constraints from 40ar 39ar geochronology on the tectonothermal history of the kapuskasing uplift in the canadian superior province the kapuskasing uplift ku in the superior province of the canadian shield has been interpreted as an oblique cross section through the archean mid crust however the time of juxtaposition of the granulites of the ku against the lower grade rocks of the abitibi greenstone belt agb along the ivanhoe lake fault zone is problematic to constrain the postmetamorphic tectonothermal history of the ku we have conducted 57 40ar 39ar step heating analyses on mineral and rock samples collected in a transect across the southern ku and adjacent agb the age spectra record a complex thermal history amphiboles from the agb in the footwall of the ivanhoe lake fault zone have ca 2 66 ga dates similar to closure ages for amphiboles from farther east in the agb amphibole dates of 2 46 2 52 ga from the deepest structural levels of the ku place an upper limit on the time of major uplift of the granulites and their juxtaposition with the agb biotite and muscovite dates from the transect cluster into three age groups

intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

on the significance of aqueous fluid inclusions in gold bearing quartz vein deposits from the southeastern abitibi subprovince quebec canada fluid inclusions have been studied in a quartz epidote actinolite vein within a proterozoic diabase dike crosscutting the donalda 1 gold bearing quartz vein near noranda quebec two types of fluid inclusions were recognized the first type is represented by two phase aqueous fluid inclusions characterized by low eutectic 200dgc temperatures the second type is represented by two or three phase or solid aqueous fluid inclusions characterized by low eutectic 2 o co 2 and co 2 fluid inclusions in archean gold bearing quartz veins of the southeastern abitibi belt and has a chemical composition ca na cl bearing with variable salinity comparable to that of brines and ground waters found in the superior province this study demonstrates that these low t h aqueous fluids showing variable salinity are unrelated to gold deposition but should rather be correlated with younger brines and ground waters which percolated downward in the continental crust in these gold bearing quartz veins only the high t h aqueous fluids may be linked to gold bearing fluids

submarine silicic caldera at the front of the izu bonin arc japan voluminous seafloor eruptions of rhyolite pumice myojin knoll caldera a submarine rhyolitic center 400 km south of tokyo is one of nine silicic calderas along the northern 600 km of the izu bonin ogasawara arc and the first anywhere to receive detailed submersible based study the caldera slightly smaller than the crater lake structure in oregon is 6 7 km in diameter its inner walls are 500 900 m high and it has a remarkably flat floor at 1400 m below sea level mbsl the caldera collapse volume is 18 km 3 suggesting that more than 40 km 3 of pumiceous tephra may have been erupted at the time the caldera formed precaldera seafloor eruptions built a broad volcanic edifice consisting of overlapping composite volcanoes made of rhyolitic lavas shallow intrusions and a variety of volcaniclastic deposits including thick accumulations of rhyolitic pumice erupted at 900 500 mbsl the caldera forming eruption produced a 150 200 m deposit of nonwelded fines depleted pumice that resembles a colossal layer of popcorn at the top of the caldera wall freshly erupted pumice behaved as sinkers or floaters depending on the environment in which it cooled the pumice clasts deposited proximally and exposed in the caldera wall were likely quenched in eruption columns that remained below sea level this pumice ingested seawater and sank as gases filling its vesicles cooled particularly as steam in its vesicles condensed to liquid water some eruption columns may have broken through the sea surface and entered the air especially during vigorous phases of the caldera forming eruption these pumices had the opportunity to ingest air as they cooled becoming floaters as they fell back to the sea these could have been carried distally on the sea surface by the combined effects of ocean currents and wind the age of the caldera is unknown but it may be as young as several thousand years its magmatic system at depth retains sufficient heat to sustain an actively growing intracaldera kuroko type polymetallic sulfide deposit rich in gold and silver and topped by chimneys emitting fluids as hot as 278 c sufficient time has elapsed however for a 250 m high postcaldera dome to grow on the caldera floor and for the caldera rim to be deeply scalloped by slumping

rb sr ages of late archean metavolcanics and granites dharwar craton south india and evidence for early proterozoic thermotectonic event s abstract the archean greenstone sequence of the dharwar craton is intruded by late and post kinematic granites like the chitradurga and toranagallu closepet granites with whole rock rb sr isochron ages of 2603 28 ma 2 and 2452 50 ma respectively the whole rock rb sr ages of their host metavolcanic rocks show a wide variation bababudan 2728 102 ma shimoga 2520 62 ma ingaldhal 2240 50 ma mardihalli 2160 174 ma gadag 2456 76 ma and sandur 2377 646 ma while the ages of the bababudan and the shimoga volcanic suites can be related to the time of the pervasive regional folding and metamorphic events 2 7 2 6 ga those of the other volcanic suites from the chitradurga and sandur supracrustal belts indicate effects of post archean thermal event s the internal isochron ages of 2 0 0 1 ga for the chitradurga and toranagallu granites suggest isotopic resetting on a mineral scale about 500 ma after their emplacement and support the evidence from the metavolcanic suites for an early proterozoic thermal event at 2 0 ga in the dharwar greenstone granite gneiss terrain

subduction influence on magma supply at the east scotia ridge despite a spreading rate of 65 70 km ma 1 the east scotia ridge has along most of its length a form typically associated with slower rates of sea floor spreading this may be a consequence of cooler than normal mantle upwelling which could be a feature of back arc spreading at the northern end of the ridge recently acquired sonar data show a complex rapidly evolving pattern of extension within 100 km of the south sandwich trench new ridge segments appear to be nucleating at or near the boundary between the south american and scotia sea plates and propagating southwards supplanting older segments the most prominent of these north of 56 30 s has been propagating at a rate of approximately 60 km ma 1 for at least 1 ma and displays a morphology unique on this plate boundary a 40 km long axial high exists at the centre of this segment forming one of the shallowest sections of the east scotia ridge beneath it seismic reflection profiles reveal an axial magma chamber or amc reflector similar to those observed beneath the east pacific rise and valu fa ridge simple calculations indicate the existence here of a narrow 1 km wide body of melt at a depth of approximately 3 km beneath the sea floor from the topographic and seismic data we deduce that a localised mantle melting anomaly lies beneath this segment rates of spreading in the east scotia sea show little variation along axis hence the changes in melt supply are related to the unique tectonic setting in which the south american plate is tearing to the east perhaps allowing mantle flow around the end of the subducting slab volatiles released from the torn plate edge and entrained in the flow are a potential cause of the anomalous melting observed a southward mantle flow may have existed beneath the axis of the east scotia ridge throughout its history

sonar studies of submarine mass wasting and volcanic structures off savaii island samoa sidescan sonar observations show that mass wasting plays an important role in the geologic development of the savaii island edifice observations on the south and west flanks indicate that debris movement on the submarine slopes between rift zones is characterized by large sheets of unchannelized debris farther downslope these sheets have slumped into folded although still relatively coherent slump sheets closer to the rift zones more chaotic slumps are found the presence of large detached landslide blocks without obvious upslope headwall scarps suggests that earlier slumps are covered by subsequent veneers of debris moving downslope in contrast on stearns bank west of the island of savaii most of the features are of constructional origin formed during the building of this volcanic edifice of unknown age two prominentsubmarine platforms are evident the shallower one with a summit cone sea cliffs and subdued terraces record platforms cut by sea level oscillations late in the history of the volcanic edifice fractures and fissures are present on the bank however there is little evidence of landslides in this area the absence of landslides may reflect differing ages of the bank and the island or the edifice could have remained submarine during its construction with few or no subaerially derived ashes and clays present to facilitate mass wasting we conclude that mass wasting is an important influence on the evolution of the savaii volcanic edifice it appears that sediment and debris cover most of the slope outside the submarine rift zones the sonar images indicate that mass wasting is a common process in the submarine environment unlike the giant landslides documented by gloria imagery around the hawaiian islands the southern margin of samoa is characterized by numerous small slumps and slides although we have little information at present regarding the recurrence interval for submarine landslides their ubiquitous presence in these sidescan sonar records indicates that they are an important component of the geologic record of the samoan islands

early proterozoic deformation in the western superior province canadian shield late archean granitic plutons 2700 to 2665 ma u pb zircon of the superior structural province are cut by a variety of brittle discontinuities including joints fractures and faults the latter of which show evidence of cataclasis and meter to tens of meters displacements fluid circulation alteration of wall rocks and neomineralization of epidote actinolite and chlorite occurred under greenschist facies conditions in these structures at the time of their formation the rb sr ages of host rocks are 2650 ma and the fracture zone materials are 2300 ma indicating that most of this activity occurred long after archean plutonism and was concentrated in early proterozoic time the brittle structures formed in response to horizontal compression on a regional scale possibly caused by tectonic processes at margins of the craton the structures are seen as important clues to the tectonic evolution of the superior province

a kuroko type polymetallic sulfide deposit in a submarine silicic caldera manned submersible studies have delineated a large and actively growing kuroko type volcanogenic massive sulfide deposit 400 kilometers south of tokyo in myojin knoll submarine caldera the sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters has an area of 400 by 400 by 30 meters and is notably rich in gold and silver the discovery of a large kuroko type polymetallic sulfide deposit in this arc front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

litho structural layering within the archean lac du bonnet batholith at aecl s underground research laboratory southeastern manitoba abstract the lac du bonnet batholith ldbb is one of many late to post tectonic granites in the western superior province which appear to be compositionally homogeneous and structurally simple on the surface however mapping in the 443 m deep access shaft at the underground research laboratory url borehole logs and detailed surface mapping clearly demonstrate that decametre scale layering is widespread in the ldbb individual layers or litho structural domains are distinguished by the type and abundance of xenoliths and late residual or metasomatic segregations by auto intrusive contacts and by variations in style and orientation of mesoscopic fabric the litho structural domains are inconspicuous at surface due to their low dip and the flat topography however detailed mapping in the central part of the url has identified their surface expression as a series of broad and open domes and intervening saddles the litho structural domains host three systems of auto intrusive dykes sills and recrystallized zones whose abundance and mode of occurrence change with depth late magmatic granodioritic dykes are the predominant rock type below 300 m depth at the url but the swarm narrows rapidly up dip and at surface is represented only by narrow zones of alteration and ductile deformation late pegmatite aplite dykes are pervasive across all rock types at surface but are limited to the larger granodiorite dykes at 420 m depth at the url the distribution of inclusions alteration and fractures in the ldbb suggest the present topographic surface is close to the original roof zone of the batholith

discovery of a recurrent lava lake on saunders island south sandwich islands using avhrr imagery abstract monitoring of the remote south sandwich islands volcanic arc using advanced very high resolution radiometer avhrr data has identified a radiant pixel on channels 3 3 55 3 93 m and rarely 4 10 3 11 3 m the position of the pixel is coincident with mount michael saunders island the active summit crater of a snow covered basaltic stratovolcano with a persistent steam plume the radiant pixel was continuously present in successive avhrr images acquired during intervals of several months in the period examined march 1995 february 1998 although apparently disappearing for similar time intervals more than 5000 images were examined during this study the radiant pixel is interpreted to indicate that the crater has contained a lava lake the first to be recorded in the south sandwich islands the lake appears to persist in the crater for several months at a time at least it may have drained completely at times and was probably absent when the crater was viewed briefly during an overflight in january 1997 persistent or recurring lava lakes are very uncommon world wide and that at mount michael is one of only two recorded in the antarctic region

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

proterozoic reactivation of the southern superior province and its role in the evolution of the midcontinent rift major reverse faults associated with the late compressional phase of the 1 1 ga midcontinent rift in the western lake superior region appear to cut across the rift at the eastern end of the lake and join with reverse faults on the eastern shoreline defined on the basis of geological and potential field data the continuation of the faults across eastern lake superior is inferred on evidence drawn from nearshore shipborne magnetic surveys together with new interpretations of published bathymetric and glimpce aeromagnetic data in the archean superior province about 100 km east of lake superior paleomagnetic and petrographic data from the 2 45 ga matachewan dyke swarm show that the kapuskasing zone a narrow belt of uplifted crust can be extended to within 50 km of the lake superior shoreline and has bounding reverse faults that are almost continuous with two faults of similar dip and sense of displacement that define the inversion of the midcontinent rift in the central and western parts of the lake si

volcanic geomorphology and tectonics of the aeolian archipelago southern italy based on integrated dem data the geomorphological and morphometric analysis of the sea floor topography surrounding the aeolian islands south tyrrhenian sea italy provides insights into the relationships between the volcanological evolution of the islands and their tectonic features we constructed geomorphological maps of the submarine portions of the seven large edifices constituting the islands on the basis of a dem with a 5 m resolution step these maps include constructional and destructional landforms such as submarine volcanic vents located west of lipari and north of alicudi and hummocky surfaces recognised north of lipari and salina the latter landforms together with the occurrence of large scars affecting the main edifices on land suggest that sector collapses affected some islands geomorphological data indicate that the location of subaerial and submarine vents is strongly controlled by local tectonic structures striking wnw ese alicudi filicudi sector nnw sse salina lipari vulcano sector and ne sw panarea stromboli sector the islands can be divided into two groups on the basis of some morphometric parameters a first group with a pancake like shape dp d abrasion platform diameter basal diameter higher than 0 40 and h d total height basal diameter lower than 0 13 and a second group with a conical shape characterised by dp d lower than 0 34 and h d higher than 0 14 these ratios and other morphometric parameters reflect the different volcanological and structural evolution of the aeolian islands the pancake like shaped complexes have been created in addition to their submarine stage by extrusive and highly explosive activity whereas the cone shaped edifices have been characterised by effusive or moderate explosive activity

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

contrasting responses of rb sr systematics to regional and contact metamorphism laramie mountains wyoming usa archean supracrustal sequences of pelitic quartzitic calcareous and mafic compositions in the central laramie mountains wyoming have been affected by two metamorphic events a 1 78 ga amphibolite grade regional metamorphism and a 1 43 ga contact metamorphism resulting from the intrusion of the laramie anorthosite complex lac rb sr whole rock isotopic data from both outside and within the lac contact aureole define a linear array that lies along a 1 78 ga isochron this date has been independently established as the time of amphibolite facies regional metamorphism associated with collision of the archean wyoming province and the proterozoic colorado province along the cheyenne belt the rb sr isotopic data require that sr was redistributed during regional metamorphism on a scale of at least tens of metres although within the 2 km wide aureole of lac the pelitic rocks were thermally metamorphosed at temperatures greater than 800 c none of the whole rock rb sr data from samples within the lac aureole show evidence of resetting at 1 43 ga it is interpreted that the regional metamorphism involved fluid transport which facilitated sr isotopic resetting whereas the contact metamorphism occurred in a relatively dry environment in which isotopic mobility was restricted to centimetre scale or less rb sr data for biotite feldspar and whole rock from a regional metamorphosed pelitic schist give an isochron age of 1450 40 ma which is interpreted as a cooling age resulting from crustal uplift rb sr data for biotite quartz feldspar and whole rock from a pelitic schist affected by contact metamorphism give an isochron age of 1420 43 ma the time of isotopic re equilibration in response either to crustal uplift or to both contact metamorphism and crustal uplift this study demonstrates that although the response of isotopic systems to metamorphism is complex isotopic data provide insight into metamorphic processes that is difficult to obtain by other means

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

growth and mass wasting of volcanic centers in the northern south sandwich arc south atlantic revealed by new multibeam mapping new multibeam swath bathymetric sonar data acquired using an em120 system on the rrs james clark ross supplemented by sub bottom profiling reveals the underwater morphology of a not vert similar 12 000 km2 area in the northern part of the mainly submarine south sandwich volcanic arc the new data extend between 55 45 s and 57 20 s and include protector shoal and the areas around zavodovski visokoi and the candlemas islands groups each of these areas is a discrete volcanic center the entirely submarine protector shoal area close to the northern limit of the arc forms a 55 km long east west trending seamount chain that is at least partly of silicic composition the seamounts are comparable to small subaerial stratovolcanoes in size with volumes up to 83 km3 indicating that they are the product of multiple eruptions over extended periods zavodovski visokoi and the candlemas island group are the summits of three 3 3 5 km high volcanic edifices the bathymetric data show evidence for relationships between constructional volcanic features including migrating volcanic centers structurally controlled constructional ridges satellite lava flows and domes and mass wasting of the edifices mass wasting takes place mainly by strong erosion at sea level and dispersal of this material along chutes probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields large scale mass wasting structures include movement of unconsolidated debris in slides slumps and debris avalanches volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical being steep with abundant recent volcanism on their western flanks and gently sloping with extinct eroded volcanic sequences to their east this is consistent with the calculated rate of subduction erosion of the fore arc

structural analysis of the miniss river and related faults western superior province post collisional displacement initiated at terrane boundaries mountain building in the western part of the archean superior province culminated with the formation of regional strike slip faults this paper reports on the kinematics and timing of several major faults at the juncture between the uchi english river winnipeg river and western wabigoon subprovinces sinistral oblique mylonitization along the northeast striking miniss river fault occurred at 2681 ma this involved 40 km of sinistral offset and a scissor like motion whereby vertical displacement increased southwestward toward a restraining bend near sioux lookout to the north the miniss river fault is intersected by the east striking dextral strike slip sydney lake lake st joseph fault the latter merges along strike with the pashkokogan fault restoration of respective displacements indicates that the faults formed sequentially not simultaneously in response to tectonic indentation dextral strike slip motion along the sydney lake lake st joseph pashkokogan fault was instigated at 2670

first recorded eruption of mount belinda volcano montagu island south sandwich islands the modvolc satellite monitoring system has revealed the first recorded eruption of mount belinda volcano on montagu island in the remote south sandwich islands here we present some initial qualitative observations gleaned from a collection of satellite imagery covering the eruption including modis landsat 7 etm aster and radarsat 1 data modvolc thermal alerts indicate that the eruption started sometime between 12 september and 20 october 2001 with low intensity subaerial explosive activity from the island s summit peak mount belinda by january 2002 a small lava flow had been emplaced near the summit and activity subsequently increased to some of the highest observed levels in august 2002 observations from passing ships in february and march 2003 provided the first visual confirmation of the eruption aster images obtained in august 2003 show that the eruption at mount belinda entered a new phase around this time with fresh lava effusion into the surrounding icefield modis radiance trends also suggest that the overall activity level increased significantly after july 2003 thermal anomalies continued to be observed in modis imagery in early 2004 indicating a prolonged low intensity eruption and the likely establishment of a persistent summit lava lake similar to that observed on neighboring saunders island in 2001 our new observations also indicate that lava lake activity continues on saunders island

keel depths of modern antarctic icebergs and implications for sea floor scouring in the geological record abstract icebergs affect the geological record through the scouring or ploughing action of their keels reworking sediments where they contact the sea floor satellite radar altimeter measurements of the surface elevation of the marine margins of the antarctic ice sheet are inverted to produce ice thickness values these data are assumed to represent the keel depths of newly calved icebergs there are three peaks in the frequency distribution of antarctic iceberg keel depths a about 140 200 m in thickness associated with smaller ice shelves fringing antarctica e g wilkins george vi and brunt ice shelves b about 250 300 m from large ice shelves e g ross ronne amery and c approximately 500 600 m from fast flowing ice sheet outlet glaciers e g pine island and dibble glaciers together with the filchner ice shelf controls on iceberg keel depth are ice thickness at the grounding line creep thinning and the rate of melting freezing at the floating ice shelf base with distance to the calving margin the distribution of sea floor scours produced by iceberg grounding is dependent on the changing form and flow of the glaciers and ice sheets from which icebergs are derived and on berg drift tracks and melt rates sea floor evidence for icebergs with particularly deep keels has sometimes been interpreted to indicate the presence of extensive former ice shelves however the largest modern antarctic ice shelves do not produce large numbers of icebergs thicker than about 350 m implying that sea floor scours found in deeper water are unlikely to be an indicator of extensive past ice shelf development iceberg scours found at water depths in excess of about 500 m in the geological record are instead probably indicative of either a the former presence of fast flowing ice sheet outlet glaciers b ice shelves fed from major interior basins where lateral spreading is constrained topographically or c a pulse of large icebergs released during major deglaciation or ice sheet collapse

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

submarine geology of hana ridge and haleakala volcano s northeast flank maui abstract we present a morphostructural analysis of the submarine portions of haleakala volcano and environs based upon a 4 year program of geophysical surveys and submersible explorations of the underwater flanks of hawaiian volcanoes that was conducted by numerous academic and governmental research organizations in japan and the u s and funded primarily by the japan agency for marine earth science and technology a resulting reconnaissance geologic map features the 135 km long hana ridge the 3000 km 2 hana slump on the volcano s northeast flank and island surrounding terraces that are the submerged parts of volcanic shields hana ridge below 2000 m water depth exhibits the lobate morphology typical of the subaqueously erupted parts of hawaiian rift zones with some important distinctions namely subparallel crestlines which we propose result from the down rift migration of offsets in the dike intrusion zone and an amphitheater at its distal toe where a submarine landslide has embayed the ridge tip deformation of haleakala s northeast flank is limited to that part identified as the hana slump which lies downslope from the volcano s submerged shield indicating that flank mobility is also limited in plan inconsistent with hypothesized volcanic spreading driven by rift zone dilation the leading edge of the slump has transverse basins and ridges that resemble the thrust ramps of accretionary prisms and we present a model to describe the slump s development that emphasizes the role of coastally generated fragmental basalt on gravitational instability of haleakala s northeast flank and that may be broadly applicable to other ocean island slumps

presence of large pumice blocks on tierra del fuego and south shetland islands shorelines from 1962 south sandwich islands eruption abstract we report on the source of pumice found on beaches of tierra del fuego argentina and the south shetland islands antarctica north and south of the drake passage petrological studies chemical analyses and experiments on this pumice indicate it is most likely from a 1962 submarine eruption in the south sandwich islands previous work stated that clockwise marine currents carried such pumice as far as tasmania our findings show that the currents continued to transport the pumice to drake passage nearly completing a circuit around antarctica and up to southern argentina showing that this material can follow complex pathways for more than 20 000 km

the role of fluids during formation and evolution of the southern superior province lithosphere an overview models for fluid flow and hydrothermal alteration for the abitibi greenstone belt are reviewed in the light of lithoprobe results in the region in the abitibi greenstone belt eruption of volcanic sequences over 2750 2700 ma was accompanied by pervasive low temperature hydrothermal alteration at high water rock ratios giving systematic 18o enrichment archean ambient ocean water bottom temperatures were likely ca 30 c and 18o 0 1 chert iron formations precipitated from low temperature hydrothermal discharge base metal massive sulphide deposits formed at or near the seafloor from focussed discharge of high temperature 300 400 c fluids in convective cells sited above subvolcanic intrusions the ore fluids were evolved seawater that had undergone compositional and isotopic evolution by high temperature low water rock exchange with the volcanic pile to nacl 3 7 wt or cacl2 nacl up to 30 wt brines of 18o 0 8 these volcanic associated hydrothermal deposits are associated with greenst

the stromboli 2002 tsunamigenic submarine slide characteristics and possible failure mechanisms 1 on 30 december 2002 a major instability event deeply involving the submarine slope occurred on the sciara del fuoco on the western flank of stromboli volcano in the aeolian islands tsunami waves with a maximum runup of over 10 m in stromboli were generated having a measurable impact as far as the sicily coast just 10 months before the event a multibeam bathymetry had been collected in the area down to 1000 m of depth a repetition of the survey after the slide allowed the unique opportunity to verify the occurrence of a large submarine slide and to define volumes involved and morphology generated by the event through the comparison of the preevent and postevent bathymetric grids a morphological characterization of the slope before and after the submarine landslide is presented showing how the preexisting features interacted with the slide event in controlling the instability mechanisms of the submarine failure are discussed on the basis of the geometrical characters of the landslide event structural and stratigraphic setting of the submerged slope and geotechnical considerations on the behavior of slope material

the 1741 oshima oshima eruption extent and volume of submarine debris avalanche oshima oshima is a small volcanic island southwest off hokkaido in japan sea the violent eruption on august 29 1741 caused a sector collapse of the north flank very destructive tsunami with 2000 casualties was also documented but the generation mechanism has been controversial volume of subaerial sector collapse about 0 4 km was considered too small to generate such a devastating tsunami we compile and analyze recently obtained swath bathymetry data around the island the volcano is more than 2 3 km high from ocean bottom with its base diameter of 18 km the total slide volume both subaerial and submarine is estimated as 2 4 km nearly an order of magnitude larger than the subaerial part to the north of island hummocky terrain of debris deposits extends in an area of 69 km with the total volume of 2 5 km a value similar to the total slide volume it is one of the largest debris avalanches in historic time and probably responsible to the tsunami generation

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

sedimentary volcanic and tectonic processes of the central mariana arc mariana trough back arc basin formation and the west mariana ridge 1 we present new multichannel seismic profiles and bathymetric data from the central marianas that image the west mariana ridge wmr remnant arc both margins of the mariana trough back arc basin the modern arc and eocene frontal arc high these data reveal structure and stratigraphy related to three periods of arc volcanism and two periods of arc rifting we interpret the boundary between accreted back arc basin and rifted arc crust along the mariana trough and support these findings with drilling results and recent seismic refraction and gravity studies we show that with the exception of a few volcanoes behind the volcanic front that straddle the boundary between crustal types the modern mariana arc is built entirely on rifted arc crust between 14 and 19 n our data indicate that there is more accreted back arc seafloor to the west of the mariana trough spreading axis than to the east confirming previous evidence for an asymmetric basin the rifted margin of the wmr remnant arc forms a stepped pattern along the western boundary of the mariana trough between 15 30 and 19 n in this region linear volcanic cross chains behind the wmr are aligned with the trend of mariana trough spreading segments and the wmr ridges extend into the back arc basin along the same strike these ridges are magmatic accommodation zones which to the north along the izu bonin arc punctuate tectonic extension for the wmr we hypothesize that rift basins are more commonly the sites where spreading segment offsets nucleate whereas magmatic centers of spreading segments are sites where magmatism continues from arc volcanism through rifting to back arc spreading the mariana trough is opening nonrigidly and is characterized by two predominant abyssal hill trends nnw sse in the north and n s in the south between the only two basin crossing fracture zones at 15 5 and 17 5 n s axes propagated north at the expense of nnw axes

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

compositional controls on 40 ar 39 ar ages of zoned mica from a rare element pegmatite a high spatial resolution ar ar dating study of compositionally zoned micas using uv laser extraction has been used to investigate the effect of composition and compositional boundaries upon argon diffusion in mica the crystals are characterised by muscovite cores and li f rb cs rich lepidolite rims produced by the interaction of a residual melt vapour phase with the original muscovite during the late stages of pegmatite crystallisation single crystals exhibit dramatic intra grain age variations with a maximum range of 2 880 2 117 ma backscattered electron images combined with uv laser analyses reveal that apparent ages younger than 2 600 ma are directly associated with the compositionally distinct rims suggesting that ar diffusion was faster in the lepidolite than in muscovite although it is not possible to be fully quantitative using the present data it seems that argon diffusion rates in lepidolite are similar to those in biotite major rearrangements of the crystal structure needed to accommodate high concentrations of lithium fluorine and large interlayer cations rb cs in muscovite account for lower argon retentivity of the crystal rims in most cases the age profiles show no disturbance at the compositional boundary despite the transition from a di octahedral to tri octahedral mica indicating that in general the boundaries do not act as fast diffusion pathways however in some cases there is a clear drop in ages at the compositional boundary which acts as an effective sub grain boundary the difference between the two types may be related to the internal structure of the compositional boundaries or their degree of contact with the grain boundary network of the rock

generation and migration of coarse grained sediment waves in turbidity current channels and channel lobe transition zones large scale sediment waves composed of gravels and sands have been studied using deep water sidescan systems new data are presented from submarine channels off the canary islands and from canyon mouths off portugal data from other areas are briefly reviewed including a re interpretation of data from laurentian fan in order to summarise the varied morphology and setting of these bedforms coarse grained sediment waves are found in the proximal dominantly bypassing areas of deep water turbidite systems within canyons channels and channel lobe transition zones wave heights are in the region of 1 10 m and wavelengths are up to several hundred metres the distribution of waves and sparse sedimentological evidence from modern and ancient sediment wave fields suggests that initial transport and deposition of coarse sediment occurs within a high density turbidity current and not as a non newtonian debris flow in some cases the development of pronounced wave asymmetry and evidence of wave disruption and reworking suggests that the wave morphology is at least partially controlled by a later phase of low density turbidity flow grain size also appears to exert some control on wave morphology for example gravel rich waves have a greater height for the same wavelength than sand rich waves coarse grained sediment waves are often difficult to recognise on the seafloor because of reworking or burial by younger turbidity currents and are equally difficult to recognise in outcrop because of their large size

deep water sedimentary environments of the northwestern weddell sea and south sandwich islands antarctica abstract two transects have been sampled using short cores multi and box seabed photography video sequences and sediment profile images across the northwestern weddell sea and south sandwich forearc antarctica a total of 12 core stations were examined for sediment structure texture and composition to determine their depositional history four of the core stations from the weddell continental slope abyssal plain and south sandwich forearc and trench were further examined for trace metal analysis ba u mn and pb for sediment source and palaeoproductivity and 210pb for age profiles and depth of mixing by bioturbation the 3055 m station at the base of the weddell continental slope recovered laminated muddy silty contourites with a surface layer of hemipelagites with abundant ice rafted debris possibly originating from the 1995 larsen a and 2002 larsen b ice shelf disintegration this is interpreted as a moderate energy depositional environment influenced by weddell sea bottom water along slope current reworking sediment sediment sources to this station include the direct input of clastic material from ice with variation in sediment sources from in situ current winnowing and along slope transport reflected in the mn li and ba li ratios the 4760 m station on the weddell abyssal plain recovered hemipelagites interpreted as a low energy depositional environment with sediment supplied both from direct ice rafting and pelagic settling during productive seasonally ice free periods the 210pb profiles indicate a sedimentation rate of 0 024 cm year 1 with the 206 207pb isotope ratios suggesting a principle sediment source from ice rafting the 2292 and 6326 m stations from the slope and floor of the south sandwich forearc recovered pelagic and turbiditic sediments this is interpreted as a high energy down slope depositional environment with high surface biogenic productivity and sediment supply leading to localised down slope mass movements on the slope and floor high levels of mn li and elevated u li ratios demonstrate a strong concentration of mn in organic poor sediment the mn redoxcline is present at 10 cm depth the high ba li 500 ppm in the forearc floor core reflects some limited enhanced productivity source sediment for the forearc may in part be derived from the northwest weddell abyssal plain based on the 206 207pb isotope ratios reflecting transport by weddell sea bottom water

40ar 39ar geochronometry of pseudotachylytes by vacuum encapsulation north cascade mountains washington usa to determine a reliable means of dating pseudotachylytes we obtained total gas ages plateau ages and argon retention ages on samples from the north cascade mountains washington quartz ampoule vacuum encapsulation analysis of small grains a few milligrams from six samples allowed evaluation of 39 ar loss through recoil during irradiation and laser ablation on four samples allowed textural control in microlitic samples recoil loss 39 ar ranges from 0 2 to 8 4 the total gas ages incorporating this 39 ar are inconsistent but retention ages are much more internally consistent and within analytical error they match or nearly match plateau ages from most of the microlitic samples at 54 55 ma samples analyzed by laser ablation suggest one episode of faulting and pseudotachylyte formation at 55 59 ma and an earlier episode at ca 80 ma the partly glassy pseudotachylyte yielded laser ablation total gas and retention ages of ca 65 ma the microlitic pseudotachylytes indicate formation close to 55 ma with possible older faulting and pseudotachylyte formation at ca 81 84 ma the good consistency among the retention ages the laser ages with highest precision and especially the plateau dates combined with the ages falling within the anticipated time span provides confidence in the geologic reality of the ages nevertheless it is clear that large clasts and crystal fragments within these particular veins did not completely degas or may have an anomalous inherited radiogenic 40 ar component

a new bathymetric compilation for the south orkney islands region antarctic peninsula 49 39 w to 64 59 s insights into the glacial development of the continental shelf we present a new high resolution 300 m bathymetric grid of the continental shelf surrounding the south orkney islands northeast of the antarctic peninsula the new grid derived from a compilation of marine echo sounding data improves previous regional bathymetric representations and helps to visualize the morphology of the shelf in unrivalled detail the compilation forms important baseline information for a range of scientific applications and end users including oceanographers glacial modelers biologists and geologists in particular due to the limited understanding of glacial history in this region the bathymetry provides the first detailed insights into past glacial regimes the continental shelf is dominated by seven glacially eroded troughs marking the pathways of glacial outlets that once drained a former ice cap centered on the south orkney islands during previous glacial periods grounded ice extended to the shelf edge north of the islands a large 250 km long sediment depocenter interpreted as a maximum former ice limit of one or more cenozoic glaciations suggests that ice was only grounded to the 300 350 m contour in the south hypsometric analyses support this interpretation indicating that a significant proportion of the shelf has been unaffected by glacial erosion using these observations we propose a preliminary ice cap reconstruction for maximum glaciation of the south orkney plateau suggesting an ice coverage of about 19 000 km2 the timing of maximum ice extent number of past advances and pattern of subsequent deglaciation s remain uncertain and will require further targeted marine geological and geophysical investigations to resolve

new multibeam mapping and geochemistry of the 30 35 s sector and overview of southern kermadec arc volcanism new multibeam mapping and whole rock geochemistry establish the first order definition of the modem submarine kermadec arc between 30 degrees and 35 degrees s twenty two volcanoes with basal diameters 5 km are newly discovered or fully mapped for the first time giggenbacb macauley havre haungaroa kuiwai ngatoroirangi sonne kibblewhite and yokosuka for each large volcano edifice morphology and structure surficial deposits lava fields distribution of sector collapses and lava compositions are determined macauley and havre are large silicic intra oceanic caldera complexes for both concentric ridges on the outer flanks are interpreted as recording mega bedforms associated with pyroclastic density flows and edifice foundering other stratovolcanoes reveal complex histories with repeated cycles of tectonically controlled construction and sector collapse extensive basaltic flow fields and the development of summit craters and or small nested calderas combined with existing data for the southernmost arc segment we provide an overview of the spatial distribution and magmatic heterogeneity along similar to 780 km of the kermadec arc at 30 degrees 36 degrees 30 s coincident changes in arc elevation and lava composition define three volcano tectonic segments a central deeper segment at 32 degrees 20 34 degrees 10 s has basement elevations of 3200 m water depth and relatively simple stratovolcanoes dominated by low k series basalt basaltic andesite in contrast the adjoining arc segments have higher basement elevations typically 3 km coincide with the shallower arc segments the dominant mode of large caldera formation is interpreted as mass discharge pyroclastic eruption with syn eruptive collapse hence the shallower arc segments are characterized by both the generation of volatile enriched magmas from crustal melting and a reduced hydrostatic load allowing magma vesiculation and fragmentation to initiate and sustain pyroclastic eruptions proposed initiation parameters for submarine pyroclastic eruptions are water depths 70 wt sio2 and a high discharge rate c 2005 elsevier b v all rights reserved

motion of the scotia sea plates earthquake data from the scotia arc to early 2002 are reviewed in the light of satellite gravity and other data in order to derive a model for the motion of plates in the scotia sea region events with magnitude greater than or equal to5 which occurred on or near the boundaries of the scotia and sandwich plates and for which centroid moment tensor cmt solutions are available are examined the newer data fill some of the previous sampling gaps along the boundaries of the scotia and sandwich plates and provide tighter constraints on relative motions variations in the width of the brunhes anomaly on evenly spaced marine magnetic profiles over the east scotia ridge provide new estimates of scotia sandwich plate spreading rates since there are no stable fracture zones in the east scotia sea the mean azimuth of sea floor fabric mapped by sidescan is used to constrain the direction of spreading 18 newrate estimates and four azimuths from the east scotia ridge are combined with 68 selected earthquake slip vectors from the boundaries of the scotia sea in a least squares inversion for the best fitting set of euler poles and angular rotation rates describing the present day motions of the scotia and sandwich plates relative to south america and antarctica our preferred model tlp2003 gives poles that are similar to previous estimates except for scotia plate motion with respect to south america which is significantly different from earlier estimates predicted rates of motion also differ slightly our results are much more robust than earlier work we examine the implications of the model for motion and deformation along the various plate boundaries with particular reference to the north and south scotia ridges where rates are obtained by closure

geomorphological evolution of montserrat west indies importance of flank collapse and erosional processes analysis of topography and new swath bathymetry as well as geophysical data provides information about aerial and submarine morphological features and mass transfer processes on montserrat the island has a characteristic shallow c 4000 years ago or the boxing day event during the current eruption 26 december 1997 montserrat9s older volcanic centres the centre hills and silver hills illustrate the third stage of evolution extinction and erosion magma production long term erosion and total sedimentation rates on montserrat have been estimated as 0 17 km 3 ka 1 0 0125 km 3 ka 1 and 0 11 km 3 ka 1 i e 1 1 cm ka 1 respectively

in situ stress compared to structures in lac du bonnet batholith manitoba canada abstract structural fabrics in a late archean early proterozoic granite batholith at lac du bonnet manitoba canada have been used to develop the temporal sequence of paleostress axis orientations orientations of the in situ stress field have been measured both at surface and below surface at atomic energy of canada ltd s underground research laboratory through the techniques of borehole hydraulic fracturing overcoring and shaft wall convergence and through quarry data and surface pop ups the fabric interpreted paleostress and in situ stress directions are compared with each other and with regional stress orientations suggested by other authors for the western superior province north and nne to ne trends for in situ maximum compressive stresses measured above the 250 m depth possibly contain a large component of remanent stress in situ stresses with se to sse trends are common near ne striking thrust faults below the 250 m depth this could be a proterozoic remanent stress recovery or it could be fabric controlled neither ne nor se trending in situ measurements wholly represent that of the present day plate induced active tectonic stress

isotope hydrology of the chalk river laboratories site ontario canada abstract this paper presents results of hydrochemical and isotopic analyses of groundwater fracture water and porewater and physical property and water content measurements of bedrock core at the chalk river laboratories crl site in ontario density and water contents were determined and water loss porosity values were calculated for core samples average and standard deviations of density and water loss porosity of 50 core samples from four boreholes are 2 73 12 g cc and 1 32 1 24 percent respective median values are 2 68 and 0 83 indicating a positive skewness in the distributions groundwater samples from four deep boreholes were analyzed for strontium 87 sr 86 sr and uranium 234 u 238 u isotope ratios oxygen and hydrogen isotope analyses and selected solute concentrations determined by crl are included for comparison groundwater from borehole crg 1 in a zone between approximately 60 and 240 m elevation is relatively depleted in 18 o and 2 h perhaps reflecting a slug of water recharged during colder climatic conditions porewater was extracted from core samples by centrifugation and analyzed for major dissolved ions and for strontium and uranium isotopes on average the extracted water contains 15 times larger concentration of solutes than the groundwater 234 u 238 u and correlation of 87 sr 86 sr with rb sr values indicate that the porewater may be substantially older than the groundwater results of this study show that the precambrian gneisses at chalk river are similar in physical properties and hydrochemical aspects to crystalline rocks being considered for the construction of nuclear waste repositories in other regions

a comprehensive upb smnd rbsr and 40ar39ar geochronological study on guidong granodiorite southeast china records of multiple tectonothermal events in a single pluton a complicated tectonothermal history of the guidong granodiorite from the huanan fold belt has been revealed by using combined dating techniques u pb single zircon and whole rock nd model ages suggest that the granodiorite was derived from an ancient crustal source which was probably composed of a mixture of 1 2 2 4 ga crustal materials with a nd model age of 1 6 ga the granodiorite emplacement age of 427 3 ma is defined by concordant u pb single zircon analysis plagioclase biotite hornblende apatite sphene and whole rock yield an internal sm nd isochron age of 428 12 ma consistent within the analytical errors with the u pb zircon age due to the presence of inherited zircon however the zircon data point deviates from the sm nd isochron four whole rocks and two mineral separates plagioclase and hornblende yield a rb sr isochron age of 422 14 ma which is coincident with zircon u pb and sm nd isochron ages hornblende 40ar 39ar step heating analysis gives a main plateau age of 371 4 1 3 ma which is considerably younger than the crystallization age this age is interpreted as recording a post crystallization folding event which produced the prominent unconformity between pre devonian and middle devonian strata and resulted in the deformation of all major minerals of the granodiorite since most deformed minerals have remained closed to sm nd and rb sr isotopic migration since emplacement of the granodiorite it can be suggested that this folding event took place without significant fluid circulation and contemporaneous metamorphism a low temperature heating step of hornblende yields an apparent 40ar 39ar age of 208 5 2 0 ma which may or may not have a connection to the minimum age of the huanan indosinian orogeny a biotite 40ar 39ar age spectrum yields much younger apparent ages of 145 and 92 ma which are coincident with two important yanshanian magmatic episodes

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

open system dehydration of amphibolite morton pass wyoming elemental and nd and sr isotopic effects we have undertaken a geochemical and sm nd and rb sr isotopic study of banded metabasites in the contact aureole of the 1 43 ga laramie anorthosite complex wyoming in order to determine the isotopic effects of open system high temperature metamorphism samples were collected from two locations along strike one that experienced peak temperatures of 720 c and one that was subjected to temperatures up to 810 c at the higher temperature location metabasites adjacent to marble have undergone extreme dehydration presumably due to fluxing of co 2 rich fluids these hornblende poor rocks also show textural evidence of high temperature shearing element mobility is most evident within this zone of dehydration variations in chemical composition are homogenized and elements including ti fe k na rb sr y sm and nd have been removed metabasites at greater distances from the marble also provide evidence of open system behavior albeit less dramatic rb k and sr contents are low throughout the hi

morphologic resilience and depositional processes due to the rapid evolution of the submerged sciara del fuoco stromboli island after the december 2002 submarine slide and tsunami abstract in order to monitor the stromboli submarine slope after the 30 december 2002 landslide and tsunami repeated marine surveys were carried out offshore of sciara del fuoco the morphological changes and depositional processes that brought to the gradual filling of the slide scar have been studied in detail thirteen surveys in a period of little more than 4 years provided a unique opportunity to reconstruct the morpho sedimentary evolution of the submarine slope and its recovery after the mass wasting event the scar has been progressively filled with lava and volcanoclastic debris in the first month and a half the filling rate was very high due to the entrance of lava flows into the sea and to the morphological readjustment of the slope in the following months years the rate dramatically decreased when the eruptive vents moved upwards and the eruption finally stopped after 4 years february 2007 more than 40 of the scar was already filled in early 2007 a new eruption occurred and a lava delta was constructed in the 2002 scar influencing the natural readjustment of the slope therefore our reconstruction only encompasses the period between the 2002 and 2007 eruptions the swath bathymetry reconstruction of geometry and volume of scar filling during the period 2002 2007 evidenced a punctuated and fast shift of depocenters and debris emplacement through avalanching processes this process quickly obliterated the features produced by the 2002 tsunamigenic landslide so that a major question about the preservation potential of mass wasting features on active volcanic flanks emerges

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

thorite in fault zones of a granitic pluton atikokan canada implications for nuclear fuel waste disposal abstract thorite identified under a scanning electron microscope occurs in fault zones investigated throughout the eye dashwa pluton the undeformed nature and development of corona structures around the thorite suggest its growth during post kinematic conditions tho2 and sio2 constitute the major oxides in the thorite found in the pluton while ce2o3 fe2o3 cao uo2 p2o5 and s are present in minor amounts thermodynamic analysis shows that this thorite is a stable phase in contact with ambient groundwater in granitic environments the antiquity 2 3 ga and the chemical inertness of this thorite in contact with granite groundwater can be used as an example of a natural analogue for some aspects of nuclear fuel waste disposal

sediment subduction subduction erosion and strain regime in the northern south sandwich forearc 1 the first swath bathymetry and side scan sonar imagery from the south sandwich forearc reveals detailed seafloor morphology tectonic fabric and sedimentary features in an area where plate convergence is approximately normal to the trench simultaneously collected seismic reflection gravity and magnetic data provide information about the structure and composition of the forearc crust interpretation of these data together with the marine magnetic record of seafloor spreading in the east scotia sea back arc basin since 15 ma has enabled quantitative estimation of sediment subduction and subduction erosion rates any accretionary prism present is constrained to be very small extending 6 km or less from the trench the contrast between this result and a time integrated estimate of potential accretionary prism volume suggests that 95 of the sediment which has entered the trench since 15 ma has been subducted the position of the south sandwich island arc in relation to back arc magnetic lineations implies that the arc has migrated 70 km westward relative to the sandwich plate since 15 ma taking account of published observations concerning the typical geometric evolution of arc trench systems the average rate of forearc slope retreat during this interval is inferred to be 3 1 4 7 km myr 1 gravity modeling suggests that the forearc crust averages 10 km in thickness within 110 km of the trench for 10 km thick forearc crust the rate of slope retreat implies an average rate of subduction erosion of forearc crust of 31 47 km3 km 1 myr 1 at the present convergence rate of 74 km myr 1 this erosion rate requires a 420 635 m thick layer of subducting material derived from the forearc crust a time integrated estimate of the potential volume of forearc derived trench fill sediments subducted since 15 ma implies that frontal erosion can only account for 40 of total subduction erosion therefore basal erosion must significantly exceed frontal erosion the new data also provide insights concerning forearc strain regime and forearc basin evolution in the area studied extensional faulting near the trench slope break is probably caused by gravitational instability of the steep lower forearc slope a lack of extensional strain indicators in the upper forearc and arc may be a consequence of the fact that the east scotia sea is a mature back arc basin contributing significant ridge push in the vicinity of the arc the data reveal no evidence of arc parallel extension or of large serpentinite seamounts as found in the mariana forearc and a causal link between these two observations is proposed seismic profiles across the forearc basin suggest that the balance between sediment accumulation and erosion is sensitive to changes in the elevation of the trench slope break it is hypothesized that the basin is a dynamic feature which goes through repeated cycles of growth and destruction controlled by cyclic uplift and collapse of the trench slope break

contourite deposits in the central scotia sea the importance of the antarctic circumpolar current and the weddell gyre flows abstract new swath bathymetry with multichannel and high resolution seismic profiles shows a variety of contourite drift sediment wave morphologies and seismic facies in the central scotia sea the deposits are to be found at the confluence between the two most important bottom current flows in the southern ocean the eastward flowing antarctic circumpolar current acc and the northward outflow of the weddell sea deep water wsdw the contourite drifts are wedge like deposits up to 1 km thick that exhibit aggradational reflectors along axis thinning towards the margins the contourite drifts occur in areas of weaker flows along the margins of contourite channels and in areas protected by obstacles the elongate mounded drifts are best developed along the left hand margins of channelized bottom current flows due to the coriolis force a contourite fan has a main channel and two distributary channels that expand over a gentle seafloor the proximal fan exhibits sediment waves with the distal fan incised by furrows sediment wave fields are well developed in areas of intensified bottom flows without channels particularly at the confluence of the acc and the wsdw small sediment waves occur where unidirectional bottom current flows predominate sediment waves may develop under the influence of internal waves produced by the interaction of the flows and sea bottom relief the stratigraphic sequence above the oceanic crust of early to middle miocene age contains six seismic units separated by major reflectors all the units were shaped under the influence of strong bottom current flows although they exhibit distinct seismic facies changes that record the variations of the bottom current pathways over time the age of the units was calculated based on the age of the oceanic crust and sedimentation rates of deep sea deposits in the region the oldest units vi iv are of early to middle miocene age and developed under the influence of the acc they are characterized by a southward progradational pattern of the seismic units and sedimentation rates of 5 8 cm ky unit iii with an estimated middle miocene age evidences the first incursion of wsdw into the central scotia sea when plate movement caused openings in the south scotia ridge and allowed the connection with the northern weddell sea through jane basin and gaps in the ridge unit ii estimated to be of late miocene to early pliocene age extends over the area and is characterized by internal unconformities a major unconformity at the base of unit ii records an important reorganization of bottom current flows that may predate the onset of grounded ice sheets on the antarctic peninsula shelf unit i of late pliocene to quaternary age shows intensified bottom currents the unconformity at the base of unit i probably predates the onset of major northern hemisphere glaciations and the greater expansion of antarctic ice sheets during the late pliocene the extensive distribution of contourite deposits above the oceanic crust testifies to the long term production of antarctic bottom water cold deep water was swept northward from the weddell gyre interacting with the acc and possibly exerting profound influences on the global circulation system and the onset of major glaciations

sumisu volcano izu bonin arc japan site of a silicic caldera forming eruption from a small open ocean island sumisu volcano was the site of an eruption during 30 60 ka that introduced 48 50 km3 of rhyolite tephra into the open ocean environment at the front of the izu bonin arc the resulting caldera is 8 10 km in diameter has steep inner walls 550 780 m high and a floor averaging 900 m below sea level in the course of five research cruises to the sumisu area a manned submersible two rovs a deep tow camera sled and dredge samples were used to study the caldera and surrounding areas these studies were augmented by newly acquired single channel seismic profiles and multi beam seafloor swath mapping caldera wall traverses show that pre caldera eruptions built a complex of overlapping dacitic and basaltic edifices that eventually grew above sea level to form an island about 200 m high the caldera forming eruption began on the island and probably produced a large eruption column we interpret that prodigious rates of tephra fallback overwhelmed the sumisu area forming huge rafts of floating pumice choking the nearby water column with hyperconcentrations of slowly settling tephra and generating pyroclastic gravity currents of water saturated pumice that traveled downslope along the sea floor thick compositionally similar pumice deposits encountered in odp leg 126 cores 70 km to the south could have been deposited by these gravity currents the caldera rim presently at ocean depths of 100 400 m is mantled by an extensive layer of coarse dense lithic clasts but syn caldera pumice deposits are only thin and locally preserved the paucity of syn caldera pumice could be due to the combined effects of proximal non deposition and later erosion by strong ocean currents post caldera edifice instability resulted in the collapse of a 15 sector of the eastern caldera rim and the formation of bathymetrically conspicuous wavy slump structures that disturb much of the volcano s surface

first results of study of sulphur rich hydrothermal activity from an island arc environment esmeralda bank in the mariana arc during cruise so 69 of r v sonne active hydrothermal exhalation and deposition along the northern caldera rim of esmeralda bank was observed and sampled esmeralda bank is one of the active submarine volcanoes in the southern seamount province of the mariana island are hydrothermal porous mounds and volcaniclastic breccias cover an area of at least 0 2 km2 on the caldera seafloor and exude vent waters with a minimum temperature of 78 5 c the hydrothermal mounds consist of layers of pyrite marcasite and pure sulphur that are at least 0 8 m thick bottom videos show turbulent gas rich plumes characterized by high methane concentrations of 2 9 104 nl l which are comparable to those found at the hydrothermal site of macdonald seamount in the southwest pacific the deposition of large amount of sulphides is probably related to rock water interaction and degassing from a shallow summit magma chamber in an island arc environment

lateral development of coalification in the czech part of the upper silesian coal basin and its connection with gas deposits abstract the degree of coalification is an essential parameter influencing the quality of coal reserves modelling of the development of this parameter in the czech part of the upper silesian coal basin carboniferous mississippian to pennsylvanian lower namurian to westphalian a revealed the distribution of coalification within the basin in all its stratal units the grade of coalification was found in principle to be similar but its intensity in general decreases upwards into the hanging wall because of different areal extents of individual stratal units the degree of coalification is demonstrated on the oldest and areally most extensive unit the pet kovice member the studies and their results presented in this paper are based on more than 29 000 analyses of the dry and ash free volatile matter v daf in coal samples from surface and underground boreholes drilled in the years 1946 2000 three zones of enhanced coalification were distinguished the ostrava p ibor zone the ro nov frenstat zone and the p ibor t sin zone these zones were found to correlate fairly well with the occurrence of gas deposits confined to the weathered carboniferous rock massif or its mantle consequently the degree of coalification does not only determine the quality of coal reserves but may also be used as an auxiliary tool in the search for gas deposits in coal basins

volcanic tectonic and mass wasting processes offshore terceira island azores revealed by high resolution seafloor mapping terceira island in the azores archipelago lies at the intersection of four submarine volcanic ridges new high resolution bathymetric and seismic reflection data have been used to analyze the main volcanic tectonic and mass wasting features of the island offshore volcanic features such as linear volcanic centers and pointy and flat topped cones are mainly concentrated on the narrow western and north western ridges characterized by an overall rugged morphology fault scarps dominate mainly the broad eastern and south eastern ridges which are characterized by an overall smooth and terrace like morphology on the eastern ridge faults form a series of horsts and grabens related to the onshore lajes graben the strikes of the fault scarps linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends wnw ese and nnw sse consistent with the main tectonic structures observed on the azores plateau in contrast a large variability of strike was observed in inter ridge areas reflecting the relative importance of regional and local stresses in producing these structures mass wasting features are subordinate and mostly represented by hundred meter wide scars that indent the edge of the insular shelf surrounding the island apart from two large deeper scars identified on the southern steep flank of the western ridge finally the remarkable morpho structural differences between the western and eastern ridges are discussed in the framework of the evolution of the terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution

distinguishing sediment waves from slope failure deposits field examples including the humboldt slide and modelling results abstract migrating sediment waves have been reported in a variety of marine settings including submarine levee fan systems floors of fjords and other basin or continental slope environments examination of such wave fields reveals nine diagnostic characteristics when these characteristics are applied to several features previously attributed to submarine landslide deformation they suggest that the features should most likely be reinterpreted as migrating sediment wave fields sites that have been reinterpreted include the humboldt slide on the eel river margin in northern california the continental slope in the gulf of cadiz the continental shelf off the malaspina glacier in the gulf of alaska and the adriatic shelf a reassessment of all four features strongly suggests that numerous turbidity currents separated by intervals of ambient hemipelagic sedimentation deposited the wave fields over thousands of years a numerical model of hyperpycnal discharge from the eel river for example shows that under certain alongshore current conditions such events can produce turbidity currents that flow across the humboldt slide serving as the mechanism for the development of migrating sediment waves numerical experiments also demonstrate that where a series of turbidity currents flows across a rough seafloor i e numerical steps sediment waves can form and migrate upslope hemipelagic sedimentation between turbidity current events further facilitates the upslope migration of the sediment waves physical modelling of turbidity currents also confirms the formation and migration of seafloor bedforms the morphologies of sediment waves generated both numerically and physically in the laboratory bear a strong resemblance to those observed in the field including those that were previously described as submarine landslides

silicic magmas of protector shoal south sandwich arc indicators of generation of primitive continental crust in an island arc protector shoal the northernmost and most silicic volcano of the south sandwich arc erupted dacite rhyolite pumice in 1962 we report geochemical data for a new suite of samples dredged from the volcano geochemically the dredge and 1962 samples form four distinct magma groups that cannot have been related to each other and are unlikely to have been related to a single basaltic parent by fractional crystallization instead the silicic rocks are more likely to have been generated by partial melting of basaltic lower crust within the arc trace element and sr nd isotope data indicate that the silicic volcanics have compositions that are more similar to the volcanic arc than the oceanic basement formed at a back arc spreading centre and volcanic arc basalts are considered to be the likely source for the silicic magmas the south sandwich islands are one of several intra oceanic arcs tonga kermadec izu bonin that have 1 significant amounts of compositionally bimodal mafic silicic volcanic products and 2 6 0 6 5 km s 1 p wave velocity layers in their mid crusts that have been imaged by wide angle seismic surveys and interpreted as intermediate silicic plutons geochemical and volume considerations indicate that both the silicic volcanics and plutonic layers were generated by partial melting of basaltic arc crust representing an early stage in the fractionation of oceanic basalt to form continental crust

saline ground waters and brines in the canadian shield geochemical and isotopic evidence for a residual evaporite brine component abstract saline ca na cl type groundwaters and brines sampled in deep mines over an extensive area of the canadian precambrian shield have elevated br cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines remnants of the great marine incursions of the paleozoic era boron concentrations in these waters are generally low i e 11 b 10 b ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values 4 19 approaching that of present day seawater 4 20 moreover the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the br cl relationship that most of the chloride in shield brines is of marine origin rather than a product of water rock interactions if this is correct crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

slice of intraoceanic arc insights from the first multichannel seismic reflection profile across the south sandwich island arc we present the first multichannel seismic mcs reflection line that crosses the south sandwich trench south sandwich island arc and east scotia sea backarc basin the line is used in combination with earthquake catalogue data to interpret the strain distribution across the sandwich plate and the relationship of forearc structures to processes operating at the trench the mcs data reveal a 1 2 km high fault scarp associated with a 20 km wide arcward tilted block in the mid forearc these features indicate large scale gravitational collapse and earthquake data are consistent with trench normal extension at shallow depth in this area there is however little evidence of distributed extension within the interior of the sandwich plate the mcs data show a small frontal wedge that achieves its maximum thickness only 18 km from the trench backarc magnetic data mid forearc extension and the small size of the frontal wedge are all consistent with long term and ongoing subduction erosion earthquake data suggest that this erosion is taking place in an environment of low interplate stress

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity