ages of some intrusive rocks of southwestern maine u s a whole rock rb sr and u pb zircon age measurements on intrusive rocks in southwestern maine indicate igneous activity at 400 340 and 320 ma these plutonic rocks were emplaced into deformed ordovi

melt under cutting and buoyancy driven calving from tidewater glaciers new insights from discrete element and continuum model simulations the simple calving laws currently used in ice sheet models do not adequately reflect the complexity and diversity of calving processes to be effective calving laws must be grounded in a sound understanding of how calving actually works here we develop a new strategy for formulating calving laws using a the helsinki discrete element model hidem to explicitly model fracture and calving processes and b the continuum model elmer ice to identify critical stress states associated with hidem calving events a range of observed calving processes emerges spontaneously from hidem in response to variations in ice front buoyancy and the size of subaqueous undercuts calving driven by buoyancy and melt under cutting is under predicted by existing calving laws but we show that the location and magnitude of hidem calving events can be predicted in elmer ice from characteristic stress patterns our results open the way to developing calving laws that properly reflect the diversity of calving processes and provide a framework for a unified theory of the calving process continuum

the use of borehole video in investigating the hydrology of a temperate glacier a geovision micro colour video camera was used to investigate the internal structure of 11 boreholes at haut glacier d arolla switzerland the boreholes were distributed across a half section of the glacier with closest spacing towards the glacier margin the boreholes were used to investigate the hydrology of the glacier through automatic monitoring of borehole water level and electrical conductivity ec at the glacier bed ec profiling was undertaken in several boreholes to determine the existence of water quality stratification temporal variations in ec stratification were used to infer borehole water sources and patterns of water circulation borehole video was used to confirm the conclusions made from these indirect sources of evidence and to provide an independent source of information on the structure and hydrology of this temperate valley glacier the video showed variations in water turbidity englacial channels and voids conditions at the glacier bed and down borehole changes in ice structure based on the video observations englacial channels accounted for approximately 0 1 of the vertical ice thickness and englacial voids for approximately 0 4 overall the video images provided useful qualitative and semi quantitative data that reinforce interpretations of a range of physical and chemical parameters measured in boreholes 1997 by john wiley sons ltd

tidal flexure at ice shelf margins hinge zones accommodate the differential tidal movement between floating ice shelves which move with the sea tide and grounded ice sheets which do not observations on rutford ice stream and ronne ice shelf antarctica using the kinematic method of global positioning system have yielded the first continuous tidal displacement profiles from an ice sheet hinge zone the form of these tidal displacement profiles indicates that the flexure can be fit to an elastic beam model using a parameter space optimization technique the model matches the observed tidal deflection profile to within 5 cm which is similar to the observational uncertainty the same model and parameter fitting technique is then successfully applied to various other published and unpublished tidal displacement data from doake ice rumples bach ice shelf and ekstrom ice shelf antarctica and jakobshavns glacier greenland i conclude that the elastic beam model with a single value of the elastic modulus 0 88 0 35 gpa adequately describes almost all the data and so can usefully be applied elsewhere earlier studies of tidal dissipation in ice shelf hinge zones based on a viscous or transient creep rheology showed that perhaps 30 of global tidal energy dissipation could be occurring in ice shelf hinge zones this study suggests however that an elastic rheology may be equally appropriate in which case this estimation of the tidal energy dissipation is excessively high

icequakes coupled with surface displacements for predicting glacier break off a hanging glacier at the east face of weisshorn switzerland broke off in 2005 we were able to monitor and measure surface motion and icequake activity for 25 days up to 3 days prior to the break off the analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture 1 an increase in seismic activity within the glacier 2 a change in the size frequency distribution of icequake energy 3 a modification in the structure of the waiting time distributions between two successive icequakes and 4 a correlation between the seismic activity and the log periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation analysis of the seismic activity led us to identify two regimes a stable phase with diffuse damage and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered

the distribution of gold in rocks and minerals of the meguma group of nova scotia canada abstract rocks and constituent minerals of the meguma group from southeastern nova scotia were analyzed for gold by far the highest levels 4311 ng g ppb whole rocks 1 0 ppb and other minerals

sm nd isotopic investigation of the age and origin of the meguma zone metasedimentary rocks the meguma zone of southern nova scotia is a suspect terrane in the eastern appalachians sm nd isotopic data on six samples from the thick sequence of flyschoid metasediments of the meguma group show that these rocks have a mean crustal residence age of tdm 1773 95 ma considerably older than their cambro ordovician depositional age this information should be useful in locating the matching terrane for the meguma and ultimately in determining whether it was derived from one or more precambrian sources with different crustal residence times

geochemical behavior of sulfur in granitoids during intrusion of the south mountain batholith nova scotia canada abstract a detailed stable isotope s o and elemental major trace s content study of peraluminous s type granites and granodiorites of the south mountain batholith and the meguma group metasediments into which the batholith was intruded has been conducted on a regional and local scale near mt uniacke sulfur contents of the metasediments range from 5 to 2440 ppm and 34 s ranges from 3 7 to 26 3 sulfur contents of the igneous rocks range from 6 to 570 ppm with the granites 20 ppm having lower sulfur contents than the granodiorites 300 ppm approximately 30 to 60 of the sulfur in the granodiorites is present as pyrrhotite a late phase with most of the remainder being present as sulfur substituted into biotite an early phase 18 oq quartz values of the mt uniacke granodiorites are heavy a 12 2 indicating formation of the magmas by partial melting of sedimentary rocks major element variations suggest that the granites are related to the granodiorites by fractional crystallization of plagioclase quartz and biotite comparison of the sulfur contents of the granodiorites with experimental determinations of sulfur solubility suggest that the distribution coefficient of sulfur d s between the cumulate and the magma during fractional crystallization 4 the regional granodiorites have a relatively restricted range of 34 s values 5 4 to 8 4 while the regional granites have a wide range of 34 s values 1 6 to 15 0 granodiorites at mt uniacke with normal magmatic values 0 76 to 1 42 for 18 o quartz feldspar have 34 s values between 6 6 and 12 3 and show good negative correlations between 34 s and s feo and mgo contents some granodiorites at mt uniacke have anomalously low sulfur contents for their major element composition and 18 o quartz feldspar values 0 45 to 0 67 indicate that these samples have undergone hydrothermal alteration and this alteration event is probably responsible for the low sulfur contents a number of processes have been considered in order to understand the variations of 34 s partial melting of inhomogeneous source rocks may be responsible for some of the regional 34 s variations but this implies that the granites are not genetically related to the granodiorites inhomogeneous source rocks are an unlikely explanation for the systematic variations of 34 s observed over only a few kilometres at mt uniacke rayleigh fractionation accompanying the fractional crystallization of biotite 34 s pyrrhotites silicate s 0 5 to 1 0 can account for only a small component of the observed 34 s variations the assimilation of isotopically variable sulfur derived from the meguma group metasediments during fractional crystallization combined assimilation fractional crystallization or afc provides the best explanation for the 34 s variations transfer of sulfur from the country rock may have been possible by either bulk afc where all of the country rock material is incorporated into the magma or by selective afc where sulfur and other volatile elements only are transferred from the country rock into the magma selective afc could have been effected by a sloping mechanism of intrusion followed by the heating of country rock xenoliths to the point where extensive desulfidation reactions took place with sulfur being transferred from the country rock to the magma by a fluid phase

differentiation of strongly peraluminous perphosphorus granites the pedrobernardo pluton central spain the pedrobernardo pluton 295 2 ma initial 87sr 86sr 0 7122 is a layered sheet like granite body with distinct vertical zoning biotite muscovite bearing granites in the lower zone muscovite biotite leucogranites in the middle zone and muscovite bearing aplites and pegmatites in the upper zone the magma was anatectically generated intruded almost free of restite and evolved as a closed system by crystallization in situ geochemical modelling indicates that the lower and middle zones followed an equilibrium crystallization path with no separation between solids and melt and the upper zone followed a fractional crystallization path magmatic fractionation produced leucocratic differentiates with high p concentrations and a p ca ratio higher than in apatite the excess p is located in plagioclase and k feldspar monazite apatite fractionation in the lower and middle zones produced extreme depletions in th u y and the rees and chondrite normalized ree patterns with low lrees hrees and a slight discontinuity between nd and sm about 90 of the th u y and rees reside in accessory minerals especially in monazite biotite and muscovite have very low ree contents with small positive or no eu anomalies k feldspar and plagioclase in both the lower and upper zones have moderate ree contents with positive eu anomalies feldspars from the upper zone in contrast have negative eu anomalies and have very low ree contents compared to available data from literature dsr ba th u y reesbio mineral are lower by one to three orders of magnitude and dreesplag kfsp are also lower by one order of magnitude these huge discrepancies are attributed not only to contamination with ree rich inclusions in mineral concentrates used in previous studies but to real differences in geochemical behavior of trace elements in peraluminous systems with respect to subaluminous systems biotite melt and probably k feldspar melt distribution coefficients for th u y and the rees in peraluminous magmas must be much lower than previously considered

chemical and isotopic pb sr zonation in a peraluminous granite pluton role of fluid fractionation the davis lake pluton dlp 800 km2 of southwestern nova scotia canada part of the large peraluminous south mountain batholith of ca 380 ma u pb zircon ar ar mica consists of granite and subordinate topaz muscovite leucogranite that hosts greisen tin base metal mineralization a new pb pb isochron age for leucogranite from the most evolved part of the dlp indicates a crystallization age of 378 3 6 ma coincident with other radiometric ages of the dlp rb sr re os pb pb the intrusion displays a compositional zonation defined by lead and strontium isotopic ratios as well as some major elements e g si f incompatible trace elements e g li rb ta u sn and elemental ratios e g k rb and nb ta the greisens and the leucogranites that host them are characterized by extreme radiogenic compositions for pb and sr and their chemical isotopic trends are extensions of the trends displayed by the less evolved granites the covariations of the isotopic ratios with several major and trace elements and elemental ratios as well as the pb pb and rb sr isochrones indicate that all phases of the intrusion originated from a homogeneous parental magma the granitoid magma underwent extensive fractional crystallization of feldspars minor biotite and accessory minerals monazite apatite and zircon in a compositionally zoned magma chamber that was subsequently accompanied by fluid fractionation during which time the internally derived fluorine rich fluids modified the rb sr u pb and th pb ratios leading to distinct variations of 87sr 86sr 206pb 204pb 238u 204pb and 232th 204pb isotopic ratios these data therefore document the evolution of a granitic magma through magmatic i e crystal fractionation orthomagmatic i e crystal fluid fractionation and hydrothermal i e fluid fractionation stages that culminated in the formation of a tin base metal deposit the pb isotope data also constrain the source region for the dlp as being avalonian basement that by inference must underlie much of the meguma terrane

post paleocene cooling in the southern canadian atlantic region evidence from apatite fission track models the traditional view of the geomorphic evolution of the southern canadian atlantic margin is one of gradual exhumation and peneplanation following triassic jurassic rifting thermal modelling of apatite fission track data from pre carboniferous granitic basement in nova scotia and from permian and triassic sandstones from nova scotia new brunswick and prince edward island suggest a more complex thermal evolution of the onshore part of the margin models clearly indicate significantly elevated regional paleotemperatures during jurassic time and as much as 30 c of post paleocene cooling model predicted paleogeothermal gradients for granitic samples from the digby d 1 well are normal ranging from 15 to 20 c km post paleocene cooling may be attributable to the combined effects of 13 c of exhumational cooling from erosion of approximately 700 m of post aptian sediments caused by decreased eustatic sea levels and 8 17 c of cooling from the propagation to depth of a 10 20 c decrease in paleo mean ann

the geochemistry of phosphorus in granite rocks and the effect of aluminium phosphorus has been shown to have a profound influence on the evolution of silicate melt systems it also controls the geochemical behavior of rare earths uranium thorium strontium and other elements through the relationships between melt and accessory phosphates based on experimental data harrison and watson 1984 proposed a model of saturation behavior of apatite in crustal melts as a function of temperature and silica content subaluminous granites fit in well with such a model but departures are evident in the case of peraluminous granites a systematic study of the distribution of p2o5 in granitoids from all over the world shows that there are two modes to describe phosphorus enrichment in peraluminous granitic rocks 1 the hoyos type trend which is parallel to the one in harrison and watson s hw model but with higher p2o5 concentrations at the same silica contents and 2 the pedrobernardo type trend implying an increase in phosphorus in the most sio2 rich differentiates of strongly peraluminous low ca granites pedrobernardo type leucogranites are characterized by the presence of rare phosphates or p rich feld spars since they have excess p2o5 over cao to form normative apatite we here propose the term perphosphorous granites high phosphorus contents appear to be due to elevated apatite solubility in peraluminous granitic melts rather than to high amounts of restitic apatite both the hoyos and pedrobernardo type departures from the hw model can be corrected by using the expression p2o5corrected p2o5hw efactor where p2o5hw is the prediction according to the hw model and factor is asi 1 6429t asi being the al2o3 cao na2o k2o molar ratio we suggest that such departures could be caused by a decrease in the ca activity in the melt as a result of increased peraluminousity the pedrobernardo type trend is a limiting case in which ca activity in the melt is nearly zero and calcium instead of phosphorus becomes the essential structural constituent esc of the apatite when this happens phosphorus starts behaving as an incompatible element that is concentrated in late fluids high p2o5 contents are more characteristic of s than other granite types no significant departures from the hw model have been found for i a or m type granites in central iberia granites associated with u sn and w mineralizations usually have high phosphorus contents values of p2o50 5 wt at sio270 wt are good indicators of economic mineralization

two early holocene rock avalanches in the bernese alps rinderhorn switzerland abstract large rock avalanches constitute a critical process modulating the evolution of alpine landscapes however the relatively infrequent occurrence of these high magnitude events makes identifying underlying process controls challenging here we describe two rock avalanches in the rinderhorn area of the bernese alps switzerland providing new mapping of rock avalanche source areas and deposits refined volume estimates for each event runout modeling back analyses and absolute age constraint from cosmogenic 36 cl surface exposure dating results reveal that the daubensee rock avalanche released 4 million m 3 of limestone sliding from the western crest of the rinderhorn debris ran out across a lateglacial moraine before reaching the valley bottom and spreading leaving thin on average 7 m deposits across a broad area the runout resulted in a fahrboschung angle of 21 part of the deposit now lies beneath lake daubensee the klein rinderhorn rock avalanche released 37 million m 3 of limestone along a dip slope sliding plane with a maximum runout distance of 4 3 km and estimated fahrboschung angle of 14 deposits bulked to 47 million m 3 running up the opposing slope with distinct hummocky morphology in the proximal area and a distal longitudinal flow ridge these deposits were later modified and partly obscured by ice avalanches from the nearby altels peak cosmogenic 36 cl surface exposure dating revealed nearly coincident ages for both rock avalanches of 9 8 0 5 ka the large lag time between local deglaciation and failure suggests that the events were not directly triggered by deglaciation rather the concurrent exposure ages also coinciding with the nearby kander valley rock avalanche as well as paleoseismic records from nearby lakes strongly suggest seismic triggering

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

40ar 39ar dating of micas from the east kemptville tin deposit yarmouth county nova scotia the east kemptville tin deposit in nova scotia the largest known tin deposit in north america lies in a greisen zone within the davis lake pluton generally considered to be part of the devonian south mountain batholith our dating of micas from within the deposit suggests that the greisenization process that accompanied mineralization took place about 295 5 ma ago that is ca 60 ma after the emplacement of the batholith hydrothermal alteration mineralization activity in southern nova scotia coincided with extensive shearing and tectonism throughout the hercynian orogen the east kemptville deposit appears to be approximately coeval with similar mineralization in southwest england the iberian peninsula and northwest africa and much younger than the devonian acadian orogeny

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

recent drumlins flutes and lineations at vestari hagafellsjokull iceland in the foreland of the vestari hagafellsjokull glacier langajokull central iceland three scales of subglacial bed forms are found drumlins flutes and lineations the smaller bed forms are superimposed upon the larger these three bed forms probably formed as a result of the presence of a rigid subglacial core producing a lee side low pressure area into which sediment flowed and collected the cores of the drumlins are tumuli lava blisters whilst the cores of the flutes and lineations were large clasts differences between the three scales of bed forms are that a the flutes and lineations are far more mobile features as their cores could move within the deforming layer whilst the drumlin bedrock cores were fixed b the lineations formed in association with a clast pavement the change in scale of the bed forms may be related to changes in thickness of the deforming layer and size of the core at this site smaller bed forms were superimposed upon larger bed forms and these may have formed as the deforming layer progressively thinned in association with glacial retreat

ages of regional metamorphism and ductile deformation in the central and southern appalachians abstract a summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation the ca 480 435 ma taconic event affected most of the piedmont and blue ridge provinces the ca 380 340 ma acadian event was milder and was centered in the west central piedmont and eastern blue ridge the 330 230 ma alleghanian event exhibits an abrupt ductile deformation front in the eastern piedmont and extends an unknown distance eastward below the atlantic coastal plain

40ar 39ar ages from the narragansett basin and southern rhode island basement terrane their bearing on the extent and timing of alleghenian tectonothermal events in new england pennsylvanian sedimentary rocks record the effects of progressive barrovian metamorphism and polydeformation in the narragansett basin of rhode island whole rock phyllite samples from low grade portions of this terrane display internally concordant 40 ar 39 ar age spectra with plateau ages of 248 to 258 m y four samples biotite from higher grade rocks records plateau ages of 240 to 248 m y eight samples similar 40 ar 39 ar biotite ages are displayed westward across the southern rhode island basement terrane 239 to 250 m y nine samples although coexisting hornblende records slightly older plateau ages of 255 m y two samples the 40 ar 39 ar plateau ages are interpreted to date times of post metamorphic cooling through temperatures required for argon retention in the various mineral phases examined the ages suggest that a distinct late paleozoic alleghenian thermal event affected much of southern rhode island together with the depositional ages of the variably metamorphosed pennsylvanian rocks westphalian b stephanian a or b the 40 ar 39 ar data permit calibration of the sequence of alleghenian tectonothermal events recorded in the narragansett basin the controls suggest a permian event lasting about 40 to 50 m y between initial barrovian regional metamorphism and synchronous d 1 d 2 ductile deformation between 295 and 275 m y and post d 3 cooling below argon retention temperatures between 250 and 240 m y

assessment of thermal change in cold avalanching glaciers in relation to climate warming high elevation glaciers covered by cold firn are undergoing substantial warming in response to ongoing climate change this warming is affecting the ice rock interface temperature the primary driver of avalanching glacier instability on steep slopes prediction of future potential instability therefore requires appropriate modeling of the thermal evolution of these glaciers application of a state of the art model to a glacier in the french alps taconnaz has provided the first evaluation of the temperature evolution of a cold hanging glacier through this century our observations and three dimensional modeling of the glacier response velocity thickness temperature density and water content to climate change indicate that taconnaz glacier will become temperate and potentially unstable over a large area by the end of the 21st century the risk induced by this glacier hazard is high for the populated region below and makes observation and modeling of such glaciers a priority

the use of salt injection and conductivity monitoring to infer near margin hydrological conditions on vestari hagafellsjokull iceland vestari hagafellsjokull is a surge type outlet glacier from the langjokull ice cap iceland intensive hydrological investigations were carried out during non surge conditions in the summers of 1999 and 2000 and 14 boreholes were drilled using pressurized hot water over an area 800 m from the margin and approximately 5000 m 2 in size where ice thickness ranged from 60 to 70 m initial investigations showed that a large fraction of the boreholes drilled to the bed did not drain and were assumed not to connect to the subglacial drainage system subsequently we investigated the hypothesis that boreholes which remain full may do so as a consequence of a balance between englacial inflow and basal drainage rather than the standard assumption that such boreholes are simply unconnected in testing this hypothesis we developed a new technique for measuring water motion within the borehole by monitoring the passage of a saline solution down the borehole s water column the technique allows rates of motion to be established as well as allowing the quantification of net addition and loss of water from the borehole observations based on the motion of saline plumes within the boreholes lead us to the conclusion that some boreholes do indeed remain full as a consequence of a balance between englacial inflow and subglacial drainage the abrupt dilution that occurs at the top of these boreholes suggests inflow from a near surface englacial water source while the descent of the saline plumes implies that water is being lost at the base to the subglacial system the system appears to be driven by excess water head in the boreholes over flotation and implies that the borehole bedrock interface can be leaky

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

archean inheritance in zircon from late paleozoic granites from the avalon zone of southeastern new england an african connection abstract in southeastern new england the narragansett pier granite locally intrudes carboniferous metasedimentary rocks of the narragansett basin and yields a monazite u pb permian emplacement age of 273 2ma zircon from the narragansett pier granite contains a minor but detectable amount of an older inherited component and shows modern loss of lead zircon from the late stage aplitic westerly granite exhibits a more pronounced lead inheritance permitting the inherited component to be identified as late archean such old relict zircon has not been previously recognized in proterozoic to paleozoic igneous rocks in new england and may be restricted to late paleozoic rocks of the avalon zone we suggest that the archean crustal component reflects an african connection in which old archean crust was underplated to the avalon zone microplate in the late paleozoic during collision of gondwanaland with avalonia

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

geologic fluid inclusion and stable isotope studies of the gays river lead zinc deposit nova scotia canada the gays river deposit is the largest carbonate hosted lead zinc deposit known in the mississippian windsor group of atlantic canada the orebody mainly occupies one flank of a porous dolomitized carbonate bank that unconformably overlies a basement ridge of the metasedimentary lower paleozoic megurea group the orebody consists of stratiform disseminated sulfides as open space fillings in primary and secondary pores of the dolomite and fault controlled veinlike bodies of high grade massive sphalerite and galena the carbonate bank is overlain by evaporite deposits of mississippian age underground mapping and laboratory studies suggest four main stages of evolution for gays river 1 deposition of the visean carbonate bank preore evaporite deposition pervasive dolomitization and growth of diagenetic marcasite 2 deposition of sphalerite galena chalcopyrite and calcite as a result of influx of hydrothermal metal rich saline brines into fractures and porous dolomite 3 postore deposition of calcite fluorite barite marcasite pyrite and selenite and 4 uplift localized dedolomitization of the mineralized carbonates and exposure by erosion in cretaceous times microthermometry of fluid inclusions yields the following mean homogenization temperatures sphalerite 215oc ore stage calcite 173oc postore calcite 142oc fluorite 142oc and barite 137oc pressure corrections should be minimal for these temperatures no evidence of boiling was observed in the inclusions salinity determinations from the ice melting temperatures of inclusions in postore fluorite and calcite yield a value of ca 20 4 equivalent wt percent naci for the hydrothermal fluid during the waning stages of mineralization isotopic analyses indicate that anhydrite and gypsum in the overlying evaporites and barite within the orebody are enriched in heavy sulfur t 34s 13 1 16 5 0 suggesting a mississippian seawater source ore stage sphalerite galena and chalcopyrite probably derived their sulfur b34s 8 0 13 65 0 from sulfates or possibly a homogenized basement source postore marcasite and pyrite are characterized by light probably biogenic sulfur ba4s 9 7 to 46 0 mineralized carbonates are significantly depleted in the heavier isotopes of oxygen and carbon with respect to their unmineralized equivalents preliminary lead isotope data for galena suggest that the metasedimentary basement was a source of lead this study disputes an earlier interpretation that the stratiform lead zinc ores are an early low temperature diagenetic cement of the carbonate bank the high grade zones are not residual concentrations related to sinkholes as originally thought instead both disseminated and massive ores are probably the result of the same mineralizing episode involving deeply convecting brines or brines expelled during basin dewatering under high geothermal gradients in the late paleozoic

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

dating mineralization using several isotopic methods an example from the south mountain batholith nova scotia canada abstract granitic plutons in the meguma terrane may be broadly divided into two suites 1 an areally predominant cogenetic suite of peraluminous granitoid rocks tonalite leucogranite and 2 an areally subordinate paraintrusive suite specialized in sn w mo cu f u p zn as which appears to have been produced by fluid interaction with either residual magma or crystallized rock granite related mineralization is generally considered to have developed during terminal stages of magmatic crystallization that lead to metasomatism and hydrothermal alteration previous geochronological data have suggested that the main cogenetic suite was emplaced at 350 375 ma whereas some of the paraintrusive suite is markedly younger 250 350 ma the apparently large time interval between the intrusion of the cogenetic suite and some of the mineralization suggests that they are not coeval and has led to the conclusions that the younger mineralization may be related to later magmatism and or tectonothermal events rocks associated with two mineral occurrences in the south mountain batholith that had previously yielded anomalously young isotopic ages millet brook and westfield have been analyzed for u pb and ar isotopes in an attempt to resolve this dilemma new geochronological data from the millet brook area indicate that intrusion of granodiorite at 377 5 3 ma nearly concordant monazite age was closely followed by intrusion of most other phases all of which had cooled through 375 c closure temperature for ar in muscovite by 377 373 6 ma 40 ar 39 ar plateau ages new data from westfield indicate that a paraintrusive porphyry was intruded at 385 2 ma upper intercept of a chord through four nearly concordant zircon fractions and that greisen muscovite cooled through the closure temperature by 368 2 6 ma 40 ar 39 ar plateau age these data indicate that a previously reported rb sr whole rock isochron age of 270 ma at westfield reflect isotopic resetting that occurred below the blocking temperature for 40 ar 39 ar in muscovite 375 c clearly further rb sr analysis is required to document this process other 250 300 ma ages in the meguma terrane are recorded along the tobeatic fault zone away from the fault ages increase upto 370 ma suggesting that the fault may have acted as an important pathway for fluids and heat that facilitated isotopic resetting rb sr whole rock and mineral systems may be affected after formation of an alteration assemblage associated with mineralization by the migration of rb and its concentration in secondary minerals

the petrology geochemistry and economic potential of the musquodoboit batholith nova scotia the musquodoboit batholith of southwestern nova scotia is a massive post tectonic granitoid intrusion that was emplaced into the regionally deformed and metamorphosed meguma group metasedimentary rocks the batholith is composed primarily of medium to coarse grained monzogranites into which two small 1 km2 porphyries and numerous dykes have been injected all rocks contain quartz alkali feldspar plagioclase muscovite and biotite with the exception of some leucocratic dykes cordierite is a major constituent in most monzogranitic rocks and also occurs in some leucocratic dykes andalusite and garnet 0are also present as accessory phases in some rocks major element chemical analyses indicate that all rock types in the musquodoboit batholith are peraluminous compositions resemble those of the eastern part south mountain batholith however slightly higher concentrations of al2o3 and p2o5 distinguish the musquodoboit batholith from the central part of the south mountain batholith major and trace

evidence of log periodic oscillations and increasing icequake activity during the breaking off of large ice masses in 1973 surface velocities were measured for the first time on an unstable hanging glacier to predict its collapse the observed velocities have been shown to increase as a power law function of time up to infinity at the theoretical time of failure known as finite time singularity this is the characteristic signature of critical phenomena and has been observed in the case of various other naturally occurring ruptures such as earthquakes landslides and snow avalanches recent velocity measurements performed on weisshorn and monch hanging glaciers switzerland confirmed this behaviour while log periodic oscillations superimposed on this general acceleration were also detected despite different rupture mechanisms in both cases the log frequency of the oscillations is shown to be the same the seismic activity was recorded near the unstable weisshorn hanging glacier simultaneously with the velocity measurements results show dramatically increasing icequake activity 3 days before the final collapse combined motion seismic monitoring seems to be a promising way to accurately predict the breaking off of hanging glaciers such a combined analysis is also useful for capturing the physical mechanisms of rupture in natural heterogeneous materials

rb sr whole rock and 40 ar 39 ar mineral ages of the hartland stock south central maine a post acadian representative of the new hampshire plutonic series the hartland granodioritic stock is an undeformed post acadian representative of the new hampshire plutonic series that intrudes low grade silurian devonian metasedimentary rocks in south central maine a nine point rb sr whole rock isochron defines an age of 360 8 m y for the pluton initial sup 87 sr sup 86 sr 0 7056 3 biotite and hornblende from the pluton display undisturbed sup 40 ar sup 39 ar age spectra with mutually overlapping dates of 362 5 m y seven samples the undisturbed character of the argon isotopic systems suggests that the sup 40 ar sup 39 ar ages date times of post magmatic cooling through temperatures required for retention of argon comparison of the emplacement age defined for the hartland stock with rb sr whole rock isochron dates reported for crystallization of other new hampshire series plutons suggests continuous devonian intrusive activity in new england preceding during and following the acadian orogeny no geochronologic evidence for separating distinct subseries of intrusion can be provided with presently available data

tectonic evolution of southwestern newfoundland as indicated by granitoid petrogenesis four granitoid suites are recognized in the region of the cape ray fault zone of southwestern newfoundland the two oldest ordovician silurian suites represent partial melts of their enclosing host rocks the port aux basques granite is modelled as a partial melt of the gneissic component of its host port aux basques complex the cape ray granite forms a dominantly tonalitic terrane derived by partial melting of ophiolitic material the red rocks granite and a megacrystic phase of the cape ray granite form coherent lines of geochemical descent from the parental tonalite but show evidence of some continental crust contamination the late devonian windowglass hill granite is a subvolcanic equivalent of felsic volcanic rocks in the windsor point group both units were derived as partial melts of continental crust the post tectonic late devonian to early carboniferous strawberry and isle aux morts brook granites constitute the youngest granitoid suite in the region these a type granitoids were derived as partial melts of an underlying depleted granulitic felsic crust the depleted nature of the source may have resulted from previous generation of the windowglass hill granite and windsor point group the only possible protolith for the granulitic source is precambrian grenvillian gneiss the presence of this gneiss beneath the cape ray fault zone of southwestern newfoundland implies that the complete series of lithologies is allochthonous

borehole drainage and its implications for the investigation of glacier hydrology experiences from haut glacier d arolla switzerland studies of glacier hydrology rely increasingly on measurements made in boreholes as a basis for reconstructing the character and behaviour of subglacial drainage systems in temperate glaciers in which boreholes remain open to the atmosphere following drilling the interpretation of such data may be complicated by supraglacial or englacial water flows to and from boreholes we report on a suite of techniques used to identify borehole water sources and to reconstruct patterns of water circulation within boreholes at haut glacier d arolla switzerland results are used to define a number of borehole drainage types examples of each drainage type are presented along with the manner in which they influence interpretations of borehole water levels borehole water quality data and borehole dye traces the analysis indicates that a full understanding of possible borehole drainage modes is required for the correct interpretation of many borehole observations and that those observations provide an accurate indication of subglacial conditions only under relatively restricted circumstances copyright 2001 john wiley sons ltd

classification and kinematics of the planpincieux glacier break offs using photographic time lapse analysis herein we present results obtained from time lapse imagery acquired by a digital single lens reflex camera during 2014 18 used to monitor the planpincieux glacier on the italian side of the grandes jorasses mont blanc massif we processed the images using image cross correlation to measure the surface kinematics of the most active lobe of the glacier that presents a high velocity and frequent ice detachments during the monitoring we observed two or three periods of sharp acceleration per year that culminated with large break offs followed by analogous decelerations overall we registered more than 350 failures with a volume 100 m3 of which 14 events had volumes larger than 10 000 m3 the study identified a monotonic positive relationship between the velocity and failure volume that may be used to estimate the volume of the collapses before an event we identified the thresholds of velocity and acceleration that characterise the activation of the speed up periods the study allowed the characterisation of three different instability processes that lead to the break off of ice chunks from the glacier terminus i disaggregation ii slab fracture and iii water tunnelling failure which can be differentiated based on the rheology the volume involved and the trigger process

precise u pb dating of meguma basement xenoliths new evidence for avalonian underthrusting u pb zircon and monazite dates for granulite facies basement xenoliths from the popes harbour dyke on the eastern shore of nova scotia provide strong evidence that the meguma terrane overlies avalo

plutonic and hydrothermal events in the ackley granite southeast newfoundland as indicated by total fusion 40ar 39ar geochronology results of total fusion 40ar 39ar dating eight biotites four muscovites and one hornblende of magmatic and hydrothermal stages of the high silica chemically zoned ackley granite indicate three distinct episodes of magmatic activity viz 410 378 374 and 355 ma and that the metallogenic system w sn mo evolved synchronously with only one of the magmatic phases the oldest suite is indicated by two biotite dates at 410 4 4 4 and 392 5 7 6 ma which are themselves considered as representing partial resetting related to a tectonothermal event of acadian age thus the 410 ma age offers the best estimate of intrusion although it must be considered a minimum the main magmatic pulse for the ackley granite is indicated by dates between 378 and 374 ma with most of these phases occurring in the southern part of the complex concordant hornblende biotite ages 374 8 3 8 and 372 3 4 8 ma respectively for one of the southern phases rencontre lake granite suggests rapid cooling for this part o

a 3 d thermal regime model suitable for cold accumulation zones of polythermal mountain glaciers analysis of the thermal and mechanical response of high altitude glaciers to climate change is crucial to assess future glacier hazards associated with thermal regime changes this paper presents a new fully thermo mechanically coupled transient thermal regime model including enthalpy transport firn densification full stokes porous flow free surface evolution strain heating surface meltwater percolation and refreezing the model is forced by daily air temperature data and can therefore be used to perform prognostic simulations for different future climate scenarios the set of equations is solved using the finite element ice sheet ice flow model elmer ice this model is applied to the col du dome glacier mont blanc area 4250 m a s l france where a comprehensive data set is available the results show that the model is capable of reproducing observed density and velocity fields as well as borehole temperature evolution the strong spatial variability of englacial temperature change observed at col du dome is well reproduced this spatial variability is mainly a result of the variability of the slope aspect of the glacier surface and snow accumulation results support the use of this model to study the influence of climate change on cold accumulation zones in particular to estimate where and under what conditions glaciers will become temperate in the future

chemical and isotopic composition of the lower crust beneath the meguma lithotectonic zone nova scotia evidence from granulite facies xenoliths granulite facies xenoliths from an upper devonian lamprophyre dyke near tangier nova scotia provide new information about the lower crust in the meguma zone two mineralogically and chemically distinet groups of xenoliths occur both groups contain quartz feldspar biotite fe ti oxides sulfides in addition group a contains garnet graphite aluminosilicates spinel sapphirine hight al2o3 subgroups a1 and a2 or clinopyroxene sphene apatite high cao sub group a3 group b has highly variable proportions of orthopyroxene b1 clinopyroxene b2 and amphibole b3 trace element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other undepleted granulite facies rocks lowp t sedimentary assemblages of quartz chlorite clay minerals calcite albite or paragonite can account for the compositions of group a xenoliths within group b a high mgo mgo 13 wt subgroup with high transition metal contents and low mgo mgo 9 wt sub groups with higher lil large ion lithophile element contents exist although the rare earth and high field strength elements indicate a tholeiitic or low k calc alkaline chemistry the lil elements are as high as those from high k calc alkaline volcanic are rocks isotopically group a ranges from endt 2 56 to 0 80 and87sr 86srt 0 7046 to 0 7182 fort 370 ma for group b these values are 1 45 to 5 33 and 0 7028 to 0 7048 respectively model ages tchur are correspondingly low and are tightly constrained 544 52 ma these young ages contrast with the middle proterozoic nd model ages of the overlying meguma zone low grade flysch this time inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous tangier lower crust avalon and an older allochthonous meguma group upper crust

oxygen isotopic compositions of the late orogenic granites in the southern piedmont of the appalachian mountains u s a and their relationship to subcrustal structures and lithologies abstract data were acquired from 143 whole rock samples from 20 late orogenic post metamorphic hercynian age granitic plutons from the piedmont of the southern appalachians principally in georgia and south carolina these plutons exhibit a regional gradient in oxygen isotopic compositions in which the granites confined to the inner piedmont to the northwest are 18 o enriched 11 4 to 7 9 whereas those toward the southeast within the charlotte slate and portions of the kiokee belts have distinctly lower 18 o 16 o compositions 8 2 to 5 5 one body that lies along the southeastern edge of the piedmont in south carolina however appears to be anomalously 18 o enriched 8 9 most plutons display 18 o 16 o variations of 18 o enriched plutons occupy areas characterized by negative anomalies whereas low 18 o bodies are invariably restricted to regions of positive anomalies 2 87 sr 86 sr data where granites with 18 o values 18 o enriched plutons 9 have ratios 0 710 3 contrasting chemical and accessory mineral compositions in which many 18 o depleted granites have a number of i type characteristics whereas several of the most 18 o enriched plutons exhibit a number of s type features it can be inferred from these data that the 18 o enriched granites were formed from continental crustal protoliths that underlie much of the inner piedmont and portions of the kiokee belt whereas the low 18 o plutons were derived from more mafic sources beneath the charlotte slate and portions of the kiokee belt the overall correspondence between the regional 18 o 16 o patterns exhibited by the granites and gravity data implies that these grantes may be essentially rooted to their protoliths in turn suggesting that the large scale translational movement recently proposed for the southern piedmont may have occurred prior to intrusion of these granites 320 m y ago

basal hydraulic system of a west antarctic ice stream constraints from borehole observations pressure and tracer measurements in boreholes drilled to the bottom of ice stream b west antarctica are used to obtain information about the basal water conduit system in which high water pressures are developed these high pressures presumably make possible the rapid movement of the ice stream pressure in the system is indicated by the borehole water level once connection to the conduit system is made on initial connection here also called breakthrough to the basal water system the water level drops in a few minutes to an initial depth in the range 96 117 m below the surface these water levels are near but mostly somewhat deeper than the flotation level of about 100m depth water level at which basal water pressure and ice overburden pressure are equal which is calculated from depth density profiles and is measured in one borehole the conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed the thickness of the gap has to be about 2 mm to account for the water level drop on breakthrough and about 4 mm to fit the results of a salt tracer experiment indicating downstream transport at a speed of 7 5 mm s 1 the above gap conduit model is however ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole and also by the large hole to hole variation in measured basal pressure which if present in a gap conduit system with 2 or 4 mm would result in unacceptably large local water fluxes an alternative model that avoids the e objections called the gap opening model involves opening a gap as injection proceeds starting with a thin film the injection of water under pressure lifts the ice mass a round the borehole creating a gap 3 or 4 mm wide at the ice bed interface evaluated quantitatively the gap opening model accounts for the volume of water that the basal watery system accepts on breakthrough which obviates the gap conduit model in order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits of which the most promising type is the canal conduit proposed theoretically by walder and fowler 1994 flat low conduits incised into the till 0 1 m deep and perhaps 1 m wide with a flat ice roof the basal water pressure data suggest that the canals are spaced 50 300 m apart much closer than r tunnel would be the deepest observed water level 117 m i the most likely to reflect the actual water pressure in the canals corresponding to a basal effective pressure of 1 6 bar in this interpretation the shallower water levels are affected by loss of hydraulic head in the narrow passageway s that connect along the bed from borehole to canal s once a borehole has frozen up and any passageways connecting with canals have become closed a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till given enough time for pressure equilibration this pressure varies considerably with time over the equivalent water level range from 100 to 113 m basal pressure sensors 500 m apart report uncorrelated variations whereas sensors in boreholes 25 m apart report mostly but not entirely well correlated variations of unknown origin in part of the record remarkable anticorrelated variations are interspersed with positively correlated one and there are rare abrupt excursions to extreme water levels as deep as 125m and as shallow as 74 m a diurnal pressure fluctuation intermittently observed may possibly be caused by the ocean tide in the ross sea the lack of any observed variation in ice stream motion when large percentagewise variations in basal effective pressure were occurring according to our data suggests that the observed pressure variations are sufficiently local and so randomly variable from place to place that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

geophysical and structural signatures of syntectonic batholith construction the south mountain batholith meguma terrane nova scotia summary the late devonian south mountain batholith is a very large 7000 km2 composite peraluminous granitoid complex situated within the meguma terrane of the northern appalachians it is made up of two suites of granodioritic to leucogranitic plutons emplaced at approximately 380 370 ma during the acadian orogeny i e during the collision of gondwana with the eastern margin of north america a significant geophysical and geological database makes the south mountain batholith a type example of a very large syntectonic batholith emplaced within a collisional orogen gravity models reveal the plutons have flat or gently dipping floors at approximately 7 0 km depth and aspect ratios 651 they are underlain by deeper 10 km elongate northeast southwest trending roots that may indicate magma feeder zones dyke transport of granitic magma and the progressive construction of plutons by sheet injections are supported by field observations and by mapping of the anisotropy of magnetic susceptibility at the pluton scale the very narrow deformation aureole within the country rocks suggests lateral spreading of the plutons was not the main space creation mechanism during emplacement space was mostly created by vertical displacements of country rocks the data are consistent with a laccolithic model for syntectonic batholith assembly the laccolithic plutons may have been emplaced at the base of the meguma supergroup metasedimentary rocks suggesting a maximum thickness of approximately 7 0 km for the supracrustal rocks in the meguma terrane

the east kemptville tin deposit yarmouth county nova scotia a pb isotope study of the leucogranite and mineralized greisens evidence for a 366 ma metallogenic event pb isotopic data for whole rock leucogranite and mineral separates variably mineralized greisen and galena from the east kemptville sn cu zn ag deposit yarmouth county southwestern nova scoti

late devonian lamprophyric dykes in the meguma zone of nova scotia hornblende rich lamprophyric dykes from southeastern nova scotia are contemporaneous with the large peraluminous granitic batholiths ca 370 ma of the meguma zone and may be closely associated with their origin

a multivariate approach to geochemical distinction between tin specialized and uranium specialized granites of southern nova scotia like most granitoid bodies that host significant granophile deposits the south mountain batholith smb of nova scotia consists of an earlier suite intruded by a later suite of smaller plutons that are more silicic and peraluminous the latter generally show a range of other geochemical features that readily identify them as specialized and allow for their separation from the earlier non specialized granites in the case of mineralization associated with the smb we can go one step further and clearly separate the specialized granites into stanniferous and uraniferous series which can be identified even where no sn or u enrichment is present although this can be done successfully using simple histograms of a number of elements li p sn and f we show that combining all elements in discriminant analysis guarantees 100 success in separating the two groups r mode factor analysis aids in accounting for the variance within each group the most important effect being a biotite factor because of bo

the scotian basin offshore nova scotia thermal history and provenance of sandstones from apatite fission track and 40ar 39ar data apatite fission track and 40ar 39ar age spectrum data from sandstone drill core minerals taken from depths of 2 5 km in nine wells from the scotian basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments the focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization isomerization a i reactions in biomarker compounds from the same or nearby wells apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of 4 km corrected bottom hole temperature 120 c shallower lower present temperature samples are partially annealed the degree of partial annealing correlates closely with the degree of a i reactions both thermal indicators are activated over the temperature range 60 120 c samples from two wells mic mac j 77 and erie d 26 are anomalous they are more annealed than present formati

characteristics of ree and other trace elements in response to successive and superimposed metasomatism within a portion of the south mountain batholith nova scotia canada abstract successive and superimposed periods of late to post magmatic metasomatism have resulted in mineralogical and textural modification within leuco monzogranitic rocks of the big indian lake polyphase intrusive suite bipis the alteration and associated mineralization exhibit a transition from an early pervasive style to a later fracture controlled style and can be defined by diagnostic ree and other trace element behavior while the anomalous behavior of some elements mno ta u k rb hree is attributed to metasomatic hydrothermal activity the compatible behavior of b f li w and rb appears to have been governed by predominately magmatic processes all elements including al can be mobilized during repeated fluid rock interaction the behavior of ree during evolution of the bipis indicates that they also were affected by both magmatic lree depletion eu depletion and metasomatic hree lree enrichment eu enrichment depletion processes the remobilization and subsequent redeposition of trace elements is dependent upon the nature and stability of the metasomatic mineral assemblages in this respect a metasomatized granitic rock could reflect a ree pattern similar to that of an unaltered equivalent

heterogeneous distribution of the dynamic source parameters of the 1999 chi chi taiwan earthquake 1 the spatial and temporal distribution of the stress on the fault plane of the 1999 chi chi taiwan earthquake is calculated from kinematic inversion results using a three dimensional finite difference method for solving the elastodynamic equations we analyze the relations between stress and slip for all grid positions on the fault and use these relations to infer the friction law for the rupture the dynamic source parameters were also determined our results show that for most of the points on the fault the relation between stress and slip was consistent with the slip weakening law during the rupture process especially for those points with large slip however consistency with the velocity weakening law is not clear from the observed relation between stress and slip velocity the distributions of the dynamic parameters on the fault are very heterogeneous the peak value of the static stress drop is 35 mpa in general high stress drop occurred in the areas with large slip the estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock the slip weakening distance dc and the fracture energy gc are proportional to the final slip the aftershock activity correlates with the spatial distribution of dynamic source parameters usually the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop and there were few aftershocks in regions which had large values of critical slip weakening distance dc

volume and frequency of ice avalanches from taconnaz hanging glacier french alps very large volumes of ice break off regularly from taconnaz hanging glacier french alps during winter when the snow mantle is unstable these collapses can trigger very large avalanches that represent a serious threat to inhabited areas below photogrammetric measurements have been performed over 1 year to assess the volume and frequency of the largest collapses major collapses occur when the glacier reaches a critical geometry after a major ice collapse the glacier is in a minimal position and subsequently recharges over 6 months to reach the maximum position again this critical geometry is a necessary but not sufficient condition for further large collapses large collapses do not systematically occur in the maximum position as ice is often removed by disintegration into small ice blocks for two major collapses the volume of ice breaking off has been assessed at 275000m 3 photogrammetric measurements were used to determine an ice flux of 820000m 3 a 1 through the studied ice stream in agreement with an assessment based on ice flow modeling this ice flux estimation was used to determine the average ice volumes breaking off over surveyed periods

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

on the instability of avalanching glaciers the instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the european alps a classification of avalanching glaciers is proposed which allows a primary appreciation of the danger inherent in these glaciers on the basis of field observations and results of numerical simulations of crevassing the fracture processes which lead to major icefalls as well as their recurrence are analyzed a method for predicting the time of failure is then discussed the disaggregation of the unstable ice masses usually observed prior to large icefalls is investigated and its implications for the forecasting of icefalls analyzed

a rate and state friction law for saline ice sea ice friction models are necessary to predict the nature of interactions between sea ice floes these interactions are of interest on a range of scales for example to predict loads on engineering structures in icy waters or to understand the basin scale motion of sea ice many models use amonton s friction law due to its simplicity more advanced models allow for hydrodynamic lubrication and refreezing of asperities however modeling these processes leads to greatly increased complexity in this paper we propose by analogy with rock physics that a rate and state dependent friction law allows us to incorporate memory and thus the effects of lubrication and bonding into ice friction models without a great increase in complexity we support this proposal with experimental data on both the laboratory 0 1 m and ice tank 1 m scale these experiments show that the effects of static contact under normal load can be incorporated into a friction model we find the parameters for a first order rate and state model to be a 0 310 b 0 382 and m0 0 872 such a model then allows us to make predictions about the nature of memory effects in moving ice ice contacts

numerical modeling of a gravity driven instability of a cold hanging glacier reanalysis of the 1895 break off of altelsgletscher switzerland

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

geochronological evidence for multiple tectono thermal overprinting events in the east kemptville muscovite topaz leucogranite yarmouth county nova scotia canada the east kemptville muscovite topaz leucogranite located in yarmouth county nova scotia canada is host rock to the only producing primary tin deposit in north america 56 mt 0 165 sn previous geochronological studies include i rb sr whole rock analyses of the quartz topaz greisens which indicated a date of 337 5 ma and ii 40ar 39ar analyses of greisen muscovite which indicated apparent plateau dates of ca 300 ma however the pervasive development of deformational fabrics at east kemptville suggests that both the rb sr whole rock and 40ar 39ar muscovite ages are at best minimum estimates for the inferred time of mineralization in the present study rb sr whole rock and mineral muscovite plagioclase k feldspar analyses and 40ar 39ar incremental step heating of a muscovite separate indicate the following i diffusion of sr on the whole rock scale terminated at 344 5 ma 11 point isochron date coincident with closure of muscovite to intracrystalline diffusion of ar apparent plat

origin of topaz bearing and related peraluminous granites of the late devonian davis lake pluton nova scotia canada crystal versus fluid fractionation abstract the davis lake pluton in the late devonian south mountain batholith in southwestern nova scotia canada is composed of peraluminous leucomonzogranites and subordinate topaz bearing leucogranites that host greisens and a primary tin deposit the concentrations of incompatible trace elements e g rb li u f ta and sn and element e g k rb nb ta and la sm and isotopic ratios e g 206 pb 204 pb and 87 sr 86 sr display a spatial zonation the granitic rocks were generated by extensive fractional crystallization of major phases feldspars and biotite and accessory minerals monazite apatite and zircon in a compositionally zoned magma chamber fractional crystallization of the evolving f rich peraluminous granitic magma was accompanied particularly in later stages by fluid fractionation involving fluorine complexing fluid fractionation was a major differentiation process during the terminal stages of the pluton s evolution it played an important role in the genesis of the evolved rocks which are characterized by low k rb 24 150 nb ta 1 6 la sm 1 5 4 and eu eu 0 01 0 3 ratios these ratios as well as the enhanced concentrations of li rb u ta and sn in these rocks correlate with f fluorine rich fluids modified the rb sr and u pb ratios which produced the distinct variations of 87 sr 86 sr and 206 pb 204 pb isotopic ratios the parent magma was formed by dehydration melting of lower crustal metasedimentary rocks the melting was related to crustal thickening in association with terrane and collision along the eastern margin of the appalachians

unraveling driving factors for large rock ice avalanche mobility large rock ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities a relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising to improve hazard assessment of potential rock ice avalanches their mobility is a critical factor this contribution is an attempt to unravel driving factors for the mobility of large rock ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock ice avalanches with volumes 1x106 m3 from glacierized high mountain regions around the world the influence of avalanche volume water and ice content low friction surfaces and topography on the apparent coefficient of friction as a measure of mobility is assessed in laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20 while water led to a reduction around 50 for completely saturated material compared with dry flows evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data while the influence of the ice content could not be confirmed to be of much relevance in nature besides liquefaction it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility effects of the topography along the flow path as well as channeling are assumed to be other critical factors the results provide an empirical basis to roughly account for different path and flow characteristics of large rock ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments copyright 2011 john wiley sons ltd

elevation change mass balance dynamics and surging of langjokull iceland from 1997 to 2007 in situ mass balance survey is a joint effort of the glaciology group institute of earth sciences university of iceland and the national power company landsvirkjun we thank philippe crochet and tomas johannesson from the icelandic meteorological office for providing the gridded climate data and for useful discussions about the climatology of langjokull the 2007 lidar data were collected by the uk natural environment research council airborne research and survey facility grant ipy 07 08 additional funding was provided by the united states national science foundation grant no dge 1038596 st catharine s st john s and trinity colleges and the university of cambridge b b roberts and scandinavian studies funds we thank cameron rye for initial help coding the mass balance model

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

the acadian thermal history of the merrimack synclinorium in new hampshire the acadian structural history of the merrimack synclinorium involves a phase of nappe emplacement and thrusting at 400 m y b p followed by a second thickening event before 370 m y b p at the end of this phase the present erosion surface was buried at pressures of 6 to 8 kbar and subsequently experienced peak metamorphic temperatures in the range of 500 c to 650 c the thermal history of the acadian metamor phism of the merrimack synclinorium is examined in a well studied area of central new hampshire to determine the conditions required for the high grade metamorphism of the region constraints are provided by metamorphic pressure estimates by information on the erosional history and by present day heat flow determinations in the synclinorium one dimensional heat transfer calculations show that the high grade metamorphism could readily have been produced during thermal relaxation of the thickened continental crust under conditions of normal continental heat flow these conditions also permit the me

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified

40ar 39ar dating of hydrothermal biotite from high grade gold ore tangier gold deposit nova scotia further evidence for 370 ma gold metallogeny in the meguma terrane a hydrothermal biotite carbonate alteration zone adjacent to a high grade multi ounce gold vein in the tangier gold deposit meguma terrane nova scotia has given an 40 ar 39 ar plateau age of 374 ma the alteration halo is part of a vein package in the hinge zone of the tangier anticline which contains abundant auriferous quartz veins formed during flexural slip folding during a late stage reactivation of the regional fold belt the 374 ma age is similar to 40 ar 39 ar ages determined for hydrothermal vein minerals at seven other meguma gold districts thereby suggesting a terrane wide metallogenic event a similar age of vein formation and by inference gold mineralization and granite emplacement across the meguma terrane suggest that the cospatial and cotemporal nature of the two geological events may be related an integrated model including anatexis and devolitization of the lower crust possibly as a consequence of overriding a mantle plume in concert with late stage reactivation of the fold belt owing to continued transpression along a terrane bounding fault is proposed

protolith carbon isotope ratios in cordierite from metamorphic and igneous rocks cordierite commonly contains h 2 o and co 2 in the channels formed by its ring structure in many studies cordierite has been shown to have volatile contents and carbon isotope ratios consistent with high temperature equilibrium suggesting preservation of protolith carbon isotope ratios and motivating this survey of carbon isotopes in cordierite co 2 cordierite co 2 from pelitic country rocks in the etive aureole have 13 c values of 20 70 1 27 n 10 that are unaffected by a ca 150 c thermal gradient and fluid saturated and undersaturated regimes these 13 c values are consistent with expected carbon isotope ratios of organic carbon in protolith sediments similar lithologies from the cooma and huntly aureoles show more variable behavior in a more limited data set with some rocks preserving organic carbon 13 c values and others that may have been affected by externally derived fluids in cordierite gedrite gneisses carbon isotopes of cordierite crd are distinct from those of cordierite in pelites when excluding one outlier new data plus those from the literature average 13 c crd 12 51 2 45 n 17 these isotope ratios are higher than those of cordierite in typical metasedimentary protoliths and are similar to published carbon isotope ratios of trace carbonate in altered submarine volcanic rocks which are likely analogs for protoliths of many cordierite gedrite rocks igneous cordierite from granitic plutons have 13 c 23 61 2 08 n 13 which is interpreted as reflecting a magmatic carbon budget dominated by organic carbon from sedimentary source rocks in contrast small pegmatites reported in the literature have 13 c crd 10 20 3 06 n 6 which may indicate derivation from orthogneiss source materials these new data show that carbon isotopes in cordierite can be used to help understand the protolith of even carbon poor metamorphic rocks and can also shed light on carbon in the sources of magmatic rocks this latter approach has the potential for helping constrain the source rocks of peraluminous granitoids which is controversial determining the extent to which organic carbon 13 c is preserved in granitoids is important for understanding the deep carbon cycle and could serve as an important constraint in the search for low 13 c graphite inclusions in hadean detrital zircons which have been reported as a potential biosignature for the early earth