tsunami of december 26 2004 on the southwest coast of india post tsunami geomorphic and sediment characteristics this paper discusses the impact of the december 26 2004 tsunami on the geomorphic features and sediment characteristics along the southwest coast of india the data used include field observations made after the tsunami and the inferences drawn from the satellite imagery taken before and after the tsunami sediment samples collected from the inner shelf beach and estuarine environments were analyzed to understand post tsunami changes in grain size characteristics the tsunami eroded and transported landwards significant volumes of distinct black sands rich in heavy minerals from the shelf onto the beaches of the kerala region and up to 500 m inland of the present coast

late archaean to early proterozoic granitoid magmatism and high grade metamorphism in the central limpopo belt south africa the central zone of the limpopo belt in southern africa has previously been interpreted as a segment of archaean crust which experienced its main deformation and metamorphism around 2 7 ga ago we report new single zircon u pb and pb pb ages for granitoid gneisses supracrustal rocks and anatectically derived granitic melt patches in the area around messina south africa the sand river gneiss is a composite suite of tonalitic to trondhjemitic rocks with protolith ages between 2 6 and 3 2 ga the singelele gneiss a heterogeneous granodioritic to quartz monzonitic rock has protolith ages between 2 55 and 2 58 ga since both the sand river and singelele gneisses experienced polyphase high strain ductile deformation this must have occurred later than 2 55 ga ago granulite facies pelitic gneisses of the beit bridge complex contain abundant spherical multifacetted zircons which reflect new zircon growth near or at the peak of metamorphism these zircons provide ages with a mean at 2026 5 6 3 ma which is interpreted as reflecting a high p t event 10 kbar 825 25 c granitic melt patches in the metapelites as well as in the sand river gneiss and anatectic granites are probably related to rapid near isothermal decompression to below 3 5 kbar and 600 750 c these rocks contain new magmatic zircons which yielded a mean age of 2005 6 4 4 ma and probably reflect a crustal melting event resulting from rehydration of the granulitic assemblage our zircon data support previous suggestions for only one single granulite facies event in the central zone and we suggest that this event occurred c 2027 ma ago since most of the deformation seen in the gneisses of the messina area must have occurred later than 2 55 ga ago it is likely that the limpopo orogeny at least in the central zone is not an archaean event but took place in the early proterozoic

complexity of characterizing mafic ultramafic remnants of archean layered complexes in high grade terranes the scenario from motloutse complex southwestern zimbabwe craton abstract mafic to ultramafic rocks of archean layered complexes in high grade terranes typically occur as inclusions closely associated with supracrustal rocks in granitoid gneiss the reconstruction of the original stratigraphy and sequence of events related to archean layered complexes is complicated by the fragmental occurrence and effect of overprint event s the case study presented here highlight these issues from the motloutse complex terrane southwestern zimbabwe craton peridotite pyroxenite and gabbro leucogabbro anorthosite form separate bodies closely associated with amphibolite in the lechana area they occur as inclusions within 2 65 ga tonalite gneiss amphibolite is massive has a stratiform occurrence and is folded with gabbro leucogabbro anorthosite intruding along the fold limbs rare amphibolite xenoliths occur in gabbro leucogabbro anorthosite and peridotite pyroxenite modal and cyclic layering is well preserved in the mafic and ultramafic intrusive bodies anatectic and alkali metasomatic overprints the later related to shear deformation locally affected the lechana rocks the late stage events are contemporaneous and is dated by the 2 0 ga 2013 18 ma u pb zircon overgrowth age amphibolite exhibit prominent granoblastic polygonal fabric defined by amphibole plagioclase gabbro leucogabbro anorthosite are locally gneissic the different mafic rocks are variably affected by overprint events and contain garnet related to anatectic overprint and epidote related to metasomatic overprint peridotite pyroxenite exhibits no metamorphic re equilibration textures but are serpentinized and host widespread magnetite rich layers amphibolite and associated gabbro have conspicuous sulphide concentration up to 5 modal and include pyrrhotite chalcopyrite replaced by covellite pyrite and pentlandite no magnetite or sulphide concentration occur with leucogabbro anorthosite whole rock geochemical characteristics of the amphibolites are similar to tholeiitic basalts but that of the peridotite pyroxenite and gabbro leucogabbro anorthosite indicate different lineage the suggested model considers amphibolite as a stratiform meta basalt which was folded during an earlier deformation event based on the presence of meta basalt amphibolite roof pendants on top of both mafic and ultramafic intrusions it is argued that the peridotite pyroxenite and gabbro leucogabbro anorthosite were emplaced into archean oceanic crust the mafic ultramafic intrusions could either be part of a single mesoarchean layered complex or represent two different suites in view of the restricted occurrence lack of interlayering different pyroxene affinities clinopyroxene in gabbro and orthopyroxene in peridotite pyroxenite and wide compositional gap between mafic and ultramafic intrusions we favour the later scenario peridotite pyroxenite interpreted as part of a mesoarchean layered ultramafic complex intruded the mafic volcanics layered gabbro leucogabbro anorthosite also intruded into the basaltic rock separate from the ultramafic complex the intrusion of protolith of the tonalite gneiss then dismembered the mafic and ultramafic sequences the results of the present study highlight the need for detailed evaluation of spatially associated mafic ultramafic rock remnants in high grade terranes they need not be genetically related but could be part of different magmatic episodes such exercise has implications in properly understanding the geodynamic setting of formation of these archean upper mantle derived rocks the current arguments polarised between two end member settings plate margin versus intraplate setting

partial melting of metagreywackes part ii compositions of minerals and melts a series of experiments on the fluid absent melting of a quartz rich aluminous metagreywacke has been carried out in this paper we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe this analytical work includes biotite plagioclase orthopyroxene garnet cordierite hercynite staurolite gedrite oxide and glass over the range 100 1000 mpa 780 1025 c biotites are na and mg rich with ti contents increasing with temperature the compositions of plagioclase range from an17 to an35 with a significant orthoclase component and are always different from the starting minerals at high temperature plagioclase crystals correspond to ternary feldspars with or contents in the range 11 20 mol garnets are almandine pyrope grossular spessartine solid solutions with a regular and significant increase of the grossular content with pressure all glasses are silicic sio2 67 6 74 4 wt peraluminous and leucocratic feo mgo 0 9 2 9 wt with a bulk composition close to that of peraluminous leucogranites even for degrees of melting as high as 60 vol with increasing pressure sio2 contents decrease while k2o increases at any pressure the melt compositions are more potassic than the water saturated granitic minima the h2o contents estimated by mass balance are in the range 2 5 5 6 wt these values are higher than those predicted by thermodynamic models modal compositions were estimated by mass balance calculations and by image processing of the sem photographs the positions of the 20 to 70 isotects curves of equal proportion of melt have been located in the pressure temperature space between 100 mpa and 1000 mpa with increasing pressure the isotects shift toward lower temperature between 100 and 200 mpa then bend back toward higher temperature the melting interval increases with pressure the difference in temperature between the 20 and the 70 isotects is 40 c at 100 mpa and 150 c at 800 mpa the position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process a comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 mpa the difference in fertility between pelites and greywackes decreases with decreasing pressure a review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust greywackes pelites or orthogneisses produces only peraluminous leucogranites more mafic granitic compositions such as the various types of calk alkaline rocks or mafic s type rocks have never been obtained during partial melting experiments thus only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments other types of granites involve other components or processes such as restite unmixing from the source region and or interaction with mafic mantle derived materials

leucogranites of the teton range wyoming a record of archean collisional orogeny abstract leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages this study describes leucogranitic gneisses associated with an archean collisional orogeny preserved in the teton range of northwestern wyoming usa these leucogneisses formed at 2 68 ga and initial nd isotopic compositions suggest they are derived from relatively juvenile sources two distinct groups of leucogneisses both trondhjemitic are identified on the basis of field relations petrology and geochemistry the webb canyon gneiss forms large sheet like bodies of hornblende biotite trondhjemite and granodiorite this gneiss is silica rich sio2 70 80 strongly ferroan comparatively low in alumina and is characterized by high zr and y low sr and high ree contents that define seagull shaped ree patterns the bitch creek gneiss forms small sills dikes and plutons of biotite trondhjemite silica zr y and ree are lower and alumina and sr are higher than in the webb canyon gneiss these differences reflect different melting conditions the webb canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down accounting for the low alumina high feo high silica content and observed trace element characteristics the bitch creek gneiss formed by h2o excess melting in which plagioclase breaks down leaving an amphibole rich restite producing magmas higher in alumina and sr and lower in feo and hree both melt mechanisms are expected in collisional environments dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust and water excess melting may occur when collision places a relatively cool hydrous lower plate beneath a hotter upper plate the archean leucogranitic gneisses of the teton range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites the difference in leucogranite composition reflects the geochemically immature archean crust that partially melted in the teton range compared to the more geochemically evolved rocks typically involved in younger collisional orogens

the timing of sub solidus hydrothermal alteration in the central zone limpopo belt south africa constraints from titanite u pb geochronology and ree partitioning abstract in the central zone of the limpopo belt south africa palaeoproterozoic granulite facies metamorphism was superimposed on an earlier archaean orogenic history previously determined ages of 2030 2020 ma obtained from high temperature chronometers zircon garnet monazite are generally thought to provide the best estimate of the peak of palaeoproterozoic granulite facies metamorphism in the central zone whereas ages as young as 2006 ma from late melt patches suggest that temperatures remained above the wet solidus for an extended period we present a new mc icp ms 207 pb 206 pb age of 2030 9 1 5 ma for titanite found in amphibolite to greenschist facies alteration zones developed adjacent to quartz vein systems and related pegmatites that cut a strongly deformed central zone metabasite this age could potentially date cooling of rocks at this locality to temperatures below the wet solidus alternatively the titanite could be inherited from the metabasite host and the age determined from it date the peak of metamorphism integration of the geochronology with la icp ms trace element data for minerals from the metabasite the hydrothermal vein systems and comparable rocks elsewhere shows that the titanite formed during the amphibolite facies hydrothermal alteration not at the metamorphic peak or during the greenschist facies phase of veining this suggests that high grade rocks in the central zone have cooled differentially through the wet solidus and provides timing constraints on when palaeoproterozoic reworking in the central zone began this study illustrates the potential of combined geochronological and high resolution geochemical studies to accurately match mineral ages to distinct crustal processes

mafic magma intraplating anatexis and hybridization in arc crust bindal batholith norway distinct with nd and o in the migmatites from 7 6 to 9 6 the dioritic velfjord plutons 448 ma were emplaced into and from 10 9 to 13 5 and in the contact granites regional migmatitic metapelitic and metacarbonate rocks at midfrom 5 2 to 7 5 and from 9 6 to 12 3 respectively crustal levels corresponding to pressures of 700 mpa exthus the contact granites could have a source that is isotopically humation to 400 mpa began while the migmatites were in a distinct from but mineralogically similar to the diatexites or they partly molten state with increasing proximity to the plutons could result from mixing of magma similar to the high k leucosomes regional stromatic migmatites change to diatexite and diatexitic with dioritic magmas mass balance calculations are consistent dikes are common within 500 m of the contacts we interpret these with the latter interpretation with proportions of granitic to dioritic relationships to indicate that heat from the plutons resulted in contact magmas from 7 1 to 7 3 emplacement and solidification of the migmatization in a zone up to 1 km wide typical residual dioritic plutons provided zones of structural anisotropy along which mineralogy in the diatexites is plagioclase quartz biotite high k leucosome magmas and contact granite magmas collected garnet sillimanite k feldspar consistent with biotite these magmas were injected by additional dioritic magma and dehydration melting podand dike like leucosomes consist of two further hybridized because the solidi of the plutons were several types earlier high k granitic ones with mineral assemblages hundred degrees higher than that of the granitic magmas the pluton identical to the migmatites and later low k tonalitic ones in which walls acted as long lived hot rigid surfaces along which magmas sillimanite is sparse and garnet absent the high k leucosome collected and migrated magmas can be explained by biotite dehydration melting at 700 mpa within the aureole mafic magmas were locally injected into and hybridized with the diatexites and the high k leucosome

contact partial melting of granitic country rock melt segregation and re injection as dikes into ferrar dolerite sills mcmurdo dry valleys antarctica numerous interconnected granitic dikes 530 cm in width and hundeds of meters in length cut ferrar dolerite sills of the mcmurdo dry valleys antarctica the source of the granitic dikes is partial melting of granitic country rock which took place in the crust at a depth of about 2 3 km adjacent to contacts with dolerite sills sustained flow of doleritic magma through the sill generated a partial melting front that propagated into the granitic country rock granitic partial melts segregated and collected at the contact in a melt rich nearly crystal free reservoir adjacent to the initial dolerite chilled margin this dolerite chilled margin was subsequently fractured open in the fashion of a trapdoor by the granitic melt evacuating the reservoir to form an extensive complex of granitic dikes within the dolerite sills at the time of dike injection the dolerite was nearly solidified unusually complete exposures allow the full physical and chemical processes of partial melting segregation and dike formation to be examined in great detail the compositions of the granitic dikes and the textures of partially melted granitic wall rock suggest that partial melting was characterized by disequilibrium mineral dissolution of dominantly quartz and alkali feldspar rather than by equilibrium melting it is also unlikely that melting occurred under water saturated conditions the protolith granite contains only 7 vol biotite and estimated contact temperatures of 900 9508c suggest that melting was possible in a dry system granite partial melting under closed conditions extended tens of meters away from the dolerite sill yet melt segregation occurred only over less than one half a meter from the dolerite chilled margin where the degree of partial melting was of the order of 50 vol this segregation distance is consistent with calculated length scales expected in a compaction driven process we suggest that the driving force for compaction was differential stress generated by a combination of volume expansion as a result of granite partial melting contraction during dolerite solidification and relaxation of the overpressure driving dolerite emplacement on a purely chemical basis the extent of melt segregation necessary under fractional and batch melting to match the rb concentrations between melt and parent rock is a maximum of 48 and 83 vol melt respectively

evidence of tsunami sedimentation on the southeastern coast of australia in coastal regions the highest magnitude storms cannot always be invoked to account for large scale anomalous sediment features any coastline in the pacific ocean region can be affected by tsunamis including australia which historically lacks evidence of such events geologically tsunamis along the new south wales coast have deposited a suite of holocene features that consist of anomalous boulder masses either chaotically tossed onto rock platforms and backshores or jammed into crevices highly bimodal mixtures of sand and boulders and dump deposits consisting of well sorted coarse debris in addition many coastal aboriginal middens were distributed by such events within estuaries tsunamis have left a record of stranded run up ridges that have been interpreted mistakenly as cheniers dating of such deposits indicates that several events have affected this coastline since 3000 bp in contrast to storm waves tsunamis can leave a depositional imprint of their passage characterized by chaotic sort

geochronological evidence for an extension of the northern lobe of the bushveld complex limpopo province south africa abstract we have conducted the first geochronological study of the ultramafic mafic succession the waterberg project located in the southern marginal zone of the limpopo belt north of the northern lobe of the bushveld complex using u pb dating on zircons extracted from both mineralized reefs as well as on detrital zircons of the waterberg group unconformably overlying the mafics this contribution is the first in a series of publications describing the well mineralized succession and will therefore give an overview of the local geology u pb baddeleyite ages for the main mafic sill intruding the area supplement the data the succession is extremely well mineralized and therefore of interest to the wider geological community the intrusion ages for the lobe are 2059 3 and 2053 5 ma and within error coeval with the intrusion ages of the bushveld complex detrital zircon age probability density distributions indicate a maximum age of deposition of c 2045 ma for the waterberg group and show abundant peaks of archean age paleoproterozoic zircons are interpreted to represent zircon from the detritus of the now eroded roof rocks of the lobe while the archean zircons are most likely sourced from the limpopo complex to the northeast the major dolerite sill intruding the project area has been confirmed to belong the umkondo igneous province with a baddeleyite age of 1125 5 ma the combination of these new age dates local geology and existing literature is used to argue that i the ultramafic mafic succession is related to the bushveld complex ii a significant unconformity is present between igneous rocks and the overlying sediments and iii the area was exposed to a level of paleoproterozoic tectonism not previously observed in the bushveld complex

mesoarchean ttg magmatism from the northeastern margin of the kaapvaal craton southern africa arguments for an exotic terrane remnant of pilbara craton abstract high grade terranes along archean cratonic margins either represent remobilized equivalents of the adjacent low grade domain or an exotic entity which accreted to the developing craton this study addresses this debate for the southern marginal zone high grade terrane along the northeastern margin of the kaapvaal craton the hout river shear zone separates the high grade terrane from the adjacent low grade pietersburg block of the kaapvaal craton tonalite trondhjemites of the baviaanskloof gneiss unit constitute the dominant rock in the southern marginal zone both pyroxene bearing and pyroxene absent variants occur locally the granitoids are affected by anatectic and metasomatic overprints magmatic textures are better preserved in the massive granitoids u pb zircon analyses of two orthopyroxene bearing granitoids gave mesoarchean crystallization ages 3088 11 ma massive 3121 9 ma banded however overprint ages differ with 2706 50 34 ma from the massive variety and 1925 19 ma 1976 11 ma from the banded variety the syn tectonic 2 71 ga is interpreted as metamorphic overprint age while the post tectonic 2 ga represent age of local overprint available geochemical data on the baviaanskloof granitoids are similar to archean ttgs a possible spatial temporal transition from 3 13 ga low pressure through 3 12 2 98 ga medium pressure to 2 92 ga high pressure ttg is delineated from the northwest towards the southeastern southern marginal zone this trend is compatible with the southward directed polarity of accretion events recognised in the adjacent low grade pietersburg block we argue that the northeastern margin of the kaapvaal craton north of the hout river shear zone is an exotic terrane because 1 the baviaanskloof granitoid event 3 1 2 9 ga with peak at 3 1 ga is older than the accretion episodes 2 97 2 92 ga with peak at 2 95 ga and 2 87 2 84 ga with peak at 2 86 ga in the adjacent pietersburg block 2 the younger 2 86 ga event occurs closer to the hout river shear zone while the older 2 95 ga event was away from it and 3 contemporaneous 3 1 3 0 ga detrital zircons are absent in greenstone belts of the pietersburg block that are proximal to the hout river shear zone possible connection to rocks of similar age from the pilbara craton as part of the vaalbara supercraton is explored

the bushveld metamorphic aureole in the potgietersrus area evidence for a two stage metamorphic event the metamorphic aureole of the bushveld complex in the potgietersrus area was created in a two stage metamorphic event in the first stage which was related to the intrusion of the lower zone magma maximum temperatures of 750 degrees c were attained at 1 5 kb pressure pressure estimates are based on the rare cordierite olivine orthopyroxene or spinel or quartz assemblage at lower temperatures the cordierite chloritoid assemblage also appears to have been stable equilibrium temperatures and pressures during the second stage which was brought about by the intrusion of more voluminous gabbroic liquids that gave rise to the upper critical main and upper zones were considerably higher at 900 degrees c and 4 to 5 kb pressure geothermobarometry is based on the garnet cordierite orthopyroxene biotite clinopyroxene plagioclase quartz and cordierite spinel or sillimanite or corundum or orthopyroxene or olivine assemblages the temperature dependence of the fe mg exchange reaction between cordieritc and spinel was used as the basis of a geothermometer calibrated against published data for natural mineral assemblages high alumina 44 wt low silica 36 wt and low alkali pelites from the timeball hill formation also originated during this stage through the removal of about 65 percent granitic melt from normal pelites the maximum pressures calculated for the second stage of the metamorphic event are about 2 kb higher than the lithostatic pressure that could have been exercised by the presently exposed succession of layered and roof rocks this difference can be accounted for by a directed stress contribution for which there is evidence in the form of a large fold in the floor rocks and by assuming that the lithostatic pressure during the second stage of the metamorphic event was about 1 0 kb higher than the value suggested by the current field relations brought about by superincumbent load of layered rocks

late holocene evolution of the southwestern donana national park guadalquivir estuary sw spain a multivariate approach four phases are distinguished in the late holocene evolution of the southwestern donana national park sw spain based on a multidisciplinary analysis of the sediments present in drill cores in the oldest phase 2400 2500 cal yr bp a coastal lagoon the roman lacus ligustinus was recognized in the central part of this area partly closed by the donana spit and limited by fluvial levees the following phase 2400 2200 cal yr bp is characterized by high energy events which caused the breakthrough of the donana spit and the creation of new littoral strands in the inner areas in the third phase 2200 2050 cal yr bp this new outlet was closed coinciding with the progradation of the donana spit the last phase 2050 cal yr bp recent comprises three periods a an unstable period 2050 1950 cal yr bp with the deposit of cheniers over the previous levees b an infilling period with a diminution of the marine influence and c the appearance of temporary ponds between the emerged levees and cheniers

on the valency state of radiogenic lead in zircon and its consequences in zircon u pb systematics extreme robustness up to the temperatures of granulite facies and anatexis contrasts with apparently easy loss of radiogenic pb at low temperatures often without any metamorphic event being in evidence here we propose that this paradoxical behaviour can be understood with the hypothesis that radiogenic pb in zircon is tetravalent we review data and arguments in favour of this hypothesis diffusion profiles calculated for pb sup 2 in a 25 micro m radius zircon xenocryst in a melt at 1000 c combined with the incompatibility of pb sup 2 or for a zircon core inside a younger zircon rim at this temperature show age effects that should have been observed in sims dating further in zircon evaporation as well as in leaching experiments common pb is generally released preferentially to radiogenic pb after removal of less radiogenic pb the evaporation record generally shows pure radiogenic pb during the final evaporation steps the distribution of residual pb in a leached titanite revealed by pixe is similar to that of ti lastly xanes spectra of a 1 ga old titanite predominantly radiogenic pb and an alpine one predominantly common pb are significantly different although the former does not resemble that ofmore pbo sub 2 the arguments why radiogenic pb should be tetravalent are based on analogies with studies relating to the tetravalent state of sup 234 th and the hexavalent state of sup 234 u which show that alpha recoil in silicates generates a strongly oxidizing environment at the site where the recoiling nucleus comes to rest further a zircon grain being small should remain highly oxidizing in its interior by the constant loss of beta particles maintaining the 4 state of radiogenic pb from its effective ion radius similar to that of zr sup 4 and its charge pb sup 4 has to be compatible in the zircon lattice also by analogy with u sup 4 th sup 4 and hf sup 4 its diffusivity should be several orders of magnitude lower than that measured for pb sup 2 in zircon these factors can account for the extreme retentivity of u pb clocks even at high temperatures on the other hand radiogenic pb situated in alpha recoil damaged sites could be leached out by any electrolyte solution that reduces it to the divalent state making it both incompatible and soluble thus discordia can be generated in weathering the curious observation that discordant archaean zircon suites generally define trends to lower intercepts at up to 800 ma instead of zero appears to reflect a c 14 to 28 better average accessibility to leaching of radiogenic sup 207 pb compared to sup 206 pb in accord with the somewhat higher recoil energy of the last branched alpha decays in the sup 235 u chain less

flow conditions of the 2004 indian ocean tsunami in thailand inferred from capping bedforms and sedimentary structures the 2004 indian ocean tsunami deposited a sheet of sand with surficial bedforms at the andaman coast of thailand here we show the recognition of bedforms and the key internal sedimentary structures as criteria of the tsunami supercritical flow condition the presence of well preserved capping bedforms implied a dominant tsunami inflow sets of internal sedimentary structures including parallel lamination seaward and landward inclined laminations and downstream dipping laminae indicated antidune structures that were generated by a supercritical flow current in a depositional stage during the inflow a set of seaward dipping cross laminations containing sand with mud drape on the surface of one depositional layer are a unique indication of an outflow structure a majority of deposits show normal grading but in some areas localized reverse grading was also observed the recognition of these capping bedforms and determination of the internal sedimentary structures provides new key criteria to help derive a better understanding of tsunami flow conditions

sedimentary record of a tsunami during roman times bay of cadiz spain abstract historical data show that the gulf of cadiz has been exposed to destructive tsunamisduring at least the past 2000 yr the last tsunami was generated by the ad 1755 lisbon earthquake which affected the atlantic coasts of spain portugal and morocco today these littoral areas areintensely populated and the expected damage could be much greater tsunami studies are of greatimportance in helping to determine the recurrence interval of these events the presence of washover fan deposits on the inland margin of the valdelagrana spit bar cadiz spain indicates the occurrence of a high energy marine event ca 2300 cal yr bp historical geomorphological sedimentological palaeontological and geochronological data suggest that atsunami could have affected the area during roman times copyright 2002 john wiley sons ltd journal of quaternary science keywords tsunami deposits grain size palaeontology gulf of cadiz south spain introduction investigations of the geological records of past tsunamis arean important tool in helping to determine the recurrenceinterval of such events in a region these investigations arealso the only way of determining the prehistoric occurrenceand tsunami hazard in areas of infrequent seismic activity however at present it is dif cult to distinguish betweentsunami deposits and those laid down by other high energyevents such as a storm surge or hurricane recent work bygoff et al 2001 has helped to identify a series of diagnosticcriteria for tsunami deposits and research is underway tohighlight the differences between these and other high energyevents goff and chagu e goff in preparation j goff personalcommunication 2002 wave hydrodynamics the speci ccoastal setting morphology orientation availability and typeof sediments depositional environments tsunami magnitudeand tidal range are all factors that help to de ne the type andpreservation of tsunami deposits furthermore the ability todetermine the tsunamigenic source largely depends upon thepalaeoseismic and historical record e g goff et al 2001

the behaviour of nd and pb isotopes during 2 0 ga migmatization in paragneisses of the central zone of the limpopo belt south africa and botswana we have carried out major and trace element analyses and nd pb isotope measurements on different components of two migmatite outcrops in the limpopo belt lose quarry botswana and palala south africa in order to assess the effect of migmatization during a high grade metamorphic event on sm nd systematics and nd model ages the outcrops studied are located in the mahalapye tshipise straightening zone at the south western part of the limpopo central zone close to its contact with the kaapvaal craton leucosomes of peraluminous granitic composition were formed by incongruent biotite melting in an fe rich metagreywacke lose quarry and in a metapelite palala respectively monazite u pb and garnet sm nd ages yield close to 2 0 ga for the high grade event confirming other recent work in the central zone the chemical compositions of the main mineral phases feldspar biotite and garnet indicate minimum melt formation at t 750 c and low pressure isocon plots and pb isotope data indicate that the partial melts are locally derived however lil trace element distribution between the leucosomes and paleosomes indicate the incomplete equilibration of the nascent melts with the residual feldspars and biotite in the paleosomes sm nd results on leucosomes and paleosomes of the metagreywacke migmatite show considerable scatter when calculated back to 2 0 ga the paleosomes fall in a narrow range of nd 4 and give tdm model ages between 2 45 and 2 66 ga the nd values of leucosomes are on average four units lower causing them to have apparent tdm ages of 2 7 2 92 ga on average 250 ma older than those of the paleosomes the ree th p2o5 and zr budgets of paleosomes and leucosomes indicate dominance of the lree by monazite and the hree by apatite incorporation of proportionally more monazite than apatite into the melt is inferred as the cause for the nd isotope discrepancy and hence the uncertainty of the average protolith mantle derivation age in contrast pb pb results define an apparent age of 2025 29 ma reflecting nearly full pb isotope exchange in the case of the palala metapelitic migmatite the nd values at 2 0 ga of all but two migmatitic constituents cluster between 7 and 9 5 pointing out extensive nd isotope equilibration during migmatization whereas the pb isotopes yield an errorchron date of 2311 65 ma indicating incomplete pb isotope exchange here garnet dominates the hree distribution whereas the lree are controlled by feldspar and monazite considering that nd isotope equilibration was nearly reached during migmatization nd model ages on the whole rocks represent a good approximation of those of the original protolith 3 0 3 2 ga in the regional context the pb isotope data from the lose quarry locality combined with the nd model age uncertain but within the range of 2 5 2 9 are reminiscent of the northern marginal zone of the limpopo belt and the southern zimbabwe craton whereas the nd and pb isotope data from the palala locality are typical for the limpopo southern marginal zone and the northern kaapvaal craton

the triangle shearzone zimbabwe revisited new data document an important event at 2 0 ga in the limpopo belt abstract the limpopo belt in southern africa has been used to demonstrate that modern style continent continent collision operated during the late archaean 2 6 2 7 ga we have studied the age and pt conditions of strike slip tectonism along the important right lateral triangle shearzone our results substantiate existing proterozoic metamorphic mineral age data of prior uncertain significance using the pb pb and sm nd garnet chronometers and the ar ar step heating technique for amphibole we have dated pre and syn tectonic metamorphic minerals at 2 2 and 2 0 ga thus the triangle shearzone can now be regarded as an important proterozoic suture examination of corresponding high grade pt conditions reaching 800 c at 9 kbar indicates a clockwise metamorphic evolution with pronounced isothermal uplift although the evidence that thrusting of the marginal zones of the limpopo belt over the adjoining cratons occurred during the late archaean clearly remains it is now very uncertain to which event the various pt paths obtained in the limpopo belt may be assigned therefore the question of whether the 2 6 2 7 ga tectonism fits on its own a modern style continental collision model remains open and has to be reassessed

a 2 051 ga anatectic event and peraluminous leucogranite from the mahalapye complex northern edge of the kaapvaal craton record of an effect of bushveld mafic magmatism abstract anatectic events and related leucogranites are rarely reported from precambrian large igneous provinces lips however their appearance is possible in relation to the intrusion of later pulses of mafic magmas into the earlier rocks silicic intrusive rocks associated with the 2 06 2 05 ga bushveld lip within the kaapvaal craton include granites syenites or granophyres this study reports syn bushveld partial melting of 2 061 ga diorite gneiss producing leucogranite from the mahalapye complex high grade terrane at the northern edge of the kaapvaal craton both the migmatitic diorite gneiss and associated leucogranite are crosscut by the 2 039 ga granodiorite the different stages of melting of the biotite bearing diorite gneiss from onset of melting to melt segregation are well preserved petrographic continuity between the leucosomes and concordant and discordant leucogranite bodies point to a melt flow accumulation network garnet formed after biotite during partial melting phase equilibria modelling and conventional thermobarometry indicate conditions of 730 c and 7 2 7 5 kbar for the anatectic event the predicted melt composition is peraluminous magnesian and alkali calcic that is comparable to the chemistry of leucogranites the low content of anatectic melt for the estimated p t condition corresponds to the occurrence of leucogranites as thin veins to dykes la mc icpms u pb zircon age of 2051 3 6 8 ma is interpreted to date the anatectic event the leucogranite exhibits co mingling structures with dyke like and sill like syn bushveld norite intrusions associated with diorite gneiss preferential accumulation of the leucocratic material along the contact of diorite gneiss and norite and the liquid liquid interface with the norite indicate the close age of leucogranite and norite this is supported by the la q icpms u pb zircon age of 2054 7 9 ma from the norite thus the partial melting of the diorite gneiss and formation of the leucogranites is argued as a response to bushveld mafic magmatism the present study shows that one of the causative agents of overprint event s in high grade terranes along archean cratonic margins can be mafic magmatism of similar age within the craton however in the case of lip related magmatism the footprints are restricted to terranes immediately adjacent to the cratonic margins

geochronology and petrology of migmatites from the proterozoic damara belt importance of episodic fluid present disequilibrium melting and consequences for granite petrology abstract the oetmoed granite migmatite complex ogmc central damara orogen namibia consists of grt and crd bearing s type granites and hbl and titanite bearing a type granites that intruded into crd sil kfs bearing metasedimentary rocks stromatic migmatites and nebulites stromatic migmatites formed by limited in situ partial melting of metapelites under h2o saturated conditions at 700 c and 4 5 kbar this partial melting event took place close to the peak of regional metamorphism at 510 ma as revealed by sm nd garnet whole rock ages as well as u pb monazite ages the newly formed melt remained more or less at the site of origin melanosomes of the stromatic migmatites do not resemble true residues instead they represent reaction zones between in situ melt and the metasedimentary host rock leucosomes from the stromatic migmatites are lree and hfse depleted which is typical for the low melt fractions generally observed in migmatite terranes mass balance calculations suggest that these leucosomes may be disequilibrium melts similar 18 o whole rock values between 13 and 14 observed in leucosomes and corresponding melanosomes suggest homogenization of oxygen isotopes between the different rock types via the melt and an internal fluid phase during melting other leucosomes with a major element chemistry similar to the leucosomes from the stromatic migmatites but higher ree contents suggest significant incorporation of lree enriched phases monazite from the country rocks for these leucosomes sm nd garnet whole rock ages are 473 ma indicating a second phase of melting nebulites mainly result from injection of granitic melts into the country rocks but their residual chemistry indicates that partial melting and limited melt removal must have occurred monazites from these nebulites record concordant u pb ages between 540 ma and 470 ma indicating episodic migmatization during high grade regional metamorphism intrusive peraluminous granites are likely generated by partial melting of pelitic sources in the lower crust and different source rocks are probably not the controlling factor for the different chemistry of leucosomes and granites therefore different melting conditions fluid absent vs fluid present and different modes of entrainment and solubilities of accessory phases control the elemental budgets of the leucosomes large scale migmatite granite complexes are a substantial part of some high grade terrains but the distinctive geochemical composition of some leucosomes make these rocks unlikely precursors of large scale granitic bodies

a linear hf isotope age array despite different granitoid sources and complex archean geodynamics example from the pietersburg block south africa abstract combined u pb and lu hf isotope data from zircon populations are widely used to constrain hadean archean crustal evolution linear hf isotope age arrays are interpreted to reflect the protracted internal reworking of crust derived from the depleted mantle during a short lived magmatic event and related 176lu 177hf ratios are used to constrain the composition of the reworked crustal reservoir results of this study however indicate that hf isotope age arrays can also result from complex geodynamic processes and crust mantle interactions as shown by u pb and lu hf isotope analyses of zircons from well characterized granitoids of the pietersburg block pb northern kaapvaal craton south africa apart from scarce remnants of paleoarchean crust most granitoids of the pb with ages between 2 94 and 2 05 ga n 32 define a straight hf isotope age array with low 176lu 177hf of 0 0022 although they show a wide compositional range were derived from various sources and emplaced successively in different geodynamic settings the crustal evolution occurred in five stages i predominately mafic crust formation in an intra oceanic environment 3 4 3 0 ga ii voluminous ttg crust formation in an early accretionary orogen 3 0 2 92 ga iii internal ttg crust reworking and subduction of ttg derived sediments in an andean type setting 2 89 2 75 ga iv post collisional high k magmatism from both mantle and crustal sources 2 71 2 67 ga and v alkaline magmatism in an intra cratonic environment 2 05 2 03 ga the inferred array results from voluminous ttg crust formation during stage ii and involvement of this crust during all subsequent stages by two different processes i internal crust reworking through both partial melting and assimilation at 2 89 2 75 ga leading to the formation of biotite granites coeval with minor ttgs and ii subduction of ttg derived sediments underneath the pb causing enrichment of the mantle that subsequently became source for high k granitoids and mafic rocks at 2 68 and 2 05 ga some scatter along the array might have resulted either from significant assimilation of ancient crust intracrustal lu hf fractionation or melting of heterogeneous mantle sources those results show that without any information about the nature and composition of zircon hosting granitoids hf isotope age data are of limited use to constrain hadean archean magmatogenesis and geodynamics

recovery from a large tsunami mapped over time the aceh coast sumatra this is a record of the rapid recovery of the aceh coast northwest sumatra after its destruction in the tsunami of 26 december 2004 using high resolution ikonos images and field visits we mapped the same 175 km of coastline at 1 m resolution five times 2003 before the tsunami 2004 and early 2005 immediately after the tsunami 2006 2007 and 2008 the aceh coast was eroded back for about 500 m in the tsunami except at the rocky headlands and almost the entire suite of depositional landforms of beaches low sand dunes and wetlands were removed a new coast started to appear within weeks closely resembling the pre tsunami version the new suite of depositional forms not only masked the erosional effect of the tsunami within a very brief period but also mimicked the old coast the post tsunami coast was subjected to the normal coastal processes and the new coast was formed within the constraints of the prevalent coastal environment thus resembling the old one the new beaches tend to be bigger than the old one although they have not yet reached their former seaward positions on this coast a tsunami appears to be an episodic destructive event at an interval of 500 years followed by a set of geomorphic processes that rapidly tend to remove or mask the evidence of such destruction the recovery is hindered where anthropogenic influences have modified the coastal forms and configuration we suggest that a the optimal management of coasts of this type after a tsunami is to leave it to nature and b sedimentary deposits are better indicators of past tsunamis than coastal morphology as demonstrated high resolution satellite images can be used not only for measuring changes caused by a high magnitude event but also for tracing the recovery over time this was impossible earlier except for very small areas which could be mapped on foot

precise age of the platiniferous merensky reef bushveld complex south africa by the u pb zircon chemical abrasion id tims technique the bushveld complex south africa is the world s largest layered intrusion and host to the majority of the known resources of platinum group elements chromium and vanadium despite intensive study determining the precise crystallization age of the bushveld complex has proven to be difficult in this study zircon and rutile were identified in thin section and separated from a sample of pegmatitic feldspathic orthopyroxenite from the pge rich merensky reef west mine townlands shaft rustenburg section low u 21 105 ppm zircon occurs with interstitial biotite and is locally in direct contact with sulfide rutile occurs mainly as inclusions within or overgrowths on chromite especially in the chromitite stringers that bound the reef and also as acicular grains with biotite a u pb crystallization age of 2054 4 1 3 ma was determined from single crystal chemical abrasion id tims u pb dating of zircon and multigrain fractions of rutile yielded a u pb cooling age of 2055 0 3 9 ma integration of the merensky reef crystallization age with existing u pb age determinations for intrusions that pre and postdate emplacement and crystallization of the layered rocks of the bushveld complex indicate that magmatism occurred at ca 2054 ma and is contemporaneous with related magmatic activity across the northern kaapvaal craton of south africa and botswana

field data and satellite imagery of tsunami effects in banda aceh after the 26 december 2004 earthquake and tsunami field data on the extent of the inundation in banda aceh sumatra were combined with satellite imagery to quantify the tsunami effects flow depths along the shores of banda aceh exceeded 9 meters with inundation reaching 3 to 4 kilometers inland to the southwest at lhoknga flow depths were more than 15 meters at the shoreline and runup exceeded 25 meters erosion and subsidence moved the shoreline of banda aceh inland up to 1 5 kilometers and 65 square kilometers of land between banda aceh and lhoknga were flooded

pervasive melt migration from migmatites to leucogranite in the shuswap metamorphic core complex canada control of regional deformation abstract the shuswap metamorphic core complex exhumed in the hinterland of the canadian cordillera displays a 15 km structural section from migmatites to leucogranite it comprises a lower unit dominated by anatectic migmatites exposed in the core of domes at higher structural level the transition from a middle amphibolite facies unit to an upper crustal unit is marked by a low angle detachment associated with the emplacement of laccoliths of leucogranite the amphibolite facies middle unit is permeated by a network of granitic veins feeding the laccoliths and structurally connected to the migmatites of the lower unit this paper describes the geometric textural and structural characteristics and the distribution of the granitic fraction at the outcrop scale in the amphibolite facies unit separating the migmatites from the leucogranite this analysis constrains the mechanisms of melt migration within a plurikilometer scale section across high grade rocks of the middle crust in fertile lithologies metapelites felsic amphibolites the granitic fraction in part generated in situ forms a diffuse network of concordant veins feeding discordant veins and structural sites such as the foliation shear zones and boudin necks discordant granitic veins are oriented perpendicular and to a lesser extent parallel to the mineral and stretching lineation in refractory lithologies the granitic fraction is dominantly intrusive and displays sharp contacts with the host rock however distribution of the granitic fraction shows the same characteristics as for fertile lithologies the melt fraction migrated through a network of fractures taking advantage of mechanical weaknesses such as the foliation plane or forming dikes oriented dominantly perpendicular to the regional stretching and mineral lineations these geometric and textural characteristics suggest that granite migration in these rocks is achieved dominantly by viscous flow of the melt solid through the solid matrix driven by its buoyancy and controlled by mechanical anisotropy of the rock and local dilation created by heterogeneous deformation the relationship between the regional fabric and the distribution of the granitic fraction indicates that regional deformation incremental and finite played a major role in providing pathways for melt migration the formation of laccoliths of leucogranite at higher structural levels suggests that upward melt migration led to accumulation of granitic magmas these observations are consistent with a model of pervasive melt migration through a network of interconnected concordant and discordant granitic veins feeding laccolithic plutons extracted from the dominantly solid matrix during vertical thinning and compaction at a regional scale the presence of both transposed and intact granitic networks indicate an overlap between deformation and granite migration as a continuum or in pulses the methodology and terminology proposed in this paper provide some insights on the behavior of the granitic fraction in the middle crust this approach should be applicable to other high grade terrains exhumed in the cores of orogenic belts

melt generation and fluid flow in the thermal aureole of the bushveld complex granite sheets emplaced into the migmatite zone of the eastern contact aureole of the bushveld complex resulted from fluid enhanced incongruent biotite melting of the underlying silverton formation shales during prograde metamorphism ba concentrations are extreme in both the sheets 1000 ppm and the hornfels 800 ppm into which they have been emplaced we conclude that a ba rich hydrothermal fluid induced melting in the aureole and that fluid transport of ba2 and to a lesser extent sr2 and eu2 persisted in the melt zones under subsolidus conditions sr isotope systematics from high ba localities define an errorchron of 2161 106 ma with an initial 87sr 86sr ratio of 0 705 0 001 metasedimentary rocks unaffected by fluid infiltration were homogenized at the same time but with an increased initial ratio suggesting that whereas isotope homogenization was achieved between outcrops permeated by fluids there is no evidence of regional homogenization oxygen isotope compositions of psammitic metasediments in the aureole are uncorrelated with distance from the contact suggesting the infiltrating fluid equilibrated isotopically with the metasediments their elevated 18o values 11 3 12 1 are consistent with a fluid source from devolatilization of the sedimentary lithologies textural analysis at both outcrop and thin section scale of arkose and psammites in the aureole lakenvalei and magaliesberg formations shows that the extent of melting was highly heterogeneous even on the grain scale and resulted from heterogeneously distributed infiltration of aqueous fluid on dilatant cracks and grain boundaries cathodoluminescence imaging of quartz shows a marked difference in the amount of fine structure with that in the melted rocks having uniform luminescence in contrast to that in rocks containing little or no melt which preserve textures inherited from the regionally metamorphosed protolith simple finite difference thermal modelling of the aureole suggests that the width of the melt zone 500 m is inconsistent with conductive heat transfer and hence that the thermal structure has been modified by fluid advection

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

archaean to proterozoic crustal evolution in the central zone of the limpopo belt south africa botswana constraints from combined u pb and lu hf isotope analyses of zircon a combined set of u pb and lu hf in situ laser ablation icp mc ms zircon analyses were obtained from orthogneisses and granitoids in the central zone of the limpopo belt which comprises the beit bridge and mahalapye complexes the results indicate that by combining the two isotope systems primary magmatic zircon domains can be distinguished from those formed during later metamorphic events even if the distinct zircon domains underwent multiple pb loss and the texture age relationships as obtained by cathodoluminescence images and u pb analyses are ambiguous furthermore the applied technique allows distinction of zircon grains formed in juvenile magmas from those generated by melting of older continental crust or affected by substantial crustal contamination the combined u pb and lu hf data reveal that the sand river gneiss suite of the beit bridge complex was emplaced at 3283 8ma and formed from melting of an older archaean crust which was derived from a depleted mantle source at around 3 65 ga the hafnium model age tdm is significantly older than those obtained from zircons from numerous neoarchaean granitoids of the beit bridge complex comprising the singelele gneiss 2647 12ma the bulai granite 2612 7ma the regina gneiss 2649 9ma and two samples of the zanzibar gneiss 2613 6ma these granitoids show initial ehf t values between 0 5 and 7 1 which correspond to initialtdm between 3 46 and 3 01ga these variable tdminitial and ehf t initial values are interpreted to be the result of different mixtures of reworked 3 65 ga palaeoarchaean crust with juvenile magmas extracted from the depleted mantle during the neoarchaean at 2 65 ga this conclusion is supported by results obtained from the mahalapye complex which was affected by migmatization and granite intrusions during the palaeoproterozoic at 2 02 2 06 ga the mokgware granite 2019 9ma contains zircon xenocrysts with pb pb ages of 2 52 2 65 ga and 2 93 ga and hafnium model ages of 3 0 3 4 ga indicating that this granite is derived from remelting of archaean crust in contrast uniformtdm hf initial ages of 2 61 2 67 ga obtained from a diorite gneiss 2061 6ma of the mahalapye complex indicate that its protolith may have been formed from remelting of a neoarchaean juvenile crust variable ehf t initial values from 3 7 to 6 3 of zircon cores 2711 11ma in an adjacent leucosome also support a model of mixing of juvenile mantle derived matter with older crust in the neoarchaean

geomarkers of the 218 209 bc atlantic tsunami in the roman lacus ligustinus sw spain a palaeogeographical approach between 218 and 209 bc the western coasts of iberia suffered the impact of a historical tsunami with an epicentre probably located in the atlantic ocean near the cape st vincent area sw portugal palaeogeographical changes in the river guadalquivir estuary the ancient roman lacus ligustinus have been recorded in erosional and depositional landforms both stratigraphically and as landscape relicts the tsunamigenic waves run up of w5 m and their subsequent backwash eroded the previous littoral spits transversally generating rectilinear cliffs and incisions the littoral foredunes were also eroded and reactivated as transgressive dunes over the edge of the marshes former coastal sediments w520e100 bc generated overwash deposits ebb tide deltas and sand sheets within the estuary as well as a subsequent bioclastic beach on the lagoon shore defining the post tsunami 130 bce80 ad estuarine shoreline roman lagoon some coastal pre roman 7th to 3rd centuries bc human settlements were abandoned and later in the roman period 1st century ad saltworks were installed morphological and sedimentological changes in the coast triggered by this event were similar or greater than the changes in coastal features related to the ad 1755 lisbon tsunami

the timing of successive fluid events in the southern marginal zone of the limpopo complex south africa constraints from 40ar 39ar geochronology abstract we have carried out a geochronological study in the high grade metamorphic southern marginal zone of the limpopo complex south africa aimed at providing time constraints on episodes of fluid activity this work chiefly comprises 40 ar 39 ar dating with accompanying petrography of amphibole and mica and further incudes zircon u pb geochronology on a post peak metamorphic trondhjemite intrusion the so called zone of rehydration within 30 km n of the hout river shear zone where the southern marginal zone is thrust over the kaapvaal craton was studied in particular but sampling also included areas of patchy metasomatism in the granulite zone further north where no post peak metamorphic rehydration on a regional scale occurred amphibole in a mafic granulite and an older generation of zircons in the petronella trondhjemite yielded dates in the 2700 2730 ma range corresponding to the published age of peak granulite metamorphism in the southern marginal zone a cluster of 40 ar 39 ar dates on amphiboles from the zone of rehydration indicate an age between 2660 and 2670 ma for this event in accord with results from previous work on the hout river shear zone the main population of u pb zircon dates from the trondhjemite dating its intrusion also falls in this age range as does the published age of the matok pluton these data suggest that rehydration at 2660 2670 ma was a discrete episode a further 40 ar 39 ar age cluster defined by dates on both amphiboles and micas is seen at 2010 2040 ma which is the age of a major tectonometamorphic event in the central zone of the limpopo complex and previously reported from the southern marginal zone as rb sr biotite dates events we found in the 2010 2040 ma bracket are strike slip shearing dated by fabric forming amphibole as well as localized potassic metasomatism dated by both amphiboles and micas the latter was not confined to the zone of rehydration and appears in one case to be associated with gold mineralization a number of 40 ar 39 ar dates intermediate between 2600 and 2000 ma were obtained but these are diverse and can be accounted for by mixing incomplete resetting and or excess 40 ar they do not indicate events in this intermediate age bracket

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

the significance of rb sr ages of biotite and phlogopite for the thermal history of the central and southern marginal zones of the limpopo belt of southern africa and the adjacent portions of the kaapvaal craton abstract generally rb sr biotite and phlogopite ages range from 2050 ma to 1950 ma between the murchison thabazimbi and triangle tuli sabi shear zones of southern africa in the rocks comprising the central and southern marginal zones of the limpopo belt and adjacent portions of the kaapvaal craton in some shear zones however similar ages ocurr as young as 800 ma in contrast within the kaapvaal craton south of the murchison thabazimbi shear zone rb sr biotite ages range between 3150 ma and 2100 ma and show no regular distribution in all cases the ages are interpreted to indicate the time elapsed since the biotite last cooled below its closure temperature approximately 320 c the regular pattern of 2050 ma to 1950 ma rb sr biotite ages north of the murchison thabazimbi shear zone suggests that the present erosional surface approximates a paleo isothermal surface this surface was exposed by uplift and erosion which was completed by 1900 ma to 1800 ma ago when the sedimentary and volcanic rocks of the soutpansberg group were deposited the regional uplift was accommodated by motion on the murchison thabazimbi and triangle tuli sabi shear zones and probably was related to tectonism associated with the emplacement of the anorogenic bushveld and phalaborwa complexes other anorogenic granitic magmatism accompanied uplift the depth represented by the paleo isothermal surface and the magnitude of the uplift that exhumed it cannot be constrained precisely it is suggested however that the majority of the 10 to 15 km by which crust in this area is thinner than that of the adjacent cratons is the manifestation of this uplift

coastal sedimentation associated with the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract with wave heights of 30 m and runups reaching 50 m a s l and 6 km inland the december 26 2004 tsunami in sumatra was one of the largest tsunamis in recorded human history in this paper we present a description of the event in the lhok nga bay west coast of banda aceh and an interpretation of the tsunami sand deposits mostly based upon grain size analysis the 3 5 km long transect of lampuuk displays two landward fining thinning and sorting sequences the thickest cross sections of the first sequence of deposits 0 1 5 km inland suggest a deposition by three consecutive runups inflows and a final backwash return flow or outflow from 1 5 to 3 5 km inland the record is dominated by the second and highest wave 15 30 m normally graded couplets or triplets of layers were used to identify the runup of each wave the topmost layers interpreted as the backwash deposition describe a seaward sequence of increasing mean grain size and decreasing degree of sorting the local effects of the topography could be identified thickest deposits in the topographic lows 50 80 cm great spatial variations in thickness and upper laminated texture when the sedimentation was limited by steep slopes landward coarsening and very poor sorting at the wave breaking point bimodal grain size distributions reflecting different sources of sediments finally by coupling the longitudinal and vertical trends of the 26 cross sections we propose a model of sediment transport and deposition in a large tsunami wave

incongruent dissolution of ree and sr rich apatite in peraluminous granitic liquids differential apatite monazite and xenotime solubilities during anatexis the relative solubilities of monazite mnz xenotime xno and apatite ap ree and sr rich and ree and sr poor have been studied in peraluminous granitic liquids in month long experiments at 750 c and 200 mpa ph20 in contrast with the high solubility of the apatite 0 7 wtojop205 in strongly peraluminous liquids monazite and xenotime have much lower solubilities 0 05 wt jop205 in mildly to strongly peraluminous compositions p205 in the liquid is 0 03 0 04 wt joat xenotime saturation and 0 02 0 05 wt jo at monazite saturation in keeping with the low p in the glasses re203 contents are below emp detection thresholds 50 08 wt jo for all conditions of experiments saturation of liquid at equilibrium and local saturation around apatite apatite dissolves incongruently crystallizing ree rich monazite on its surface 1 4 m iong grains resulting in similar low ree contents in liquids monazite precipitation occurs along the margins of dissolving apatite crystals even though the bulk liquid is not monazite saturated the abundance of monazite microcrystals increases with the ree content of the apatite and the degree of apatite dissolution the reaction relationship ap liqi mnz liq2 stemming from differences in relative solubilities greater than an order of magnitude between apatite and monazite results in the dissolution of much smaller amounts of ree into peraluminous liquids than expected by simple evaluation of apatite ree contents the amount of ree contributed from apatite directly to peraluminous granitic liquid is related to the amount of apatite dissolved by simple mass balance only if the total ree content of the apatite is sufficiently low that monazite saturation in liquid 50 100 ppm re203 at 750 c is avoided during dissolution of sr rich apatite the sr partitions into the liquid and at 750 c and 200 mpa ph20 the diffusion coefficient of sr in liquid is 2 x 10 10 cm2js r2 0 659 the reaction relationships described above may have application to some textural features observed in natural igneous rocks for example clusters of monazite microcrystals might be indicators of dissolved apatite monazite morphology can be used to distinguish the source of its ree and the general petrological process rock anatexis or magma crystallization under which the monazite formed in addition monazite microcrystals could serve as nucleation sites for other minerals which might explain their common inclusion in biotite and amphibole within granitoids

neoarchean leucogranitoids of the kianta complex karelian province finland source characteristics and processes responsible for the observed heterogeneity abstract in this study we describe the geochemistry and discuss the genesis of neoarchean ca 2 7 ga leucogranitoids of the kianta complex within the karelian province of the fennoscandian shield the leucogranitoids occur extensively as dykes and intrusions of varying size and represent substantial recycling of older crust occurring as the last magmatic event before final cratonization of the karelian province geochemically the leucogranitoids resemble the leucosomes of migmatized ttgs both groups are compositionally heterogenous but are characterized by high silica contents mean sio2 73 4 wt and leucocratic appearance reflecting a paucity of mafic minerals mean mgo 0 37 wt mg 32 6 the majority of samples analyzed are weakly peraluminous mean a cnk 1 05 mineralogically the leucogranitoids form a series grading from trondhjemite to leucogranite which is observable as highly variable cao 0 07 3 84 wt mean 1 47 k2o 0 30 8 76 wt mean 3 53 and na2o 2 22 7 23 wt mean 4 49 we consider the local ttgs sensu lato which comprise both true ttgs k2o na2o 0 5 to be the predominant source material for the leucogranitoids however some samples overlap compositionally with local ttgs and could represent either partial melting of garnet amphibolites or alternatively products of nearly complete fusion of ttgs leucogranitoids and transitional ttgs can be differentiated to some extent on the basis of geochemistry but definitive discrimination requires demonstration of field relationships and or isotope dating the observed compositional scatter is interpreted to be a result of source heterogeneity retention of variable accessory minerals and accumulation processes melting is attributed to thickening of the crust in response to collisional tectonics and occurred dominantly under water fluxed conditions possible fluid sources are the sanukitoid and quartz diorite suites plus dehydration reactions and partial melting of the lower crust

geologic history of the central zone of the limpopo complex the west alldays area abstract new field structural petrologic and age data show that tectonic styles and metamorphic histories in the west alldays area of the central zone of the limpopo complex southern africa can be linked to neo archean and paleoproterozoic high grade granulite facies tectonometamorphic events the styles comprise 1 a regionally developed high grade s2 gneissic fabric that evolved into a regional d2 system of sheath folds mapped as circular to oval shaped structures with lineations plunging steeply to the wsw and 2 a system of mainly n s trending and north verging d3 shear zones characterized by high grade tectonites straight gneisses with well developed s3 gneissic fabrics in the west alldays area the superimposition of d3 onto the regional d2 fold pattern produced the kilometer scale n s trending baklykraal shear zone which before this study was mapped as the baklykraal fold and interpreted as part of the regional d2 fold pattern in the central zone the paleoproterozoic high

origin and evolution of granitoids associated with the kadiri greenstone belt eastern dharwar craton a history of orogenic to anorogenic magmatism abstract different tectonic models have been proposed to explain the neoarchaean evolution of the eastern dharwar craton edc here we present whole rock elemental and nd isotopic compositions coupled with zircon u pb age and trace elemental data on granitoids associated with the neoarchaean kadiri greenstone belt edc to track the tectonic evolutionary history of the terrain earlier works on volcanic rocks of the kadiri belt tholeiitic oceanic plateau basalt high mg andesite and potassic adakite envisaged continental margin arc oceanic plateau collision in this work the oldest recognized granitoid is a 2 56 ga syntectonic sanukitoid like hornblende granodiorite enriched in large ion lithophile as well as ferromagnesian elements it was probably derived from a metasomatized mantle wedge above a subduction zone this is followed by syntectonic emplacement of 2 54 ga transitional ttgs and potassic adakitic volcanic rocks intrusion of 2 51 2 52 ga crustally derived granites mostly k rich nd 0 9 to 3 7 marks the end of orogenesis in the area a convergent orogenic setting characterized by assembly of diverse terranes repeated slab break off and crustal reworking is proposed to interpret the association of various granitoids and volcanic rocks finally intrusion of crustally derived highly silicic k rich a type granite nd 0 6 to 4 8 and mantle derived syenite occurred in a post subduction non compressive environment during palaeoproterozoic lithospheric delamination and attendant mantle melting and crustal reworking are suggested as possible mechanism for generation of these rocks the negative nd values and mesoarchaean nd depleted mantle model ages of some neoarchaean to palaeoproterozoic kadiri granitoids attest to the presence of older crust in the eastern part of the edc the final cratonization of the edc 2 52 2 50 ga occurred later than in most of the other cratons

geochemical signature as paleoenvironmental markers in holocene sediments of the tinto river estuary southwestern spain high absolute concentrations of metals associated to sulfide deposits located at the river source fe cu zn pb cd and as have been determined from the study of major and trace element concentrations in sediment samples obtained in two vibracores in the tinto river estuary in most cases the enrichment factor ef for these metals is over 2 cu zn and as have much higher ef over 10 in surficial samples fe oxy hydroxide precipitation in high chlorinity zones and its scavenging effect on metals is the main control process on the chemical composition of sediment vertical evolution of the sedimentary and geochemical characteristics of the cores show that the estuary has undergone a process of progressive shallowness and a relative increase in acidic river water volume with respect to seawater this effect has originated a downstream displacement of acid mixing processes affecting the estuary which is reflected in higher metal concentrations in sediments of the outer zones of the system

norite from the mahalapye granitoid complex northern edge of kaapvaal craton implications for the extent of the paleoproterozoic bushveld lip abstract the paleoproterozoic centred at 2 054 ga bushveld lip is one of the largest intracratonic lips in the world its components are primarily distributed within the archean kaapvaal craton this study reports dyke like and sill like norite intrusions from lose quarry within the mahalapye complex a paleoproterozoic granitoid migmatitic gneiss terrane along the northern edge of kaapvaal craton field relations indicate the norite postdate the 2 061 ga diorite gneiss and predate the 2 039 ga granodiorite significantly it exhibit structures indicative of comingling with 2 053 ga leucosome leucogranite a product of partial melting of diorite gneiss the cross cutting relations provide unequivocal evidence that the norite and the leucogranite were liquid at the same time and should be of similar age fe rich orthopyroxene xmg 0 43 0 46 constitutes the dominant mafic mineral in the norite geochemical characteristics of the mahalapye complex norites are similar to those of marginal facies norites from the bushveld complex b1 sills and molopo farms complex layered intrusions two of the prominent constituents of the bushveld lip this is the first solid evidence that the original extent of the bushveld lip covered an area larger than the current known limits of the archean kaapvaal craton into the youngest and westernmost terrane of the high grade limpopo complex the potential of high grade terranes along archean cratonic margins as locales to look for lip fragments is explored

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

in situ bubble vesiculation in silicic magmas volatile degassing is a major process driving volcanic eruptions therefore a full understanding of mechanisms ranging from bubble nucleation growth coalescence to magma fragmentation is required we have simulated magma degassing during ascent in the volcanic conduit by depressurizing hydrated haplogranite melts in high pressure and high temperature optical cells a hydrothermal diamond anvil cell and an internally heated pressure vessel fitted with sapphire windows this allowed the whole process of bubble nucleation growth and coalescence to be directly observed in situ through images captured from the recording videos bubble nucleation pressures number densities growth laws and characteristics of coalescence were estimated as a function of melt water content decompression rate and temperature melt vapor surface tension during bubble nucleation and coalescence was calculated our data show good agreement with those previously obtained in classical vessels methodological improvements are proposed for the experimental simulation of magma degassing in volcanic conduits

recent coastal evolution of the donana national park sw spain abstract since the last holocene sea level rise about 6900 bp a series of depositional littoral landforms has been generated at the outlet of the guadalquivir river with progradation along the predominant longshore drift towards the east the first coastal progradation occurred between 6900 and 4500 bp the donana and perhaps la algaida spits both associated with the oldest and highest marshland in the donana national park are assumed to have been developed at an early stage originally the guadalquivir estuary was wider and deeper than now and its environment was mainly marine the oldest littoral formations have been dated as ca 4735 bp they show erosional events and indicate the breaking up of earlier spit barriers to form inlets the marine environment became increasingly dominant with heavy erosion of cliffs and a retreating coastline this period was followed by another sedimentary cycle 4200 2600 bp that surrounded the earlier eroded barriers the size of the estuary decreased due to the increasing marsh deposits and a fluvial environment was born about 2600 years ago progradation gave way to a new period of intense erosion the resulting morphology of littoral strands and erosional surfaces permitted the return to a marine environment the shoreline again retreated from 2300 bp coastal progradation has prevailed with an erosional interruption at 1000 bp the present day outlet of the guadalquivir is an estuarine delta of inactive marshland the donana national park the dominant environment is fluvial

tsunamis as geomorphic crises lessons from the december 26 2004 tsunami in lhok nga west banda aceh sumatra indonesia abstract large tsunamis are major geomorphic crises since they imply extensive erosion sediment transport and deposition in a few minutes and over hundreds of kilometres of coast nevertheless little is known about their geomorphologic imprints the december 26 2004 tsunami in sumatra indonesia was one of the largest and deadliest tsunamis in recorded human history we present a description of the coastal erosion and boulder deposition induced by the 2004 tsunami in the lhok nga bay located to the west of banda aceh northwest sumatra the geomorphological impact of the tsunami is evidenced by beach erosion some beaches have almost disappeared destruction of sand barriers protecting the lagoons or at river mouths numerous erosion escarpments typically in the order of 0 5 1 5 m when capped by soil and more than 2 m in dunes bank erosion in the river beds the retreat along the main river is in the order of 5 15 m with local retreats exceeding 30 m large scars typically 20 50 cm deep on slopes dislodgement of blocks along fractures and structural ramps on cliffs the upper limit of erosion appears as a continuous trimline at 20 30 m a s l locally reaching 50 m the erosional imprints of the tsunami extend to 500 m from the shoreline and exceed 2 km along riverbeds the overall coastal retreat from lampuuk to leupung was 60 m 550 000 m 2 and locally exceeded 150 m over 276 000 m 3 of coastal sediments were eroded by the tsunami along the 9 2 km of sandy coast the mean erosion rate of the beaches was 30 m 3 m of coast and locally exceeded 80 m 3 m the most eroded coasts were tangent to the tsunami wave train which was coming from the southwest the fringing reefs were not efficient in reducing the erosional impact of the tsunami the 220 boulders measured range from 0 3 to 7 2 m large typically 0 7 1 5 m with weights from over 50 kg up to 85 t we found one boulder less than 1 m large at 1 km from the coastline but all the others were transported less than 450 m 30 m and the moderate tsunamis height

ultrahigh temperature granulites and magnesian charnockites evidence for neoarchean accretion along the northern margin of the kaapvaal craton abstract shrimp u pb analysis of zircon grains from an ultrahigh temperature mg al granulite from the northern margin of the kaapvaal craton southern marginal zone shows ages of 2 72 ga for the peak metamorphism geochemical characteristics of syn tectonic charnockites in the area are similar to magnesian charnockites typically formed in subduction settings in contrast to the prevailing models on peak metamorphism in the context of neoarchean continent collision between archean zimbabwe and kaapvaal cratons resulting in the formation of the limpopo complex we relate the neoarchean events to the accretion of this marginal block to the rest of the kaapvaal craton in this model the subduction event is marked by the formation of magnesian charnockites and the ultrahigh temperature metamorphism dates the collision event