay to document 18o values of lake waters immediately prior to drainage valves of candona sp an ostracod from lacustrine varved sediments underlying marine clays yielded 18o values clustered around 20 5 versus vpdb vienna peedee belemnite assuming a lake bottom temperature of about 0 c an isotopic composition of 25 versus vsmow vienna standard mean ocean water is calculated for paleolake waters not unlike values reported for earlier stages of lake agassiz this value is only slightly more negative than those estimated for laurentide ice sheet lis meltwaters during the

fluid circulation at stromboli volcano aeolian islands italy from self potential and co2 surveys this work addresses the study of fluid circulation of the stromboli island using a dense coverage of self potential sp and soil co2 data a marked difference exists between the northern flank and the other flanks of the island the northern flank exhibits 1 a typical negative sp altitude gradient not observed on the other flanks and 2 higher levels of co2 the general sp pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water in the sciara del fuoco and rina grande le schicciole landslide complexes breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere poorly permeable fine grained pyroclastites or altered lava flows may be present this general model of the flanks also explains the main co2 patterns concentration of co2 at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward co2 flux the active upper part of the island is underlain by a well defined hydrothermal system bounded by short wavelength negative sp anomalies and high peaks of co2 these boundaries coincide with faults limiting ancient collapses of calderas craters and flank landslides the hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters the latter are located near its border this divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters if the heat source strictly corresponds to intrusions at depth around the active conduits the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters caldera walls or gliding planes of flank collapse as suggested by the correspondence between sp co2 anomalies and structural limits the inner zone of the hydrothermal subsystems is characterized by positive sp anomalies indicating upward movements of fluids and by very low values of co2 emanation this pattern suggests that the hydrothermal zone becomes self sealed at depth thus creating a barrier to the co2 flux in this hypothesis the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone finally on the base of co2 degassing measurements we present evidence for the presence of two regional faults oriented n41 and n64 and decoupled from the volcanic structures

insights on the events surrounding the final drainage of lake ojibway based on james bay stratigraphic sequences abstract deglaciation of the james bay region was highly dynamic with the occurrence of ice cochrane readvances into glacial lake ojibway around final deglaciation time which culminated with the drainage of ojibway waters into hudson bay and subsequent incursion of the tyrrell sea at 8 ka renewed interest on these events comes from the possible link between the drainage of the ice dammed lake agassiz ojibway and a major climate deterioration known as the 8 2 ka cooling event recent glaciological modeling suggests that this drainage may have occurred subglacially a mechanism that can accommodate more than one lake discharge as suggested by marine records the exact number and timing of drainage events as well as location of the lake discharge pathway s remain however largely unconstrained here we focus on the events that led to the drainage of lake ojibway by documenting late glacial sedimentary sequences located east of james bay our investigations indicate that the deglacial sequence consists of a readvance till extensive ojibway rhythmites and thick marine sediments the glaciolacustrine and marine units are separated by a 60 cm thick horizon composed of laminated silt beds containing rounded clay balls and disseminated clasts resulting from the abrupt drainage of the lake radiocarbon dating of marine fossils lying above the drainage horizon indicates that the glaciolacustrine episode ended around 8128 8282 cal yr bp micropaleontological analyses reveal that freshwater ostracods candona sp and marine microfossils foraminifers dinocysts occur together in the upper part of the ojibway sediments analysis of oxygen isotopes 18 o of ostracods and foraminifers originating from the same stratigraphic position show highly contrasting values that suggest possible subglacial exchanges between lake ojibway and tyrrell sea waters prior to the final drainage event the complexity of the deglacial events is further indicated by radiocarbon dating of marine shells retrieved from a cochrane till that suggests that the last ice readvance occurred almost simultaneously with the final lake discharge these results bring additional constraints on the drainage mechanism of the coalesced lake agassiz ojibway and indicate that the james bay region formed an important drainage pathway for meltwaters at the end of the last deglaciation

high temperature rapid pyrometamorphism induced by a charcoal pit burning the case of ricetto central italy bulk chemistry and mineralogy of the peculiar rock of ricetto carseolani mts central apennines italy was studied to resolve its controversial origin igneous dyke or anthropic product this hybrid rock consists of a colorless felsic component made up of glass plus quartz and a brown femic component made up of fans and spherulites of diopside calcic plagioclase wollastonite and melilite textural relationships indicate very rapid cooling and immiscibility phenomena the bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone the 14c analysis of a coal fragment from bottom of the body yields the conventional age of 227 50 years the ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning the small size of the heat source at ricetto caused an intense but short lived melting of the country rock prograde metamorphism caused a temperature increase up to 1 000 1 100 c when melilite crystallization conditions were reached at appreciable p co2 and high f o2 melting occurred in a close system represented by the simplified equation 3cal 16 5qtz ms bt mel melt 2h2o 3co2 0 5o2 diopside calcic plagioclase wollastonite formed by melilite breakdown during rapid cooling through the reaction 6mel 6qtz 0 5o2 3di 2an 7wo liquid immiscibility caused the separation between the felsic melt component and the femic melilite bearing component immiscibility was characterized by different fractionation of alumina and alkalies between these two phases differences in bulk glass and mineral chemistry between the ricetto and other melilite bearing pyrometamorphic rocks can be attributed mainly to different protoliths

glass bearing crustal xenoliths buchites erupted during the recent activity of stromboli aeolian islands abstract three xenoliths erupted as ejecta during recent violent explosion of stromboli volcano aeolian islands were investigated in this paper they consist of high temperature mineral association cordierite hercynite spinels sillimanite plagioclase mullite corundum and abundant glass 10 70 vol and may be classified as buchites the peraluminous composition of the xenoliths their trace element distribution and ree patterns support their origin from granulite and amphibolite facies metapelites of the calabrian continental crust which is considered the crystalline basement beneath stromboli buchites have an isotopic composition comparable to that of stromboli extrusives and significantly different from that of the calabrian basement the glass is generally colourless and has a si al alkali rich composition except for one sample where a fe mg ca rich reddish brown glass also occurs these two kinds of glass show complicated textures where patches of reddish brown glass are often surrounded by plagioclase and or cordierite or forms streaks and swirls with the colourless glass cordierite plagioclase and oxides have different compositions according to their position in the xenoliths ca rich plagioclase an72 95 mg poor cordierite mg values 47 66 and al rich spinels are in the inner portions of the xenoliths and associated with colourless glass on the contrary close to the contact with the host lava or associated with coloured glass cordierite shows higher mg values ti fe bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts an66 71 the abundant and fresh glass and the idiomorphic shape of the high temperature minerals suggest that the xenoliths were hold in the basaltic magma before its extrusion for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases during this stage the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and in some cases produced glass and mineral phases cordierite plagioclase and oxides with different composition

high resolution varve sequences record one major late glacial ice readvance and two drainage events in the eastern lake agassiz ojibway basin abstract lake ojibway developed at the southern laurentide ice sheet margin during the last deglaciation and covered vast expanses of northeastern ontario and northwestern quebec canada the late stage history of the lake is complex presumably marked by a coalescence with lake agassiz and by late glacial ice readvances into the basin shortly before its final drainage 8200 years ago however these events are poorly defined in the lake ojibway varve record here we present evidence for the occurrence of one major ice readvance and two distinct drainage events from two varve sequences in northwestern quebec the matagami section contains 231 varves that comprise an interval recording a late glacial cochrane ice readvance the la reine section spans 100 varves and the base of the sequence is characterized by a set of chaotic and coarse grained silty rhythmites that marks the first lake drainage these bottom rhythmites are overlain by a set of 65 thick varves which are in turn capped by a thick silt bed associated with the final drainage of lake ojibway varve thickness measurements allow the correlation of these sections with the main ojibway varve record that spans 2129 years in the region where varve 1 represents the start of sedimentation the matagami sequence covers varve years 1644 1874 and the onset of the cochrane readvance occurred in varve year 1817 the lower part of the la reine sequence below the bottom chaotic rhythmites was deposited between varve years 1843 1877 while the overlying set of thick varves is correlated to varve years 2065 2129 thus indicating a hiatus of 188 varves the distinct thick varves show strong compositional and stratigraphic similarities with the connaught sequence reported elsewhere in the basin and point to a connection with the late glacial cochrane ice dynamics which appear to have played an important role on the lake evolution these results indicate that the late stage history of lake ojibway was marked by the already known cochrane major ice readvance which was followed by two drainage events separated by at least 65 years consistent with north atlantic sediment records that document a two step drainage of lake agassiz ojibway

pyrometamorphism and the contamination of basaltic magma at tieveragh co antrim a tertiary dolerite plug at tieveragh co antrim cuts old red sandstone tuffaceous sedimentary rocks glassy buchites have formed by disequilibrium partial melting induced by convective heat transfer from the basaltic magma variation in bulk rock chemistry has produced glasses coexisting with variable proportions of pyroxene cordierite ilmenite hematite magnetite mullite plagioclase and alkali feldspar mixing of the basaltic magma with acid melt illustrates how up to 10 contamination may occur without radically altering the course of crystallization mineral geothermometers indicate maximum temperatures at the contact around 1100 c falling to only 940 at 10 m

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

evidence of a partial melt zone beneath stromboli volcano italy from inversion of teleseismic receiver functions teleseismic body waves from broadband seismic stations are used to investigate the crustal and uppermost mantle structure of stromboli volcano through inversion of the receiver functions rfs first we computed rfs in the frequency domain using a multiple taper spectral correlation technique then the non linear neighbourhood algorithm was applied to estimate the seismic shear wave velocity of the crust and uppermost mantle and to define the main seismic velocity discontinuities the stability of the inversion solution was tested using a range of initial random seeds and model parameterizations a shallow moho present at depth of 14 8 km is evidence of a thinned crust beneath stromboli volcano however the most intriguing and innovative result is a low s velocity layer in the uppermost mantle below 32 km the low s velocity layer suggests a possible partial melt region associated with the volcanism as also recently supported by tomographic studies and petrological estimations

changes in the bathymetry and volume of glacial lake agassiz between 11 000 and 9300 14c yr b p abstract computer reconstructions of the bathymetry of the lake were used to quantify variations in the size and form of lake agassiz during its final two phases the nipigon and ojibway phases between about 9200 and 7700 14c yr b p ca 10 300 8400 cal yr b p new bathymetric models for four nipigon phase stages corresponding to the mccauleyville hillsboro burnside and the pas strandlines indicate that lake agassiz ranged between about 19 200 and 4600 km3 in volume and 254 000 and 151 000 km2 in areal extent at those times a bathymetric model of the last ponton stage of the lake corresponding to the period in which lake agassiz was combined with glacial lake ojbway to the east shows that lake agassiz ojibway was about 163 000 km3 in volume and 841 000 km2 in areal extent prior to the final release of lake waters into the tyrrell sea during the nipigon phase a number of catastrophic releases of water from lake agassiz occurred as more northerly lower outlets were made available by the retreating southern margin of the laurentide ice sheet we estimate that each of the four newly investigated nipigon phase releases involved water volumes of between 1600 and 2300 km3 the final release of lake agassiz waters into the tyrrell sea at about 7700 14c yr b p is estimated to have been about 163 000 km3 in volume

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

megaflooding associated with glacial lake agassiz abstract significant baseline and episodic megaflooding from glacial lake agassiz was routed to the south east and north coasts of north america over the lake s nearly 6000 year history the five phases of lake level change were controlled by which outlet was active which in turn was controlled by ice margin position and glacioisostatic adjustment the southern outlet is the oldest and best understood outlet while successively younger outlets are progressively less understood eastern drainage synchronous with the younger dryas chronozone had been assumed by most studies but a spillway to accommodate the 90 m drop in lake level is yet to be described with the south and east outlets unable to accommodate the necessary lake level drawdown the northwest outlet has become the default outlet with arctic ocean core data supporting it however extant terrestrial data from the continent only provides data for a large flood from the fort mcmurray area closer to the end of the younger dryas coinciding with the timing of the preboreal oscillation the challenge remains to find agreement between the marine and terrestrial records uncontroversial is the geomorphic and sedimentologic evidence for flooding into and out of the lake consisting of large spillways large boulders and in places giant current ripples composed of boulders flood discharge estimates into and out of the lake range from 0 04 to 1 sv with final subglacial drainage into the tyrell sea estimated at 5 sv sufficient to raise global sea level by 0 18 m and initiate the 8 2 ka stadial

transient processes in stromboli s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 april 2003 paroxysm we describe the mineralogy geochemistry and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 april 2003 paroxysm of stromboli aeolian islands italy these blocks represent 50 vol of the total erupted ejecta and consist of fine to medium grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias the breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated lava like to scoriae crystal rich cr basalt all of the studied blocks are cognates with the cr basalt of the normal strombolian activity or lavas and they are often coated by a few centimeter thick layer of crystal poor cp basaltic pumice erupted during the paroxysm we suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 april 2003 explosion when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas rich cp basalt that triggered the eruption dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the cr basalts erupted during normal strombolian activity and effusive events at stromboli volcano dolerites consist of a phenocrysts normally found in the cr basalts and b late stage magmatic minerals such as sanidine an60 28 plagioclase fe mn rich olivines fo68 48 phlogopite apatite and opaque mineral pairs magnetite and ilmenite most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical strombolian behavior subvolcanic crystallization of the stromboli cr magma leading to slowly cooled equivalents of basalts could result from transient drainage of the magma from the summit craters to lower levels fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 december 2002 coupled with the short break in the summit persistent explosions between december 2002 and march 2003 permitted the cr magma pockets to solidify as dolerites which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity crystal size distribution of the basaltic blocks and crystallization of the finer grained 0 1 mm mafic minerals of the dolerites over a time interval of 100 days closely agrees with the above interpretation vesicle filling miarolitic cavities locally found in some dolerites with minerals deposited as vapor phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system poorly welded magmatic breccias formed during syn eruptive processes of 5 april 2003 when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the cr magma in contrast the high degree of welding between the dolerite clasts and the cr basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the cr basalt into the dolerite when after a 2 month break in activity cr magmas started to rise again to the summit craters blocks similar to these subvolcanic ejecta of 5 april 2003 were also erupted during previous paroxysms e g 1930 suggesting that changes in the usual strombolian activity e g short breaks in the persistent mild explosions and or flank effusive activity lead to transient crystallization of dolerites in the shallow plumbing system

late stage phases of glacial lake ojibway in the central abitibi region eastern canada abstract the decay of the laurentide ice sheet southern margin during the last deglaciation led to the development of lake ojibway that covered large expanses of northeastern ontario and northwestern quebec the history of ojibway lake phases is poorly detailed mainly because of the physical configuration of the lake basin and the dominance of fine grained glaciolacustrine sediments that prevent the formation of well developed and extensive sandy strandlines here we use a complex sequence of relict terraces carved in glaciolacustrine rhythmites to document the evolution of lake ojibway in northwestern quebec specifically lake levels were constrained by measuring the elevation of 154 raised wave cut scarps present in the eastern lake abitibi region results provide evidence for four distinct shorelines with elevations of 299 289 282 and 272 m 1 m at the latitude of la sarre the highest lake level documented appears to be linked to one of the two known kinojevis phases of lake ojibway while the three other lake levels project well below the main outlet system that controlled the elevation of the lake during the deglaciation the elevation uplift gradients and areal extent of these lower shorelines suggest that the two intermediate lake levels likely formed during late stages of the deglaciation following abrupt drawdowns of the lake s surface the fourth and lowest shoreline is associated with a postglacial lake that developed after the complete withdrawal of ojibway water from the region these low elevation shorelines bring new evidence for significant changes in the areal extent and depth of lake ojibway near the end of the deglaciation although the origin of these late stage phases remains unspecified the associated drawdowns likely implied routing events into newly deglaciated regions and or subglacial meltwater discharges into the north atlantic

behavior of the rare earth elements and other trace elements during interactions between acidic hydrothermal solutions and silicic volcanic rocks southwestern japan abstract rare earth elements and other trace elements in some roseki deposits mostly pyrophyllite and sericite silicastones alunites and related rocks were determined in order to examine behavior of the trace elements in the acidic hydrothermal alteration of silicic volcanic rocks the analyzed concentrations were normalized to the probable unaltered original rock values inferred from the averaged data of some silicic volcanic rocks the trace element characteristics for those materials are as follows 1 most of the elements such as na fe ba and light ree were leached from the silicastones while heavy ree th hf and zr were retained in them 2 alunite samples have light ree enriched and heavy ree depleted features 3 the typical roseki deposits are characterized by middle ree depletions and have v shaped ree patterns on the normalized concentrations vs atomic number diagram such characteristic patterns of the roseki deposits can be explained by superimposition of the light ree enriched and heavy ree enriched materials such as alunite and silica it is important that trace element behaviors are highly selective and some elements e g yb lu hf and zr were strongly retained in the rocks even under strongly acidic hydrothermal processes

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

formation of rock coatings induced by the acid fumarole plume of the passively degassing volcano of la fossa vulcano island italy at la fossa volcano vulcano island and in the surrounding environment rock coatings rc develop owing to exposure of the ground surface to a volcanic acid plume this plume is produced by the passive degassing of la fossa active cone proximal and distal with respect to the high temperature fumarolic field rc have been identified which differ in mineralogy texture and chemical composition proximal rc are characterised by high silica content massive texture and strong leaching at the expense of the pyroclastic material distal rc are characterised by the presence of silica jarosite and minor goethite laminated texture and less developed evidence of leaching the rc are produced by direct interaction between the acid fumarolic aerosol and rocks and by reaction of dews and rains acidified by the absorption of acid gases so2 hcl hf of the fumarole plume with volcanic material proximal rc are produced at conditions of ph 2 distal rc form at ph 2 3 based on the presence of jarosite although the occurrence of goethite in some samples suggests higher values of ph the influence of the volcanic plume in the development of these rc is indicated also by the coincidence of the rc areal distribution with the distribution of the volcanic plume controlled by the local wind field this is furthermore supported by the presence in rc of chloride and or sulphur bearing compounds enriched in volatile elements and metals commonly carried by volcanic aerosols

glacial lake agassiz the northwestern outlet and paleoflood valley morphology and sediment in the fort mcmurray region of alberta indicate that a catastrophic flood discharged down the lower clearwater and athabasca river valleys 9900 yr b p geomorphic and chronologic evidence suggests that glacial lake agassiz emerson phase was the probable water source as the flood incised a drainage divide located near the alberta saskatchewan border the level of glacial lake agassiz decreased by 46 m discharged 2 4 x 106 m3 s for at least 78 days and stabilized at 438 m above sea level in the lake wasekamio area at that time water entered the arctic ocean via glacial lake mcconnell and the mackenzie river rather than the gulf of mexico via the mississippi river as previously thought such a large influx of fresh water 8 6 km3 h into the arctic at the close of the last glaciation may have had an abrupt major influence on northern climate

a detailed lake level reconstruction shows evidence for two abrupt lake drawdowns in the late stage history of the eastern lake agassiz ojibway basin abstract glacial lake ojibway occupied large areas in northeastern ontario and northwestern quebec during the last deglaciation paleogeographic reconstructions depict lake ojibway and lake agassiz sharing a common water plane shortly before the final drainage of this lake 8200 years ago however the pre drainage surface elevation and extent of this large coalesced lake is based on scattered raised shorelines in the ojibway basin and poorly constrained geomorphological considerations which convey large uncertainties in lake level reconstructions and the attendant meltwater volume estimates used to assess the impact of this freshwater discharge here we address this issue by using 3098 elevation measurements of shorelines mapped on a lidar digital terrain model covering a key area in the ojibway basin our reconstruction is based on a gis model integrating the paleotopography which reinforces correlation of shorelines and the identification of lake levels the spatial distribution of shoreline elevation data points shows well defined clusters of shorelines aligned on distinct elevation ranges that delineate three widespread lake levels which are separated by two intervals with atypically low number of shorelines reflecting abrupt lake drawdowns this reconstruction considerably refines the sequence in the eastern ojibway basin and shows evidence for a two step drainage of lake agassiz ojibway the results provide constraints on the magnitude of the lake level drops and indicate that the pre drainage surface elevation of lake agassiz ojibway of earlier reconstructions was likely overestimated accordingly the configuration and structure of this lake stage should be re evaluated to that effect the new shoreline record provides an important framework for assessing late stage changes in lake levels across the agassiz ojibway basin which is a critical step towards the production of realistic models depicting the drainage of this large lake

mineralogy at the magma hydrothermal system interface in andesite volcanoes new zealand ejecta from phreatomagmatic eruptions of ruapehu and white island andesite volcanoes in new zealand provide insight into the mineralogical reactions that occur when magma invades a vent hosted hydrothermal system at the surface and in ejected blocks from shallow depths hydrothermal alteration mineralogies are dominated by silica polymorphs anhydrite natroalunite and pyrite blocks from greater depths are composed mainly of cristobalite anhydrite halite and magnetite where altered material was heated to magmatic temperatures thermal decomposition reactions produced mullite wollastonite and indialite some ejected breccias contain osumilite cordierite sanidine and hypersthene indicative of reactions occurring near the osumilite cordierite phase boundary at 800 c and water pressure 0 2 kbar hedenbergite wollastonite andradite and magnetite are found in rare skarn fragments possibly formed by metasomatism of silica poor sulfate rich hydrothermal deposits high temperature parageneses of these types have not been reported before in shallow acidic volcano hydrothermal systems however they may be typical of the magma hydrothermal contact zone at many andesite volcanoes

paleohydraulics of the last outburst flood from glacial lake agassiz and the 8200 bp cold event abstract during the last deglaciation of north america huge proglacial lakes formed along the southern margin of the laurentide ice sheet the largest of these was glacial lake agassiz which formed about 11 7 14 c kyr and drained into hudson bay about 7 7 14 c kyr 8 45 cal kyr overflow from these lakes was variably directed to the mississippi st lawrence and mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events when the ice dam across hudson bay finally was breached a massive flood drained lake agassiz which was routed through hudson strait to the labrador sea in terms of stored water volume the largest reservoir was associated with the kinojevis level of lake agassiz for this maximum filling the impounded water volume available to produce floods is estimated as 40 000 151 000 km 3 depending on the location of the ice margin and route used the timing of this rapid release of stored freshwater just precedes the early holocene cooling event at 8 2 cal kyr bp we use the spring hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are 5 sv and 0 5 yr multiple fillings and floods are possible as are single floods having a complex multipulse structure modelling results suggest that the outburst flood from lake agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established connecting lake agassiz to the tyrrell sea

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

lakes of the huron basin their record of runoff from the laurentide ice sheet the 189 000 km2 hur n basin is central in the catchment area f the present q s r lanrentian great lakes that now drain via the st lawrence river to the north atlantic ocean during deglaciation from 21 7 5 ka bp and owing to the interactions of ice margin positions crustal rebound and regional topography this basin was much more widely connected hydrologi cally draining by various routes to the gulf of mexico and atlantic ocean and receiving over flows from lakes impounded north and west of the great lakes hudson bay drainage divide early ice marginal lakes formed by impoundment between the laurentide ice sheet and the southern margin of the basin during recessions to interstadial positions at 15 5 and 13 2 ka be in i each of these recessions lake drainage was initially southward to the mississippi river and gulf of mexico in the first recession drainage subsequently switched eastward along the ice margin to the north atlantic ocean in the second recession drainage continued southward through the michigan basin and later eastward via the ontario basin and mohawk river valley to the north atlantic ocean during the final retreat of ice in the huron basin from 13 to 10 ka be proglacial lake drainage switched twice from the michigan basin and the mississippi river system to the i north atlantic via the ontario basin and mohawk river valley finally diverting to the champlain sea in the st lawrence river valley at about 11 6 ka be new seismo and litbo stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines uplift histories of outlets and radio carbon dated shallow water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern huron basin for the 11 7 ka bp period negative excursions in the 8 80 isotopic composition of ostracodes and bivalves in southern lake michigan southwestern lake huron and eastern lake erie indicate an influx of water from ice marginal lake agassiz in central north america about 11 ka be a major decline in water levels of the huron basin after 10 5 ka bp followed the high level main lake algonquin phase as ice receded and drainage was established through the north bay area to ottawa river valley during the subsequent mattawa stanley phase the lake level history was dominated by fluctuations of tens of meters highstands of the earliest oscillations whose origin is not clear might be related to some of the well known post algonquin shorelines after 9 6 ka be it is suggested that large inflows from lake agassiz and hydraulic damming in downstream outlets were the likely cause of the lake mattawa highstands a lowstand at 9 3 9 1 ka bp occurred when these inflows were diverted or impeded by an ice advance in the nipigon basin area while undiluted meltwater continued to enter the huron basin assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7 5 ka be and precipitation runoff with comparatively higher dissolved solids dur ing the highstands we speculate that the water composition of the lake mattawa highstands was dom inated by the agassiz inflows by that time much of lake agassiz was remote from ice marginal envi ronments and the inflows were drawn from surface water of the southern sector of the lake which was largely supplied by runoff and dissolved solids from the exposed land area of western canada major inflows apparently ended about 8 ka be but northern proglacial lakes apparently continued as melt water persisted in the huron basin until about 7 5 ka bp the cessation of major inflows initiated the final lowstand in the huron basin and the present hydrological regime of local runoff

evolution and paleohydrology of glacial lakes barlow and ojibway abstract the evolution of lakes barlow and ojibway two large ice contact glacial lakes that covered parts of northern ontario and western quebec from about 10 1 8 0 ka bp during the retreat of the laurentide ice sheet was reconstructed using deglaciation landforms ice flow indicators inscribed on bedrock 14 c dates of early postglacial vegetation accumulated in lake basins the distribution of mysis relicta a biological indicator of lacustrine submergence varve chronology and a detailed photogrammetric survey of the lake limit although the rate of ice retreat varied greatly throughout the basin the average rate in lake barlow ojibway was 450 m year rates of ice retreat deduced from varve chronology were assessed using predictable relationships between the lake limit the shoreline gradient and the rate of relative uplift over a 590 km long profile the gradient on the maximum elevation of the lake defines a parabola that is attributed to restrained rebound although in part it could be due to the position of the profile with respect to the overall uplift pattern generated by the ice sheet the life span of the lake determined from varve chronology 2110 years shows excellent agreement with the age difference obtained between that of marine shells overlying lake ojibway sediments at its northern end in hudson bay and the oldest radiocarbon ages on basal organics in lakes in the southern part of the barlow ojibway basin both lakes drained eastward through the ottawa river between 10 1 and 8 0 ka bp and the average yearly discharge to the north atlantic ocean during the last 1000 1500 years is estimated at about 946 km 3 at break up of the ice sheet in southern hudson bay at about 8 0 ka bp lake ojibway drained abruptly releasing an estimated 114 396 km 3 of freshwater into the tyrrell sea and raising sea level by about 30 cm

water sheet outburst floods from the laurentide ice sheet field evidence and a theoretical model support the concept that during wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the hudson bay ba

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

deglaciation ages and meltwater routing in the fort mcmurray region northeastern alberta and northwestern saskatchewan canada a field based reconstruction of the deglacial paleogeography in the fort mcmurray area permits 1 constraining the timing of meltwater routing to the arctic from the present hudson bay drainage basin and 2 minimum age estimates for ice margin positions that can be used to constrain ice sheet modeling results a downslope recession of the laurentide ice sheet resulted in a series of proglacial lakes forming between the ice margin and higher land to the southwest the paleogeography of these lakes is poorly constrained in part from the masking effect of boreal forest vegetation and map scale issues however recent space shuttle based dems increase the number and spatial extent of moraines identified within the study area resulting in a coherent pattern of ice margin retreat focused on the athabasca river valley an intensive lake coring program resulted in a minimum ten fold increase in the radiocarbon database used to limit moraine ages results indicate that deglaciation in this region was younger than previously reported and it is likely that the meltwater could not drain northward to the arctic ocean from any source southeast of the fort mcmurray area until approximately 9850 9660 14 cbp

the evolution of the magmatic system of stromboli volcano during the vancori period 26 13 8 ky stratigraphic changes in bulk rock and mineral chemistry within a volcanic sequence can be used to understand the evolution of the magma storage system beneath the volcano in particular changing eruptive styles and major changes in magma chemistry can be linked to open or closed system behaviour changes in phenocryst mineral chemistry often expressed as core rim zonation patterns or the development of reaction rims combined with thermodynamic analysis of appropriate mineral equilibria can provide powerful insights into the timing of inputs of new more primitive magma the vancori period 26 13 8 ky of the eruptive activity of stromboli has a relatively simple stratigraphy comprising three sub periods lower middle and upper vancori each one beginning and ending with an explosive volcanic event marked by breccias electron microprobe analyses of phenocryst and groundmass minerals olivine clinopyroxene plagioclase fe ti oxides in representative samples from the lower middle and upper vancori phases of activity allow tracking of the evolution of the magma chamber system with time thermodynamic analysis of olivine clinopyroxene mineral equilibria is used to constrain changes in temperature within the magmatic system the main stratigraphic discontinuities within the vancori sequence are clearly reflected by changes in bulk rock and mineral chemistry and evidence of textural and thermodynamic disequilibrium calculated temperatures in the eruptive products on the basis of these data the lower and middle vancori periods of the eruptive history of stromboli appear to be characterised by an open magma chamber system repeatedly re filled with basaltic magma which was continuously being erupted at the end of the middle vancori period the system became closed corresponding to a period of dormancy of the volcano and fractional crystallisation dominated following a major flank collapse of the volcanic edifice the upper vancori eruptive products show the most extreme range in bulk rock chemistry as the chamber was progressively flushed with new basaltic magma d 2005 elsevier b v all rights reserved

lake agassiz final drainage event in the northwest north atlantic 1 the 8 2 ka climate event recorded in greenland ice cores is subject of debates with respect to causal linkage with a collapse of the atlantic meridional overturning due to the drainage of the late glacial lake agassiz here we present records from the nw north atlantic down current the flood discharge route showing that the 9 5 8 ka interval was marked by a succession of events the drainage itself corresponds to a twin layer of carbonate rich turbidites deposited within the calibrated 8 35 8 5 ka interval proxies of sea surface and deep current conditions do not indicate significant concomitant changes in the nw north atlantic the dataset however supports the concept that the 8 2 ka climate event may represent one of the manifestations of climate instability during an interval with major changes of land drainage in ne america due to the collapse of the laurentide ice sheet subsequent fast sea level rise and large scale reorganization of the north atlantic thermohaline circulation pattern

refining the glacial lake coverage of the southern laurentide ice margin using lidar dem based reconstructions the case of lake obedjiwan in south central quebec canada abstract the existence of former glacial lakes remains poorly documented in the remote regions of the canadian shield where the dense forest cover and poor access complicate classical mapping methods here we use a high resolution digital elevation model dem 1 m pixel based on lidar data to map quaternary deposits and landforms in the vicinity of the gouin reservoir in the laurentian highlands of quebec canada a total of 598 raised shorelines were identified providing new evidence for the presence of a large proglacial lake lake obedjiwan that formed in front of the northward retreating laurentide ice sheet margin during the last deglaciation a few kilometers east of the larger lake ojibway that covered extensive areas in northern ontario and quebec the elevation of shorelines outlines a tilted water plane that depicts the influence of the glacio isostatic adjustment across the basin with shorelines ranging from 409 m in the south to 439 m in the north the calculated uplift gradient of 0 78 m km indicates that the lake developed during the early stages of the deglaciation our reconstruction constrains the full areal extent and maximum elevation of the lake which covered an area of 1800 km2 and reached an elevation of 450 m it also indicates that lake obedjiwan developed independently from lake ojibway the lake surface elevation was controlled by an outlet located in the southeastern part of the basin where a topographic depression lying at an elevation of 390 m routed meltwater overflow southward through the saint maurice river and into the st lawrence river another important outlet is located in the northernmost part of the basin and ice retreat beyond this topographic depression 427 m caused the drawdown of the lake obedjiwan which drained westward into lake ojibway this discharge added around 19 km3 of meltwater an event that likely impacted the hydrological budget and sedimentology of lake ojibway the results suggest that other glacial lakes probably developed along the southern lis ice margin and that the approach developed in this study may contribute to the refinement of their areal coverage and improve paleogeographic reconstructions

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

armalcolite bearing fe ti oxide assemblages in graphite equilibrated salic volcanic rocks with native iron from disko central west greenland native iron bearing strongly sediment contaminated andesitic to dacitic lavas from the malig t formation on disko contain an early phenocryst assemblage of plagioclase low ca pyroxene s and ilmenite the phenocrystic ilmenite has reacted to form complex fe ti oxide metal sulphide aggregates which contain one or more of the oxides ilmenite armalcolite and rutile the armalcolite is very similar to the lunar type 1 armalcolite of haggerty 1973 and approximate compositionally the ternary system feti2o5 mgti2o5 ti3o5 92 to 97 mol when evidence from several salic rocks is combined the fe ti oxide metal sulphide aggregates display reactions which may represent one isobaric invariant assemblage ilmenite armalcolite rutile iron and the 3 boundary univariant reactions in the system fe ti o the compositional and textural features of ferro magnesian silicates oxides and metals show that most rocks were affected by a rapidly declining fo2 during magma ascent and cooling as displayed in the fe ti oxide metal sulphide aggregates by the cross cutting of one or several t fo2 buffer curves in the system fe ti o prominent sulphidation reactions are observed in the oxide aggregates and are always of the type where feo in oxide is replaced by fes while the liberated oxygen is consumed in a reduction process carbon bound as graphite or cohenite occurs throughout the rocks and is mostly enclosed in phenocrysts and xenocrysts when the salic magmas ascended from pre eruption reservoirs at 1 to 1 5 kb the reduction was largely controlled by strongly pressure dependent carbon oxygen equilibria resulting in rapidly declining t fo2 paths recorded by the oxide assemblages in the simplified c o gas system carbon barometry sato 1979 applied to the selected rocks would indicate final equilibrium pressures of between 10 and 100 bars the scarcity of preserved graphite in the lavas would suggest that the carbon controlled reductions were terminated when available carbon was exhausted during the magma ascent and solidification

complex responses of phototrophic communities to climate warming during the holocene of northeastern ontario canada historical changes in holocene climate in northeastern ontario were quantified using analyses of sedimentary pollen diatoms and pigments in a small boreal lake modern analog reconstructions of a

chlorine rich pyrometamorphic magma at white island volcano new zealand abstract the 25 january 1987 phreatomagmatic eruption of congress vent on white island volcano ejected paralava bombs derived from pockets of pyrometamorphic magma the current white island magmas are calc alkaline basaltic andesite andesite but the paralavas are mostly highly peralkaline with molar na 2 o k 2 o al 2 o 3 ratios from 1 to 22 recorded in matrix glasses the glass compositions are highly variable though quench crystals of tridymite wollastonite and green clinopyroxene are ubiquitous while albite occurs only in the least peralkaline samples all have high alkali contents na 2 o k 2 o 10 and chlorine mostly 1 and up to 1 7 the paralava glasses represent the most cl rich volcanic melts yet discovered they display a strong positive correlation between cl and total fe but a negative correlation between cl and normative alkali feldspar content it is likely that the fe content of melts was the dominant control over cl solubility not their alumina alkali systematics possible parent rocks for the pyrometamorphic magmas include halite cemented crater lake sediments and acid sulfate hydrothermally altered vent breccias and tuffs as found in the eruption deposits together with the paralava bombs fusion probably occurred at temperatures between 830 and 1000 c and at a pressure below 5 mpa in a regime where silicate melts were buffered by immiscible nacl saturated aqueous vapor and hydrosaline melt the conditions required to form the paralava bombs appear to be uncommon but it is likely that similar pyrometamorphic melts could be generated at many volcanoes where shallow magma penetrates a hydrothermal system

complex interaction of aluminous metasedimentary xenoliths and siliceous magma an example from mt amiata central italy aluminous silica deficient metasedimentary xenoliths in siliceous lavas of mt amiata have preserved composite zoning patterns indicative for complex processes of magma rock interaction petrographic observations and small scale mineralogical and chemical differences between up to five distinct zones including the core and envelope of lava provide evidence that quartz poor muscovite biotite schists are considered to be the most likely parent rocks and it is believed that release of volatiles from decomposing micas played a significant role in the high temperature metamorphic evolution of the xenoliths and their interaction with the magma the conditions favourable for assimilation were enhanced by injection of mafic magma into the magma chamber although this concurrent operation of magma mixing precludes a quantitative estimate of contamination from the wall rocks which was probably of minor importance the present example indicates that dry acid magma may potentially become more mafic by interaction with partially melted hydrous rocks

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

mafic and ultramafic xenoliths in san bartolo lava field new insights on the ascent and storage of stromboli magmas mafic and ultramafic xenoliths are well represented within a large basaltic lava field of stromboli these basalts known as san bartolo lavas show a high k calc alkaline hkca affinity and were erupted 5 ka bp xenoliths consist of olivin gabbro gabbronorite anorthosite dunite wehrlite and clinopyroxenite thermobarometric estimates for the crystallization of gabbroic materials show minima equilibration pressures of 0 17 0 24 gpa at temperatures ranging from 940 to 1 030 c these materials interacted with hydrous ascending hkca basaltic magmas with temperatures of 1 050 1 100 c at pressures of about 0 2 0 4 gpa these pressure regimes are nearly identical to those found for the crystallization of phenocrystic phases within hkca basaltic lavas gabbroic inclusions are regarded as cumulates and represent crystallized portions of earlier hkca strombolian basalts

postglacial paleoceanography of hudson bay stratigraphic microfaunal and palynological evidence cores containing representative sequences of postglacial sediments in northern and southern hudson bay were analyzed for their microfaunal foraminifers and ostracods and palynological dinocysts