landslide generated tsunamis at reunion island 1 landslides that occur on oceanic volcanoes can reach the sea and trigger catastrophic tsunamis reunion island has been the location of numerous huge landslides involving tens to hundreds of cubic kilometers of material we use a new two fluid seawater and landslide numerical model to estimate the wave amplitudes and the propagation of tsunamis associated with landslide events on reunion island a 10 km3 landslide from the eastern flank of piton de la fournaise volcano would lift the water surface by about 150 m where it entered the sea the wave thus generated would reach saint denis the capital of reunion island population of about 150 000 people in only 12 min with an amplitude of more than 10 m and would reach mauritius island in 18 min although mauritius is located about 175 km from the impact waves reaching its coast would be greater than those for reunion island this is due to the initial shape of the wave and its propagation normal to the coast at mauritius but generally coast parallel at reunion island a submarine landslide of the coastal shelf of 2 km3 would trigger a 40 m high wave that would severely affect the proximal coast in the western part of reunion island for a landslide of the shelf of only 0 5 km3 waves of about 2 m in amplitude would affect the proximal coast

laboratory investigations on impulsive waves caused by underwater landslide laboratory investigations have been performed on the submarine landslide generated waves by performing 120 laboratory tests both rigid and deforming slide masses are considered the effects of bed slope angle initial submergence slide geometry shape and deformation on impulse wave characteristics have been inspected impulse wave amplitude period energy and nonlinearity are studied in this work the effects of bed slope angle on energy conversion from slide into wave are also investigated laboratory based prediction equations are presented for impulse wave amplitude and period in near and far field and are successfully verified using the available data in previous laboratory and numerical works

cross examining earth s oldest stromatolites seeing through the effects of heterogeneous deformation metamorphism and metasomatism affecting isua greenland 3700 ma sedimentary rocks abstract the 3700 ma and 3800 ma meta volcanic and sedimentary rocks in the isua supracrustal belt greenland were affected by heterogeneous ductile deformation under amphibolite facies conditions 500 650 c and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids rare low deformation areas preserve original volcanic features submarine basaltic pillows and sedimentary features including bedding these are best preserved in two dimensions on flat to moderately inclined outcrop surfaces but invariably are tectonically stretched along a steeply plunging third dimension through stretching in the direction of fold axes a style of deformation found throughout earth s history there is a debate about whether rare relicts of 3700 ma stromatolites preserved in metadolomites that formed in a shallow marine setting nutman et al 2016 represent bona fide biogenic primary structures fortuitously preserved in low deformation or whether these structures are manifestations of deformation combined with non biogenic deposition of secondary carbonate allwood et al 2018 here we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites by addressing the following questions i are the rocks an in situ outcrop of known age or displaced blocks of unknown age or origin ii how much of the carbonate is of an originally sedimentary versus a secondary i e metasomatic introduced origin iii is the seawater like ree y rare earth element and yttrium trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool surficial sedimentary system iv are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine scale layering or could they be the product of soft sediment or structural deformation compression in folding the answers to these questions which combine diverse observations from geologic context geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes

geochronological constraints on paleoarchean thrust nappe and neoarchean accretionary tectonics in southern west greenland abstract major regional deformation and metamorphic events in the godthabsfjord region southern west greenland occurred at 3650 and 2820 2720 ma e g precambrian res 78 1996 1 new geochronological constraints u pb zircon sensitive high resolution ion microprobe shrimp and thermal ionisation mass spectrometry tims have been obtained from a stack of mylonitic crystalline thrust nappes in the footwall of the western part of the paleoarchean 3 8 3 7 ga isua greenstone belt isukasia a mylonitic tonalite sheet interpreted to have intruded synkinematically with respect to mylonitisation yields a magmatic crystallisation age of 3640 3 ma a cross cutting pegmatite and a post kinematic tonalite pluton yield magmatic crystallisation ages of 2948 8 and 2991 2 ma respectively accordingly we interpret the thrust nappe stack to have formed during the paleoarchean 3640 ma making it the oldest example known on earth the similarity of this structural regime to that of modern mountain belts suggests that paleoarchean and modern continental crust were comparable in terms of mechanical strength and constitution southern west greenland has been interpreted in terms of neoarchean accretion comparable with modern plate tectonics e g earth planet sci lett 142 1996 353 isukasia lies just east of a purported neoarchean accretionary boundary between the akia terrane to the northwest and the akulleq terrane to the southeast the akia terrane was previously considered to overthrust the akulleq terrane at 2820 2720 ma our geochronological and geological data indicate i that the two terranes as presently defined were stitched at 2991 2 ma and ii that thrusting across the boundary was directed toward the akia terrane therefore we suggest that the akia akulleq interface was not a fundamental tectonic structure during the neoarchean and we question its identification as an accretionary boundary

the least radiogenic terrestrial leads implications for the early archean crustal evolution and hydrothermal metasomatic processes in the isua supracrustal belt west greenland abstract vein type galenas from within metasomatized tonalitic gneiss sheets in a metamorphosed oceanic crustal sequence of the arc outbound isua supracrustal belt isb west greenland reveal the hitherto least radiogenic terrestrial lead isotope compositions these leads deviate from commonly applied average continental crust evolution curves for lead and can be modeled by a single stage growth with starting parameters 238u 204pb 7 70 and 232th 238u 4 37 inferring model ages of 3 81 and 3 76 ga for these galenas the initial constraints are indicative of higher u pb and th u in the source of the hydrothermal fluids and arguably in the magmatic precursors of the gneisses they support contentions regarding a time integrated terrestrial pre history with an elevated th u in the early earth s mantle necessary to reconcile the difference between the observed th u and the time integrated th u recorded by pb isotope ratios of present depleted morb mantle derived rocks in addition they are in line with the requirement of preferential enrichment of u relative to pb in a proto continental crust relative to depleted upper mantle in the early earth s history the age equivalency between the galena generations and abundant tonalitic gneiss sheets and their mutual spatial relationship within the isb favors an interpretation of the least radiogenic terrestrial leads to closely approximate the initial pb of 3 75 ga and pre 3 8 ga old tonalitic protoliths and therefore prompts a close genetic relationship between early archean fluid flow and the magmatic events the inferred 3 81 ga model age of the least radiogenic galena pb particularly agrees with previous u pb zircon geochronological results on tonalite sheets within the supracrustals which constrain a ca 3 79 3 81 ga minimum age for the formation to the earth s oldest oceanic crustal sequence in combination with 3 74 ga pb pb ages of post deformational hydrothermal metasomatic minerals our results imply that early archean metasomatic activity is indistinguishable in time from the earliest metamorphic overprint and from the ca 3 75 ga major pulse of tonalite intrusions in the isua area

eoarchean contrasting ultra high pressure to low pressure metamorphisms 1000 c gpa explained by tectonic plate convergence in deep time abstract greenland s itsaq gneiss complex igc shows eoarchean 3600 ma 250 400 c gpa low t p high pressure and 1000 c gpa high t p metamorphic regimes demonstrating a similarity of contrasting metamorphic t p regimes from the phanerozoic back to the start of earth s rock record low t p metamorphism produced i deep crustal eclogitised mafic rocks which upon partial melting formed the tonalites dominating the igc ii 550 c 2 6 gpa conditions 250 c gpa demonstrated by an olivine antigorite titano chondrodite titano clinohumite relict assemblage within mantle slivers showing geochemical and crystallographic features of a suprasubduction environment that were exhumed into the crust by 3712 ma iii rare vestiges of 3658 ma high pressure garnet clinopyroxene granulite and iv barrovian style kyanite staurolite assemblages high t p metamorphism is shown by 3669 ma crustal melts equilibrated with orthopyroxene this was coeval to the youngest juvenile tonalitic crust in the complex latter derived by anatexis under low t p conditions and a 3670 3570 ma history of deep crust migmatisation under low pressure garnet free conditions structural geology of the igc indicates its low t p regimes coincide with crustal imbrication by compression of arc like tholeiites boninite like lavas andesites felsic intermediate volcano sedimentary rocks and chemical sedimentary rocks whereas post 3660 ma high t p metamorphism was marked by late orogenic extension exhumation and deep crustal flow with mafic underplating and partial melting generating granites thus the diversity of earth s earliest recorded geodynamic settings resembles more those of modern geodynamics than the lithological and structural relationships expected from theoretical non uniformitarian scenarios like drip tectonics in a stagnant lid regime the recognition of an ultra high pressure 250 c gpa metamorphic regime at 3700 ma in the igc removes the last argument against a form of plate tectonics operating throughout the archean hence since the start of the rock record a mobile lid plate tectonic regime contributed to interior heat loss facilitating chemical communication and feedbacks between earth s surface and its deep interior

tracing archaean terranes under greenland s icecap u th pb hf isotopic study of zircons from melt water rivers in the isua area abstract the archaean gneisses of the nuuk area southern west greenland are partitioned into tectonostratigraphic terranes blocks of arc like crust that evolved independently until they coalesced by collisional orogeny to map terranes to the east under the inland ice sand samples were taken from rivers issuing from the edge of the icecap three from the isua area and one from 20 km to the south bedrock along this part of the ice front consists of 3820 3600 ma amphibolite facies rocks 40 km south of isua kapisilik terrane in the ivisaartoq area and also from 10 km to the north there are mesoarchaean amphibolite facies gneisses 3070 2950 ma exposed at the ice front in the moraine fields in the isua area there are erratic blocks of granulite facies gneisses these were sourced from a hidden terrane to the east under the ice because no such rocks are exposed in the isua area the majority of the zircons from the sand samples yielded close to concordant u pb ages apart from one 2414 ma grain all are archaean the isua sands show 2695 2710 and 2730 ma then 2790 2805 and 2840 ma clusters with a few grains back to 2950 ma and then a complex 3440 3960 ma spectrum less than 1 of the grains have ages between 3000 and 3400 ma in the isua sands neoarchaean and late mesoarchaean zircons form 50 of the population the sand 20 km to the south shows a similar span of zircon ages but there is a 2960 ma peak not seen in the isua sands as the eoarchaean and late mesoarchaean neoarchaean cycles progress the spread of th u and hf values seen in each zircon age population increases this is interpreted as repeated addition of juvenile material to the crust but also with increasing amounts of high temperature tectonothermal recycling of older materials within a package however there is no isotopic evidence for any contribution of eoarchaean crust to the later 2750 ma archaean cycle s showing evolution in disparate terranes furthermore no evidence for hadean material beneath the ice is seen in either the u pb ages or hf isotopic compositions of the detrital zircons on the other hand 2750 2500 ma metamorphic zircons show a spread of initial hf values of zero to 25 with the most negative indicating zircon growth in eoarchaean rocks overall these results closely mirror those obtained from direct sampling of rocks of the archaean terranes exposed beyond the icecap the zircon data indicate that mesoarchaean rocks equivalent to the kapisilik terrane are absent under the ice instead zircons were sourced from a late mesoarchaean to neoarchaean terrane affected by high grade metamorphism whose age spectra perfectly matches the tasiusarsuaq terrane to the southeast of nuuk guided by the zircon results and aeromagnetic signatures a terrane map is presented that extrapolates the tasiusarsuaq terrane northwards under the inland ice towards the tuno terrane in the north of the craton implications for different syntheses on the evolution of archaean crust in southern west greenland are discussed

a granitic inclusion suite within igneous zircons from a 3 81 ga tonalite w greenland restrictions for hadean crustal evolution studies using detrital zircons abstract this paper presents an electron microprobe study of inclusions within igneous zircons from ca 3800 ma metatonalite sample g97 18 crystalline inclusions are k feldspar plagioclase quartz hornblende biotite ilmenite and apatite additionally one globular polymineralic inclusion interpreted as crystallised melt occurs at the surface of a polished grain mount this consists of plagioclase quartz k feldspar around a biotite lath other similar but rare globular inclusions were seen buried within other zircons below the polished surface these inclusions particularly the presence of k feldspar and plagioclase in broadly equal amounts entail crystallisation of the zircons from a residual granitic sensu stricto melt rather than a tonalitic melt shrimp sensitive high resolution ion microprobe u pb dating of zircons with inclusions indicates that they grew at ca 3800 ma the accepted igneous age of the rock this inclusion suite is compatible with the low ti in zircon temperatures for g97 18 igneous zircon hiess et al 2008 therefore low ti in zircon temperatures and granitic inclusions found in hadean detrital zircons do not necessitate crystallisation from low temperature granites because such features would also be found if hadean zircons had crystallised late from higher temperature zircon undersaturated melts of tonalitic composition

sedfoam a multi dimensional eulerian two phase model for sediment transport and its application to momentary bed failure abstract a multi dimensional eulerian two phase model for sediment transport called sedfoam is presented the model was developed under the open source framework via the cfd toolbox openfoam with closures of particle stresses and fluid particle interactions the model is able to resolve processes in the concentrated region of sediment transport and hence does not require conventional bedload suspended load assumptions a modified k closure was adopted for the carrier flow turbulence the model was validated for reynolds averaged steady and oscillatory sheet flows and verified with empirical formulae for scour downstream of an apron the model was used to study momentary bed failure or plug flow under sheet flow conditions model results revealed the existence of instabilities of the near bed transport layer when momentary bed failure criteria was exceeded these instabilities evolved into 5 10 cm billows and were responsible for the large transport rate the instabilities were associated with a large erosion depth which was triggered by the combination of large bed shear stresses and large horizontal pressure gradients further numerical experiments confirmed the conjecture by previous studies that a criterion for onset of momentary bed failure in oscillatory sheet flow was a function of both the shields parameter and sleath parameter

sedimentology and stratigraphy in the cave hamnsundhelleren western norway the stratigraphy in hamnsundhelleren is as follows a basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the laschamp excursion 43 47 000 yr bp angular blocks bones and clay above this are 14c dated to the alesund interstadial 28 38 000 yr bp another stadial laminated clay following the alesund interstadial includes a palaeomagnetic excursion correlated with lake mungo 28 000 yr bp the newly discovered hamnsund interstadial above this consists of frost weathered clay and scattered angular blocks it is 14c dated to 24 500 yr bp on bones mixed into the alesund interstadial the hamnsund interstadial is succeeded by another stadial laminated clay and then a late glacial holocene mixture of bones and blocks in hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice free ice covered cycle have been identified i ice free phase deposition of bones and frost weathered blocks ii subaerial ice dammed lake phase sand or silt deposited in a lateral glacial lake iii subglacial ice dammed lake phase cave closed by ice deposition of till debris flows and laminated clay d ice plugged phase cave is plugged by frozen lake water and or glacial ice no deposition

on the transfer of momentum from a granular landslide to a water wave abstract the momentum flux from a landslide at impact in a water body is the driving force behind the generation of landslide tsunamis analysis of this problem is presented and used to derive idealized theoretical relationships for the maximum wave amplitude in the near field zone this is accomplished for momentum transfer using both hydrostatic and hydrodynamic assumptions for rapidly evolving near field waves with a supercritical densimetric froude number the maximum wave amplitude is also constrained according to the fluid continuity equation simplification of the hydrostatic momentum equation is also presented by considering fluid acceleration resulting in an expression that is independent of length and time scales during wave generation the results of the novel momentum based equations are in agreement with laboratory data collected using high speed digital cameras for granular landslides and previously published experimental data used to develop a semi empirical equation furthermore the results provide new insight on the range of applicability of theoretical and semi empirical equations for predicting the maximum near field wave amplitude of landslide generated tsunamis

eoarchaean crustal growth in west greenland itsaq gneiss complex and in northeastern china anshan area review and synthesis eoarchaean crust in west greenland the itsaq gneiss complex 3870 3600 ma is 80 by volume orthogneisses derived from plutonic tonalite trondhjemite granodiorite ttg suites 3850 c 3810 and c 3710 mahave some compositional similarities to modern island arc basalts iab suggesting their origin by hydrous fluxing of a suprasubduction zone upper mantle wedge most of the eoarchaean tonalites match in composition highsilica low magnesian adakites whose petrogenesis is dominated by partial melting of garnetiferous mafic rocks at high pressure however associated with the tonalites are volumetrically minor more magnesian quartz diorites whose genesis probably involved melting of depleted mantle to which some slab derived component had been added this assemblage is evocative of suites of magmas produced at phanerozoic convergent plate boundaries in the case where subducted crust is young and hot thus eoarchaean subduction first gave rise to short lived episodes of mantle wedge melting by hydrous fluxing yielding iablike basalts boninites in the hotter eoarchaean earth flux dominated destructive plate boundary magma generation quickly switched to slab melting of subducted oceanic crust this latter process produced the voluminous tonalites that were intruded into the slightly older sequences consisting of tectonically imbricated assemblages of iab like pillow lavas sedimentary rocks gabbros and upper mantle peridotite slivers zircon datingshows that eoarchaean ttg production in the itsaq gneiss complex was episodic 3870 3850 3840 3820 3810 3795 3760 3740 3710 3695 and 3660 ma in each case emplacement of small volumes of magma was probably followed by 10 40 maquiescence which allowed the associated thermal pulse to dissipate this explains why greenland eoarchaean crustal growth did not have granulite facies metamorphismdirectly associated with it instead 3660 3600 ma granulite facies metamorphism s in the itsaq gneiss complex were consequential to collisional orogeny and underplating upon termination of crustal growth similar eoarchaean crustal history is recorded in the anshan area of china where a few wellpreserved rocks as old as 3800 ma have been found including high mgo quartz diorites for 3800 ma rocks this is a rare if not unique situation outside of the itsaq gneiss complex the presence of volumetrically minor 3800 mamantle derived high mgo quartz diorites in both the itsaq gneiss complex and the anshan area indicates either that eoarchaean subduction zones were overlain by a narrow mantlewedge or that the shallow subduction trapped slivers of upper mantle between the conserved and consumed plates the geological society of london 2009

numerical simulation of waves generated by landslides using a multiple fluid navier stokes model abstract this work reports on the application and experimental validation for idealized geometries of a multiple fluid navier stokes model of waves generated by rigid and deforming slides with the purpose of improving predictive simulations of landslide tsunamis in such simulations the computational domain is divided into water air and slide regions all treated as newtonian fluids for rigid slides a penalty method allows for parts of the fluid domain to behave as a solid with the latter method the coupling between a rigid slide and water is implicitly computed rather than specifying a known slide kinematics two different volume of fluid algorithms are tested for tracking interfaces between actual fluid regions the simulated kinematics of a semi elliptical block moving down a water covered plane slope is first compared to an earlier analytical solution results for the vertical fall of a rectangular block in water are then compared to earlier experimental results finally more realistic simulations of two and three dimensional wedges sliding down an incline are compared to earlier experiments overall in all cases solid block velocities and free surface deformations are accurately reproduced in the model provided that a sufficiently resolved discretization is used the potential of the model is then illustrated on more complex scenarios involving waves caused by multi block or deformable slides

metamorphic fluid flow in the northeastern part of the 3 8 3 7 ga isua greenstone belt sw greenland a re evalution of fluid inclusion evidence for early archean seafloor hydrothermal systems abstract fluid inclusions in quartz globules and quartz veins of a 3 8 3 7 ga old well preserved pillow lava breccia in the northeastern isua greenstone belt igb were studied using microthermometry raman spectrometry and sem cathodoluminescence imaging petrographic study of the different quartz segregations showed that they were affected by variable recrystallization which controlled their fluid inclusion content the oldest unaltered fluid inclusions found are present in vein crystals that survived dynamic and static recrystallization these crystals contain a cogenetic immiscible assemblage of co2 rich h2o graphite and brine rich co2 halite carbonate inclusions the gas rich inclusions have molar volumes between 44 8 and 47 5 cm3 mol while the brine inclusions have a salinity of 33 eq wt nacl modeling equilibrium immiscibility using volumetric and compositional properties of the endmember fluids indicates that fluid unmixing occurred at or near peak metamorphic conditions of 460 c and 4 kbar carbonate and graphite were precipitated cogenetically from the physically separated endmember fluids and were trapped in fluid inclusions in most quartz crystals however recrystallization obliterated such early fluid inclusion assemblages and left graphite and carbonate as solid inclusions in recrystallized grains intragranular fluid inclusion trails in the recrystallized grains of breccia cementing and crosscutting quartz veins have co2 rich assemblages with distinctly different molar volumes either between 43 7 and 47 5 cm3 mol or between 53 5 and 74 1 cm3 mol and immiscible halite saturated h2o co2 nacl other salt inclusions later intergranular trails have ch4 h2 x h 2 up to 0 3 inclusions of variable density ranging from 48 0 to 105 3 cm3 mol and metastable h2o nacl other salt brines 28 eq wt nacl finally the youngest fluid inclusion assemblages are found in non luminescent secondary quartz and contain low density ch4 molar volume 105 33 cm3 mol and low salinity h2o nacl 0 2 3 7 eq wt nacl these successive fluid inclusion assemblages record a retrograde p t evolution close to a geothermal gradient of 30 c km but also indicate fluid pressure variations and the introduction of highly reducing fluids at 200 300 c and 0 5 2 kbar the quartz globules in the pillow fragments only contain sporadic ch4 h2 and brine inclusions corresponding with the late generations present in the cementing and crosscutting veins we argue that due to the large extent of static recrystallization in quartz globules in the pillow breccia fragments only these relatively late fluid inclusions have been preserved and that they do not represent remnants of an early seafloor hydrothermal system as was previously proposed modeling the oxidation state of the fluids indicates a rock buffered system at peak metamorphic conditions but suggests a change towards fluid graphite disequilibrium and a log f h 2 f h 2 o above the quartz fayalite magnetite buffer during retrograde evolution most likely this indicates a control on redox conditions and on fluid speciation by ultramafic rocks in the igb finally this study shows that microscopic solid graphite in recrystallized metamorphic rocks from isua can be deposited inorganically from a fluid phase adding to the complexity of processes that formed reduced carbon in the oldest well preserved supracrustal rocks on earth

a modern structural regime in the paleoarchean 3 64 ga isua greenstone belt southern west greenland abstract the footwall gneisses beneath the western part of the paleoarchean 3 8 ga isua greenstone belt southern west greenland are interpreted here in terms of a 3 64 ga stack of mylonitic crystalline thrust nappes the oldest example known on earth in present coordinates the kinematic history of the thrust nappe stack is couched in terms of initial longitudinal strike parallel thrusting towards the southwest followed by transverse thrusting to the northwest and subsequent extensional collapse of the thickened crust toward the southeast diorite and tonalite that form the western margin of granitoids structurally overlying the western part of the isua greenstone belt and its footwall contain 3 5 ga mafic dykes some of which are deformed and or truncated at fault contacts within the granitoids accordingly a component of the deformation structurally above the isua greenstone belt occurred after 3 5 ga significantly later than the formation of the underlying mylonitic nappes probably during the neoarchean the structural regime of mylonitic thrust nappe stacking is very similar to that in modern mountain belts it would appear that the deformational behaviour rheological constitution and overall strength of paleoarchean and modern continental crust were similar

ti in zircon thermometry applied to contrasting archean metamorphic and igneous systems abstract ti in zircon thermometry with shrimp ii multi collector has been applied to two well documented archean igneous and metamorphic samples from southern west greenland zircons from 2 71 ga partial melt segregation g03 38 formed in a small 1000 c yield a low temperature focused normal distribution with a mean of 683 32 c further demonstrated by high resolution ti mapping of two individual grains this distribution is interpreted to represent the temperature of the residual magma at zircon saturation late in the crystallization history of the tonalite hypothetically ti in zircon thermometry on eoarchaean detrital zircons sourced from such a high temperature tonalite would present a low temperature biased image of the host magma which could be misconstrued as being a minimum melt granite multiple analyses from individual zircons can yield complex ti distributions and associated apparent temperature patterns reflecting cooling history and local chemical environments in large magma chambers in addition to inclusions and crystal imperfections which can yield apparent high temperature anomalies zircon surfaces can also record extreme 1000 c apparent ti temperatures in our studies these were traced to 49ti or a molecular isobaric interference contamination derived from the double sided adhesive tape used in sample preparation and should not be assigned geological significance

numerical modelling of tsunami generation and propagation from submarine slumps the 1998 papua new guinea event summary deep and large submarine slumps may generate tsunamis as disastrous as tsunamis of tectonic origin such a landslide is likely to be the origin of the 1998 july 17 tsunami of papua new guinea the deadliest tsunami in the last 50 years water waves devastated a 20 km stretch of coastline wiping out three villages and killing more than 2200 people a numerical model has been developed to study the efficiency of deep slumps in producing tsunamis and has been applied to the papua new guinea event the landslide is treated as the flow of a homogeneous gravity driven continuum governed by a rheological law water waves are generated by sea bottom displacements induced by the landslide the shallow water approximation is adopted for both the landslide and the associated water waves the resulting differential equations are solved by a finite difference method based on shock capturing the shallow water hypothesis is tested by comparison with a model solving navier stokes equations for a mixture of water and sediments sensitivity tests carried out for a 2 d simplified geometry show that the water surface profile depends strongly on the constitutive law of the landslide the 1998 event is simulated numerically by the shallow water model testing different friction laws the observed inundation height distribution is well reproduced by the model for a volume of 4 km3 with its top located at a water depth of 550 m and sliding with a coulomb type friction law over a distance of 5 km

tsunamis generated by long and thin granular landslides in a large flume in this experimental study granular material is released down slope to investigate landslide generated waves starting with a known volume and initial position of the landslide source detailed data are obtained on the velocity and thickness of the granular flow the shape and location of the submarine landslide deposit the amplitude and shape of the near field wave the far field wave evolution and the wave runup elevation on a smooth impermeable slope the experiments are performed on a 6 7 m long 30 slope on which gravity accelerates the landslides into a 2 1 m wide and 33 0 m long wave flume that terminates with a 27 runup ramp for a fixed landslide volume of 0 34 m3 tests are conducted in a range of still water depths from 0 05 to 0 50 m observations from high speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material and that only a portion of the landslide termed the effective mass is engaged in activating the leading wave the wave behavior is highly dependent on the water depth relative to the size of the landslide in deeper water the near field wave behaves as a stable solitary like wave while in shallower water the wave behaves as a breaking dissipative bore overall the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near field wave amplitude the far field amplitude and the runup of tsunamis generated by granular landslides

gold occurrences of the archean north atlantic craton southwestern greenland a comprehensive genetic model abstract the north atlantic craton of southwestern greenland hosts several orogenic gold occurrences although to date none is in production four gold provinces are distinguished and include godthabsfjord tasiusarsuaq paamiut and tartoq in the godthabsfjord gold province the hypozonal gold occurrences are aligned along the major ca 2660 2600 ma ivinnguit fault orogenic gold mineralization correlates temporally with and is related to ductile deformation along this first order structure the northern part of the tasiusarsuaq gold province is characterized by small hypozonal gold occurrences that are controlled by 2670 2610 ma folds and shear zones auriferous fluids were focused into the structures in both gold provinces during west directed accretion of the kapisilik terrane 2650 2580 ma to the already amalgamated terranes of the north atlantic craton in the southern part of the tasiusarsuaq gold province hypozonal gold mineralization is hosted in back thrusts sermilik prospect and thrusts bjornesund prospect that formed at 2740 ma and 2860 2830 ma respectively the deformation is related to the ca 2850 ma accretion of the sioraq block and the tasiusarsuaq terrane and the 2800 2700 ma accretion of the tasiusarsuaq terrane and the faeringehavn and tre brodre terranes mesozonal orogenic gold mineralization is hosted in an accretionary complex in the paamiut and tartoq gold provinces gold occurrences cluster over a strike extent of approx 40 km in thrusts and complex strike slip settings in lateral ramps the timing of the e vergent terrane accretion in both areas is unknown and could either be at ca 2850 ma or 2740 ma in the eastern part of the paamiut gold province quartz veins and associated alteration zones were overprinted by granulite facies metamorphism and show evidence for partial melting these outermost parts of the accretionary complex were involved in burial exhumation tectonics during crustal accretion mainly three different orogenic stages related to gold mineralization are distinguished in the north atlantic craton between ca 2850 ma and 2610 ma these are generally accretionary tectonic episodes and gold mineralization is hosted either in reactivated fault systems between terranes or accretionary complex structures along the deformed cratonic margin the larger orogenic gold occurrences formed at ca 2740 2600 ma that appears to be a period of orogenic gold mineralization globally although significant gold resources in the north atlantic craton have yet to be identified

reconstruction of a 3700 ma transgressive marine environment from isua greenland sedimentology stratigraphy and geochemical signatures abstract the rare preservation of a stratigraphy in the northwest of the eoarchean isua supracrustal belt greenland demonstrates the world s earliest recognised marine transgression stratigraphically lowest is the 3710 ma solvang volcanic formation of picrites basalts and basaltic andesites with arc like geochemical signatures close to its erosional top this formation s volcanic rocks show increase in k2o with depletion of na2o depletion in sr with no alteration in eu abundance and 18ovsmow increase to 16 interpreted as subaerial weathering at 3700 ma the sedimentary snowpatch formation was deposited unconformably on the solvang volcanic formation locally the unconformity is marked by the laterally discontinuous conglomerate member dominated by rounded quartz clasts but also with clasts of basalt and andesite up to 10 cm across layered chert and ultramafic rocks the conglomerate member carries sparse detrital zircons the youngest of which are 3710 ma the conglomerates are succeeded by the sandstone and dolostone member of layered quartz and dolomite clastic sandstones that locally preserve relict shallow marine cross bedding with scoured layers tempestite breccia beds and very rare stromatolite horizons the sandstone and dolostone member is succeeded by the 3695 ma bif member the snowpatch formation quartz dolomite sandstones and interlayered stromatolites have seawater like ree y trace element patterns variably modified by a negligible to significant influx of a terrigenous component trace element signatures such as ti v ratios and normalising ree y data to a 3710 ma weathered volcanic rock rather than post archean average shale suggest this component was derived from a juvenile arc source resembling the basement solvang volcanic formation the detailed field and geochemical evidence such as positive correlation between fe mg and pr yb in the snowpatch formation dolostones and bif banded iron formation indicates that the dolomitic lithologies developed in a shallow water setting with clastic sedimentation during a marine transgression over a weathered 3710 ma volcanic arc basement followed by bif deposition in deeper water thus by 3700 ma shallow water exposed settings had already been established which were the site of stromatolite development

the early archaean itsaq gneiss complex of southern west greenland the importance of field observations in interpreting age and isotopic constraints for early terrestrial evolution geochemical and isotopic studies of small volumes of variably preserved 3600 ma rocks in gneiss complexes are crucial for documenting early earth history in the itsaq gneiss complex of the nuuk region west greenland there is dispute whether the granitic sensu lato orthogneisses dominating it are mainly products of a single ca 3650 ma crust formation super event or whether they formed in several unrelated events between ca 3850 and 3560 ma which of these interpretations of the dates is correct has major implications regarding what the whole rock radiogenic isotopic record pb pb sm nd rb sr reveals about continental crust formation and early terrestrial differentiation there is also debate whether some west greenland metasedimentary rocks with 12c 13c data interpreted as evidence for life are 3850 ma or only 3650 ma old establishing the correct age for these rocks is important for debates concerning early surficial environments and origin of life controversies have arisen because of different approaches taken by different workers specifically with respect to how much emphasis is placed on field geology in interpreting dates and isotopic data in this paper field observations and sampling from low strain zones where the origin and geological context of the rocks are best preserved and understood are closely integrated with u pb zircon dates and cathodoluminescence cl imagery of the zircons this approach shows that most single phase well preserved meta granitoid samples have simple zircon populations dominated by oscillatory zoned prismatic grains formed when their host magmas crystallized on the other hand migmatites and some strongly deformed banded gneisses have much more complex zircon populations the combined field evidence and zircon geochronology on the itsaq gneiss complex demonstrate that 1 some areas contain exposed orthogneisses formed during multiple magmatic thermal events between ca 3850 and 3560 ma and are not as suggested by kamber and moorbath 1998 dominated by ca 3650 ma granitoids containing abundant 3650 ma zircons inherited from cryptic unexposed older rocks 2 abundant 3750 ma granitoids are present which are locally well preserved 3 some water lain sediments reported as showing c isotope evidence for life were deposited as early as 3850 ma 4 the whole rock sm nd isochron approach fails to distinguish with any confidence 3650 ma from 3800 ma rocks 5 however it reinforces previous indications for markedly depleted 2 5 nd domains in the pre 3750 ma mantle

new pieces to the archaean terrane jigsaw puzzle in the nuuk region southern west greenland steps in transforming a simple insight into a complex regional tectonothermal model in the south of the nuuk region of west greenland our 1980s mapping recognized four archaean gneiss terranes f ringehavn tre brodre tasiusarsuaq and akia terranes with different protolith ages and separate early tectonothermal histories later in the archaean these were juxtaposed and then experienced the same 2700 2500 ma tectonothermal events here we abandon extrapolation of only these four terranes across the whole region and distinguish two new terranes in the ne the northernmost isukasia terrane previously regarded as the northernmost exposure of the f ringehavn terrane consists of palaeoarchaean rocks 3600 ma tectonically bounded on its south by the 3075 2960 ma kapisilik terrane these were juxtaposed and metamorphosed together by 2950 ma the previously recognized f ringehavn terrane to the sw is another separate entity of palaeoarchaean rocks that was juxtaposed with adjacent terranes only after c 2800 ma hence in an increasingly complex regional model there were several mid to neoarchaean terrane assembly events with superimposed orogenies from c 2950 ma until after 2700 ma although the f ringehavn and isukasia terranes were incorporated into the later archaean terrane collage at different times they might be fragments from a larger palaeoarchaean complex rifted apart from c 3500 ma onwards

a general numerical model for surface waves generated by granular material intruding into a water body abstract surface water waves generated by large scale landslides have been a major concern of many geoscientists and coastal engineers because they may result in disastrous consequences this study presents an advanced two phase model for dry granular material intruding into an otherwise still water body as well as their resulting waves the water air interface both within and outside the granular material is captured by the volume of fluid method the inter granular stresses are formulated based on a general collisional frictional law developed for underwater granular flows and a modified k e model is adopted to describe the turbulence effect of the ambient fluid phase interaction is characterized by the drag force caused by the relative motion between the granular particles and the fluid the effect of the ambient fluid on the restitution coefficient of granular particles is also considered the newly proposed two phase model is validated following a reasonable agreement of the numerical results with measured data from small scale laboratory tests on surface waves caused by collapse of a subaerial granular column and by intrusion of a landslide into water generation and propagation of the waves as well as the motion and deformation of the granular body are all adequately represented by the numerical model a relatively more general applicability of the proposed model to the study of waves generated by granular landslides can thus be expected

comment on a vestige of earth s oldest ophiolite furnes et al reports 23 march 2007 p 1704 reported the identification of an ophiolite sequence within the approximately 3 8 billion year old isua supracrustal belt however they did not acknowledge that the belt contains supracrustal rocks and mafic dikes of different ages nor did they demonstrate that the proposed components of the ophiolite are coeval

subglacial hydrology in north western germany during the last glaciation groundwater flow tunnel valleys and hydrological cycles abstract numerical modelling of groundwater dynamics in an overpressured system of subglacial aquifers and aquitards under the marginal portion of the scandinavian ice sheet in northwestern germany has been coupled with calculations of basal meltwater production rates and with field evidence of meltwater erosional features largely fine grained subglacial sediments with relatively low hydraulic conductivities had a capacity to drain only about 25 of all basal meltwater produced in the relevant subglacial catchment area the rest of the meltwater was evacuated through tunnel valleys in spontaneous outburst events subglacial drainage cycles are proposed in which each cycle begins with meltwater drainage through the substratum groundwater flow followed by water ponding at the ice bed interface and ends in catastrophic meltwater releases through tunnel valleys

timing and nature of multiple 3700 3600 ma tectonic events in intrusive rocks north of the isua greenstone belt southern west greenland one of the oldest well preserved sequences of tectonic events on earth is recorded in intrusive rocks that lie north of the isua greenstone belt southern west greenland detailed mapping and u pb dating of zircon and titanite build upon previous work to better define the timing and nature of the 3700 3600 ma tectonic history voluminous 3698 2 ma tonalite was converted into gneiss during a deformation event d 1 that predated intrusion of 3659 2 ma diorite dikes the dikes and the earliest gneissosity s 1 are most abundant in a zone of low regional deformation d 2 located 8 km north of the isua greenstone belt f 2 folding produced the dominant gneissosity s 2 during injection of meter wide granite and pegmatite sheets along s 2 at ca 3650 ma d 3 shearing transposed s 2 into a narrow mylonite zone at the contact between the intrusive rocks and the isua greenstone belt motion on this contact must have occurred in the early archean mylonites are cut by dolerite dikes that are correlated with nearby middle archean dikes titanite from the low d 2 strain zone yielded concordant u pb dates of 3606 3 ma indicating that these rocks were little affected by late archean metamorphism in contrast significant late archean heating of rocks adjacent to the isua greenstone belt is shown by titanite that lost considerable pb and or was largely recrystallized at 2915 32 ma late archean strain was also restricted to rocks adjacent to the belt this sequence of overprinting deformation and metamorphism is similar to that in younger orogenic belts

water storage and subglacial drainage conditions inferred from borehole measurements on gornergletscher valais switzerland measurements of change in length of a borehole or displacements of poles and of subglacial water pressure were combined with drainage tests and electrode tests in boreholes in experiments near the northern margin of gornergletscher valais switzerland at the upstream side of an overdeepening the measurements suggest that the subglacial drainage system consisted of discrete conduits at that location presumably linked cavities on clean bedrock changes in subglacial water pressure were followed by variations in subglacial water storage together with similar variations in elevation of a pole the variations in subglacial water storage caused changes in cross sections of subglacial passageways and thereby changed the frequencies of slug test oscillations similar experiments conducted near the center line of the glacier revealed different subglacial conditions impeded drainage through a sediment layer and different depths of water levels in different boreholes these results are discussed in relation to previous studies

earliest part of earth s stratigraphic record a reappraisal of the 3 7 ga isua greenland supracrustal sequence investigations of the isua supracrustal rocks in west greenland allow us to identify the protoliths and alteration history for most isua rocks the protoliths consisted of alternating basalt and banded iron formation this sequence was invaded by dunitic sills metamorphosed and later intruded by felsic gneisses pervasive carbonation and k metasomatism produced a sequence of lithologies mimicking those found in modern platform deposits however the protoliths could have originated in a purely oceanic environment with no sialic detrital components the isua sequence probably consists of several tectonic panels some of which are cut by 3810 ma felsic intrusive rocks

detrital zircon sedimentary provenance ages for the eoarchaean isua supracrustal belt southern west greenland juxtaposition of an imbricated ca 3700 ma juvenile arc against an older complex with 3920 3760 ma components abstract the amphibolite facies eoarchaean isua supracrustal belt northern part of the nuuk region southern west greenland is dominated by strongly deformed metabasalts with chert banded iron formation felsic volcanic and volcano sedimentary rocks and minor gabbro and sedimentary carbonates it comprises a suture zone between a northern terrane formed at ca 3700 ma and a southern one formed at ca 3800 ma at the junction between these two terranes is a strongly tectonised thin unit of metachert bif and carbonate bearing rocks with minor detrital components named the dividing sedimentary unit away from the belt the northern terrane is dominated by ca 3700 ma tonalites and the southern one by ca 3800 ma tonalites the isua supracrustal belt chemical metasedimentary rocks give low yields of small commonly 50 m long prismatic oscillatory zoned zircons with less common somewhat rounded zircons of volcanic and or detrital origin the most siliceous of the felsic schists give a larger yield of volcanic or detrital zircons the ages of these zircons are distinct in different parts of the belt in the northern terrane most have ages of 3710 3690 ma with a few slightly older 3750 ma detrital zircons suggests that these volcanic assemblages evolved remote from 3800 ma crust in contrast the up to 3940 ma detrital zircons from the dividing sedimentary unit and the southern fuchsite quartzite shows that the southern ca 3800 ma terrane although dominated by arc related rocks might contain older pre 3800 ma crust we propose that the dividing sedimentary unit was deposited on top of already deformed southern terrane rocks and then acted as a decollement when the northern terrane ca 3700 ma arc complex collided with the southern terrane by ca 3660 ma from previous age constraints thus the detrital zircon age data is compatible with proposals from other evidence for juxtaposition of ca 3700 and 3800 ma terranes in the isua area some thin siliceous metasedimentary rocks along post assembly mylonite zones in the isua supracrustal belt yield some

the neoarchaean storo supracrustal belt nuuk region southern west greenland an arc related basin with continent derived sedimentation we present new major and trace element data as well as sm nd isotope compositions for archaean supracrustal rocks and a gabbro anorthosite complex from the island of storo in godthabsfjord southern west greenland we also provide new u pb isotope data for zircon extracted from these rocks the storo rocks have experienced amphibolite facies metamorphism and the entire sequence forms an east dipping frontal thrust ramp in tectonic contact with mesoarchaean nuk gneisses to the west and eoarchaean itsaq gneisses to the east these orthogneisses record a complex regional accretion history as established by previous work the present study aims at explaining the geochemical features of the storo supracrustal belt ssb which comprises metavolcanic and metasedimentary rocks that are situated within this collisional zone the ssb has a maximum age of ca 2800 ma constrained by the youngest detrital zircon population found in a metasedimentary unit the minimum age of the ssb is 2707 8 ma defined by previously published re os isotope data the metavolcanic rocks have a tholeiitic basaltic composition with relatively flat primitive mantle normalised trace element patterns and generally negative nb anomalies nb nb 0 30 0 90 they plot above the mantle array in th yb nb yb space consistent with a subduction zone affinity as also proposed by previous studies a thin fault contact separates the ssb from a gabbro anorthosite complex formally defined here as the storo anorthosite complex which has an age of ca 3050 ma the sm nd isotope data of the ssb suggest that these metavolcanic rocks experienced contamination by a crustal source that was isotopically similar to the storo anorthosite complex sac this in turn suggests that the sac could have formed the basement for the younger volcanic sequence of the ssb or alternatively that the mantle source of the ssb was contaminated by melts derived from sac aged crust or sediments the metasedimentary rocks of ssb show a mixed mafic felsic component with variable degrees of maturity highly mature metasediments of the ssb contain several age populations of regionally well known magmatic events and thus support a significant local crustal provenance furthermore the youngest documented detrital zircon is found in a thin metasedimentary unit within the metavolcanic rocks and thereby shows that the ssb formed in close proximity to subaerially exposed continental crust i e a back arc environment and not a distal island arc setting as previously proposed finally this suggests that relatively cool lower continental crust which was capable of supporting subaerial mountains existed at least locally during the meso neoarchaean

the complex age of orthogneiss protoliths exemplified by the eoarchaean itsaq gneiss complex greenland shrimp and old rocks abstract field studies integrated with cathodoluminescence petrography and shrimp u pb dating of zircons from 150 orthogneisses and metatonalites from the eoarchaean itsaq gneiss complex southern west greenland shows that only a minority contain 3840 ma zircons whereas the majority carry only younger ones rocks containing 3840 ma zircons vary from very rare single phase metatonalites to more common complexly banded tonalitic migmatites the former metatonalites have simple oscillatory zoned 3840 ma zircon with limited recrystallisation and overgrowth whereas the more common migmatites have much more complicated zircon populations with both 3840 ma and 3650 3600 ma oscillatory zoned zircon more extensive recrystallisation and widespread complex core rim multiple growth relationships with only 100 160 ppm zr in the tonalites and likely melt generation temperatures of 1000 c the experimentally determined zircon solubility melt composition relationships established by other workers shows that the precursor melts to the itsaq complex tonalites were strongly undersaturated in zircon thus any entrained xenocrystic zircon would have been rapidly dissolved therefore the 3840 ma oscillatory zoned zircons crystallised out of tonalitic melt and gives magmatic age of the rock in which they occur with an established igneous age of 3840 ma established from such relationships we interpret the correlated variation between the field nature of these rocks and their zircon petrography age structure as due to superimposition onto 3840 ma tonalite protoliths of variable amounts of heterogeneous strain heterogeneous distribution of melt patches formed during in situ anatexis at up to 800 c plus granitic veining this explains why geologically simple metatonalites have simple zircon populations whereas complex orthogneisses have complex zircons the large amount of integrated field geochemical and zircon data rule out an alternative interpretation that the 3840 ma zircons represent an igneous xenocrystic component present in younger rocks to varying degrees if this were true then the structurally simple less reworked rocks should still display complex zircon populations gneisses with 3840 ma zircon are commonest on akilia and neighbouring islands in itilleq fjord 65 km east akilia and on the north of ivisaartoq 150 km northeast of akilia these include from itilleq a 3891 6 ma gneissic tonalite with minor neosome which is currently the oldest rock recognised in the itsaq gneiss complex overall the 3840 ma tonalites are a widespread and unevenly distributed in the itsaq gneiss complex and they are a volumetrically minor component compared with 3800 3750 and 3700 ma tonalite generations using the subset of our data covering itilleq and the neighbouring fjords migmatite samples with 3800 ma igneous zircon are mutually exclusive from migmatite samples with 3700 ma igneous zircon this suggests that prior to an amalgamation event followed by 3660 3600 ma high grade metamorphism 3840 ma tonalites might have resided in a terrane discrete from 3700 ma tonalites this is in accord with interpretation of the non migmatised part of the complex in the isua area where a terrane of 3800 ma tonalites with a minor associated 3840 ma component and a terrane with 3700 ma tonalites were tectonically juxtaposed at 3660 ma

highly depleted hadean mantle reservoirs in the sources of early archean arc like rocks isua supracrustal belt southern west greenland abstract growing evidence from the accessible geological record reveals that crust mantle differentiation on earth started as early as 4 4 ga in order to assess the extent of early archean mantle depletion we obtained 176lu 176hf 147sm 143nd and high field strength element hfse concentration data for the least altered well characterized boninite like metabasalts and associated metasedimentary rocks from the isua supracrustal belt southern west greenland the metasediments exhibit initial ehf 3720 values from 0 7 to 1 5 and initial end 3720 values from 1 6 to 2 1 initial ehf 3720 values of the least altered boninite like metabasalts span a range from 3 5 to 12 9 and initial end 3720 values from 0 3 to 3 2 these initial hf isotope ratios display coherent trends with sio2 al2o3 tio2 and other relatively immobile elements indicating contamination via assimilation of enriched components most likely sediments derived from the earliest crust in the region this model is also consistent with previously reported initial os 3720 values for some of the samples in addition to the positive ehf 3720 values the least disturbed samples exhibit positive end 3720 values and a co variation of ehf 3720 and e d 3720 values based on these observations it is argued that the most depleted samples with initial ehf 3720 values of up to 12 9 and high 176lu 177hf of 0 05 to 0 09 tap a highly depleted mantle source with a long term depletion history in the garnet stability field high precision high field strength element hfse data obtained for the isua samples confirm the contamination trend even the most primitive samples display negative nb ta anomalies and elevated nb ta indicating a subduction zone setting and overprint of the depleted mantle sources by felsic melts generated by partial melting of eclogite collectively the data for boninite like metabasalts support the presence of strongly depleted mantle reservoirs as previously inferred from hf isotope data for hadean zircons and combined 142nd 143nd isotope data for early archean rocks

mesoarchaean collision of kapisilik terrane 3070ma juvenile arc rocks and 3600ma isukasia terrane continental crust greenland abstract the mesoarchaean kapisilik and eoarchaean isukasia terranes in the nuuk region of southern west greenland were tectonically juxtaposed in the archaean the north of the isukasia terrane is distal from the kapisilik terrane and has only rare growth of 2690 ma metamorphic zircon and no 2980 2950 ma metamorphic zircon the southern part of the isukasia terrane lies between two 2690 ma shear zones and has locally preserved high pressure granulite facies assemblages and widespread growth of 2980 2950 ma metamorphic zircon and also sporadic growth of 2690 ma metamorphic zircon within this southern part of the isukasia terrane there is a folded klippe of mylonitised mesoarchaean detrital meta sedimentary rocks carrying 3600 and 3070 ma detrital zircons mafic and ultramafic rocks with 2970 ma metamorphic zircon overgrowths south of the isukasia terrane is the kapisilik terrane containing 3070 ma arc related volcanic rocks gabbro anorthosites and meta tonalites intruded by 2970 2960 ma granites zircons of an ivis rtoq supracrustal belt 3075 ma intermediate volcanic rock have initial hf values of 2 to 5 thus are juvenile crustal additions 3070 ma tonalites along the northern edge of the kapisilik terrane have whole rock positive initial nd values and thus are also juvenile crustal additions in contrast igneous zircons in 2960 ma granites intruded into juvenile 3075 ma supracrustal rocks of the kapisilik terrane have initial hf values of 5 to 10 and must have involved the partial melting of 3600 ma isukasia terrane rocks the integrated structural and zircon u th pb hf isotopic data show that at 2980 2950 ma the kapisilik terrane juvenile arc components collided with and over rid the isukasia terrane the southern edge of the isukasia terrane came to lie in the deep crust under the ivis rtoq supracrustal belt and melted at 2970 2960 ma to produce granites these granites derived from ancient crust rose into the upper crust where they intruded the overlying allochthonous juvenile 3075 ma ivis rtoq supracrustal belt arc assemblages the southern edge of the isukasia terrane is interpreted as an interior nappe of eoarchaean basement rocks interfolded with a klippe of mesoarchaean metasedimentary and mafic ultramafic rocks both of which are affected by 2980 2950 ma metamorphism the mixed eoarchaean mesoarchaean detrital provenance suggests that the klippe could be dismembered components of an accretionary prism or forearc crust the northern part of the isukasia terrane is interpreted as foreland free of 2980 2950 ma high grade metamorphic overprint this shows that the isukasia terrane is not a coherent block but contains ancient rocks that are parautochthonous or allochthonous to each other with contrasting later metamorphic history at 2690 ma the crustal architecture arisen from mesoarchaean collision between an older continental block and an island arc was reworked along intra crustal shear zones coeval with amphibolite facies metamorphism this reworking followed on from major terrane assembly at 2710 2700 ma in the southern part of the nuuk region when the eoarchaean faeringehavn terrane was juxtaposed with 2840 2825 ma arc rocks thus the 2980 2950 ma assembly of the isukasia and kapisilik terranes is distinct from the later 2710 2700 ma terrane assembly further south in the nuuk region

testing the model of late archean terrane accretion in southern west greenland a comparison of the timing of geological events across the qarliit nunaat fault buksefjorden region abstract the prevailing tectonic model for the archean gneiss complex of southern west greenland holds that terranes with different metamorphic histories and protolith ages were juxtaposed between 2 80 and 2 72 ga this model was tested by using detailed mapping and u pb geochronology to compare the timing of geological events across the qarliit nunaat fault the boundary between terranes in the buksefjorden region the fault was interpreted as a terrane boundary mostly because it is a narrow zone of mylonitic rocks that separates granulite or retrograde amphibolite facies gneisses of the tasiusarsuaq terrane tt from prograde amphibolite facies gneisses of the akulleq terrane at and it separates tonalitic gneisses of different age 3 87 3 60 and 2 80 ga in the at versus 2 92 2 86 ga in the tt dating of similar homogeneous gneisses in each terrane yielded ages of 2843 3 ma in the tt tonalite and 2824 2 ma in the at granodiorite ikkattoq gneiss granulite facies metamorphism in the tt is thought to have coincided with intrusion of a 2805 2 ma orthopyroxene pegmatite and zircon and titanite from nearby amphibolitic gneiss yielded ages of 2779 2 and 2660 10 ma respectively metamorphic minerals in the at are younger zircon and titanite from amphibolitic gneiss are 2717 3 and 2510 10 ma respectively and monazite from pelitic schist is 2732 5 and 2708 4 ma a concordant pegmatite layer that underwent a substantial amount of shearing along the qarliit nunaat fault was dated at 2725 2 other pegmatites that intruded relatively late in the structural history crystallized at 2710 2 in the tt and 2541 2 ma in the at these results support the prevailing tectonic model by showing that i similar homogeneous gneisses in each terrane are different age ii 2805 ma granulite facies metamorphism in the tt predated 2740 2700 ma amphibolite facies metamorphism in the at and iii shearing along the terrane boundary occurred after 2725 ma

multiple sulfur isotope signature of early archean oceanic crust isua sw greenland abstract the archean sulfur cycle was different from the present day cycle as the emission of volcanogenic sulfurous gases was the dominant process in the anoxic environment of the early earth this emitted sulfur exhibits mass independently fractionated sulfur isotopes mif s resulting from photochemical reactions in the atmosphere and it differs substantially from unfractionated sulfur in the mantle so far the main focus of multiple sulfur analyses 32 s 33 s 34 s and 36 s was placed on the sedimentary part of the archean sulfur cycle in order to constrain the magmatic part of the sulfur cycle we analyzed the sulfur isotopic composition of oceanic crustal rocks from the ca 3 7 3 8 ga isua supracrustal belt isb differently altered samples were taken from two units 1 the undifferentiated amphibolites ua and 2 the younger amphibolites with boninitic affinity ab the mean values are 34 s crs 0 01 0 65 values range from 0 87 to 1 37 crs chromium reducible sulfur 33 s crs 0 02 0 12 values range from 0 17 to 0 26 36 s crs 0 47 0 06 values range from 0 56 to 0 38 thus the mean isotope values support the assumption that the sulfur isotopic signature reflects the expected near zero signature of their mantle origin however differences in 33 s crs values are discernible and non zero suggesting that different sources are contributing to the isotopic signature an influence of alteration is excluded for all samples as different alteration sensitive geochemical parameters do not show any correlation with the multiple sulfur isotope signatures further it is unlikely that the small magnitudes in 33 s crs are generated by microbial mass dependent processes because of the narrow range of 34 s crs values possible sources contributing an atmospheric mif s signature include seawater sulfate negative 33 s crs values through hydrothermal circulation the assimilation of ocean floor sediments during the ascent of the melt and or a mantle source contamination by subducted oceanic slab

geology of the eoarchean 3 95 ga nulliak supracrustal rocks in the saglek block northern labrador canada the oldest geological evidence for plate tectonics the earth is a unique planet which has been highly evolved diversified and complicated through geologic time and underwent many key events including giant impact magma ocean core formation large scale mantle differentiation and late heavy bombardment especially in its dawn but our knowledge of early earth is limited due to the lack of the hadean supracrustal rocks the supracrustal rocks with the eoarchean ages provide key evidence for the earth s early evolution but few supracrustal rocks have been comprehensively investigated therefore we mapped in seven areas of the saglek block northern labrador where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses early studies suggested that some of them have the mesoarchean ages because of the lack of the mesoarchean saglek dyke but we found the saglek dykes in the areas to recognize the eoarchean nulliak supracrustal rocks and uivak gneiss in all the areas recent reassessment of u pb dating and cathodoluminescence observation of zircons from the oldest suites of the uivak gneiss showed that the uivak gneiss has the eoarchean age 3 95 ga and forms the iqaluk uivak gneiss series because our geological survey clearly showed that the iqaluk uivak gneisses were intruded into the nulliak supracrustal belts the nulliak supracrustal rocks are the oldest supracrustal rock in the world the supracrustal belts consist of piles of fault bounded blocks which are composed of the ultramafic rocks mafic rocks and sedimentary rocks in ascending order similar to modern ocean plate stratigraphy ops in addition small scale duplex structures are found over the areas the presence of duplex structure and ops indicates that the 3 95 ga nulliak supracrustal belts originate from an accretionary complex the presence of the accretionary complex ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early earth

groundwater flow beneath late weichselian glacier ice in nordfjord norway basal water pressure and water flow patterns are significant factors in controlling the behavior of an ice sheet because they influence ice sheet thickness stability and extent water produced by basal melting may infiltrate the subsurface or occur as sheet or channelized flow at the ice bed interface we examine subglacial groundwater conditions along a flowline of the scandinavian ice sheet through nordfjord in the western fjords region of southern norway using a steady state two dimensional groundwater flow model meltwater input to the groundwater model is calculated by a two dimensional time dependent thermomechanically coupled ice flow model oriented along the same flowline model results show that the subglacial sediments could not have transmitted all the meltwater out of the fjord during times of ice advance and when the ice sheet was at its maximum position at the edge of the continental shelf in order for pore water pressures to remain below the overburden pressure of the overlying ice other paths of subglacial drainage are necessary to remove excess water during times of retreat the subglacial aquifer is incapable of transmitting all the meltwater that was probably generated pulses of meltwater reaching the bed could explain non climatically driven margin readvances during the overall retreat phase

the eoarchean legacy of isua greenland worth preserving for future generations abstract the eoarchean 3600 ma or millions of years ago folded and metamorphosed isua supracrustal belt and the adjacent orthogneiss exposures of greenland contain rare low deformation lenses that display some uniquely preserved components of earth s oldest rock record these include world s oldest but contested stromatolites in dolomitic carbonates conglomerates pillow basalts demonstrating submarine eruption slivers of upper mantle rocks formation of earliest continental crust by multistage tonalite diorite emplacement followed by intracrustal granite production all these diverse occurrences are keys to establish early earth s processes at the start of the geological record although some of these features are preserved at several localities other critical ones are exposed on only a few m2 of rock at single localities or are of historical significance none of these sites are currently protected and there is a reliance on responsible sampling to keep them intact for future generations given the high interest in the archean eon combined with the increased ease of fieldwork in remote localities many significant deep time localities in not only greenland but worldwide are in danger of eradication here five key isua area geological sites are presented with an explanation of their significance and worthiness for initially reliance on already collected samples but hopefully ultimately government protection this highlights an increasing problem of destruction of in situ evidence of earth s unique early geological heritage and the need for collaboration in protecting and archiving of these key scientific resources

3700 ma pre metamorphic dolomite formed by microbial mediation in the isua supracrustal belt w greenland simple evidence for early life chemical meta sedimentary rocks in the amphibolite facies 3700 ma isua supracrustal belt w greenland are mostly strongly deformed so there is only a small chance of the survival of features such as stromatolites or microfossils that would be direct proof of a 3700 ma biosphere therefore the search for evidence of 3700 ma life in isua rocks has focused on chemical signatures particularly c isotopes the new approach presented here is based on whole rock chemistry rather than isotopic signatures isua chemical sedimentary rocks have ca mg fe bulk compositions that coincide with ferroan dolomite siderite fe oxide mixtures most have low al2o3 tio2 contents 0 5 and 0 05 wt respectively showing minimal contamination from terriginous materials identical seawater like ree y shale normalised trace element signatures with la ce eu and y positive anomalies are found in magnetite rich banded iron formation bif such as the geochemical standard if g dolomite rich rocks and quartz carbonate calcsilicate rocks additionally from a rare small area of low deformation in isua there are 3700 ma pillow lava interstices consisting of quartz tremolite calcite derived from pre metamorphic dolomite silica thus the dolomite in the chemical sediments and the pillow interstice was part of the pre metamorphic assemblage and was deposited from seawater and or low temperature groundwater as shown by the ree y chemistry therefore at least some isua carbonate rocks are sedimentary or diagenetic in origin rather than being formed by metasomatism at 600 500

early archaean amitsoq tonalites and granites of the isukasia area southern west greenland development of the oldest known sial amphibolite facies early archaean amitsoq gneisses envelop and intrude the c 3 800 ma isua supracrustal belt isukasia area southern west greenland most of these gneisses are strongly deformed but in a c 75 km2 augen of lower deformation the amitsoq gneisses are seen to comprise predominantly 3 750 3 700 ma tonalitic grey gneisses that were intruded first by thin bodies of mafic to dioritic composition known collectively as the inaluk dykes and then by c 3 600 ma white gneisses and finally by sporadic c 3 400 ma pegmatitic gneiss sheets the grey gneisses could have formed by partial melting of crust consisting predominantly of basic rocks the inaluk dykes are interpreted as strongly fractionated basic melts of mantle origin contaminated by crustal material the white gneisses consist mostly of medium grained granite and occur as lenses and anastomosing sheets throughout their host of grey gneisses with subordinate inclusions of supracrustal rocks the white gneisses have chemistry compatible with formation by partial melting at depth of a source dominated by grey gneisses the igneous chemistry including ree abundances of the grey gneisses and white gneisses has been modified to varying degrees by metasomatism and assimilation reactions during the crystallisation of the white gneisses and also during subsequent tectonometamorphic events the white gneisses are evidence for considerable reworking by anatexis of sialic crust in the early archaean 150 to 100 ma after its formation the white gneisses and the pegmatitic gneisses show that granitic rocks s s were important in the earliest archaean and are further evidence of the diversity of the oldest known sial

evolution of early crust in chondritic or non chondritic earth inferred from u pb and lu hf data for chemically abraded zircon from the itsaq gneiss complex west greenland zircon grains in rocks collected from the itsaq gneiss complex southwest greenland were analyzed for u pb and lu hf in the same grain using isotope dilution thermal ionization mass spectrometry tims and multicollector inductively coupled plasma mass spectrometry mc icp ms grains were pretreated using chemical abrasion or air abrasion to assure that only zircon material unaffected by the migration of parent and daughter elements was analyzed the data are consistent with derivation of all studied rocks from a single enriched mantle source or mafic crustal protolith with 176lu 177hf of 0 022 0 003 that was repeatedly melted and produced tonalitic magmas the assessment of the primary mantle source from which this mafic protolith was derived at or before 3 85 ga greatly depends on the assumed composition of the bulk silicate earth using the currently accepted lu hf bulk earth parameters based on the analysis of chondrites yields ehf t of 0 to 1 for the 3 80 3 86 ga rocks suggesting that

physical modeling of tsunamis generated by three dimensional deformable granular landslides 1 tsunamis generated by deformable granular landslides are physically modeled in a three dimensional tsunami wave basin based on the generalized froude similarity the dynamic landslide impact characteristics were controlled by means of a novel pneumatic landslide generator the wave amplitudes periods and wavelengths are related to the landslide parameters at impact with the landslide froude number being a dominant parameter between 1 and 15 of the landslide kinetic energy at impact is converted into the wave train energy the wave amplitudes decay in radial and angular directions from the landslide axis the first wave crest mostly travels with speeds close to the theoretical approximation of the solitary wave speed the measured tsunami wave profiles were either of the nonlinear oscillatory or nonlinear transition type depending primarily on the landslide froude number and relative slide thickness at impact the generated waves range from shallow to deep water depth regimes with the majority being in the intermediate water depth regime wave characteristics are compared with other two and three dimensional landslide tsunami studies and the results are discussed

controversial pb pb and sm nd isotope results in the early archean isua west greenland oxide iron formation preservation of primary signatures versus secondary disturbances pb stepwise leaching pbsl determinations on two magnetite enriched fractions of a bif sample from the northeastern part of the isua supracrustal belt west greenland yield an isochron of 3691 22 ma mswd 0 4 in combination with previously published geochronological constraints for a minimum deposition age of 3 71 ga for volcanic sequences nutman et al 1997 comprising the studied bifs and supported by microtextural observations this demonstrates an early archean amphibolite facies metamorphic event in the supracrustal pbsl data on magnetite from slightly discordant veins within the same iron stone together with bulk pb isotope values of paragenetically late pyrite yield a 3 63 0 07 ga mswd 8 6 errorchron with significantly different pb isotopic compositions from those obtained from the main magnetite layers and this suggests that the discordant layers of magnetite and sulfides crystallized when externally derived fluids passed through the formation a few tens of million of years later the fluids controlling this redistribution of magnetite can be tentatively correlated with metasomatic alteration features produced during the widespread intrusion of 3 6 ga granitic into 3 7 ga tonalitic amitsoq gneisses enclosing the belt tremolite rich layers in the bif are characterized by sm nd ratios close to chondritic end 3800 of 1 7 and 2 1 within error of published results from adjacent basic units in the supracrustal suite in contrast the magnetite dominated layers yield unrealistically high end 3800 of 14 8 and 14 4 indicative of sm nd ratios resembling ree fractionated continental sources these high end 3800 together with radiogenic sr leached from the magnetite enriched separates is ascribed to secondary hydroxyapatite which predominantly forms as crystal overgrowths in the magnetite rich bands the timing of the hydrothermal event during which apatite was deposited within the bif remains uncertain but a tchur model age of 1 85 ga from the apatite dominated hcl leachate may point to a close genetic relationship with local proterozoic metamorphism and granite formation by crustal remelting in the isukasia area step leaching of magnetite from a similar silicate oxide facies bif from the western part of the isua supracrustal belt yield a pb pb isochron age of 2 84 0 05 ga mswd 1 43 the agreement between the pbsl age and previously published field and isotopic evidence for a major late archean metamorphic event affecting the western area suggests there was widespread equilibration accompanying the intrusion of the 2 75 2 83 ga granodioritic ikkattoq gneisses west and southwest of the western limb of the isua supracrustal belt we argue that the pbsl isochron ages date the peak of amphibolite facies metamorphic events which respectively affected the eastern and western sections of the isua supracrustal belt during the early and late archean our results give additional support to the suggestion that the scatter on published end t values from the isua supracrustal belt and adjoining gneisses can be assigned to post formational hydrothermal processes and underline the need for care in the interpretation of sm nd bulk data from polymetamorphic rocks to constrain isotopic models of early earth s evolution

new insights into the appalachian orogen from geology and geochronology along the cape ray fault zone southwest newfoundland reverse oblique overthrusting of high grade port aux basques gneiss over the lower grade supracrustal windsor point group along the cape ray fault zone occurred during late silurian to early devonian time and is attributed to major oblique collision between gondwanan and laurentian continental blocks new u pb zircon 40 ar 39 ar and k ar data limit the timing of this orogenic event the megacrystic granitic phase of the cape ray igneous complex and the cape ray tonalite have been dated at 488 3 ma and 469 2 ma respectively a black rhyolite from the windsor point group yielded an ordovician age 453 5 4 ma a pretectonic gabbro sill within the windsor point group dated at 424 4 3 ma is cut by the windowglass hill granite dated at 424 2 ma synkinematic hornblende and biotite from the grand bay complex mylonites of the port aux basques gneiss have 40 ar 39 ar ages of 407 4 ma and 403 4 ma respectively which is indicative of a late silurian early devonian age for the amphibolite grade deformation these ages are compatible with a previously determined 415 ma monazite age interpreted as the time of peak metamorphism in the port aux basques gneiss and suggests rapid exhumation the east west flexure of the cape ray fault zone represents a tear fault accommodating differential shortening between the cape ray fault zone and the correlative fault system in central newfoundland mid devonian granites 386 3 384 2 ma intervene between the thrusting events and a younger sinistral transcurrent movement this deformation and magmatic history can be correlated throughout the northern appalachians along other major fault boundaries

sm nd and u pb systematics of single titanite grains abstract combined sm nd and u pb isotopic systems in single titanite grains from archean rocks may be used to obtain nd isotope composition at the time of titanite growth the closed sm nd system requirement is applied to titanite and its integrity is monitored using the u pb system in a similar way as u pb in zircon is used to interpret lu hf data the nd isotope composition at the time of titanite formation can be used to infer initial nd isotopic values of the rocks at the time of zircon crystallization this approach does not involve assumption that the sm nd system in the rocks remained closed since their formation whereas such assumption underlies all initial nd determinations based on whole rock analyses titanite is a common accessory mineral in felsic rocks and a major concentrator of ree and uranium titanite populations are in many cases heterogeneous and resolving the isotopic characteristics of old and young titanite populations requires isotopic analysis of multiple single grains here i report sm nd and u pb data from single titanite grains from four early archean gneisses previously studied for lu hf and u pb systematics of zircon gneisses from the isua area contain heterogeneous populations of titanite which form roughly linear arrays in the u pb concordia diagram with ca 3600 ma upper intercepts and ca 2600 2700 ma lower intercepts or contain individual concordant grains of the latter age two of these gneisses also contain titanite grains of a high u variety which plot below these discordia lines probably as a result of post archean loss of radiogenic pb titanite from a gneiss from the nuuk area is concordant at 2520 2600 ma sm nd analyses of several single titanite grains from the isua area gneiss ggu163263 yielded an isochron age of 3555 150 ma identical to the upper intercept u pb age of 3601 15 ma the e nd t tit values of these grains calculated using their 207 pb 206 pb ages are uniform for the oldest titanite fractions with nd content 1000 ppm and give the average e nd t tit 0 32 0 20 at 3601 ma extrapolation from this value to 3708 25 ma an average of the ages of two zircon populations using an average crustal 147 sm 144 nd 0 12 0 04 yields e nd t zir 1 4 0 6 at the time of crystallization zircon from the same rock has average e hf t zir 1 9 1 0 titanite grains from two other gneisses from the isua area show more complex sm nd patterns predominant pale brown to colorless populations have variable 147 sm 144 nd ratios reaching as high as 0 7 and do not form isochrons suggesting that recrystallization of titanite was possibly accompanied by modification of the sm nd system in the whole rock no reliable initial nd value has been obtained from these gneisses the sm nd analyses of titanite fractions from the gneiss from the nuuk area yielded an average e nd t 9 00 0 37 extrapolation to the zircon crystallization age of 3610 10 ma yields an e nd t value of 1 8 5 4 which has low precision due to extrapolation over a billion year period the results presented here show that precise and tenable initial nd values for early archean gneisses can be obtained from analyses of best preserved titanite grains in favorable cases even if these grains represent a small fraction of an otherwise young or altered titanite population

recognizable primary volcanic and sedimentary features in a low strain domain of the highly deformed oldest known 3 7 3 8 gyr greenstone belt isua west greenland a low strain domain has been identified in the metamorphosed mostly highly deformed volcanic and sedimentary rocks of the early archaean isua supracrustal belt this domain contains well preserved volcanic and sedimentary features including basaltic pillow lavas pillow breccia heterogeneous volcanic breccia amygdules in metabasalt and polymict conglomerate dominated by recrystallized chert and volcanic clasts the low strain domain is bounded by highly deformed rocks mostly derived from basalt chert and banded iron formation these discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and furthermore strengthen the characterization of the isua supracrustals as a typical greenstone belt

consolidation of sediments by glaciers relations between sediment geotechnics soft bed glacier dynamics and subglacial ground water flow a theory of subglacial consolidation is developed which shows how the meltwater flux beneath a glacier leaves a consolidation signature from which many important glacier dynamic properties can be inferred conditions under which water is discharged through channels or in a thin film at the ice bed interface or by ground water flow are discussed and it is concluded that glaciers flowing over aquifers of high transmissibility can induce deep circulation patterns quite different from non glacial circulation

in situ iron isotope analysis of pyrites in 3 7ga sedimentary protoliths from the isua supracrustal belt southern west greenland abstract the timing of the emergence of life remains one of the principal unresolved questions in the earth sciences putative relicts of microorganisms in the eoarchean ca 3 6 3 85 ga high grade metamorphic terranes do not preserve morphological evidence for early life but some relicts can be identified by their geochemical signatures created by metabolic processes among the oldest rocks of sedimentary origin ca 3 8 ga occur in the isua supracrustal belt isb southern west greenland these have undergone metamorphism up to the amphibolite facies despite intense metamorphism the carbon isotope compositions of graphite clots from the isua metasedimentary rocks suggest biological carbon fixation and provide the oldest evidence for this biological process microbial dissimilatory iron reduction dir is considered to be an early form of metabolism the microbial dir produced fe 2 aq with a lower 56 fe value from a precursor fe 3 bearing iron mineral however 56 fe values lower than 1 are not found in sedimentary rocks prior to about 2 9 ga here we report in situ iron isotope analysis of pyrites in sedimentary rocks from the isb using a near infrared femtosecond laser ablation multicollector icp ms nir fs la mc icp ms a large variation of 56 fe values from 2 41 to 2 35 was documented from 190 points within pyrite grains from 11 rock specimens including those interpreted to be banded iron formations bifs chert amphibole rich chert quartz rich clastic sedimentary rocks mafic clastic sedimentary rocks carbonate rocks and conglomerates we found that the distribution of 56 fe values depends on the lithology whereas there is no correlation between their 56 fe values and the metamorphic grade the 56 fe values of pyrites in bifs range from 0 25 to 2 35 indicating partial oxidation in the deep ocean especially the high 56 fe values up to 2 35 suggest that the bif was formed through interaction of ferruginous seawater with a highly alkaline hydrothermal fluid under anoxic conditions pyrite grains in a conglomerate carbonate rocks mafic clastic sedimentary rocks and amphibole rich cherts show negative 56 fe values around 1 5 down to 2 41 pointing to microbial dir in the eoarchean shallow sea in addition the relatively low 56 fe values of pyrites in the shallow water sediments suggest anoxic anoxygenic photoautotrophic iron oxidation in the photic zone

initial pb of the amitsoq gneiss revisited implications for the timing of early archaean crustal evolution in west greenland reply abstract the rapid change in 207 pb 206 pb ratio during early earth history provides a powerful constraint for temporal resolution of archaean crustal evolution new and published data for amitsoq gneiss feldspars and whole rocks define the earth s least radiogenic silicate pb known until now the most important feature of the data is that independent of the exact slope of the regression in a common pb diagram a very well defined intercept with plausible terrestrial pb evolution lines is obtained between 3 63 and 3 66 ga identical to a combined pb pb regression age of 3654 73 ma mswd 17 6 we conclude that the magmatic precursors of the amitsoq orthogneisses separated from a depleted mantle like source at ca 3 65 ga this contrasts sharply with claims based on ion probe u pb zircon dating that the amitsoq gneisses had a prolonged episodic magmatic evolution extending from ca 3 87 to 3 60 ga pb isotopes offer no evidence that any amitsoq gneiss analysed until now began its evolution in the crust as long ago as 3 85 ga we propose that zircons significantly older than 3 65 ga were inherited from chemically evolved rocks as old as ca 3 85 ga geochemical arguments are presented to support this proposal new feldspar and whole rock pb isotope data are also reported for sheets of quartz dioritic gneiss on akilia island that yield the oldest zircon u pb age clusters in the range 3 84 3 87 ga these sheets are discordant to a metasedimentary enclave containing accessory apatite with graphite inclusions whose c isotope ratios are regarded as biogenic in origin as above pb isotopes in the sheets are consistent with a magmatic age of 3 65 ga which we regard as the true minimum age for these waterlain sediments and their possibly biogenic markers additional pb isotope data as well as limited published sm nd and u pb zircon data on the akilia enclaves themselves suggest an age between ca 3 65 and 3 70 ga for their original deposition some 150 200 ma younger than proposed previously thus the question of overlap of earliest life with a bolide impact scenario terminating 3 80 ga as on the moon becomes irrelevant

timing of late archaean terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland abstract a breakthrough in understanding the structural and metamorphic evolution of archaean gneiss complexes occurred with the recognition that the nuuk region of southern west greenland comprised separate terranes assembled in the late archaean from northwest to southeast these are the akia 3220 2970 ma akulleq 3870 3600 and 2820 ma and tasiusarsuaq 2920 2860 ma terranes the minimum time of assembly is recorded by the first event common to all component terranes using shrimp u pb zircon geochronology the oldest events common to all terranes including emplacement of crustally derived granites contemporaneous metamorphism and anatexis have been dated at 2710 2725 ma in the akulleq terrane areas where in situ diatexite formed abundant granitoid sheets were intruded and common growth of metamorphic zircon mostly low th u in most lithologies occurred in the akia and tasiusarsuaq terranes there was only intrusion of a lesser number of 2720 ma granitoid sheets because metamorphic zircons of that age have not been found the 2720 ma event is interpreted as marking or shortly following terrane assembly when the diverse components of the akulleq terrane were tectonically juxtaposed with the other two this new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of archaean gneisses can be due to accretionary tectonics long after the individual components were first formed

rapid soft bed sliding of the puget glacial lobe the puget lobe of the late pleis inferred to be lodgment till based on the tocene cordilleran ice sheet advanced into presence of oriented stones oriented stria western washington over a thick sequence of tions on stones overconsolidation and unlithified sediments the basal drag due to deformation features sliding over this surface was calculated by 1 this paper investigates the rapid motion of idealizing the sediment bed as a rigid planar the puget lobe over its bed of deformable sedi surface scattered with roughness elements cor ment studies of large vanished glaciers com responding to individual sedimentary particles plement basal motion studies of modern glaci and 2 taking the minimum reconstructed slid ers in which the glacier geometry and velocity ing velocity to be 500 m yr 1 the calculated are well constrained but the characteristics of basal drag minimized by choices of parameters the bed can only be inferred from observations is 400 kpa much higher than the reconstructed over very limited areas kamb et al 1985 gravitational driving stress of 40 kpa indi seismic measurements blankenship et al 1986 cating that a rigid bed and low water pressure or modelling lingle and brown 1987 obser are not consistent with the glacierfs rapid vations on glacier beds recently exposed by motion high subglacial water pressure aver glacial retreat can provide information about aging 90 of the ice overburden 10 mpa is conditions during a somewhat greater time span inferred from overconsolidation of subglacial but are restricted to the marginal environ clays the occurrence and deformation of ment in addition inferences about the bed of water deposited sediments within the till and modern glaciers are limited by the short dura the requirement to drain large quantities of tion and seasonality of the observations a water from the interface suggest that water notable benefit of studying the beds of pieis pressure reached 99 of the ice overburden tocene glaciers is that they record basal ploughing of till by ice entrained clasts per conditions for intervals spanning entire glaci vasive shearing and finally ice bed separa ations and accessible far from the glacier tion become possible as water pressure margins increases at the low inferred effective nor after a brief summary of data available from mal stress the basal drag is reduced from the previous reconstructions of the puget lobe the rigid bed case by water layers which decouple basal conditions of the lobe are explored along the smallest particles from the glacier sole two complementary lines we first present cal and ploughing which reduces the resistance culations of basal drag due to glacier sliding offered by the largest particles the limited for different models of till bed roughness that shear strain observed in much of the till indicate that rapid sliding requires very low implies pervasive shearing did not contribute effective stresses and extensive ice bed significantly to ice motion basal motion was decoupling or ploughing second we summarize confined to the ice bed interface or to dis geological and geotechnical data that indicate tinct faults within the substrate

protoliths of the 3 8 3 7 ga isua greenstone belt west greenland abstract the isua greenstone belt fig 1 contains the oldest known relatively well preserved metavolcanic and metasedimentary rocks on earth the rocks are all deformed and many were substantially altered by metasomatism but both the deformation and metasomatism were heterogeneous transitional stages can be seen from relatively well preserved primary volcanic and sedimentary structures to schists in which all primary features have been obliterated likewise different kinds and different episodes of metasomatic alteration can be seen that produced a diversity of different compositions and metamorphic mineral assemblages from similar protoliths new geological mapping has traced out gradations between the best preserved protoliths and their diverse deformed and metasomatised equivalents by this means the primary nature of the schists that make up most of the isua greenstone belt was reinterpreted and a new map that better portrays the primary nature of the rocks has been produced the previously mapped stratigraphy was found to be of little value in understanding the geology stratigraphic units were defined by different and diverse criteria such as current composition structure metamorphic texture and inferred protoliths much of this stratigraphy represents a misinterpretation of the primary nature of the rocks the new work indicates that most of the isua greenstone belt consists of fault bounded rock packages mainly derived from basaltic and high mg basaltic pillow lava and pillow lava breccia chert bif and a minor component of clastic sedimentary rocks derived from chert and basaltic volcanic rocks a previously mapped extensive unit of felsic volcanic rocks was found to be derived from metasomatised basaltic pillow lava and pillow breccia intruded by numerous sheets of tonalite

lituya bay landslide impact generated mega tsunami 50th anniversary on july 10 1958 an earthquake mw 8 3 along the fairweather fault triggered a major subaerial landslide into gilbert inlet at the head of lituya bay on the southern coast of alaska the landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history the mega tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis a cross section of gilbert inlet was rebuilt at 1 675 scale in a two dimensional physical laboratory model based on the generalized froude similarity a pneumatic landslide tsunami generator was used to generate a high speed granular slide with controlled impact characteristics state of the art laser measurement techniques such as particle image velocimetry piv and laser distance sensors lds were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland piv provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup the entire process of a high speed granular landslide impact may be subdivided into two main stages a landslide impact and penetration with flow separation cavity formation and wave generation and b air cavity collapse with landslide run out and debris detrainment causing massive phase mixing formation of a large air cavity similar to an asteroid impact in the back of the landslide is highlighted a three dimenional pneumatic landslide tsunami generator was designed constructed and successfully deployed in the tsunami wave basin at osu the lituya bay landslide was reproduced in a three dimensional physical model at 1 400 scale the landslide surface velocities distribution was measured with piv the measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models

the origin of early archean banded iron formations and of continental crust isua southern west greenland abstract a long standing geological debate is whether the fe component of precambrian banded iron formations bifs was derived from continental sources or had its origin in hydrothermal alteration of the oceanic crust recent ree and nd and fe isotope studies of iron rich layers in bifs have provided strong supporting evidence for the hydrothermal origin of the fe component pillow basalts from the 3800 3700 ma isua greenstone belt west greenland underwent significant enrichment of fe up to 21 wt fe2o3 and some chalcophile elements e g pb 5 4 7 2 ppm prior to a late archean tectonothermal metamorphic event recorded in the region published and new pb pb isotopic data from the isua pillow basalts and the spatially associated bifs suggest that the enrichment of fe and pb and deposition of the bifs took place between 3800 and 3600 ma similar pb isotopic compositions in pillow basalts and bifs are consistent with a common source of pb for both supracrustal rocks iron and pb were probably scavenged from the oceanic crust and were re deposited on the ocean floor by hydrothermal fluids suggesting that high temperature hydrothermal alteration of early archean oceanic crust played an important role in the deposition of the isua bifs geochemical lithological and structural data from the isua greenstone belt are all collectively consistent with a convergent margin geodynamic setting the isua bifs are spatially and temporally associated with boninitic and island arc picritic pillow basalts given the observations that cenozoic boninites and picrites tend to form in an intra oceanic arc forearc setting we suggest that the isua bif boninite and bif picrite associations were also deposited in a similar geodynamic setting the original pillow basalt bif stratigraphy was dismembered and transposed throughout the belt during early to late archean tectonothermal events the high temperature hydrothermal alteration of the oceanic crust produced significant hydrothermal discharge with large quantities of fe necessary to contribute to the deposition of the isua bifs the hydrothermal alteration may have resulted from the opening of an asthenospheric window developed as a consequence of ridge subduction beneath an early archean arc forearc region the ridge subduction model can also explain the origin of the contemporaneous tonalite trondhjemite granodiorite ttg intrusions in the isua region partial melting of laterally accreted and thickened oceanic crust under amphibolite to eclogite metamorphic conditions by upwelling of asthenospheric windows may have produced ttg melts the diapirically upwelling ttg melts formed the early archean continental crust and the complementary eclogitic residues contributed to the sub continental lithospheric mantle

u pb geochronology of 3810 3630 ma granitoid rocks south of the isua greenstone belt southern west greenland abstract the oldest well preserved granitoid rocks on earth envelope the isua greenstone belt southern west greenland the timing and nature of geological events that affected granitoid rocks south of the isua belt southern gneisses are refined with new mapping and u pb geochronology these results and previous work allow for a detailed comparison between the southern gneisses and similar granitoid rocks north of the arcuate isua belt northern gneisses zircons from tonalitic gneiss and meta tonalite that yielded ages of 3810 3795 ma are interpreted as having grown during igneous crystallisation of their protoliths based on the consistency of ages within and between samples and the oscillatory internal zoning that is typical of magmatic zircons two dated tonalitic rocks are particularly important because they occur as concordant layers within supracrustal rocks amphibolite with deformed pillow lava structures in the southwestern part of the isua belt and quartz rich gneiss likely derived from a chemical sediment that forms an enclave in the southern gneisses although these layers lack cross cutting intrusive relationships they are interpreted as having intruded as sheets into 3800 ma supracrustal rocks most tonalite was converted into gneiss before intrusion of diorite dated at 3658 3 1 2 ma and deformed again during or shortly after intrusion of 3650 3630 ma granitic rocks whereas a few small lenticular zones of meta tonalite escaped nearly all strain the timing of amphibolite facies metamorphism may be recorded by zircon and titanite growth in amphibolitic gneiss at 3632 3620 ma other thermal events were recorded by zircon growth at 3550 and 2660 ma and titanite growth or pb loss at 2650 and 2600 ma these new data and interpretations suggest that the southern gneisses underwent many geological events along with the northern gneisses including 3658 ma deformation 3658 ma diorite intrusion and 3655 3630 ma crystallisation of granitic rocks during significant metamorphism and deformation the major differences are that most tonalite in the southern gneisses is 100 my older than the northern tonalite and the intensity of the neoarchaean tectonothermal activity increased southward any large scale juxtaposition of the southern gneisses against the northern gneisses across the isua belt likely occurred before intrusion of the 3658 ma diorite

a review of structural patterns and melting processes in the archean craton of west greenland evidence for crustal growth at convergent plate margins as opposed to non uniformitarian models abstract the archean craton of west greenland consists of many fault bounded eoarchean to neoarchean tectonic terranes crustal blocks these tectonic terranes are composed mainly of tonalite trondhjemite granodiorite ttg gneisses granitic gneisses metavolcanic dominated supracrustal belts layered anorthositic complexes and late to post tectonic granites rock assemblages and geochemical signatures in these terranes suggest that they represent fragments of dismembered oceanic island arcs consisting mainly of ttg plutons tholeiitic to calc alkaline basalts boninites picrites and cumulate layers of ultramafic rocks gabbros leucogabbros and anorthosites with minor sedimentary rocks the structural characteristics of the terrane boundaries are consistent with the assembly of these island arcs through modern style of horizontal tectonics suggesting that the archean craton of west greenland grew at convergent plate margins several supracrustal belts that occur at or near the terrane boundaries are interpreted as relict accretionary prisms the terranes display fold and thrust structures and contain numerous 10 cm to 20 m wide bifurcating ductile shear zones that are characterized by a variety of structures including transposed and redistributed isoclinal folds geometrically these structures are similar to those occurring on regional scales suggesting that the archean craton of west greenland can be interpreted as a continental scale accretionary complex such as the paleozoic altaids melting of metavolcanic rocks during tectonic thickening in the arcs played an important role in the generation of ttgs non uniformitarian models proposed for the origin of archean terranes have no analogs in the geologic record and are inconsistent with structural lithological petrological and geochemical data collected from archean terranes over the last four decades the style of deformation and generation of felsic rocks on outcrop scales in the archean craton of west greenland and the mesozoic sulu orogenic belt of eastern china are similar consistent with the formation of archean continental crust by subduction zone processes

isua supracrustal belt greenland a vestige of a 3 8 ga suprasubduction zone ophiolite and the implications for archean geology abstract the mafic ultramafic units of the 3 8 ga isua supracrustal belt isb in greenland occur in a two armed arcuate zone eastern and western arms and are grouped into two major tectonostratigraphic units based on their lithological and geochemical characteristics 1 undifferentiated amphibolites ua and 2 garbenschiefer amphibolites ga the ua contains all major lithological units of a typical penrose type complete ophiolite sequence the ga is composed dominantly of volcaniclastic and volcanic rocks commonly found in immature island arcs the available geochemical data from ua and ga show distinct differences between the two units compared with the geochemical evolution of some of the well known phanerozoic ophiolites the pillow lavas and associated dikes of the ua show a compositional range that is similar to typical morb type ligurian ophiolites in the western alps apennines and those displayed by lip type caribbean ophiolites the ga is characterized by island arc tholeiite iat to boninite like rocks and defines a magmatic evolution that is comparable to that of suprasubduction zone ssz ophiolites in the mediterranean region our proposed geodynamic model for the isb suggests that the ua was built by primary to differentiated mantle generated melts during seafloor spreading little to moderately affected by subduction processes and that the iat to boninitic like rocks of the ga formed at a later stage by melting from a strongly subduction affected depleted and hydrated mantle our interpretation of the isb is that the ua and ga represent early and late stages respectively in the formation of a ssz ophiolite this implies that phanerozoic type plate tectonic processes such as seafloor spreading and subduction were operating by 3 8 ga in the palaeoarchean

precise u pb baddeleyite ages of mafic dykes and intrusions in southern west greenland and implications for a possible reconstruction with the superior craton the archaean block of southern greenland constitutes the core of the north atlantic craton nac and is host to a large number of precambrian mafic intrusions and dyke swarms many of which are regionally extensive but poorly dated for southern west greenland we present a u pb zircon age of 2990 13 ma for the amikoq mafic ultramafic layered intrusion fiskefjord area and four baddeleyite u pb ages of precambrian dolerite dykes specifically a dyke located se of ameralik fjord is dated at 2499 2 ma similar to a previously reported ar 40 ar 39 age of a dyke in the kangamiut area for these and related intrusions of ca 2 5 ga age in southern west greenland we propose the name kilaarsarfik dykes three wnw trending dykes of the md3 swarm yield ages of 2050 2 ma 2041 3 ma and 2029 3 ma a similar u pb baddeleyite age of 2045 2 ma is also presented for a se trending dolerite iglusuataliksuak dyke in the nain province the rifted western block of the nac in labrador we speculate that the md3 dykes and age equivalent nne trending kangamiut dykes of southern west greenland together with the iglusuataliksuak dyke after closure of the labrador sea represent components of a single areally extensive radiating swarm that signaled the arrival of a mantle plume centred on what is presently the western margin of the north atlantic craton comparison of the magmatic barcodes from the nain and greenland portions of the north atlantic craton with the established record from the north eastern superior craton shows matches at 2500 ma 2214 ma 2050 2030 ma and 1960 1950 ma we use these new age constraints together with orientations of the dyke swarms to offer a preliminary reconstruction of the north atlantic craton near the north eastern margin of the superior craton during the latest archaean and early palaeoproterozoic possibly with the core zone craton of eastern canada intervening c 2010 elsevier b v all rights reserved less

anatomy of an early archean gneiss complex 3900 to 3600 ma crustal evolution in southern west greenland the early archean complex of southern west greenland consists of polyphase tonalitic trondhjemitic granodioritic ttg and granitic amitsoq gneisses with inclusions of volcanic and sedimentary rocks gabbros and ultramafic rocks in this complex rocks of similar appearance and composition were found to be of different ages by u pb zircon dating the amitsoq gneisses comprise 3870 3820 3810 3760 3730 3700 and 3625 ma ttg and 3660 3650 and 3625 ma granites and their inclusions belong to several supracrustal sequences with a similar spread of ages these results show that the complex grew by episodic addition of new ttg and welding together of rocks of different ages a possible plate tectonics scenario is as follows melting of subducted mafic oceanic crust formed 3700 ma microcontinents consisting of ttg suites with predominantly mafic inclusions at 3650 ma collision between microcontinents caused crustal thickening high grade metamorphism and emplacement of leucogranites at 3625 ma subduction at the edge of the 3625 ma continental mass created a new crustal addition comprising both ttg and granite while granites were emplaced into the 3625 ma continental mass