new somali basin magnetic anomalies and a plate model for the early indian ocean abstract the oldest portions of the indian ocean formed via the breakup of gondwana and the subsequent fragmentation of east gondwana we present a constrained plate model for this early indian ocean development for the time period from gondwana breakup until the start of the cretaceous normal superchron the motions of the east gondwana terranes are determined using new geophysical observations in the somali basin and existing geophysical interpretations from other coeval indian ocean basins within the somali basin recent satellite gravity data clearly resolve traces of an east west trending extinct spreading ridge and north south oriented fracture zones a thorough compilation of somali basin ship track magnetic data allows us to interpret magnetic anomalies m24bn through m0r about this extinct ridge our magnetic interpretations from the somali basin are similar in age spreading rate and spreading directions to magnetic anomalies previously interpreted in the neighboring mozambique basin and riiser larsen sea the similarity between the two magnetic anomaly datasets allows us to match both basin s older magnetic anomaly picks by defining a pole of rotation for a single and cohesive east gondwana plate however following magnetic anomaly m15n we find it is no longer possible to match magnetic picks from both basins and maintain plausible plate motions in order to match the post m15n geophysical data we are forced to model the motions of madagascar india and east antarctica australia as independent plates the requirement to utilize two independent plates after anomaly m15n provides strong circumstantial evidence that suggests east gondwana breakup began around 135 ma

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

strike slip tectonics during the neoproterozoic cambrian assembly of east gondwana evidence from a newly discovered microcontinent in the indian ocean batavia knoll the first dredge samples recovered from the batavia knoll in the eastern indian ocean demonstrate it is a rifted continental fragment that now lies submerged in 2 km of water between the perth abyssal plain and wharton basin 1600 km offshore western australia this knoll is the second microcontinent to have been discovered in this region lying 180 km to the ne of gulden draak knoll both knolls rifted from the indian margin at c 104 101 ma during the breakup of east gondwana dredged rocks include granite granodiorite charnockite and quartz rich pegmatite preserving igneous microstructure and biotite schlieren the composite nature of many samples suggests derivation from a felsic igneous complex this basement is at least partly covered by late cretaceous sedimentary strata zircon grains from five representative granitoid samples primarily display modified oscillatory zoning and u pb data that spread along concordia over 50 70 m y suggesting protracted magmatism and pb loss during the latest neoproterozoic early cambrian c 580 530 ma despite the span in u pb zircon ages the primary igneous populations exhibit a relatively narrow range of initial hf isotopic ratios hfi 0 281290 0 281814 ehfi 41 40 to 23 32 this evolved nature of the hf signature suggests derivation of melts from ancient crust tdm2 4 05 2 92 ga with very limited juvenile input plate models based on sparse paleomagnetic data imply significant relative motion between india and australia during the late neoproterozoic cambrian we suggest the new isotopic data from the batavia knoll granitic rocks coupled with other regional geological constraints are consistent with magmatic intrusion and subsequent disturbance of u pb systems along a late neoproterozoic cambrian sinistral strike slip margin related to gondwana assembly

a recipe for microcontinent formation accreted slivers of continental margins are common in the geologic record but the processes that lead to their formation are poorly understood we observe an association of plume related microcontinent isolation and subsequent long term asymmetries in oceanic crustal accretion based on four recent examples the seychelles in the indian ocean jan mayen in the norwegian greenland sea and the east tasman plateau and the gilbert seamount complex in the tasman sea these microcontinents formed by rerifting of a young continental margin 25 m y old in the vicinity of a mantle plume stem followed by asymmetric seafloor spreading two dimensional numerical stochastic basin modeling suggests that a yield strength minimum along the landward edge of a rifted margin thermally enhanced by heating from a mantle plume may cause a spreading ridge to jump onto this zone of weakness this action isolates a passive margin segment the association of large igneous provinces and microcontinents should be useful for identifying similar events in the geological record

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

breakup and early seafloor spreading between india and antarctica summary we present a tectonic interpretation of the breakup and early seafloor spreading between india and antarctica based on improved coverage of potential field and seismic data off the east antarctic margin between the gunnerus ridge and the bruce rise we have identified a series of ene trending mesozoic magnetic anomalies from chron m9o 130 2 ma to m2o 124 1 ma in the enderby basin and m9o to m4o 126 7 ma in the princess elizabeth trough and davis sea basin indicating that india antarctica and india australia breakups were roughly contemporaneous we present evidence for an abandoned spreading centre south of the elan bank microcontinent the estimated timing of its extinction corresponds to the early surface expression of the kerguelen plume at the southern kerguelen plateau around 120 ma we observe an increase in spreading rate from west to east between chron m9 and m4 38 54 mm yr 1 along the antarctic margin and suggest the tectono magmatic segmentation of oceanic crust has been influenced by inherited crustal structure the kinematics of gondwanaland breakup and the proximity to the kerguelen hotspot a high amplitude e w oriented magnetic lineation named the mac robertson coast anomaly mca coinciding with a landwards step down in basement observed in seismic reflection data is tentatively interpreted as the boundary between continental transitional zone and oceanic crust the exposure of lower crustal rocks along the coast suggests that this margin formed in a metamorphic core complex extension mode with a high strength ratio between upper and lower crust which typically occurs above anomalously hot mantle together with the existence of the mca zone this observation suggests that a mantle temperature anomaly predated the early surface outpouring steady state magmatic production of the kerguelen lip an alternative model suggests that the northward ridge jump was limited to the elan bank region whereas seafloor spreading continued in the west enderby basin and its sri lankan conjugate margin in this case the mca magnetic anomaly could be interpreted as the southern arm of a ridge propagator that stopped around 120 ma

autopsy on a dead spreading center the phoenix ridge drake passage antarctica new bathymetric and magnetic anomaly data from the phoenix ridge antarctica show that extinction of all three remaining segments occurred at the time of magnetic chron c2a 3 3 0 2 ma synchronous with a ridge trench collision south of the hero fracture zone this implies that the ultimate cause of extinction was a change in plate boundary forces occasioned by this collision spreading rates slowed abruptly at the time of chron c4 7 8 0 3 ma probably as a result of extinction of the west scotia ridge which would have led to an increase in slip rate and transpressional stress across the shackleton fracture zone spectacular high relief ridges flanking the extinct spreading center mapped for the first time using multibeam swath bathymetry are interpreted as a consequence of a reduction in spreading rate involving a temporary magma oversupply immediately prior to extinction

eastern indian ocean microcontinent formation driven by plate motion changes the roles of plate tectonic or mantle dynamic forces in rupturing continental lithosphere remain controversial particularly enigmatic is the rifting of microcontinents from mature continental rifted margins with plume driven thermal weakening commonly inferred to facilitate calving however a role for plate tectonic reorganisations has also been suggested here we show that a combination of plate tectonic reorganisation and plume driven thermal weakening were required to calve the batavia and gulden draak microcontinents in the cretaceous indian ocean we reconstruct the evolution of these two microcontinents using constraints from new paleontological samples 40ar 39ar ages and geophysical data calving from india occurred at 101 104 ma coinciding with the onset of a dramatic change in indian plate motion critically kerguelen plume volcanism does not appear to have directly triggered calving rather it is likely that plume related thermal weakening of the indian passive margin preconditioned it for microcontinent formation but calving was triggered by changes in plate tectonic boundary forces

geochemical sourcing of basalt artifacts from kaua i hawaiian islands abstract we report on energy dispersive x ray fluorescence edxrf sourcing of 807 basalt artifacts and 34 basalt ecofacts recovered from stratified midden at nu alolo kai kaua i these data are compared with edxrf analyses of 473 alluvial pebbles from waimea canyon 34 adzes from the kaua i museum and published geochemical data for kaua i basalts formal tools such as adzes chisels and mirrors were predominantly manufactured from sources not available at nu alolo kai most adzes and chisels are consistent with sources available elsewhere on kaua i but two basalt mirrors are outside the expected geochemical range of kaua i basalts in contrast almost all expedient tools were manufactured from basalts available at nu alolo kai these findings support the existence of an island wide distribution system for adze material on kaua i and challenges extant models of pre contact hawaiian economics to consider the mechanisms through which specialized commodities were produced and distributed

evolution of the western margin of australia during the rodinian and gondwanan supercontinent cycles abstract the proto darling fault zone and its successor the darling fault extend for 1 000 km along the western continental margin of australia and appear to have been active at several periods during the geological past deformation commenced at 2 570 ma and affected late archaean granitoids along the western margin of the yilgarn craton much of the later activity reflects events related to the accretion and breakup associated with the rodinia and gondwanaland supercontinent cycles in the north rocks of the northampton and mullingarra complexes form part of a high grade grenvillian orogenic belt lying to the west of the darling fault referred to as the pinjarra orogen they underwent granulite facies metamorphism 1080 ma ago and form part of the global collisional event that resulted in the amalgamation of rodinia these rocks extend southward beneath phanerozoic sedimentary cover the perth basin where they are constrained to the east by the darling fault and to the west by the dunsborough fault the latter marking the eastern boundary of the leeuwin complex the leeuwin complex is a fragment of pan african crust that has traditionally been considered part of the pinjarra orogen it is composed predominantly of upper amphibolite to granulite facies felsic orthogneisses derived from a type anorogenic granitoids conventional and shrimp u pb zircon geochronology has established that the granitoids evolved between 780 ma and 520 ma and were metamorphosed at 615 ma these events are equated with rifting associated with the breakup of rodinia sm nd whole rock data support the juvenile nature of the crust and provide no evidence for the involvement of pre existing archaean continental material during the phanerozoic the dunsborough and darling faults were reactivated as normal faults defining the inner arm of a major rift system within eastern gondwanaland and controlling sedimentation in the perth basin that now overlies the grenvillian terrane major normal movement on the darling fault ceased by the late jurassic and it appears that continental breakup in the early cretaceous occurred along fractures closely related to the western boundary of the leeuwin complex that defined the eastern margin of the outer arm of the rift system breakup between australia and greater india commenced at 132 ma and was followed by eruption of the bunbury basalt at 130 ma and 123 ma this possibly resulted from hot spot activity beneath eastern gondwanaland and may have been a reflection of the kerguelen plume though the evidence is equivocal it is argued from the petrographic geochemical and isotopic characteristics together with the likely contiguity of the eastern gondwanaland continents since the assembly of rodinia that the leeuwin complex evolved within an intracrustal rift and is not an exotic terrane it is distinct from adjacent portions of the pinjarra orogen and should be considered a separate terrane it is recommended that use of the term pinjarra orogen be confined to rocks recording the grenvillian events thereby excluding those rocks the leeuwin complex that evolved during the later pan african orogeny

discovery of a microcontinent gulden draak knoll offshore western australia implications for east gondwana reconstructions analysis of dredged samples from the gulden draak knoll demonstrates that it is a submarine rifted continental fragment that lies at the boundary between the western perth abyssal plain and wharton basin indian ocean the knoll comprises a granulite facies basement including pelitic paragneiss and mafic orthogneiss with a cambrian granite inferred to intrude the other rocks boulders and cobbles of felsic gneiss with mesoproterozoic and cambrian protolith ages were also sampled likely reflecting a complex basement to variable sedimentary and volcanic rocks the u pb isotopic system in the archean and mesoproterozoic zircon is significantly disturbed reflecting cambrian orogenesis that affected all samples the protolith to garnet sillimanite biotite paragneiss has a maximum deposition age of 1163 24 ma and includes older detrital zircon grains with populations at c 2 65 ga and between 1 4 and 1 1 ga a younger population in this sample is interpreted as a mix of newly grown metamorphic zircon and isotopically reset zircon implying that the granulite facies metamorphism occurred at c 511 5 ma protracted cambrian orogenesis is indicated by a metamorphic age in the mafic orthogneiss of 530 6 ma and isotopic disturbance shortly following emplacement of granite c 540 ma with zircon ages disturbed to 509 7 ma and the protolith to the felsic orthogneiss c 528 ma with zircon ages disturbed to 510 3 ma xenocrystic zircon grains in the cambrian rocks include archean c 2839 9 ma and mesoproterozoic 1230 1370 ma populations also isotopically disturbed during cambrian orogenesis igneous cambrian zircon grains have less radiogenic hf isotope compositions hfi 0 281821 0 281367 than mesoproterozoic xenocrysts hfi 0 282267 0 281993 indicating limited involvement of the mesoproterozoic crust in granite production a more likely source includes archean crust represented by xenocrysts with hfi 0 281399 0 280863 the gulden draak knoll is reconstructed in gondwana leeuwin full fit model along strike of a major structure termed the indo australo antarctic suture iaas recently mapped from geophysical interpretations in wilkes land antarctica new isotopic data suggest that basement rocks from the gulden draak knoll have affinity to crust exposed either side of the iaas determining if this structure is a suture zone sensu stricto remains to be tested

temperature and emissivity retrieval from remotely sensed images using the grey body emissivity method the problem of extracting temperature and emissivity information from thermal infrared multispectral radiance data is of great importance in remote sensing applications the earth surface temperature is a relevant parameter for climatology meteorology oceanography fire mapping wind field determination and energy balance at the atmosphere earth interface in addition ground emissivity is very important for lithological mapping geological inspection petrography the dating of lava flows etc a new method for emissivity and temperature retrieval has been developed in the authors laboratory which is based on the assumption that emissivity is a slowly varying function of wavelength it is shown that this assumption holds true for many kinds of natural targets the resulting model is called grey body emissivity and may be used to retrieve the emissivity of soils and other natural materials the problem with using an effective wavelength or a bandwidth integral in order to represent the sampled radiance is discussed thus leading to the implementation of two algorithms for the grey body emissivity it is demonstrated that one of them extensively discussed throughout the paper provides the maximum likelihood values for temperature and emissivity the other reveals two drawbacks it produces noisy processed images and works well only for target temperatures greater than 274 k comparisons with other models are carried out utilizing remotely sensed images laboratory measurements and numerical simulations the main approximations and the resulting errors contained in the considered models are briefly discussed the influence of the atmospheric effects on utilized remote sensing data is taken into account finally the authors investigate the emissivity dependence on the viewing angle theoretical predictions which rely on fresnel s and kirchhoff s laws are compared with the emissivity maps extracted from tims images over sea starting from the image data alone the procedure allows them to compute the refraction index and the absorption coefficient of the concerned marine water

high resolution urban thermal sharpener huts high resolution urban thermal sharpener huts anthony dominguez a jan kleissl a jeffrey c luvall b and douglas l rickman b a university of california san diego department of mechanical and aerospace engineering b corresponding author jan kleissl jkleissl ucsd edu office 858 534 8087 fax 858 534 7599 address 9500 gilman dr ebuii 580 university of california san diego la jolla ca 92093 abstract a high resolution urban thermal sharpener huts was developed that increases the resolution nasa marshall space flight center al 35812 usa of thermal infrared tir data to that of visible and near infrared vnir data by fitting the relationship between radiometric surface temperature normalized difference vegetation index ndvi and surface albedo huts was applied to tir data aggregated to 90 m to represent a satellite acquired dataset and validated against the measured 10 m data from aircraft over san juan puerto rico huts sharpening reduced the root mean square error of surface temperature at the high resolution by 17 compared to no sharpening and outperformed other sharpening methods huts is proposed as a useful tool to study urban meteorology and climatology at the microscale using aster satellite data keywords land surface temperature thermal sharpening urban heat island urban meteorology

malaysia airlines flight mh370 search data reveal geomorphology and seafloor processes in the remote southeast indian ocean abstract a high resolution multibeam echosounder mbes dataset covering over 279 000 km2 was acquired in the southeastern indian ocean to assist the search for malaysia airlines flight 370 mh370 that disappeared on 8 march 2014 the data provided an essential geospatial framework for the search and is the first large scale coverage of mbes data in this region here we report on geomorphic analyses of the new mbes data including a comparison with the global seafloor geomorphic features map gsfm that is based on coarser resolution satellite altimetry data and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area our comparison between the new mbes bathymetric model and the latest global topographic bathymetric model srtm15 plus reveals that 62 of the satellite derived data points for the study area are comparable with mbes measurements within the estimated vertical uncertainty of the srtm15 plus model 100 m however 38 of the srtm15 plus depth estimates disagree with the mbes data by 100 m in places by up to 1900 m the new mbes data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the gsfm with a 20 increase in the extent of hills and mountains the new model also reveals four times more seamounts than presented in the gsfm suggesting more of these features than previously estimated for the broader region this is important considering the ecological significance of high relief structures on the seabed such as hosting high levels of biodiversity analyses of the new data also enabled sea knolls fans valleys canyons troughs and holes to be identified doubling the number of discrete features mapped importantly mapping the study area using mbes data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes for example a large series of ridges extending over approximately 20 of the mapped area in places capped by sea knolls highlight the preserved seafloor spreading fabric and provide valuable insights into southeast indian ridge seafloor spreading processes especially volcanism rifting is also recorded along the broken ridge diamantina escarpment with rift blocks and well bedded sedimentary bedrock outcrops discernible down to 2400 m water depth modern ocean floor sedimentary processes are documented by sediment mass transport features especially along the northern margin of broken ridge and in pockmarks the finest scale features mapped which are numerous south of diamantina trench and appear to record gas and or fluid discharge from underlying marine sediments the new mbes data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with mbes the availability of high resolution and accurate maps of the ocean floor can clearly provide new insights into the earth s geological evolution modern ocean floor processes and the location of sites that are likely to have relatively high biodiversity

the subglacial geology of wilkes land east antarctica wilkes land is a key region for studying the configuration of gondwana and for appreciating the role of tectonic boundary conditions on east antarctic ice sheet eais behavior despite this importance it remains one of the largest regions on earth where we lack a basic knowledge of geology new magnetic gravity and subglacial topography data allow the region s first comprehensive geological interpretation we map lithospheric domains and their bounding faults including the suture between indo antarctica and australo antarctica furthermore we image subglacial sedimentary basins including the aurora and knox subglacial basins and the previously unknown sabrina subglacial basin commonality of structure in magnetic gravity and topography data suggest that pre eais tectonic features are a primary control on subglacial topography the preservation of this relationship after glaciation suggests that these tectonic features provide topographic and basal boundary conditions that have strongly influenced the structure and evolution of the eais

asymmetric sea floor spreading caused by ridge plume interactions crustal accretion at mid ocean ridges is generally modelled as a symmetric process regional analyses however often show either small scale asymmetries which vary rapidly between individual spreading corridors or large scale asymmetries represented by consistent excess accretion on one of the two separating plates over geological time spans1 2 3 4 5 6 in neither case is the origin of the asymmetry well understood here we present a comprehensive analysis of the asymmetry of crustal accretion over the past 83 myr based on a set of self consistent digital isochrons7 and models of absolute plate motion8 9 we find that deficits in crustal accretion occur mainly on ridge flanks overlying one or several hotspots we therefore propose that asymmetric accretion is caused by ridge propagation towards mantle plumes or minor ridge jumps sustained by asthenospheric flow10 11 between ridges and plumes quantifying the asymmetry of crustal accretion provides a complementary approach to that based on geochemical12 and other geophysical data13 14 in helping to unravel how mantle plumes and mid ocean ridges are linked through mantle convection processes

geochronology of the 1 55 ga bengal anorthosite and grenvillian metamorphism in the chotanagpur gneissic complex eastern india abstract the thermal tectonic history of the eastern part of the chotanagpur gneissic complex cgc in the eastern indian shield was investigated through u pb dating of zircon in anorthosite u th pb chemical dating of monazite in metapelite granulite and metamorphic textural analysis gabbroic anorthosite in the bengal anorthosite massif was emplaced at 1550 12 ma 2 error including error from decay constants 50 150 myr after an earlier metamorphic event probably related to the late stage of continental collision between the northern and the southern indian blocks subsequent metamorphism in the cgc is recorded by 947 27 ma zircon growth in the anorthosite and 950 20 ma and 995 24 ma monazite growths in the matrix and within garnet of metapelite granulite located north of the anorthosite peak pressures and temperatures of 7 10 5 kb and 775 825 c in the metapelite granulite and 8 5 11 kb and 850 900 c in the anorthosite indicate granulite facies conditions during the 995 947 ma metamorphic event hence as in the eastern ghats belt grenvillian granulite facies metamorphism played an important role in the thermal tectonic evolution of the cgc

geomagnetic field variability during the cretaceous normal superchron during the cretaceous normal superchron 121 83 million years ago the polarity of the earth s geomagnetic field remained stable for an unusually long time deep tow magnetic data suggest that despite the stability of the polarity the field varied greatly throughout the interval

in situ u pb geochronology and hf isotope analyses of the rayner complex east antarctica in situ zircon u pb and hf isotopic analysis via laser ablation microprobe inductively coupled plasma mass spectrometer lam icpms of samples from kemp and macrobertson lands east antarctica suggests that the kemp land terrane evolved separately from the rest of the rayner complex prior to the ca 940 ma rayner structural episode several archaean metamorphic events in rocks from western kemp land can be correlated with events previously reported for the adjacent napier complex recently reported ca 1 600 ma isotopic disturbance in rocks from the oygarden group may be correlated with a charnockitic intrusion in the stillwell hills before ca 1 550 ma despite being separated by some 200 km t hf dm ages indicate felsic orthogneiss from rippon point the oygarden group havstein island and the stillwell hills share a ca 3 660 3 560 ma source that is indistinguishable from that previously reported for parts of the napier complex more recent additions to this crust include proterozoic charnockite in the stillwell hills and the vicinity of mawson station these plutons have distinct 176hf 177hf ratios and formed via the melting of crust generated at ca 2 150 2 550 ma and ca 1 790 1 870 ma respectively

a reassessment of paleogeographic reconstructions of eastern gondwana bringing geology back into the equation abstract in recent years several tectonic reconstructions have been presented for australia antarctica break up with each putting the australian plate in a different location with respect to antarctica these differences reflect the different datasets and techniques employed to create a particular reconstruction here we show that some of the more recent reconstructions proposed for australia antarctica break up are inconsistent with both our current knowledge of margin evolution as well as the inferred match in basement terranes on the two opposing conjugate margins we also show how these incorrect reconstructions influence the fit of the indian plate against antarctica if its movement is tied to the australian plate such errors can have a major influence on the tectonic models of other parts of the world in this case we show how the position of the australia plate can predetermine the extent of greater india which is rightly or wrongly used by many as a constraint in determining the timing of india asia or india island arc collisions during the closure of tethys we also discuss the timing of australia antarctica break up and which linear magnetic features are a product of symmetric sea floor spreading versus those linear magnetic features that result from rifting of a margin the 46 ma to 84 ma rotational poles previously proposed for australia antarctica break up and confined to transitional crust and the continent ocean transition zone more likely formed during earlier stages of rifting rather than during symmetric sea floor spreading of oceanic crust so rotation poles that have been derived from magnetic anomalies in such regions cannot be used as input in a plate reconstruction a new reconstruction of the australia antarctica margin is therefore proposed that remains faithful to the best available geological and geophysical data

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

volcanic margin formation and mesozoic rift propagators in the cuvier abyssal plain off western australia the western margin of australia is characterized by synrift and postrift magmatism which is not well understood a joint interpretation of magnetic anomaly satellite gravity anomaly and seismic data from the cuvier abyssal plain and margin shows that the breakup between india and australia started circa 136 ma m14 and was followed by two rift propagation events which transferred portions of the indian plate to the australian plate post breakup magmatism continued with the emplacement of the wallaby and zenith plateaus 17 18 km thick at their centers along a transform margin two narrow magmatic edifices adjacent to the wallaby plateau sonne and sonja ridges represent an extinct ridge and a pseudofault respectively they formed by excess volcanism probably by lateral migration of buoyant melt along upside down crustal drainage channels from the melt source underneath the wallaby plateau in a mantle plume scenario a small plume 400 km diameter located underneath the rift could have locally uplifted the bernier platform and exmouth sub basin in the early cretaceous and left a track consistent with the azimuth of the wallaby and zenith plateaus in this case ridge plume interaction would have caused two consecutive ridge propagation events towards the plume while the ridge moved away from the hotspot the abrupt end of the hotspot track west of the zenith plateau would be a consequence of the accelerating south eastward motion of the spreading ridge relative to the mantle after 120 ma leaving the mantle plume underneath the indian plate an alternative nonmantle plume scenario is based on the observation that between breakup and chron m0 120 ma the ocean crust in the southern cuvier abyssal plain was formed while the spreading ridge abutted indian continental crust small scale convection may have been initiated during rifting in the early cretaceous and maintained until the wallaby zenith ridge transform intersection passed by the eastern edge of indian continental crust at chron m0

australian antarctic breakup and seafloor spreading balancing geological and geophysical constraints abstract the motion of diverging tectonic plates is typically constrained by geophysical data from preserved ocean crust however constraining plate motions during continental rifting and the breakup process relies on balancing evidence from a diverse range of geological and geophysical observations often subject to differing interpretations reconstructing the evolution of rifting and breakup between australia and antarctica epitomizes the challenges involved in creating detailed models of pangea breakup in this example differing degrees of emphasis on and alternative interpretations of offshore geophysical data in particular magnetic anomalies and seismic reflection profiles and onshore geological data lead to starkly contrasting views of how the continents were configured at the onset of mesozoic rifting here we critically review reconstructions of rifting and breakup in the light of all available geological and geophysical data including magnetic anomalies fracture zones conjugate crustal domains amounts of continental extension continental geology plate boundary locations break up ages and stratigraphy we identify the most viable plate tectonic reconstructions both with and without the input of the oldest more controversial magnetic anomaly interpretations and discuss implications for reconstructions of other margin pairs our analysis highlights key discrepancies between reconstructions based solely on geological piercing points and those based on a range of constraints these insights provide a powerful framework for reducing the range of viable models for australian antarctic rifting and provide key lessons for future efforts aimed at constraining pre and syn rift plate tectonic reconstructions

mapping surface mineralogy and scattering behavior using backscattered reflectance from a hyperspectral midinfrared airborne co sub 2 laser system miraco sub 2 las airborne high spectral resolution thermal infrared tir miraco sub 2 las reflectance data were evaluated for mapping surface mineralogy and scattering behavior for a variety of semi arid geological test sites in australia miraco sub 2 las is a rapidly tuned airborne co sub 2 laser system that measures backscattered bidirectional reflectance at 100 wavelengths between 9 1 and 11 2 spl mu m for 2 m footprints in line profile mode an operational methodology is described that permits reduction of the raw airborne signal to ground reflectance this ground reflectance has two major properties namely wavelength dependent mineralogical variations and reflection albedo variations related to surface roughness comparisons between the airborne miraco sub 2 las spectra and laboratory directional hemispherical reflectance dhr spectra show the same spectral shapes though differences in average reflectance albedo occur for some types of rocks the minerals identified using miraco sub 2 las include silicates for example quartz microcline plagiodase almandine spessartine talc tremolite and kaolinite and carbonates dolomite and magnesite as well as vegetation dry and green many of the diagnostic spectral features that allow identification of these materials are narrow 0 2 spl mu m making them difficult to detect with broadband tir systems like the airborne tims and satelliteborne aster based on an empirical relationship between the minimum and maximum reflectance established using laboratory dhr spectra a method is proposed that allows the use of miraco sub 2 las data to identify surfaces that are characterized by lambertian or specular scattering the miraco sub 2 las results show that lambertian type scatterers include soils and many types of isotropic rocks

combined use of visible reflected infrared and thermal infrared images for mapping hawaiian lava flows the weathering of hawaiian basalts is accompanied by chemical and physical changes of the surfaces these changes have been mapped using remote sensing data from the visible and reflected infrared and thermal infrared wavelength regions they are related to the physical breakdown of surface chill coats the development and erosion of silica coatings the oxidation of mafic minerals and the development of vegetation cover these effects show systematic behavior with age and can be mapped using the image data and related to relative ages of pahoehoe and aa flows the thermal data are sensitive to silica rind development and fine structure of the scene the reflectance data show the degree of oxidation and differentiate vegetation from aa and cinders together data from the two wavelength regions show more than either separately the combined data potentially provide a powerful tool for mapping basalt flows in arid to semiarid volcanic environments

a global scale plate reorganization event at 105 100 ma abstract a major plate reorganization is postulated to have occurred at approximately 100 ma however this reorganization has received limited attention despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events we investigate tectonic events from the period 110 to 90 ma and show that the reorganization occurred between 105 and 100 ma was global in scale and affected all major plates seafloor evidence for plate motion changes is abundant during this period with either fracture zone bends or terminations preserved in all ocean basins long lived eastern gondwanaland subduction ended along a 7000 km long section of the margin while elsewhere around the proto pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates thrusting in western north america transpression and basin inversion in eastern asia and development of the present day andean style margin along western south america occurred contemporaneous with the development of an extensional regime in eastern gondwanaland basin instability in africa and western europe further demonstrates that lithospheric stress regime changes were widespread at this time considering the timing of the reorganization and the nature of associated plate boundary changes we suggest that eastern gondwanaland subduction cessation is the most likely driving mechanism for the reorganization subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto pacific and neighboring plates whereby producing widespread changes in plate motion and continental lithospheric stress patterns we propose that major changes in ridge trench interaction triggered the cessation of subduction the progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern gondwanaland subduction zone to the east of australia and new zealand respectively resulted in very young crust entering the trench and we suggest that by 105 100 ma there was insufficient negative buoyancy to drive subduction finally we propose that the plume push force of the bouvet plume that erupted near the african antarctic south american triple junction contributed to plate motion changes in the southern atlantic region

evidence for two shield volcanoes exposed on the island of kauai hawaii the island of kauai has always been interpreted as a single shield volcano but lavas of previously correlated reversed to normal magnetic polarity transitions on opposite sides of the island differ significantly in isotopic composition samples from west kauai have 87sr 86sr 18 25 samples from east kauai have 87sr 86sr 0 7037 nd 6 14 and 206pb 204pb 18 25 available data suggest that a younger eastern shield grew on the collapsed flank of an older western one

growth history of kilauea inferred from volatile concentrations in submarine collected basalts abstract major element and volatile h2o co2 s compositions of glasses from the submarine flanks of kilauea volcano record its growth from pre shield into tholeiite shield stage pillow lavas of mildly alkalic basalt at 2600 1900 mbsl on the upper slope of the south flank are an intermediate link between deeper alkalic volcaniclastics and the modern tholeiite shield lava clast glasses from the west flank of papau seamount are subaerial mauna loa like tholeiite and mark the contact between the two volcanoes h2o and co2 in sandstone and breccia glasses from the hilina bench and in alkalic to tholeiitic pillow glasses above and to the east were measured by ftir volatile saturation pressures equal sampling depths 10 mpa 1000 m water for south flank and puna ridge pillow lavas suggesting recovery near eruption depths and or vapor re equilibration during down slope flow south flank glasses are divisible into low pressure co2 0 5 wt s 1000 1700 ppm and high pressure groups co2 40 ppm s 1000 ppm corresponding to eruption sea level at moderate water depths 300 1000 m or shallower but in disequilibrium and in deep water 1000 m saturation pressures range widely in early alkalic to strongly alkalic breccia clast and sandstone glasses establishing that early k lauea s vents spanned much of mauna loa s submarine flank with some vents exceeding sea level later south flank alkalic pillow lavas expose a sizeable submarine edifice that grew concurrent with nearby subaerial alkalic eruptions the onset of the tholeiitic shield stage is marked by extension of eruptions eastward and into deeper water to 5500 m during growth of the puna ridge subaerial and shallow water eruptions from earliest kilauea show that it is underlain shallowly by mauna loa implying that mauna loa is larger and kilauea smaller than previously recognized

relative dating of hawaiian lava flows using multispectral thermal infrared images a new tool for geologic mapping of young volcanic terranes the weathering of hawaiian basalts in arid and semiarid environments is accompanied by change in their thermal infrared emittance spectra the spectral differences can be measured and mapped with multispectral imaging systems the differences appear to be related to the degree of development preservation and alteration of glassy crusts the oxidation of iron and the accretion of silica rich surface veneers because the measurements are quantitative and in image format they are useful for estimating relative ages in geologic mapping of lava flows in hawaii this technique is most diagnostic for distinguishing among sparsely vegetated flows less than 1 5 ka in age

community infrastructure and repository for marine magnetic identifications magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined although these identifications are an invaluable resource their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize host and update these interpretations we have developed an open source community driven online infrastructure as a repository for quality checked magnetic anomaly identifications from all ocean basins we provide a global sample data set that comprises 96 733 individually picked magnetic anomaly identifications organized by ocean basin and publication reference and provide accompanying hellingerformat files where available our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions for both experts and nonexperts alike to further enhance the existing repository and strengthen its value we encourage others in the community to contribute to this effort

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

cenozoic extension along the reactivated aurora fault system in the east antarctic craton abstract the east antarctic craton is characterized by major intracontinental basins and highlands buried under the 34 ma east antarctic ice sheet their formation remains a major open question paleozoic to cenozoic intraplate extensional tectonic activity has been proposed for their development and in this work the latter hypothesis is supported here we focus on the aurora trench at within the aurora subglacial basin latitude 75 77 s longitude 117 118 e whose origin is still poorly constrained the at is an over 150 km long 25 km wide subglacial trough elongated in the nnw sse direction geophysical campaigns allowed better definition of the at physiography showing typical half graben geometry the rounded morphology of the western flank of the at was simulated through tectonic numerical modelling we consider the subglacial landscape to primarily reflect the locally preserved relict morphology of the tectonic processes affecting the interior of east antarctica in the cenozoic the bedrock morphology was replicated through the activity of the listric aurora trench fault characterized by a basal detachment at 34 km considered the base of the crust according to available geophysical interpretations and vertical displacements ranging between 700 and 300 m the predicted displacement is interpreted as the partial reactivation of a weaker zone along a major precambrian crustal scale tectonic boundary we propose that the aurora trench fault is the southern continuation of the 1000 km long aurora fault independently recognized by previous studies together they form the aurora fault system a long lived tectonic boundary with poly phased tectonic history within the eac that bounds the eastern side of the aurora subglacial basin the younger cenozoic reactivation of the investigated segment of the aurora fault system relates to the intraplate propagation of far field stresses associated to the plate scale kinematics in the southern ocean

revised tectonic evolution of the eastern indian ocean published plate tectonic models for the australian antarctic plate pair imply geologically improbable scenarios at either or both ends of the cretaceous rift and spreading system controversy also exists around the location of and motion at the plate boundary extending west of australia antarctica through the kerguelen plateau region we present a plate tectonic model of relative motions among india australia and antarctica from the onset of continental rifting to the establishment of rapid seafloor spreading at 43 ma the model conforms to a wide range of geological geophysical evidence and reconstructs the formation of both the western kerguelen region and the eastern tasman region the incorporation of spatio temporally continuous plate boundaries reveals the presence of a plate boundary beneath the contiguous central kerguelen plateau and broken ridge for 65 million years to investigate the relationship between the plate boundary system and the kerguelen plume we test three alternative absolute reference frames using a fixed hotspot reference frame the indian ocean mid ocean ridge system remains within 500 km of the kerguelen plume while the proximity of the plate boundaries and the plume is more variable with a moving hotspot reference frame proximity between the plume plate boundaries and the central kerguelen plateau broken ridge for 65myrs suggests that these specific features were not formed by a single short lived 5 10 myr pulse of magmatic activity but rather by a 25 myr period of relatively high magma flux followed by 40 myr period of lower volume magmatic activity an interpretation not excluded by the relatively sparse dredge and drill ages

a highly oxidized ferrian salite kennedyite forsterite and rhoenite bearing alkali gabbro from kauai hawaii and its mantle xenoliths three types of rock each with unusually oxidized mineral assemblages are found in close association as part of a probable feeder pipe to the alkalic lavas on kauai hawaii the first type is an alkali gabbro consisting ofpotassic oligoclase 66voby volume ferrian salite 27vo kennedyite 3vo magnesioferrite 3 and trace amounts of rh6nite kaersutite apatite hematite and nearly pure forsterite electron microprobe analyses of these phases show them to be exceptionally enriched in mg and ferric iron these data combined with textural observations demonstrate that the alkali gabbro melt existed in a highly oxidized state prior to the onset of crystallization and that this condition prevailed throughout the course of crystallization the second lilhlogic type consists of an assortment of mantle xenoliths mostly spinel iherzolites that were entrained by the alkali gabbro at depth prior to its crystallization there was extensive development of oxidation symplectites within the primary grains in the outer two cm of the xenoliths original mantle olivine foss sr has oxidized to form bleb like intergrowths of orthopyroxene enq and magnesioferrite mtse in a more magnesian foe5 olivine host comparison of these data with relevant i atm experimental data in the system mgo feo fe2o3 sio2 indicates conditions of l0r o2 and 1165 c for the formation of these symplectites the th ird lithologic type is referred to here as the fine grained groundmass like the alkali gatbro the fine grained groundmass has a high fe3 fe2 but consists only offerrian salite 62 potassic oligoclase l7vo forsterite 14 magnesioferrite 7 and trace amounts of apatite the gradational contacts of the fine grained groundmass with the xenoliths and comparative microprobe analyses suggest that the groundmass liquid was derived in part from the xenoliths by partial melting and the subsequent crystallization of that liquid was complete prior to the introduction of the alkali gabbro the formation of the oxidation symplectites is closely associated with the fine grained groundmass and hence the melting event and appears to have been prior to alkali gabbro intrusion

repeat ridge jumps associated with plume ridge interaction melt transport and ridge migration 1 repeated shifts or jumps of mid ocean ridge segments toward nearby hot spots can produce large long term changes to the geometry and location of the tectonic plate boundaries ridge jumps associated with hot spot ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off axis volcanism to study how these processes influence ridge jumps we use numerical models to simulate 2 d in cross section viscous flow of the mantle viscoplastic deformation of the lithosphere and melt migration upward from the asthenospheric melting zone laterally along the base of the lithosphere and vertically through the lithosphere the locations and rates that magma penetrates and heats the lithosphere are controlled by the time varying accumulation of melt beneath the plate and the depth averaged lithospheric porosity we examine the effect of four key parameters magmatic heating rate of the lithosphere plate spreading rate age of the seafloor overlying the plume and the plume ridge migration rate results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate the time required to complete a ridge jump decreases with larger values of magmatic heating rate younger plate age and faster spreading rate for cases with migrating ridges models predict a range of behaviors including repeating ridge jumps much like those exhibited on earth repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere the tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the mid atlantic ridge model results also suggest that magmatic heating may significantly thin the lithosphere as has been suggested at hawaii and other hot spots

middle cretaceous geomagnetic field anomalies in the eastern indian ocean and their implication to the tectonic evolution of the bay of bengal abstract the middle cretaceous period is largely known for its stable normal polarity in the earth s magnetic field a few reversals isea m 3r m 2r and m 1r have been postulated during this period but are yet to be accepted in total recently two anomalies q1 92 ma and q2 108 ma have been identified globally and proposed as internal time markers useful to trace the evolution of the world oceans while the evolutionary history of the indian ocean from late cretaceous to present is well established the older middle to early cretaceous record is still ambiguous the occurrence of a major plate reorganization during the middle cretaceous period has added to the dilemma in understanding the early evolution of the eastern indian ocean the detailed evolution of the bay of bengal and its conjugate enderby basin has remained speculative to date due to various constraints such as lack of good geophysical dataset and drill sites and the presence of thick sedimentary load in the present study an attempt is made to validate the occurrence of the middle cretaceous internal time markers in the eastern indian ocean these time markers are used to provide additional constraints for tracing the evolution of the eastern indian ocean since late jurassic identification of these markers aided to confirm the timing of spreading ridge extinction in the perth basin as 102 ma in the bay of bengal these markers facilitated to infer the evolution of the middle cretaceous crust east of the buried 85 e ridge the age of the oceanic crust increases from south to 115 ma at the northern tip of the bay of bengal seafloor spreading occurred in nne ssw direction between 115 ma and 102 ma and thereafter it changed its direction to n s half spreading rates ranging from 4 0 to 4 2 cm yr between 108 ma and 84 ma in the bay of bengal are higher than its conjugate enderby basin this spreading system belongs to the second rifting episode between antarctica and india and was caused by the kerguelen mantle plume activity the 85 e ridge south of 12 n is emplaced on a transform fault that constitutes the northern extension of the 86 e fracture zone and active since 102 ma the study suggests that excess crustal accretion occurred on the indian plate since the middle cretaceous

zircon u pb ages and geochemistry of newly discovered neoproterozoic orthogneisses in the mishan region ne china constraints on the high grade metamorphism and tectonic affinity of the jiamusi khanka block abstract the jiamusi khanka block located in the easternmost segment of the central asian orogenic belt caob is one of the least understood blocks in northeastern china the age of its basement the timing of the high grade metamorphism and the tectonic affinity of this block have all been subjects of controversy here we describe newly discovered neoproterozoic orthogneisses from the mishan region in the central jiamusi khanka block sims and la icp ms u pb dating of the magmatic cores of zircons from three of these high grade orthogneisses yielded weighted mean ages that range from 898 4 to 891 13 ma indicating that early neoproterozoic magmatism did occur in the jiamusi khanka block twenty two analyses of metamorphic zircons rims as well as some grains gave two groups of concordant ages one at ca 563 ma interpreted as the timing of the high grade metamorphism and the other around 518 496 ma interpreted as representing a subsequent retrograde metamorphism the orthogneisses represent metamorphosed peraluminous syn collisional syenogranites with sio2 71 29 78 08 wt a cnk 1 06 1 99 and na2o k2o 0 03 1 49 and they belong chemically to the high potassium calc alkaline series they have low sr 32 134 ppm contents and sr y ratios 1 6 16 9 and display strongly fractionated to nearly flat ree patterns with negative eu anomalies eu 0 22 0 95 and depletions in nb ta these geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks perhaps in a subduction related setting that was undergoing transition from compression to extension in the context of the reconstruction of gondwana the ca 898 891 ma magmatic activity and the ca 563 ma high grade metamorphism in the mishan region provide constraints on the possible linkages between the jiamusi khanka block and east gondwana during the neoproterozoic to early paleozoic

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

the tectonic fabric of the ocean basins 1 we present a global community data set of fracture zones fzs discordant zones propagating ridges v shaped structures and extinct ridges digitized from vertical gravity gradient vgg maps we use a new semi automatic fz tracking program to test the precision of our hand digitized traces and find a mean absolute deviation of less than 3 4 km from the raw vgg minima that most clearly delineate each feature and less than 5 4 km from the fz location predicted by fitting model profiles to the vgg data that represent the morphology of the individual fzs these offsets are small considering gravity data only provide an approximation for the underlying basement morphology we further investigate the origin of non fz seafloor fabric by combining published abyssal hill heights computed from gravity anomalies with global half spreading rates a residual abyssal hill height grid with spreading rate effects removed combined with our interpreted tectonic fabric reveals several types of seafloor fabric distinct from typical abyssal hills where discordant zones do not overprint abyssal hill signals residual abyssal hill height anomalies correspond to seafloor that accreted near mantle thermal anomalies or zones of melt depletion our analysis reveals several areas where residual abyssal hill height anomalies reflect pseudo faults and extinct ridges associated with ridge propagation and or microplate formation in the southern pacific ocean

gravity anomalies over extinct spreading centers a test of gravity models of active centers gravity fields over active mid ocean ridges display long wavelength free air gravity highs with superimposed short wavelength anomalies over the spreading axis these axial anomalies are negative over slow spreading active ridges with amplitudes of typically 30 70 mgal and wavelengths of 40 60 km but decrease in amplitude and wavelength with increasing spreading rate until at fast spreading centers the anomalies are positive 10 20 mgal with wavelengths of about 20 30 km similar free air anomalies are observed over extinct spreading ridges and typically show the same paleo spreading rate dependency suggesting that a large component of the anomaly is not dynamically maintained calculation and removal of gravitational effects from basement relief results in significant residual gravity lows at the extinct ridges analyzed here even though the thermal effects associated with active spreading have diminished and no longer contribute to such short wavelength gravity lows the amplitudes of the residual lows at slow paleo spreading rates are 25 45 mgal with half widths of about 20 45 km and decrease with increasing spreading rate to about 5 mgal amplitude and 10 15 km half width over fast paleo spreading ridges the amplitudes and wavelengths of these residual anomalies are nearly identical to those of the residual anomalies observed over active spreading centers most previously proposed models of mid ocean ridge structure are unable to explain these anomalies and many are inconsistent with a least some aspect of the large body of knowledge currently available for mid ocean ridges this research provides a further constraint on geometric models of accretion as these models predict vastly different gravity fields results indicate that a frozen in low density accretionary structure is probably confined to within about 10 km of either side of the extinct axis this conclusion is consistent with the presence of a low density gabbroic root situated at shallow mantle depths beneath the ridge axis this root tends to narrow with increasing spreading rate producing the required residual gravity field variation

geochemistry and origin of some unusually oxidized alkaline rocks from kauai hawaii abstract we report major element and trace element transition metal ree ba rb sr th analyses and sr nd and o isotopic ratios from a poorly exposed plug that may represent the remnant of a feeder pipe to the post erosional koloa volcanic series on kauai hawaii the plug is zoned with respect to oxidation state and is composed of ijolite with a relatively low oxidation state near nno that apparently forms a central core and a highly oxidized mh border facies consisting of abundant mantle derived xenoliths within a highly vesicular composite matrix of alkali picrite and alkali gabbro both of which have exceptionally high fe 3 fe 2 atomic ratios 9 0 the isotopic evidence demonstrates that the xenoliths are indeed unrelated to their host lithologies yet allows a genetic relationship between the ijolite alkali picrite and alkali gabbro the trace element systematics of the alkali picrite strongly suggest that it represents a primary melt derived by 5 7 partial melting of a recently metasomatized garnet lherzolite source very similar in trace element characteristics to that postulated for the honolulu volcanic series lavas by clague and frey 1982 apart from their disparate oxidation states the ijolite and alkali gabbro are compositionally identical least squares and fractional crystallization calculations suggest an origin for these lithologies by 50 fractionation of equal parts olivine and clinopyroxene from a parental melt like the alkali picrite we contend that had the contrasting oxidation states been established at the time of fractionation the alkali gabbro and ijolite would have evolved into very distinct compositions due to the effect of f o 2 on mineral melt distribution coefficients and the order in which phases crystallize upon cooling we conclude therefore that the mechanism by which the alkali gabbro developed its high fe 2 fe 2 ratio operated late in its history after fractionation and that the same mechanism probably operated on the similarly oxidized alkali picrite we believe that the unusually high oxidation states of the alkali gabbro and alkali picrite are most likely the result of atmospheric contamination of the margins of the crystallizing plug the position of the ijolite in the core of the plug apparently isolated it from this process

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined

full fit palinspastic reconstruction of the conjugate australian antarctic margins 1 despite decades of study the prerift configuration and early rifting history between australia and antarctica is not well established the plate boundary system during the cretaceous includes the evolving kerguelen broken ridge large igneous province in the west as well as the conjugate passive and transform margin segments of the australian and antarctic continents previous rigid plate reconstruction models have highlighted the difficulty in satisfying all the available observations within a single coherent reconstruction history we investigate a range of scenarios for the early rifting history of these plates by developing a deforming plate model for this conjugate margin pair potential field data are used to define the boundaries of stretched continental crust on a regional scale integrating crustal thickness along tectonic flow lines provides an estimate of the prerift location of the continental plate boundary we then use the prerift plate boundary positions along with additional constraints from geological structures and large igneous provinces within the same australian and antarctic plate system to compute full fit poles of rotation for australia relative to antarctica our preferred model implies that the leeuwin and vincennes fracture zones are conjugate features within gondwana but that the direction of initial opening between australia and antarctica does not follow the orientation of these features rather the geometry of these features is likely related to the earlier rifting of india away from australia antarctica previous full fit reconstructions based on qualitative estimates of continental margin overlaps generally yield a tighter fit than our preferred reconstruction based on palinspastic margin restoration

population density and zoning of olivine phenocrysts in tholeiites from kauai hawaii the population density of olivine phenocrysts of the tholeiites display an exponential variation which is typical of igneous as well as contact metamorphic rocks the exponential variation is explained by a new growth probability model which is consistent with experimental work the forsterite content of the olivine phenocrysts decreases with decreasing size various phenocryst features suggest that the tholeiites first crystallized slowly in a magma chamber after which they underwent crystallization for a short period of time in a feeder dyke before eruption took place

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

evolution of the carlsberg ridge between 60 and 45 ma ridge propagation spreading asymmetry and the deccan reunion hotspot despite the availability of numerous geophysical data no convincing magnetic anomaly identification and structural map of a major part of the arabian and eastern somali basins have been published to date i propose a new interpretation of the available magnetic data based on the identification of tiny wiggles i e singular second order patterns of the magnetic signal only one fracture zone and a set of propagating rifts existed between the owen fracture zone and the chagos laccadive ridge between anomalies 26 and 20 at anomalies 26 25 at least two eastward propagating rifts are identified while at anomalies 24 20 seven westward propagating rifts are confidently recognized the major consequence of this systematic ridge propagation is a tremendous regional asymmetry between anomalies 26 and 25 about 65 of the crust formed at the carlsberg ridge was accreted to the african plate while at anomalies 24 20 more than 75 benefited to the indian plate i suggest that these asymmetries result from the relative position of the carlsberg ridge and the nearby deccan reunion hotspot the ridge tending to remain near the hotspot

change of tectono stratigraphic regime in the australian plate during the 99 ma mid cretaceous and 43 ma mid eocene swerves of the pacific the clockwise bend at 99 ma mid cretaceous in linear volcanic chains in the tropical pacific coincides with a change from pre 99 ma head on chilean type subduction of the pacific plate beneath eastern gondwana to 99 43 ma sinistral oblique mariana type subduction and strike slip breakup by simple sea floor spreading between australia and antarctica and by backarc spreading in the southwest pacific the 99 ma breakup of australia from antarctica is documented by a mid cretaceous unconformity this tectono stratigraphic change founded modern australia with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south the counterclockwise bend at 43 ma mid eocene the emperor hawaiian bend coincides with the onset of structure in the challenger rift of new zealand the eromanga cooper basin of central australia and the oil shale grabens of coastal queensland

petrogenesis of plutonic rocks in a proterozoic granulite facies terrane the bunger hills east antarctica abstract several compositionally varied suites of plutonic rocks gabbro quartz monzogabbro granite quartz monzodiorite in the bunger hills were emplaced at depths of 20 km over a relatively short time interval 1170 1150 ma during the waning stages of granulite facies metamorphism the peak of which occurred 1190 ma ago alkaline syenite to granite rocks were emplaced west of the denman glacier at david island 515 ma ago most of these rocks crystallised from magmas derived by melting of heterogeneous mantle comprising at least two components nb poor long term enriched lithosphere and a nb rich oib ocean island basalt type within plate component metasomatic enrichment of the source of the plutonic rocks as well as that of 500 ma alkaline dykes may have been contemporaneous with continental crust formation in the area during the late archaean or early proterozoic much of the chemical variation of the different suites can be explained by fractional crystallisation but other processes particularly variations in the extent and or p t conditions of melting were also important crustal contamination does not appear to have been a major factor in the petrogenesis of the bunger hills magmas but cannot be entirely discounted particularly for some of the granitic rocks the more evolved david island syenitic intrusives may have been derived by melting of lower crustal rocks

spectral reflectance characterization 0 4 to 2 5 and 8 0 to 12 0 mu m of phanerozoic strata wind river basin and southern bighorn basin areas wyoming abstract reflectance spectroscopy a useful analytical tool available to geologists for over 100 years has not been widely used in petrologic or stratigraphic studies of sedimentary rocks we are routinely using laboratory spectral reflectance data covering the 0 4 to 12 0 m wavelength interval in an investigation of the stratigraphic and structural evolution of the wind river and bighorn basin areas wyoming two types of laboratory spectral reflectance measurements were made on 192 weathered outcrop bedrock and core samples 1 hemispherical reflectance from 0 4 to 2 5 m 229 spectra and 2 biconical reflectance from 8 0 to 12 0 m 84 spectra results show stratigraphic variations in the spectral properties of sedimentary rocks as encountered in the field sample mineralogy was determined using x ray diffraction and interpretation of spectra the mineralogy lithology and stratigraphic distribution of samples are diverse and representative of phanerozoic siliciclastic and carbonate strata encountered in foreland sedimentary basins spectra were sorted into 36 distinct groups according to the presence or absence of 68 visible and infrared reflectance features many spectral features can be assigned to specific molecular phenomena and allow rapid determination of specific minerals minerals detectable spectrally include gypsum kaolinite smectite analcime goethite jarosite calcite dolomite and feldspar results are contributing to our understanding of the depositional history of the wind river and bighorn basin areas more importantly results suggest that laboratory field and remote reflectance spectroscopy have more general geologic applicability in studies of sedimentary rocks reflectance spectroscopy can augment conventional laboratory and field methods for petrologic analysis correlation interpretation of depositional environments and construction of facies models

provenance of rifted continental crust at the nexus of east gondwana breakup the bruce rise a prominent bathymetric feature offshore the bunger hills east antarctica has basement of unknown crustal affinity and age in east gondwana the bruce rise is reconstructed near the naturaliste plateau offshore sw australia and microcontinents now submerged in the eastern indian ocean new zircon u pb hf data from two c 1150 ma granite samples dredged from the eastern escarpment of the bruce rise demonstrate that these rocks are dominated by xenocrystic cargo mesoproterozoic xenocrystic cores show textural evidence of melt mediated coupled dissolution precipitation to form rim domains with apparent ages that skew towards c 1150 ma the zircon u pb hf signatures from the xenocrysts in the bruce rise granites and from c 1230 to 1180 ma felsic intermediate granites and orthogneisses from the conjugate naturaliste plateau basement suggest late mesoproterozoic magmatism occurred at a transition in the regional tectonic architecture between a reworked archean cratonic margin and proterozoic juvenile crust on the basis of plate reconstructions exhumation and thinning of the basement to the bruce rise naturaliste plateau occurred predominantly during rifting of india prior to c 120 ma minor further thinning likely occurred leading up to the onset of seafloor spreading between australia naturaliste plateau and antarctica bruce rise from c 90 to 84 ma

petrogenesis and tectonic implications of 130 ma diabase dikes in the western tethyan himalaya western tibet abstract early cretaceous mafic dikes are widely exposed in the eastern tethyan himalaya however coeval mafic rocks are limited in the western tethyan himalaya we report the major and trace elements and zircon u pb ages of the newly discovered diabase dikes in the zhongba area in the western tethyan himalaya the icp ms zircon u pb analyses from one representative diabase dike yields a crystallization age of 129 8 1 3 ma mswd 6 7 these mafic dikes are characterized by high concentrations of tio2 2 81 3 27 fe2o3t 10 79 12 14 and mgo 5 11 6 71 the chondrite normalized diagram indicates the enrichment of lree and the depletion of hree the primitive mantle normalized trace element patterns do not display negative anomalies of nb ta and ti these characteristics imply an oib affinity trace element modelling sm yb vs sm suggests that the dikes originated from an enriched mantle source region composed primarily of garnet and spinel spinel

geochemical sourcing of rock specimens and stone artifacts from nihoa and necker islands hawai i we report geochemical analysis of seven rock specimens and six stone artifacts from nihoa and necker islands hawai i the analyzed rock specimens exhibit chemistry consistent with published data sets and establish a major element distinction between nihoa and necker their trace element data indicate that the analyzed rocks and artifacts are local in origin and they reliably discriminate from sources on kaua i these preliminary results support emory s thesis that early archaic hawaiian colonists on nihoa and necker relied on their local basaltic stone to manufacture stone tools containers and other portable objects

observations of ridge hotspot interactions in the southern ocean the evolution of ridge hotspot systems is not well understood in this investigation satellite derived marine gravity data are used in conjunction with underway bathymetric and magnetic anomaly profiles to investigate the nature of ridge hotspot interaction at four sparsely explored systems in the southern ocean these systems illustrate three different stages of ridge hotspot interaction in which a migrating spreading center approaches a hotspot pacific antarctic louisville passes over or is captured by the hotspot mid atlantic shona discovery and ultimately migrates away from the hotspot southeast indian kerguelen all of these systems show some evidence of discrete ridge jumps in the direction of the hotspot as the spreading center attempts to relocate toward the hotspot by asymmetric spreading interestingly these ridge jumps show no evidence of propagating offsets as have been seen on many other ridge hotspot systems a simple model predicts that typical plume excess temperatures can weaken the lithosphere sufficiently to promote asymmetric spreading and possibly allow a discrete ridge jump the presence of previously uncharted obliquely oriented aseismic ridges and gravity lineations between the ridge and the hotspot supports the notion of asthenospheric flux from the plume to the spreading center both before and after the time when the hotspot is ridge centered the azimuths of the aseismic ridges cannot be explained by plate kinematics alone they consistently extend from the ends toward the centers of the adjacent spreading segments suggesting some interaction between plume derived asthenospheric flux and local lithospheric structure the features discussed here also indicate that the transfer of asthenospheric material from the plume to the spreading center is influenced by the local plate boundary configuration and interaction with transform offsets

authigenic monazite and detrital zircon dating from the proterozoic rocky cape group tasmania links to the belt purcell supergroup north america abstract the oldest known rocks in tasmania occur in the proterozoic rocky cape group a 10 km thick quartzarenite siltstone pelite dominated succession previously constrained to have been deposited between 1450 ma and 750 ma the rocky cape group contains the enigmatic fossil horodyskia string of beads and has the potential to place tasmania within supercontinent reconstructions detrital zircon and authigenic monazite grains dated via u pb laser ablation inductively coupled plasma mass spectrometry la icpms analysis yield a deposition window between c 1450 ma youngest zircon populations and c 1330 ma oldest authigenic monazite population for the 9 km thick lower middle units pedder river siltstone lagoon river quartzite balfour subgroup which hosts horodyskia detention subgroup the upper units 1 km include the irby siltstone which is younger than c 1310 ma this unit is likely separated from both the lower middle units and the overlying c 1900 ma grains were identified authigenic monazite age distributions are complex with multiple age domains within most samples the common pb corrected 206u 238pb ages defined by oldest grains in each sample identify three statistically significant groups 1 1358 1292 ma inclusive of two sigma errors lagoon river quartzite and pedder river siltstone 2 1283 1239 ma cowrie siltstone and balfour subgroup and 3 1085 9 ma detention subgroup we suggest monazite was precipitated during episodic fluid flow events at these three stages in various parts of the basin the original source for ree bearing fluids could be detrital monazite which is rarely preserved and or organic matter from the interbedded carbonaceous shales the rocky cape group has a shared provenance with the higher grade metasediments surprise bay and fraser formations of nearby king island the newly derived depositional ages also overlap and support the correlation of these rock associations on the basis of current datasets there are no obvious correlations that can be made with mesoproterozoic basins preserved in mainland australia instead an overlap in the timing of deposition similarities in detrital zircon signatures and analogous depositional environment suggests the c 1 45 1 37 ga upper belt purcell supergroup missoula and lemhi groups of western north america constitutes a plausible correlation with the tasmanian mesoproterozoic succession if the unexposed palaeoproterozoic basement of tasmania correlates with the transantarctic mountains region of east antarctica as previously proposed we suggest that the overlying mesoproterozoic sequences were deposited during rifting of the supercontinent nuna between proto australia including the mawson craton of antarctica and laurentia as predicted by the most recent palaeogeographic reconstructions both the tasmanian and western laurentian packages were affected by episodic post depositional fluid flow events between c 1 35 and 1 05 ga possible thermotectonic imprints of the subsequent assembly of rodinia

geoid and gravity anomaly data of conjugate regions of bay of bengal and enderby basin new constraints on breakup and early spreading history between india and antarctica 1 timing of breakup of the indian continent from eastern gondwanaland and evolution of the lithosphere in the bay of bengal still remain as ambiguous issues geoid and free air gravity data of bay of bengal and enderby basin are integrated with shipborne geophysical data to investigate the early evolution of the eastern indian ocean geoid and gravity data of the bay of bengal reveal five n36 w fracture zones fzs and five isolated ne sw structural rises between the eastern continental margin of india ecmi and the 85 e ridge 86 e fz the fzs meet the 86 e fz at an angle of 39 the rises are associated with low gravity and geoid anomalies and are oriented nearly orthogonal to the fzs trend the geoid and gravity data of the western enderby basin reveal a major kerguelen fz and five n4 e fzs the fzs discretely converge to the kerguelen fz at an angle of 37 we interpret the fzs identified in bay of bengal and western enderby basin as conjugate fzs that trace the early cretaceous rifting of south ecmi from enderby land structural rises between the fzs of bay of bengal may either represent fossil ridge segments possibly have extinct during the early evolution of the bay of bengal lithosphere or may have formed later by the volcanic activity accreted the 85 e ridge two different gravity signatures short wavelength high amplitude negative gravity anomaly and relatively broader low amplitude negative gravity anomaly are observed on south and north segments of the ecmi respectively the location of continent ocean boundary cob is at relatively far distance 100 200 km from the coastline on north ecmi than that 50 100 km on the south segment on the basis of geoid gravity and seismic character and orientation of conjugate fzs in bay of bengal and western enderby basin we believe that transform motion occurred between south ecmi and enderby land at the time of breakup which might have facilitated the rifting process in the north between combined north ecmi elan bank and macrobertson land and in the south between southwest sri lanka and gunnerus ridge region of east antarctica approximately during the period between the anomalies m1 and m0 and soon after detachment of the elan bank from north ecmi the rifting process possibly had reorganized in order to establish the process along the entire eastern margins of india and sri lanka

early india australia spreading history revealed by newly detected mesozoic magnetic anomalies in the perth abyssal plain the seafloor within the perth abyssal plain pap offshorewestern australia is the only section of crust that directly records the early spreading history between india and australia during the mesozoic breakup of gondwana however this early spreading has been poorly constrained due to an absence of data including marine magnetic anomalies and data constraining the crustal nature of key tectonic features here we present new magnetic anomaly data from the pap that shows that the crust in the western part of the basin was part of the indian plate the conjugate flank to the oceanic crust immediately offshore the perth margin australia we identify a sequence of m2 and older anomalies in the west pap within crust that initially moved with the indian plate formed at intermediate half spreading rates 35 mm yr consistent with the conjugate sequence on the australian plate more speculatively we reinterpret the youngest anomalies in the east pap finding that the m0 age crust initially formed on the indian plate was transferred to the australian plate by a westward jump or propagation of the spreading ridge shortly afterm0 time samples dredged from the gulden draak and batavia knolls at the western edge of the pap reveal that these bathymetric features are continental fragments rather than igneous plateaus related to broken ridge these microcontinents rifted away from australia with greater india during initial breakup at 130ma then rifted from india following the cessation of spreading in the pap 101 103ma

geochemistry of kauai volcanics and a mixing model for the origin of hawaiian alkali basalts a comprehensive model is developed to explain the major trace element and strontium and neodymium isotopic characteristics of alkali basalts from hawaii the model is similar to that of chen and frey 1983 in that it requires mixing of a small melt fraction of morb source material with another component to generate the alkalic suite of a particular hawaiian volcano it differs from the chen and frey model in that the other end member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data alkali basalts and tholeiites from kauai analyzed in this study show a nearly complete transition in sr and nd isotopes there is a relatively well constrained array on a nd sr isotope correlation plot that can be explained by two component mixing of kauai tholeiite magma and a small amount of melt of east pacific rise source rock after corrections are made for fractional crystallization involving primarily clinopyroxene and olivine the sr and ba concentrations of kauai lavas plot along mixing curves defined by the above sources providing positive tests of the mixing hypothesis implications of this model are 1 the main source of hawaiian shield building tholeiites is a mixture of subducted crust primitive mantle and depleted asthenosphere that has been homogenized prior to melting 2 early alkalic volcanism as at loihi seamount will be characterized by greater isotopic heterogeneity than will late stage alkali basalt production and 3 there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given hawaiian volcano one represents smaller degrees of melting of the same source that generated shield building tholeiites kohala type the other derives from the mixed source discussed in this paper haleakala kauai type

paleomagnetic and geochronological results from the zhela and weimei formations lava flows of the eastern tethyan himalaya new insights into the breakup of eastern gondwana