evidence for eocene oligocene glaciation in the landscape of the east greenland margin assessing the onset and extent of northern hemisphere glaciation is required to understand cenozoic climate change and its impact on topography while the onset of accelerated cenozoic erosion is generally associated with the quaternary at mid latitudes some high latitude passive margins may have undergone earlier glaciation starting at 38 30 ma or even 45 ma here we document a rapid phase of exhumation in the east greenland margin between 68 n and 76 n starting at 30 5 ma the timing is coincident with the dramatic worldwide fall of surface temperature at the eocene oligocene transition our inference is based on apatite fission track and apatite helium data we suggest that a transition from an eocene fluvial to an oligocene glacial dominated landscape triggered a period of enhanced erosion this study provides the first onshore potential evidence of the onset of continental ice in east greenland margin at the eocene oligocene transition ca 34 ma contemporaneously with the onset of antarctica glaciation and erosion our interpretation is consistent with that based on the oldest ice rafted debris found in the sedimentary records offshore east greenland and implies that east greenland exhibits the oldest onshore record of cenozoic glacial erosion on earth

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

the faroe shetland basin a regional perspective from the paleocene to the present day and its relationship to the opening of the north atlantic ocean the faroe shetland basin is located offshore nw scotland on the se margin of the atlantic ocean and comprises numerous sub basins and intra basin highs that are host to a number of significant hydrocarbon discoveries the principal hydrocarbon discoveries are in palaeocene eocene strata though earlier ones are known and therefore their existence is intimately linked to the opening and evolution of the north atlantic from 54 ma the final rifting and separation of greenland from eurasia is commonly attributed to the arrival of a mantle plume which impacted beneath greenland in the early tertiary moreover the ensuing plate separation is commonly described in terms of instantaneous unzipping of the north atlantic whereas in reality proto plate boundaries were more diffuse during their inception and the linked rift system including connections with the arctic which we see today was not established until late palaeogene early neogene time from a regional analysis of ocean basin development including the stratigraphic record on the adjacent continental margins the significance of the greenland iceland faroe ridge and the age and role of iceland we propose a dual rift model whereby north atlantic breakup was only partial until the oligo miocene with true final breakup only being achieved when the reykjanes and kolbeinsey ridges became linked as final breakup coincides with the appearance of iceland this model negates the need for a plume to develop the north atlantic with rifting reliant on purely plate tectonic mechanisms lithospheric thinning and variable decompressive upper mantle melt along the rifts

ultracataclasis sintering and frictional melting in pseudotachylytes from east greenland abstract large volumes of pseudotachylyte an intrusive fault related rock interpreted to form by a combination of cataclasis and melting occur in tertiary normal faults and accommodation zones along 400 km of the east greenland volcanic rifted margin analysis of representative pseudotachylyte samples reveals a wide range of mesoscopic and microscopic textures mineralogies and chemistries in the aphanitic pseudotachylyte matrix three distinct types of pseudotachylyte referred to as angular rounded and glassy are identified based on these characteristics angular pseudotachylyte found primarily in dike like reservoir zones is characterized by angular grains visible on all scales with micron scale fragments of mica and amphibole its matrix is enriched in fe2o3 mgo and tio2 relative to the host rock with minor increases in cao k2o and small decreases in na2o rounded pseudotachylyte is found in reservoir zones injection veins pseudotachylyte filled extension fractures and fault veins small faults with pseudotachylyte along their surfaces it is characterized by smooth surfaced compacted grains on microscopic scales and encloses rounded interpenetrative lithic clasts on outcrop scale its matrix is enriched in fe2o3 mgo tio2 and al2o3 relative to the host rock with minor depletion in na2o and k2o glassy pseudotachylyte is found primarily along fault surfaces its matrix is characterized by isotropic conchoidally fractured material containing microscopic strain free amphibole phenocrysts and is enriched in tio2 al2o3 k2o fe2o3 mgo cao and na2o relative to the host rock these observations suggest that angular pseudotachylyte was produced by cataclasis with enrichment in metallic oxides resulting from preferential crushing of mechanically weak amphibole and mica minerals found in the gneissic host rock cataclasis and concomitant frictional heating resulted in the textural and chemical modification of angular pseudotachylyte by sintering or melting producing rounded and glassy pseudotachylyte respectively compositional and textural observations constrain the temperatures reached during frictional heating 700 900 c which in turn delimit the amount of frictional heat imparted to the pseudotachylytes during slip our results suggest that the east greenland pseudotachylytes formed during small seismic events along faults at shallow crustal levels consistent relative ages and widespread occurrence of pseudotachylyte bearing faults in east greenland suggest that widespread microseismicity accompanied the early development of this volcanic rifted margin

fluid inclusion evidence for a cretaceous palaeogene petroleum system kangerlussuaq basin east greenland abstract petrographic and fluid inclusion studies of sandstone samples from the cretaceous palaeogene kangerlussuaq basin reveal the presence of oil inclusions as secondary trails across grains fluid inclusion petrographic and microthermometric investigations suggest that oil was trapped at temperatures in excess of about 108 c although due to deep burial in excess of 6 km and subsequent exhumation the kangerlussuaq basin itself cannot be considered as prospective for petroleum it provides a useful analogue for nearby basins on the north atlantic margin given the fact that no sediments older than aptian albian are present in the basin a conventional upper jurassic source rock can be ruled out oil may have been generated from an aptian albian estuarine mudstone whose potential as a regional source rock needs to be assessed oil inclusions also occur in injected sandstones that cross cut the whole sedimentary section and these sandstones may have acted as conduits for petroleum migration their presence in offshore north atlantic basins underneath the tertiary basalts also needs to be considered in play concepts

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

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

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

the variability of baffin bay seafloor sediment mineralogy the identification of discrete glacial sediment sources and application to late quaternary downcore analysis quantitative x ray diffraction qxrd mineralogy of bedrock ice rafted and fluvial clasts 239 seafloor samples 2 mm and samples from two long piston cores were used to i define regional pa

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

evidence from the rare earth element record of mantle melting for cooling of the tertiary iceland plume widespread flood basalt volcanism and continental rifting in the northeast atlantic in the early tertiary period 55 myr ago have been linked to the mantle plume now residing beneath iceland1 2 3 4 5 although much is known about the present day iceland plume6 7 8 9 its thermal structure composition and position in the early tertiary period remain unresolved estimates of its temperature for example range from 1 600 c in some plume models3 to 1 500 c based on the volume and composition of basaltic crust10 11 12 several recent studies4 have emphasized similarities in the thermal and chemical structure of the tertiary and present day plumes to argue for stability of the mantle anomaly whereas others12 13 relate variations in basalt volumes and compositions to changes in plume flux moreover some authors1 2 13 have assumed that the plume was rift centred for its entire history whereas others argue that it became ridge centred only after plate separation14 15 here we report compositional data for 6 000 metres of flood basalts erupted in east greenland close to the inferred plume axis that we use to constrain the tertiary plume structure rare earth element systematics place limits on the pressures and extents of mantle melting and show that the mantle was initially moderately hot 1 500 c but that its temperature declined during flood volcanism these observations are difficult to reconcile with current plume head models and call for important lithospheric control5 10 16 17 18 on actively upwelling mantle along the rifted margin

basin evolution in southern east greenland an outcrop analog for cretaceous paleogene basins on the north atlantic volcanic margins the cretaceous paleogene kangerlussuaq basin in southern east greenland represents a unique outcrop analog for the frontier petroleum provinces along the deep water volcanic margins of the northern north atlantic the 1 km thick sedimentary succession comprises six facies associations 1 alluvial plain and shallow marine late aptian 2 fluvio estuarine late aptian early albian 3 offshore marine late cretaceous early paleocene 4 submarine fan and channel levee early paleocene 5 fluvial mid paleocene and 6 volcanic late paleocene sedimentation was terminated in the late paleocene by extrusion of flood basalts related to continental breakup the basin fill is divided into two depositional megasequences related to regional tectonic events and sea level changes the oldest megasequence sq1 spans the late aptian to the earliest paleocene with sea level rise in the late aptian and maximum flooding in the late albian cenomanian followed by sea level highstand in the late cretaceous early paleocene sq1 is truncated by a basin wide unconformity related to regional uplift and basin reorganization in the mid paleocene the upper megasequence sq2 spans the mid to late paleocene and comprises sediments deposited during early sea level rise extensive volcanic deposits and continental flood basalts overlie it deep burial 6 km and middle eocene early oligocene uplift excludes the kangerlussuaq basin as a petroleum basin in itself however to evaluate the petroleum potential of similar volcanic influenced offshore basins such as the west shetland faeroe more and voring basins we discuss three conceptual play models based on the kangerlussuaq basin 1 early albian stratigraphic trap 2 early paleocene structural trap and 3 paleocene stratigraphic trap

the magnetostratigraphy of coniacian late campanian chalk sequences in southern england abstract magnetostratigraphic data are reported from the coniacian to early late campanian chalk sequences at culver cliff and scratchell s bay on the isle of wight and seaford head in east sussex uk mean natural remanent magnetisation nrm intensity values for individual sample sites range from 0 0013 to 1 6008 ma m with an overall mean of 0 0165 ma m reliable determination of the remanence of the very weakly magnetic units was achieved by carrying out replicate palaeomagnetic measurements on large volume samples using a 2 g wholecore cryogenic magnetometer palaeomagnetic measurements on other standard sized samples were made with a ccl discrete sample cryogenic magnetometer incremental thermal and af demagnetisation treatment was used to remove magnetic overprints and to isolate the characteristic remanent magnetisation chrm a reliability classification scheme has been developed and applied in this study to provide an objective assessment of the quality of the palaeomagnetic results irm acquisition experiments suggest that the dominant magnetic mineral in these sediments is magnetite but mixtures of hematite and magnetite occur also sem and tem studies of magnetic mineral extracts indicate the presence of magnetite and hematite preserved as inclusions within silicate grains together with abundant bacterial magnetite preserved as individual grains and chains in some samples samples containing the greatest proportions of bacterial magnetite generally have the highest nrm intensity the composite magnetic polarity sequence derived by combining the data from all three sections is characterised by three principal magnetic polarity zones which can be correlated with geomagnetic chrons c34n c33r and c33n respectively the positions of the chron boundaries have been tied to macrofossil and nannofossil biostratigraphic zones in these sections a series of previously undocumented short magnetic polarity sub chrons has been identified within the longer magnetochrons these have potential value for high resolution stratigraphic correlations and significance for theories of geodynamo behaviour

internal structure of the 85 e ridge bay of bengal evidence for multiphase volcanism abstract the 85 e ridge located in the bay of bengal of the northeastern indian ocean is an enigmatic geological feature as it possesses unusual geophysical signatures the ridge s internal structure and mode of eruptions are unknown due to lack of deep seismic reflection and borehole data control here we analyze 10 km of long streamer seismic reflection data to unravel the ridge s internal structure and thereby to enhance the understanding of how the ridge was originated and grew over a geologic time seismic facies analysis reveals the ridge structure consisting of volcanic vent and several stratigraphic units including packs of prograding clinoforms the clinoform sequences are interpreted as volcanic successions and led to the formation of lava delta fronts interpreted features of lava fed deltas and intervening erosional surfaces and mass flows along ridge flanks suggest that the 85 e ridge is a volcanic construct and was built by both subaqueous and multiphase sub marine volcanism during the late cretaceous approximately from 85 to 80 ma at later time from oligocene miocene 23 ma onwards the ridge was buried under the thick sediments of the bengal fan system

the jan mayen microcontinent s cenozoic stratigraphic succession and structural evolution within the ne atlantic abstract cenozoic seismic stratigraphic units of the jan mayen microcontinent jmmc are presented in context with kinematic modelling of plate reorganisation correlation with conjugate margins and their chrono stratigraphic correlations our model of development of the microcontinent from continental breakup to present day is based on the interpretation of new and legacy geological and geophysical data from these data we have established eleven cenozoic seismic stratigraphic units jm 70 to jm 01 separated by ten locally varying unconformities and disconformities six of which are regional and reflect discrete tectonostratigraphic phases in the evolution of the jan mayen region these six main phases are 1 pre breakup paleocene 55 ma extension represented by seismic unit jm 70 which comprises terrigenous and marine sedimentary rocks and a thick plateau basalt volcanic succession 2 early eocene 55 52 ma syn breakup rift to drift represented by seismic unit jm 60 and comprises a mix of intrusive igneous rocks subaerial lavas and hyaloclastites and non marine to shallow marine sedimentary rocks 3 early to mid eocene 52 43 ma syn breakup rift to drift and rift transfer across the iceland plateau rift represented by seismic unit jm 50 that comprises volcanic rocks and shelf margin deltaic sediment succession 4 late eocene early oligocene 43 30 ma ridge transfer and tectonic re arrangement in proximity of the iceland hotspot represented in the rock record by shallow to deep marine deposits preserved as units jm 40 jm 35 and jm 30 5 in the late oligocene 30 22 ma a second breakup occurred along the western jmmc igneous margin together with the formation of the south western jan mayen igneous province the proto kolbeinsey ridge and the initiation of proto iceland all of which is represented in the rock record by seismic units jm 20 and jm 15 and 6 miocene to present day separation of the jmmc from east greenland since 22 ma which is represented by seismic units jm 10 jm 05 and jm 01 that reflect a general deepening of the microcontinent

a reassessment of the role of ice sheet glaciation in the long term evolution of the east greenland fjord region abstract the long term evolution of the east greenland fjord region is investigated using geomorphological and stratigraphical evidence to 1 assess the nature of landscape modification caused by late cenozoic ice sheet glaciation and 2 relate patterns of glacial landscape modification to first order i e continent margin scale topography and geology geomorphological and stratigraphical evidence demonstrates evolution of the first order topography and incision of at least part of the present first order fjord system by 55 ma this hypothesis is tested using apatite u th he ages for samples from two bedrock profiles near kong oscar fjord the thermochronology supports landscape evolution before 55 ma followed by relative tectonic stability because it indicates rapid denudation around the time of rifting that occurred prior to continental breakup i e between 75 and 55 ma the nature of landscape modification caused by late cenozoic glacial erosion appears to have been controlled by first order topography and geology with selective ice sheet erosion in areas of high elevation caledonian basement and apparently little glacial erosion of low elevation mesozoic sedimentary strata nevertheless fjord morphometry demonstrates systematic evolution of the first order fjord system from confined and overdeepened fjords in caledonian basement to wider and disproportionately larger fjords in mesozoic strata the latter indicates that changes in lithological strength enabled the development of more efficient fjord morphology under full glacial conditions that may have promoted fast ice flow

cyclical variation in composition in continental tholeiites of east greenland the prinsen of wales bjerge pwb part of the tertiary volcanic province of east greenland consists of tholeiitic basalts overlain by alkalic basalts that were erupted 100 150 km west of the original axis of continental rifting and active ocean floor development during the creation of the north atlantic ocean they have many features of continental flood basalts but are somewhat enriched in fe and in ti relative to fe and have slightly lower al2o3 they have slight enrichments in the light rare earth elements la yb 3 4 a nunatak within the pwb displays four cycles of tholeiitic basalt each about 50 m thick which are defined by trace element variations ni cr sr zr and zr y in three of the four cycles the lowermost flows are the most highly differentiated and successive flows are increasingly primitive these changes are thought to be the result of frequent injection of primitive mantle derived tholeiitic magma into small crustal magma chambers that contain evolved tholeiitic magma the re

baddeleyite and zircon u pb ages from the kaerven area kangerlussuaq implications for the timing of paleogene continental breakup in the north atlantic abstract we report u pb zircon and baddeleyite age results for two mafic units in the kangerlussuaq area which are part of the paleogene east greenland igneous province the kangerlussuaq macrodyke which represents a feeder to some flood basalts and the nearby kaerven gabbro baddeleyite from the macrodyke yielded a concordant age of 54 7 0 4 2 ma and this is among the most precise age determinations from the province this age is interpreted to reflect the time of emplacement the macrodyke belongs to a swarm of dykes emplaced perhaps in a failed arm during continental rifting and the age predates the completion of continental breakup at the end of emplacement of the plateau basalts of the east greenland eruption sequence geochemically the macrodyke is correlated with the milne land formation lavas the magma experienced slight crustal contamination based on the age and geochemistry of the macrodyke the age of the skaergaard intrusion and skraenterne formation lavas an age span of 1 2 ma is confirmed for the extrusion of the entire plateau basalts u pb analysis of zircon from the kaerven gabbro yields an age of 53 0 0 3 2 ma the kaerven gabbro was intruded after extension had ceased in the area and we suggest that the post plateau basalt magmatism did not take place at a distinct later time but instead that igneous activity continued for some time at a lower rate slightly fractionated hrees indicate that the kaerven gabbro magma was extracted at relatively shallow levels in the mantle

age of tertiary volcanic rocks on the west greenland continental margin volcanic evolution and event correlation to other parts of the north atlantic igneous province radiometric ages for undated parts of the volcanic succession and intrusions in west greenland were obtained by the 40ar 39ar incremental heating method acceptable crystallization ages were obtained for 27 samples combined with published results the new data provide a volcanic stratigraphy correlatable throughout the nuussuaq basin the thick onshore volcanic pile consists of four widespread formations 62 5 61 ma picrites vaigat formation 61 60 ma depleted basalts malig t formation and the hellefisk 1 well 60 58 ma less depleted basalts svartenhuk formation and 56 54 ma enriched basalts naqerloq formation two local successions comprise 53 5 ma alkali basalts erqua formation and 38 7 ma transitional basalts talerua member a central volcano developed on ubekendt ejland leading to the sarq ta qaq gabbro granophyre intrusion at 57 55 ma pre break up volcanism took place further south as early as 64 63 ma the offshore volcanic succession most probably comprises the known onshore succession plus some younger lavas the change in spreading direction near the paleocene eocene boundary took place west of the nuussuaq basin c 56 2 ma some tectonomagmatic events are correlatable across the entire north atlantic igneous province a quiescent 58 56 ma period correlates with similar periods in east greenland and the faroes and the naqerloq formation is coeval with the eocene basalts in east greenland the paleocene and eocene tholeiitic basalts are distinguishable chemically in early eocene time mantle typical of the iceland plume seems to have extended beneath the whole west greenland margin as well as the central east greenland margin

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

high rate flexure of the east greenland volcanic margin constraints from 40ar 39ar dating of basaltic dykes abstract in the north atlantic domain the se greenland volcanic margin developed in response to continental break up at 57 54 ma progressive tilting and intrusion of dykes reflect a major tectonic seaward dipping flexing of the continental crust we report eight new ages of tilted pre flexure and vertical post flexure dykes determined by 40ar 39ar incremental heating experiments despite strong excess argon on plagioclase measured 40ar 39ar plateau and mini plateau ages of dykes from detailed step heating experiments on mineral separates appear reliable and a systematic difference of ages is found between tilted and vertical dykes in both studied areas kap wandel 66 20 n and kap gustav holm 66 40 n tilted dykes show ages of 54 55 ma whereas vertical dykes are younger with ages of 51 ma therefore it appears that the crustal flexing of the volcanic passive margin is a short duration event

paleomagnetic study of the cretaceous morelos formation guerrero state southern mexico abstract paleomagnetic results are reported for a 30 m thick limestone section of the albian cenomanian morelos formation guerrero state in southern mexico 17 75 n 99 50 w seventy two specimens from 35 samples were subjected to detailed alternating field af or thermal demagnetizations most specimens were stable and presented a single magnetization component remaining after removal of low coercivity low blocking temperature components end point and vector analyses give a mean direction and pole position after structural correction dip 14 of d 332 7 i 46 8 k 215 95 4 and 63 n 198 e dp 3 dm 5 respectively the pole position agrees with mid cretaceous poles reported for cratonic north america suggesting that the area was already keeping a similar latitudinal position relative to the north american craton by mid cretaceous time most samples present normal polarity as expected within the cretaceous normal interval but four samples from a single bed present intermediate and reverse polarity suggesting the occurrence of a reverse event during the late albian earliest cenomanian

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

structure and stratigraphy of the early tertiary basalts of the blosseville kyst east greenland the central part of the 65 000 km 2 lava plateau in east greenland between kangerlussuaq and scoresby sund has been investigated by multi model photogrammetry and profile sampling and a three dimensional framework for the lava plateau has been established post volcanic movements have divided the region into several structural blocks with dips varying from 1 2 n ne in the inland areas to 12 se at the coast a major n s trending fracture zone may reflect an underlying caledonian structure early volcanic and sedimentary rocks are overlain by widespread plateau basalts locally with an angular unconformity of 8 the basalt stratigraphy established in the scoresby sund area has been extended over most of the region the plateau basalts were erupted over a zone more than 150 km wide from the present coast and inland the succession attains a vertical thickness of more than 5 5 km in the central coastal areas and thins inland to 2 3 km a differential sagging of the coastal areas by at least 2 3 km took place during the emplacement of the lavas accelerating with time the features suggest increasing focusing of the magmatic production into a developing rift zone close to the present coast

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

mafic volcaniclastic deposits in flood basalt provinces a review flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks mostly sills with any pyroclastic rocks limited to silicic compositions however mafic volcaniclastic deposits mvds exist in many provinces and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions the province where mvds are the most voluminous the siberian traps is also the one temporally associated with the greatest phanerozoic mass extinction a lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established but as a first step this contribution reviews in some detail the current knowledge on mvds for the provinces in which they are better known i e the north atlantic igneous province including greenland the faeroe islands the british isles and tephra layers in the north sea basin and vicinity the ontong java plateau the ferrar and the karoo we also provide a brief overview of what is known about mvds in other provinces such as the columbia river basalts the afro arabian province the deccan traps the siberian traps the emeishan and an archean example from australia the thickest accumulations of mvds occur in flood basalt provinces where they underlie the lava pile faeroes n1 km ferrar province z400 m siberian traps 700 m in the faeroes case the great thickness of mvds can be attributed to accumulation in a local sedimentary basin but in the ferrar and siberian provinces the deposits are widespread n310 5 km 2 for the latter on the ontong java plateau over 300 m of mvds occur in one drill hole without any overlying lavas where the volcaniclastic deposits are sandwiched between lavas their thickness is much less in most of the cases reviewed primary mvds are predominantly of phreatomagmatic origin as indicated by the clast assemblage generally consisting of basaltic clasts of variable vesicularity dominantly non to poorly vesicular mixed with abundant country rock debris the accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins east greenland ferrar karoo these underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity in the

multi model photogrammetric analysis of the 1990s surge of sortebrae east greenland sortebrae is a surge type tidewater glacier complex draining southeastward from the geikie plateau east greenland sortebrae s main flow unit surged around 1950 and again between 1992 and 1995 the 1990s surge affected the lower 50 km of sorte brae over an area of approximately 335 km2 over a period of 5 km surge velocities in the order of kilometres per annum are about 100 fold the quiescent velocities multi model photogrammetric analysis shows a thinning of the reservoir zone of up to 219 m and thickening of the receiving zone of up to 74 m the surge transported approximately 18 6 km 3 of ice down glacier the total calving volume as a result of the surge amounted to 11 7 km 3 equivalent to a calving flux of 3 9 7 3 km a 1 the surge characteristics and environmental setting suggest that the surge mechanism involves a switch in the subglacial drainage this surge of sortebrae is more similar to the fast short alaskan type surges than to the sluggish long svalbard type surges

re os isotope geochemistry of tertiary picritic and basaltic magmatism of east greenland constraints on plume lithosphere interactions and the genesis of the platinova reef skaergaard intrusion abstract re os abundance and isotopic studies on a small number of samples from the lowermost part of the east greenland lava pile and the nearby skaergaard intrusion show that picrite and ankaramite lavas tend to have high os abundances and low re os ratios with most rocks having near chondritic values for initial 187 os 188 os one olivine basaltic sample with very high 187 os 188 os has most likely been affected by upper crustal contamination there is no clear evidence for recycled crustal material in the ancestral iceland plume source or for a significant degree of interaction of the picrites with ancient subcontinental lithospheric mantle of the north atlantic craton the platinova reef the precious metal enriched zone in the skaergaard intrusion has very high au and pd contents but very low pt and os contents compared to platiniferous horizons in other layered intrusions these characteristics are almost certainly due to the very late stage in the evolution of the skaergaard magma chamber at which the platinova reef formed the platinova reef yields a re os tchur model age that is younger than the age of the intrusion which was most likely produced by some form of post depositional disturbance to the re os isotopic system the high pge contents of the east greenland volcanic rocks indicate that they were formed from magmas that had the potential to form major accumulations of ni cu pge sulphide deposits had similar magmas undergone significant interaction with continental crust elsewhere in east greenland they may have formed massive magmatic sulphide deposits thus the potential for the discovery of large magmatic sulphide deposits of the noril sk talnakh type in east greenland must be considered excellent

definition and global correlation of the santonian campanian boundary review of biostratigraphical evidence from different regions shows that criteria used by workers on various marine fossil groups to define the santonian campanian boundary differ considerably in relative age and position probably the most widely recognizable of these criteria is the extinction of the distinctive crinoid marsupites testudinarius north america europe asia north africa australia which coincides exactly with two separate definitions of the boundary appearances of the ammonite placenticeras bidorsatum and the belemnite gonioteuthis granulataquadrata and may also coincide with a third entry of the planktic foraminiferan globotruncana elevata a comparison of evidence from upper santonian and lower campanian successions in widely separated regions allows us to place a series of important biostratigraphical markers in correct order defining the boundary at the extinction of m testudinarius corresponds to a 87sr 86sr of 0 707479 and a small positive excursion in 13c the base of magnetochron 33r generally considered to coincide with or fall just above the base of the campanian is shown to lie within the upper santonian uintacrinus socialis zone

magnetostratigraphy of displaced upper cretaceous strata in southern california a magnetostratigraphic study of upper cretaceous marine strata from the santa ana mountains in southern california has identified a campanian reversed magnetozone this reversed interval corresponding to marine magnetic anomaly 33 34 chron 33r of campanian age can be correlated with a campanian reversed magnetozone that has been reported from strata of the great valley sequence in central california the late cretaceous paleolatitude of the santa ana mountains is estimated from this study to be 26 6 n this is significantly different from the region9s expected cretaceous paleolatitude of 43 8 n as part of the north american stable craton and indicates that this region part of the peninsular ranges terrane was 1900 km farther south in cretaceous time relative to the stable craton

significant differences in late quaternary bedrock erosion and transport east versus west greenland 70 n evidence from the mineralogy of offshore glacial marine sediments

hydrodynamic analysis of a mediterranean aquifer system with the use of hydrochemical and isotopical analysis as supporting tools the management of groundwater resources in coastal environments within the mediterranean basin has become of paramount importance especially in the light of global changes a typical example of such a hydrosystem is the lavrio basin in greece this research site involves two aquifer types granular and karstic formations that are hydraulically interconnected furthermore the proximity to the sea and the abstractions for irrigation and drinking water supply have led to the phenomenon of seawater intrusion the present study aims at analyzing the hydraulic hydrological and hydrogeological conditions of the area by means of hydrochemical and isotopical data interpretation as supporting tools which will inform and support the development of an integrated conceptual hydrogeological model of the area field investigations were conducted in order to collect piezometric and chemical data and use them to retrieve the quantitative and qualitative status of the local aquifer units new interpretation of an older dataset gave an insight into how the karstic aquifer behaves in terms of hydraulics the results have also demonstrated that there is a hydraulic connection between the different aquifers and the mediterranean sea while natural recharge was quantified for both aquifer types

source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern north atlantic magnetic properties of eight particle size ranges from nine locations in iceland and 26 locations in southern greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment these terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand fine pseudo single domain psd size magnetic grains dominate the magnetic assemblage of all icelandic fractions in contrast greenlandic samples possess greater variation in magnetic grain size only fine silt and clay are as magnetically fine as the icelandic psd grains while greenlandic silts and sands are dominated by coarser psd and multi domain grains these observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between icelandic and greenlandic sources using these results to examine magnetic grain size records from marine sediment cores collected across the northern north atlantic suggests that source not just transport controlled physical grain size has a significant impact on determining the magnetic grain size at a particular location homogeneity of magnetic grain size in icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding iceland and their ability to buffer large environmental changes

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 behaviour of platinum group elements in basalts from the east greenland rifted margin the continental flood basalts of the east greenland volcanic rifted margin were extruded during continental breakup above the ancestral iceland mantle plume at 55 ma three distinct magma types the low ti high ti and very high ti series lts hts and vhts respectively are found intercalated in the 6 km thick plateau lava sequence incompatible trace elements indicate that the lts are derived from a more depleted mantle source compared to hts and vhts the lts is characterised by increasing cu 105 to 248 ppm and pd 7 to 24 ppb constant cu pd ratio 10 000 and decreasing ir 1 1 to 0 05 ppb and ru 1 8 to 0 3 ppb concentrations during magmatic differentiation 16 to 7 wt mgo the constant cu pd ratio reflects silicate and chromite dominated fractionation without concurrent segregation of sulphide s undersaturated differentiation is also indicated in the hts which also displays increasing pd 6 16 ppb and decreasing ir concentrations 1 to 0 05 ppb during differentiation and the cu pd ratios for the entire series average 21 000 however some hts samples have elevated cu pd ratios up to 33 000 cu pd ratios in the hts do not correlate with mgo and this is interpreted to reflect varying cu pd ratios of hts parental magmas rather than s saturated differentiation during s undersaturated differentiation of the lts and hts pt pd ratios decrease from 1 3 to 0 11 and 1 1 to 0 2 respectively which indicates that pd is much more incompatible than pt during s undersaturated differentiation the vhts consists exclusively of highly evolved samples with low mgo 6 6 6 1 wt and pd ir ratios 98 228 here cu pd ratios increase from 17 500 to 35 000 with decreasing cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide the lts represent melting of a depleted source and show high pge concentrations and constant cu pd ratios during s undersaturated differentiation melting of a normal depleted upper mantle source generates s saturated melts morb and the depleted lts source is therefore considered an extraordinary s poor component within the ancestral iceland plume of the three series the vhts contain the largest contribution from enriched mantle portions the vhts have similar pge but much higher nb concentrations for instance compared to the most evolved lts and hts samples indicating that the enriched source contributes nb but not pge

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of the holmar and grjota olivine basalt groups abstract holmar and grjota are two stratigraphically distinct transitional alkaline olivine basalt lava groups within the westward dipping neogene flood basalts of eastern iceland the holmar olivine basalt group separated from the overlying grjota olivine basalt group by only a few tholeiite flows can be traced over 80 km north south with thicknesses varying from 250 m where thickest to 30 m where thinnest the grjota group can be traced over 50 km also north south reaching thicknesses of 250 m and thinning down dip to 10 m in contrast to other groups in eastern iceland that thicken down dip the studied olivine basalt groups thicken up dip the groups filled topographic confinements and formed aprons around central volcanoes we have estimated the minimum volumes to be 119 km 3 for holmar and 86 km 3 for grjota scoria cones are found in the holmar group and two thick olivine dolerite sills cross cut the holmar group and probably belong to the plumbing system that fed the grjota group the architecture of the lava groups are near identical the architecture is compound with lobes stacked horizontally and vertically varying from 1 15 m thick and 2 200 m long but do also encompass a number of thicker 15 20 m and more extensive 1 km long lava lobe in the stacks filled lava tubes are commonly observed within the lava flows the constituent lobes of the flows are often directly emplaced or welded together suggesting rapid buildup but are also found interbedded with redbeds and thicker tuff deposits and occasionally preserve tree molds the internal structure follows the characteristics for lava lobe morphology in general with an upper vesicular crust forming half to one third of the total thickness a massive core with abundant vesicle cylinders and a thin basal vesicular crust flow tops are of the pahoehoe type seldom found with scoria or clinker inflation structures such as tumuli and inflation clefts were identified in the flows the eruptions were dominantly fissure fed with a few vents evolving to short lived point source volcanism the pre existing topography exerted control on the advancement of the flows and influenced the final architecture of the groups at each location it is evident that the large and dense spatial distribution of these groups including numerous thick lava units suggests large volcanic episodes together the groups imply a period with higher production of olivine basalts in iceland and form well defined stratigraphic markers the transitional alkaline olivine basalt groups are interpreted to delineate a fossil southward propagating rift flank volcanic zone located east of a now extinct and buried mature rift zone

reversed polarity characteristic magnetizations in the albian contessa section umbrian apennines italy implications for the existence of a mid cretaceous mixed polarity interval paleomagnetic and paleontologic data from the valle della contessa umbrian apennines italy span a 14 m y gap in previous magnetostratigraphic sections and reveal several intervals of reversed characteristic remanent magnetization chrm in limestones and marls of the albian marne a fucoidi rock magnetic data indicate that the reversed chrm is carried by hematite having high unblocking temperatures 625 690 c hematite with these unblocking temperatures also carries a normal polarity chrm in other intervals a potential bias towards the identification of normal polarity is present since at every horizon measured a normal polarity component carried by magnetite and hematite is isolated at lower unblocking temperatures 300 600 c bulk magnetic properties vary throughout the measured section in the portion containing most of the reversed chrm intervals hematite is the dominant carrier of natural remanent magnetization while magnetite is the dominant carrier stratigraphically above and below these changes correspond approximately with lithology the zone of dominant hematite magnetization is marked by reddish bands pigmentary hematite which can be correlated throughout umbria and are thought to record changes in the oxidation state of the seafloor during deposition two models may account for the observed magnetization directions the reversed magnetizations may record a remagnetization which occurred at least 18 m y after deposition while the beds were still flat lying in reversed polarity chron 33r 83 79 ma or later if the reversed chrm represents a remagnetization the process is potentially of great importance since it can produce magnetization patterns which resemble polarity intervals alternatively the reversed magnetizations may have been acquired during intense seafloor oxidation episodes during the mid albian 107 104 ma and may record unrecognized intervals of reversed geomagnetic field polarity milankovitch like bedding cyclicity can be used to tune the sedimentation rate and obtain estimates of the duration of the potential reversed intervals using these estimates two of the potential reversed polarity intervals are of sufficient duration 100 kyr to be recognizable in both detailed stratigraphic sections and marine magnetic anomaly surveys a primary magnetization model predicts that several intervals of reversed magnetization should be found near the boundary of the biticinella breggiensis and ticinella primula foraminiferal zones and within the prediscosphaera cretacea nannofossil zone on a worldwide basis

magma chamber processes in the formation of the low sulphide magmatic au pge mineralization of the platinova reef in the skaergaard intrusion east greenland

grain size dependent magnetic discrimination of iceland and south greenland terrestrial sediments in the northern north atlantic sediment record abstract we use isothermal and temperature dependent in field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in iceland and southern greenland the magnetic fraction of greenland silts 3 63 m and sands 63 m is primarily composed of near stoichiometric magnetite that may be oxidized in the finer clay

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

brief reversed polarity interval during the cretaceous normal polarity superchron a striking feature of the geomagnetic time scale is the 34 m y period of normal polarity field bias known as the cretaceous normal polarity superchron new paleomagnetic data from three deep sea drilling project cores sites 317a 402a and 463 indicate that a brief interval of reversed polarity occurred during the superchron this reversed polarity interval may help refine past motions of the pacific plate and aid resolution of the statistical structure of the geomagnetic reversal chronology

pb isotopes during crustal melting and magma mingling a cautionary tale from the miki fjord macrodike central east greenland abstract pb isotopic data are presented for hybrid rocks formed by mingling between mantle derived tholeiitic magma of the eocene miki fjord macrodike east greenland and melt derived from the adjacent precambrian basement bulk mixing and afc processes between end members readily identified in the field fail to model the pb isotope systematics selective contamination during diffusional exchange which can explain the complex sr and nd isotope compositions of the hybrid rocks blichert toft et al 1992 cannot fully account for the variability of the pb isotopic data using the identified crustal end members the crustal anatectic end member although similar in sr and nd isotope composition has a markedly different pb isotopic composition than its source gneiss the differences are consistent with preferential incorporation of radiogenic pb from accessory phases such as metamict zircon or loosely bound pb from grain boundaries during disequilibrium melting of the host rock by the mafic magma the crustal melt involved in magma interactions was therefore heterogeneous with respect to pb isotopes on a metre scale these results illustrate the difficulties inherent in interpreting isotopic variations in contaminated mafic magmas even when the end members are well constrained by field relations we show that the pb isotopic composition of the crustal contaminants and contamination trajectories for the miki fjord hybrid magmatic lithologies are markedly different from regional basement gneisses and contaminated lavas of the associated flood basalt province that were contaminated by characteristically unradiogenic pb and sr lithologies resembling lewisian basement not exposed locally

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of simple aphyric basalt groups simple flows tabular in the neogene flood basalt sections of iceland are described and their mode of emplacement assessed the flows belong to three aphyric basalt groups the kumlafell group the holmatindur group and the hjalmadalur group the groups can be traced over 50 km and originate in the brei dalur thingmuli volcanic zone the groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology the kumlafell and the holmatindur groups have predominantly simple flows of p hoehoe and rubbly p hoehoe morphologies with minor compound or lobate p hoehoe flows the hjalmadalur group has simple flows of rubbly p hoehoe but also includes minor compound or lobate flows of rubble and a simple flows are most common in the distal and medial areas from the vents while more lobate flows in proximal areas the simple flows are formed by extensive sheet lobes that are several kilometers long with plane parallel contacts some reaching thicknesses of 40 m aspect ratios 0 01 they have overlapping contacts and are free of tubes and inflation structures their internal structure consists generally of a simple upper vesicular crust a dense core and a thin basal vesicular zone the brecciated flow top is formed by clinker and crustal rubble the clinker often welded or agglutinated the simple flows erupted from seemingly short lived fissures and have the characteristics of cooling limited flows we estimate the effusion rates to be 105 m3 s for the simple flows of the kumlafell and holmatindur groups and 104 m3 s for the hjalmadalur group the longest flows advanced 15 20 km from the fissures with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands resulting in chaotic flowage slowing lobes with brecciated flow tops developed into a flows the groups interdigitated with lava groups from the rey arfjor ur volcanic zone to the east and the exhumed brei dalur thingmuli volcanic zone which appear to have formed as a flank lineament parallel the main rift zone flood basalt volcanism in flank areas may support a mantle anomaly more pronounced and or perhaps more widespread in the neogene of iceland than today eruptions of simple flows have not been observed in modern times and are significant for models of crustal accretion in iceland and other large igneous provinces

development of volcanic passive margins two dimensional laboratory models 1 continental breakup above an anomalously hot mantle may lead to the development of volcanic margins volcanic margins are characterized by 1 thick seaward dipping lava flow sequences 2 central intrusive complexes associated with dyke swarms parallel to the coast and 3 high seismic velocity bodies in the lower crust attributable to magma underplating a conceptual model for volcanic margins development has recently been proposed based on onshore studies of the greenland margins and the british tertiary igneous province it is proposed that the long lived central intrusions are genetically linked to underlying persistent zones of mantle fusion these localized melting domains or soft spots equivalent to small mantle diapirs may locally soften the extending continental lithosphere the low viscosity diapirs would 1 localize tectonic strain and 2 feed the volcanic margin with magma thus such soft spots can control the along strike magmatic and tectonic segmentation of volcanic margins recent geophysical investigations appear to show that the along strike structure of volcanic passive margins is compatible with such a segmentation process here we present a set of scaled experiments designed to study how such localized rheological heterogeneities in the sub moho mantle may have a mechanical effect on continental breakup four layer models were constructed using sand and silicone putties to represent the brittle and ductile layers of both crust and mantle the soft spots are simulated by low viscosity silicone putty emplaced within the brittle material at the scale of the entire breakup zone the soft spots display an oceanic type strength profile defining low strength zones where continental breakup is initiated the rift orientation and segmentation are strongly controlled by the distribution of the low viscosity heterogeneities rather than by the direction of regional extension the experiments are compared with the geometry and segmentation of the onshore part of the greenland volcanic margins

the transition from sedimentation to flood volcanism in the kangerlussuaq basin east greenland basaltic pyroclastic volcanism during initial palaeogene continental break up primary basaltic pyroclastic deposits compose volumetrically c 35 50 of the lower palaeogene vandfaldsdalen mikis and haengefjeldet formations within the lower volcanic series of the east greenland flood basalt province the eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break up and initiation of flood basalt volcanism we present a revised stratigraphy for the pre volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the kangerlussuaq basin east greenland primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds surge deposits and vent sites with cinder cones early volcanism was apparently restricted to localized basins and formed shield volcano structures 30 40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites sediments pyroclastic deposits and lavas the lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the ne paired with continued down dropping of inactive volcanic centres the complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting

the evolution of the east greenland margin as revealed from fission track studies abstract a comprehensive dataset of fission track analyses mainly of apatite covers the east greenland margin between ca 73 n geographical society island and ca 63 n skjoldungen it consists of data from archaean and caledonian basement post caledonian sedimentary rocks and magmatic rocks the studied areas represent different aspects of the east greenland evolution we report new apatite fission track ft analyses from the east greenland gneissic basement south of scoresby sund to skjoldungen and put them into context with existing data a regional pattern along the east greenland continental margin south of 73 n of deeply eroded shorelines and highstanding slowly eroding hinterland with remnants of old peneplain surfaces is overprinted in the central kangerlussuaq area by tertiary magmatic activity to the northeast the thermal evolution is dominated by a domal structure shown by apatite fission track ft ages to have cooled in the neogene this pattern may result from rapid erosion of the locally uplifted basaltic pile in the area and heating caused by late sill intrusions possibly enhanced on a regional scale by climatic deterioration in the hinterland to the south and west of kangerlussuaq the data restrict the basalt cover to

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

eocene to miocene igneous activity in ne greenland northward younging of magmatism along the east greenland margin radiometric dating by the 40 ar 39 ar incremental heating method was carried out on lavas sills dykes and a central intrusion from ne greenland eighteen samples gave acceptable crystallization ages lavas of both lower and upper plateau lava series gave ages in the range 55 5 53 5 ma and cannot be constrained to better than 56 53 ma sills and dykes from traill o to shannon with compositions fairly similar to those of the lavas gave ages of 55 1 51 3 ma contemporaneous with and slightly younger than the lavas alkaline lavas on inland nunataks have ages of 53 50 ma and the kap broer ruys intrusive centre has an age of 48 7 0 5 ma an alkaline sill on hvalroso is much younger at 20 3 0 1 ma there are no pre breakup lavas onshore ne greenland we surmise that the hot mantle of the iceland plume arrived and melted extensively beneath the northern basins only at the time of breakup around 55 ma post breakup intrusive events in ne greenland coincided with plate tectonic events such as reorganization uplift and opening in the north the hvalroso sill represents a local small melting event that may be related to coeval opening of the lena trough supplementary materials details of the source data results and the compositions and locations of the dated samples are available at www geolsoc org uk sup18738

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