the crustal structure of beira high central mozambique combined investigation of wide angle seismic and potential field data abstract the timing and geometry of the initial gondwana break up between africa and east antarctica is still poorly known due to missing information about the continent ocean boundaries along the rifted margins in this context the beira high off central mozambique forms a critical geological feature of uncertain crustal fabric based on new wide angle seismic and potential field data across beira high a p wave velocity model supported by amplitude and gravity modelling provides constraints on the crustal composition of this area in the mozambique basin mainly normal oceanic crust of 5 5 7 km thickness with velocities of 6 5 7 0 km s in the lower crust is present a sharp transition towards beira high marks the continent ocean boundary here the crust thickens to 23 km at maximum a small velocity depth gradient and a constant increase in velocity with basal velocities of maximum 7 0 km s are in good agreement with typical velocities of continental crust and continental fragments the density model indicates the existence of felsic material in greater depths and supports a fabric of stretched but highly intruded continental crust below beira high a gradual decrease in crustal thickness characterizes the transition towards the mozambican shelf area here in the zambezi delta depression 12 km of sediments cover the underlying 7 km thick crust the presence of a high velocity lower crustal body with velocities of 7 1 7 4 km s indicates underplated magmatic material in this part of the profile however the velocity structure in the shelf area allows no definite interpretation because of the experimental setup thus the crustal nature below the zambezi delta and consequently the landward position of the continent ocean boundary remains unknown the difference in stretching below the margins of beira high suggests the presence of different thinning directions and a rift jump during the early rifting stage

mudwave activity and current controlled sedimentation in powell basin northern weddell sea antarctica an area of mudwave development has been identified from the northwestern powell basin northern weddell sea antarctica the wave field is located near the base of the continental slope in water depths of 2800 3100 m along the pathway of antarctic bottom water aabw flow from the weddell sea the waves are presently active migrating up a low angle 0 6 slope to the northwest they are typically 20 50 m in amplitude and 2 4 km in wavelength and cover an area greater than 1000 km2 swath mapping and high resolution multi channel seismic reflection profiling across the area show that the waves developed in association with basin floor channels and strongly current influenced sediments acoustically the sediments can be divided into three units the uppermost unit c is 0 5 s twt two way time thick with highly continuous parallel reflectors displaying well developed waveforms mimicking those at the seabed and towards the southeast a basin floor channel unit b is up to 0 8 s twt thick with strong and continuous subhorizontal reflectors in the mid upper section of b are developed buried sinusoidal wave forms and a base of slope depression or moat and a sediment drift which is infilled and buried the reflector pattern suggesting sediment supply under current control alongslope interpreted as contouritic sediments a lower transparent unit a is 1 1 5 s twt thick with occasional reflectors the original construction of the waves may have been by turbidity currents predominantly supplied from the basin floor channels present day deposition across the waves is maintained by fine grained sediment as a result of the lateral transfer of distal turbidites from the basin floor channels by bottom currents it is suggested that the initiation of current influenced sedimentation was closely linked to the onset of aabw flow during the early miocene following the separation of the south orkney microcontinent and the opening of the powell basin during the late oligocene

sedimentary processes across the continental rise of the southern antarctic peninsula abstract a series of large sediment mounds have been identified along the pacific portion of the antarctic peninsula continental rise these mounds are composed of sediment delivered to the continental rise during the advance and retreat of grounded ice across the shelf the stratigraphic development of one of these sediment deposits the tula sediment mound is examined to investigate how the onset of glaciation influenced the deep sea depositional environment along this portion of the margin the stratal relationships associated facies distribution and the physiography observed along the southern antarctic margin reflect the waxing and waning of the antarctic ice sheets various processes erode transport and deposit sediment along the outer shelf slope and rise throughout a glacial cycle a deep sea erosional unconformity is apparent at the base of the tula deposit this surface may reflect the first onset of intensified bottom water circulation along the margin perhaps induced by the tectonic opening of the drake passage the tula sediment mound is comprised predominantly of canyon overbank systems evidence for the onset of canyon cutting and the development of the thick overbank deposits 2 km is found immediately above the deep sea erosional unconformity relating increased canyon cutting across the continental rise to the fluctuation of ice across the shelf implies that the onset of predominantly glacial conditions commenced soon after the onset of intensified bottom water circulation along this margin the volume of sediment associated with the tula deposit and the apparent point source distribution of the channel systems suggests that much sediment was transported to the slope and rise perhaps by meltwater processes through these canyons

seismic stratigraphic framework and depositional history for cretaceous and cenozoic contourite depositional systems of the mozambique channel sw indian ocean this study describes previously unrecognized contourite depositional systems cdss in the mozambique channel which constrain palaeoceanographic models for this area the stratigraphic stacking patterns record nine seismic units su1 to su9 separated by eight major discontinuities a to h oldest to youngest key seismic markers in cds evolutionary history occur during aptian albian 122 ma late cenomanian 94 ma early 38 2 36 2 ma and late 25 23 ma oligocene and early middle miocene 17 15 ma epochs these record onset 122 to 94 ma growth 94 to 25 23 ma maintenance 25 23 to 17 15 ma and burial 17 15 ma to the actual time stages for cdss cdss first develop during the onset stage which coincides with the opening and deepening of the african southern ocean gateway at 122 and 100 ma respectively the growth stage beginning in the late cenomanian 94 ma correlates with the opening and deepening of the equatorial atlantic gateway during the growth stage two major shifts in sedimentary stacking pattern occur which coincide with palaeoceanographic changes during the early 38 2 36 2 ma and late 25 23 ma oligocene these in turn coincide with the onset and local enhancement of antarctic water masses cds growth continued until the early middle miocene during the maintenance stage 17 15 ma most cds growth ceased at the end of the maintenance stage circulation of the north atlantic water mass into the southern hemisphere led to a deepening of antarctic water masses in the area

mid late pleistocene glacimarine sedimentary processes of a high latitude deep sea sediment drift antarctic peninsula pacific margin the effects of glaciation on sediment drifts is recognised from marked sedimentary facies variation in deep sea cores taken from the continental rise of the antarctic peninsula pacific margin nineteen sediment cores were visually described logged for magnetic susceptibility and x radiographed about 1000 analyses were performed for grain size clay minerals and biostratigraphy foraminifera nannofossils and diatoms four sediment types associated with distinct sedimentary processes are recognised based on textural compositional analysis 1 hemipelagic mud forms the bulk of the interglacial sediment and accumulated from the pelagic settling of bioclasts and ice rafted wind transported detritus 2 terrigenous mud forms the bulk of the glacial sediment and accumulated from a combination of sedimentary processes including turbidity currents turbid plumes and bottom current reworking of nepheloid layers 3 silty deposits occurring as laminated layers and lenses represent the lateral spillout of low density turbidity currents 4 lastly glacial interglacial gravelly mud layers derive from settling of ice rafted detritus five depositional settings are interpreted within sediment drift 7 each characterised by the dominance interaction of one or several depositional processes the repetitive succession of typical sedimentary facies is inferred to reflect a sequence of four climatic stages glaciation glacial deglaciation and interglacial each one characterised by a distinctive clay mineral assemblage and bioclastic content variations in clay mineral assemblage within interglacial stage 5 core sed 06 suggest minor colder climatic fluctuations possibly correlatable with substages 5a to 5e

gravity anomalies flexure and crustal structure at the mozambique rifted margin abstract the free air gravity edge effect anomaly associated with passive continental margins is one of the most distinctive features of the marine gravity field early studies attributed the edge effect to the juxtaposition of thick continental with thin oceanic crust while thinning of the crust due to rifting at the time of continental break up is a major contributor it is now recognised that geological processes such as sedimentation and magmatic underplating also contribute the different amounts of sediment and underplate at rifted margins help in fact to explain the diversity of the edge effect although they obscure the mechanics styles and geometry of rifting in this paper combined 2 dimensional flexural backstripping and gravity modelling techniques are used to quantify the contribution of rifting sediment loading and magmatic underplating to the edge effect anomaly at the mozambique margin this margin formed as the result of a two stage break up the first of which resulted in the separation of africa and madagascar in the early jurassic by comparing the observed edge effect to calculations based on simple elastic plate models we have been able to constrain the elastic thickness te and hence flexural rigidity of the lithosphere that underlies the sediments which accumulated at the mozambique margin following break up the model that best explains the shape i e amplitude and wavelength of the edge effect high is one in which the earliest jurassic early cretaceous sediments were deposited on relatively weak lithosphere te 17 5 km while the later miocene recent sediments accumulated on relatively rigid lithosphere te 40 km these results suggest that sedimentation at the mozambique margin has involved lithosphere which responds to loads in a similar manner as would oceanic lithosphere therefore the thinned transitional crust that underlies much of the coastal plain of the mozambique margin is probably of oceanic rather than continental origin

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

the lebombo monocline and associated feeder dyke swarm diagnostic of a successful and highly volcanic rifted margin abstract as part of the karoo large igneous province lip the 700 km long and 182 ma old lebombo monocline outcrops inland of a younger mozambique lowland cover that separates it from the indian ocean detailed mapping of a particularly well exposed olifant river traverse across this monocline correlates basaltic and rhyodacitic lava units within the lebombo group to at least three hosted generations of intrusions within the monocline parallel northern lebombo dyke swarm implying that a much denser feeder dyke swarm is covered by younger flows measured attitudes and thicknesses of up to 197 lavas and 791 dykes statistically quantify a structural cross section from which a properly weighted lava log of nearly 5 km basalts inter bedded with an overlying 3 5 km of rhyodacites is constructed the geological section is compatible with a slightly deeper sub lava section through the innermost 30 km s of a relatively narrow east greenland margin to which the lebombo monocline can be rigorously compared in both cases field relationships are consistent with early tectonic extension being overwhelmed by dyke dilation within margin parallel swarm segments that may have been injected laterally from central magma chambers thus it is argued that the lebombo monocline is part of a successfully rifted margin that furthermore belongs to a distinct class of highly volcanic and relatively narrow margins which only form proximal to classical triple rift lip centers where an elevated magma flux sustains a magmatic mode of extension for the karoo lip this conforms with 1 a tight gondwana reconstruction of africa with antarctica 2 successful breakup during intense 182 ma emplacement of the lebombo group 3 triple rift formation together with a short lived 181 178 ma okavango dyke swarm and 4 anomalously thick igneous crust formation during continued 2 5 cm yr separation into a loose 155 ma plate configuration of africa and antarctica

drainage of a deep magma reservoir near mayotte inferred from seismicity and deformation the dynamics of magma deep in the earth s crust are difficult to capture by geophysical monitoring since may 2018 a seismically quiet area offshore of mayotte in the western indian ocean has been affected by complex seismic activity including long duration very long period signals detected globally global navigation satellite system stations on mayotte have also recorded a large surface deflation offshore here we analyse regional and global seismic and deformation data to provide a one year long detailed picture of a deep rare magmatic process we identify about 7 000 volcano tectonic earthquakes and 407 very long period seismic signals early earthquakes migrated upward in response to a magmatic dyke propagating from moho depth to the surface whereas later events marked the progressive failure of the roof of a magma reservoir triggering its resonance an analysis of the very long period seismicity and deformation suggests that at least 1 3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth we demonstrate that such deep offshore magmatic activity can be captured without any on site monitoring recent seismicity near mayotte in the indian ocean is due to dyke propagation from and drainage of a 25 35 km deep magma reservoir according to an analysis of earthquake and deformation data

polyphase rifting and break up of the central mozambique margin abstract the break up of the gondwana supercontinent resulted in the formation of the central mozambique passive margin as africa and antarctica were separated during the mid jurassic period although plate kinematics during the oceanic spreading phase are well constrained the initial fit of africa and antarctica their earliest relative movements and margin architectures remain active areas of interest this study uses high quality multi channel seismic reflection profiles to identify the major crustal domains in the angoche and beira regions of the central mozambique margin our results show that the central mozambique passive margin is characterised by intense but localised magmatic activity evidenced by the existence of seaward dipping reflectors sdrs in the angoche region and magmatic sills and volcanoclastic material marking the beira high the angoche and beira regions possess faulted upper continental crusts with possible exhumation of lower crustal material forming an extended ocean continent transition oct the beira high segment reveals an offshore continental fragment which is overlain by a faulted pre rift sedimentary unit likely to belong to the karoo group the combination of our seismic interpretation with existing geophysical and geological data has allowed us to propose a break up model which supports the idea that the central mozambique margin was affected by polyphase rifting the beira high basement is formed by a strike slip deformation along a proposed lithospheric weakness the lurio pebane shear zone northwestern southeastern oriented extension follows and results in continental break up and oceanic spreading our results suggest a segmentation of the central mozambique margin with oceanisation first occurring in the angoche segment the formation of the first oceanic crust in the beira segment followed likely delayed by the formation and failure of the northern beira high rift

advanced insights into magmatism and volcanism of the mozambique ridge and mozambique basin in the view of new potential field data summary a new plate tectonic model is presented which describes the emplacement of the mozambique ridge off southeast africa as the result of long lasting volcanic activity 140 122 ma during the initial opening between africa and antarctica thus an oceanic origin for the mozambique ridge is proposed this model is based on a new and systematic high resolution magnetic anomaly data set acquired across the mozambique ridge and throughout the mozambique basin data from the mozambique basin allow the identification of mesozoic magnetic anomalies from m0r to m26 124 61 155 3 ma with previously unmatched accuracy small scale fracture zones are recognized by offsets of magnetic anomalies in the westernmost part of the basin additionally a bend in the major fracture zones f and e between m17r and m18n 142 84 144 04 ma and a recognized sinusoidal change in spreading direction with an amplitude of about 15 indicate that the basin experienced several small scale changes in spreading direction through time a maximum change in spreading direction to almost 0 at around m11n 135 69 ma is followed by a short lived increase in spreading half rate from 23 5 km ma 1 to about 27 5 km ma 1 in the time frame from m10r to m9n 134 30 132 83 ma we propose that this is related to the initial opening of the south atlantic ocean represented by the onset of seafloor spreading between the falkland plateau and africa in the conjugate georgia and natal basins across the mozambique ridge high amplitude magnetic anomalies at major structural boundaries suggest that the different plateaus of the ridge were formed at different times a simple 2 d gravity and magnetic model for the ridge supports the hypothesis of multiple volcanic episodes which formed the ridge though long lasting volcanic activity between about 140 and 122 ma together with new and verified rotation parameters from the mozambique basin and its conjugate the riiser larsen sea antarctica a series of plate tectonic reconstructions are presented which demonstrate when and how the different parts of the ridge evolved through time

fluid seepage associated with slope destabilization along the zambezi margin mozambique abstract evidences for active fluid seepages have been discovered along the zambezi continental slope offshore southern mozambique these seepages are mostly associated with pockmarks which are aligned along a trend parallel to the slope and running closely upstream of the headwall scarp of a wide zone of slope destabilization fluid seepages are interpreted as a potential trigger for the slope destabilization acoustic anomalies within the water column have been interpreted as related to moderate bubble seepages mostly located outside and only punctually inside the destabilization zone exploration with the scampi towed camera system in the widest pockmark diameter 200 m wide has shown fluid seepages associated to authigenic carbonate crusts and possibly bacterial mats these fluid seepages are also associated to the presence of chemiosynthetic organisms vesicomyidae and thyasiridae bivalves siboglinidae tubeworms the sampled gas in the sediment corresponds mainly to ch4 of microbial origin generated by hydrogenotrophic methanogenesis from a substrate of organic origin i e a conventional process of genesis of microbial gas in the marine domain no evidence for thermogenic gas was detected another type of pockmarks has been observed within the core of the slope destabilization zone most of these pockmarks are inactive in terms of fluid seepage at present time and are associated to carbonate buildups forming chimney geometries they probably correspond to diagenetic chimneys of former fluid migration pathways that have been exhumed during the mass sliding and the surrounding depression are related to recurrent activity of strong lateral slope currents which have scoured the sediments around the spatial organization of the slope destabilization features is considered as representative of the temporal evolution of the landslide giving information about the dynamics of slope instability processes this proposed evolution started by scattered seepages of formation water with dissolved gas then free gas seepages appeared notably in the upper part of the slope this was followed by progressive shallow deformation in the sediments downslope of the main gas seepages finally the whole slope was destabilized forming imbricated landslides exhuming locally former diagenetic chimneys

reconstruction of the east africa and antarctica continental margins the early jurassic separation of antarctica from africa plays an important role in our understanding of the dispersal of gondwana and pangea previous reconstruction models contain overlaps and gaps in the restored margins that reflect difficulties in accurately delineating the continent ocean boundary cob and determining the amount and distribution of extended continental crust this study focuses on the evolution of the african margin adjacent to the mozambique basin and the conjugate antarctic margin near the riiser larsen sea satellite derived gravity data have been used to trace the orientations and landward limits of fracture zones a 3 d gravity inversion has produced a crustal thickness model that reliably quantifies the extent and amount of stretched crust crustal thicknesses together with fracture zone terminations reveal cobs that are significantly closer to the african and antarctic coasts than previously recognized correlation of fracture zone azimuths and identified cobs suggests antarctica began drifting away from africa at approximately 171 ma in a roughly sse direction an areal balancing method has been used to restore the crust to a uniform prerift thickness so as to perform a nonrigid reconstruction for both nonvolcanic and volcanic margins both margins reveal a trend of increasing extension from east to west our results suggest africa underwent extension of 60 120 km while antarctic crust was stretched by 105 180 km various models tested to determine the direction of extension during rifting suggest that antarctica moved away from africa in a wnw ese direction during the period between 184 and 171 ma prior to the onset of seafloor spreading

mesozoic and early cenozoic sediment influx and morphology of the mozambique basin abstract the mozambique basin is one of the oldest extensional sedimentary basins developed along the eastern african margin the basin hosts a continuous record of sediments since the jurassic separation of antarctica from africa the objectives of this study were to extend the regional stratigraphic framework north of the zambezi delta into the deep abyssal plains and review the early evolution of the mozambique basin using nine multi channel seismic reflection profiles we identify six major stratigraphic units that were deposited in jurassic early cretaceous late cretaceous paleogene neogene and quaternary times mesozoic sedimentation rates of 5 10 cm kyr and 1 3 cm kyr during the paleogene are calculated in the deeper basin the presence of shales in neighbouring wells on the shelf implies an euxinic environment in the rapidly subsiding basin until early cretaceous times the mesozoic sediments have a high seismic velocity that exceeds 4 5 km s except in a distinct early cretaceous low velocity 3 7 km s zone that may indicate the presence of undercompacted overpressured shales in spite of the fact that the zambezi catchment was much smaller in pre miocene times the high late cretaceous sedimentation rates can be attributed to rapid denudation of the african continent after a major tectonic uplift episode at approximately 90 ma increased sediment influx into the basin from the zambezi in late cretaceous times resulted in the formation of an elongated submarine fan lobe into the mozambique channel north of beira high strong north south bottom currents commenced within the channel in late cretaceous times forcing the aggradation of sediments on the southern flank of the lobe in addition we observe several current controlled sediment deposits in the deeper basin that are influenced by north south bottom currents low paleogene sedimentation rates are attributed to a sediment starved basin during a relative quiet tectonic phase onshore

making ends meet in gondwana retracing the transforms of the indian ocean and reconnecting continental shear zones interpretation of the detailed patterns of ocean floor transforms revealed by satellite altimetry enables the creation of the indian ocean to be described quantitatively as four consecutive plate tectonic regimes separated at 200 136 89 and 43 ma each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre existing plates regain their pre regime integrity progressive elimination of the indian ocean demonstrable as a smooth computer animation http www kartoweb itc nl gondwana leads to a refined re assembly of the continental fragments of central gondwana that is substantiated by new geological data a sequence of euler interval poles that describes the dispersal of the gondwana fragments time calibrated against available magnetic anomaly data is given the model requires a mid cretaceous position for india s southern tip about 1000 km south of madagascar prior to india s rapid northward migration

the southern mozambique basin the most promising hydrocarbon province offshore east africa recent offshore acquisition of approximately 12 800 km 7 950 mi of seismic reflection data with some gravity and magnetic profiles encompassing the southern half of the mozambique basin reveals new facets of the subsurface geology integrated interpretation of these new geophysical data with old well information allows the development of depositional and tectonic models that enhance the basin s hydrocarbon potential previous drilling was sparse however predating modern seismic technology and exploration philosophy and left the area classified as a frontier province despite some encouraging hydrocarbon shows previous operators considered the entire basin gas prone and immature recent interpretation suggests that the basin s geothermal history must have been more favorable than generally was inferred from present day gradients and oil prone source rocks may be buried below the sequences drilled during wildcatting also marine oil prone source rocks may be present furthermore the liquid hydrocarbon sourcing potential of the karroo coal measures should not be underestimated wildcatters have not in retrospect optimally positioned exploratory wells in the vicinity of ample structural closures nor have they drilled to sufficient depth owing to poorly resolved outdated seismic data and to erroneous age assignments to lava flows therefore the viability of prospects mapped along a major offshore extension of the east african rift system delineated by this new survey has not been adequately assessed finally a well remains to be drilled within the rift to assess the presence of reservoirs and the maturity richness and volume of source rock sequences not necessarily represented over the eroded structures drilled to date end page 399

plio quaternary sedimentation on the wilkes land continental rise preliminary results abstract the wilkes land continental rise is characterised by mounds and channels with approximately a north south elongation perpendicular to the margin proximal mound relief is up to 1000 m decreasing to about 300 m in the central part during the geophysical and geological survey conducted on in february march 2000 by the joint italian and australian wega project onboard r v tangaroa 11 piston cores were collected along two transects crossing the channel mound system all cores were logged for physical magnetic susceptibility and density and acoustic properties p wave velocity split cores were x rayed and samples were analysed for clay mineral assemblages chemical and micropaleontological diatoms foraminifera and nannofossils content glacial and interglacial intervals have been recognised in the sediment cores the interglacial facies consists of massive mud distinguished by a bioturbated massive mud occasionally with fine grained ice rafted debris ird and b structureless massive mud with abundant fine to coarse grained ird containing well preserved open ocean diatoms the glacial facies is represented by laminated mud with planar and or cross laminations with occasional isolated dropstones and rare poorly preserved sea ice diatoms the sharp boundary characterizing the limit between massive to laminated facies is interpreted to indicate a fast glacial onset in contrast the smooth passage presents from laminated to massive sediments indicates a gradual glacial waning recent down slope gravity flows have been identified in a turbidite a normally graded coarse grained sand recovered in the thalweg of jussie canyon and probably also in the massive debris facies from the steep side of mound a the massive debris is characterised by structureless and unsorted gravel and pebbles within a muddy matrix clay mineral assemblages and grain lithologies indicate a hinterland wilkes basin and continental shelf provenance for the terrigenous fraction

basalt geochemistry and tectonic discrimination within continental flood basalt provinces abstract continental flood basalts are usually regarded as a single tectonomagmatic entity but frequently quoted examples exhibit a variety of tectonic settings in one well studied classic flood basalt province the mesozoic karoo province of southern africa magmatism occurred in the following tectonic settings a continental rifting leading to ocean floor spreading in the south atlantic ocean etendeka suite of namibia b stretched continental lithosphere and rifting not leading directly to ocean floor formation lebombo suite of southeastern africa and c an a tectonic within plate continental setting characterized by an absence of faulting or warping lesotho highlands and karoo dolerites of south africa by means of spidergrams of the elements rb ba th nb k la ce sr nd p hf zr sm ti tb y v ni and cr uncontaminated tholeiites from c above i e the lesotho type continental flood basalts ltcfb are compared with mid ocean ridge basalts morb ocean island tholeiites oit and tholeiites and calc alkali basalts from subduction environments the comparison reveals the ltcfbs are geochemically distinct the differences are reflected in relative enrichments or depletions of the more incompatible elements rb ce to less incompatible elements ce y i e the overall slope of the spidergrams and in anomalous enrichments or depletions of one or more of the elements th k nb sr ti hf and zr the distinctive geochemical character of the lesotho ltcfbs is interpreted in terms of a lithospheric mantle source for the basalts this is supported by isotopic data there are no major geochemical differences between lesotho cfbs and basalts of the rift related etendeka and lebombo suites although the latter are somewhat enriched in rb ba and k however unlike the lesotho basalts the lebombo and etendeka basalts are associated with voluminous silicic volcanics or intrusive centres and late stage dolerites having morb oit i e asthenospheric geochemical characteristics the flood basalt silicic magmatism late stage dyke swarm association is characteristic of several rift or thinned lithosphere environments e g ethiopia skye eastern greenland but in many of these the flood basalts have ocean island basalt oit geochemical characteristics the lesotho type cfb geochemistry is exhibited by the grande ronde basalt of the columbia river group a possible subduction related flood basalt province and the basic rocks associated with mesozoic rifting in the north and south atlantic basalt geochemistry alone is unhelpful in determining the tectonic setting of cfbs although the rift related environments may be identified by the petrology and geochemistry of the whole igneous suite a two source model is proposed for the mantle derived basic rocks in rift related cfb provinces early enriched basalts are derived from the lithosphere and following pronounced lithospheric attenuation or rifting later morb like melts are emplaced from the rising asthenosphere the presence of both lesotho and oit type geochemical patterns in rift related cfbs suggests that the lithosphere exhibits different styles of enrichment

the initial gondwana break up a synthesis based on new potential field data of the africa antarctica corridor abstract the initial opening of the africa antarctica corridor in the heart of gondwana is still enigmatic due to missing information on the origin of major crustal features and the exact timing of the onset of the first oceanic crust in the jurassic therefore in 2014 new ship borne magnetic data were systematically acquired in the northern mozambique basin and across beira high which we merged with all accessible magnetic data in the mozambique basin herein distinct magnetic lineations are observed which allow a refined identification of a whole set of jurassic magnetic spreading anomalies constraining the timing of the onset of oceanization beginning at m38n 2n 164 1 ma in combination with high resolution potential field data from the conjugate antarctic margin well expressed fracture zones can be traced throughout the africa antarctica corridor and allow the precise rotation of antarctica back to africa the initial fit depicts striking continuations of onshore tectonic features across the plate boundaries taking onshore aeromagnetic data of both margins into account within a tight gondwana fit the beira high can be restored along the major sinistral namama orvin shear zone of the east african antarctic orogen the beira high represents a continental block which was detached from antarctica by 157 ma at the latest simultaneously the antarctic plate cleared the area of the mcp however the crustal nature of the southern mcp remains ambiguous the northern natal valley and the mozambique ridge consist of thick oceanic crust being emplaced between m26r m18n 157 1 144 ma and m18n m6n 144 131 7 ma respectively about the half of this crust was won from the antarctic plate by a series of southwards directed ridge jumps to the northern boundary of the explora wedge a refined kinematic break up model constrained by the most extensive magnetic dataset is presented describing consistently the initial opening of the africa antarctica corridor and the somali basin

cretaceous reconstructions of east antarctica africa and madagascar abstract some cretaceous reconstructions of east antarctica africa and madagascar overlap the mozambique ridge onto the margin of dronning maud land and others place madagascar west of the gunnerus ridge into the riiser larsen sea our m10ny 131 9 ma m0 120 4 ma 96 ma and 34y 83 ma marine free air gravity and topography reconstructions illustrate a solution to the overlap problem and also demonstrate that madagascar separated from antarctica east of the gunnerus ridge our reconstructions chronicle the growth of the conjugate mozambique and riiser larsen basins created at the southwest indian spreading ridge well defined spreading corridors identified by conjugate fracture zones and mesozoic magnetic anomaly identifications extend from one basin into the other we find that the eastern scarp of the mozambique ridge aligns with the astrid ridge and there is no room for madagascar west of the gunnerus ridge the overlap of the mozambique ridge is solved by taking into account the motion of an independent mozambique ridge microplate that existed from chron m11 to circa m2

the separation of madagascar and africa identification of a sequence of east west trending magnetic anomalies of mesozoic age in the western somali basin helps define the position of madagascar in the gondwana reconstruction the anomalies are symmetric about ancient ridge segments and are flanked to the north and south by the jurassic magnetic quiet zone the motion of madagascar relative to africa was from the north and began in the middle jurassic about the same time as the initial breakup of gondwanaland sea floor spreading ceased when madagascar assumed its present position in the early cretaceous

evolution of the glorieuses seamount in the sw indian ocean and surrounding deep somali basin since the cretaceous abstract little is known about the geological history of the glorieuses seamount including basic information about its age and origin related to the regional evolution of the southern tip of the somali basin this study focused on describing and reconstructing the long term stratigraphic evolution of the glorieuses seamount sw indian ocean to identify the mechanisms that have occurred through time to finally shape the emerged modern islands distinct terrace levels currently submerged along the flanks of the seamount and surrounding seamounts have already been interpreted as resulting from successive carbonate development and back stepping episodes over the last 62 myr new isotopic and biostratigraphic dating on the flanks of the seamount coupled with sequence stratigraphic interpretation of seismic profiles acquired in the adjacent basin provide new constraints for the late cretaceous and cenozoic vertical evolution of the seamount topped by carbonate platforms and sedimentation in the surrounding deep basin even if starved steep slopes prevent a straightforward source to sink continuity between the platform and the basin domains our findings propose a consistent chronostratigraphic framework for the identified seismic markers and sequences in the deep basin and discuss a long term geological model that includes the main driving factors behind deposition volcanic events subsidence vs uplift phases climate and hydro dynamism changes and their quantitative impact on the evolution of the isolated carbonate sedimentary system our results show that i the glorieuses volcanic seamount emerged from two successive late cretaceous magmatic pulses firstly during the turonian then during the maastrichtian ii at least two potential uplift phases are recognized during the tertiary paleogene and or the eocene and tortonian iii basinal sedimentation recorded an abrupt change probably related to major regional hydro dynamical changes in late eocene times in the western indian ocean iv the export of sediments from the platform towards the basin numerous gravity flow processes is strongly enhanced after the mid miocene and is probably linked to the onset of the asian monsoon winds and bipolar circulation finally the glorieuses seamount although located in the vicinity of the comoros islands appears to have a much longer history and is geologically more comparable to the nearby seychelles this long term study has enabled us to associate the glorieuses seamount with the sse nnw madagascar seychelles alignment rather than with the comoro hot spot evolution

the terrestrial impact cratering record approximately 130 terrestrial hypervelocity impact craters are currently known due to variations in preservation and in geologic knowledge this sample is biased towards young x 20 km craters on the cratons of australia europe including the former u s s r and north america the rate of discovery of new craters is 3 5 craters per year although modified by erosion terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies such as the moon terrestrial craters provide essential ground truth data on the geologic effects of impact and the subsurface structure of impact craters which can be used to constrain interpretations of lunar samples and models of crater formation due to erosion and its effects on form terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects these include shatter cones microscopic planar deformation features solid state and fusion glasses high pressure polymorphs and whole rock melting and vaporization shock recovery experiments indicate that these features occur over shock pressures of 5 gpa to x 100 gpa terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact induced fracturing they include gravity and magnetic lows and reductions in seismic velocity the gravity anomalies are seldom greater than 30 mgal due to the limiting effects of lithostatic pressure on fracturing at large complex craters the gravity signature may include a central relative gravity high due to uplift and short wavelength central magnetic anomalies due to a variety of processes much current work is focused on the effects of impact on earth evolution previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from cretaceous tertiary boundary sites as resulting from a major impact suggestions that other biological boundaries in the stratigraphie record are due to periodic impacts are not supported by time series analysis of the terrestrial cratering record by analogy with the lunar record and modelling of the effects of very large impacts it has been proposed that biological and atmospheric evolution of the earth could not stabilize before the end of the late heavy bombardment 3 8 ga ago the present terrestrial cratering rate is 5 4 2 7 10 15 km 2a 1 for a diameter 20 km this represents a local threat on historic time scales on a global scale a major impact sufficient to cripple human civilization severely will occur on time scales of 106 a

development of the mozambique and ruvuma sedimentary basins offshore mozambique two major sedimentary basins have been identified on the continental margin of mozambique mozambique basin and ruvuma basin the formation of the basins is related to the break up of gondwana and opening of the western part of the indian ocean the basins are relatively young having developed discordantly to the structural plan of gondwana sedimentary basins the history of the formation of the east african continental margin sedimentary basins within mozambique has been studied on the basis of the present day concept of gondwana break up and madagascar s drift with respect to africa two stages in the history of the east african basins can be recognized late gondwana and post gondwana the late gondwana stage 303 157 ma is typified by sedimentary and volcanogenic rocks of the karoo group the post gondwana stage 157 0 ma corresponds to the period of active gondwana break up and the formation of indian ocean marginal basins the mozambique basin occupies both central and southern parts of the coastal plain of mozambique extending onto the continental shelf and slope the sedimentary fill is composed of upper jurassic cretaceous and cenozoic rocks which discordantly overly the karoo basalts the upper jurassic occurs as continental red beds mostly distributed within buried grabens cretaceous rocks occur as terrigenous sediments of continental and marine genesis cenozoic deposits are of predominantly marine and deltaic origin the ruvuma basin situated in the north of mozambique is part of an extended east african marginal basin which includes parts of the coastal plains and continental margins of tanzania and kenya the basement of the basin is composed of crystalline and metamorphic rocks of pre cambrian age the sedimentary fill is represented by continental terrigenous karoo sediments marine and lagoonal jurassic deposits and marine and deltaic rocks of cretaceous and cenozoic age the main difference between the sedimentary fill of the mozambique and ruvuma basins is related to the changing sedimentary environment in the period of gondwana break up jurassic and early cretaceous when the drift of madagascar and sea floor spreading took place and the marine basin gradually extended southwards between the east african margin and madagascar from the late cretaceous on the sedimentary environment within both basins was similar the mozambique and ruvuma basins forming a single system on the east african continental margin the main stages of the basins development are illustrated by a series of palaeogeographic reconstruction maps

seismo stratigraphic analysis of the wilkes land continental margin east antarctica influence of glacially driven processes on the cenozoic deposition abstract multichannel seismic reflection data were collected from the wilkes land continental margin and particularly focusing on the lower rise area by the international wilkes basin glacial history wega project existing lower resolution seismic data also are used to understand the relationship between the basement and the sedimentary cover and to correlate the evolution of the rise and the shelf on the basis of the acoustic character and the internal geometry we recognise nine different sequences named wl s1 wl s9 from the deepest to the shallowest within the sedimentary section sequence wl s1 represents syn rift sediments deposited within tilted blocks of sedimentary crystalline and volcanic basement sequences wl s2 wl s9 represent the post rift sediments that show quite a complex architecture sequence wl s2 is a well developed wedge downlapping onto the break up unconformity sequences wl s3 wl s7 are parts of a margin prograding aggrading sequence during which large sediment ridges were deposited on the slope and rise in particular sequences wl s5 wl s7 began with the deposition of a turbidite fan system sequence wl s5 that developed in a braided channel levee complex wl s6 wl s7 dominated by downslope flows indirect correlation of the sequences wl s4 wl s6 with dsdp 269 about 600 km north of the study area suggests an early late miocene age sequences wl s8 and wl s9 represent the smoothing and filling of the pre existing morphology in a generally low energy environment with reduced bottom current activity during this time most of the sediment is deposited on the shelf and slope while the rise is generally starved differences in downslope current energy and in sediment load are interpreted to reflect variation of the terrigenous input from the shelf to the rise through time we suggest that channel levee systems on the rise reflect an increase in sediment supply from the continental shelf during the early miocene marking the growth of wet based temperate ice sheet on the near continent the youngest sequences on the rise and shelf reflect decreased sediment supply to the rise that may be related to the transition from a temperate to a polar glacial system

gondwana breakup via double saloon door rifting and seafloor spreading in a backarc basin during subduction rollback abstract a model has been developed where two arc parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback the resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double saloon doors about their hinges as movement proceeds and the two terranes rotate a gap begins to extend between them where a third rift initiates and propagates in the opposite direction to subduction rollback observations from the oligocene to recent western mediterranean the miocene to recent carpathians the miocene to recent aegean and the oligocene to recent caribbean point to a two stage process initially pairs of terranes comprising a pre existing retro arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents terrane docking reduces the width of the subduction zone leading to a second phase during which subduction to strike slip transitions initiate the clockwise rotated terrane is caught up in a dextral strike slip zone whereas the counterclockwise rotated terrane is entrained in a sinistral strike slip fault system the likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline by analogy with the above model a revised five stage early jurassic to early cretaceous gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the weddell sea area seven features are considered diagnostic of double saloon door rifting and seafloor spreading i earliest movement involves clockwise and counterclockwise rotations of the falkland islands block and the ellsworth whitmore terrane respectively ii terranes comprise areas of a pre existing retro arc fold thrust belt the permo triassic gondwanide orogeny attached to an accretionary wedge magmatic arc the falklands islands block is initially attached to southern patagonia west antarctic peninsula while the ellsworth whitmore terrane is combined with the thurston island block iii paleogeographies demonstrate rifting and extension in a backarc environment relative to a pacific margin subduction zone accretionary wedge where simultaneous crustal shortening occurs iv a ridge jump towards the subduction zone from east of the falkland islands to the rocas verdes basin evinces subduction rollback v this ridge jump combined with backarc extension isolated an area of thicker continental crust the falkland islands block vi well documented ew oriented seafloor spreading anomalies in the weddell sea are perpendicular to the subduction zone and propagate in the opposite direction to rollback vii the dextral strike slip gastre and sub parallel faults form one boundary of the gondwana subduction rollback whereas the other boundary may be formed by inferred sinistral strike slip motion between a combined thurston island ellsworth whitmore terrane and marie byrd land east antarctica

popigai crater origin and distribution of diamond bearing impactites about three decades ago a formerly unknown genetic type of natural diamonds was discovered in impact craters impact diamonds are currently known from a number of impact structures in europe asia and north america and it s likely that the number of finds will increase with time the popigai crater northern siberia where impact diamonds were first found was specifically investigated in terms of geology geophysics petrography and mineralogy large resources of industrial impact diamonds were discovered and these minerals were studied in detail authigenic impact diamonds occur in situ in shocked graphite bearing gneisses that are found as inclusions in impact melt rocks tagamites and suevites according to the observed transformation of coexisting minerals the lower estimated pressure of the coherent martensite transition of graphite to diamonds is 35 gpa impact diamonds inherit the original shape of graphite crystals and are composed of a polycrystalline structured aggregate of cubic and probably hexagonal carbon microcrystals 1 5 m across numerous properties of diamonds depend on the high density of defects in the crystal lattice allothigenic impact diamonds occur in rocks produced by the homogenization and solidification of impact melt which originated from the complete fusion of graphite bearing precursor gneisses these diamonds usually reflect the influence of the hot melt and are strongly corroded diamond bearing tagamites and suevites in the popigai crater interior occur as extended lens and sheets bodies and also as irregular small bodies diamond distribution depends on the original abundance of precursor graphite in the target rocks on the superimposed shock metamorphic zonation and on the character of the ejection of shocked and melted material along different trajectories and azimuths this has resulted in radial and concentric inhomogeneities in diamond distribution in the crater interior on a second order the distribution depends on the scale of melt contamination by clasts and fragments and by the duration of cooling of certain melt bodies and their constituents enrichment in diamonds at the margins of thick tagamite sheets is the result of rapid cooling which prevents combustion of diamonds a positive correlation between diamond content and the amount of phosphorus pentoxide in impactites indicates links to c and p probably in organic matter of the primary sedimentary rocks which were subjected to granulitic metamorphism 2 4 ga ago and melted at the time of impact 35 7 ma ago

a geotectonic history of the northern mozambique basin including the beira high a contribution for the understanding of its development abstract the interpretation of a comprehensive two dimensional 2d seismic reflection data set discloses several rifting events for a typical passive rifted margin two major phases have been identified rift i phase is in agreement with the initial rifting of gondwana postulated for the early jurassic this rift resulted in break up stage 1 governed by a north eastern motion of antarctica along the reactivated pebane shear zone indications for lava flows were identified in the seismic profiles along the offshore zambezi depression they form a link between early rifting the initial break up and early sea floor spreading the nature of these lava flows may be associated with the emplacement of thick volcanic dykes during post rift magmatism that occurred when the antarctica plate with the beira high drifted dextrally from the west to east until the mid jurassic times it is more likely that the break up in stage 1 resulted from high tension due to strain relief of rift i phase above all the extensional deformation occurred in a narrow rift mode therefore the v shape of the offshore zambezi depression suggests a possible rift failure structure this is best explained by the reeves and de wit model 2000 this model postulates that the motion of antarctica changed to southward direction at around 170 ma consequently a rift jump from the offshore zambezi depression in the northwest to the south eastern edge of the beira high occurred and rift ii phase may have started leading to the break up in stage 2 during this stage rift ii phase the extension migrated towards the east thus thinning the crust and exhuming the sub continental mantle in the continental ocean transition zone the rift ii phase shows a sequence of half graben morphologies confining the syn rift infill that is subdivided in three units syn rift i syn rift ii and rift sag all three units appear to have developed under minor extensional regimes in the crust evidenced by gently dipping low angle detachment faults with respect to the presence of the two rift phases it is deduced that break up and sea floor spreading are diachronous within rift i and rift ii segments

characterization of sills associated with the u reflection on the newfoundland margin evidence for widespread early post rift magmatism on a magma poor rifted margin author posting the authors 2010 this article is posted here by permission of john wiley sons for personal use not for redistribution the definitive version was published in geophysical journal international 182 2010 113 136 doi 10 1111 j 1365 246x 2010 04635 x

the jurassic history of the africa antarctica corridor new constraints from magnetic data on the conjugate continental margins abstract finding the best fit for east and west gondwana requires a detailed knowledge of the initial jurassic movements between africa and antarctica this study presents results of systematic and densely spaced aeromagnetic measurements which have been conducted in 2009 2010 across the astrid ridge antarctica and in the western riiser larsen sea to provide constraints for the early seafloor spreading history between both continents the data reveal different magnetic signatures of the northern and southern parts of the astrid ridge which are separated by the astrid fracture zone the southern part is weakly magnetised corresponding to the low amplitude anomaly field of the southwestern riiser larsen sea in contrast the northern astrid ridge bears strong anomalies of positive value furthermore several sets of trends are visible in the data in the mozambique channel we extended the existing magnetic spreading anomaly identifications combined with the spreading anomalies in the conjugate riiser larsen sea they were used to establish a new model of the relative movements of africa and antarctica after the breakup of gondwana in jurassic times a detailed model for the emplacement of the mozambique ridge is now incorporated the model postulates a tight fit between africa and antarctica and two stages of breakup the first of which lasting until 159 ma m33n during this stage antarctica rotated anticlockwise with respect to africa the grunehogna craton cleared the coastal plains of mozambique to a position east of the mozambique fracture zone the southern astrid ridge is interpreted to consist of oceanic crust also formed during this first stage prior to the riiser larsen sea during the second stage antarctica moved southward with respect to africa forming the mozambique basin and the conjugate riiser larsen sea the mozambique ridge and the northern natal valley were formed at different spreading centres being active subsequently

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

geology and petroleum potential of adelie coast margin east antarctica the few rock outcrops on adelie coast wilkes land consist mainly of precambrian plutonic rocks and metasediments on the continental margin several multichannel seismic surveys including the 1982 ifp survey reveal the presence of a thick sedimentary basin especially beneath the outer continental shelf and upper slope where it may exceed 6000 m thin basin results from the creation and evolution of a continental margin initiated some 100 ma from the separation of australia and antarctica beneath the outer shelf which is 400 500 m deep the sedimentary series consist of four units separated by three major unconformities 1 a predrift unit including a precambrian basement possible paleozoic and early mesozoic sediments and a mesozoic syn rift sequence 2 an upper eocene to oligocene unit in a shallow marine environment and 3 a neogene glacial prograding unit the predrift and early postrift units are considered to be a promising target with reference to other passive margins although no major hydrocarbon accumulation has been discovered as yet on the australian conjugate margin

anomalous bathymetry and palaeobathymetric models of the mozambique basin and riiser larsen sea abstract in this study we introduce a palaeobathymetric model for the conjugate mozambique basin and riiser larsen sea built by employing backstripping techniques compensating for dynamic topography and plate motions the model is presented at 0 2 0 2 grid resolution making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean at the present day the seafloor next to the mozambican continental margin is around 300 m shallower and that in the central mozambique channel is almost 1300 m shallower than their conjugate areas or the predictions of oceanic thermal subsidence models the cause of this anomalous depth is difficult to determine confidently because of sparse data in particular concerning sediment thickness and because of the wide range of amplitudes in modelled present day dynamic topography the distribution of shallow seafloor suggests that it might be attributed to the presence of thicker than usual oceanic crust which in turn can be attributed to the paleogene passage of the quathlamba plume beneath the basin we portray these effects in our palaeobathymetric models in contrast the riiser larsen sea has experienced fairly stable subsidence since its formation in jurassic times with only slight observable changes attributable to the onset of antarctic glaciation and during the middle miocene climate transition both basins display flexure over half wavelengths of 60 80 km with amplitudes of 1500 m towards their continental margins this plays an important role in models of palaeobathymetry for times older than 100 ma near the margins isolated areas of transitional or debatable crustal composition including beira high and gunnerus ridge are depicted to subside in a similar fashion to oceanic crust further into the indian ocean oceanic lithosphere younger than 100 ma on both plates has subsided to depths that are typical of thermal subsidence models finally the new palaeobathymetry had distinct consequences for the current systems in the young southern ocean during the time periods the onset of coast parallel bottom currents and associated contourite deposition in the mozambique channel at palaeo water depths of 3500 4000 m may be a consequence of either an opening of a deep water passage into the south atlantic between southwest indian ridge and agulhas plateau or into the tethys ocean in the late cretaceous

yakutites are they impact diamonds from the popigai crater abstract yakutites are coarse up to 15 mm or larger aggregates dispersed for more than 500 km around the popigai meteorite crater they share many features of similarity with impact diamonds found inside the crater in elemental and phase compositions texture and optical properties as revealed by x ray photoelectron spectroscopy x ray diffraction and optical spectroscopy raman absorption luminescence and microscopic studies the n3 vibronic system appearing in the luminescence spectra of popigai impact diamonds pids indicates a presence of nitrogen impurity and a high temperature annealing of diamonds that remained in the crater after solid phase conversion from graphite yakutites lack nitrogen vacancy centers as signatures of annealing which may indicate quenching at the time of ejection thus both pids and yakutites originated during the popigai impact event and yakutites were ejected to large distances

the davie fracture zone and adjacent basins in the offshore mozambique margin a new insights for the hydrocarbon potential abstract the interpretation of 2 d seismic reflection data provides a modern structural framework including hydrocarbon potential in the present day stratigraphic and structural traps of both the davie fracture zone and the adjacent nacala and angoche basins possible stratigraphic traps were identified in submarine fan and channel depositional environments during cretaceous to tertiary times structural traps are mostly defined within compressional structures formed by a variety of fault related folds and rift grabens within the jurassic and cretaceous successions the nacala and angoche basins form two depressions separated by the davie compressional zone this compressional structure is a prominent interior high running approximately north south an event of transpression and contraction characterizes the main tectonic setting commonly hosting several detached compressional structures along the western edge of the transform zone both basins are associated with the late jurassic early cretaceous rifting during the opening of the mozambique channel the angoche basin is proposed here to have formed by the earliest stage of break up in mid jurassic time the basin is bounded landward by the angoche volcanic zone a dyke swarm branch oriented n64dege forming part of the karoo and dronning maud land magmatism at c 180 ma subsequent rifting and break up led to the drift of east gondwana southwards along the dextral strike slip davie fracture zone at about 150 ma tithonian east gondwana appears to have rotated slightly clockwise about a pivot in the proximity of the angoche basin leading to extension and rifting in the rovuma basin to the north of the pivot point and compression west of the davie fracture zone to the south consequently the eastern boundary of the angoche basin was compressed developing a typical growth wedge of massive thrust imbrication structures while extensional tectonics created several depressions and rift grabens forming the nacala and quirimbas basins basin stratigraphy is interpreted along seismic reflection lines and correlated to the regional stratigraphic information and wells from the zambezi delta and rovuma basins

the flin flon paleosol revisited a ca 1 85 ga paleosol developed on seafloor altered mafic rocks is preserved beneath continental sandstones and conglomerates of the missi group near flin flon manitoba previous work has focused

mesozoic rifting evolution of sw gondwana a poly phased subduction related extensional history responsible for basin formation along the argentinean atlantic margin abstract the opening of the south atlantic in the early cretaceous was the final stage of the complex rifting history of sw gondwana in this contribution we reassess the chronology of mesozoic basin formation in southern south america and africa and integrate it in the long term breakup history of sw gondwana triassic rifting is characterized by intracontinental rifting in africa karoo i phase and retro arc extension on the sw margin of gondwana in the early jurassic the impingement of the karoo plume triggered rifting in eastern africa producing the karoo ii basins and the colorado and salado basins on the argentinean shelf east africa rifting ultimately lead the breakup of eastern from western gondwana in the middle jurassic in patagonia the austral malvinas and other related basins formed in association with the synextensional emplacement of the chon aike magmatic province in the patagonian retro arc in the late jurassic the rocas verdes back arc basin opened in southern patagonia while oblique rifting in the core of the late paleozoic gondwanides orogen produced the outeniqua and rawson valdes basins the south atlantic rift initiated in the early cretaceous associated with present day e w extension rifting occurred diachronically from south to north initiating in the previously thinned rawson valdes outeniqua segment a precursor oblique rift system and a larger degree of extension in this segment could explain the lack of seaward dipping reflectors sdr south of the colorado cape fracture zones rifting and sdr emplacement occurred progressively to the north along different rift segments producing strongly asymmetric conjugate margins

geophysical evidence for the crustal variation and distribution of magmatism along the central coast of mozambique abstract for our understanding of the timing and geometry of the initial gondwana break up still a consistent image of the crustal composition of the conjugated margins of central mozambique and antarctica and the location of their continent ocean boundaries is missing in this regard a main objective is the explanation for the source of the different magnetic signature of the conjugate margins based on a revised investigation of wide angle seismic data along two profiles across the mozambican margin by means of an amplitude modelling this study presents the crustal composition across and along the continental margin of central mozambique supported by 2d magnetic modelling the results are compared to the conjugate margin in antarctica and allow new conclusions about their joined tectonic evolution an observed crustal diversity between the north eastern and south western parts of the central mozambican margin testifies to the complex break up history of this area conspicuous is the equal spatial extent of the hvlcb along the margin of 190 215 km the onset of oceanic crust at the central mozambican margin is refined to chron m38n 2n 164 1 ma magnetic modelling supports the presence of reversed polarized sdrs in the continent ocean transition that were mainly emplaced between 168 5 and 166 8 ma m42 m40 inferred sdrs in the riiser larsen sea might be emplaced sometime between 166 8 and 164 1 ma m39 m38 but got overprinted by normal polarized intrusions of a late stage of rift volcanism causing the opposite magnetic signature of the conjugate margins the distribution of the magmatic material along the central coast of mozambique clearly indicates the eastern extension of the north eastern branch of the karoo triple rift along the entire margin the main magmatic phase affecting this area lasted for at least 12 myr between 169 and 157 ma followed by the cease of the magmatism perhaps due to the relative southwards motion of the magmatic centre