mapping the 3d extent of the northern lobe of the bushveld layered mafic intrusion from geophysical data abstract geophysical models image the 3d geometry of the mafic portion of the bushveld complex north of the thabazimbi murchison lineament tml critical for understanding the origin of the world s largest layered mafic intrusion and platinum group element deposits the combination of the gravity and magnetic data with recent seismic mt borehole and rock property measurements powerfully constrains the models the intrusion north of the tml is generally shallowly buried generally 12 000 m averaging 4000 m a feeder suggested by a large modeled thickness 10 000 m and funnel shape for lower zone magmas could have originated near the intersection of ns and ne trending tml faults under mokopane the tml has been thought to be the feeder zone for the entire bushveld complex but the identification of local feeders and or dikes in the tml in the models is complicated by uncertainties on the syn and post bushveld deformation history however modeled moderately thick high density material near the intersection of faults within the central and western tml may represent feeders for parts of the bushveld complex if deformation was minimal the correspondence of flat high resistivity and density regions reflect the sill like geometry of the bushveld complex without evidence for feeders north of mokopane magnetotelluric models indicate that the transvaal sedimentary basin underlies much of the bushveld complex north of the tml further than previously thought and important because the degree of reaction and assimilation of the transvaal rocks with the mafic magmas resulted in a variety of mineralization zones

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

calibrating fluvial erosion laws and quantifying river response to faulting in sardinia italy abstract it is now widely accepted that rivers modify their erosion rates in response to variable rock uplift rates resulting in changes in channel slope that propagate upstream through time therefore present day river morphology may contain a record of tectonic history the simple stream power incision model can in principle be used to quantify past uplift rates over a variety of spatial and temporal scales nonetheless the erosional model s exponents of area and slope m and n respectively and bedrock erodibility k remain poorly constrained in this paper we will use a geologically and geomorphically well constrained plio pleistocene volcanic landscape in central sardinia italy to calibrate the stream power erosion equation and to investigate the slip rate of faults that have been seismically quiescent in the historic past by analysing digital elevation models geological maps and landsat imagery we have identified the geomorphic expression of several volcanic features eruption centres and basaltic lava flows and three normal faults with 6 to 8 km fault traces within the outcrop downstream river longitudinal profiles show a similar transient response to relative base level fall probably as a result of relief inversion at the edge of the volcanic outcrop from measurements of incision local slope and upstream catchment area across eight different rivers we calculate n 1 m 0 50 0 02 and using a landscape age from literature of 2 7 ma bedrock erodibility k 0 10 0 04 m 1 2m myr 1 there are also knickpoints on rivers upstream of two normal faults and we used numerical inverse modelling of the longitudinal profiles to predict the slip rate of these faults since 2 7 ma the results from the inverse model show that the erosional parameter values derived in this study can produce theoretical longitudinal profiles that closely resemble observed river profiles upstream of the faults the lowest misfit theoretical longitudinal profiles were generated by a model of temporally discontinuous footwall uplift with consistently low throw rates

filling the bushveld complex magma chamber lateral expansion roof and floor interaction magmatic unconformities and the formation of giant chromitite pge and ti v magnetitite deposits his mind was like a soup dish wide and shallow irving stone on william jennings bryan a compilation of the sr isotopic stratigraphy of the bushveld complex shows that the evolution of the magma chamber occurred in two major stages during the lower open system integration stage lower critical and lower main zone there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing crystallisation and deposition of cumulates larger influxes correspond to the boundaries of the zones and sub zones and are marked by sustained isotopic shifts major changes in mineral assemblages and development of unconformities during the upper closed system differentiation stage upper main zone and upper zone there were no major magma additions other than that which initiated the upper zone and the thick magma layers evolved by fractional crystallisation the lower and lower critical zones are restricted to a belt that runs from steelpoort and burgersfort in the northeast to rustenburg and northam in the west and an outlier of the lower and lower critical zone up to the lg4 chromitite layer in the far western extension north of zeerust it is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the lower critical zone occur these chromitites include the economically important c 1 m thick lg6 and mg1 layers exposed around both the eastern and western lobes of the bushveld complex the upper critical zone has a greater lateral extent than the lower critical zone and overlies but also onlaps the floor rocks to the south of the steelpoort area the source of the magmas also appears to have been towards the south as the mg chromitite layers degrade and thin northward whereas the lg layers are very well represented in the north and degrade southward sr and os isotope data indicate that the major chromitite layers including the lg6 mg1 and ug2 originated in a similar way extremely abrupt and stratigraphically restricted increases in the sr isotope ratio imply that there was massive contamination of intruding melt which hit the roof of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite kruger 1999 kinnaird et al 2002 therefore each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor nevertheless this was achieved by in situ contamination by roof rock melt of the intruding critical zone liquids that had an orthopyroxenitic to noritic lineage the main zone is present in the eastern and western lobes of the bushveld complex where it overlies the critical zone and onlaps the floor rocks to the south and the north where it is also the basal zone in the northern lobe the new magma first intruded the northern lobe north of the thabazimbi murchison lineament interacted with the floor rocks incorporated sulphur and precipitated the platreef along the floor rock contact before flowing south into the main chamber this exceptionally large influx of new magma then eroded an unconformity on the critical zone cumulate pile and initiated the main zone in the main chamber by precipitating the merensky reef on the unconformity the upper zone magma flowed into the chamber from the southern bethal lobe as well as the tml this gigantic influx eroded the main zone rocks and caused very large scale unconformable relationships clearly evident as the gap areas in the western bushveld complex the base of this influx which is also coincident with the pyroxenite marker and a troctolitic layer in the northern lobe is the petrological and stratigraphic base of the upper zone sr isotope data show that all the pge rich ores including chromitites are related to influxes of magma and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion with associated transgressive disconformities onto the floor rocks coincident with major zone changes these positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped the outcrop patterns and the concordance of geochemical isotopic and mineralogical stratigraphy indicate that during crystallisation the bushveld complex was a wide and shallow lobate sill like sheet and the rock strata and mineral deposits are quasi continuous over the whole intrusion

cumulative deformation and original geometry of the bushveld complex abstract a structural review and re interpretation of the bushveld complex based on 254 georeferenced maps from research technical reports and geophysical surveys suggests that its current geometry differs markedly from its original geometry broadly n s flattening left lateral transpressional shearing along an interconnected fault network steepening of cumulate layering and 10 km of uplift to the north of the northern margin of the complex s main chamber were accompanied by an eastward verging escape structure burgersfort bulge and syn cooling gap areas on its western limb southward verging deformation was transmitted from the villa nora fragment via thrusting in the rooiberg area generating 50 70 km of southward displacement uplift and erosional loss of the northern limb s western portion a string of anomalous occurrences of bushveld complex units and dense areas outlined by unconstrained gravity isoshells suggest a further 170 km southward displacement through the center of the main chamber the southern limb underwent predominantly right lateral ductile offset from the western limb along the crocodile river and rustenburg faults expressed by an in line series of nnw trending magnetic highs to the south of their mapped terminations left lateral shearing and progressive splaying of a nne trending dyke swarm to the west of an inflection point provides strain markers for this offset and 35 anticlockwise rotation of the burgersfort bulge and central parts of the main chamber although recent work suggests that the complex cooled within 1 myr late intrusion syn cooling sse wards movement of its deeper ductile central parts within at least 5 10 myr after its initial intrusion the transvaalide fold and thrust event and the expulsion of fluids to form the high ti igneous suite hitis and related bodies appear to have closely post dated the complex s intrusion removal of the effects of cumulative strain produces a more equant complex shortly after its intrusion occupying an orthogonal network of normal faults and perpendicular strike slip transverse faults

the conformable emplacement of the bushveld mafic rocks along a regional unconformity in the transvaal succession of south africa abstract a previously unrecognized regional unconformity occurs in the proterozoic transvaal succession of the kaapvaal province of southern africa the predominantly marine and siliciclastic rocks of the lower two thirds of the pretoria group are unconformably overlain by a terrestrial and largely volcanic sequence the most voluminous portion of which is the rooiberg felsite if the bushveld complex is mentally subtracted from map patterns the rooiberg felsite also locally overlies pre pretoria sequences and the archean crystalline basement the bushveld complex is not lopolithic as commonly supposed instead regionally condordant emplacement of the complex along the unconformity explains both the seemingly discordant footwall features and the lack of pretoria and older strata other than a few xenoliths in the hanging wall the lack of any geochemical evidence for major crustal contamination of bushveld magmas precludes disposing of any such hanging wall strata by wholesale assimilation the bushveld complex the unconformity and the enclosing strata are synformally folded making the bushveld appear to be lopolithic due to this folding and multiple periods of erosion the original extents of the bushveld complex the unconformity and the enclosing strata are now much reduced other smaller mafic intrusions along or immediately below the same regional unconformity probably are bushveld related

kinetic controls on the partitioning of trace elements between silicate and sulfide liquids mass transfer between sulfide and silicate liquids is often discussed elements pge has resulted from liquation immiscible by reference to a mass ratio between hypothetical liquid reservoirs liquid phase separation of sulfide liquid from mafic or at equilibrium defined as r in an open system not at equilibrium ultramafic silicate magma a central assumption of modthe mass of silicate melt from which a growing sulfide droplet els of magmatic sulfide deposit formation is that the base appears to have scavenged chalcophile elements will depend on metals and pge are strongly partitioned into the sulfide diffusivities di and dfes of the element and of the fes component melt previous discussions of the process by which sulfide in the silicate melt respectively on the degree of supersaturation of liquids become enriched in chalcophile metals have fothe melt with fes c o on the radius a of the droplet and on the cused almost exclusively on models in which coexisting velocity v with which the droplet is advected through the melt so bodies of sulfide and silicate melt are considered to be that in equilibrium at all times the intent of this paper is to demonstrate that natural sulfide deposits preserved in igneous rocks will in many r 1 c fes o di 1 2 adiv dfes 1 2 adfesv instances record metal distributions that never attained equilibrium as a result of the kinetic constraints on metal chalcophile elements are expected to show inter element variations partitioning between phases the consequences are that in d spanning several orders of magnitude in some melts leading different elements will seem to show evidence for equito large inter element variations in effective r in a given sulfide libration at different silicate sulfide mass ratios within body these variations in effective r will lead to spatial separations single sulfide bodies i describe the time dependent evolubetween zones of maximum enrichment of chalcophile elements tion of metal distributions in silicate sulfide melt systems produced during fractional segregation of sulfide in layered intrusions starting with analytical solutions for simple boundary whereas it has proven impossible to model the generation of spatially conditions and then adapting them to more complex offset stratiform horizons in the australian munni munni layered systems as numerical models intrusion using equilibrium partition coefficients the present kinetic model reproduces the observed patterns with great fidelity

petrology and mineralisation of the southern platreef northern limb of the bushveld complex south africa the platreef the putative local analogue of the merensky reef forms the floor to the mafic succession in the northern limb of the bushveld complex we define the platreef as the lithologically variable unit dominated by pyroxenite which is irregularly mineralised with pge cu and ni between the transvaal metasedimentary footwall or archaean basement and the overlying main zone gabbronorite we define the mineralisation around calcsilicate xenoliths within the main zone in the far north of the limb as a platreef style mineralisation the platreef ss has a strike extent of 30 km whereas platreef style mineralisation occurs over a strike length of 110 km the platreef varies from 400 m thick in the s to 30 modal in some intersections these are dominated by pyrrhotite with lesser pentlandite and chalcopyrite minor pyrite and traces of a wide compositional range of sulphides in the southern sector mineralised zones have cu grades of 0 1 0 25 and ni 0 15 0 36 massive sulphides are localised commonly but not exclusively towards the contact with footwall metasedimentary rocks magmatic sulphides are disseminated or net textured ranging from a few microns to 2 cm grains of pyrrhotite and pentlandite with chalcopyrite and minor pyrite much of the sulphide is associated with intergranular plagioclase or quartz feldspar symplectites along the margins of rounded cumulus orthopyroxenes the pges in the southern sector occur as tellurides bismuthides arsenides antimonides bismuthoantimonides and complex bismuthotellurides pgm are rarely included in the sulphides but occur as micron sized satellite grains around interstitial sulphides and within alteration assemblages in serpentinised zones the pt pd ratio 1 and pge grade may be decoupled from s and base metal abundance

re and os distribution and os isotope composition of the platreef at the sandsloot mogolakwena mine bushveld complex south africa abstract rhenium and os concentrations and os isotopic compositions were determined for a suite of previously characterized samples from a traverse across the platreef at the sandsloot mogolakwena mine of the northern limb of the bushveld complex the samples comprise five pyroxenites and five parapyroxenites contact rocks representing variable mixtures of calc silicate country rocks and magmatic rocks the isotopic data from the pyroxenites define a re os regression line with an age 2011 51 ma that agrees within uncertainty with the accepted age for the bushveld complex whereas the parapyroxenite data scatter about this trend the initial 187os 188os ratios of the pyroxenites 0 1820 0 1848 are similar to but slightly more radiogenic than previously published values for the merensky reef our preferred interpretation is that this section of the platreef formed from a well mixed crustally contaminated magma genetically related to that which gave rise to the merensky reef the platreef parental magma may also have experienced minor additional contamination by wall rock interaction during emplacement

overview of the magnetic signatures of the palaeoproterozoic rustenburg layered suite bushveld complex south africa abstract aeromagnetic data clearly delineate the mafic rocks of the economically significant bushveld igneous complex this is mainly due to the abundance of magnetite in the upper zone of the rustenburg layered suite of the bushveld but strongly remanently magnetised rocks in the main zone also contribute significantly in places in addition to delineating the extent of the magnetic rocks in the complex the magnetic anomalies also provide information about the dip and depth of these units the presence of varying degrees of remanent magnetisation in most of the magnetic lithologies of the rustenburg layered suite complicates the interpretation of the data the combination of available regional and high resolution airborne magnetic data with published palaeomagnetic data reveals characteristic magnetic signatures associated with the different magnetic lithologies in the rustenburg layered suite as expected the ferrogabbros of the upper zone cause the highest amplitude magnetic anomalies but in places subtle features within the main zone can also be detected a marker with strong remanent magnetisation located in the main zone close to the contact with the upper zone is responsible for very high amplitude negative anomalies in the southern parts of both the eastern and western lobes of the bushveld complex prominent anomalies are not necessarily related to a specific lithology but can result from the interaction between anomalies caused by differently magnetised bodies the magnetic data provided substantial information at different levels of detail ranging from contacts between zones and layering within zones to magnetite pipes dykes and faults that can have an impact on mine planning finally simple modelling of the magnetic data supports the concept of continuous mafic rocks between the western and eastern lobes

dinosaurs of great britain and the role of the geological society of london in their discovery ornithischia completing our survey of british non avian dinosaurs we here review the ornithischians of britain heterodontosaurids are present in the lower cretaceous lulworth formation of dorset and a few earlier possible records imply a long presence in the region of this clade britain9s thyreophoran record is rich and includes the earliest well represented taxon scelidosaurus as well as middle jurassic stegosaurs and ankylosaurs including a reasonably good cretaceous record of polacanthids and nodosaurids cretaceous stegosaurs are known only from fragmentary remains but the proposal that stegosaurs were present as early as the rhaetian is rejected among british iguanodontian ornithopods the possible dryosaurid callovosaurus is the oldest global record whereas the proposed synonymy of cumnoria with camptosaurus requires confirmation iguanodon has become a taxonomic dumping ground for assorted iguanodontians and is in need of revision most of the british species referred to this genus are almost certainly not closely allied to the neotype species i bernissartensis and require new generic names fragmentary remains suggest the early presence of hadrosaurids in britain the only british record of marginocephalia the wessex formation skull roof named yaverlandia bitholus appears not to belong to this clade but seems to be from a maniraptoran theropod

shear wave velocity structure of the lower crust in southern africa evidence for compositional heterogeneity within archaean and proterozoic terrains 1 the nature of the lower crust across the southern african shield has been investigated by jointly inverting receiver functions and rayleigh wave group velocities for 89 broadband seismic stations located in botswana south africa and zimbabwe for large parts of both archaean and proterozoic terrains the velocity models obtained from the inversions show shear wave velocities 4 0 km s below 20 30 km depth indicating a predominantly mafic lower crust however for much of the kimberley terrain and adjacent parts of the kheis province and witwatersrand terrain in south africa as well as for the western part of the tokwe terrain in zimbabwe shear wave velocities of 3 9 km s are found below 20 30 km depth indicating an intermediate to felsic lower crust the areas of intermediate to felsic lower crust in south africa coincide with regions where ventersdorp rocks have been preserved suggesting that the more evolved composition of the lower crust may have resulted from crustal reworking and extension during the ventersdorp tectonomagmatic event at c 2 7 ga citation kgaswane e m a a nyblade j julia p h g m dirks r j durrheim and m e pasyanos 2009 shear wave velocity structure of the lower crust in southern africa evidence for compositional heterogeneity within archaean and proterozoic terrains j geophys res 114 b12304 doi 10 1029 2008jb006217

continuity between eastern and western bushveld complex south africa confirmed by xenoliths from kimberlite the three dimensional shapes of mafic layered intrusions have to be inferred from surface outcrops in some cases aided by drilling and or geophysical data however geophysical models are often equivocal for the 2 06 ga bushveld complex of south africa early geological models proposed a shape of a single gently inward dipping lopolith subsequent resistivity and gravity data were interpreted to suggest that the eastern and western limbs were discrete dipping wedge shaped intrusions separated by 150 km a more recent gravity model that takes crustal flexure into account allows continuity and the reversal to the original model distinguishing between these possibilities is difficult from surface based studies because the central regions of the complex are obscured by large volumes of younger granites and sedimentary volcanic cover rocks here we describe xenoliths from the cretaceous palmietgat kimberlite pipe located mid way between the exposed western and eastern lobes of the complex they are chromite bearing feldspathic pyroxenites considered equivalent to those of the typical outcropping critical zone of the bushveld complex this result provides strong support for a regionally interconnected bushveld complex implying its emplacement as a single sill like body confirming the continuity of the bushveld complex greatly expands exploration opportunities and implies that other layered mafic intrusions could have similar geometry

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

structure of the bushveld complex from resistivity measurements knowledge of the deep structure of the arc like bodies constituting the bushveld complex south africa is essential not only to understand the emplacement history of this huge layered intrusion but also for success in the exploration for the platiniferous merensky reef and chromitite layers occurring near its base despite many studies the structure of the complex has remained obscure here we describe new insights into the structure and additional geophysical boundary conditions based on a geoelectrical study this has provided a geoelectrical stratigraphy according to which a conductive layer below the granitic rocks of both the eastern and western compartments of the complex is correlated with sedimentary rocks of the transvaal sequence over large areas rather than with the mafic sequence as conventionally assumed a new feature of this model is that the mafic sequence in both compartments occurs as segments of an inward dipping sheet transgressing the layering of the sedimentary rocks into which it intruded the geoelectrical model supports earlier gravity models in that mafic rocks are absent from the central part of the complex but shows that here the bushveld granite directly overlies archaean basement rather than transvaal sequence rocks as previously accepted

dinosaur landscape interactions at a diverse early cretaceous tracksite lee ness sandstone ashdown formation southern england abstract an assemblage of dinosaur footprints is reported from the lower cretaceous berriasian valanginian ashdown formation of east sussex southern england the ichnofauna is concentrated around a 2 m thick stratigraphic marker the lee ness sandstone where recent cliff retreat has revealed 85 recognisable footprints attributable to 13 morphotypes many of which bear high fidelity skin impressions the newly identified morphotypes mean that this tracksite hosts one of the most diverse dinosaur ichnoassemblages in the well documented mesozoic record of britain recording the activity of theropod ornithopod thyreophoran and possibly sauropod tracemakers most of the footprints were emplaced on a single floodplain mudstone horizon beneath a fluvial crevasse splay sandstone where preservation was favoured by cohesive sediment and a prolonged interval of sedimentary stasis during which trackways could be imparted the sedimentological context of the trackways reveals evidence of interactions between dinosaurs and the riverine landscape that they inhabited including the development of microtopographies around footprints which impacted invertebrate burrowing activity and evidence for dinosaur wading below the bankfull level of small meandering channels and oxbow lakes modern analogue suggests that the large dinosaurs may have played a significant role as zoogeomorphic engineers within the ancient floodplain setting but the imperfect translation of sedimentary environment to sedimentary rock means that geological evidence for such is ambiguous

evidence for the transition to an oxygen rich atmosphere in the rooiberg group south africa a note abstract the rooiberg felsite group is a rare example of a conformable succession that apparently spans the period of evolution of an oxygen rich atmosphere this conclusion is reached indirectly from a review of the proterozoic stratigraphy of south africa and directly from a consideration of the rooiberg itself the atmospheric transition coincides with the stratigraphic interval between the dark silicic lavas and associated grey volcaniclastics of the damwal formation and the overlying red rhyodacites and intercalated red bed sedimentary rocks of the selonsrivier formation radiometric age measurements indicate that this transition occurred after 2224 21 ma but before 2090 40 ma

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

geochemistry of contrasting siliceous magmatic suites in the bushveld complex genetic aspects and implications for tectonic discrimination diagrams abstract the intracratonic bushveld igneous province that formed 2 1 1 9 ga ago contains three contrasting suites of siliceous rocks that are demonstrably of magmatic origin the oldest of these are the high mg hmf and low mg lmf felsites which form interstratified flows in the rooiberg group bushveld granites intrude the rooiberg group and constitute the youngest component of the province well defined interelement variation trends illustrate that the granites do not share the same petrogenetic history as the rooiberg magmas nd isotope measurements indicate that the two eruptive suites probably formed under similar differentiation conditions but from parental magmas that were derived from compositionally different sources on trace element discrimination diagrams the bushveld granites and lmf are usually correctly assigned to a within plate setting but conversely the hmf are generally misclassified as subduction related eruptives it is argued that the trace element signatures of the granites and felsites do not identify their tectonic setting per se but rather point to the melting and crystallization histories of the source regions from which their parent magmas were extracted as such tectonic discrimination diagrams may provide valuable pointers to processes that have affected igneous source materials in much earlier magmatic cycles

sardinia coastal uplift and volcanism the low variability of mis 5 5 sea level m i s marine isotopic stage with respect to the present day sea level allows the sardinian coast to be used as an eustatic reference for the entire mediterranean region this level is generally at 7 2 m above current sea level along the sardinian coast one sector along the orosei gulf eastern sardinia includes a characteristic and well conserved tidal notch that changes in elevation from 7 6 to 11 5 m over only 30 km tilting upwards towards the north generally height deviations of such a tidal notch would be due to tectonic or volcanic activity the sardinia coast however is considered to have too little tectonic activity and also too small post glacial rebound in order to explain the anomaly the remaining possibility is neogene quaternary continental and or submarine volcanic activity which we investigate as a possible cause for the observed anomalies in this paper our goal is to explain the anomaly by modelling recent volcanic loading or updoming related to magmatic intrusion emplacement we review the literature on the recent volcanic deposits both on shore and off shore and investigate to what extent volcanic loads can influence the coastline from a theoretical standpoint using the isostatic flexure model and a range of loads we find that the observed notch height anomaly cannot be explained by volcanic loading but must be produced by an upward welling due to the emplacement of volcanic material as produced for instance by a laccolith or batholith the upward movement could be related to the submarine volcano only recently detected or to a source located on the eastern sardinia coast near orosei

a grenville age layered intrusion in the subsurface of west texas petrology petrography and possible tectonic setting the nellie intrusion is a thick more than 4420 m mafic to ultramafic layered intrusion with a radiometric age of 1163 ma rock types change abruptly with stratigraphic height and include norite pyroxenite gabbronorite hornblende gabbro gabbro anorthosite harzburgite and lherzolite norite is most abundant but gabbro and hornblende gabbro are locally abundant rare olivine rich layers are also present the general order of crystallization was olivine orthopyroxene plagioclase clinopyroxene and hornblende mg s expressed as 100 mg mg fe range from 76 3 to 85 8 for olivine 56 7 to 84 9 for orthopyroxene 62 5 to 90 3 for clinopyroxene and 52 4 to 82 8 for amphibole mg s vary with height and display abrupt reversals which indicate open system addition of new mafic magma eleven cyclic units were identified on the basis of evidence for injection of basaltic magma these can be grouped into three megacyclic units the abundance of orthopyroxene and mineral compositional evidence for

connectivity between the western and eastern limbs of the bushveld complex abstract the mafic layered rocks of the bushveld complex are 6 8 km thick and crop out over an area of 65 000 km 2 previous interpretations of the bouguer gravity anomalies suggested that the intrusion consisted of two totally separate bodies however the mafic sequences in these arcuate western and eastern limbs are remarkably similar with at least six petrologically distinctive layers and sequences being recognisable in both limbs such similarity of sequences in two totally discrete bodies 200 300 km apart is petrologically implausible and it is suggested that they formed within a single lopolithic intrusion all previous bouguer gravity models failed to consider the isostatic response of the crust to emplacement of this huge mass of mafic magma isostatic adjustment as a result of this intrusion would have caused the base of the crust to be depressed by as much as 6 km with this revised whole crustal model it becomes possible to construct a gravity model consistent with observed data which includes a 6 km thick sequence of mafic rocks connecting the western and eastern limbs of the bushveld complex the exact depth at which the mafic rocks of the bushveld complex lie in the centre of the structure cannot be constrained by the gravity data such a first order model is an approximation because there have been subsequent deformation and structural readjustments in the crust some of them probably related to the emplacement of the bushveld complex specifically the observed geometry of the rocks around the crocodile river dennilton marble hall and malope domes suggests that major upwarping of the crust occurred on a variety of scales triggered by emplacement of the bushveld complex

hylaeosaurus polacanthus and the systematics and stratigraphy of wealden armoured dinosaurs two genera of armoured dinosaurs ankylosauria are present in the lower cretaceous wealden beds of england polacanthus owencan be distinguished from hylaeosaurus mantell on the basis of significant differences in the pectoral girdle hindlimb and dermal armour a comprehensive review of the dinosaurs from the wealden series of england and contemporary basins of western europe adds further evidence of a biologicalseparation between lower wealden hastings beds containing hylaeosaurusarmatus and upper wealden faunas wealden group of the isle of wight containing polacanthus foxii and nearly equivalent units in belgium france germany and spain

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

chemistry morphology and origin of magmatic reaction chromite stringers associated with anorthosite in the upper critical zone at winnaarshoek eastern limb of the bushveld complex

a new occurrence of merensky reef on the flanks of the zaaikloof dome northeastern bushveld complex relationship between diapirism and magma replenishment exploration for platinum group elements has resulted in the discovery of an occurrence of merensky reef in the eastern limb of the bushveld complex south africa the new discovery was made on the dwarsrand property in the poorly known boundary area between the intensively explored western and central sectors of the eastern limb this boundary area is largely composed of domes and basins that may in part be aligned along a regional lineament the wonderkop fault transvaal supergroup metasediments in the core parts of the domes form prominent hills whereas the bushveld complex in the intervening basins is restricted to areas of poor outcrop the formation of domes is attributed to diapirism triggered by gravitational loading and heating of the transvaal supergroup in response to intrusion of the bushveld complex merensky reef was located beneath cover rocks in an area where the critical and main zones are uplifted and attenuated against the southern flank of the zaaikloof dome drill holes although collared in upper zone intersected the critical and main zones at relatively shallow depths as a result of the uplift the critical and main zones including the merensky reef are steeply dipping the base of the upper zone forms an intrusive unconformity and the layering in this zone has a much shallower dip economically significant grades were obtained on the dwarsrand property but exploration was terminated because of poor strike continuity the new findings suggest that uplift and attenuation of the bushveld complex on the flanks of domes in the northeastern part of the complex are both more extensive and more severe than previously realized a complex history of intrusion and uplift is implied some domes even penetrate into the overlying bushveld granite the occurrence of markedly angular unconformities may be contrasted with the layercake sequences typically associated with the bushveld complex diapirism in response to crustal loading and heating by ultramafic sequences occurred in the early stages of magma emplacement episodic intrusion and uplift are consistent with multiple replenishment models in which each of the many dozens of cycles that comprise the critical and main zones corresponds to a new magma pulse with the oldest layers being dragged to higher structural levels in response to the uplift periodic reactivation of doming is indicated by the lowermost layers within the critical and main zones abutting against the southern flank of the zaaikloof dome at progressively higher levels the transgressive nature of the upper zone and bushveld granite relative to the critical and main zones may indicate that the upper zone formed by new intrusions of magma rather than the generally accepted model of differentiation within the chamber the discovery of hidden merensky reef at relatively shallow depths beneath transgressive upper zone and granite could provide the impetus for further exploration possibilities within the bushveld complex particularly on the flanks of regionally extensive domal structures

a tracer test in a shallow heterogeneous aquifer monitored via time lapse surface electrical resistivity tomography we illustrate a case study of a saline tracer test in a shallow highly heterogeneous aquifer monitored by means of surface time lapse ert the test was aimed at identifying the system s hydraulic properties some of the expected limitations of the method particularly caused by the strong decrease in ert resolution with depth and the consequent problems with mass balance and moment calculation could be partly balanced by the use of direct measurements of groundwater electrical conductivity and tracer concentration at one selected location the vast heterogeneity of the system ranging in lithology from clay to gravel at a scale of meters to tens of meters reflects itself in the tracer migration and distribution over time the tracer is trapped in the low permeability regions and from these it is slowly released over time high resolution surface ert proves effective at picturing this system behavior over time the extreme heterogeneity is also a challenge in the attempt to translate bulk electrical

electrical lithosphere beneath the kaapvaal craton southern africa 1 a regional scale magnetotelluric mt experiment across the southern african kaapvaal craton and surrounding terranes called the southern african magnetotelluric experiment samtex has revealed complex structure in the lithospheric mantle large variations in maximum resistivity at depths to 200 250 km relate directly to age and tectonic provenance of surface structures within the central portions of the kaapvaal craton are regions of resistive lithosphere about 230 km thick in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography but thinner than inferred from seismic body wave tomography the mt data are unable to discriminate between a completely dry or slightly damp a few hundred parts per million of water structure within the transitional region at the base of the lithosphere however the structure of the uppermost 150 km of lithosphere is consistent with enhanced but still low conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for kaapvaal xenoliths the electrical lithosphere around the kimberley and premier diamond mines is thinner than the maximum craton thickness found between kimberley and johannesburg pretoria the mantle beneath the bushveld complex is highly conducting at depths around 60 km possible explanations for these high conductivities include graphite or sulphide and or iron metals associated with the bushveld magmatic event we suggest that one of these conductive phases most likely melt related sulphides could electrically connect iron rich garnets in a garnet rich eclogitic composition associated with a relict subduction slab

a multi disciplinary study of deformation of the basaltic cover over fine grained valley fills a case study from eastern sardinia italy the pliocene to early pleistocene volcanic activity which generated the basaltic plateau of the orosei dorgali area in eastern sardinia led to the disruption of the local hydrographic network by damming some tracts of the fluvial valleys incised in the granite basement this resulted in the formation of lacustrine basins whose fine grained fills were partly interfingered and eventually covered by younger lava flows in the sw part of the plateau close to the galtelli village a number of unknown depressions locally named paules were formed in order to reconstruct their subsurface structure two electrical resistivity tomography surveys were carried out across these depressions the geophysical results which demonstrate the existence of a disrupted layered system were used to build a numerical geomechanical model that suggest the depressions originated by local collapses of the basaltic cover due to the compaction of the underlying fine grained valley fills

exploration geophysics of the bushveld complex in south africa the bushveld complex consists of three roughly coeval components namely the lebowa granite suite the rashoop granophyre and the rustenburrg layered suite rls the latter being the only economically important unit the rls underlies an area of 65 000 km2 in the northeast sector of south africa and is the oldest and largest mafic layered complex in the world figure 1 it is also the largest repository of magmatic ore deposits and hosts inter alia 80 of the world s platinum group metal pgm resources and most of the chromitite resources over an east west distance of roughly 350 km the rls outcrops as three apparently discrete crescent shaped lobes the western eastern and northern limbs and lies below cover rocks along the southeastern limb the far western limb is currently not of economic significance lithologies range across mafic and ultramafic cumulates plus anorthosites pseudo stratigraphic layering exhibits dips of 8 20 toward the center of the complex the ug2 and merensky reefs constitute the major pgm bearing horizons of mining interest and fall close to the top of the 1500 m thick critical zone an assemblage of alternating leuconorite anorthosite and pyroxene rocks outcropping midway through the rls succession

the tectonic setting of the bushveld complex in southern africa part 1 structural deformation and distribution abstract structural and stratigraphic aspects of the lebowa granite suite the granites and rustenburg layered suite the basic rocks are examined and compared in various compartments of the bushveld complex south africa the coeval molopo farms complex located largely in botswana is included in this examination structural features are evaluated in terms of relationships to major structural features of the kaapvaal craton such as the thabazimbi murchison lineament and its extension in botswana the kgomodikae lineament the melinda abbotspoort rustenburg and steelpoort faults and the barberton lineament in the south histories of structural development in the eastern and western compartments indicate a pre bushveld age of some structural features and models are proposed of recurring movements along pre existing fundamental lines of weakness it is concluded that features such as the thabazimbi murchison lineament are lithospheric in extent and that they played an active role controlling the emplacement of the bushveld and molopo farms complexes

structural and compositional constraints on the emplacement of the bushveld complex south africa abstract despite a plethora of petrological studies the emplacement mechanics of the world s largest layered intrusion the 2 05 ga bushveld complex are still poorly understood early models considered the intrusion to comprise separate lopolithic intrusions or even concentric cone sheets but recently overwhelming support for a sill like intrusional form has emerged examination of the contact aureole reveals three groups of emplacement related structures interfinger deformation zones and bridges formed between intruding and dilating magma fingers preserved in both the western and eastern parts of the complex sub bushveld complex intrusions that reflect finger like emplacement into the underlying contact aureole and diapiric domes that characterize the eastern contact aureole formed by diapiric amplification of initial interfinger deformation zones associated with the earliest mafic ultramafic pulse of the bushveld complex most of these structures exhibit a strong nw se preferred orientation while longitudinal terminations and divergence of the sub bushveld intrusions away from their source horizons indicate magma emplacement towards the se this emplacement direction is supported by petrological data lateral lithological facies variations and mineral chemical variations within specific horizons the thickest and most chemically primitive accumulations of the lower zone of the complex are found adjacent to and thin towards the ne and se away from the thabazimbi murchison lineament tml a crustal scale lineament that has undergone polyphase reactivation since at least 2 7 ga the bushveld complex was most likely fed by a feeder dyke that utilised the tml spreading laterally from the dyke axis to form its current sill like geometry the stress field at 2 05 ga was suitably oriented to allow for dilation of the ene trending tml suggesting the kaapvaal craton was subject to a component of nw se extension during this time nw se directed collision of the kaapvaal and zimbabwe cratons is recorded in the limpopo belt which would suggest emplacement under conditions of far field extensional stress within a back arc setting this is corroborated by petrological data that supports a significant component of subducted crust in the bushveld magmas

an overview of the geology of the transvaal sequence and bushveld complex south africa the late archaean early proterozoic transvaal sequence is preserved within the transvaal kanye and griqualand west basins with the 2050 ma bushveld complex intrusive into the upper portion of the succession within the transvaal basin both transvaal and bushveld rocks are extensively mineralized the former containing large deposits of iron manganese asbestos andalusite gold fluorine lead zinc and tin ores and the latter some of the world s major occurrences of pge chromium and vanadium ores transvaal sedimentation began with thin predominantly clastic sedimentary rocks black reef vryburg formations which grade up into a thick package of carbonate rocks and bif chuniespoort ghaap taupone groups these lithologies reflect a carbonate bif platform sequence which covered much of the kaapvaal craton in reaction to thermal subsidence above ventersdorp aged rift related fault systems an erosional hiatus was followed by deposition of the clastic sedimentary rocks and volcanics of the pretoria postmasburg segwagwa groups within the three basins under largely closed basin conditions an uppermost predominantly volcanic succession rooiberg group loskop formation is restricted to the transvaal basin a common continental rift setting is thought to have controlled pretoria group sedimentation rooiberg volcanism and the intrusion of the mafic rocks of the rustenburg layered suite of the bushveld complex the dipping sheets of the rustenburg magmas cut across the upper pretoria group stratigraphy and lifted up the rooiberg lithologies to form the roof to the complex subsequent granitic rocks of the lebowa and rashoop suites of the bushveld complex intruded both upper rustenburg rocks and the rooiberg felsites

ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation sea level fluctuation and geodispersal abstract more species of nodosaurid ankylosaurians than ankylosaurid ankylosaurians have been found in marine sediments and some previous quantitative studies of global dinosaur occurrences provide support for an association between nodosaurids and marine depositional environments we compiled a dataset of global ankylosaurian occurrences and found that the geographic distribution of marine ankylosaurian occurrences is regionally biased with 54 of records stemming from western north america in the cretaceous a time of regional highstands in sea level and epicontinental flooding coupled with differential extirpation of ankylosaurian subclades inhabiting the western interior basin wib within the western interior basin we found little statistical support for an association between ankylosaurian subclades and palaeoenvironment in a chronological context only the albian cenomanian transgressive regressive cycle had statistical support for an overabundance of nodosaurids in marine environments compared to ankylosaurids the apparent overabundance of nodosaurids relative to ankylosaurids in marine sediments in the western interior basin overall cannot be decoupled from the extirpation of north american ankylosaurids during the cenomanian and the subsequent absence of ankylosaurids in north america during the turonian to early campanian prior to the immigration of asian ankylosaurine ankylosaurids the north american ankylosaurian record highlights the difficulty in interpreting habitat preferences in the context of a shifting seaway regional extinctions and intercontinental dispersals

shear wave velocity structure of the bushveld complex south africa the structure of the crust in the environs of the bushveld complex has been investigated by jointly inverting high frequency teleseismic receiver functions and 2 60 s period rayleigh wave group velocities for 16 broadband seismic stations located across the bushveld complex group velocities for 2 15 s periods were obtained from surface wave tomography using local and regional events while group velocities for 20 60 s periods were taken from a published model 1 d shear wave velocity models obtained for each station show the presence of thickened crust in the center of the bushveld complex and a region at the base of the crust where shear wave velocities exceed 4 0 km s the shear wave velocity models also suggest that velocities in some upper crustal layers may be as high as 3 7 3 8 km s consistent with the presence of mafic lithologies these results favor a continuous sheet model for the bushveld complex in which the outcropping mafic layers of the western and eastern limbs are continuous at depth beneath the center of the complex however detailed modeling of receiver functions at one station within the center of the complex indicates that the mafic layering may be locally disrupted due to thermal diapirism triggered by the emplacement of the bushveld complex or thermal and tectonic reactivation at a later time

a new species of polacanthus ornithischia ankylosauria from the lower cretaceous of sussex england the first specimen of the ankylosaur genus polacanthus from the mainland barremian of southeast england is described as polacanthus rudgwickensis sp nov polacanthus rudgwickensis is larger than polacanthus foxii and there are significant differences in the dermal armour the tibia and caudal vertebrae of the two species polacanthus foxii appears to be restricted at present to the isle of wight with one specimen from southwest england whilst polacanthus rudgwickensis is only known from sussex this geographical distribution the palaeobiological implications and possible sexual dimorphism are discussed for this genus

a layered basic intrusion deformed and metamorphosed in granulite facies of the sri lanka basement a layered basic intrusion has been found in the central granulite belt of the sri lanka continental basement it intruded parallel to bedding before all or early during deformation of neighbouring metasediments deformation affecting metasediments and the intrusion alike includes flattening to c 1 20 of the original thickness and nnw stretching to c 20 times the original length the intrusion is now 170 300 m thick most of the deformation was acquired under granulite facies metamorphism the intrusion was then folded still at high t by a large f4 synform with an axis parallel to str1 and a steep axial plane a steep axial plane cleavage and minor folds are related to this big fold stretching continued along its axis late during formation of this fold a granite intruded mainly following s4 cleavage planes the intrusion shows a homogeneous gabbroic series at the bottom followed upwards by a differentiated and layered series a thin sequence of ultramafic rocks occurs near the middle this indicates multiple melt injection more homogeneous partly biotite bearing amphibolites form the top of the succession magmatic layering is well preserved but no magmatic minerals or grain fabrics have escaped deformation or metamorphism static annealing under granulite facies conditions outlasted all deformation and was accompanied and followed by the beginning of cooling hornblende plagioclase coronas formed round garnets at this stage geochemical work carried out by stosch 1991 on our samples confirms the cumulate nature of the rocks

on the first partial skull of an ankylosaurian dinosaur from the lower cretaceous of the isle of wight southern england the specimen is identified as the partial cranium of a nodosaurid ankylosaur ornithischia thyreophora on the basis of the presence of bone which is fused to the dorsal surface of the skull and has secondarily closed the upper temporal fenestrae the only unequivocally nodosaurid material recovered from the isle of wight to date comes from wealden facies and has been referred to the genus polacanthus it is considered highly probable that this new skull is referable to the same genus despite having undergone abrasion through post emergence water rolling the skull and cranial walls have proved to be relatively informative of the general anatomy of the braincase and the neural and vascular anatomy of this part of the head the anatomy of the braincase of most ankylosaurs with the notable exception of the juvenile specimens of the ankylosaurid pinacosaurus is surprisingly poorly known despite the relative abundance of cranial material in north american and asian collections the cranial neural and vascular anatomy is well shown in this specimen and enables the first detailed description of nodosaurid endocranial structures the general form of the brain can be outlined from the structure of the endocast and the principal lobes can be identified the majority of the cranial nerves have been identified and a significant component of the associated vascular system is also visible in most respects the endocast shows a neural anatomy which is common to that known in most dinosaurs when compared to their nearest relatives the ankylosaurid ankylosaurs euoplocephalus the nodosaurid endocranial cast shows a more pronounced cerebral flexure a forebrain which is broader and more expanded dorsally and a more prominent cerebellum although there is no evidence for a floccular lobe there are minor differences in the arrangement of the cranial nerves and the dorsal portions of the vascular system are better shown because of erosion the olfactory lobes of this specimen of cf polacanthus are not preserved and cannot be compared to those of ankylosaurid ankylosaurs the latter are unusual in the strong separation of the lobes reflected in the divergent olfactory stalks this feature may be associated with the very complex passages within the nasal region of the skull which are lacking in the nodosaurids described to date