breakup of the newfoundland iberia rift abstract the newfoundland iberia rift is considered to be a type example of a non volcanic rift key features of the conjugate margins are transition zones tzs that lie between clearly continental crust and presumed normal penrose type oceanic crust that appears up to 150 180 km farther seaward basement ridges drilled in the iberia tz consist of exhumed serpentinized peridotite of continental affinity consistent with seismic refraction studies although the boundaries between continental crust and the tzs can be defined with relative confidence there are major questions about the position and nature of the change from rifting to normal sea floor spreading at the seaward edges of the tzs notably drilling of presumed oceanic crust in the young m series anomalies to investigate and potentially resolve these conflicts we analysed the tectonic history and deep pre cenomanian stratigraphy of the rift using seismic reflection profiles and drilling results rifting occurred in two main phases late triassic earliest jurassic and late jurassic early cretaceous the first phase formed continental rift basins without significant thinning of continental crust the second phase led to continental breakup with extension concentrated in three episodes that culminated near the end of berriasian hauterivian and aptian time the first two episodes appear to correlate with separation of continental crust in the southern and northern parts of the rift respectively suggesting that the rift opened from south to north in a two step process the third episode persisted through barremian and aptian time we suggest that during this period there was continued exhumation of subcontinental mantle lithosphere at the plate boundary and that elevated in plane tensile stress throughout the rift caused intraplate extension primarily within the exhumed mantle this rifting may have been interrupted for a time during the barremian when melt was introduced from the southern edge of the rift by plume magmatism that formed the southeast newfoundland ridge and j anomaly ridge and the conjugate madeira tore rise we propose that the rising asthenosphere breached the subcontinental mantle lithosphere in latest aptian earliest albian time initiating sea floor spreading this resulted in relaxation of in plane tensile stress i e a pulse of relative compression that caused internal plate deformation and enhanced mass wasting this aptian event produced a strong rift wide reflection that is unconformably onlapped by post rift sediments that were deposited as a stable sea floor spreading regime was established although previously considered to be a breakup unconformity associated with separation of continental crust the event instead marks the final separation of the subcontinental mantle lithosphere our analysis indicates that interpretation of tectonic events in a non volcanic rift must consider the rheology of the full thickness of the continental lithosphere in addition to spatial and temporal changes in extension that may occur from segment to segment along the rift

imaging mapping and modelling continental lithosphere extension and breakup an introduction abstact this special publication is a direct outcome of a small but dedicated group of researchers who met in pontresina switzerland to review and define the fundamental observations characterizing extensional systems and their application in guiding and constraining modelling efforts and results the various summaries of the keynote addresses give an objective overview of the state of the art in modelling lithospheric extensional systems both from the regional scale using dynamic models to individual basins using kinematic models with an emphasis on capturing the extensional history of the iberia and newfoundland margins at the heart of all of these efforts is a simple question exactly what mechanisms allow the continental lithosphere to be thinned to the point of rupture related questions are 1 do crustal and mantle faults play a major role in this thinning process if so what is their geometry and does their importance and geometry change with time 2 are there other mechanisms of lithospheric and crustal thinning that cannot be imaged on seismic sections 3 how is deformation accommodated in space and time 4 what role do inherited mechanical thermal and or chemical heterogeneities play in controlling strain distribution and localization 5 when how and to what degree does magma production affect the distribution and localization of extension and 6 what is the stratigraphic record of continental extension and how does it document the extension of the crust and thinning of the lithospheric mantle the aim of this special publication is to address many of these fundamental questions concerning the extreme extension and thinning of continental lithosphere

magnetic evidence for slow seafloor spreading during the formation of the newfoundland and iberian margins there is considerable debate concerning the nature and origin of the thin crust within the ocean continent transition oct zones of many passive non volcanic continental margins located between thinned continental and true oceanic crust this crust is usually found to be underlain by upper mantle material of 7 2 7 4 km s velocity at shallow depths 1 2 km it has been proposed that such crustal material could have originated either by exhumation of upper mantle material during rifting of continents or by slow seafloor spreading one of the examples of occurrence of such a crust are the conjugate margins of newfoundland and iberia here we present an interpretation of magnetic data from these regions to show that their oct zones are underlain by crustal material formed by slow seafloor spreading 6 7 mm yr soon after iberia separated from the grand banks of newfoundland in the late jurassic similarities in the magnetic anomalies and velocity distributions from these regions with those from the sohm abyssal plain a region lying immediately south of the newfoundland basin and formed by seafloor spreading at a similar rate of spreading give further support to such an interpretation the idea that these regions were formed by unroofing of upper mantle during rifting of iberia from newfoundland may be likely but the presence of weak magnetic anomalies in these regions which bear all the characteristics of seafloor spreading anomalies makes it difficult to ignore the possibility that these regions could be underlain by oceanic crust formed during slow seafloor spreading the similarities in velocity structure and the presence of small amplitude magnetic anomalies both across this pair of conjugate margins of the north atlantic and that of the labrador sea suggest that this oct velocity structure may be the norm rather than the exception across those passive non volcanic margins where the initial seafloor spreading was slow furthermore the existence of similar velocity distributions along a few active spreading centers raises the possibility of formation of similar crust across slow spreading ridges fl 2000 elsevier science b v all rights reserved

chronology and petrogenesis of a 1 8 g lunar granitic clast 14321 1062 abstract a study was undertaken to determine the chronology of a pristine granite clast 1062 from apollo 14 breccia 14321 using rb sr sm nd and 39ar 40ar methods the genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed chronology the rb sr internal isochron is slightly disturbed and yields an age of 4 09 0 11 ae 87 rb 0 0139 ae 1 and an imprecise initial i sr 0 702 008 if two data are excluded the age becomes 4 13 0 03 ae and i sr 0 698 003 the whole rock and mineral separates are extremely radiogenic they yield model ages which are relatively well defined the average model age is 4 12 0 03 ae relative to babi 0 69898 the sm nd internal isochron is also slightly disturbed and gives an age of 4 11 0 20 ae 147 sm 0 00654 ae 1 the 39ar 40ar average age of the non magnetic fraction of the sample yields a slightly younger age of 3 88 0 03 ae k ar constants from steiger and a 1977 the concordancy of rb sr and sm nd internal isochrons with the rb sr model age strongly suggests that the granitic clast formed at 4 1 ae ago in the shallow crust and was later excavated and brecciated about 3 88 ae ago petrogenesis isotopic and trace element data of the lunar granite show large k la and rb sr fractionations small sm nd fractionation and the distinct v shaped ree distribution pattern at the time of crystallization a two stage model involving crystal fractionation followed by silicate liquid immiscibility sli is proposed for lunar granite genesis we propose that the granite can be the immiscible acidic liquid produced by sli from a residual liquid which underwent fractionation of ca 3 of phases with ree distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with ree contents about twice those of the 15405 85 quartz monzodiorite qmd the extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean our isotopic results and trace elements data from other workers suggest that granites qmd and probably mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro granophyre associations in terrestrial layered intrusions such as the skaergaard intrusions

petrology and chemistry of two large granite clasts from the moon abstract pristine granite clasts in apollo 14 breccias 14321 and 14303 have estimated masses of 1 8 and 0 17 g respectively the 14321 clast is 60 k feldspar and 40 quartz with traces of extremely mg poor mafic silicates and ilmenite the 14303 clast is roughly 33 plagioclase 32 k feldspar 23 quartz 11 pyroxene and 1 ilmenite pyroxene and ilmenite are moderately mg rich plagioclase and pyroxene are strongly zoned both clasts are severely brecciated but monomict pristine both have abundant graphic intergrowths of k feldspar with quartz unlike the majority of similar earth rocks both clasts are devoid of hydrous phases the bulk composition of the 14321 clast is similar to those of several other lunar granitic samples but the 14303 clast is unique it bears as close a resemblance to kreep as it does to other lunar granites silicate liquid immiscibility may explain why the granites are low in ree relative to kreep

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

contourite drifts on early passive margins as an indicator of established lithospheric breakup the albian cenomanian breakup sequence bs offshore northwest iberia is mapped described and characterised for the first time in terms of its seismic and depositional facies the interpreted dataset comprises a large grid of regional 2d seismic reflection profiles complemented by industry and odp dsdp borehole data within the bs are observed distinct seismic facies that reflect the presence of a black shales and fine grained turbidites b mass transport deposits mtds and coarse grained turbidites and c contourite drifts borehole data show that these depositional systems developed as mixed carbonate siliciclastic sediments proximally and as organic carbon rich mudstones black shales distally on the northwest iberia margin mtds and turbidites tend to occur on the continental slope frequently in association with large scale olistostromes distally these change into interbedded fine grained turbidites and black shales showing widespread evidence of deep water current activity towards the top of the bs current activity is expressed by intra bs erosional surfaces and sediment drifts the results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after aptian albian lithospheric breakup therefore we interpret the recognition of contourite drifts in northwest iberia as having significant palaeogeographic implications contourite drifts materialise the onset of important deep water circulation marking the establishment of oceanic gateways between two fully separated continental margins as a corollary we postulate the generation of deep water geostrophic currents to have had significant impact on north atlantic climate and ocean circulation during the albian cenomanian with the record of such impacts being preserved in the contourite drifts analysed in this work

investigating the role of the galicia bank on the formation of the north west iberian margin using deformable plate tectonic models abstract the kinematic evolution of the west iberian margin during the opening of the southern north atlantic has been of interest for several decades and provides a well constrained environment to study and develop new concepts related to the formation of non volcanic magma poor passive margins building upon previous rigid and deformable plate tectonic modelling studies the aim of this work is to create deformable plate tectonic models of the west iberian margin using previously published constraints in gplates to investigate the role of the galicia bank as an independent continental ribbon during deformation of the west iberian margin from 200 ma to present day a comparison of present day crustal thickness results calculated from deformable plate tectonic reconstructions with those obtained from gravity inversion has allowed the plate kinematics of the galicia bank relative to the flemish cap to be investigated additionally this comparison provided detailed insights into the most probable kinematic scenarios for the galicia bank continental ribbon including its impact on the deformation experienced within the galicia interior basin two preferred kinematic models for the galicia bank are proposed one that implies synchronous motion with the flemish cap until 160 ma after which the galicia bank begins to move southward causing crustal thinning within the galicia interior basin the other preferred model despite its discrepancies with gravity inversion results implies synchronous motion of the galicia bank and southeastern flemish cap until breakup between the southeastern newfoundland and iberian margins initiating 140 ma in addition to the deformation induced by the motion of the galicia bank this study demonstrates the influence of inherited variscan structures and their impact on rift segmentation experienced within the galicia interior basin this is inferred through attempts to discretize triangular meshes within regions of deformation in areas where inherited structures have been previously interpreted

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

the ocean continent boundary off the western continental margin of iberia crustal structure west of galicia bank a seismic refraction transect across the galicia bank continental margin shows that the original continental crust thins westward from 17 to 2 km immediately east of a margin parallel peridotite ridge pr immediately west of the pr oceanic crust is only 2 5 3 5 km thick but farther west oceanward it thickens to 7 km the pr caps a similar to 60 km wide lens shaped serpentinized peridotite body underlying both thinned continental and thin oceanic crust when superimposed on a reflection time version of the velocity model the s reflector is clearly intracrustal at its east end westward s cuts down to lower crustal levels eventually coinciding with the top of the serpentinized peridotite lens original crust mantle boundary these observations render almost impossible the seafloor exposure of the pr by s acting as a top to the west detachment fault numerical models of melting and borehole subsidence information constrain our rifting model the easternmost continental crust experienced a total stretching factor of 4 3 most likely in two stages it probably occurred over similar to 25 m y with the highest fate of stretching at the beginning of the main earlier rift phase valanginian 141 135 ma the 3 4 7 km thick continental crust depending on whether serpentinized peridotite is assigned to crust or mantle which may include melt products requires stretching factors 6 more than 11 7 and a rift duration of more than 25 13 m y the thin oceanic crust immediately west of the pr is explained by conductive cooling of the mantle during the long prebreakup stretching phase which temporarily caused reduced melting immediately after breakup

hyperextension serpentinization and weakening a new paradigm for rifted margin compressional deformation the early eocene magma rich northeast atlantic rifted margins contain a large number of pre breakup and post breakup compressional structures located in abandoned early cretaceous hyperextended basins with crustal stretching factors of 3 4 or more the deformation both predates and postdates the magma rich breakup the hyperextended basins are often underlain by high velocity lower crustal bodies which we argue represent partially serpentinized upper mantle long lived lithospheric weakening and proneness to deformation is proposed to relate to crustal hyperextension probably enhanced by mantle hydration

sixth foray for pristine nonmare rocks and an assessment of the diversity of lunar anorthosites eleven nonmare samples are characterized generally both compositionally and petrographically five are almost certainly pristine ferroan anorthosite 10056c alkali anorthosite 14047c ferroan anorthosite 14312c anorthositic troctolite 14321c3 and granite 14321c4 and four are probably pristine norite 14318c noritic anorthosite 67215 quasi pristine ferroan anorthosite 73217c and norite 78527 five are unique anorthosites extending the diversity of lunar anorthosites considerably alkali anorthosites particularly 14047c are extremely rich in incompatible elements the first anorthosite from apollo 11 with manifestations of pristinity 10056c appears to be a normal member of the ferroan group however the first pristine ferroan anorthosites from apollo 14 and 17 to be studied in detail 14312c and 73217c both have unusually sodic plagioclase by ferroan standards with only 75 plagioclase 67215 is the first large 273 g probably pristine ferroan sample with less than 83 plagioclase the nature of the correlations between longitude and such parameters as eu and sm concentrations and sc sm ti sm and ca na ratios among pristine ant samples has been elucidated because five of the new pristine samples are from a western site apollo 14 interestingly ferroan anorthosite 14312c has ca na sc sm and ti sm ratios close to the normal ferroan values but significantly displaced in the direction of the nonferroan western pristine rocks this suggests that the composition longitude relationships are as old as the late stages of the crystallization of the putative magma ocean

lithospheric extension and magmatism in the porcupine basin west of ireland the porcupine seabight basin is a north south trending extensional sedimentary basin situated on the continental shelf west of ireland it is filled with sedimentary rocks which range in age from devonian to present day a large amount of geological and geophysical data is now available for this basin mainly as a result of oil industry exploration in this paper information from 23 well logs and from regional seismic reflection surveys is used to determine the lithospheric stretching history of the basin subsidence analyses indicate that there was one main phase of stretching which began in late liassic times 180 ma ending in earliest cretaceous 145 ma stretching factors at the northern end of the basin are relatively small 1 1 1 7 but increase rapidly southwards along the axis of the main porcupine basin in the southern part of the region the seabight basin is greater than 6 the simplest way to accommodate this rapid variation in stretching is by clockwise rotation of the porcupine ridge through approximately 20 away from the irish shelf subsidence derived stretching values are in reasonable agreement with those determined previously from crustal thicknesses based on gravity models and deep seismic data normal incidence and wide angle the existence location and inferred age of the porcupine median volcanic ridge are also consistent with the subsidence derived stretching factors after intermittent paleocene igneous activity an anomalous increase in the rate of subsidence occurred in the eocene between 55 and 42 ma there is little evidence that this rapid increase is caused by lithospheric stretching and we conclude that it must be associated in some unknown way with melt generated by development of the iceland hotspot

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

processes involved in the formation of magnesian suite plutonic rocks from the highlands of the earth s moon the earliest evolution of the moon likely included the formation of a magma ocean and the subsequent development of anorthositic flotation cumulates this primary anorthositic crust was then intruded by mafic magmas which crystallized to form the lunar highlands magnesian suite the present study is a compilation of petrologic mineral chemical and geochemical information on all pristine magnesian suite plutonic rocks and the interpretation of this data in light of 18 new samples of these 18 clasts taken from apollo 14 breccias 12 are probably pristine and include four dunites two norites four troctolites and two anorthosites radiogenic isotopic whole rock data also are reported for one of the probably pristine anorthositic troctolites sample 14303 347 the relatively low rb content and high sm and nd abundances of 14303 347 suggest that this cumulate rock was derived from a parental magma which had these chemical characteristics trace element isotopic and mineral chemical data are used to interpret the total highlands magnesian suite as crustal precipitates of a primitive kreep possessing a k rare earth element ree and p enriched chemical signature basalt magma this kreep basalt was created by the mixing of ascending ultramafic melts from the lunar interior with urkreep the late k ree and p enriched residuum of the lunar magma ocean the trace and major element compositions of nearly all magnesian suite cumulates can be generated by 0 55 fractional crystallization of a primitive kreep basalt combined with the trapping of varied proportions generally 20 of instantaneous residual kreep basalt liquid a few samples of the magnesian suite with extremely elevated large ion lithophile elements 5 10 other magnesian suite rocks cannot be explained by this model or any other model of autometasomatism equilibrium crystallization or local melt pocket equilibrium without recourse to an extremely large ion lithophile element enriched parent liquid it is difficult to generate parental liquids which are 2 4 higher in the ree than average lunar kreep unless the liquids are the basic complement of a liquid liquid pair i e the so called reep fraction from the silicate liquid immiscibility of urkreep scarce age information on lunar rocks suggests that magnesian suite magmatism was initiated at progressively more recent time from the northeast to the southwest on the lunar nearside from 4 45 to 4 25 ga this magmatic event could be due to melting of the lunar mantle beneath these regions and could have been generated either by latent heat during crystallization of the final kreep rich and thus th and u rich residual lunar magma ocean liquid or heating due to radioactive decay of k th and u

results from a detailed aeromagnetic survey across the northeast newfoundland margin part i spreading anomalies and relationship between magnetic anomalies and the ocean continent boundary abstract a detailed aeromagnetic survey carried out across the northeast newfoundland margin clearly shows the presence of sea floor spreading anomalies 25 to 34 correlation of these anomalies with synthetic profiles shows an increase in the rate of spreading soon after anomaly 27 time three fracture zones can be identified by dislocations in the magnetic anomalies their positions are confirmed on the depth to basement map of this region an eastward extension of the southernmost fracture zone at latitude 49 n matches well with the faraday fracture zone across the mid atlantic ridge and with a basement ridge known as pastouret ridge mapped off goban spur by combining the present survey data with the previously collected shipborne measurements we have also traced the westward continuation of the charlie gibbs fracture zone under the newfoundland shelf a large amplitude magnetic anomaly lies along the margin and separates two zones with different magnetic characteristics long wavelength small amplitude anomalies on the landward side and quasi lineated anomalies on the seaward side seismic data compilations show that this large anomaly coincides with the ocean continent boundary at most places north of flemish cap modelling of the magnetic anomalies indicate that the large amplitude anomaly is caused by the juxtaposition of highly magnetized oceanic crust against weakly magnetized continental crust this situation is similar to that observed across the goban spur margin which is a conjugate of the flemish cap margin the presence of highly magnetized oceanic crust landward of anomaly 34 and within the cretaceous magnetic quiet zone is attested to by the presence of similar large amplitude anomalies south of the flemish cap and goban spur regions but these do not mark the ocean continent transition

apollo 14 mare basalts petrology and geochemistry of clasts from consortium breccia 14321 eleven mare basalt clasts have been extracted from polymict lunar breccia 14321 for a combined petrologic and geochemical study by our consortium ten of these clasts are high al low ti mare basalts similar to those discovered previously at apollo 14 the other is a highly evolved tridymite ferrobasalt with low al and intermediate ti contents a high al ilmenite ferrobasalt from lunar breccia 14305 is the most evolved high al basalt described from the apollo 14 site the major and trace element characteristics of the basalts studied here allow them to be grouped into five compositional types that range from lree depleted to lree enriched some of these types may be related by varying percents of partial melting of the same source but at least two separate sources that differ by a factor of two in incompatible trace element concentrations are required the 14321 type basalts and vitrophyres have steep chondritenormalized hree slopes and may have formed by assimilation of intermediate k fra mauro kreep which is presumed to represent a partial melt of the lower crust the age of these basalts 3 9 aeons suggests that mare volcanism played an important role in the evolution of the early lunar crust

variations in heat flow across the ocean continent transition in the iberia abyssal plain abstract new heat flow observations have been made in the iberia abyssal plain off the galicia margin along the transect of ocean drilling program leg 149 drill sites in order to investigate the nature of this unusually wide and deep continent ocean transition region our results indicate the presence of three separate zones average values of 47 5 3 mw m 2 in the westernmost zone iii agree with predictions of standard oceanic lithospheric models for its estimated age of 126 ma in contrast the heat flow within zone ii is 5 15 mw m 2 higher than predicted assuming that the mantle heat flow remains constant across the basin this region of high values is coincident with the location of a major intra crustal s type reflector east of odp site 900 and the anomaly is consistent with the presence of 2 3 km of primarily upper continental crust above the reflector with concentrations of radiogenic components similar to those from granodiorite samples dredged off galicia bank it is not however consistent with the low values of heat production measured on gabbroic samples from its western end at odp site 900 in zone i detailed measurements across the tilted fault block south of odp site 901 show consistent variations which closely match predictions due to the effects of basement structure and sediment deposition there is no evidence for variations due to vertical convective transport along the dipping basement fault block once corrected for these variations measurements in zone 1 yield average values that agree quite well with previous measurements across galicia bank indicating no systematic landward increase in heat flow with decreasing amounts of continental extension

metasomatic products of the lunar magma ocean the role of kreep dissemination the origin of the incompatible element rich lunar component kreep is in the lunar magma ocean lmo the fractionated residual melt after crystallization of the lmo represents urkreep after warren and wasson 1979 the percentage of this residual melt is low enough to be within the realm of silicate liquid immiscibility sli this process has the ability to split the kreep signature into k and reep fractions which are manifest as lunar granite k and phosphate phases present in highland lithologies or as quartz ferrotroctolite in lunar soils reep we envisage this as a localized but significant process since only a small portion of urkreep undergoes sli norms of experimental and apollo 15 basaltic immiscible glasses suggest that thevreep fraction found in the lunar highlands has undergone post sli fractionation of at least fayalite this significantly reduces the density of the reep fraction and coupled with its low viscosity 10 15 poise it can percolate upward metasomatizing the lunar crust the higher viscosity of the granitic melt 30000 poise inhibits its mobility and it forms pods in the lower rust as required for vhk basalt petrogenesis with the identification of kreepy components the composition of urkreep can be calculated using experimental evidence the kreep components may be recombined to give the pre sli composition or liquid liquid kd s can be used to calculate a pre sli composition from lunar granite both calculated urkreep compositions are lower in mgo and al2o3 and higher in feo and p2o5 than reported low and high k kreep compositions the calculated ree abundances are higher and the ree profiles are slightly more lree enriched than the previously reported kreep compositions however the ree profile calculated using liquid liquid kd s is concave upwards compared to the lree enriched profile produced by recombining the kreep components pre sli whitlockite apatite fractionation occurred prior to immiscibility in order to generate the concave upwards profile the lree enriched profile represents the pre sli magma prior to phosphate fractionation the presence of superkreepy rock types can be accounted for by k and reep fraction assimilation and the compositions of olivine vitrophyres can now be modeled using analyzed lunar rock types without the inference of a mythical high mg component other more widespread kreepy rocks e g apollo 14 breccias apollo 15 kreep basalts lkfm basalts are produced by incorporation of the more widespread pre sli urkreep component the splitting of kreep into identifiable lithological components allows the petrogenesis and role of kreep in lunar evolution to be better understood

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

thorium concentrations in the lunar surface iv deconvolution of the mare imbrium aristarchus and adjacent regions the distribution of th over the mare imbrium and northern oceanus procellarum portions of the apollo 15 lunar ground track has been modeled by deconvolving several fields of orbital gamma ray spectroscopy data including a prior study of the apenninus region a continuous swath from 10 e to 60 w in the northwest quadrant has now been analyzed in the aristarchus region the crater dominates the th distribution with a concentration of 20 ppm other enhancements are seen on the aristarchus plateau and south of the plateau the concentration across the aristarchus plateau is not uniform the average th concentration in oceanus procellarum is less to the west than to the east of the aristarchus plateau substantial enhancements are found in mare regions around brayley and at the ejecta blankets of timocharis and lambert th in the eratosthenian mare regions is generally low with one notable exception lying roughly between the craters euler and carlini the existence of enhanced th concentrations in mare basalt regions suggests that reservoirs of some late stage mare basalts incorporated kreep rich material during formation or transit

crustal structure of the ocean continent transition at flemish cap seismic refraction results 1 we conducted a seismic refraction experiment across flemish cap and into the deep basin east of newfoundland canada and developed a velocity model for the crust and mantle from forward and inverse modeling of data from 25 ocean bottom seismometers and dense air gun shots the continental crust at flemish cap is 30 km thick and is divided into three layers with p wave velocities of 6 0 6 7 km s across the southeast flemish cap margin the continental crust thins over a 90 km wide zone to only 1 2 km the ocean continent boundary is near the base of flemish cap and is marked by a fault between thinned continental crust and 3 km thick crust with velocities of 4 7 7 0 km s interpreted as crust from magma starved oceanic accretion this thin crust continues seaward for 55 km and thins locally to 1 5 km below a sediment cover 1 9 3 1 km s oceanic layer 2 4 7 4 9 km s is 1 5 km thick while layer 3 6 9 km s seems to disappear in the thinnest segment of the oceanic crust at the seawardmost end of the line the crust thickens to 6 km mantle with velocities of 7 6 8 0 km s underlies both the thin continental and thin oceanic crust in an 80 km wide zone a gradual downward increase to normal mantle velocities is interpreted to reflect decreasing degree of serpentinization with depth normal mantle velocities of 8 0 km s are observed 6 km below basement there are major differences compared to the conjugate galicia bank margin which has a wide zone of extended continental crust more faulting and prominent detachment faults crust formed by seafloor spreading appears symmetric however with 30 km wide zones of oceanic crust accreted on both margins beginning about 4 5 m y before formation of magnetic anomaly m0 118 ma

the geodynamic province of transitional lithosphere adjacent to magma poor continental margins two different types of transitional lithosphere have been documented along magma poor rifted margins one consists of apparently subcontinental mantle that has been exhumed brit tlely deformed and serpentinized during late stages of rifting a second is thinned 10 km con tinental crust which in some cases is known to have been supported near sea level at least early in the rift history and thus is interpreted to reflect depth dependent extension in both cases it is typically assumed that oceanic crust forms at the time that the brittle continental crust is breached or soon thereafter and thus that transitional lithosphere has relatively limited width here three representa tive cases of transitional lithosphere are examined one in the newfoundland iberia rift and one at goban spur both exhumed mantle and one off the angola congo margin thin continental crust flanked seaward by apparently exhumed lower continental crust exhumed mantle considering the geological and geophysical evidence it appears that depth dependent extension riftward flow of weak lower continental crust and or upper mantle may be a common phenomenon on magma poor margins and that this can result in a much broader zone of transitional lithosphere than has hitherto been assumed transitional lithosphere in this wide zone may consist of subcontinental mantle lower continental crust or some combination thereof depending on the strength profile of the pre rift continental lithosphere transitional lithosphere ceases to be emplaced i e final break up occurs only when emplacement of heat and melt from the rising asthenosphere becomes domi nant over lateral flow of the weak lower lithosphere this model implies a two stage break up first the rupture of the brittle continental crust and second the eventual separation of the ductile sub continental lithosphere which is coincident with emplacement of normal oceanic crust well defined magnetic anomalies can form in transitional lithosphere that consists of highly serpenti nized exhumed mantle and such anomalies therefore are not diagnostic of oceanic crust where present the anomalies can be helpful in interpreting and dating the rifting history

early cretaceous motion of flemish cap with respect to north america implications on the formation of orphan basin and se flemish cap galicia bank conjugate margins bouguer gravity anomalies together with deep seismic reflection and magnetic data on both sides of the north atlantic are used to locate the hinge zones of the flemish cap and galicia bank within the iberian and north american plates regions across which there were abrupt changes in lithospheric extension the characteristic shape and alignment of these hinge zones suggest that they were conjugate features generated during chrons m25 m0 late jurassic early aptian around a distally located euler pole of rotation rifting between iberia and north america involved these two larger plates and the two smaller microplates the flemish cap and galicia bank microplates the motion of the microplates which were adjacent to eurasia was much more complex than those of the larger plates the motion between the microplates from chron m25 or older to chron m0 was complicated by the fact that they remained attached to each other for most of the time when regions to the south were rifting apart as a result continental regions landward of these segments were subjected to extension that created the orphan and flemish pass basins on the north american side and the galicia interior basin on the iberian side by comparing the hinge zones delineated off galicia bank and flemish cap using the bouguer anomalies we were able to infer that flemish cap rotated approximately 438 relative to galicia bank and iberia and moved 200 300 km se with respect to north america such motions of flemish cap and galicia bank agree remarkably well with extensional episodes deduced from industry multichannel seismic reflection data acquired in the orphan basin normal fault orientations identified in the west orphan basin trend n0208 and are approximately perpendicular to the flow lines of our proposed flemish cap north american motion during the m25 m0 period which provides an independent constraint on our proposed kinematic model therefore extensional events affected not only the galicia bank flemish cap conjugate margins but also the galicia interior and orphan basins and need to be taken into account in any assessment of the geological development of the iberian and north american continental margins during the intermargins workshop meeting modelling the extensional deformation of the lithosphere imedl held in pontresina in 2004 a benchmark exercise was proposed to model the crustal and mantle rifting processes between the western galicia bank and the se flemish cap conjugate margins where high quality seismic reflection and refraction data exist screech line 1 funck et al 2003 hopper et al 2004 and ise line 17 perez gussinye et al 2003 henning et al 2004 during the meeting it became apparent that additional boundary conditions and constraints were needed to correctly characterize the known extension across the iberian newfoundland margin the aim of this paper is to provide some of these conditions and constraints namely a knowledge of the initial positions of plates and microplates before their separation by sea floor spreading processes the positions of flemish cap and galicia bank are well constrained at chron m0 fig 1a because of the identification of correlatable sea floor magnetic anomalies in both the bay of biscay sibuet et al 2004b and in the north atlantic srivastava et al 2000 the resulting euler pole position was constrained by the geometry of the triple junction that had remained at the mouth of the bay of from karner g d manatschal g pinheiro l m eds imaging mapping and modelling continental lithosphere extension and breakup geological society london special publications 282 63 76 doi 10 1144 sp282 4 0305 8719 07 15 00 the geological society of london 2007 fig 1 a reconstruction of the north atlantic between africa af iberia ib and north america na at chron m0 with respect to eurasia eu as given by srivastava et al 2000 ib eu 43 858n 5 838w 244 768 af eu 43 618n 6 938w 240 898 na eu 69 678n 154 268e 23 178 m0 picks west of ib crosses and east of j c sibuet et al 64

the rotations opening the central and northern atlantic ocean compilation drift lines and flow lines we provide an up to date compilation of euler rotations that model the evolution of the central and northern atlantic ocean table 1 the data basis forms seafloor spreading magnetic anomalies of the atlantic we checked the published rotations and selected those that form a consistent model the increments of the euler rotations going back in time from magnetic anomaly to magnetic anomaly can be illustrated by chains of points on drift lines that are paths of motions from continent to continent along these paths the continents bordering the atlantic ocean can be moved back to their mesozoic position within pangea other figures exhibit the early rifting of the north atlantic the drift of iberia and the evolution of the greenland ellesmere region the points on the drift lines do not correspond directly to the lines of magnetic anomalies or their picks displayed today symmetrically in the atlantic ocean to acquire correspondence symmetric flow lines are constructed analogous to the spreading procedure but points on the flow lines constructed by half of the increments partially also deviate from the expected symmetric position and in this way quantify displacements or jumps of the axis of rifting or spreading most of the selected rotations are from the excellent analyses of previous work essential deviations from published rotations are the m 0 rotations of eurasia and of the porcupine unit with respect to north america eur nam and por nam they lead to a better coincidence between the back rotated m 0 magnetic anomalies in the bay of biscay on the one side and a change of the first transform motions between greenland and svalbard on the other side through this explanation an overlap in pangea sw of svalbard is avoided and transform motions instead of strong extension are predicted some additional data are needed to complete the model the earliest part of the path of iberia to north america iba nam up to m 4 is calculated assuming that iberia moved parallel to the african plate though with slower spreading rates the evolution of the central and north atlantic ocean system is described in short this model of the central and north atlantic was produced with the primary intention of clearing and fixing the positions of africa iberia and eurasia as a framework for an improved reconstruction of the western tethys evolution

lunar granulites and their precursor anorthositic norites of the early lunar crust lunar granulites are breccias with metamorphic textures they are not pristine having been contaminated with meteoritic siderophiles nonetheless they constitute an abundant class of highlands rocks that are important because they are ancient and kreep free they may represent our best samples of the early lunar crust the granulites can be divided into ferroan and magnesian groups and each group can be subdivided on the basis of mineral composition and ree concentrations textural and compositional data show that some of the granulites especially 67215 and 67415 may be derived from distinct anorthositic norite precursors while some other granulites 79215 78155 are clearly polymict even the polymict granulites probably had anorthositic norites as their dominant precursors and not anorthosites norites or troctolites the granulites have compositions similar to those of the two lunar meteorites one of which yamato 791197 is ferroan the other alha81005 magnesian these meteorites are soil breccias from an unknown location distant from the apollo landing sites and contain anorthositic norites as abundant clasts compositions of granulites and lunar meteorites more closely resemble the average composition of lunar highlands as determined by remote sensing than do those of any other returned lunar samples the predominance of plutonic anorthositic norite precursors in material having the composition typical of highlands suggests that plutonic anorthositic norites were more abundant in the early lunar crust than is implied by their scarcity among pristine rocks from apollo missions

partitioning in ree saturating minerals theory experiment and modelling of whitlockite apatite and evolution of lunar residual magmas we present compositions including rees determined by ion microprobe of apatite and whitlockite in lunar rock assemblages rich in incompatible trace elements total concentrations of ree oxides in whitlockites range from 9 13 wt and those in apatites range from 0 15 to 1 wt ratios of ree concentrations in whitlockite to those in coexisting apatite range from 10 to 60 the distribution of mg and fe between apatite and whitlockite is correlated to that of coexisting mafic silicates magnesium is strongly preferred by whitlockite and fe is preferred by apatite incorporation of rees in whitlockite is dominated by the coupled substitution of 2ree3 in ca b sites vacancy in ca iia for 2ca 2 in ca b sites and ca2 na in ca iia other substitutions account for only a small portion of the rees in whitlockite over the observed concentration range thus ree concentrations become partially saturated as the primary substitution approaches its stoichiometric limit of two rees per fifty six oxygens leading to reduced whitlockite melt distribution coefficients e g decreasing from twenty five to ten for nd the ree concentrations of lunar residual melts are not depleted by whitlockite crystallization in assemblages consisting mainly of other minerals in typical proportions distribution coefficients for the rees in lunar apatite appear to be low and variable e g 0 2 0 8 for nd variations in the modal ratio of whitlockite to apatite specifically the abundance of whitlockite lead to a range of ree concentrations in the phosphates and variations in the magnitude of ree concentration ratios between whitlockite and apatite if apatite crystallizes before whitlockite or in the absence of whitlockite as textures in several samples indicate then apatite zoned in rees and apatite crystals of different ree concentrations may occur in a given sample provided there is some amount of fractional crystallization and apatite does not later equilibrate this may occur because in the absence of whitlockite in the crystallizing assemblage the rees are highly incompatible relative to the crystalline assemblage so ree concentrations in lunar residual melts increase strongly during small increments of late stage crystallization once whitlockite begins to crystallize bulk distribution coefficients for the rees although still 1 are only mildly incompatible so the change in ree concentrations of residual melts with further crystallization is small consistent with the lack of ree zoning in whitlockite the ree concentrations in lunar whitlockites are modelled as resulting mainly from equilibrium crystallization of the assemblages in which they occur metasomatism or other secondary metamorphic processes are not indicated local melt pocket equilibrium at advanced stages of crystallization may lead to variable ree concentrations and variable whitlockite apatite concentration ratios within the same sample parent melts with extremely high ree concentrations are not required in order to crystallize ree rich lunar whitlockite if modal proportions of whitlockite are low

ages of pristine noritic clasts from lunar breccias 15445 and 15455 abstract rb sr and sm nd isotopic studies were undertaken of two apollo 15 breccias 15445 and 15455 collected near spur crater on the apennine front seven pristine lithic clasts including four norites one anorthositic norite one troctolitic anorthosite and one spinel troctolite as well as a matrix sample of 15445 were analysed in addition a k ar age determination was also made for a plagioclase separate from a different anorthositic norite clast sm nd isotopic data of a pristine mg norite sample 15445 17 from the large white clast b of breccia 15445 yielded a precise internal isochron age of 4 46 0 07 ga for 147 sm 0 00654 ga 1 and an initial 143 nd 144 nd of 0 506058 0 000078 normalized to 148 nd 144 nd 0 24308 corresponding to an initial nd of 0 71 however sm nd isotopic results of another mg norite sample 15445 247 chipped from the same clast b about 1 cm away from 15445 17 yielded a significantly younger isochron age of 4 28 0 03 ga and a higher initial 143 nd 144 nd of 0 506246 0 000037 corresponding to an initial nd of 0 35 the sm nd data indicate that clast b is heterogeneous and contains at least two similar lithologies the rb sr isotopic systems were severely disturbed for both norites no useful isochron ages were observed the sm nd age and nd data for a 15 mg norites 15445 17 and 15445 247 a 17 mgnorite 78236 and two mg gabbronorites 73255 27 45 and 67667 are clearly resolved from each other four distinct parental magmas are required for derivation of these two major groups of mg suite noritic rocks the rb sr isotopic system of an anorthositic norite clast 15455 228 was slightly disturbed and isotopic data defined an isochron age of 4 59 0 13 ga for 87 rb 0 0139 ga 1 or 4 55 0 13 ga for 87 rb 0 01402 ga 1 the corresponding initial 87 sr 86 sr for the rock is 0 69899 0 00006 and is in satisfactory agreement with the luni value of nyquist et al 1974 the sm nd system is more disturbed than the rb sr system for this rock a tie line between whole rock samples and a pyroxene separate gives a sm nd age of 4 53 0 29 ga which is in nominal agreement with the rb sr isochron age the 39ar40ar age of a plagioclase separate of the rock has a weighted average value of 3 83 ga suggesting that the age was reset by the imbrium impact event probably the sm nd and rb sr systems of the clast were also partly reset by this event our age results indicate that some mg suite rocks are as old as ferroan anorthosite suite rocks furthermore age data of three major crustal rocks a mg suite a ferroan anorthosite suite and an evolved suite show that they all have variable ages these observations are difficult to explain by the magma ocean hypothesis alone petrogenetic processes such as production of mg suite rocks by serial magmatism walker 1983 of ferroan anorthosite suite rocks by multiple diapiric intrusions longhi and ashwal 1985 and evolved suite rocks by continuous magmatism meyer et al 1988 1989 probably all played a role these processes seem to be able to accommodate the wide ranges of ages and different origins observed for lunar crustal rocks

crustal structure beneath orphan basin and implications for nonvolcanic continental rifting a wide angle seismic profile was acquired across the northeast newfoundland margin seaward to orphan knoll the profile is complemented by existing multichannel reflection data two online deep wells and other deep seismic reflection and refraction lines modeling of data from 15 ocean bottom seismometers provides the seismic velocity structure for a significant portion of the 400 km wide stretched continental crust on this margin prerift metasedimentary rocks have a topographic relief of up to 5 km with a velocity of 5 2 km s increasing to 5 9 km s unaltered crystalline crust below the metasedimentary section has a velocity range of 6 1 6 5 km s most of the lower crust landward of orphan knoll has a typical continental lower crustal velocity 6 8 7 0 km s and the lower crust shallows significantly beneath orphan knoll our model shows no evidence for the 5 km thick 7 35 km s layer modeled from data of an earlier experiment and interpreted as magmatic underplating but instead indicates that thinned continental crust extends seaward for 360 km without underplating implying nonvolcanic rifting for the ne newfoundland margin we suggest that continental stretching persisted from 180 ma to chron 34n time 101 ma when the final breakup between canada and western europe took place leaving a 400 km wide zone of thinned continental crust underneath the shelf and deep water area of the orphan basin on the landward side of the basin gravity modeling indicates a zone of very thin 6 8 km crust possibly a failed rift center formed as a result of the northward progression of nonvolcanic rifting between canada and europe a possible sub moho reflector suggests generally uniform stretching of the crust and upper mantle and the absence of volcanics and underplating is in contrast to the observations on related rift basins of the grand banks

provenance and paleodrainage patterns of upper jurassic and lower cretaceous synrift sandstones in the flemish pass basin offshore newfoundland east coast of canada upper jurassic to lower cretaceous synrift sandstones from two industry exploratory wells in the flemish pass basin were studied for provenance using heavy mineral proxies these sandstones were deposited during the north atlantic rifting stage at which time rifting intensified between iberia and the grand banks several heavy mineral methods were used including in situ u pb geochronology and morphological and chemical analysis of detrital zircons chemical discrimination of detrital tourmalines and heavy mineral ratios clastic bed load material entering the northern flemish pass basin during the tithonian to berriasian was connected to transport systems reaching west as far as 400 to 500 km 249 311 mi source areas to the west included igneous rocks and associated cover sequences of the avalon zone as well as the magmatic rocks metasedimentary rocks and associated cover sequences present in the central mobile belt the eastward directed input of bed load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin with deteriorating reservoir grade toward the east given the regional extent of drainage systems it is likely that similar constraints apply to equivalent sandstones in the adjacent east orphan basin by the valanginian barremian paleodrainage orientations had switched and bed load material began to enter the flemish pass basin from more proximal areas to the southeast with the avalon zone basement overall no evidence exists to support sediment sourcing from the iberian margin or the flemish cap galicia bank continental fragment to the east and material from these areas is instead interpreted to have been shed into the incipient atlantic ocean or bay of biscay also no evidence exists to support sourcing from grenville basement farther to the west implying that a drainage divide may have existed somewhere between central and western newfoundland west of which material was presumably being transported to the south or southwest

anorthosite assimilation and the origin of the mg fe related bimodality of pristine moon rocks support for the magmasphere hypothesis the lunar magma ocean or magmasphere hypothesis always controversial has required considerable revision in recent years the geochemical bimodality of pristine rocks epitomized by a diagram of na na ca versus mg ratio has led to proposals that a major fraction of the crust the mg rich suite formed as cumulates in numerous intrusions slightly younger than the magmasphere the precise origin of the bimodality has been elusive however one previous suggestion was that na was lost as a volatile before the ferroan anorthosites crystallized from the magmasphere whereas the mg rich intrusives retained all of their original na however this model cannot fully explain the bimodality because the same bimodal pattern is manifested by plotting eu al a ratio of involatile elements versus mg ratio assimilation probably helped to engender the bimodal patterns mass energy balance calculations indicate that large proportions of plagioclase were probably assimilated from the older magmasphere generated ferroan anorthosite crust by most of the mg rich intrusive melts the magmasphere in the absence of assimilation probably did not yield appreciable plagioclase the ferroan anorthosite crust until fractional crystallization of mafic silicates had diminished the melt mg ratio to about 0 42 however assuming identical initial melt composition an mg rich intrusion assimilating ferroan anorthosite and perhaps also a small proportion of urkreep would have reached plagioclase saturation at much higher mg about 0 66 the current version of the magmasphere hypothesis ferroan anorthosites magmasphere flotation cumulates mg rich rocks products of slightly younger localized intrusions appears to be the only plausible mechanism for engendering the mg fe related bimodality

pristine moon rocks a large felsite and a metal rich ferroan anorthosite we report new chemical analyses and in most cases descriptions for 19 lunar rock samples including 5 mare basalts from apollo 15 and 5 uncommonly feldspathic rocklets from apollo 17 two of the samples studied are most extraordinary a large 1 g felsite from apollo 12 and a pristine ferroan anorthosite from apollo 15 that is unusually rich in fe metal and trace siderophile elements the felsite 12033 507 is mainly a graphic intergrowth of k feldspar and a silica phase with about 6 plagioclase and 1 each of ferroaugite ilmenite and fayalitic olivine this crystalline assemblage is crisscrossed and apparently intruded by thin veins of brownish felsic average sio2 57 wt glass the glass veins are far from uniform in composition evidently after the glass was intruded it reacted to varying extents with the crystalline felsite dark globules scattered at apparent nodes in the network of glass veins are interpreted as the least altered of the intruded glasses these globule glasses are relatively sio2 poor average 48 wt but extremely feo rich average 36 wt they may have formed as liquid immiscibility caused the same melt that produced the crystalline felsite to split into fe rich melt the globule glasses plus fe poor si rich melt according to this model deformation most likely caused by an impact then squeezed the fe rich melt into the still nearby and still hot crystalline felsite the fe metal content of ferroan anorthosite 15363 is 1 2 wt in the thin section we studied but must have been based on mass balance for co and ni considerably lower in the chip we used for bulk rock analysis even so the measured bulk rock concentrations for several siderophile elements re os and ir are far higher than previously observed among pristine lunar anorthosites these results underscore the huge uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon s crust among pristine rocks from the apollo 17 site located on the rim of the serenitatis basin ferroan anorthosites continue to be far outnumbered by mg rich rocks

alkali gabbronorite ultra kreepy melt rock and the diverse suite of clasts in north ray crater feldspathic fragmental breccia 67975 lunar breccia 67975 is a feldspathic fragmental breccia from north ray crater apollo 16 it contains clasts of alkali gabbronorite and ultra kreepy mafic fragment laden melt breccias which are unique among apollo 16 samples both are alkali and iron rich rocks with moderate to high ree concentrations they more strongly resemble apollo 14 gabbronorites and alkali anorthosites and kreep rich rocks than they do other apollo 16 samples the other clasts in 67975 are the ferroan anorthosites feldspathic melt rocks and magnesian granulites which are typical of other feldspathic fragmental breccias examination of bulk and mineral compositions of other breccias and melt rocks suggests that alkali gabbronorite may be a minor component in other north ray crater breccias and feldspathic melt rocks this implies that alkali gabbronorite was a fairly early 4 0 b y crustal component in the north ray crater region

pyrenean orogeny and plate kinematics 1 the evolution of the pyrenees a mountain range between iberia and eurasia has remained the subject of many debates between geologists and geophysicists for a long time by combining the identification of seafloor spreading anomalies a33o to m0 in the bay of biscay with those in the north atlantic we have derived a position of a mean pole of rotation for the entire opening of the bay of biscay four hundred kilometers of shortening took place between the iberian and eurasian plates in the pyrenean domain during the opening of the bay of biscay from chrons m0 to a33o time 118 to 80 ma the deep seismic etude continentale et oceanique par reflexion et refraction sismique ecors profile shot across the pyrenees and teleseismic data show the presence of two distinct slabs which dip to the north the southern slab is linked to the subduction of the neo tethys ocean which was created from late jurassic to early aptian simultaneously elongated back arc basins formed along the future pyrenean domain this slab was active from at least 118 ma early aptian to 100 ma late albian the northern slab active since 85 ma is linked to the subduction of the lower continental crust located south of the pyrenean domain in the upper crust normal faults as well as the north pyrenean fault became reverse faults and former back arc basins were inverted giving rise to the uplift of the pyrenees as a double asymmetrical wedge

plate tectonic reconstructions and paleogeographic maps of the central and north atlantic oceans1 2 1this article is one of a series of papers published in this cjes special issue on the theme of mesozoic cenozoic geology of the scotian basin 2earth sciences sector contribution 20120172 we have established a new plate kinematic model of the central and north atlantic oceans between north america africa meseta iberia flemish cap and galicia bank from late triassic to late cretaceous to better understand the nature and timing of rifting of nova scotia and morocco conjugate continental margins since late triassic the maps of salt distributions at the sinemurian pliensbachian limit 190 ma after salt deposition and in middle bajocian 170 ma show that an area of the nova scotia margin is devoid of allochthonous salt and that an area of similar size located oceanward of the west african coast magnetic anomaly shows salt deposits suggesting that a portion of the nova scotia margin with its overlying salt deposits could have been transferred onto the moroccan side right after the formation of the conjugate east coast magnetic anomaly and west african coast magnetic anomaly seven paleogeographic maps from late triassic to late cretaceous are presented with structural elements and ma

quantification and restoration of extensional deformation along the western iberia and newfoundland rifted margins 1 many recent papers describe the structure of the iberia and newfoundland rifted margins however none of them propose kinematic restorations of the complete rift system to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading in our study we use two pairs of cross sections considered as conjugate lines one across the galicia bank flemish cap and the other across the southern iberia abyssal plain flemish pass both transects have been imaged by reflection and refraction seismic methods and have been drilled during ocean drilling program legs 103 149 173 and 210 drilling penetrated parts of the rift stratigraphy and the underlying basement the cross sections can therefore be considered as the best documented conjugate transects across present day hyperextended magma poor rifted margins the aim of this paper is threefold 1 provide a detailed description of the crustal architecture of the two conjugate sections 2 define the extensional structures and their ages and 3 quantify the amount of strain and strain rate accommodated along these lines this paper proposes a quantitative description of extension along the iberia newfoundland rift system and discusses the limitations and problems in quantifying extensional deformation along hyperextended rifted margins

kinematic evolution of the southern north atlantic implications for the formation of hyperextended rift systems we focus on the southern north atlantic rifted margins to investigate the partitioning and propagation of deformation in hyperextended rift systems using plate kinematic modeling the kinematic evolution of this area is well determined by oceanic magnetic anomalies after the cretaceous normal polarity superchron however the rift and early seafloor spreading evolution 200 83 ma remains highly disputed due to contentious interpretations of the j magnetic anomaly on the iberia newfoundland conjugate margins recent studies highlight that the j anomaly is probably polygenic related to polyphased magmatic events and therefore does not correspond to an isochron we present a new palinspastic restoration without using the j magnetic anomaly as the chron m0 we combine 3 d gravity inversion results with local structural stratigraphic and geochronological constraints on the rift deformation history the restoration of the southern north atlantic itself is not the primary aim of the study but rather is used as a method to investigate the spatiotemporal evolution of hyperextended rift systems we include continental microblocks that enable the partitioning of the deformation between different rift segments which is of particular importance for the evolution of the iberia eurasia plate boundary our modeling highlights the following 1 the segmentation of the iberia newfoundland rift system during continental crust thinning 2 the northward v shape propagation of mantle exhumation and seafloor spreading 3 the complex partitioning of deformation along the iberia eurasia plate boundary and 4 a three plate propagation model which implies transtension

ancient crustal components in the fra mauro breccias texturally pristine clasts preserve primary petrographic relationships and mineral compositions yielding insights into igneous processes of the early lunar crust that cannot be gained from highly shocked and brecciated chemically pristine samples the use of texture as a prime criterion allows for expansion of the data base derived solely from chemical criteria and provides complementary data texturally pristine clasts from the apollo 14 site studied here include anorthosite troctolites gabbronorites and basalts alkali anorthosites are plagioclase orthocumulates and may form by flotation in mg suite plutons ferroan anorthosite was cataclastically deformed and metamorphosed to granulite facies troctolites include both 01 plg and 01 en plg cumulates major and trace element analyses of two troctolites reveal eastern geochemical affinities that contrast other western troctolites gabbronorites are plg plg sp cumulates whose parent magmas may range from high al to intermediate ti mare basalt at least three varieties of mare basalt are found at apollo 14 high al low ti low al intermediate ti and low al ti vhk basalt vhk very high potassium basalt is a new variety indigenous to apollo 14

magnesian anorthosites and associated troctolites and dunite in apollo 14 breccias magnesian anorthosite a new type of pristine lunar highlands rock has been found in apollo 14 breccias it has primitive high ca and mg silicate mineral compositions and high and variable ree concentrations variations in ree contents can be accounted for by variations in modal abundance of ree rich apatite magnesian anorthosites are associated with troctolites and a dunite with very similar mineral compositions and it is suggested that all crystallized from a differentiated troctolitic intrusion the origin of the ree rich apatite is enigmatic it is unlikely to have crystallized from an igneous liquid in equilibrium with the major minerals in the anorthosite possible origins are assimilation of urkreep or metasomatism by ree rich fluids ree rich alkali anorthosites and gabbronorites are also found and are likely to be related to kreep basalt magmas lunar compositional associations are distributed in a regional rather than global manner

structure and evolution of the galicia interior basin atlantic western iberian continental margin abstract an industrial multichannel seismic reflection data set is presented on the galicia interior basin g i b a sedimentary basin that has been poorly studied until now seismic stratigraphic units defined in other areas of the western iberian continental margin as well as some deeper reflections can also be identified within this basin although they show some particular characteristics the g i b is bounded to the east by a major fault identified beneath the continental shelf and to the west by an alignment of highs western banks the structural framework of the area consists of nnw sse trending normal faults cross cut by ne sw transfer faults the inception of the g i b probably ocurred during triassic times within the late jurassic early cretaceous rifting phase it probably experienced several extensional episodes the most intense one being during valanginian times evidence for compressional tectonic activity in this basin during cenozoic times has also been found when comparing the g i b with the adjacent deep galicia margin a gap in the timing of the main extensional events as well as some differences in the structural styles have been found in a wider regional context an integration of data about the timing of the processes of continental rifting and oceanic spreading along the whole western iberian margin is consistent with a northward propagating rift for the late jurassic early cretaceous phase

seventh foray whitlockite rich lithologies a diopside bearing troctolitic anorthosite ferroan anorthosites and kreep seventeen nonmare samples most of them pristine are characterized and implications of the new data are discussed five pristine samples are from apollo 14 near the center of the kreep rich zone in the moon s western hemisphere three of them are alkali anorthosites rich in ca phosphate whitlockite which apparently crystallized from magmas with ree contents roughly 6 those of high k kreep the alkali anorthosites probably formed from mg rich magmas that assimilated large amounts of urkreep but some might have formed by metasomatism of ferroan anorthosite by urkreep the gabbronorite norite classification scheme is not well suited to western hemisphere lithologies probably due mainly to the overriding effects of longitude petrochemistry correlations a diopside bearing mg rich lithology indicates that a low degree of melting was not a prerequisite for producing gabbroic high ca pyroxene rich mg rich magmas and suggests that some source regions of mg rich magmas were relatively ca rich several pristine kreep fragments from apollo 15 station 2 are texturally and compositionally much like other pristine kreep and thus reinforce the evidence that kreep is highly uniform the pristine anorthosites on the other hand demonstrate further that lunar anorthosites are diverse

orthopyroxene as a recorder of lunar crust evolution an ion microprobe investigation of mg suite norites the lunar mg suite which includes dunites troctolites and norites could make up 20 30 of the moon s crust down to a depth of 60 km the remainder is largely anorthositic this report focuses on norites because we have found that the chemical characteristics of orthopyroxene are effective recorders of their parental melt compositions many of the samples representing the mg suite are small and unrepresentative in addition they are cumulates and thus are difficult to study by whole rock techniques therefore we decided to study these rocks by sims techniques to analyze a suite of trace elements in orthopyroxene the 12 norite samples were selected from a recent compilation by warren who attempted to select the best candidate samples from the standpoint of their pristine character our present database includes greater than 300 superior electromagnetic pulse emp analyses and greater than 50 scanning ion mass spectroscopy sims analyses for 8 rare earth elements ree zr y and sr the mg s for the parental melts calculated from mg s in orthopyroxene show that most melts have mg s in the range of 0 36 0 60 this compares with a range of mg s for lunar volcanic picritic glass beads of 0 4 0 68 therefore although the cumulate whole rock compositions of the mg suite can be extremely magnesian the calculated parental melts are not anomalously high in mg a chemical characteristic of the mg suite norites that is more difficult to explain is the high kreep content of the calculated parental melts the ree contents for the calculated norite parental melts have ree that match or exceed the high k kreep component of warren therefore mixing of a kreep component and a picritic melt cannot by itself explain the high estimated ree contents of the melts parental to norites advanced crystallization following kreep incorporation especially of plagiclase may also be required

an ancient sm nd age for a ferroan noritic anorthosite clast from lunar breccia 67016 strontium and neodymium systematics have been examined in a clast of ferroan noritic anorthosite from apollo 16 breccia 67016 two splits 328 and 326 of the same clast give different sm nd results split 328 gives a well defined internal isochron age of 4 562 0 068 ga and an initial 143nd 144nd ratio of 0 50673 10 corresponding to nd 0 1 0 2 2 optimized error relative to the murchinson carbonaceous chondrite the pyroxene separate from split 326 lies on the same isochron in contrast the plagioclase and whole rock from split 326 fall below this line indicating a small scale disturbance of the sm nd system this may reflect either an isotopic exchange between the plagioclase and a low sm nd mineral or a loss of radiogenic 143nd from the plagioclase possibly during the period of major impacts at 3 9 ga the preservation of an extremely old age for the noritic ferroan anorthosite 67016 328 suggests a rapid cooling of this rock at an early stage in the evolution of the lunar magma ocean this old age is also consistent with giant impact models for the formation of the moon but implies a relatively early event pre 4 50 ga and therefore rapid accretion and differentiation of the terrestrial planets

mechanisms of extension at nonvolcanic margins evidence from the galicia interior basin west of iberia 1 we have studied a nonvolcanic margin the west iberia margin to understand how the mechanisms of thinning evolve with increasing extension we present a coincident prestack depth migrated seismic section and a wide angle profile across a mesozoic abandoned rift the galicia interior basin gib the data show that the basin is asymmetric with major faults dipping to the east the velocity structure at both basin flanks is different suggesting that the basin formed along a paleozoic terrain boundary the ratios of upper to lower crustal thickness and tectonic structure are used to infer the mechanisms of extension at the rift flanks stretching factor 2 the ratio is fairly constant indicating that stretching of upper and lower crust was uniform toward the center of the basin 3 5 5 5 fault block size decreases as the crust thins and faults reach progressively deeper crustal levels indicating a switch from ductile to brittle behavior of the lower crust at 3 5 faults exhume lower crustal rocks to shallow levels creating an excess of lower crust within their footwalls we infer that initially extension occurred by large scale uniform pure shear but as extension increased it switched to simple shear along deep penetrating faults as most of the crust was brittle the predominant brittle deformation might have driven small scale flow 40 km of the deepest crust to accommodate fault offsets resulting in a smooth moho topography the gib might provide a type example of nonvolcanic rifting of cold and thin crust

pieces of the ancient lunar crust ages and composition of clasts in consortium breccia 67915 we discuss the composition and chronology of clasts representing three minor lithologies in consortium breccia 67915 the lithologies studied are sodic ferrogabbro pristine troctolitic anorthosite 67915 26 and granulitic troctolitic anorthosite 67915 67 these lithologies were presumed to represent samples of the ancient lunar crust the pristine troctolitic anorthosite a typical member of the pristine anorthosite suite contains little or no trapped liquid consistent with its two phase mineralogy the plagioclase separates have 39ar 40ar plateau ages of 4 10 0 06 b y and a final rise in the age pattern may represent a memory of the earlier evolution the granulitic troctolitic anorthosite which has 13 times larger ree abundances displays a continuous rise of the 40ar 39ar ratio the last 25 of the 39ar release data establish a minimum age of 3 5 b y but the 244pu nd chronology suggests an age of 4 3 b y the sodic ferrogabbro samples which appear to be members of the mg gabbronorite group of pristine rocks show large ar losses but indicate plateaus in the low temperature data suggesting a metamorphic event more recently than 260 m y ago a time that is consistent with the north ray impact event 50 m y ago

magmatism at the west iberia non volcanic rifted continental margin evidence from analyses of magnetic anomalies we discuss the magmatic development of the west iberia non volcanic rifted continental margin in the north atlantic ocean so called non volcanic rifted continental margins are characterized by a lack of syn rift magmatism and are considered to be largely amagmatic however this is clearly an oversimplification since seafloor spreading itself is a magmatic process and it is implausible that seafloor spreading begins instantaneously we concentrate our attention on the recently described zone of exhumed continental mantle zecm to investigate what magmatic processes accompanied the breakup of the continental lithosphere and the subsequent formation of the zecm leading to the onset of seafloor spreading we use magnetic anomalies supplemented by the interpretations of multichannel seismic reflection profiles and wide angle seismic experiments presented elsewhere forward and inverse modelling of a sea surface magnetic anomaly chart and of surface and deep towed magnetometer profiles shows that anomalies within the zecm differ in trend amplitude and source type from those in the adjacent oceanic crust and thinned continental crust the zecm anomalies appear to be caused by elongated source bodies within 8 km of the top of the acoustic basement aligned parallel to the margin we interpret such bodies as syn extensional intrusions that increase in volume oceanward they eventually merge in the vicinity of a margin parallel basement peridotite ridge to give rise to a continuous crust that records reversals in the earth s magnetic field from the time of anomaly m4 n m5 r i e to mark the onset of seafloor spreading we find no evidence for anomalies formed by seafloor spreading at either slow or ultraslow rates before m5 r 128 ma

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

evidence for metasomatism of the lunar highlands and the origin of whitlockite abstract the presence of rare earth element rich ree rich whitlockite in the relatively primitive ree poor lunar highlands presents a paragenetic problem to the petrologist comparison with occurrences in mare basalt mesostasis assemblages demonstrates that whitlockite in the lunar highlands has not resulted from the crystallization of the residual interstitial melt furthermore by the nature of ree partition coefficients for whitlockite it is demonstrated that they cannot have crystallized from kreepy melts rather we suggest that the only lunar melt which contains high enough ree abundances is the basic immiscible melt derived from a kreepy liquid we envisage that whitlockite found in the lunar highlands is a post cumulus metasomatic phase precipitated from a melt formed when urkreep underwent silicate liquid immiscibility the basic immiscible melt thus produced was able to percolate through the lunar highlands due to its low viscosity and act as a metasomatizing agent apatite is occasionally found as either epitactic overgrowths on the whitlockites mantled by whitlockite or in composite grains with whitlockite in all cases these apatites contain much lower ree contents than the corresponding whitlockite experimental results suggest either 1 1 apatite and whitlockite have essentially the same ree kd s 2 2 apatite has lower ree kd s than whitlockite both scenarios can be used to explain certain apatite whitlockite associations for example apatite and whitlockite having the same ree kd s can explain the situation where apatite appears to have crystallized after whitlockite this is because apatite crystallization requires a certain level of halogens in the melt these levels are only realized after whitlockite crystallization which enriches the residual melt in f and cl but depletes it in the rees therefore when apatite crystallizes it will contain lower ree abundances than whitlockite however relationships where apatite and whitlockite appear to have co crystallized or apatite crystallized before whitlockite require apatite to have lower ree kd s even if both experimental results are correct the whitlockite parental melt still requires ree abundances greater than in kreep urkreep the parental melt has similar ree abundances to a calculated reepy immiscible melt from kreep urkreep

alternating crustal architecture in west iberia a review of its significance in the context of ne atlantic rifting the crustal architecture of the western iberian margin is investigated so that the relationship between synrift intra plate segmentation magmatic events and subsequent margin convergence can be discussed in the context of the evolution of the central north atlantic ocean the evidence in this paper indicates distinct crustal architectures for nw iberia lower plate and sw iberia upper plate as shown by 1 the different geometries of the rotated tilt blocks across thinned continental crust 2 the distinct dips of deep crustal detachments and 3 the presence of first order strike slip zones bounding different crustal segments we demonstrate that a switch in the dip direction of the crustal detachment is accomplished by accommodating persistent transcurrent deformation along first order transfer zones and associated uplifted hinges both of which accommodated synrift displacement and post rift margin inversion this alternating architecture explains why recurrent magmatism is conspicuously located on the upper plate margin which we consider to have favoured in discrete pulses the emplacement of magma finally the crustal detachment underlying the upper plate is interpreted to have been reactivated since the eocene as the weak zone accommodating ocean continent convergence and the putative onset of margin subduction supplementary material summary of the three main magmatic events on the onshore and offshore west iberia and their associated occurrences location and magmatism type in relation with the syn to post rift evolution of the margin are available at https doi org 10 6084 m9 figshare c 3591209

a concise compilation of petrologic information on possibly pristine nonmare moon rocks ansrn q cr to facilitate systematic study of the surviving compositionally pristine endogenously igneous rocks of the ancient lunar crust a compilation has been generated of all likely samples along with key information on the petrologic characteristics and chemistry of each sample the compilation includes 260 samples besides information related to the likelihood of each sample being truly pristine i e mainly its texture and siderophile element abundances information is compiled on mineral content listing major phases present as well as basic information on mineral compositions on size expressed as mass and on whether a reasonably comprehensive chemical analysis has been published the compilation also classifies the samples into seven categories of confidence in the pristine composition of the samples reflecting an estimation of the relative likelihood that each arguably pristine sample is in fact pristine for many purposes it is crucial to avoid inclusion of polymict rocks in a data base on petrologic diagrams such as a plot of average mg mg 100 x molar mg mg fe in a low ca mafic silicate vs average an content in plagioclase rocks in the top three categories of the confidence in pristine character appear distinctly bimodal in composition with roughly half belonging to a ferroan suite characterized by high an despite relatively low mg when samples of low to moderate pristine character are included the bimodality appears less distinct sample mass can also be important with a data base restricted to samples more massive than i g there is a clear distinction in feldspar content and bulk density between ferroan and nonferroan mgsuite rocks such that only the ferroan suite rocks are likely to have formed as flotation cumulates with a data base including smaller samples the same basic pattern is seen but only in a blurred form as the two rock types show considerable overlap in their modal feldspar contents

origin of petroleum in bangladesh fewer than 70 exploration wells have been drilled in bangladesh 207 000 km2 mostly in the eastern onshore and offshore areas making it one of the least explored countries in the world tectonic developments have controlled the accommodation space available for sediment deposition since the early cretaceous collision between the indian plate and eurasia to the north of bangladesh and between the indian plate and the burma platelet on the east provided favorable conditions for development of oligocene miocene source rocks and miocene reservoir sands in eastern bangladesh the resulting jenam bhuban boka bil petroleum system is the most active system identified to date and is dominant in eastern bangladesh hydrocarbons likely also have been generated from the organic rich shales of the miocene bhuban formation the jenam bhuban boka bil petroleum system alone is responsible for the generation of more than 16 tcf of gas in place discovered to date mostly in the surma basin of the chittagong tripura fold belt several other petroleum systems have been postulated in bangladesh together the best technical estimate of the total resource base is about 61 tcf including reserves within the discovered fields anticipated field growth and new field discoveries with the exception of small bacterial contributions in some surface seep gases and two subsurface accumulations the gases of bangladesh are thermogenic modeling results indicate that the gases and associated condensates are sourced at peak generation depths of at least 6 km many of the gas accumulations are associated with retrograde condensates whose compositions are defined by two distinct source facies and by the solution exsolution effects of vertical migration most of the condensates possess molecular signatures that indicate a major hydrogen rich angiospermous flowering land plant contribution to the organic matter of their source rock s the carbon isotope ratios of the methane in the gases and the isotopic and molecular characteristics of the associated condensates indicate a distinct source facies for petroleums of the northern surma basin relative to those in the south these isotopic and molecular results when interpreted in light of the geological framework and our basin models suggest that the oligocene jenam formation is the major contributor north of 24 4 degreesn and that the miocene bhuban formation is the major contributor to the south

structure and rifting evolution of the northern newfoundland basin from erable multichannel seismic reflection profiles across the southeastern margin of flemish cap we present the results from processing and interpreting five lines from the 1992 erable multichannel seismic reflection experiment extending from the southeastern margin of flemish cap into the northern newfoundland basin these profiles reveal significant along strike variations in the rifting styles experienced by flemish cap in the southwest a 100 km wide transition zone is identified between thinned continental crust and thin oceanic crust similar to the conjugate galicia bank and iberian margins this transition zone contains a section of deep basement adjacent to a series of shallower ridges and is interpreted as exhumed serpentinized mantle along strike towards the northeast this transition zone pinches out completely within 100 km and is replaced by thin oceanic crust directly adjacent to thinned continental crust by interpreting nearby seismic profiles and profiles on the conjugate margins using the same classification criteria we construct regional maps of the distribution of crustal domains on both sides of the north atlantic these maps reveal significant variations in rifting style on the conjugate margins and along strike of each margin and also highlight the role of ancient transfer zones in compartmentalizing these rifting variations into four distinct regions we propose that the limited localization of shallow topographically high serpentinized peridotite ridges on the newfoundland iberia and flemish cap galicia bank conjugate margins was directly related to an increase in the rate of extension following the separation of flemish cap and galicia bank which exhumed deeper less serpentinized mantle

apollo 14 aluminous mare basalts and their possible relationship to kreep thirty six aluminous mare basalt fragments from breccia 14321 and other apollo 14 basalts are statistically divided into two broad groups comprising five subgroups using la sm and yb data major element compositions petrographic characteristics and mineral compositions are similar for the five groups however there is an eight fold increase in ree abundances from group 5 to group 1 with group 1 having a ree pattern similar to kreep groups 1 to 3 may be related by partial melting of a source similar to that proposed by unruh et al 1984 for feldspathic basalt 12038 however groups 4 and 5 cannot be as closely matched by larger degrees of partial melting of this source groups 1 to 4 could also be produced by assimilation of a kreep component by a magma similar in composition to group 5 such a magma can be produced by partial melting of an olivine orthopyroxene source that crystallized from a magma with chondritic relative ree abundances

continental breakup and the onset of ultraslow seafloor spreading off flemish cap on the newfoundland rifted margin prestack depth migrated seismic reflection data collected off flemish cap on the newfoundland margin show a structure of abruptly thinning continental crust that leads into an oceanic accretion system within continental crust there is no clear evidence for detachment surfaces analogous to the s reflection off the conjugate galicia bank margin demonstrating a first order asymmetry in final rift development anomalously thin 3 4 km magmatically produced oceanic crust abuts very thin continental crust and is highly tectonized this indicates that initial accretion of the oceanic crust was in a magma limited setting similar to present day ultraslow spreading environments seaward oceanic crust thins to 1 3 km and exhibits an unusual highly reflective layering we propose that a period of magma starvation led to exhumation of mantle in an oceanic core complex that was subsequently buried by deep marine sheet flows to form this layering subsequent seafloor spreading formed normal 6 km thick oceanic crust this interpretation implies large fluctuations in the available melt supply during the early stages of seafloor spreading before a more typical slow spreading system was established

from continental hyperextension to seafloor spreading new insights on the porcupine basin from wide angle seismic data key points new analysis of wide angle seismic data from the southern porcupine basin evidence for presence of oceanic crust in the southern porcupine basin jurassic rifting propagated from south to north resulting in non uniform strain when rifting stopped the deep structure and sedimentary record of rift basins provide an important insight into understanding the geological processes involved in lithospheric extension we investigate the crustal structure and large scale sedimentary architecture of the southern porcupine basin offshore ireland along three wide angle seismic profiles supplemented by thirteen selected seismic reflection profiles the seismic velocity and crustal geometry models obtained by joint refraction and reflection travel time inversion clearly image the deep structure of the basin our results suggest the presence of three distinct crustal domains along the rifting axis a continental crust becoming progressively hyperextended from north to south through the basin b a transitional zone of uncertain nature and c a 7 8 km thick zone of oceanic crust the latter is overlain by a 8 km compacted upper paleozoic mesozoic succession and 2 km of cenozoic strata due to the lack of clear magnetic anomalies and in the absence of well control the precise age of interpreted oceanic crust is unknown however we can determine an age range of late jurassic to late cretaceous from the regional context we propose a northward propagating rifting process in the porcupine basin resulting in variations in strain along the rift axis

the age of ferroan anorthosite 60025 oldest crust on a young moon abstract sm nd isotopic data for mineral separates from the ferroan anorthosite 60025 define a precise isochron of 4 44 0 02ga age this age is roughly 110 m y younger than the formation of the first large solid objects in the solar nebula as recorded by the radiometric ages of the differentiated meteorites in the magma ocean model for early lunar differentiation ferroan anorthosites are the first crustal rocks to form on the moon if the moon is as old as the oldest meteorites the relatively young age determined for 60025 implies either that the magma ocean did not form synchronously with lunar formation or that the magma ocean required over 100 m y before reaching the stage of ferroan anorthosite crystallization alternatively we propose that the accumulated body of radiogenic isotope data for lunar rocks permit the moon to be as young as 4 44 4 51 ga if so isotopic evidence for chemical differentiation on the earth at about this same time suggests that the formation of the moon is reflected in the chemical evolution of the earth this in turn is consistent with the idea that the materials that now make up the moon were derived from the earth perhaps ejected by collision between the earth and another very large planetesimal during the final stages of accumulation of the terrestrial planets terrestrial origin models for the moon lessen the requirement that the earth and moon each have near chondritic relative abundances of the refractory elements and could require that certain chemical and isotopic characteristics of both bodies be considered in the framework of the chemical mass balance of the combined earth moon system

petrogenesis of lunar troctolites models of petrogenesis for lunar troctolites are severely constrained by the high mg 88 values of the most primitive members of the mg rich suite melts derived by partial melting of olivine cumulates to the lunar magma ocean have high mg but are strongly undersaturated with respect to plagioclase assimilation of lunar crust cannot bring these melts to the plagioclase liquidus without unduly reducing the mg values of olivine partial melts derived by melting a iherzolite primitive interior have higher normative plagioclase contents but require sources with mg 90 more terrestrial like mg 88 values are permitted if rising thermal plumes are capable of entraining the most mg rich cumulates of the magma ocean the mg values of lunar troctolites may therefore reflect a hybrid source composed of primitive mantle and mg rich cumulates of the magma ocean higher mg values may also arise from the reduction of small amounts of feo to fe alternatively the parent magmas to lunar troctolites may be impact melts of the anorthositic crust and the mg rich dunite cumulates of the magma ocean the latter were brought to the upper mantle during the overturn of the unstable cumulate pile of the magma ocean

determining continuous basins across conjugate margins the east orphan porcupine and galicia interior basins of the southern north atlantic ocean abstract the east orphan porcupine and galicia interior basins are several of the most promising basins for hydrocarbon exploration along the rifted continental margins of the southern north atlantic ocean despite having formed at similar geological times the basins exhibit fundamental differences in symmetry crustal thickness sedimentary cover thickness and amount of extension interpretation of seismic reflection and well data was integrated with published 3d grids of depth to basement and moho proxy depth to interpret and restore select seismic reflection lines publicly available kinematic evolution models were also integrated to evaluate and compare the restored seismic reflection lines in a more global regional context interpretation of five seismo stratigraphic units and three tectonostratigraphic megasequences along the east orphan porcupine and galicia interior basins reveals similar seismic character for each unit and comparable tectonic history the structural restoration of the selected lines indicates that evolution sedimentary cover thickness faulting style crustal structure and kinematic evolution of the east orphan and porcupine basins differ significantly a variable and asymmetrical crustal structure is found in the east orphan basin contrasting with the elongated and symmetric porcupine and galicia interior basins rift domain maps of the three basins reveal that they are each underlain by hyperextended crust with possible exhumed mantle in the centre of the porcupine basin based on a holistic analysis of the results obtained the linkage between the east orphan and the porcupine basins seems implausible but rather a contemporaneous relationship is interpreted moreover a potential connection between the galicia interior basin and the porcupine basin during the early to late jurassic is proposed such scenarios imply an oblique and synchronous rifting evolution around the bay of biscay triple junction of the southern north atlantic

traveltime tomography of a dense wide angle profile across orphan basin abstractwe used first arrivals and moho reflections from the 500 km long orphan basin wide angle velocity experiment obwave profile with 3 5 km instrument spacing to construct a traveltime tomography section and to delineate the moho discontinuity across the orphan basin the orphan basin is a failed rift located offshore newfoundland canada showing thinned continental crust over an unusually wide region we observed 1 a zone of extreme crustal thinning 7 km thick crust with no evidence for mantle serpentinization 2 basement morphology exhibiting tilted blocks linked to the crustal thinning and 3 a thicker central crustal segment that is probably related to prerift structural inheritance comparison with the adjacent jeanne d arc basin to the southeast suggested the presence of a decoupling zone between the two basins accommodating the difference in extension rates there was a good correlation between the tomographic velocities and the reflection structure derived from a coincident seismic

comparison of lithosphere structure across the orphan basin flemish cap and irish atlantic conjugate continental margins from constrained 3d gravity inversions regionally constrained 3d gravity inversion results on the orphan basin flemish cap and the irish atlantic conjugate continental margins are compared to investigate crustal structure early rifting history and geological evolution of this part of the north atlantic the full crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins broad similarities in crustal structure are identified with some noticeable differences linked to rifting and crustal stretching processes extreme crustal thinning stretching factors 3 5 is indicated beneath much of the southern porcupine basin the western half of west orphan basin the eastern half of jeanne d arc basin the southeastern half of east orphan basin and in pockets beneath rockall basin this appears to have resulted in the serpentinization and possible exhumation of mantle lithosphere on the irish atlantic and flemish cap margins but not beneath orphan basin a simple evolution model is proposed for the early stages of rifting between the margins it is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of flemish cap out of orphan basin supplementary material enlarged maps from this paper are available at www geolsoc org uk sup18527

investigating the goban spur rifted continental margin offshore ireland through integration of new seismic reflection and potential field data abstract the goban spur offshore ireland is a magma poor rifted continental margin conjugate to the well studied newfoundland margin offshore canada published studies demonstrated that a 70 km wide zone of exhumed serpentinized mantle lies between oceanic crust and stretched continental crust at the seaward limit of goban spur however the along strike extent of this serpentinized zone has until now been unknown due to insufficient data coverage the crustal architecture of the margin is complicated due to its multi staged tectonic history here six newly acquired multi channel seismic reflection lines are processed and interpreted along with vintage seismic profiles to characterize its structure and evolution these seismic profiles reveal significant along strike structural variations along the goban spur margin and allow us to delimit five distinct crustal zones related to different rifting stages and their regional extents the geometries of each crustal domain are variable along the margin strike probably suggestive of different extension rates during the evolution of the margin or inherited variations in crustal composition and rheology the transitional zone between oceanic crust and stretched continental crust consists of both shallow peridotite ridges and deeper exhumed serpentinized mantle much like the conjugate iberian and newfoundland margins above the top basement in the exhumed domain the syn exhumed sediments show strikingly weak reflectivity rarely seen at other magma poor margins magmatic events occur coincident with each rifting stage and the volume of magmatic accretions increases from nw to se more than previously interpreted plate reconstruction of the goban spur and its possible conjugate the flemish cap shows asymmetry in the crustal architectures likely due to rift evolution involving more 3 d complexity than can be explained by simple 2 d extensional kinematics

patterns of basement structure and reactivation along the ne atlantic margin a lineament pattern on the ne atlantic margin is discussed illustrated by gravity and magnetic images in the norwegian sea and reviewed in the context of onshore field evidence while most possible fault trends exist three major sets predominate a ne sw left stepping lineament set defines the gross geometry of the margin while interposing northerly trends impose a rhomboidal geometry at a variety of scales the margin is segmented by nw se transfer zones sometimes involving significant offsets the principal trends are primarily a function of mesozoic cenozoic plate wide extensional stress fields certain proterozoic and caledonian lineaments were however opportunistically reactivated according to the extension direction caledonian ne sw orogen oblique shears typified by the more trondelag fault zone were reactivated via jurassic strike slip or oblique slip and were further exploited during cretaceous early cenozoic extensional episodes leading to continental break up jurassic e w extension may also have reactivated n s faults existing in the basement or generated in duplex systems between the ne sw shears precambrian and caledonian basement lineaments striking at a low angle to the extension direction probably predisposed the formation of major transfer zones

chronology and petrogenesis of the lunar highlands alkali suite cumulates from kreep basalt crystallization alkalic rocks from the highlands of the moon though relatively minor in volume yield important information in understanding the later development of the lunar crust however until recently little information has been available on the crystallization ages of samples from this diverse suite of rocks previous workers suggested a link between pristine kreep basalts and lunar quartz monzodiorites and granites through mineral and chemical modelling of all known pristine highlands alkali suite has rocks and radiogenic isotopic analyses of rather large has clasts from the apollo 14 landing site we explore further this potential link two clasts of alkalic affinity from the western highlands of the moon have been analyzed for their neodymium and strontium isotopic compositions an alkali anorthosite 14304 267 yields a smnd mineral isochron of 4108 53 ma mswd 0 06 and an end t of 1 0 0 2 two splits of the same alkali norite clast 14304 270 and 14304 272 yield similar end values when calculated for this age rbsr systematics for alkali anorthosite 14304 267 scatter about a line which yields an age of 4336 81 ma however the large mean square of weighted deviates mswd for this line 12 3 indicates that the age is suspect and that rbsr sytematics may have been disturbed the smnd age for 14304 267 in conjunction with upb zircon ages for two other highlands alkali suite has rocks from the apollo 14 landing site and one from the apollo 16 landing site indicate production of has rocks over an extended time period spanning at least 300 million years from 4 34 to 4 02 ga since the last dregs of the lunar magma ocean lmo likely crystallized prior to 4 3 ma all rocks from this alkalic period cannot represent direct remnants of the late lmo and may include material resulting from the remelting of evolved portions of the moon by upward moving basaltic melts from the deep lunar interior these contaminated melts may be represented by pristine kreep basalts from the apollo 15 landing site these kreep basalt melts could have crystallized within the crust to form cumulate gabbros norites anorthosites monzodiorites and possibly granites with the proportion of trapped kreepy residual liquid determining the large ion lithophile element enrichment of the rock generally the proportion of trapped kreepy liquid is small 2 15 the broad age range for the lunar has indicates that parental kreep basalt magmatism was not a unique event but was an important process possibly repeated several times throughout the first 600 to 700 million years of lunar history

early carboniferous extension in east avalonia 350 my record of lithospheric memory abstract despite reactivations during variscan and alpine orogenies and the opening of the northern atlantic avalonia is one of the few regions where the initial mid paleozoic basin structure is still recognisable largely intact and well studied its kinematics and dynamics remain however largely unknown in particular in view of the successive late paleozoic to recent evolution of the basin consequently the importance of the mid palaeozoic tectonic evolution and structural controls are often overlooked and poorly understood in basin studies in this paper we reassess the importance of mid palaeozoic tectonics on subsequent sedimentary basin evolution of north western europe to this end we analyse the dynamics of early variscan extension in avalonia based on the integration and re evaluation of available geophysical and geological data from lithosphere to basin scales based on a revised crustal map of the thor suture zone we present a new paleo tectonic reconstruction and tectonic scenario for the devonian carboniferous rifting these findings are key for a better understanding of long lived tectonic segmentation and post rifting deformation phases our findings indicate that the structural grain of many crustal fault dominated sedimentary basin structures such as the north sea central graben were created in the early carboniferous consequently the main basement structuration of northwest europe was completed before the variscan orogeny and successive post variscan extension and inversion phases reactivated the existing basement structures without creating major new fault groups incorporation of the paleozoic structural grain allows for a consistent tectonic framework for the mesozoic contributing to fundamental understanding of basin evolution from our tectonic framework analysis avalonia therefore stands out as a fine example of long lived lithosphere memory spanning over 350 my of structural control in geodynamic evolution

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

post rift submarine volcanic complexes and fault activities in the baiyun sag pearl river mouth basin new insights into the breakup sequence of the northern south china sea abstract post rift volcanisms and fault activities are significant for understanding the tectonic sedimentary evolution of rifted continental margins and associated hydrocarbon entrapments in this study a series of post rift fault associated volcanic activities have been found in the northern continental margin of the south china sea scs however their episodes and relationships with the progressive continental breakup are still doubtful here new 2d 3d seismic borehole dating and biostratigraphic data are used to investigate the characteristics of the post rift volcanism and fault activities in the baiyun sag bys pearl river mouth basin the newly found fault associated volcanic complexes include thirteen submarine volcanic mounds and associated lava flows together with igneous sills that are mainly composed of basalts and tuffs seismic stratigraphic analysis combined with k ar dating from cores confirms that post rift volcanism in the bys climaxed along with the breakup of the scs mainly in three episodes 1 the first episode near oligocene miocene boundary 23 3 ma 2 the second at the middle early miocene 17 6 ma and 3 the new found third episode at the late early miocene 17 1 ma also fifty three syn sedimentary faults are interpreted which are characterized by a wnw trending normal fault group separated by an ene trending transcurrent fault group and there is evidence that these fifty three faults were long lived from ca 32 17 1 ma and served as important conduits for the upward migration of the magma the three episodes of volcanism and tectonic fault activities are related to the progressive continental breakup in the northern scs margin and they represent the tectonic signature of the early stage of the post rift subsidence after the lithospheric breakup which extends to the top of a hypothetical breakup sequence 32 17 1 ma in the bys furthermore this study proves that the diachronous continental breakup in the scs margin can result in corresponding changes in depositional architectures along with a breakup sequence characterized by the deposition of a sandstone carbonate shale regressive transgressive cycle the sedimentological changes and associated tectonic features recorded in the baiyun sag suggest an exceptionally active tectonic setting in the time of the formation of the breakup sequence early oligocene early miocene along the northern scs margin

pristine highland clasts in consortium breccia 14305 petrology and geochemistry the apollo 14 site continues to provide pristine non mare rocks that contrast sharply with those from apollo 16 the archetypical highland site we characterize six small 1 cm samples of pristine highland crust that occur as clasts in polymict lunar breccia 14305 one is an alkali anorthosite the others include troctolite norite and anorthosite of the mg suite the alkali anorthosite 400 is a plagioclase adcumulate with minor intercumulus augite cerian fluorapatite with lree contents 30 000 x chondrite occurs as an inclusion in plagioclase enstatite troctolite 358 and magnesian anorthosite 361 have trace element characteristics similar to eastern mg suite rocks highlighting the importance of local variations in geochemical systematics that are superimposed on moon wide longitudinal variations the highly fractionated trace element abundances and highly magnesian mineral compositions of olivine orthopyroxenite 389 suggest a new previously unknown magma type related to the mg suite this magma may have formed in equilibrium with garnet alkali anorthosites and magnesian anorthosites troctolites cannot be related to a single parent magma by fractional crystallization or by variable kreep assimilation these suites represent separate parent magmas each of which may have been modified by mixing with kreep

exhumed mantle forming transitional crust in the newfoundland iberia rift and associated magnetic anomalies transitional zones located between iberia and north america formed during continental rifting and mostly consist of exhumed mantle in this study we show that ages of exhumed mantle at ocean drilling program odp sites 1068 and 1070 in the iberia abyssal plain and site 1277 in the newfoundland basin are similar to ages determined from magnetic lineations created by serpentinization during mantle exhumation on the basis of paleomagnetic and geological data and a comparison with a fossil ocean continent transition in the alps we envisage a first episode of mantle serpentinization during which a strong component of magnetization was acquired followed by a second episode occurring at the contact with cold seawater and which only affects the upper tens of meters of the exhumed mantle the inversion of magnetic data euler deconvolution shows that magnetic sources are n s trending horizontal cylindrical bodies located within the highly serpentinized upper crust therefore the serpentinization process is able to produce magnetic lineations formed in a similar way to those formed by seafloor spreading within transition zones sequences of magnetic anomalies can provide information concerning the timing of the emplacement of crust but not on its nature oceanic versus exhumed mantle this discovery enables us to date the exhumation of mantle rocks in transition zones and allows kinematic reconstructions of the final stages of continental rifting during rifting the deep distal continental margins and the adjacent transitional zones in the newfoundland iberia rift system were formed by ultraslow extension from early berriasian to late valanginian early hauterivian and by slow extension from early hauterivian to the late aptian early albian boundary therefore transitional zones share many similarities with slow and ultraslow spreading midoceanic ridges

alkali norite troctolites and vhk mare basalts from breccia 14304 twelve clasts were separated from breccia 14304 for consortium study six pristine highlands rocks two mare basalts and four nonpristine highlands rocks the pristine highlands rocks include representatives of the magnesian troctolite anorthosite and alkali suites the two most common subgroups of the mg suite found at the apollo 14 site two troctolite clasts have olivine fo 90 and plagioclase an 94 compositions similar to one group of apollo htroctolites one also contains spinel mg 66 85 incompatible element abundances in one are similar to those of 14305 troctolites although the hree heavy rare earth elements pattern is distinct among apollo 14 troctolites a dunite clast fo 89 may be an unrepresentative piece of a troctolite alkali lithologies include an alkali anorthosite and an alkali norite which is a rock type not previously described the alkali norite has a pristine igneous texture and contains inverted pigeonite mg 64 plagioclase an82 k feldspar ternary feldspar ree rich phosphates and silica it resembles alkali gabbronorites from apollo 14 and 67975 in mineralogy and mineral compositions alkali lithologies and phosphate bearing magnesian anorthosites from apollo 14 may have formed from mg rich magmas that assimilated various amounts of material rich in p and ree this material could be a fractionated derivative of urkreep another pristine clast from 14304 is an mg gabbronorite the two mare basalt clasts are very high potassium vhk basalts they have 4 mg g k and k la ratios of 580 and 700 the parent magmas of vhk basalts could have formed from typical low ti high al basaltic magmas by assimilation of k rich material this material could also be a fractionated derivative or urkreep nonpristine 14304 clasts include melt textured anorthosites and an augite rich poikilitic melt rock the latter is probably polymict but its major component must be an mg suite gabbro

exhumed upper mantle within the ocean continent transition on the northern west iberia margin evidence from prestack depth migration and total tectonic subsidence analyses 1 the west iberia continental margin contains an enigmatic north south ridge of serpentinized peridotite located within the ocean continent transition we used prestack depth migration and total tectonic subsidence analysis to constrain the basement type adjacent to the ridge in order to learn more about its emplacement prestack depth migration was performed on segments of the nine east west lines from the iberia seismic experiment ise 97 and total tectonic subsidence analyses were performed on the depth sections the seismic data and subsidence analyses are consistent with exhumed upper mantle occurring immediately landward of the ridge suggesting that the ridge is located within a broad zone of exhumed mantle that has been serpentinized the subsidence analyses also provide minimum bounds on the thickness of the serpentinized layer which extends from the zone of exhumed mantle landward under thinned continental crust exhumed upper mantle has previously been identified in the wider ocean continent transition to the south in the southern iberia abyssal plain and we conclude that similar but narrower exposures occur to the north in the galicia bank area while upper mantle appears to have been tectonically exhumed along all the ise 97 lines it does not always form a distinct basement ridge there is no well defined ridge on three seismic profiles in the middle of the ise 97 survey where it is well developed the peridotite ridge parallels a deeply penetrating west dipping normal fault and the three middle lines appear to represent a transfer zone where this normal fault is not well developed

crustal structure of the newfoundland rifted continental margin from constrained 3 d gravity inversion the rifting history of the atlantic continental margin of newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2 d seismic surveys while informative the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin a 3 d gravity inversion of the free air data over the newfoundland margin allows us to generate a 3 d density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage results of the gravity inversion show good correspondence with moho depths from seismic results a shallowing of the moho to 12 km depth is resolved on the shelf at the northern edge of the grand banks in a region poorly sampled by other methods comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends such insights must act as constraints for future palaeoreconstructions of north atlantic rifting