formation of low δ 18 o magmas of the kangerlussuaq intrusion by addition of water derived from dehydration of foundered basaltic roof rocks the kangerlussuaq intrusion in east greenland is concentrically zoned from quartz nordmarkite quartz syenite at the margin through pulaskite to foyaite nepheline syenite in the centre with no apparent intrusive contacts the 18o values of coexisting minerals are consistent with oxygen isotope equilibrium at magmatic temperatures most of the intrusion formed from low 18o magma magma 18o values generally increased upwards from about 3 3 in the quartz nordmarkites to 5 6 in the foyaites the lowest magma 18o value of about 1 0 is from the upper part of the nordmarkites where there is a high concentration of foundered basaltic xenoliths stoped from the roof of the intrusion the amphiboles in the syenites have d values that range from those typical of hydrous mantle derived minerals to much lower values 86 to 157 as do whole rock samples of xenolith and country rock 125 to 148 the low magma 18o and d values are consistent with continuous incorporation exchange and upward escape of low 18o and d fluids released from stoped basaltic roof material mass balance suggests that the integrated amount of water involved was 7 wt of the volume of the magma but locally reached 30 wt water the requirement for large amounts of water with low 18o value is satisfied only if the foundered basalt contained most of its water in cavities as opposed to hydrous minerals even with this requirement the volume of stoped basalt would have been equal to the volume of the magma repeated recharge of the residual magma with progressively less contaminated silica undersaturated melt resulted in a gradual shift across the low pressure thermal divide crystallisation was suppressed by the depression of the liquidus due to water saturation of the residual magma ph2o 1 kbar

40ar 39ar ages of intrusions in east greenland rift to drift transition over the iceland hotspot abstract sixteen 40 ar 39 ar ages are presented for alkaline intrusions to appraise prolonged post breakup magmatism of the central east greenland rifted margin the chronology of rift to drift transition and the asymmetry of magmatic activity in the northeast atlantic igneous province the alkaline intrusions mainly crop out in tectonic and magmatic lineaments orthogonal to the rifted margin and occur up to 100 km inland the area south of the kangerlussuaq fjord includes at least four tectonic lineaments and the intrusions are confined to three time windows at 56 54 ma 50 47 ma and 37 35 ma in the kangerlussuaq fjord which coincides with a major tectonic lineament possibly the failed arm of a triple junction the alkaline plutons span from 56 to 40 ma to the north and within the continental flood basalt succession alkaline intrusions of the north south trending wiedemann fjord kronborg gletscher lineament range from 52 to 36 ma we show that post breakup magmatism of the east greenland rifted margin can be linked to reconfiguration of spreading ridges in the northeast atlantic northwards propagation of the proto kolbeinsey ridge rifted the jan mayen micro continent away from central east greenland and resulted in protracted rift to drift transition the intrusions of the wiedemann fjord kronborg gletscher lineament are interpreted as a failed continental rift system and the intrusions of the kangerlussuaq fjord as off axis magmatism the post breakup intrusions south of kangerlussuaq fjord occur landward of the greenland iceland rise and are explained by mantle melting caused first by the crossing of the central east greenland rifted margin over the axis of the iceland mantle plume 50 47 ma and later by uplift associated with regional plate tectonic reorganization 37 35 ma the iceland mantle plume was instrumental in causing protracted rift to drift transition and post breakup tholeiitic and alkaline magmatism on the east greenland rifted margin and asymmetry in the magmatic history of the conjugate margins of the central northeast atlantic

pyroclastic deposits within the east greenland tertiary flood basalts stratigraphic geochemical and mineralogical characterization of pyroclastic deposits on the gronau west nunatak of east greenland indicates that both alkaline and basaltic tephras occurred during the eruption of flood basalts associated with the opening of the north atlantic ocean in the early tertiary within the exposed section of gronau west nunatak c 1 km thick representing c 1 6 ma 17 of the horizons are phreatomagmatic basaltic tephras near the top of the section an alkaline tuff was dated at 53 8 0 3 ma by 40 ar 39 ar method this tuff contains a distinctive mineralogy sanidine mg katophorite aegirine and geochemistry melt inclusion compositions and trace and rare earth element abundances that indicate it was erupted from the gardiner melanephelinite carbonatite volcanic complex located 175 km to the se which was active from c 55 to 52 ma the alkaline tuff can be correlated to age equivalent compositionally similar alkaline pyroclastic horizons reported in north atlantic sediment cores and in outcrops in northern europe making it an important regional time stratigraphic marker this study indicates that north atlantic explosive volcanic events were prevalent regionally widespread and originated in east greenland during continental rifting suggesting the need for reappraisal of the impact of north atlantic volcanism on climate change during the early tertiary

trans atlantic correlation of the palaeogene volcanic successions in the faeroe islands and east greenland before continental break up in the ne atlantic the faeroe islands and central east greenland were within a distance of 100 120 km chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous palaeogene flood basalts in the faeroe islands and in the nansen fjord area in east greenland show very similar basalt compositions and evolution patterns with time the faeroes lower basalt formation and the equivalent nansen fjord formation in east greenland form a pre break up succession overlain by a sediment horizon a syn break up succession consists of the faeroes middle and upper basalt formations and the equivalent milne land formation in east greenland in which five intervals can be correlated with a compositional evolution from ti rich magnesian basalts and picrites at the base to a dominance of morb like low ti basalts at the top the successions were generated in the same mantle melting column beneath a thinning continent with a rift zone that eventually ruptured the continent the evolution pattern is very similar to that seen on the se greenland margin but spreading according to the palmason model of 1973 was not yet established the pre and syn break up successions formed volcanic megasystems stretching across the rift zone with areal extents of 70 000 and 220 000 km 2 and volumes of 120 000 and 250 000 km 3 rocks from the pre and syn break up successions can be discriminated based on a simple major element plot the overlying succession was 3 3 5 km thick in e greenland but was thin or absent in the faeroes the energy source for the melting appears to have been concentrated on the greenland side

hot spot activity and the break up of pangea abstract the mesozoic and cenozoic positions of the continents that formed pangea in the triassic jurassic were derived from paleomagnetic and intraplate volcanic data paleoclimatic observations such as reef and fossil flora distribution and geological observations major hot spots helped to determine the longitudinal position of pangea and to construct a model of plate motion during the pangean break up the position of the northern part of pangea was constrained using iceland and jan mayen hot spots the iceland hot spot was traced from its present day position to greenland in the paleocene to baffin bay in the late cretaceous to the alpha ridge in the early cretaceous to the chukchi borderland in the middle late jurassic to franz joseph land in the early jurassic the yenisei khatanga trough in the middle triassic and finally to west siberia in the late permian early triassic the hot spot activity is expressed by eastern and western greenland volcanics the siberian trap basalts and perhaps by alpha ridge and chukchi borderland volcanics the chukchi borderland volcanics are related to the early stage of the opening of the canadian basin the position of the southern part of pangea was constrained using the bouvet hot spot this hot spot was tracked from its present day position to western antarctica in the early cretaceous late jurassic and to south africa in the early jurassic late triassic this hot spot activity produced the ferrar and karoo volcanics the model of plate motion obtained agrees with other data on intraplate volcanics which are also related to hot spots at the time of the opening of the central atlantic the cape verde and canary island hot spots were located along the ocean s spreading axis the long lasting location of hot spot and associated mantle upwelling plumes could help to explain forces driving the tethys transit plates opening of the ligurian ocean and eastern mediterranean the european hot spots are related to the several mesozoic phases of rifting for example the rhine graben hot spot may have been located at the rifting axis in the north sea several authors have already discussed the contribution of hot spots to the opening of the south atlantic and indian oceans mantle plumes associated with hot spots play an active role in rifting and initial phases of spreading the lithospheric displacement caused by upwelling combined with sometimes remote collisional forces on the other side of continental plate may result in compression and basin inversion

temporal evolution of a long lived syenitic centre the kangerlussuaq alkaline complex east greenland abstract we present new mineral and whole rock compositions and sr nd hf pb o h isotope data on samples from the kangerlussuaq alkaline complex 1000 km2 in central east greenland part of the north atlantic igneous province this complex mainly consists of the kangerlussuaq intrusion but includes at least 13 separate satellite intrusions emplaced in the uppermost crust close to the unconformity between archaean gneisses and overlying palaeogene flood basalts the complex is divided into i older satellite intrusions 55 53 ma composed of multiple syenites and granites and minor gabbros and peridotites ii the voluminous kangerlussuaq intrusion 50 ma which displays a gradual transition from quartz syenites nordmarkites at the margin to nepheline syenites foyaites in the centre and iii younger satellite intrusions 47 45 ma of minor syenites granites and diorites concentrated southeast of the kangerlussuaq intrusion the complex displays a temporal evolution in which sio2 decreases 74 56 wt and total alkalis 6 16 wt amphibole na k content 206pb 204pbmeas endi and ehfi 3 to 11 increase from the older intrusions through the nepheline syenites this is followed by a reversal to higher silica 62 73 wt and lower total alkalis 9 12 wt amphibole na k content 206pb 204pbmeas endi and ehfi 13 to 2 in the younger satellite intrusions temporal changes in the location of magma plumbing systems and in magma production rates played a profound role in controlling silica content alkalinity and degree of crustal contamination during development of the complex phonolitic magma was only generated after prolonged magmatism had shielded the conduits from interaction with country rock the parental magmas were probably basanitic to alkali olivine basaltic in composition the older satellite intrusions and the kangerlussuaq intrusion have low 18o magma values 1 to 6 compared to the younger more crustally contaminated satellite intrusions 4 5 to 7 it appears that the magmas only had sufficient over pressure to intrude the basalt cover when larger volumes of less contaminated trachyte magma were produced resulting in the generation of low 18o magmas due to dehydration of hydrothermally altered basalt xenoliths

a gold and platinum mineralized layer in gabbros of the kap edvard holm complex field petrologic and geochemical relations the lower layered series a cumulates of the kap edvard holm complex contain a stratiform layer 1 to 20 m thick and 6 km long that is mineralized with gold and platinum group elements pges the lower layered series a cumulates 650 m thick are dominated by modally layered gabbro with lesser volumes of granular anorthosite and troctolite that together form 2 to 30 m thick layers that are most abundant above the mineralized layer minor volumes of poikilitic wehrlite form a few 1 to 2 m thick layers throughout the section field and petrographic relations as well as cryptic variations in cumulus mineral compositions indicate that the lower layered series a formed in an open system magma chamber from repeated magma injections within the mineralized layer average concentrations over 3 m thickness are 250 ppb pt 40 ppb pd and 50 ppb au with individual samples containing up to 5 ppm pt and 6 ppm au the concentrations of ir os ru and rh are uniformly low 20 ppb stratigraphic zoning of pt pd and au is consistent along strike with peak au concentrations overlying pt and pd peaks platinum minerals are primary pt fe alloy sperrylite and moncheite with secondary pt sulfide overgrowths gold occurs as alloys with ag and cu these minerals are found in contact with primary and secondary silicates and oxides and with intercumulus base metal sulfides that consist of the assemblage bornite chalcopyrite digenite deposition of the mineralized layer is associated in space and time with injections of plagioclase saturated primitive magma that mixed with more evolved resident magma these events caused efficient partitioning of au and pge into sulfides derived from a large volume of magma deposition of these sulfides to form the mineralized layer and subsequent deposition of the overlying anorthosite layers the wehrlite layers however were formed by postcumulus reactions between gabbro cumulates and hydrous intercumulus melts probably derived from the compacting cumulus pile subsolidus reactions between primary minerals and meteoric hydrothermal solutions caused extensive alteration of the mineralized gabbro oxidation and desulfurization of cu fe sulfides and local recrystallization of pge minerals

the ultramafic cumulate series gardiner complex east greenland the ultramafic cumulate series of the ultramafic alkaline and carbonatite bearing gardiner complex in east greenland is divided in 1 contact zone of plagio clase bearing alkaline rocks chilled to the surrounding gneisses and alkaline lavas 2 a banded sequence of dunites to mt pyroxenites 3 a zoned dunite cpx dunite ring and 4 in the centre of the complex ol pyroxenites and mt pyroxenites

an improved tectonic model for the eocene opening of the norwegian greenland sea use of modern magnetic data abstract compilation of new and vintage aeromagnetric data from the norwegian and greenland seas of the ne atlantic provides evidence for a different interpretation of several tectonic elements the previously interpreted oceanic fracture zones gleipne surt bivrost jenegga and vesteralen do not exist these were artefacts of poor navigation and wide line spacing of the vintage dataset this reinterpretation impacts our understanding of the early spreading history of the north atlantic as the opening of the norwegian greenland sea between the jan mayen and senja greenland fracture zones occurred along a stable axis without offsets of the oceanic spreading anomalies or jumps in spreading axis these results contradict the hypothesis that a spatial relationship exists between transfer zones and fracture zones on the lofoten margin and on the ne greenland margin to which they have been projected simplified palaeogeographic reconstruction of the aeromagnetic map to anomaly 22 reveals that a c 50 km wide magnetic anomaly cuts across spreading anomalies 24a 24b and 23 from the voring marginal high on the norwegian margin to traill o on the east greenland coast the anomaly is interpreted to represent an igneous complex referred to as the traill voring igneous complex tvic the complex crosscuts anomaly 22 on the greenland margin suggesting that the igneous activity was active until c 50 ma and can be linked up with the nne trending initial magmatic lineament iml extending between traill o and kangerlussuaq the iml has been suggested to relate to a failed attempt of direct linkage between the reykjanes and mohns ridges the magnetic response of the tvic along the voring margin has previously been interpreted as representing anomaly 24a and 24b such an interpretation required the erroneous introduction of an abandoned spreading ridge

chemical evolution of intercumulus liquid as recorded in plagioclase overgrowth rims from the skaergaard intrusion the intercumulus liquid of a crystal mush fills pore spaces and typically solidifies to form overgrowths on cumulus grains and poikilitic post cumulus minerals if the liquid is immobile solidification produces zoned intercumulus minerals as a result of progressive fractionation of the residual liquid convection within the mush results in buffering of the liquid composition and thus limits mineral zonation for fully solidified cumulates fossil changes in liquid composition or porosity are difficult to identify however detailed study of immobile minor components of plagioclase overgrowth rims can provide information about the progressive solidification of intercumulus material ti contents of plagioclase overgrowths in samples from the lowermost parts of the skaergaard intrusion show strong variations with anorthite content with decreasing xan ti concentrations first rise and then fall consistent with changing tio2 contents of the intercumulus liquid during solidification tio2 in plagioclase decreases sharply at an55 reflecting local saturation of fe ti oxides ti in clinopyroxene oikocrysts also falls rimward but zoning in faster diffusing species fe mg is limited other than slight reverse zones that may occur on the plagioclase margins xan falls continuously during crystallization the reverse zoning is interpreted as the result of compaction driven dissolution and reprecipitation of plagioclase the continual decrease in xan is exploited together with back scattered electron images of the cumulates to produce calibrated images showing regions of progressive crystallization this allows the regions crystallizing at each stage of solidification to be visualized these images show that the final remnants of interstitial melt were present in triangular pockets and as thin grain boundary melt films this approach can provide information about the progressive reduction of porosity during cumulate solidification

the e greenland rifted continental margin an examination of the coastal flexure the structure of the e greenland coastal flexure a major structure developed during continental break up is interpreted on the basis of field observations an earlier model which involves normal inland dipping antithetic faulting and seaward rotation of fault blocks is confirmed and amplified this model requires that regional dips are very much less than dips measured on bedding planes thus leading to considerably reduced thicknesses for the tertiary volcanic succession in e greenland detailed mapping confirms the validity of these thickness estimates and leads to the conclusion that the volcanic extrusion rate was similar to that of present day iceland thus obviating the need for special mechanisms of magma generation comparable structures occur in other regions of continental break up and voluminous basalt discharge and it is suggested that the flexure developed by collapse of the attenuated crust subsequent to the massive extrusion of plateau basalts

episodic volcanism during break up of the north atlantic evidence from the east greenland plateau basalts abstract the lower tertiary upper paleocene lower eocene plateau basalts in the scoresby sund region of east greenland formed during three distinct magmatic episodes the activity of the first episode was centred in the present inland areas to the northwest and produced a voluminous regional basalt sequence lower sequence the activity of the second episode was centred to the southeast offshore the present atlantic coast and this also produced a voluminous regional basalt sequence upper sequence the third episode was centred on the atlantic coast and gave rise to a dense coastal dyke swarm and local lavas which are now only locally preserved by downfaulting the lavas are all tholeiitic basalts after an initial phase the two regional lava sequences of the first and second episodes show a similar vertical compositional zonation pattern a thin lower formation with variable composition is followed by a thick uniform formation which shows systematic compositional change with height from tio2 rich feti basalts to tio2 poor basalts and ending with a reversal to tio2 rich basalts each of these cyclic patterns apparently resulted from a temporary rifting episode and much of the compositional variation found can be explained by magma development in open magma chambers the dykes and lavas of the third episode of activity have chemical affinities to ocean floor basalts and their tio2 p2o5 ratios indicate formation at a spreading ridge centre the pattern of two failed rifting episodes and one event that produced oceanic crust can be correlated with stages in the complicated initiation of seafloor spreading in the region and the volcanism itself is closely related to this process

the lamprophyres of ubekendt ejland west greenland products of renewed partial melting or extreme differentiation the late tholeiitic lavas of southwestern ubekendt ejland 63 54 ma are intruded by lamprophyre dykes 33 ma the compositional and temporal differences would seem to preclude any genetic relationship between the two igneous episodes competing models of renewed partial melting versus extended batch fractionation are considered to explain the origin of the lamprophyres mathematically modelled lamprophyres produced by batch fractionation are very close to observed lamprophyre compositions and this combined with other temporal and spatial evidence suggests that renewed partial melting of the mantle is not the best way to explain such bimodal suites

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

40ar39ar geochronology of tertiary mafic intrusions along the east greenland rifted margin relation to flood basalts and the iceland hotspot track abstract the east greeland tertiary igneous province includes the largest exposed continental flood basalt sequence within the north atlantic borderlands more than ten layered gabbro complexes including the 55 ma skaergaard intrusion and a large dolerite sill complex are the plutonic equivalents of flood basalts both lavas and intrusions have been regarded as synchronous with continental breakup at 57 54 ma we report ten new ages of the mafic intrusions determined by40ar 39ar incremental heating experiments demonstrating that the mafic intrusions formed in two distinct time windows only intrusion ii of the imilik gabbro complex the skaergaard intrusion and the sorgenfri glestcher sill complex formed at 57 55 ma coeval with the eruption of regional flood basalts and continental breakup other layered gabbro intrusions at imilik intrusion iii kruuse fjord igtutarajik nordre aputite q kap edvard holm and lilloise are distinctly younger and formed between 50 and 47 ma plate kinematic models indicate the axis of the ancestral iceland mantle plume was located under central greenland at 60 ma and subsequently crossed the east greenland rifted continental margin we propose that tholeiitic magmatism along the east greenland rifted margin largely occurred in three distinct pulses at 62 59 ma lavas and dykes 57 54 ma lavas dykes sills and some gabbros and 50 47 ma gabbros dykes and rare lavas related to discrete mantle melting episodes triggered by plume impact continental breakup and passage of the plume axis respectively this model implies northwestward continental drift of greenland relative to the plume axis by 3 9 5 0 cm yr between 60 and 49 ma consistent with estimates from seismic studies of submerged flood basalts

the e greenland continental margin a transition between oceanic and continental magmatism the e greenland continental margin differs from typical margins in having a superimposed regional uplift which has exposed the early rift products for direct examination most of the igneous rocks in this region find counterparts in the oceanic setting with the proviso that the area is part of an aseismic ridge thus picrites basalts sheeted dyke swarms and layered gabbros are present and these can be used to shed light on oceanic magmatic events nephelinitic rocks are products of off axis volcanism and find no counterparts in the present oceanic rift system although they occur in marginal regions of the ocean basins and were generated in distal regions at the initiation of rifting in icelandic anomaly voluminous salic rocks in the area owe their generation largely to continental crust which has undergone extensive melting they find no direct counterparts in oceanic areas the outstanding degree of exposure in this area combined with its transitional nature and wide spectrum of rock types make it a unique laboratory for the elucidation of a variety of problems regarding both oceanic and continental volcanism together with the nature of rifted continental margins in general

petrology of early tertiary nephelinites off mid norway additional evidence for an enriched endmember of the ancestral iceland plume abstract plugs of alkaline volcanic rocks 56 ma penetrating mesozoic sediments crop out at 63 25 n on the continental shelf off norway the rocks are highly silica undersaturated comprising both nephelinites and basanite the nephelinitic rocks are porphyritic with abundant phenocrysts of mg rich olivine and some clinopyroxene many olivine crystals are altered along grain margins and fractures the fine grained matrix consists of fresh augite biotite rhonite chlorite oxides and altered nepheline apatite and calcite are accessories the basanite has much less olivine and abundant matrix plagioclase the occurrence of rhonite indicates crystallization in the presence of a fluid phase at p 2 o 5 ni cr sr and incompatible elements the ree are highly fractionated with lree up to 500 chondrite initial strontium isotope ratios 87 sr 86 sr i range from 0 703685 to 0 704025 and nd from 3 13 to 3 31 in the nephelinites in the basanite 87 sr 86 sr i is 0 704447 and nd 0 01 the nephelinites are enriched in 208 pb 204 pb we suggest that the basanite formed from enriched lithospheric mantle and that the nephelinites were low melt fractions of a sublithospheric asthenospheric source this source probably represents an enriched low temperature melting end member component of the north atlantic icelandic plume

mantle plume uplift in the sedimentary record origin of kilometre deep canyons within late neoproterozoic successions south australia in south australia canyons 200 250 km long are incised to depths of c 1 5 km in late neoproterozoic after c 590 ma marine deposits of the adelaide fold belt and canyons 90 km long and 700 m deep occur in correlative marine strata of the officer basin 1000 km to the nw in the adelaide fold belt the isotopic signature of limestone veneering canyon walls canyon sinuosity and sedimentary structures in canyon fill suggest that the canyons were cut subaerially and filled by shallow water marine deposits during coastal onlap eustacy cannot account for the kilometre scale change in sea level required for subaerial canyon erosion and chemostratigraphy and the lack of evaporites at that stratigraphic level in southern australia argue against a messinian style drawdown in each region uplift and crustal extension preceding or coeval with canyon incision are indicated by a regional unconformity turbidite or mass flow deposition and extensional faults these features and canyon incision may be explained by regional uplift above a rising mantle plume over a distance of 1000 km in southern australia flood basalt volcanism in the officer basin tentatively dated at 563 40 ma may have followed this uplift mantle plume uplift is expressed in the sedimentary record by emergent trends in facies regional thinning regional unconformities turbidites gravity slides normal faults and incised canyons and palaeovalleys

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

resolving bathymetry from airborne gravity along greenland fjords recent glacier mass loss in greenland has been attributed to encroaching warming waters but knowledge of fjord bathymetry is required to investigate this mechanism the bathymetry in many greenland fjords is unmapped and difficult to measure from 2010 to 2012 national aeronautics and space administration s operation icebridge collected a unique set of airborne gravity magnetic radar and lidar data along the major outlet glaciers and fjords in greenland we applied a consistent technique using the icebridge gravity data to create 90 bathymetric profiles along 54 greenland fjords we also used this technique to recover subice topography where warm or crevassed ice prevents the radar system from imaging the bed here we discuss our methodology basic assumptions and error analysis we present the new bathymetry data and discuss observations in six major regions of greenland covered by icebridge the gravity models provide a total of 1950 line kilometers of bathymetry 875 line kilometers of subice topography and 12 new grounding line depths

late proterozoic and carboniferous ultramafic magmatism of carbonatitic affinity in southern norway ultramafic dikes with carbonatitic affinities damtjernites in southern norway were generated during two magmatic events separated by about 275 ma the older event is late proterozoic and the younger is mid carboniferous more than 50 satellitic damtjernite intrusions occur within a 1500 km2 large region surrounding the fen central complex phlogopite macrocrysts from 10 of these satellites yield a rb sr isochron age of 578 24 ma 2 expanded errors this demonstrates that the late proterozoic carbonatitic magmatism centered at the fen central complex occurred on a regional scale this region is termed the fen province the emplacement of the magmas in the fen province most likely occurred in connection with minor extensional tectonic activity on the baltic platform during the drift phase after the proto atlantic opening sr isotopic data also show that a dike mineralogically and chemically similar to the fen damtjernites was emplaced at 324 4 ma mid carboniferous this dike very likely dates the initiation of magmatism in the oslo rift consequently very similar carbonate bearing ultramafic magmas were generated within the south norwegian mantle during the relatively minor fen event and in the initial extensional period when the magma production in the oslo rift was still low

pressure conditions for the solidification of the skaergaard intrusion eruption of east greenland flood basalts in less than 300 000 years abstract primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the skaergaard intrusion east greenland samples from the lower zones a c lza c the middle zone mz and the sandwich horizon sh are included in the present study together with granophyric accumulations in gabbroic pegmatite from lza c fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the skaergaard intrusion crystallised pegmatitic granophyre from lza c consists mainly of quartz plagioclase an 4 7 and alkali feldspar or 40 80 enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende fayalite fo 4 5 titanite biotite and fluor apatite granophyric quartz albite and alkali feldspar crystallised from water saturated granitic melts near eutectic minimum conditions between 680 and 660 c the pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions pressures recalculated to the roof pendant of the intrusion are 0 7 0 5 for lza 2 0 0 2 for lzb c 2 3 0 8 for mz the triple group level and 3 3 1 3 kb for sh amphibole geobarometry independently confirm the pressure estimates for pegmatitic granophyres in lza c the granophyres formed as the intrusion cooled through the minimum melt solidus in lza lzb lzc mz and sh respectively the pressure increase from lza to sh granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5 3 6 3 2 7 km of flood basalts during the initial opening of the northeast atlantic ocean accordingly the skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep seated igneous system during terminal crystallization when the majority of the intercumulus phases formed the present cooling history suggests the intrusion cooled through the temperature of granophyre formation in less than 300 000 years the increase in the pressure of granophyre formation therefore implies that 5 3 6 3 2 7 km of flood basalts were emplaced within this time window

fractionated alkaline rare metal granites two examples abstract two suites of tin related alkaline granites are compared the seagull thirtymile granites of the yukon which were emplaced in a cordilleran setting and the parana suite of goias which were emplaced in an incipient rift environment the geochemistry of these two suites is similar and both have evolved small volumes of li rb rich alkali feldspar leucogranites both fall partly but not wholly within the compositional fields defined for a types on various tectonic discrimination diagrams halogen contents and major element chemistry of fe li micas from the seagull thirtymile suite indicate that these plutons were reduced magmas that evolved magmatic hydrothermal systems with increasing cl content in a shallow at least periodically open system the most important sn granites of the parana suite of goias were also emplaced at shallow depth and developed extensive greisen in active shear zones which contrasts with a more passive environment for the seagull granites both of these suites may be classified as low p 2 o 5 alkaline types and they display particularly fe 2 rich biotite micas that separate the alkaline plutons from s type tin granites

petrogenesis of syenites at a rifted continental margin origin contamination and interaction of alkaline mafic and felsic magmas in the astrophyllite bay complex east greenland the astrophyllite bay complex in east greenland part of the palaeogene north atlantic igneous province consists of an alkaline diorite plug with detached trachyandesitic pillows surrounded by co magmatic syenite that was emplaced into archaean basement the diorite intrusion has yielded a 47 11 0 68 ma rb sr isochron age saw cut profiles through pillow syenite gneiss sections have been taken to resolve close spatial elemental and isotopic sr nd hf pb o variations the diorite and syenite formed from alkaline basaltic mantle derived melts with complex histories of prolonged assimilation and fractional crystallisation each evolved to different extents in separate magma chambers during the establishment of new plumbing systems in the kangerlussuaq area the diorite is dominated by lower crustal granulite facies contamination whereas the syenite shows evidence for greater degrees of upper crustal amphibolite facies contamination indicating stalling and fractionation of magmas at different levels within the crust the syenite and diorite magmas were subsequently emplaced as separate pulses into the basement gneisses at astrophyllite bay giving rise to superimposed local contamination trends between pillow syenite and syenite gneiss respectively