the devonian lacustrine sediments of orkney scotland implications for climate cyclicity basin structure and maturation history the orcadian basin of northern scotland largely of middle devonian age is a major lacustrine rift basin with the widely correlateable achanarras sandwick lake bed extending for at least 800 km along the rift above this lake bed there are about 540 m of cyclic lacustrine sediments with lake sedimentation terminated by alluvial fan progadation the upper stromness flagstone formation and the rousay flagstone formation making up this lacustrine sequence are given revised and precise definitions within four reference sections from the orkney islands the sequence consists of about 45 first order cycles averaging about 12 m in thickness which resulted from long term climatic fluctuations in rainfall with a cycle time scale of about 25 000 years longer climatic fluctuations of about 100000 and 400000 years are also present these periods correspond to the precession and two eccentricity orbital cycles detailed knowledge of the stratigraphy constrains the structural and maturation history of the basin the basin formed in a series of extensional half graben and the orkney area suffered later inversion the lake sediments first reached the oil window at relatively shallow depths c 2000 m probably in the early carboniferous implying very high geothermal gradients during the early part of the basin history as corroborated by the presence of devonian volcanics in the region in the orkney area uplift probably started in the late carboniferous

generation and evolution of siliceous high magnesium basaltic magmas in the formation of the permian huangshandong intrusion xinjiang nw china abstract numerous permian orthopyroxene rich mafic ultramafic intrusions in the southern margin of the central asian orogenic belt caob have been emplaced in a post orogenic environment the huangshandong mafic ultramafic intrusion is the largest in the eastern tianshan orogenic belt of the caob and consists of a layered unit intruded by a massive unit the layered unit consists of lherzolite troctolite olivine gabbro hornblende gabbro gabbrodiorite and diorite whereas the massive unit is made of gabbronorite and olivine gabbronorite olivine from the layered unit has fo values of 75 to 84 and contains low nio and mno rocks from this unit have initial 87sr 86sr ratios 0 7031 0 7043 and end values 3 4 7 1 while plagioclase has initial 87sr 86sr ratios ranging from 0 70010 to 0 71569 olivine from the massive unit has relatively low fo values of 59 to 70 and high nio and mno rocks from this unit have relatively low and uniform initial 87sr 86sr ratios 0 7030 and high end values 6 0 7 5 and contain plagioclase with relatively low initial 87sr 86sr ratios 0 70042 to 0 70520 olivines from both units have low cao and cr2o3 both units formed from siliceous high magnesium basaltic magmas were derived from a hydrous depleted mantle source magma forming the layered unit experienced earlier removal of sulfides before emplacement with the earlier sulfide saturation caused by the addition of crustal material the magma that formed the massive unit has undergone fractional crystallization of olivine cr spinel siliceous high magnesium basaltic magmatism produced by melting of a hydrous depleted mantle source may be an important feature of orogenic belts

geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part ii ree and the trapped liquid fraction rare earth elements in bulk cumulates and in separated minerals plagioclase apatite ca poor and ca rich pyroxenes ilmenite and magnetite from the bjerkreim sokndal layered intrusion rogaland anorthosite province sw norway are investigated to better define the proportion of trapped liquid and its influence on bulk cumulate composition in leuconoritic rocks made up of plagioclase ca poor pyroxene ilmenite fmagnetite folivine where apatite is an intercumulus phase even a small fraction of trapped liquid significantly affects the ree pattern of the bulk cumulate together with cumulus minerals proportion and composition contrastingly in gabbronoritic cumulates characterized by the presence of cumulus ca rich pyroxene and apatite cumulus apatite buffers the ree content la sm and eu eu vs p2o5 variations in leuconorites display mixing trends between a pure adcumulate and the composition of the trapped liquid assumed to be similar to the parental magma assessment of the trapped liquid fraction in leuconorites ranges from 2 to 25 and is systematically higher in the north eastern part of the intrusion the likely reason for this wide range of tlf is different cooling rates in different parts of the intrusion depending on the distance to the gneissic margins the ree patterns of liquids in equilibrium with primitive cumulates are calculated with mass balance equations major elements modelling duchesne j c charlier b 2005 geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos 83 299 254 permits calculation of the ree content of melt in equilibrium with gabbronorites partition coefficients for ree between cumulus minerals and a jotunitic liquid are then calculated calculated liquids from the most primitive cumulates are similar to a primitive jotunite representing the parental magma of the intrusion taking into account the trapped liquid fraction calculated from the p2o5 content consistent results demonstrate the reliability of liquid compositions calculated from bulk cumulates and confirm the hypothesis that the trapped liquid has crystallized as a closed system without subsequent mobility of ree in a migrating interstitial liquid d 2005 elsevier b v all rights reserved

buried granites within the mid north sea high a gravity survey of the uk sector of the north sea reveals the presence of three gravity lows over the mid north sea high seismic data eliminate the possibility that these lows are due either to thicker sediments or to salt structures consequently the anomalies may be related to buried granites within the palaeozoic basement gravity modelling demonstrates that the amplitude and shape of the observed anomalies may be explained by buried batholith shaped bodies with densities appropriate for granites the tectonic influence of the buried granites may explain to some extent the continued stability of the mid north sea high throughout much of the development of the north sea basins

structural development of the devono carboniferous plays of the uk north sea decades of oil and gas exploration across the north sea have led to a detailed understanding of its cenozoic mesozoic structure however the deeper basin architecture of paleozoic petroleum systems has been less well defined by seismic data this regional structural overview of the devono carboniferous petroleum systems incorporates interpretations from more than 85 000 line kilometres of 2d seismic data and 50 3d seismic volumes plus a gravity density and magnetic study from the central silverpit basin to the east orkney basin a complex picture of previously unmapped or poorly known basins emerges on an inherited basement fabric with numerous granite cored blocks these basins are controlled by devono carboniferous normal strike slip and reverse faults the main basins across quadrants 29 44 trend nw se influenced by the tornquist trend inherited from the caledonian basement north of quadrants 27 and 28 and the presumed iapetus suture the major depocentres are ne sw e g the forth approaches and inner moray firth basins to east west e g the caithness graben and wnw ese trending e g the east orkney basin reflecting the basement structural inheritance from seismic interpretation there are indications of an older north south fault trend in the inner moray firth that is difficult to image since it has been dissected by subsequent permo carboniferous and mesozoic faulting and rifting

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

quantification of tertiary erosion in the inner moray firth using sonic velocity data from the chalk and the kimmeridge clay abstract sonic velocities for the chalk and kimmeridge clay were analysed to determine the importance and magnitude of tertiary erosion for 26 wells in the inner moray firth apparent erosion height above maximum burial depth was derived by the displacement along the depth axis of a given velocity depth trend from the normal undisturbed trend the similarity in apparent erosion results derived from the cretaceous chalk and late jurassic kimmeridge clay successions of the inner moray firth suggests that burial beyond present depths caused the observed overcompaction rather than any sedimentological and or diagenetic process resultant apparent erosion estimates are variable across the inner moray firth such values reach approximately 1 km in the western part of the basin and decrease progressively to zero in the eastern inner moray firth however the actual magnitude of erosion equal to the sum of apparent erosion and post erosional tertiary burial was approximately 1 km throughout the whole inner moray firth area indicating that early tertiary erosion was regional and not simply restricted to the inverted basin margins however a well defined mechanism sufficient to have generated the regional event is still sought

the 1 75 1 68ga anorthosite mangerite alkali granitoid rapakivi granite suite from the northern north china craton magmatism related to a paleoproterozoic orogen abstract the amgrs is a suite of anorthosite mangerite alkali granitoid rapakivi granite in the northern north china craton ncc new zircon shrimp and laser ablation inductively coupled plasma mass spectrometry la icpms u pb dating of the damiao anorthosite changsaoying k feldspar granite lanying anorthosite and quartz syenite and the gubeikou k feldspar granite yielded emplacement ages of 1726 9 ma 1753 23 ma 1739 43 ma 1712 15 ma and 1692 19 ma respectively combined with previous geochronological data from the damiao norite and mangerite and shachang rapakivi granite it indicates that the whole amgrs was intruded between 1750 ma and 1680 ma the damiao anorthosites and norites exhibit a high mg and this decreases from mafic up to 63 to felsic t dm c ages ranging from 2 32 ga to 2 43 ga and 2 70 ga to 2 88 ga respectively this suggests that these rocks are the fractional crystallization products of one parental magma zircon hf and whole rock sr nd pb isotopic systematics combined with high la yb 10 and intermediate th ta ratios suggest that the parental magma of the amgrs could have been derived from em i lithosphere mantle enriched by recycled archean continent crustal materials accompanied by some assimilation of lower crustal components the mafic to felsic compositions of the amgrs are different from typical bimodal rocks formed in an anorogenic intra continent rift setting but resemble those emplaced during post collisional post orogenic extensional tectonic setting this is compatible with their age of

geochemical and isotopic zoning patterns of plagioclase megacrysts in gabbroic dykes from the gardar province south greenland implications for crystallisation processes in anorthositic magmas chemical and sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the gardar province can be used to elucidate magma chamber and emplacement processes the megacrysts occur either as single crystals or assembled as anorthosite xenoliths the size of the megacrysts varies from 1 cm to 1 m they consist of a large core with variable zonation an58 39 and a relatively small 600 m normally zoned rim an62 27 the contact between core and rim is sharp and marked by a sharp increase in anorthite content which can reach 11 mol an this gap is interpreted as having formed during dyke emplacement due to a sudden pressure release some of the megacryst cores show a fairly constant composition whereas others exhibit an unusual wavy oscillatory zoning which has not been reported elsewhere to our knowledge the oscillatory zoning has wavelengths of up to 2 500 m and a maximum amplitude of 7 mol an it is interpreted as reflecting movements of the crystals in the magma reservoir the sr isotopic composition of one crystal shows a radiogenic inner core 87sr 86sr i 0 7044 and a less radiogenic outer core 87sr 86sr i 0 7039 0 7036 the lack of a significant change between outer core and rim 87sr 86sr i 0 7037 is consistent with formation of the more an rich rim due to pressure release variations in the core may be related to movements of the crystal and or magma mixing a trace element profile across a megacryst shows a small increase in sr and small decreases in ba and la contents of the recalculated melt composition across the core rim boundary whereas p ce nd and eu remain constant melt compositional changes upon emplacement are therefore considered to be of minor importance constant ratios of incompatible trace elements in the megacryst cores indicate a dominant influence of a lower crustal source on trace element budgets

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

deep crustal structure and carboniferous basin development within the iapetus convergence zone northern england seismic reflection data from northern england are interpreted to show a northward dipping caledonian thrust zone lying beneath the faulted southern margin of the northumberland trough the thrust zone lies upon the updip projection of a northward dipping high conductivity layer in the middle and lower crust identified by magnetotelluric sounding together these features indicate the presence of a crustal scale caledonian shear zone dipping north at an average angle of 20 25 extensional reactivation of the middle and upper crustal parts of the shear zone in carboniferous times led to development of the northumberland trough reappraisal of the birps nec seismic profile suggests the presence of the same or similar crustal shear zone reactivated to form the offshore extension of the northumberland trough the shear zone probably formed as a major compressive or transpressive feature during late caledonian acadian continental collision in the lower crust the shear zone lies close to or may actually represent the iapetus suture at middle to upper crustal levels the shear zone lies wholly within avalonian english crust well to the south of the faunally determined iapetus suture westward extrapolation of the shear zone indicates that it may crop out within the northern lake district perhaps as the causey pike and associated thrusts the faunal suture is likely to subcrop north of the lake district and alston block beneath the central part of the northumberland trough

pyroxene megacrysts in proterozoic anorthosites implications for tectonic setting magma source and magmatic processes at the moho abstract proterozoic anorthosites from the 1630 1650 ma mealy mountains intrusive suite grenville province canada the 1289 1363 ma nain plutonic suite nain churchill provinces canada and the 920 949 ma rogaland anorthosite province sveconorwegian province norway all entrain comagmatic cumulate high alumina orthopyroxene megacrysts haoms the orthopyroxene megacrysts range in size from 0 2 to 1 m and all contain exsolution lamellae of plagioclase that indicate the incorporation of an excess ca al component inherited from the host magma at pressures in excess of 10 kbar at or near moho depths 30 40 km suites of haoms from each intrusion display a large range in 147sm 144nd 0 10 to 0 34 making them amenable for precise age dating with the sm nd system sm nd isochrons for haoms give ages of 1765 12 ma mealy mountains 1041 17 ma rogaland and 1444 100 ma nain all of them older by about 80 to 120 m y than the respective 1630 1650 920 949 and 1289 1363 ma crystallization ages of their host anorthosites internal mineral sm nd isochrons between plagioclase exsolution lamellae and the orthopyroxene host for haoms from the rogaland and nain complexes yield ages of 968 43 and 1347 6 ma respectively identical within error to the ages of the anorthosites themselves this age concordance establishes that decompression exsolution in the haom was coincident with magmatic emplacement of the anorthosites 100 m y after haoms crystallization at the moho correspondence of pb isotope ages 206pb 204pb vs 207pb 204pb with sm nd ages and other strong lines of evidence indicate that the older megacryst ages represent true crystallization ages and not the effects of time integrated mixing processes in the magmas nd isotopic evolution curves afc mixing calculations and the age relations between the hoams and their anorthosite hosts show that the haoms are much less contaminated with crustal components and are an older part of the same magmatic system from which the anorthosites are derived modeling of these anorthositic magmas with melts indicates that their ultramafic cumulates would have sunk in the magma and been sequestered at the moho where they may have sunk deeper into the mantle resulting in large scale compositional differentiation the haoms thus represent a rare example of part of a cumulate assemblage that was carried to the upper crust during anorthosite emplacement and together with the anorthosites illustrate the dramatic influence that magma ponding and differentiation at the moho has on residual magmas traveling towards the surface the new geochronologic and isotopic data indicate that the magmas were derived by melting of the mantle forming magmatic systems that could have been long lived e g 80 100 m y a geologic setting that would fit these temporal constraints is a long lived andean type margin

nature of the connection between the northern and southern zechstein basins across the mid north sea high abstract the seismic expression of a salt filled channel which cuts across the mid north sea high in quadrant 37 is described with features interpreted as being produced by salt edge dissolution forming both eastern and western margins of the channel the apparent half graben nature of the channel is shown to be only superficial and due to complex faulting associated with but not defining its western margin the shallower faulting here is a mesozoic to early tertiary growth fault related to local dissolution of zechstein salt the dissolution effect appears in turn to have been localized by the presence of a deeper fault that was already downthrown to the east in zechstein times when it seems to have limited the eastward progradation of zechstein shelf carbonates and anhydrites and had probably ceased to move significantly before the onset of the late cimmerian erosional phase the origin of this arcuate fault is tentatively ascribed to subsidence around a granite batholith zechstein salt originally spread some distance to the east and west of the channel it was dissolved from the edges inwards mainly before the late cretaceous giving rise to a thicker mesozoic sequence on parts of the flanks of the channel than in the middle besides providing an interesting structural case history the features described have implications regarding zechstein sedimentation reservoir potential the tectonic history of the north sea and the nature of the mid north sea high itself

structural evolution of the witch ground graben the witch ground graben is a nw se trending extensional basin in the central part of the northern north sea lying between the moray firth and the viking graben ne sw extension occurred from triassic to cretaceous times extension took place on listric normal faults along the sw margin with downthrow to the ne giving rise to the asymmetry of the basin one of the principal phases of fault controlled subsidence occurred in the lower cretaceous from the valanginian to albian compilation of biostratigraphic data from this interval shows the development of an increasing number of stratigraphic breaks across the basin from sw to ne these breaks increasing in time span also in this direction this is a result of rotation of the subsiding fault block on the listric extensional faults the rotation is recorded in dipmeter data and occurred in several distinct episodes the triassic the volgian and the valanginian to aptian in reconstructing a cross section of the basin the interpreted fault curvature is constrained by the observed rotation of bedding surfaces and the amount of extension across the listric faults is constrained by the observed basin subsidence a depth to decollement for the faults of 4 km below sea level and an extension across the basin of 40 are estimated

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

the crustal tongue melting model and the origin of massive anorthosites recent detailed field studies in several anorthosite complexes have shown that anorthosites are frequently associated with weakness zones in the crust which may have favoured their emplacement at mid crust levels recent experimental data have shown that the parent magma compositions of various anorthosite massifs lie on thermal highs in the relevant phase diagrams at 10 13 kbar indicating that these magmas cannot be derived by fractionation of peridotitic mantle melts but by melting of gabbronoritic sources in the lower crust at 40 50 km depths in the sveconorwegian province terne boundaries have been traced in deep seismic profiles to moho offsets or to tongues of lower crustal material underthrust to depths higher than 40 km in southern norway we suggest that a lithospheric scale weakness zone the feda transition zone has channelled the rogaland anorthosites through linear delamination asthenospheric uprise and melting of a mafic lower crustal tongue

paleomagnetism of the miocene jantetelco granodiorites and tepexco volcanic group and inferences for crustal block rotations in central mexico reevaluation abstract miocene igneous rocks from a location in central mexico provide paleomagnetic data that allow re evaluation of previous data by urrutia fucugauchi 1981 that were interpreted to suggest a counter clockwise rotation of a crustal block by about 50 we sampled 31 sites from the miocene trondhjemitic chalcatzingo domes the tepexco volcanic group and the xalostoc diorite covering the same area of approximately 50 km 2 about 90 km se of mexico city magnetic analysis shows that these rocks contain magnetic phases of variable composition with curie temperatures characteristic for magnetite but often accompanied by lower curie temperature components magnetic hysteresis measurements point to the presence of psd particles and in combination these properties suggest that these rocks are also suitable for paleomagnetic study scanning electron microscope analysis supports the rock magnetic results indicating the presence of magnetite and high intermediate titanium titanomagnetite in many samples demagnetization experiments showed in most cases characteristic remanence directions of reasonable to good quality and for 26 sites mean directions could be determined of these 14 12 are of normal reverse polarity overall mean directions of normal and reverse sites are antipodal and pass a reversal test at the 95 probability level the paleodirection from 26 sites is d 348 1 e i 35 7 95 7 4 and the paleopole is located at lat 78 3 n long 184 2 e a 95 7 0 which is indistinguishable from the 20 ma reference pole for the stable north america plate these data do not support any tectonic deformation of the sampling area since the miocene based on the number of sites studied their rock magnetic characteristics and the quality of the magnetic remanence that results in a positive reversal test we consider our data to be reliable and we therefore suggest that this result supersedes that of urrutia fucugauchi 1981 the reason for this previous and much different result remains unknown

parental magmas of the nain plutonic suite anorthosites and mafic cumulates a trace element modelling approach equilibrium melt trace element contents are calculated from proterozoic nain plutonic suite nps mafic and anorthositic cumulates and from plagioclase and orthopyroxene megacrysts assumed trapped melt fractions tmf 20 generally eliminate all minor phases in most mafic cumulate rocks reducing them to mixtures of feldspar pyroxene and olivine which would represent the high temperature cumulus assemblage in anorthosites tmf 15 generally reduce the mode to a feldspar only assemblage all model melts have trace element profiles enriched in highly incompatible elements relative to normal mid ocean ridge basalt nmorb commonly with negative nb and th anomalies most mafic cumulates yield similar profiles with constant incompatible element ratios and can be linked through fractional crystallization high k la subtypes probably represent crust contaminated facies mafic cumulates are inferred to belong to a tholeiitic differentiation series variably contaminated by upper and lower crustal components and probably related to coeval tholeiitic basaltic dyke swarms and lavas in labrador model melts from anorthosites and megacrysts have normalized trace element profiles with steeper slopes than those calculated from mafic cumulates indicating that mafic cumulates and anorthosites did not crystallize from the same melts orthopyroxene megacrysts yield model melts that are more enriched than typical anorthositic model melts precluding an origin from parental melts jotunites have lower k rb ba y yb and higher la ce than model residues from fractionation of anorthositic model melts suggesting they are not cosanguineous with them but provide reasonable fits to evolved mafic cumulate model melts incompatible element profiles of anorthositic model melts closely resemble those of crustal melts such as tonalites with steep y yb lu segments that suggest residual garnet in the source inversion models yield protoliths similar to depleted lower crustal granulite xenoliths with aluminous compositions suggesting that the incompatible trace element budget of the anorthosites are derived from remobilization of the lower crust the similarity of the highly incompatible trace elements and lile between anorthositic and mafic cumulate model melts suggests that the basalts parental to the mafic cumulates locally assimilated considerable quantities of the same crust that yielded the anorthosites the reaction between underplating basalt and aluminous lower crust would have forced crystallization of abundant plagioclase and remobilization of these hybrid plagioclase rich mushes then produced the anorthosite massifs

the north eastern polish anorthosite massifs petrological geochemical and isotopic evidence for a crustal derivation deeply buried 1 5 ga polish anorthosites accessible only by bore holes reveal diagnostic features of some massif type anorthosites polybarism jotunitic parent magma diapirically emplaced in the mid crust together with the rapakivi granites of the ew trending mazury complex intruded along a major crustal discontinuity geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions the source rock of the parental magma is a gabbronorite necessarily lying in the lower crust since no archaean crust is known in the region high initial 188 os 187 os ratios for sulphide oxide isochrons and negative end values are best accounted for by melting a 2 0 ga mafic crust

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

partitioned transtension an alternative to basin inversion models inversion structures e g folds reverse faults spatially associated with basin bounding faults are very widely recognised in rift basins in both onshore and offshore settings worldwide the great majority of such structures are attributed to local or regional crustal shortening events there is however an alternative which is investigated in this paper inversion could reflect a horizontal shortening component of deformation formed during progressive and partitioned transtension a case study from the carboniferous northumberland basin shows that shortening structures can also form in obliquely divergent rifts if the bulk strain undergoes kinematic partitioning into distinct regions of wrench and extension dominated transtension such strain partitioning appears to be particularly favoured in basins where fault localisation is strongly influenced by pre existing basement structures this may occur because the pre existing anisotropies are zones of long lived weakness that lie in an orientation particularly favourable to the preferential accommodation of either strike slip or dip slip displacements our strain analysis applied to the northumberland basin traditionally considered as a classic example of a variscan inverted basin reduces the deformation history to a single kinematically partitioned phase of dextral transtension during the late carboniferous early permian our findings have profound implications for the interpretation of inversion structures in any rift basin where the direction of extension may be significantly oblique to the basin margins

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

petrogenesis of the labrieville alkalic anorthosite massif grenville province quebec the labrieville massif 1010 ma is an eroded dome consisting mineral plagioclase feldspar the circumstances whereby such nearly monomineralic plutons can be produced of three zones 1 a foliated inner core of pink anorthosite an30or13 2100 ppm sr 1300 ppm ba with minor have puzzled geologists for more than a century and massif anorthosites remain petrologic enigmas in adleuconorite 2 a foliated outer core of pink anorthosite an35or10 1900 ppm sr 850 ppm ba with more abundant leuconorite dition to this fundamental aspect of the anorthosite problem see bowen 1917 scoates 2000 the petro 3 a border of foliated to massive green leucogabbro antiperthitic plagioclase orthopyroxene hemoilmenite and small amounts of genesis of massif anorthosites was apparently restricted in time and space specifically virtually all of the world s biotite are present in all rocks the border zone contains additional clinopyroxene magnetite and apatite labrieville is more alkalic supply of massif anorthosite was formed during the proterozoic and much of it is found in the grenville and srand ba rich than almost all other massif anorthosites the widespread presence of biotite and the high hematite content of province of quebec and labrador kranck 1961 anderson 1969 ashwal 1993 hemoilmenite suggest crystallization from a relatively oxidizing and water bearing magma collectively these features imply that despite their similar plagioclase rich nature it is now apparent that massif anorthosites worldwide are minlabrieville originated from a magma that differed considerably from typical tholeiitic liquids majorand trace element variations suggest eralogically and compositionally diverse see xue that all rock types represent mixtures of cumulus minerals with morse 1993 implying involvement of a wide range of negligible trapped melt the compositionally distinct zones imply parental magma compositions or petrogenetic processes differentiation during crystallization although plagioclase comin their formation however comprehensive studies on positions become more evolved inward other indicators e g xmg individual anorthosite complexes that can elucidate their in pyroxene suggest differentiation outward from core to border we petrogenesis combining field and petrographic obfavor the latter interpretation and suggest that the increase in servations with mineral chemical data and with complete plagioclase an content reflects a decline in pressure during crysmajorand trace element data on a wide range of rock tallization types are few in number admittedly the immense size of certain massifs e g lac st jean complex woussen et al 1988 and the remote or inhospitable locations of

the structure and evolution of the northumberland trough from new seismic reflection data and its bearing on modes of continental extension an 18 km long n s seismic reflection profile has been acquired across the faulted boundary between the alston block and the northumberland trough a nw se geological cross section has been constructed across the trough by integrating this line with other data and a tricentrol seismic profile confirms the suitability of this model the trough has a markedly asymmetric form with a thickness of more than 4 2 km of dinantian strata adjacent to its faulted southern margin the present day surface faults stublick ninety fathom are related to variscan and later inversion and transpression and do not everywhere correspond precisely to the earlier syn depositional normal faults the basin is believed to have formed in response to reactivation of the iapetus suture in a dominantly n s extensional stress field basin evolution has been analysed by fault restorations and subsidence modelling the fault restorations indicate an upper crustal extension factor of 1 15 to 1 19 subsidence modelling indicates a whole crustal extension factor of 1 30 with similar sub crustal lithospheric extension it is possible that the difference between the inferred extension factors is due to non uniform increasing downwards lithospheric extension but the uncertainties inherent in both methods are such that this cannot yet be confirmed

mineral scale sr isotope constraints on magma evolution and chamber dynamics in the rum layered intrusion scotland sr isotopic zoning within single plagioclase crystals from rocks from unit 9 of the rum layered intrusion is used to infer events during crystal growth in a magma undergoing contamination the 87sr 86sr diversity among minerals and between cores and rims of plagioclase crystals increases as the boundary between unit 9 and the overlying unit 10 peridotite is approached models of near solidus interaction of the cumulate with a fluid or melt or large scale textural re equilibration cannot easily account for the systematic differences in 87sr 86sr between small crystals and the rims of larger crystals

controls on structural styles basin development and petroleum prospectivity in the midland valley of scotland integration of well calibrated seismic data from the firth of forth with field and subsurface data from neighbouring onshore areas provides important new insights into the structural evolution and petroleum habitat in the midland valley of scotland the results demonstrate that the nne ssw striking midlothian leven syncline and its flanking burntisland and d arcy cousland anticlines developed as major growth folds during the late palaeozoic under a predominantly dextral strike slip regime these syn sedimentary folds controlled depositional thicknesses facies and dispersal patterns in early to late carboniferous visean westphalian times structural geometries suggest that the folds experienced tightening during late carboniferous variscan deformation events before being transected by e w striking dykes and extensional faulting during the late carboniferous westphalian d and early permian although direct evidence for the basin s post permian burial history is no longer present it can be inferred that the area had at least 1 km of cover prior to paleogene uplift the new understanding of the eastern midland valley s structural and subsidence history provides the means by which the occurrence of petroleum in the basin can be explained burial of lower carboniferous mississippian oil shale source rocks beneath the midlothian leven syncline now appears to have been the primary driver in the maturation and up dip migration of waxy crude oil into age equivalent clastic reservoirs located in the adjacent anticlines rather than oil generation by direct contact between the source rocks and igneous intrusions initial oil charging is thought to have taken place during the late carboniferous was renewed during mesozoic reburial and appears to continue locally today despite the detrimental effect of significant early cenozoic uplift it is now evident that the basin s limited exploration success has been almost entirely governed by the presence of unbreached palaeostructures lying directly up dip from an oil kitchen developed in the core of the midlothian leven syncline during late carboniferous and mesozoic recent burial

interactions between dioritic and granodioritic magmas in mingling zones plagioclase record of mixing mingling and subsolidus interactions in the gesiniec intrusion ne bohemian massif sw poland dioritic and granodioritic rocks coexist in the gesiniec intrusion in sw poland showing typical relationships in many mafic felsic mingling zones worldwide such as dioritic syn putonic dykes and microgranular enclaves within granodioritic host plagioclase zonation from granodioritic rocks suggests late stage mixing probably with dioritic magma whereas no magma mixing is recorded in plagioclase from dioritic rocks the diorites seem to show effects of interaction with evolved leucocratic melts derived from granodiorite not with the granodioritic melt itself we conclude that the diorites compositions were modified after their emplacement within the granodioritic host when the diorites were essentially solidified and injection of evolved melt from granodiorite did not involve marked modification of plagioclase composition compositional zoning patterns of plagioclase in diorites can be modeled by closed system fractional crystallization interrupted by resorption induced probably by decompression granodioritic plagioclase seems to be affected by the same resorption event plagioclase that crystallized in dioritic magma before the resorption does not record interaction between dioritic and granodioritic magmas suggesting that both magmas evolved separately

new evidence for evaporitic middle devonian lacustrine sediments with hydrocarbon source potential on the east shetland platform north sea the ukcs united kingdom continental shelf well 9 16 3 drilled on the western flank of the beryl embayment encountered a middle devonian sequence interpreted as part of the lacustrine orcadian basin an anhydrite layer found within the sequence provides confirmation of the local development of hypersaline environments within the orcadian basin detailed geochemical analysis of a representative source interval equivalent to the achanarras sandwick fish bed has revealed a close affinity with contemporaneous middle devonian source rocks found in the inner moray firth and crude oil from the beatrice oil field

the effect of pressure on dsr plag melt and dcr opx melt implications for anorthosite petrogenesis the crystal liquid partition coefficients for sr and cr dsr and dcr have been determined from electron microprobe analyses of plagioclase liquid and orthopyroxene liquid pairs produced in melting experiments run at pressures from 1 bar to 27 kbar on two compositions relevant to anorthosite petrogenesis one is a primitive jotunite hypersthene monzodiorite tj the other is a sample of an anorthositic dyke 500b results indicate that dsr plag liq remains nearly constant with increasing pressure tj 1 7 to 2 6 500b 0 9 to 1 4 this modest variation apparently results from the combined and opposing effects of crystal chemistry and pressure dsr increases with the albite content of plagioclase which itself increases with pressure along a composition s liquidus so pressure must have an intrinsic negative effect the two models for dsr j blundy b wood geochim cosmochim acta 55 1991 193 209 i bindeman a davis m drake geochim cosmochim acta 62 1998 1175 1193 that take into account the strong correlation between dsr and plagioclase composition overestimate dsr at high pressure whereas the two models that ignore plagioclase composition s morse geochim cosmochim acta 56 1992 1735 1738 r nielsen comput geosci 18 1992 773 788 underestimate it moreover since none of these models takes into account any pressure effect the discrepancies between predicted and observed dsr increase with pressure for all models the new results also show that dcr opx liq increases significantly with pressure dcr 2 at 1 atm and 14 2 at 10 kbar these new data confirm earlier less precise determinations of dcr that were used to infer a high pressure origin for al and cr rich orthopyroxene megacrysts the calculated sr and cr concentrations of liquids in equilibrium at 10 kbar with plagioclase and orthopyroxene megacrysts from anorthosite massifs sr 370 to 610 ppm and cr 20 to 130 ppm are in the range of what is observed in high al gabbros and primitive jotunites the inferred parent magmas of massive anorthosites fl 2000 published by elsevier science b v all rights reserved

1700 ma shachang complex northeast china proterozoic rapakivi granite not associated with paleoproterozoic orogenic crust proterozoic rapakivi granites are found on all continents and are characteristically associated with paleoproterozoic crustal domains that predate the granites by

fraser a j gawthorpe r l 2003 an atlas of carboniferous basin evolution in northern england geological society memoir no 28 vi 79 pp large format 42 30 cm london bath geological society of london price 55 00 paperback spiral bound isbn 1 86239 135 1 the geological society s memoirs have provided a useful and adaptable vehicle for a range of important works most of style or content not easily accommodated by other academic serials some memoirs have been map rich large format volumes such as the two on uk oil and gas fields 14 and 20 and the palaeogeographical atlas 13 others have essentially been commentaries on large fold out maps such as leonard wills palaeogeological map volumes 7 and 8 and the compilation of caledonian orogenic activity 9 there have been single author volumes on regional geology such as the recent ones on svalbard

numerical simulations of crystallization processes of plagioclase in complex melts the origin of major and oscillatory zoning in plagioclase numerical simulations of the growth of a large crystal face of plagioclase in response to an instantaneous undercooling below the equilibrium temperature are presented for model granodiorite and basalt melts with varying water contents the simulations suggest that the anorthite content of plagioclase decreases uniformly from the composition in equilibrium with the bulk melt as undercooling is increased and that the water content in the melt has little influence on this result comparison of the simulations with sharp compositional changes in natural profiles suggests that undercoolings of tens of degrees c can be rapidly imposed on plutonic phenocrysts large changes of undercooling most likely result from chilling of the magma and local convection around growing crystals the observation in experiments that growth rate does not increase rapidly with increasing water content in the starting melting composition can be attributed to the concentration of water at the crystal face during growth the action of water to reduce liquidus temperature and undercooling has a greater effect on growth rate than its action to increase transport rates even at large undercooling there is no significant increase in temperature at the interface caused by the release of heat of crystallization

some phase equilibrium constraints on the origin of proterozoic massif anorthosites and related rocks experimental data in the range of 1 bar to 13 kbar enable us to introduction map the liquidus equilibria relevant to proterozoic massif anorthere is hardly a consensus on the petrogenesis of thosites and related mafic rocks massif anorthosites are widely proterozoic massif anorthosites but many investigators believed to have formed by accumulation of plagioclase into highbelieve in a petrogenetic scheme that involves at least al basaltic liquids mantle derived basaltic liquids fractionating two major stages 1 extensive crystallization asat pressures sufficiently high 10 13 kbar to crystallize the highly similation of a mantle derived magma ponded at or aluminous orthopyroxene megacrysts typically observed in anorthosite near the base of the crust that produces suspensions of massifs reach plagioclase saturation at low normative silica contents plagioclase in fe rich high al gabbroic liquids followed peritectic like equilibria e g liq opx plag cpx sp by 2 intrusion of these suspensions into the mid upper and a thermal divide on the plagioclase pyroxene liquidus surface crust where they form complex magma chambers e g ensure that mantle derived liquids become nepheline normative with duchesne 1984 emslie 1985 ashwal 1993 wiebe further crystallization and crustal assimilation at depth such 1994 a key component of the scheme is the presence liquids cannot produce the full range of troctolitic noritic to trocin most massifs of high al orthopyroxene megacrysts tolitic gabbroic mineral assemblages observed in anorthosite massifs haom emslie 1975 that appear to preserve a record without extensive low pressure granite assimilation conversely the of the high pressure stage maquil duchesne 1984 array of plausible anorthosite parental liquids not only lies along longhi et al 1993 the structures of massifs vary from the trace of the plagioclase two pyroxene cotectic from 10 to 13 those that are composites of multiple diapiric intrusions kbar but also straddles the thermal divide on the plagioclase harp lake emslie 1980 rogaland duchesne 1984 pyroxene liquidus surface this condition requires mafic source to intrusive bodies with well developed layering of regions such as lower continental crust or foundered mafic plutons leucocratic troctolites and leuconorites or leucogabbros for liquids parental to massif anorthosites and associated mafic overlain by masses of anorthosite michikamau emslie intrusions 1970 laramie frost et al 1993 so there may be

a partisan review of proterozoic anorthosites most anorthosites of the massif type crystallized in the episode 1 7 1 2 gyr with a pronounced peak of the age distribution near 1 4 gyr they were emplaced anorogenically at depths as shallow as 7 km where the ambient temperature of country rocks was probably less than 250 c depths of emplacement may have been as great as 25 km or more in rare cases the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths but in any case they are demonstrably not required or characteristic of anorthosite emplacement penetrative deformation and metamorphism of anorthosites are post emplacement accidents of the local geologic history and are not directly caused by the presence of anorthosites granitic rocks mangerite charnockite suite associated with anorthosite are in general later or contemporaneous products of crustal anatexis with chemical and isotopic signatures distinct from the anorthosites and their residua such granitic rocks should not therefore be summed with the anorthositic rocks to obtain bulk compositions the magmas that produced most anorthosites were dry as shown by high temperature mineralogy and anhydrous mineral assemblages in contact aureoles residua from their crystallization are ferrodiorites to ferrosyenites typical of closed system fractionation these residua were locally and frequently ejected into contemporaneously molten granite where they formed pillows and cooled rapidly the overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle olivine bearing magmas locally ranged from leucotroctolite anorthosite to later but coexisting picrite or melatroctolite in the same pluton confirming a wide spectrum of magma types a signal feature of troctolitic and noritic magmas is their low augite content implying high content of spinel component large anorthosite complexes such as nain and harp lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry the abundant true anorthosites richer in plagioclase than magmas cosaturated with a mafic phase must represent plagioclase enrichment by either mechanical or chemical processes or both the role of kinetics in nucleation and solidification of such rocks may be centrally important it is proposed that hyperfeldspathic plagioclase supersaturated liquids were generated by quasi isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth s mantle

re os isotopic evidence for a lower crustal origin of massif type anorthosites massif type anorthosites are large igneous complexes of proterozoic age they are almost monomineralic representing vast accumulations of plagioclase with subordinate pyroxene or olivine and fe ti oxides the 930 myr old rogaland anorthosite province in southwest norway1 represents one of the youngest known expressions of such magmatism the source of the magma and geodynamic setting of massif type anorthosites remain long standing controversies in precambrian geology with no consensus existing as to the nature of the parental magmas or whether these magmas primarily originate in the earth s mantle or crust at present massif type anorthosites are believed to have crystallized from either crustally contaminated mantle derived melts that have fractionated olivine and pyroxenes at depth2 or primary aluminous gabbroic to jotunitic melts derived from the lower continental crust3 here we report rhenium and osmium isotopic data from the rogaland anorthosite province that strongly support a lower crustal source for the parental magmas there is no evidence of significantly older crust in southwest scandinavia and models invoking crustal contamination of mantle derived magmas fail to account for the isotopic data from the rogaland province initial osmium and neodymium isotopic values testify to the melting of mafic source rocks in the lower crust with an age of 1 400 1 550 myr

the origin of proterozoic massif type anorthosites evidence from interactions between crustal xenoliths and basaltic magma plagioclase rich reaction zones occur around numerous aluminous crustal xenoliths within a suite of palaeogene sub volcanic basic sheets on the isle of mull nw scotland the xenoliths consist of a glassy core containing mullite needles generated from the melting of pelitic source rocks thick plagioclase mantles grew at the interface between the aluminous liquid and the enclosing basaltic magma and provide a high level analogue for the petrogenesis of proterozoic massif type anorthosites similar interactions between mantle derived basic magmas ponded at the base of the crust and relatively al rich lower crustal lithologies would result in the precipitation of large volumes of plagioclase anorthosite massifs were then emplaced at higher crustal levels as crystal rich mushes within relatively juvenile proterozoic crust the model negates the need to crystallize large volumes of mafic minerals prior to the production of plagioclase saturated liquids and also accounts for the significant influence of crustal sources on the isotopic signatures of all members of the anorthosite suite

oscillatory sr isotopic signature in plagioclase megacrysts from the damiao anorthosite complex north china implication for petrogenesis of massif type anorthosite abstract formation of proterozoic massif type anorthosites is known to be related to polybaric process involving early high pressure crystallization of plagioclase and high al orthopyroxene megacrysts at mantle crust boundary followed by emplacement of plagioclase dominated mushes to shallow level crust therefore the plagioclase megacrysts record important information about the magmatic sources and crystallization process of anorthosites the 1 74 ga damiao complex north china comprises 90 vol anorthosites and leuconorites containing abundant plagioclase megacrysts associated with minor high al orthopyroxene megacrysts haoms the plagioclase megacrysts are generally euhedral to subhedral mostly 1 to 30 cm in diameter and some of them contain very fine lamellae of orthoclase and undefined fe ti rich minerals 1 5 m the haoms occur as subhedral grains or as angular grains with an intercumulus relationship to the plagioclase megacrysts they contain abundant thin regular lamellae of exsolved plagioclase 15 20 vol indicative of originally high al features originally 6 0 7 3 wt al2o3 based on the al in orthopyroxene geobarometry the haoms and associated plagioclase megacrysts are constrained to be crystallized together at pressures of 9 4 11 2 kbar 33 36 km indicative of their crystallization at lower crust depths or crust mantle boundary in contrast orthopyroxene grains from late differentiation phases such as oxide apatite gabbronorites do not contain plagioclase lamellae and have much lower al2o3 contents 1 5 to 1 7 wt indicating final crystallization at

the structural evolution of dilational stepovers in regional transtensional zones we propose a theoretical model supported by a field study to describe the patterns of fault fracture meshes formed within dilational stepovers developed along faults accommodating regional scale wrench dominated transtension the geometry and kinematics of the faulting in the dilational stepovers is related to the angle of divergence and differs from the patterns traditionally predicted in dilation zones associated with boundary faults accommodating strike slip displacements where 0 for low values of oblique divergence 30 and low strain the fault fracture mesh comprises interlinked tensile fractures and shear extensional planes consistent with wrench dominated transtension at higher values of strain a switch occurs from wrench to extension dominated transtension leading to the reactivation and or disruption of the early formed structures these structural processes lead to the development of a geometrically complex and kinematically heterogeneous fault pattern which may affect and or perturb the development of a through going fault linking and facilitating the slip transfer between the two overlapping fault segments as a result dilational stepover zones will tend to form long lived sites of localized extension and subsidence in regional transtensional tectonic settings cyclic increases decreases of structural permeability will be related to slip on the major boundary faults that control the distribution of fluid flow paths and consequently the long and short term structural evolution of these sites our model also predicts complex and more realistic subsurface fluid migration pathways relevant to our current understanding of hydrothermal ore deposits and hydrocarbon migration and storage

regional velocity depth anomalies north sea chalk a record of overpressure and neogene uplift and erosion a normal velocity depth trend for the upper cretaceous danian chalk group is determined by identifying interval velocity data that represent maximum burial in areas unaffected by overpressuring these data are derived from 845 wells throughout the north sea basin data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the north sea basin and reflect regional neogene uplift and erosion of up to 1 km along the present day limit of the chalk a hiatus at the base of the quaternary increases in magnitude away from the basin center where a complete cenozoic succession is found this hiatus is consistent in size with the missing section estimated from chalk velocities when allowance is made for the quaternary reburial of the chalk negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the chalk exceed 10 mpa equivalent to a burial anomaly greater than 1 km relative to the normal trend the chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden therefore the chalk is considered to represent a regional aquitard and the hydrodynamic model of long distance migration within the chalk is rejected the neogene uplift and erosion of the margins of the north sea basin and the rapid late cenozoic subsidence of its center fit into a pattern of late cenozoic vertical movements around the north atlantic

geochemical and nd hf isotopic constraints on the origin of the 1 74 ga damiao anorthosite complex north china craton abstract the 1 74 ga damiao complex in the north china craton consists of anorthosite 85 norite 10 mangerite 4 and minor troctolite 75 would have been required to form the parental high al gabbroic magma from the lower crust we propose that the crustal rocks were dragged into the upper mantle during amalgamation of the north china craton where the ambient temperature was high enough 1271 c at 12 kbar to cause extensive melting producing a deep seated magma chamber the melt then evolved through polybaric crystallization producing anorthositic magmas with abundant suspended plagioclase that were finally injected at mid crustal depth to form the damiao complex

palaeoproterozoic assembly of the north china craton the basement of the north china craton consists of the eastern and western blocks separated by the central zone both the eastern and western blocks are dominated by late archaean tonalitic trondhjemitic granodioritic gneiss complexes interdigitated with minor supracrustal rocks metamorphosed at 2 5 ga with anticlockwise p t paths the central zone is composed of reworked late archaean components and palaeoproterozoic juvenile crustal materials that underwent regional metamorphism at 1 85 ga with clockwise p t paths involving isothermal decompression as a result of collision between the eastern and western blocks which resulted in the final assembly of the north china craton

iapetus suture located beneath the north sea by birps deep seismic reflection profiling the iapetus suture one of the more fundamental geologic boundaries of the british isles has been located beneath the north sea by deep seismic reflection profiling carried out by the british institutions reflection profiling syndicate birps reflection profiling and magnetotelluric sounding have previously been used to infer the position of the iapetus suture beneath the irish sea and the southern uplands but the present study provides the first direct evidence for the location of the iapetus suture east of britain a comparison of the seismic reflection profiles over the iapetus suture east and west of britain shows variations in the dip of the suture which steepens to the northeast beneath the north sea the comparison also reveals unexpected changes in lower crustal reflectivity along the strike of the suture and suggests that there may be no straightforward relation in this area between the crustal reflectivity and the crustal age

crystallization processes in the rocky hill granodiorite pluton california an interpretation based on compositional zoning of plagioclase the rocky hill pluton was chosen for study of plagioclase zoning because it has an apparently simple geometry and one stage emplacement history documented by putman and alfors 1969 the pluton is divided texturally into a hypidiomorphic granular rim fades and porphyritic core facies both comprising zoned plagioclase phenocrysts averaging 2 4 mm in diameter major features of compositional zoning profiles of plagioclase were found to be consistent within a sample showing resorbed core regions followed by a sharp drop of ca 10 an to a plateau region and ending with normal zoning the width of the plateau region is narrow in samples near the pluton rim but increases systematically toward the pluton core and the outer part of the plateau develops reverse zoning in the core facies a review of the effects of pressure water content of the melt and temperature on equilibrium and disequilibrium crystallization processes concludes that only variations of temperature and water content during disequilibrium crystallization of plagioclase phenocrysts can produce the observed zoning patterns experimental data suggest that the trend toward finer grain size toward the interior of the pluton may be due to increasing water content rather than due to increasing cooling rate the compositional zoning of plagioclase and textural variations in the pluton can be explained by a model in which the pluton crystallized by migration of a partly crystalline mush zone inward from the edge of the plutonic chamber while convection within the residual magma 1 redistributed water excluded from the mush zone and 2 slowed the cooling rate of the mush zone the reverse zoning of plagioclase growing in the convecting magma changed to normal zoning after capture in the mush zone because the cooling rate increased and water was removed comparison of the results from our study of rocky hill with published descriptions of plutons and experimental and theoretical studies of crystallization processes leads to the conclusions that 1 convection is an active process during the crystallization of many plutons causing redistribution of mainly water and heat in silicic ones but differentiating other components in intermediate ones 2 most of the crystallization of granitic rocks may occur in a mush zone or static boundary layer between the solid boundary and convecting inner magma body 3 water content may be an important factor controlling grain size 4 reverse zoning of plagioclase may be more typical of plagioclase grown under slowly cooled conditions than normal zoning and 5 variations of plagioclase zoning in plutons can provide useful information on crystallization processes

carboniferous petroleum systems around the mid north sea high uk the existence of an extensive prospective visean namurian carboniferous petroleum system in and around the hitherto under explored mid north sea high is documented evidence is drawn from integrated analysis of over 50 000 line kilometres of seismic data and well data together with regional source rock screening reservoir analysis and basin modelling visean namurian marine and non marine mudstones and coal source rocks are interbedded within fluvial and marine reservoir sandstones within a stacked succession up to 5 km thick source rocks are dominantly gas prone with oil prone intervals and have reached oil to gas maturity levels dependent on location burial thermal history modelling indicates a kitchen area on the southern margin of the mid north sea high with northwest and northeastwards migration of gas and oil during mesozoic and cenozoic times a variety of structural and stratigraphic traps are possible including intraformational carboniferous traps with a regional seal at permian zechstein level synthesis of many previously unpublished datasets demonstrates the visean namurian play south of the mid north sea high as part of an extensive petroleum system from the east irish sea across onshore to offshore uk and into the netherlands sector of the north sea the purpose of this synthesis is to highlight future exploration opportunities beneath and northwards of the productive westphalian southern north sea gas basin and to begin to de risk the petroleum systems that are exemplified by the lower carboniferous breagh field in a frontier area of the mature north sea province

the iapetus suture zone in england scotland and eastern ireland a reconciliation of geological and deep seismic data deep seismic profiles in the irish and north seas have successfully imaged crustal structure across the iapetus suture zone a problem with current interpretations is that the reflectors chosen as the suture project to the top of the basement well to the south of the solway line the palaeontologically defined trace of the suture we present a revised interpretation in which a reflectivity boundary common to all the profiles is identified as the leading edge of imbricated avalonian crust in effect the footwall of the suture zone this projects to the surface close to the solway line obviating the need to invoke northward backthrusting of the suture

revised stratigraphic framework of pre westphalian carboniferous petroleum system elements from the outer moray firth to the silverpit basin north sea uk

polybaric fractional crystallization of high alumina basalt parental magmas in the egersund ogna massif type anorthosite rogaland sw norway constrained by plagioclase and high alumina orthopyroxene megacrysts bulk analyses of plagioclase and high alumina orthopyroxene megacrysts decimetreto metre sized crystals with plagioclase lamellae from the late proterozoic egersund ogna massif type anorthosite rogaland anorthosite province swnorway are used to constrain the parental magma compositions and differentiation processes within this 30 km diameter diapir spatial compositional variations show that two types of anorthosite occur high sr 720 1090 ppm andesine anorthosite an48 4 in the centre of the intrusion and low sr 320 620 ppm labradorite anorthosite an59 6 in the margin two populations of orthopyroxene megacrysts are clearly discriminated by their mn and cr contents but display similar ranges of mg number 55 79 interpretation of trace element data and comparison with inversion models suggest that the two types of anorthosite result from crystallization of different parental magma compositions with high alumina basalt affinities and similar mg numbers but different wollastonite sr mn and cr contents a rayleigh fractional crystallization model of the trace element concentrations vs mgo content in orthopyroxene constrains the cotectic orthopyroxene plagioclase proportions to 0 33 0 67 in both magma types before the appearance of fe ti oxide minerals on the liquidus at f 0 7 where f is melt fraction polybaric crystallization is recorded by variable alumina contents in the orthopyroxene megacrysts 2 3 8 5 wt corresponding to crystallization pressures in the 3 13 kbar range as shown by experimental data this implies that the high alumina orthopyroxene megacrysts mainly crystallized en route during diapiric rise of the anorthositic mush modelling the plagioclase compositions with experimentally determined partition coefficients for ca k sr and ba confirms that pressure variation during polybaric crystallization is the main controlling factor on compositional variations in the anorthosite pluton

crustal evolution by arc magmatism arc magmas generated at depths near 100 km by dehydration of subducting slabs are olivine rich melabasalts but the magmas that reach the surface in mature continental magmatic arcs have an average composition near that of rhyodacite depth varying fractionations and equilibrations profoundly modify the initial magmas plate tectonics has operated throughout proterozoic and phanerozoic time much as it does now and so many deeply eroded terrains must expose products of arc magmatism most exposed middle and deep continental crust consists of igneous rocks plus older rocks equilibrated at magmatic temperatures variably deformed and metamorphosed subsequently each crustal level displays a typical assemblage of magmatic rock types which are here deduced to be products mostly of arc magmatism pre arc mantle consists of depleted dunite and harzburgite rising arc magmas precipitate much additional olivine and add the equivalent of 10 or 15 of basalt in clinopyroxene orthopyroxene garnet and spinel the seismic m discontinuity may be controlled primarily by the shallow limit of the depth zone in which crystallization is mostly of ultramafic components and the fractionated magmas that reach the crust are mostly of gabbroic to granodioritic compositions the lower crust is characterized by differentiated layered complexes which often contain mafic or ultramafic basal cumulates medial floated plagioclase anorthosite and upper quartz poor pyroxene mesoperthite granites and by other magmatic rocks magmatic rocks are more voluminous than pre existing rocks supracrustal rocks are in middle granulite facies and much granitic material has been melted from them by magmatic heat the magmatically modified middle crust consists primarily of migmatites in lower granulite facies in the deeper part and upper amphibolite facies in the shallower part much dissociation of hydrous mineral assemblages is caused by the magmatic heat producing water rich aluminous magmas assimilation and anatexis the high water contents restrict rise of the equilibrated magmas voluminous pegmatites are expelled into the wall rocks and crystallization is forced sheets of two mica granites characterize the upper part of the middle crust the comparatively dry magmas that rise into the upper crust are mostly tonalite to adamellite these magmas spread out in steep sided batholiths above the migmatites erupt as ash flow sheets from calderas and produce voluminous far travelling volcanic ash inverted metamorphic gradients and outward verging structures are produced beneath the spreading batholiths magmatic arcs are extensional at all crustal levels

devonian marine incursions into the orcadian basin scotland bp chevron well 14 6 1 drilled in the east orkney basin has penetrated devonian sedimentary rocks which can be dated palynologically as within the latest givetian to early frasnian interval this microflora contains the first substantiated record in western europe of archaeoperisaccus a spore hitherto regarded as restricted to northern laurasia three grey green intervals within the well contain marine microfossils which provide the first direct evidence for the movement of marine waters into the northern part of the old red sandstone continent onshore an eday marls section in the bay of berstane orkney contains a marine microfauna which demonstrates the presence of a marine incursion of mid late givetian age this is the first record of a devonian marine incursion in scotland combination of this palaeontological data with sedimentological studies of the eday marls and upper old red sandstone suggests that a wide flat sabkha plain extended eastwards from the onshore orcadian basin during the later stages of its infill and was subjected to episodic marine incursions these incursions are tentatively linked with marine transgressions into the argyll area of the central north sea two orders of cyclicity occur within the dated devonian interval of 14 6 1 and are interpreted as resulting from orbital cyclicity at periodicities of 39 5 and 413 9 ky this indicates that the control on the devonian sea level maxima may have been orbital cyclicity these marine incursions are speculatively correlated to high stands on the devonian sea level curve the bay of berstane marine incursion representing the taghanic onlap whilst those in 14 6 1 are the rhinestreet middlesex and genundewa transgressions reconsideration of the palaeogeography of the northern margin to the marine devonian indicates that the sea entered the orcadian basin from the east along the tornquist zone at the margin of the fenno scandian high

magma recharge contamination and residence times revealed by in situ laser ablation isotopic analysis of feldspar in volcanic rocks we illustrate a rapid and effective method for determining variations in 87sr 86sr across single plagioclase feldspar crystals using laser ablation interfaced to a multicollector inductively coupled plasma source mass spectrometer the speed of analysis proves to be a particular advantage permitting representative populations of crystals to be characterized or enabling reconnaissance analysis of rocks to test for mineral scale isotopic heterogeneity our results from magmatic crystals in lavas from el chichon volcano confirm trends previously obtained by the more time consuming microdrilling method for the first time with confidence the laser data allow us to associate abrupt changes in 87sr 86sr with distinct petrographic discontinuities such as dissolution surfaces in the crystal because the isotopic variations within crystals would be expected to equilibrate diffusively with time the width over which abrupt changes in 87sr 86sr occur can also be used to constrain timescales at which the crystal has been held at magmatic temperatures

salt dissolution and salt related deformation of the forth approaches basin uk north sea abstract this paper addresses the potential role of regional scale salt dissolution as a mechanism responsible for salt related deformation this analysis is based on an investigation of the late permian to triassic succession of the forth approaches basin on the nw margin of the north permian basin and makes use of a regional 2d seismic grid tied to five key exploration wells this basin is ideal for this study because it consists of a deformed central region with a ne sw trending axis and an undeformed periphery which provides a template and key datums for reconstruction of the adjacent zone of deformation structural styles in this zone include simple salt cored anticlines salt walls salt diapirs detachment faults and unusually for the north sea intra zechstein salt cored folds pre triassic detailed mapping was carried out in uk block 26 10 and this shows that the dominant structural trend is ne sw suggesting that basement tilting influenced structural development the stratal geometry of the numerous triassic mini basins is used to constrain the way in which accommodation space in the mini basins was created by depletion of mobile salt the spatial pattern of salt depletion can be accounted for by two contrasting mechanisms or some combination thereof 1 deformation through downbuilding during a phase of regional subsidence or 2 flow induced by regional salt dissolution volumetric arguments necessary to discriminate between these two mechanisms are inconclusive due to later deformation of the top zechstein datum selective preservation of z3 and z4 cycles of the zechstein over large parts of the block 26 10 study area suggests that much of the salt depletion process preferentially removed z2 halite this observation is compatible with a process of subjacent dissolution possibly resulting from low salinity groundwater circulating in the pre zechstein aquifers

magma mixing in the genesis of the kalatongke dioritic intrusion implications for the tectonic switch from subduction to post collision chinese altay nw china abstract the kalatongke complex located in south chinese altay of the central asian orogenic belt caob consists of the 308 ma dioritic suite intruded by the 287 ma noritic suite the noritic suite is composed of olivine norite and hornblende norite and hosts sulfide mineralization the dioritic suite is composed of ferrodiorite diorite and quartz diorite ferrodiorites have 43 6 to 51 8 wt sio 2 8 2 to 12 1 wt fe 2 o 3 t 2 87 to 4 86 wt mgo with mg ranging from 42 to 53 they have highly variable al 2 o 3 17 4 20 7 wt na 2 o 2 78 4 50 k 2 o 0 58 3 70 sr 280 1300 ppm and ba 219 3100 ppm diorites and quartz diorites have 15 2 19 6 wt al 2 o 3 239 890 ppm sr and170 1100 ppm ba 11 2 25 5 ppm y and1 2 2 2 ppm yb all rocks have lree enriched ree patterns and do not display eu anomalies they have primitive mantle normalized trace element patterns enriched in large ion lithosphile elements lile e g ba and sr and depleted in ti nb and ta both ferrodiorites and diorites have relatively constant initial 87 sr 86 sr ratios of 0 7037 to 0 7040 but highly variable e nd t values of 4 5 to 11 6 whereas quartz diorites have higher initial 87 sr 86 sr ratios 0 7056 and lower e nd t values 0 5 plagioclase from ferrodiorites diorites and quartz diorites has similar initial 87 sr 86 sr ratios of 0 7015 to 0 7055 the dioritic suite formed from a mixed magma of an evolved mantle derived basaltic magma by partial melting of subduction modified mantle source in response to slab breakoff and a crustal derived granitic magma at 308 ma before mixing with granitic magmas basaltic magmas underwent fractional crystallization of olivine to form ferrodiorite the mixed magma also formed diorite and quartz diorite combining fractionation clinopyroxene amphibole and plagioclase the noritic suite formed from a mantle derived high mg magma in a post collisional environment both the dioritic and noritic suites in kalatongke suggest the switch from subduction to extension and the final collision between the junggar block and chinese altay at 308 ma

facies analysis of a back tilted lacustrine basin in a strike slip zone lower devonian scotland abstract lower devonian lower old red sandstone basins developed along active faults in northern scotland the dingwall strathpeffer basin is a half graben which thickens into the helmsdale polinturk fault a splay off the major strike slip great glen fault zone facies analysis allows the distinction of facies associations which represent alluvial fan perennial lake and playa mudflat ephemeral stream environments syn sedimentary faulting at the margin was the major control on alluvial fan sedimentation the lacustrine facies were fringed by alluvial facies but at times of high water level extended to the active basin margin sedimentary structures and pseudomorphs after gypsum suggest an arid to semiarid environment in which the alluvial fan stream and floodplain sedimentation was largely ephemeral during arid periods the basin centre lake environment was constricted and the surrounding mudflats experienced intense evaporation while after flooding episodes the lake increased in size the thickest lacustrine sequences occur close to the basin margin alluvial fans due to back tilting of the fault blocks fault motion and or climatic fluctuations caused significant interdigitation of the facies the mixture of alluvial fan and organic rich lacustrine facies close to the bounding fault offers some potential for trapping of hydrocarbons

differentiation of nelsonitic magmas in the formation of the 1 74 ga damiao fe ti p ore deposit north china the 1 74 ga damiao anorthosite complex north china is composed of anorthosite and leuconorite with subordinate melanorite mangerite oxide apatite gabbronorite perthite noritic i e jotunitic and ferrodioritic dykes the complex hosts abundant vein pod and lens like fe ti p ores containing variable amounts of apatite 10 60 modal and fe ti oxides in addition to fe ti p ores there are also abundant fe ti ores which are closely associated with fe ti p ores in the deposit most of fe ti p ores are dominated by fe ti oxides and apatite devoid of silicate minerals mineralogically similar to the common nelsonites elsewhere in contrast fe ti ores are dominated by fe ti oxides with minor apatite 5 modal the parental magma of these ores estimated from olivine and apatite compositions using mineral melt partition coefficients has composition similar to the ferrodioritic dykes fe ti p ores have variable fe ti oxides and apatite proportions indicating that they are cumulates their simple assemblage of fe ti oxides and apatite and local net texture suggest that the fe ti p ores in damiao have formed from nelsonitic melts immiscibly separated from the ferrodioritic magma during late stage differentiation fe ti ores are also cumulates and have mineral compositions similar to fe ti p ores the close association between fe ti and fe ti p ores indicates that the fe ti ores may have also formed from the nelsonitic melts we proposed that differentiation of nelsonitic melts accompanied by gravity settling is responsible for the formation of fe ti and fe ti p ores such a differentiation process in nelsonitic melts is well supported by variations of sr y th u ree and eu eu of apatite in fe ti p ores using oxides apatite ratio of 2 1 and compositions of apatite and calculated primary oxides we estimate the composition of the nelsonitic melt as 52 0 wt fe2o3t 18 5 wt cao 14 2 wt p2o5 8 7 wt tio2 4 0 wt al2o3 and 1 1 wt mgo with minor sio2 k2o na2o and f such a nelsonitic melt is suggested to be possibly conjugated with si rich melts compositionally similar to the damiao jotunitic dykes 50 wt sio2 and 15 wt fe2o3t which may subsequently evolve to mangeritic rocks in damiao our modeling also indicates that the onset of immiscibility occurs at a time when the evolved melt has 44 wt sio2 21 wt fe2o3t 3 0 wt tio2 and 2 6 wt p2o5 high oxygen fugacity and phosphorous content in magmas may play important roles in the immiscibility of nelsonitic magmas including promoting iron enrichments and widening the two liquid field

structural geology of easter ross scotland implications for movement on the great glen fault zone the integration of a recently drilled exploration well sited near the town of tain ross shire with a seismic database and onshore exposures allows a new interpretation of the structure in the easter ross peninsula ne scotland it is now evident that previous interpretations which highlighted the importance of ne sw striking lineaments need some modification instead numerous n s to nne ssw trending folds and faults affect devonian sequences and show evidence of compressional reactivation of structures which had previously experienced extension these inversion structures only appear to be dissected by ne sw and e w striking faults and extensional fractures in areas adjacent to the great glen fault zone integration of the onshore data with results from adjacent offshore areas suggests that the peninsula has undergone a complex structural history since the early devonian it appears to have been characterized by early devonian probably rift related extensional faulting and subsequent mid late devonian regional thermal subsidence the restriction of similar structural relations to devonian sequences on offshore seismic lines from adjacent areas suggests that the contractional and inversion structures which similarly affect the late palaeozoic sequences in onshore areas were probably related to permo carboniferous structural events rather than younger deformation further integration of offshore data with the occurrence of jurassic sequences on the coast suggests that the peninsula may be considered an integral part of the inner moray firth basin and experienced a similar mesozoic subsidence history to offshore areas before undergoing regional uplift and dissection due to reactivation of the great glen fault zone during the cenozoic there is no evidence to suggest that this fault zone had any significant control on basin development sedimentary sequences or structural geometries during palaeozoic or mesozoic periods of extension and it probably only had minor effect during permo carboniferous inversion similarily its role in tectonic events after the early cretaceous appears to have been limited to local deformation with little evidence for any large scale strike slip offset along its length the unusual occurrence of jurassic coastal exposures in easter ross appears to represent fault bounded slices of sediment downfaulted to accommodate the formation of a negative flower structure in response to limited dextral strike slip movement the results suggest that the great glen fault zone was a strike slip fault system effectively locked during phases of extension in the inner moray firth but was reactivated during phases of inversion when extensional slip vectors sub paralleled the lineament