uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

martian atmospheric and interior volatiles in the meteorite nakhla abstract we report isotopic abundances of xenon argon and nitrogen for the observed distinct components in martian meteorite nakhla in a stepwise release the 129xe 132xe ratios in the 800 c and 1000 c fractions show the signature of the modern atmosphere and other xe ratios when corrected for the cosmogenic component confirm the isotopically fractionated modern atmospheric component on the other hand the xe isotope ratios in the 1000 c steps reveal an isotopically unfractionated interior component but with radiogenic 129xe excesses the isotopic composition of this interior component is consistent with chass s xe solar type but is augmented by 244pu derived fission xe the fission components in interior trapped xe in both nakhla and chassigny suggest that mars effectively retained 244pu derived fission gas a heavy relative to interior n nitrogen signature in the 600 900 c temperature steps also suggests a recent incorporation of martian atmospheric gases the n signatures in the high temperature 1000 c steps are strongly affected by cosmic ray produced 15nc and 36ar and 38ar abundances are dominated by the cosmogenic component we discuss the signatures of martian interior nitrogen and heavy noble gases and the constraints they provide on the evolutionary history of mars

nitrogen and carbon isotopic composition in the diamonds of mbuji mayi zaire the concentration and isotopic composition of nitrogen measured in large diamonds gram size from the mbuji mayi kimberlite district zaire show a large range of variation 100 n 2100 ppm 11 2 15n 6 0 the15n depleted nitrogen is associated with the higher nitrogen concentrations the large diamonds are individually rather homogeneous in13c range of 13c 0 9 while variations occur within small octahedral diamonds from the same district range up to 5 8 the total range of 13c variation is about the same for the large diamonds 10 5 13c 5 5 the small octahedral diamonds 10 13c 4 6 and the carbonates from local kimberlites 11 8 13c 5 5 the diamond carbon isotopic data could indicate a complex story of crystallization within a deep seated system fractionating its carbon isotopes the nitrogen results indicate that nitrogen in diamonds is on the average markedly depleted in15n weighted average 5 15 relative to atmosphere sediments and upper mantle

evolution of the louisiade triple junction we derived new finite rotations for the opening of the coral sea using revised magnetic anomaly interpretations and fracture zone data from a gravity anomaly grid based on from satellite altimetry these rotations differ from the finite rotations that describe the opening of the tasman sea this confirms the existence of a triple junction between the australian plate the mellish rise and the louisiade plateau active during the opening of the coral sea 62 to 52 ma magnetic anomalies fracture zones visible on the gravity grid and strike slip faults indicate that extension occurred between the mellish rise and the louisiade plateau and extensional and transform motion occurred between australia and the mellish rise attached to the chesterfield and kenn plateaus the configuration of the triple junction from chron 27 to 26 was either ridge ridge ridge rrr or ridge fault fault rff at chron 26 58 ma the triple junction had a rff configuration and migrated southward as the relative motion between the louisiade plateau and the mellish rise was transferred to the boundary between the mellish rise and the kenn plateau the gravity low between the kenn plateau and the mellish rise is interpreted as a strike slip fault active from about 57 to 52 ma this configuration lasted until seafloor spreading ceased in the coral and tasman seas at about 52 ma our model implies extension in the osprey embayment that might explain small areas of oceanic crust west of the coral sea basin the western boundary of the coral sea was a ne sw strike slip fault active between 58 and 52 ma

early to mid tertiary inverted metamorphic gradient under the colorado plateau evidence from eclogite xenoliths in ultramafic microbreccias navajo volcanic field mid tertiary ultramafic microbreccia diatremes from the navajo volcanic field in the four corners area of the colorado plateau contain an ultramafic xenoliths suite in which lower temperature prograde metamorphic eclogites are associated with higher temperature garnet clinopyroxenites that were retrograded and hydrated to chlorite eclogite assemblages and directions of metamorphic reactions are consistent with the model of a laramide age inverted metamorphic gradient established as prograde reactions in a dehydrating oceanic slab caused hydration and cooling in the overlying subcontinental upper mantle wedge comparison with an inverse metamorphic gradient in the pelona schists inferred to represent an exposed part of the same subduction system in southwestern arizona and southern california confirms the shallow dip of the laramide subduction zone predicted by the regional distribution of subduction related volcanic rocks

refrigeration of the western cordilleran lithosphere during laramide shallow angle subduction the laramide orogeny has generally been attributed to a shift from normal angle to shallow angle subduction beneath the western margin of the north american plate in addition to important mechanical effects this shift may have had important thermal effects on the lithosphere in the western cordillera before the laramide geothermal gradients in the western cordillera were probably normal to high because of the presence below of a hot asthenospheric wedge with the shift to shallow subduction the wedge was probably expelled and replaced by a cold subducting slab that extended just below the cordilleran lithosphere this would shift the western cordillera into a cold forearc like thermal setting dominated by the refrigeration effects of the subducting slab thermochronologic data from the sierra nevada great basin mojave desert western arizona and perhaps the colorado plateau record latest cretaceous early tertiary cooling that may be evidence of such refrigeration if regional refrigeration occurred it would have several important implications 1 metamorphism in the western cordillera would have waned with the start of the laramide orogeny 2 the crust in the western cordillera would have strengthened and become much more resistant to deformation e g gravitational collapse and extension of thickened crust in the sevier hinterland would have been impeded and 3 latest cretaceous early tertiary isotopic cooling ages may not be valid indicators of a period of major regional uplift and unroofng

light element geochemistry and spallogenesis in lunar rocks abstract the abundances and isotopic compositions of carbon nitrogen and sulfur were measured in eleven lunar rocks samples were combusted sequentially at three temperatures to resolve terrestrial contamination from indigenous volatiles sulfur abundances in apollo 16 highland rocks range from 73 to 1165 g g whereas sulfur contents in apollo 15 and 17 basalts range from 719 to 1455 g g and correlate with tio 2 content lunar rocks as a group have a remarkably uniform sulfur isotopic composition which may reflect the low oxygen fugacity of the basaltic magmas much of the range of reported 34 s cd values 2 to 2 5 permil is caused by systematic analytical discrepancies between laboratories lunar rocks very likely contain less than 0 1 g g of nitrogen the measured spallogenic production rate 4 1 10 6 g 15 n g sample m y agrees remarkably closely with previous estimates an estimate which includes all available data is 3 7 10 6 g 15 n g sample m y lunar basalts may contain no indigenous lunar carbon in excess of procedural blank levels 0 7 g g highlands rocks consistently release about 1 to 5 g g of carbon in excess of blank levels but this carbon might either derive from ancient meteoritic debris or be a mineralogie product of terrestrial weathering the average measured spallogenic 13 c production rate is 4 1 10 6 g 13 c g sample m y the 13 c spallation exposure ages of rocks 15058 and 15499 are 184 and 135 m y respectively

geologic and kinematic constraints on late cretaceous to mid eocene plate boundaries in the southwest pacific abstract starkly contrasting tectonic reconstructions have been proposed for the late cretaceous to mid eocene 85 45 ma evolution of the southwest pacific reflecting sparse and ambiguous data furthermore uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest pacific plate circuit it is agreed that the southwest pacific comprised three spreading ridges during this time in the southeast indian ocean tasman sea and amundsen sea however one and possibly two other plate boundaries also accommodated relative plate motions in the west antarctic rift system wars and between the lord howe rise lhr and pacific relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period and determine the time dependent evolution of the southwest pacific regional plate circuit a model of 1 west dipping subduction and basin opening to the east of the lhr from 85 55 ma and 2 initiation of northeast dipping subduction and basin closure east of new caledonia at 55 ma is supported west dipping subduction and basin opening were not driven by convergence as has previously been proposed our plate circuit analysis suggests that between at least 74 ma and subduction initiation at 55 ma there was little net relative motion between the pacific plate and lhr

petrology and petrogenesis of cumulate peridotites and gabbros from the marum ophiolite complex northern papua new guinea

bundled turbidite deposition in the central pandora trough gulf of papua since last glacial maximum linking sediment nature and accumulation to sea level fluctuations at millennial timescale since last glacial maximum 23 19 ka earth climate warming and deglaciation occurred in two major steps bolling allerod and preboreal interrupted by a short cooling interval referred to as the younger dryas 12 5 11 5 ka b p in this study three cores mv 33 mv 66 and md 40 collected in the central part of pandora trough gulf of papua have been analyzed and they reveal a detailed sedimentary pattern at millennial timescale siliciclastic turbidites disappeared during the bolling allerod and preboreal intervals to systematically reoccur during the younger dryas interval subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1b the holocene interval was characterized by a lack of siliciclastic turbidites relatively high carbonate content and fine bank derived aragonitic sediment the observed millennial timescale sedimentary variability can be explained by sea level fluctuations during the last glacial maximum siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge although they did not occur during the intervals of maximum flooding of the shelf during meltwater pulses 1a and 1b siliciclastic turbidites reappear briefly during the younger dryas an interval when sea level rise slowed stopped or perhaps even fell the timing of the calciturbidite coincides with the first reflooding of eastern fields reef an atoll that remained exposed for most of the glacial stages

serpentinization of oceanic peridotites 2 kinetics and processes of san carlos olivine hydrothermal alteration 1 the kinetics of the reaction mg fe olivine h 2 o serpentine magnetite brucite h 2 were investigated at 500 bars in the 250 350 c range using natural olivine san carlos fo 91 with grain sizes between 1 and 150 mm and for run durations up to 514 d the amount of magnetite produced which directly relates to reaction progress was accurately monitored using up to 24 time resolved magnetic measurements per experiment eighty percent of serpentinization was achieved after 60 d for olivine grain sizes of 5 15 mm and after 500 d for grain sizes of 50 63 mm serpentinization kinetics were found to be inversely proportional to the geometrical surface area of the starting olivine grains they were one or two orders of magnitude slower than serpentinization kinetics commonly used for modeling serpentinization related processes the nature of the serpentine mineral product depended on the initial olivine grain size igs for igs in the 5 150 mm range lizardite formed and olivine dissolution was the rate limiting process at igs below 5 mm chrysotile crystallized instead of lizardite and the relationship between olivine surface area and reaction kinetics no longer held we infer that for such small olivine grain sizes dissolution is no longer the rate limiting process serpentinization in our experiments was associated with the creation of new reactive surface area according to two cooperative processes etch pits formation associated with dissolution and grain fracturing for igs above 20 mm interestingly fractures and etch pits with similar geometry and sizes were also observed for residual olivine with a typical grain size of 50 mm in serpentinized peridotite samples from the southwest indian ridge this suggests that the processes governing olivine serpentinization kinetics in our experiments are similar to those prevailing in natural systems we therefore suggest that the new kinetic data set that we present here which encompasses a range of olivine grain sizes and reaction temperatures is relevant to the serpentinization of olivine in the oceanic crust insofar as water is available

olivine antigorite orientation relationships microstructures phase boundary misorientations and the effect of cracks in the seismic properties of serpentinites antigorite bearing rocks are thought to contribute significantly to the seismic properties in the mantle wedge of subduction zones here we present a detailed study of the microstructures and seismic properties in a sample of antigorite olivine schist previously studied by kern et al 1997 2015 we have measured crystallographic orientations and calculated the seismic properties in three orthogonal thin sections microstructures indicate that deformation is localized in the bands with high antigorite fractions resulting in strong crystallographic preferred orientations cpos with point maxima of poles to 100 parallel to lineation and poles to 001 to the foliation normal olivine cpo suggests deformation under high temperature and low stress with a 100 fiber texture the cpo strength varies with grain size but is strong even in fine grained antigorite and larger grains tend to display higher internal misorientation orientation relationships between olivine and antigorite are evident in phase boundary misorientation analysis 100 ol 001 atg being more frequent than 001 ol 010 atg two new orientation relationships between olivine and antigorite have been documented seismic velocities decrease while anisotropy increases with increasing antigorite modal content antigorite grain shape has a weak effect on seismic velocities but it is important on anisotropy comparison between cpo derived seismic velocities using voigt reuss hill averages and geometric mean only showed good agreement in 1 3 of experimental velocities if the crack porosity of 1 63 measured experimentally at 600 mpa was used in the self consistent model with two crack orientations with planes normal to z and y good match with all experimental velocities was achieved the self consistent model implies important crack porosity in the foliation plane at 600 mpa that reduces vp normal to the foliation by 0 3 km s

rift propagation in rotational versus orthogonal extension insights from 4d analogue models abstract in rift settings extension rates often vary along strike due to rotation about a vertical axis or euler pole yet tectonic modelers traditionally apply constant along strike deformation rates here we compare rift development and propagation under traditional orthogonal extension versus rotational extension conditions the set ups involve brittle viscous layering and localize deformation through structural weaknesses seeds our models provide first order insights into the differences in rift development between both boundary conditions orthogonal extension produces a rift basin with constant synchronous along strike features whereas rotational extension induces along strike structural gradients diachronous rift development causing rift propagation and the development of v shaped basins we observe important viscous flow associated with differential pressure gradients in rotational extension we also describe the important effects of strain partitioning between rift axis and model boundaries the quantifying of which is crucial to avoid incorrect model interpretations although our model results are first order only they are in good agreement with various natural examples and previous modeling studies and highlight the importance of considering the third dimension when studying tectonic systems

australian plate motion and topography linked to fossil new guinea slab below lake eyre abstract unravelling causes for absolute plate velocity change and continental dynamic topography change is challenging because of the interdependence of large scale geodynamic driving processes here we unravel a clear spatio temporal relation between latest cretaceous early cenozoic subduction at the northern edge of the australian plate early cenozoic australian plate motion changes and cenozoic topography evolution of the australian continent we present evidence for a 4000 km wide subduction zone which culminated in ophiolite obduction and arc continent collision in the new guinea pocklington trough region during subduction termination coinciding with cessation of spreading in the coral sea a 5 cm yr decrease in northward australian plate velocity and slab detachment renewed northward motion caused the australian plate to override the sinking subduction remnant which we detect with seismic tomography at 800 1200 km depth in the mantle under central southeast australia at a position predicted by our absolute plate reconstructions with a numerical model of slab sinking and mantle flow we predict a long wavelength subsidence negative dynamic topography migrating southward from 50 ma to present explaining eocene oligocene subsidence of the queensland plateau 330 m of late eocene early oligocene subsidence in the gulf of carpentaria oligocene miocene subsidence of the marion plateau and providing a first order fit to the present day 200 m deep topographic depression of the lake eyre basin and murray darling basin we propound that dynamic topography evolution provides an independent means to couple geological processes to a mantle reference frame this is complementary to and can be integrated with other approaches such as hotspot and slab reference frames

tectonics of the new guinea area new guinea is a very large island 2500 km long by 600 km wide whose southern half geologically forms the northern part of the australian con tinent the long fold and thrust mountain range rising to heights above 4000 m that extends along the spine of central new guinea is the result of collisions of this northern margin of australia with island arcs during the northward drift of australia by some 3000 km during the last 37 m y the mountainous and hilly part of northern new guinea exposes igneous and metamorphic rocks milsom 1985 representing accreted parts of these collided arcs which are overlain by younger episutural or successor basins figure 1 the complex system of island arcs that sweep around the eastern side of australia and continue around northern australia new guinea linking the southwestern pacific region with eastern indonesia and the indian ocean essentially result from interactions between the wnw moving pacific plate and the nne moving india australia plate figure 2 the cenozoic fold and thrust mountain belts which characterize the aus tralian continental margin in new caledonia new guinea and eastern indonesia record the collisions figure 1 during the last 40 m y most occurred during the last 25 m y some in the last 3 m y associated with the continental margin and island arcs marginal to this continent over a strike length of 15 000 km

understanding the lunar surface and space moon interactions the surface of the moon is a critical boundary that shapes our understanding of the moon as a whole all geologic mapping and remote sensing techniques utilize only the outermost portion of the moon before leaving the moon for study in our laboratories all lunar samples that have been studied existed at or very near the surface with the exception of the deeply probing geophysical techniques our understanding of the interior of the moon is derived from surficial but not superficial information coupled with boundary of the lunar crust it is the lower boundary layer of the tenuous lunar atmosphere and constitutes both a source and a sink for atmospheric gases the surface is also where the moon interacts with the space environment causing changes in the physical nature of lunar materials and provides a laboratory for the study of processes that occur on all airless bodies the data obtained remotely by the galileo clementine and lunar prospector missions as well as data derived from lunar meteorites have resulted in major changes to our understanding of global distributions of chemistry and rocks this chapter summarizes the current understanding of this critical interface the surface of the moon in its role as the lower boundary of the lunar atmosphere the upper boundary of the crust and the window through which we view through remote sensing the composition of the crust and the history of the moon in this post lunar prospector time the view of the moon has changed lending new perspectives to lunar samples and lunar processes but the new view will likely remain in flux as we continue to digest the results from these recent space missions and move forward to a new era of lunar exploration despite the freshness of our perspective this is an important moment to capture

seismic velocities anisotropy and shear wave splitting of antigorite serpentinites and tectonic implications for subduction zones 1 antigorite the high temperature ht form of serpentinite is believed to play a critical role in various geological processes of subduction zones we have measured p and s wave velocities vp and vs anisotropy and shear wave splitting of 17 serpentinite samples containing 90 antigorite at pressures up to 650 mpa the new results combined with data for low temperature lt lizardite and or chrysolite reveal distinct effects of lt and ht serpentinization on the seismic properties of mantle rocks at 600 mpa vp 5 10 and 6 68 km s vs 2 32 and 3 67 km s and vp vs 2 15 and 1 81 for pure lt and ht serpentinites respectively above the crack closure pressure 150 mpa the velocity ratio of antigorite serpentinites displays little dependence on pressure or temperature serpentine contents within subduction zones and forearc mantle wedges where temperature is 300 c should be at least twice that of previous estimates based on lt serpentinization the presence of seismic anisotropy high pressure fluids or partial melt is also needed to interpret ht serpentinized mantle with vp 1 81 the intrinsic anisotropy of the serpentinites 3 8 16 9 with an average value of 10 5 for vp and 3 6 18 3 with an average value of 10 4 for vs is caused by dislocation creep induced lattice preferred orientation of antigorite three distinct patterns of seismic anisotropy correspond to three types of antigorite fabrics s l and ls tectonites formed by three categories of strain geometry i e coaxial flattening coaxial constriction and simple shear respectively our results are thought to provide a new explanation for various anisotropic patterns of subduction systems observed worldwide

modelling the anisotropic seismic properties of partially molten rocks found at mid ocean ridges abstract the problem of modelling the seismic properties of mid ocean ridge rocks of the axial magma chamber amc and the low velocity triangle lvt immediately below it has been addressed using two samples from oman ophiolite as examples the specimens are a layered gabbro from the lower oceanic crustal sequence and a harzburgite from the upper most mantle section at the palaeo ridge axis the seismic properties have been simulated at a temperature of 1200 c and pressure of 200 mpa so that the basalt melt is above its solidus various effective medium methods are discussed in the perspective of modelling rocks that have a strong background elastic anisotropy due to crystal preferred orientation cpo and an introduced anisotropy due to oriented melt filled inclusions calculations using various methods show a wide range of predicted melt fractions for a given seismic velocity the self consistent scheme scs and differential effective medium dem are compared in some detail a tensorial model was developed using a poro elastic method of gassman at low seismic frequency and a standard dem with isolated basalt inclusions at high frequency at low frequency the basalt pore fluid is considered to be everywhere connected and the pressure uniform whereas at high frequency basalt inclusions are isolated assuming the medium to be a standard linear solid the low and high frequency velocities were used to calculate the anisotropy of attenuation calculations with spherical basalt inclusions show that the seismic velocities decrease and attenuation increase with increasing melt fraction the symmetry of the background anisotropy due to cpo is preserved but gradually reduced with increasing melt fraction for the seismic velocities observed for the axial magma chamber amc with v p of 3 5 to 4 7 km s the model predicts 50 70 melt for the low velocity triangle lvt below the amc with v p of 4 8 5 6 km s the model predicts 35 50 melt predictions from the observed attenuations q 1 at the amc of 0 05 0 02 and in the lvt of 0 02 0 01 are around 60 and 45 melt respectively seismic anisotropy has been modelled with ellipsoidal basalt pancake shaped inclusions with their circular sections in the xy foliation plane only a 2 3 of ellipsoidal basalt inclusions are required to over print the anisotropy of the background medium there is a rapid decrease in v p and increase of q 1 for propagation normal to the foliation z with increasing axial ratio of the inclusions with increasing axial ratio the model predicts decreasing amounts of melt for given velocity v p in the z direction for the lvt only 15 25 melt is predicted for a 10 1 inclusion instead of the 35 50 of the spherical inclusion

deformation associated with the denudation of mantle derived rocks at the mid atlantic ridge 13 15 n the role of magmatic injections and hydrothermal alteration 1 outcrops of deeply derived ultramafic rocks and gabbros are widespread along slow spreading ridges where they are exposed in the footwall of detachment faults we report on the microstructural and petrological characteristics of a large number of samples from ultramafic exposures in the walls of the mid atlantic ridge mar axial valley at three distinct locations at lat 13 n and 14 45 n one of these locations corresponds to the footwall beneath a corrugated paleo fault surface bearing in mind that dredging and rov sampling may not preserve the most fragile lithologies fault gouges this study allows us to document a sequence of deformation and the magmatic and hydrothermal history recorded in the footwall within a few hundred meters of the axial detachment fault at the three sampled locations we find that tremolitic amphiboles have localized deformation in the ultramafic rocks prior to the onset of serpentinization we interpret these tremolites as hydrothermal alteration products after evolved gabbroic rocks intruded into the peridotites we also document two types of brittle deformation in the ultramafic rocks which we infer could produce the sustained low magnitude seismicity recorded at ridge axis detachment faults the first type of brittle deformation affects fresh peridotite and is associated with the injection of the evolved gabbroic melts and the second type affects serpentinized peridotites and is associated with the injection of si rich hydrothermal fluids that promote talc crystallization leading to strain localization in thin talc shear zones we also observed chlorite serpentine shear zones but did not identify samples with serpentine only shear zones although the proportion of magmatic injections in the ultramafic rocks is variable these characteristics are found at each investigated location and are therefore proposed as fundamental components of the deformation in the footwall of the detachment faults associated with denudation of mantle derived rocks at the mar

new sw pacific tectonic model cyclical intraoceanic magmatic arc construction and near coeval emplacement along the australia pacific margin in the cenozoic various reconstructions of the sw pacific for the late cretaceous and cenozoic suggest that northeast dipping subduction began in the south loyalty basin slb at 55 50 ma and that subsequent closure of the slb resulted in the diachronous emplacement of cretaceous paleocene ophiolitic nappes onto the norfolk ridge in new caledonia at 40 34 ma and in northland new zealand around 24 21 ma a fundamental problem with these models is that they do not account for the fact that ne dipping subduction had already been established offshore papua new guinea by at least 65 60 ma which resulted in the emplacement of the papuan ultramafic belt pub ophiolite at 59 58 ma a second issue is that the reconstructions are based largely upon unfounded assumptions as to the age and nature of the basement beneath the loyalty arc and three kings ridge finally reconstructions of the northland region are based upon the erroneous assumption that the age of the majority of the igneous component comprising the northland allochthon is late cretaceous paleocene when in fact it is oligocene a new model is presented whereby the pub new caledonia and northland ophiolites formed and were emplaced in a cyclical fashion above an extensive ne dipping cenozoic intraoceanic arc system which diachronously propagated n s along the entire eastern margin of the australian plate these infant arc ophiolites represent fragments of suprasubduction zone lithosphere sszl generated in the earliest stages of magmatic arc formation that were emplaced shortly after 20 m y as a result of forearc australian plate collision subduction inception was the result of subsidence of older morb like lithosphere generated within an extensive back arc basin to the east of the norfolk ridge during the earliest stages of slb formation above a southwest dipping pacific plate during emplacement of each ophiolite a crustal fragment of the older lithosphere was scraped off the ne dipping slab and subsequently back thrust beneath each ophiolite during its emplacement

continental break up of the south china sea stalled by far field compression the outcome of decades of two dimensional modelling of lithosphere deformation under extension is that mechanical coupling between the continental crust and the underlying mantle controls how a continent breaks apart to form a new ocean however geological observations unequivocally show that continental break up propagates in the third dimension at rates that do not scale with the rate of opening here we perform three dimensional numerical simulations and compare them with observations from the south china sea to show that tectonic loading in the direction of propagation exerts a first order control on these propagation rates the simulations show that in the absence of compression in that direction continental break up propagates fast forming narrow continental margins independently of the coupling when compression is applied propagation stagnates forming v shaped oceanic basins and wide margins changes in out of plane loading therefore explain the alternation of fast propagation and relative stagnation these new dynamic constraints suggest that the west to east topographic gradient across the indochinese peninsula prevented continental break up propagation through the 1 000 km wide continental rift of the central and west basin of the south china sea until the direction of stretching changed 23 million years ago resulting in bypassing and acceleration of continental break up propagation tectonic loading in the direction of propagation exerts an important control on the propagation of continental break up according to three dimensional simulations of the south china sea

structure of the papuan fold belt papua new guinea 1 the structure of the papuan fold belt differs substantially from the classical thin skinned structures of the canadian rockies mainly due to the weak and broken papuan lithosphere and incompetent clastic section compared to the strong cratonic lithosphere in canada overlain by limestones and quartzites the papuan margin was dissected by mesozoic extensional faults in part reactivated during neogene compression which created basement involved anticlines or elevated plateaus in the papuan fold belt the sedimentary section in the fold belt is deformed into large ramp anticlines in the southwest smaller miocene and mesozoic duplexes in the center and fault propagation folds in the northeast hydrocarbon discoveries to date have occurred in the southwestern anticlines which are interpreted as reactivated extensional structures the precursor rollover anticlines trapped oil generated in the late cretaceous such that present accumulations probably result from preservation of that oil during neogene thrusting mesozoic duplex structures are likely to be prospective but difficult to define and fault propagation folds rely upon unproven upper cretaceous sandstones as a reservoir

neogene evolution of the mixed carbonate siliciclastic system in the gulf of papua papua new guinea this paper outlines the evolution of the late cenozoic mixed carbonate siliciclastic depositional system in the gulf of papua gop using seismic gravity multibeam bathymetry well data sets and landsat imagery the deposition of the mixed sedimentary sequences was influenced by dynamic interplay of tectonics eustasy in situ carbonate production and siliciclastic sediment supply the roles of these major factors are estimated during different periods of the gop margin evolution the cenozoic mixed system in the gop formed in distinct phases the first phase late cretaceous paleocene was mostly driven by tectonics rifting created grabens and uplifted structural blocks which served later as pedestals for carbonate edifices active neritic carbonate accumulation characterized the second phase eocene middle miocene during this phase mostly eustatic fluctuations controlled the large scale sedimentary geometries of the carbonate system the third phase late miocene early pliocene was characterized by extensive demise of the carbonate platforms in the central part of the study area which can be triggered by one or combination of several factors such as eustatic sea level fluctuations increased tectonic subsidence uplift sudden influx of siliciclastics or dramatic changes in environmental conditions and climate the fourth phase late pliocene holocene was dominated by siliciclastics which resulted in the burial of drowned and or active carbonate platforms although some platforms still remain alive until present day

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

constraints on the flux of meteoritic and cometary water on the moon from volatile element n ar analyses of single lunar soil grains luna 24 core abstract we report new nitrogen and argon isotope and abundance results for single breccia clasts and agglutinates from four different sections of the luna 24 drill core in order to re evaluate the provenance of n trapped in lunar regolith and to place limits on the flux of planetary material to the moon s surface single luna 24 grains with 40ar 36ar ratios 10 1126 science 188 4184 162 is no longer apparent when the luna and apollo data are combined instead the n isotope signatures corrected for cosmogenic 15n are consistent with binary mixing between isotopically light solar wind sw n and a planetary n component with a 15n value of 100 to 160 the lower 15n values of luna 24 grains compared to apollo samples reflect a higher relative proportion of solar n resulting from the higher sw fluence in the region of mare crisium compared to the central near side of the moon carbonaceous chondrite like micro impactors match well the required isotope characteristics of the non solar n component trapped in low antiquity lunar regolith in contrast a possible cometary contribution to the non solar n flux is constrained to be 3 13 based on the mixing ratio of sw to planetary n obtained for recently exposed lunar soils we estimate the flux of micro impactors to be 2 2 5 7 103 tons yr 1 at the surface of the moon our estimate for luna 24 agrees well with that for young apollo regolith indicating that the supply of planetary material does not depend on lunar location thus the continuous influx of water bearing cosmic dust may have represented an important source of water for the lunar surface over the past 1 ga provided that water removal rates i e by meteorite impacts photodissociation and sputtering do not exceed accumulation rates

from orogenic collapse to rifting a case study of the northern porcupine basin offshore ireland abstract offshore ireland the north atlantic opening is generally interpreted as successive 10 to 15 myr long rifting events during the mesozoic however their interaction is poorly documented in terms of structural inheritance and fault reactivation from extensive seismic and well data in the northern porcupine basin we show that extension actually evolved over an abnormal period of ca 220 myrs with overlapping tectonic stages that all together reflect the irish atlantic margin construction from the palaeozoic during the carboniferous extension initiated throughout the variscan and caledonian thickened crusts and controlled the deposition of generally slightly tilted continental clastics two subsequent rifting events during the triassic lower jurassic and upper jurassic lower cretaceous controlled shallow to deep marine sedimentation in separated sub basins that progressively widen and connect once extension localised along bounding faults we propose that extensional tectonics first controlled by a general orogenic collapse reflecting an early stage of stretching is then followed by several rifting periods that ultimately evolved toward the hyper thinning of the margin and shaped an aborted rift propagator this evolution is due to pre existing orogenic related structures and boundary conditions variations such a continuum of deformation although pulsed implies varying structural interactions of crustal scale that are often recorded in syn tectonic sediments

evolutionary trends in volatiles of the nakhlite source region of mars 1 we report new data on isotopic systematics in nitrogen ar and xe of nakhlite nwa998 and discuss the implications of nakhlite signatures on the sources evolution and closed system properties of the nakhlite magma in the martian mantle the isotopic signatures of xenon in nakhlites are consistent and reveal a source region with the chass s xenon signature but which had assimilated fission gas starting with the initial early differentiation of mars to the time of magma eruption 1 3 gyr ago we note a trend of correlated enrichments of the fission gas and of trace elements ree in the source nakhlite nwa817 which contains abundant mesostasis and a hydrous phase shows a distinct nitrogen component as well as a fission gas excess in low temperature steps radiogenic 129 xe in nakhlites is associated with neither the fission gas nor the indigenous components and indicates a later incorporation possibly during magma ascent indigenous nitrogen isotopic signatures of 15 n 13 as observed in nakhlites except nwa817 attest to very limited exchanges of modem atmospheric gases with the solid planet this nakhlite nitrogen signature corresponds to the heavier of two indigenous signatures in chassigny and supports other evidence for an origin in similar source regions

cenozoic tectonics of new guinea major hydrocarbon discoveries have been made in eastern and westernmost new guinea and there is great potential for additional discoveries although the island is a type locality for arc continent collision during the cenozoic the age number and plate kinematics of the events that formed the island are vigorously argued the northern part of the island is underlain by rocks with oceanic island arc affinities and the southern part is underlain by the australian continental crust based on regional sedimentation patterns it is argued herein that the cenozoic tectonic history of the island involves two distinct collisional orogenic events the first cenozoic event the peninsular orogeny of oligocene age 35 30 ma was restricted to easternmost new guinea emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the australian continent beneath part of the inner melanesian arc this collision uplifted the papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the aure trough between the oligocene and miocene the paleogeography of the region was similar to present day new caledonia the continental crust under central and western new guinea remained a passive margin the second event the central range orogeny began in the latest middle miocene when the bulldozing of australian passive margin strata first created emergent uplifts above a north dipping subduction zone beneath the western part of the outer melanesian arc the cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the australian continental basement is dated at about 12 ma this collision emplaced the irian ophiolite and created the present mountainous topography forming the spine of the island

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

spreading mode of backarc basins in the western pacific abstract a number of phases are suggested in backarc spreading extension of the arc lithosphere is followed by spreading and formation of oceanic crust in the backarc basin in some basins a third phase of rifting with a reorientation of the spreading direction occurs during the second and third phases spreading is governed by rotation about a nearby pole and spreading axes are oblique to the transform faults this contrasts with the geometry of mid oceanic ridges where the ridges are on great circles perpendicular to the transform faults three spreading models are defined according to the various angular relations between transform faults and spreading axes backarc basins facing the pacific plate tend to open with axes spaced among adjacent ridge segments on projections parallel to the spreading axes type i spreading mode in some cases new spreading occurs in the countiguous area forming overlapped spreading axes type ii spreading mode initial spreading to form a backarc basin tends to spread with both spaced and overlapped axes type iii spreading mode inner backarc basins intercalated with other basins between the pacific plate also tend to spread with type iii spreading mode spreading modes and possible mechanisms for these formations in the backarc basins in the western pacific are discussed

nitrogen and argon release profiles in luna 16 and luna 24 regolith samples the effects of regolith reworking fines microbreccias and agglutinates from the luna 16 mature regolith 1635 and fines from the immature submature luna 24 regolith have been analysed for n and argon isotopes in order to understand the origin of isotopically distinct n released at different temperatures all high resolution runs reveal a similarity in the release of 36ar 40ar and n over a wide temperature interval the similarity in the 40ar and 36ar releases and the near coincidence in the 1635 agglutinates implies that the implanted species were redistributed and homogenised during regolith processing such that regardless of the huge difference in ion implantation energy between solar 36ar and non solar 40ar their present distribution and their release temperatures are now essentially equal a small amount of 40ar released in the lower temperature steps with elevated 40ar 36ar is considered to be trapped after reworking while such mixing and homogenisation may also be expected for n components of different origins to date all known stepped runs regularly demonstrate a reproducible variation in 15n suggesting no homogenisation we consider regolith n to be a mixture of several components trapped at different times and some nitrogen that was not involved in the reworking relatively heavy n released around 500 c appears to be the most pure form of the component trapped after reworking probably from accreted meteoritic matter middle temperature isotopically lighter n appears to be a mixture of solar and non solar n largely homogenised and therefore solar n can not be seen in its pure form bulk 15n as well as formally deconvoluted 15n thermal profiles imply that the non solar n has a variable 15n value several non solar n sources are considered with their input resulting in increasing regolith 15n with time because n from meteorites and idps appear to be dominant a mechanism is required to reduce the c n ratio typical of meteoritic matter to that approaching the low value observed in the lunar regolith preferential loss of methane appears to be a viable explanation following generation either by proton sputtering or in reducing vapour plumes

continental breakup and uhp rock exhumation in action gps results from the woodlark rift papua new guinea we show results from a network of campaign global positioning system gps sites in the woodlark rift southeastern papua new guinea in a transition from seafloor spreading to continental rifting gps velocities indicate anticlockwise rotation at 2 2 7 myr relative to australia of crustal blocks north of the rift producing 10 15 mm yr of extension in the continental rift increasing to 20 40 mm yr of seafloor spreading at the woodlark spreading center extension in the continental rift is distributed among multiple structures these data demonstrate that low angle normal faults in the continents such as the mai iu fault can slip at high rates nearing 10 mm yr extensional deformation observed in the d entrecasteaux islands the site of the world s only actively exhuming ultra high pressure uhp rock terrane supports the idea that extensional processes play a critical role in uhp rock exhumation gps data do not require significant interseismic coupling on faults in the region suggesting that much of the deformation may be aseismic westward transfer of deformation from the woodlark spreading center to the main plate boundary fault in the continental rift the mai iu fault is accommodated by clockwise rotation of a tectonic block beneath goodenough bay and by dextral strike slip on transfer faults within and surrounding normanby island contemporary extension rates in the woodlark spreading center are 30 50 slower than those from seafloor spreading derived magnetic anomalies the 0 5 ma to present seafloor spreading estimates for the woodlark basin may be overestimated and a reevaluation of these data in the context of the gps rates is warranted

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

nitrogen in chondritic metal we report new nitrogen isotopic data in metals of h l and one ll chondrites with n abundances in the range of 0 3 to 3 3 ppm and half of these 1 ppm nitrogen isotopic signatures in metals with low indigenous n concentrations are modified by cosmic ray spallation components corrections are required to determine the indigenous n signatures the metals of type 4 and 5 show uniform indigenous nitrogen 15n 6 8 0 5 and confirm a reported possible genetic association of chondritic metal with metal in iie and iva iron meteorites distinct isotopic signatures are observed in two metal samples of the portales valley h6 meteorite which both are inconsistent with signatures in h4 and h5 chondrites but possibly reveal a record of impact induced melting and metamorphism on the parent asteroid anomalous nitrogen signatures in metals of type 3 chondrites on the other hand may reflect residues of surviving presolar isotopic signatures

tectonics of the new guinea region the new guinea region evolved within the obliquely and rapidly converging australian and pacific plate boundary zone it is arguably one of the most tectonically complex regions of the world and its geodynamic evolution involved microplate formation and rotation lithospheric rupture to form ocean basins arc continent collision subduction polarity reversal collisional orogenesis ophiolite obduction and exhumation of ultra high pressure metamorphic rocks we describe the major onshore and offshore tectonic and geologic components including plate boundaries seismicity faults and magmatism and we integrate these with emerging ideas about mantle dynamics to evaluate the cenozoic tectonic evolution of new guinea future research opportunities to resolve the mantle structure beneath new guinea will enable mantle dynamics to be linked to lithospheric and surface processes virtually all plate tectonic and mantle processes have been active in the new guinea region throughout the cenozoic and as such

aqueous corrosion of olivine in the mars meteorite miller range mil 03346 during antarctic weathering implications for water on mars abstract several nakhlites clinopyroxenite meteorites from mars contain olivine phenocrysts with corrosion features identical in size shape and distribution to the smaller etch pits of well characterized weathered terrestrial olivine miller range mil 03346 is an antarctic nakhlite find recovered after long exposure to antarctic conditions the distribution of discrete olivine etch pits almost exclusively within a few hundred microns of allocation mil 03346 171 s documentably exposed surface suggests that they formed by terrestrial weathering in antarctica the small size of olivine etch pits in mil 03346 171 relative to commonly much larger etch pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short or the weathering conditions to which it was exposed did not favor olivine corrosion in the form of etch pit formation or both time scales for the formation of etch pits estimated from experimentally determined dissolution rates of olivine over a range of phs are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on mars etch pits of the observed size on mil 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic antarctic conditions but the terrestrial age of mil 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline antarctic water the paucity of similar etch pits in olivine from the interior of mil 03346 suggests that olivine in this mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1 3 billion years on mars than its exterior was subjected to during its pleistocene holocene exposure to antarctic weathering conditions

lunar nitrogen indigenous signature and cosmic ray production rate abstract indigenous lunar nitrogen composition and abundances have been determined in old ferroan anorthosite 60025 and in anorthositic breccia 67915 from north ray crater as well as in 55 cm deep volcanic glasses of 74001 double drive core from shorty crater also included in the set is the well documented lunar basalt 75075 collected near the camelot crater indigenous lunar n abundances are low at ppm level but there is some variation between glass rich cores mare basalts and anorthosites the uniform indigenous n isotopic signature of 15 n 13 0 1 2 is consistent with data reported previously for shorty crater samples the indigenous 15 n cannot account for the light nitrogen component observed in the lunar regolith samples we have determined cosmic ray production rates p 15 n for the above rocks and the drill core samples the average production rate estimate for low shielding of p 15 n 5 8 0 6 pg 15 n g ma is 60 higher than published lunar 15 n production rates but consistent with the meteoritic production rate derived from silicates in the enon meteorite when normalized to 2 irradiation geometry from the observed cosmogenic 15 n excesses and the reported cosmogenic 21 ne abundances in core 74001 we derive a 15 n c 21 ne c production rate ratio of 4 0 0 3 for silicates

late miocene to recent formation of the aure moresby fold thrust belt and foreland basin as a consequence of woodlark microplate rotation papua new guinea the aure moresby fold thrust belt and aure moresby foreland basin are located in the eastern gulf of papua gop papua new guinea png and formed during late miocene recent as the result of large scale counterclockwise rotation of the 355 000 km2 woodlark microplate to document the structure stratigraphy and age of convergent deformation along the poorly studied western edge of the rotating woodlark microplate we integrate results of 2 538 km of previously unpublished 2 d seismic reflection data with onshore geologic and gps studies from previous workers the late miocene aure moresby fold thrust belt is a 400 km long northwest trending fold belt exposed onshore in papua new guinea that plunges to the southeast where continuous folds and northeast dipping thrusts can be imaged in the subsurface for more than 250 km the arcuate trend of the aure moresby fold thrust belt along the southwestern coast and offshore areas of the papuan peninsula parallels the shape of the adjacent offshore aure moresby foreland basin and the strike of the transpressional segment of the left lateral owen stanley fault zone osfz passing along the center of the papuan peninsula as the osfz becomes more transtensional east of 148 e folds of the aure moresby fold thrust belt along southern coast of the peninsula become less prominent and the adjacent aure moresby foreland basin transitions into an undeformed cenozoic passive margin setting these observations of convergent an left lateral deformation along the aure moresby fold thrust belt are consistent with 1 counterclockwise rotation of the woodlark microplate known from regional gps studies 2 coeval opening of the woodlark basin along its southern edge in the late miocene and 3 rapid subduction at the new britain trench along its northern edge the kinematics of the rotating woodlark microplate are driven by slab pull forces acting on the actively subducting northern edge of the microplate

plastic deformation and development of antigorite crystal preferred orientation in high pressure serpentinites we have inferred the deformation mechanisms of antigorite by high resolution ebsd mapping of samples from cerro del almirez ultramafic massif betic cordillera se spain textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600 630 c and 1 6 1 9 gpa deformation was followed by static annealing of antigorite at ca 680 c the crystal preferred orientation cpo of antigorite is characterised by a strong alignment of 001 poles normal to the foliation plane and a weaker but clear parallelism between 100 axes and the macroscopic lineation defined by the elongation of magnetite aggregates analysis of misorientations across subgrains shows predominance of 010 rotation axis consistent with activation of the 100 001 slip system however tilt subgrain boundaries subparallel to 100 probably formed by edge dislocations of this system are subsidiary most subgrain boundaries are subparallel to 001 planes they are interpreted as 001 twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins modelling of the evolution of the antigorite cpo using a lower bound approach and considering different deformation regimes and sets of basal and non basal slip systems has shown that intensities of 100 and 010 maxima reflect the relative strength of the antigorite 100 001 and 010 001 systems activation of other basal or non basal slip systems does not change significantly the cpo patterns but results in less concentrated cpo 3d transpression models better reproduce the cpo of natural antigorite serpentinites we propose that the widespread occurrence of strong cpo in high pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on hk0 001 together with the activation of twinning implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge

origin of air like noble gases in oceanic basalts noble gas studies of oceanic basalts show the ubiquitous presence of an air like component which is usually attributed to a simple atmospheric contamination however simultaneous nitrogen and argon isotopic study shows the presence of heavy nitrogen with an isotopic composition 15n 18 accompanied by 40ar 36ar values much lower than the mantle value such a component can be attributed to recycled materials from subduction zones which are incorporated into these basaltic magmas during their ascent through a shallow enriched region in the mantle this suggests that a part of the air like noble gases in oceanic basalts is due to recycled atmospheric gases thus the air like noble gases in the oceanic basalts hitherto considered a hindrance provide useful clues for understanding the geochemical evolution of these samples

analyses of nitrogen and argon in single lunar grains towards a quantification of the asteroidal contribution to planetary surfaces abstract we performed nitrogen and argon isotopic analyses in single 200 m sized ilmenite grains of lunar regolith samples 71501 79035 and 79135 cosmogenic and trapped components were discriminated using stepwise heating with a power controlled co 2 laser cosmogenic 15 n and 38 ar correlate among different ilmenite grains yielding a mean 15 n c 38 ar c production ratio of 14 4 1 0 atoms atom this yields a 15 n production rate in bulk lunar samples of 3 8 5 6 pg g rock 1 ma 1 which agrees well with previous estimates the trapped 15 n values show large variations up to 300 among different grains of a given soil reflecting complex histories of mixing between different end members the 36 ar 14 n ratio which is expected to increase with increasing contribution of solar ions varies from 0 007 to 0 44 times the solar abundance ratio the trapped 15 n values correlate roughly with the 36 ar 14 n ratios from a non solar end member characterized by a 36 ar 14 n ratio close to 0 and variable but generally positive 15 n values to lower 15 n values accompanied by increasing 36 ar 14 n ratios supporting the claim of hashizume et al 2000 that solar nitrogen is largely depleted in 15 n relative to meteoritic or terrestrial nitrogen nevertheless the 36 ar 14 n ratio of the 15 n depleted solar end member is lower than the solar abundance ratio by a factor of 2 5 5 we explain this by a reprocessing of implanted solar wind atoms during which part of the chemically inert rare gases were lost we estimate that the flux of non solar n necessary to account for the observed 15 n values is comparable to the flux of micrometeorites and interplanetary dust particles estimated for the earth hence we propose that the variations in 15 n values observed in lunar regolith can be simply explained by mixing between solar wind contributions and micrometeoritic ones infalling on the moon temporal variations of 15 n values among samples of different antiquities could be due to changes in the micrometeoritic flux through time in which case such flux has increased by up to an order of magnitude during the last 0 5 ga

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

replacement of olivine by serpentine in the queen alexandra range 93005 carbonaceous chondrite cm2 reactant product compositional relations and isovolumetric constraints on reaction stoichiometry and elemental mobility during aqueous alteration abstract isovolumetric replacement of euhedral and anhedral olivine by serpentine produced both centripetal and meshwork textures in the cm2 chondrites alh 81002 and nogoya the compositions of these textural varieties of serpentine are uniform within narrow limits within each previously studied meteorite independent of the composition of olivine being replaced and different between the two meteorites in que 93005 cm2 coarse olivines of widely varying compositions fo are replaced in a texturally similar manner by compositionally uniform serpentine mg 0 73 0 05 fe 0 27 0 05 3 si 2 o 5 oh 4 the narrow compositional range of serpentine replacing coarse olivine indicates that the aqueous solution from which the serpentine formed was compositionally uniform on scales at least as large as the meteorite 2 5 cm in longest dimension isovolumetric textures and compositional observations constrain elemental redistribution from coarse olivine to serpentine and to surrounding phases during serpentinization regardless of olivine s composition isovolumetric replacement of coarse olivines by serpentine of the observed composition released more mg and si from olivine than was required to form the serpentine excess mg and si released by olivine destruction and not retained in serpentine were exported from the replaced volume olivines with different fa fo proportions contributed different amounts of fe and mg to the serpentine ferroan olivines released more fe than required to form the serpentines replacing them so some of the fe released from ferroan olivine was exported from the replaced volumes forsteritic olivines released less fe than required to form the serpentines replacing them so some fe was imported into the replaced volumes augmenting the small amount of fe released from forsteritic olivine in que 93005 fo 83 8 is the threshold composition between fe exporting and fe importing behavior in individual olivine serpentine pairs which released exactly the amount of fe required to form serpentine of the observed uniform composition compositions of serpentines isovolumetrically replacing olivines and threshold olivine compositions in que 93005 differ from the corresponding values in nogoya solvent and solute species diffused through the serpentine between the olivine serpentine interface and the aqueous solution outside the isovolumetrically replaced volume in que 93005 some of the fe released from ferroan olivine in excess of the amount required to form serpentine reacted with s sourced from outside the pseudomorphs to form fe sulfide decorating the margins of the pseudomorphs of serpentine after fayalitic olivine such fe sulfide decorated outlines after fayalitic olivine do not occur in alh 81002 or nogoya indicating different fe and s mass transfer regimes in different cm2 chondrites mg fe si and s in the aqueous solution including the excess mg and si exported from all serpentine pseudomorphs after olivine of any composition were available to be incorporated into other phases spatially separate from the pseudomorphs after olivine including regularly interstratified serpentine tochilinite serpentines that replaced coarse olivines in que 93005 and alh 81002 are less magnesian than those in nogoya indicating that the nogoya aqueous alteration environment was more evolved toward mg rich solutions this easily located and characterized phase assemblage may be potentially useful for characterizing clasts of varying degrees of alteration in brecciated and heterogeneous cm chondrites and future returned samples from mineralogically similar asteroids

contrasting styles of seafloor spreading in the woodlark basin indications of rift induced secondary mantle convection the woodlark basin in the southwest pacific is a young ocean basin which began forming by 6 ma following the rifting of continental and arc lithosphere the n s striking moresby transform divides the oceanic basin into eastern and western parts which have contrasting characteristics seafloor spreading west of moresby transform began after 2 ma and although spreading rates decrease to the west the western basin has faster spreading characteristics than the eastern basin these include 1 500 m shallower seafloor 2 bouguer gravity anomalies that are 30 mgals lower 3 magnetic anomaly and modeled seafloor magnetization amplitudes that are higher 4 a spreading center with an axial high in contrast to the axial valleys of the eastern basin 5 smoother seafloor fabric and 6 exclusively nontransform spreading center offsets in contrast to the eastern basin which has transform faults and fracture zones that extend across most of the basin overall depth contrasts and bouguer anomalies can be matched by end member models of thicker crust 2 km or thinner lithosphere 1 3 in the western basin correlated with these contrasts the surrounding rifted margins abruptly thicken westward of the longitude of moresby transform we examine alternative explanations for these contrasts and propose that rift induced secondary mantle convection driven by thicker western margin lithosphere is most consistent with the observations although rift induced convection has been cited as a cause for the voluminous excess magmatism at some rifted margins the observations in the woodlark basin suggest that this mechanism may significantly affect the morphology structure and geophysical characteristics of young ocean basins in alternate ways which resemble increased spreading rate

age of the metamorphic sole of the papuan ultramafic belt ophiolite papua new guinea abstract the papuan ultramafic belt pub ophiolite is former oceanic crust and upper mantle emplaced onto continental crust in papua new guinea png in a zone of general convergence between the pacific and australian plates the metamorphic sole beneath the ophiolite is best exposed in the musa kumusi divide and comprises a 40 to 300 m thick body of granulite and amphibolite facies rocks geochronological studies on the metamorphic sole using amphiboles from the granulites and amphibolites yield measured k ar ages ranging from 65 0 0 7 to 57 2 0 6 ma and average 40ar 39ar direct total fusion ages ranging from 67 0 0 7 to 59 5 0 2 ma five of the six 40ar 39ar plateau ages derived from age spectra lie between 58 6 0 2 and 57 8 0 2 ma with an overall mean age of 58 3 0 4 ma the large spread in measured k ar and 40ar 39ar total fusion ages is thought to be caused by the presence of variable amounts of excess argon the mean plateau age for five samples of 58 3 0 4 ma is interpreted to mark the time of cooling of the metamorphic sole following peak metamorphism we suggest that the development of the metamorphic sole and emplacement of the pub ophiolite onto the png crust occurred in a relatively short time interval in the paleocene

pieces of the ancient lunar crust ages and composition of clasts in consortium breccia 67915 we discuss the composition and chronology of clasts representing three minor lithologies in consortium breccia 67915 the lithologies studied are sodic ferrogabbro pristine troctolitic anorthosite 67915 26 and granulitic troctolitic anorthosite 67915 67 these lithologies were presumed to represent samples of the ancient lunar crust the pristine troctolitic anorthosite a typical member of the pristine anorthosite suite contains little or no trapped liquid consistent with its two phase mineralogy the plagioclase separates have 39ar 40ar plateau ages of 4 10 0 06 b y and a final rise in the age pattern may represent a memory of the earlier evolution the granulitic troctolitic anorthosite which has 13 times larger ree abundances displays a continuous rise of the 40ar 39ar ratio the last 25 of the 39ar release data establish a minimum age of 3 5 b y but the 244pu nd chronology suggests an age of 4 3 b y the sodic ferrogabbro samples which appear to be members of the mg gabbronorite group of pristine rocks show large ar losses but indicate plateaus in the low temperature data suggesting a metamorphic event more recently than 260 m y ago a time that is consistent with the north ray impact event 50 m y ago

rifting of the northern margin of the australian continent and the origin of some microcontinents in eastern indonesia abstract continental australia is bounded on the east south and west sides by passive margins and the geological histories of these are well documented falvey and mutter 1981 the northern margin of the australian continent is now an active collision margin its previous history as a passive margin has rarely been examined this paper shows how the late palaeozoic to mesozoic sequence which forms the northern margin of the australian continent in the island of new guinea is readily related to the tectonic stages of a rift drift sequence rifting start of breakup began at about 230 m y ago at the permian triassic boundary the onset of seafloor spreading is marked by a post breakup unconformity and ranges in age along the northern margin of the continent from 185 m y in papua new guinea to 170 m y in irian jaya from there the age of the post breakup unconformity continues to young in a southwesterly direction along the western margin of the australian continent reflecting the opening of the indian ocean off western australia the timing of the onset of spreading in central papua new guinea is consistent with the timing of the initiation of spreading in the proto pacific ocean proposed by nur and ben avraham 1977 by the end of the jurassic the northern margin of the australian continent faced a seaway which linked the proto indian and proto pacific oceans this newly formed ocean was separated from the pre existing oceans of the neo tethys and panthalassa by a screen of continents or microcontinents the identity of this screen is discussed and it is suggested that part of it is preserved in the microcontinents of eastern indonesia

the petrology geochronology and tectono magmatic setting of igneous rocks in the suckling dayman metamorphic core complex papua new guinea abstract southeastern papua new guinea has hosted magmatism throughout the cenozoic with the latest phase being concurrent with active extension in the woodlark rift there the suckling dayman metamorphic core complex sdmcc has exhumed middle crustal rocks in the past few million years along a still active low angle normal fault the mai iu fault uplift of the sdmcc has exposed metasedimentary and metaigneous rocks of late cretaceous pleistocene age that record an evolution from oceanic spreading to subduction to collision and finally to subduction inversion and extensional exhumation we present new petrographic whole rock geochemical and geochronologic zircon u pb la icp ms data from the sdmcc to reconstruct its long term evolution the dominant footwall lithology of the sdmcc the goropu metabasalt has a morb composition detrital zircons from metasedimentary beds intercalated with these basalts yield u pb based maximum estimates for deposition of 103 and 72 ma suggesting a late cretaceous spreading age of the oceanic protolith bulk compositions of low grade tholeiitic meta gabbroic and tonalitic rocks yau igneous complex that intrude the goropu metabasalt reveal both enriched and depleted light rare earth element patterns zircon u pb ages from the yau igneous complex range between 60 and 57 ma providing a minimum age for the formation of the goropu metabasalt much younger syn extensional granitoids in the mafic footwall of the sdmcc have calc alkaline to high k compositions and u pb ages on zircon between 3 7 and 2 0 ma our data indicate that the mai iu fault had re activated a paleogene thrust as an extensional detachment fault by 3 7 0 2 ma u pb ages of detrital zircons in modern streams draining the footwall of the sdmcc essentially reflect the ages revealed by the paleocene and plio pleistocene intrusions xenocrystic zircons in the plio pleistocene granitoids imply that the crust underlying the metabasaltic carapace of the sdmcc consists chiefly of australian continent derived sedimentary rocks

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

phanerozoic growth of asia geodynamic processes and evolution abstract accretion processes often obscured in mountain belts can be documented with great detail in se asia where these have taken place during the tertiary the resulting configuration showing accreted continental strips and tectonised wedges is illustrated by the tethysides jammed between the northern laurasian cratons baltica and siberia and gondwanian cratons africa arabia india and australia eurasia increased progressively in size due to the amalgamation of crustal and sedimentary belts at places where the processes are documented in the recent times they can be included within a collision factory which displays the opening of basins by rifting and sea floor spreading within the upper plate until they undergo a process of shortening both stages being subduction controlled in se asia the early stages are illustrated in the eastern sunda arc where the subduction of the sunda trench is blocked in sumba and timor region and flipped into the flores trough in less than 2 my the incipient shortening is at present taking place in the pliocene damar basins another stage where half of the upper plate basin has disappeared is documented in the celebes sea the examples of deformation being transferred further inland exist in the northern celebes sea and the makassar basin the next important stage is the complete consumption of the marginal basin where both margins collide and the accretionary wedge is thrust over the margin as illustrated in nw borneo and palawan each of these stages is responsible for a single short lived tectonic event the succession of several events composes an orogen which may last for over 10 my these events predate the arrival of the conjugate margin of the large ocean which marks the beginning of continental subduction as observed in the himalaya tibet region these examples show that the closure is generally diachronous through time as illustrated in the philippines we observe that the ophiolite obducted in such context is generally of back arc origin upper plate rather than the relict of the vanishing large ocean which is rarely preserved in the philippines once the crust is accreted the subduction zone progressively moved southward until its present position we propose that the lithospheric mantle of the accreted block is delaminated and rolls back in a continuous manner whereas the crust is deformed and accreted

emplacement of deep crustal and mantle rocks on the west median valley wall of the mark area mar 23 n abstract exposures of deep crustal and mantle rocks within the axial rift valley characterize accretion processes in the slow spreading mid atlantic ridge nine dives of the submersible nautile explored the western axial valley wall in the northern cell of the mark area mid atlantic ridge kane fracture zone where peridotite and gabbro outcrops had been previously reported in order to constrain the structure and determine emplacement mechanisms the ridge transform intersection massif on the western wall shows a section of gabbros from 6000 to 2500 mbsl locally overlain by metabasalts and metadolerites capped by slightly weathered basalts the morphology is controlled by ridge parallel faults dipping moderately 40 65 to the east transform parallel scarps present in the northernmost dives become rare toward the south brittle deformation along moderately dipping fault scarps produced a dense microcrack network filled with greenschist facies minerals chlorite actinolite epidote quartz locally overprinting high temperature ductile deformation fabrics the small hill located at 23 20 in the western wall shows good exposures of serpentinized peridotite between 3700 and 3100 mbsl above 3100 mbsl the summit of the hill is composed of pillow basalts and sediments the peridotite outerops display a strong schistosity dipping 20 40 to the east parallel to striated normal fault planes some steeper east facing fault scarps truncate the lower dipping fault surfaces the serpentinites deriving from a harzburgitic protolith are cut by rare dikelets of highly differentiated gabbro these new data combined with previous results of alvin dives are used to draw a generalized geological map of the western axial valley wall this map suggests a variation in the thickness of crustal units and composition along strike in the northern cell of the mark area the gabbro body disappears toward the south where basalts appear to directly overlie the mantle peridotites which are cut by isolated gabbroic dikelets low angle stretching affecting this heterogeneous lithosphere is probably responsible for the exposure of gabbros in the intersection massif and of peridotites further south

development of a bathymetric grid for the gulf of papua and adjacent areas a note describing its development 1 a new bathymetric grid for the gulf of papua and northern australia was produced for the area 140 150 e 6 14 s with a 3 6 110 m cell size new multibeam sonar surveys have added much needed detail to a region of the seabed where previously little was known in shallow australian waters bathymetry derived from landsat satellite imagery was used to supplement traditionally acquired bathymetric data for onshore areas shuttle radar topography mission data were used for topographic control the final grid revealed numerous features not observed in previous compilations of bathymetric data for the region bathymetric surveys on the continental shelf revealed an incised shelf with highly variable valley morphology prograding clinoforms are infilling valleys on the continental shelf and mark the seaward extension of the fly river delta a linear relict shelf edge barrier marks the shelf break in the northern ashmore trough region elsewhere the shelf break is scalloped and incised by canyons large mass transport deposits are widespread on the continental slope and indicate regions where mass wasting is common

serpentine minerals discrimination by thermal analysis this paper reports a complete set of tg dtg and dta data coupled with emitted gas analysis for well constrained almost pure serpentine samples serpentine dehydroxylation takes place between 550 and 800 c with dtg and dta peak temperatures progressively decreasing from antigorite 720 and 715 c respectively to lizardite 708 and 714 c polygonal serpentine 685 and 691 c and chrysotile 650 and 654 c antigorite has an additional diagnostic signal at 740 760 c always absent in the other serpentines and dependent on antigorite superperiodicity t shift of 20 c from 36 to 49 a modulation wavelength a sharp exothermic peak occurs at extremely constant temperatures 820 c independently from the starting serpentine structure the high t mineral assemblage is always represented by forsterite and enstatite based on the observed relationships between serpentine structures and dtg dta dehydroxylation temperatures thermal analysis may represent a useful tool for serpentine identification particularly in the case of natural massive samples where different varieties are mutually intermixed the accurate definition of serpentine mineralogy would have obvious implications in both geological petrological and health related issues

benthic foraminiferal response to sea level change in the mixed siliciclastic carbonate system of southern ashmore trough gulf of papua 1 ashmore trough in the western gulf of papua gop represents an outstanding modern example of a tropical mixed siliciclastic carbonate depositional system where significant masses of both river borne silicates and bank derived neritic carbonates accumulate in this study we examine how benthic foraminiferal populations within ashmore trough vary in response to sea level driven paleoenvironmental changes particularly organic matter and sediment supply two 11 3 m long piston cores and a trigger core were collected from the slope of ashmore trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera relative abundances principal component analyses and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time assemblage 1 with high abundances of uvigerina peregrina and bolivina robusta dominated between 83 and 70 ka early regression assemblage 2 with high abundances of globocassidulina subglobosa dominated between 70 and 11 ka late regression through lowstand and early transgression and assemblage 3 with high abundances of neritic benthic species such as planorbulina mediterranensis dominated from 11 ka to the present late transgression through early highstand assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand assemblage 3 signals increased off shelf delivery of neritic carbonates likely when carbonate productivity on the outer shelf great barrier reef increased significantly when it was reflooded benthic foraminiferal assemblages in the sediment sink slopes of ashmore trough likely respond to the amount and type of sediment supplied from the proximal source outer gop shelf

tectonic controls on carbonate platform evolution in southern papua new guinea passive margin to foreland basin the middle oligocene collision of the northern margin of the australian craton with a complex subduction system resulted in emplacement of a thrust mass and formation of a foreland basin that extended from the coral sea to the indian ocean the distribution of carbonate platform facies in southwestern papua new guinea reflects the transition from an eocene passive margin setting to the early stages of foreland basin evolution the initial basin configuration with terrigenous sedimentation confined to the proximal foredeep allowed carbonate deposition in the shallow environment adjacent to the peripheral forebulge subsequent southward migration of the basin resulted in a rapid increase in the area and thickness of carbonate platform deposition when the proximal foredeep became filled by detritus shed from the emerging orogen clastic sediments buried the platform and terminated carbonate deposition the history of the southern papua new guinea carbonate platform illustrates the paradox of carbonate deposition within the foreland basin whereby basin configuration initially encourages thick and extensive carbonate deposition but inevitably leads to terrigenous inundation and the demise of the carbonate platform

the age of ferroan anorthosite 60025 oldest crust on a young moon abstract sm nd isotopic data for mineral separates from the ferroan anorthosite 60025 define a precise isochron of 4 44 0 02ga age this age is roughly 110 m y younger than the formation of the first large solid objects in the solar nebula as recorded by the radiometric ages of the differentiated meteorites in the magma ocean model for early lunar differentiation ferroan anorthosites are the first crustal rocks to form on the moon if the moon is as old as the oldest meteorites the relatively young age determined for 60025 implies either that the magma ocean did not form synchronously with lunar formation or that the magma ocean required over 100 m y before reaching the stage of ferroan anorthosite crystallization alternatively we propose that the accumulated body of radiogenic isotope data for lunar rocks permit the moon to be as young as 4 44 4 51 ga if so isotopic evidence for chemical differentiation on the earth at about this same time suggests that the formation of the moon is reflected in the chemical evolution of the earth this in turn is consistent with the idea that the materials that now make up the moon were derived from the earth perhaps ejected by collision between the earth and another very large planetesimal during the final stages of accumulation of the terrestrial planets terrestrial origin models for the moon lessen the requirement that the earth and moon each have near chondritic relative abundances of the refractory elements and could require that certain chemical and isotopic characteristics of both bodies be considered in the framework of the chemical mass balance of the combined earth moon system

serpentine mineral replacements of natural olivine and their seismic implications oceanic lizardite versus subduction related antigorite we report on microstructural data obtained by optical microscopy and transmission electron microscopy concerning the crystallographic relationships of serpentine minerals with their host olivine in two contrasting situations in the first case mesh textured lizardite liz is developed in a standard 60 serpentinized oceanic harzburgite from the oman ophiolite where olivine converts to columnar lizardite the joined columns are perpendicular to the basal plane 001 liz corresponding to the pseudofibres observed optically the plane 001 liz is locally parallel to the narrow boundary ol liz thus column orientations register the interface of serpentinization the ol liz relationships are not strictly topotactic but reflect preferred cracking orientations in olivine parallel to 010 ol in the second case antigorite atg develops in a rare sample of antigorite schist in a kimberlite from moses rock colorado plateau representative of a suprasubduction zone mantle wedge high resolution transmission electron microscopy hrtem images along 010 atg show domains of very regular modulation with a 43 center dot 5 a wavelength m 17 where m is the number of silicate tetrahedra along the wave with few defects indicative of hp ht antigorite and also heavily kinked regions as fingerprints of strong tectonic shear tem imaging and electron diffraction patterns reveal two topotactic relationships between antigorite and olivine 100 atg 010 ol and atg ol the planes in contact are 001 atg 100 ol and 001 atg 010 ol respectively the 010 atg 001 ol and antigorite lamellae are parallel to the forsterite b axis in both cases the topography of olivine serpentine interfaces is controlled by open fluid pathways along microcracks oriented according to the anisotropy of the olivine aggregate in the cases studied the serpentine aggregate exhibits a preferred orientation inherited from that of the peridotite these results have some relevance to the seismic anisotropy of serpentinized mantle anisotropy of propagation of seismic waves as a result of the olivine fabric is maintained and reinforced with the development of lizardite conversely the development of antigorite produces a trench parallel fast s wave polarization and an anisotropy that is lowered at low degrees of serpentinization and then increased with increasing serpentinization

evidence for a predominantly non solar origin of nitrogen in the lunar regolith revealed by single grain analyses we measured the amounts of 14n and 36ar in single mineral and glass grains from a lunar soil by laser extraction with the goal of studying the controversial origin of trapped nitrogen in the lunar regolith the average 14n 36ar ratio of 29 ilmenite grains is 379 similar to the value determined previously on a large ilmenite separate from the same soil and 10 times larger than the solar ratio of 37 however the 14n 36ar ratios in the individual grains vary between 1 and 440 times the solar ratio 36ar amounts in the ilmenite grains scatter by more than two orders of magnitude n amounts by less than a factor of 6 the variability of the 14n 36ar ratio forms a striking contrast to the very uniform relative abundances of ar kr and xe trapped from the solar corpuscular radiation observed earlier in ilmenite and other mineral grains from the same soil this strongly suggests that on average some 90 of the n in the grains has a non solar source contrary to the often expressed view that essentially all n in the lunar regolith has been trapped from the solar wind the conclusion that the lunar regolith testifies to a secular variation of the n isotopic composition in the solar wind of 30 becomes thus highly questionable the origin of the bulk of trapped lunar nitrogen remains unknown

the submarine tectono magmatic framework of cu au endowment in the tabar to feni island chain png abstract the southwest pacific region and papua new guinea in particular is spectacularly endowed with mineral resources including some of the youngest and richest porphyry cu mo au deposits in the world among them is the giant porphyry epithermal ladolam au deposit on lihir island in the tabar lihir tanga feni tltf island chain northeast of new ireland its setting within a former forearc basin is very different from most southwest pacific porphyry and epithermal deposits our synthesis of published and previously unreleased data from ship based multibeam and seismic studies satellite gravimetry geochemistry and geochronology reveals a far more complex crustal structure and composition than is presently understood from the geology of the islands alone we show that the unique regional au endowment results from the alignment of various preconditions that are prolific to ore formation i hydrous and metal rich metasomatic veins in the mantle source ii second stage low volume partial melting due to incipient rifting iii high volatile contents and oxygen fugacities of the melts due to preferential melting of hydrous phases in the metasomatic veins and iv in the specific case of lihir unroofing of the volcanic edifice that led to boiling and rapid metal deposition this study shows that the location of the ladolam deposit on lihir is controlled by large scale structures that can be traced offshore and are the site of continuing submarine volcanism and epithermal style au mineralization the observed structural framework is dominated by the emergence of trans lithospheric faults that provided pathways for the melts to the seafloor near surface structural focusing of the ascending melts and fluids and a regional tectonic stress regime that stabilized the conditions over a significant period of time and or repeatedly marine seismic data confirms the complex structure of the tltf island chain each island group sits on tilted blocks that form horst structures separated by half grabens developed due to regional nw se directed extension regional compression perpendicular to the extension continues as a result of the transition from subduction to collision at the leading edge of the ontong java plateau the protracted transtensional motion between distinct crustal blocks controls the location and timing of magmatism and mineralization a kinematic link between volcanism at the location of lihir and the splitting of new ireland by ne directed propagation of seafloor spreading in the manus basin is suspected by combining onshore and offshore geology we propose a new model of the evolution of the new ireland basin magmatism along the tltf island chain and ultimately ore deposit formation this study demonstrates the importance of integrating offshore geology and geophysics into models that aim to explain the structural magmatic and sedimentary evolution of marginal basins that are host to economic mineral deposits

seismic wave velocity and anisotropy of serpentinized peridotite in the oman ophiolite shallow seismic measurements in harzburgite from the oman ophiolite performed in a zone where the maximum horizontal anisotropy is expected vertical foliation and horizontal lineation point to a dominant dependence of seismic properties on fracturing optical microscopy studies show that microcracks are guided by the serpentine lizardite penetrative network oriented subparallel to the harzburgite foliation and subperpendicular to the mineral lineation and that serpentine lizardite vein filling has a maximum concentration of 001 planes parallel to the veins walls the calculated elastic properties of the oriented alteration veins filled with serpentine in an anisotropic matrix formed by oriented crystals of olivine and orthopyroxene are compared with seismic velocities measured on hand specimens laboratory ultrasonic data indicate that open microcracks are closed at 100 mpa pressure e g j geophys res 65 1960 1083 and proc odp sci results leg 118 1990 227 above this pressure laboratory measurements and modeling show that p compressional and s shear wave velocities are mainly controlled by the mineral preferred orientation veins scaled with serpentine are effective in slightly lowering p and s velocities and increasing anisotropy the penetrative lizardite network does not affect directly the geometry of seismic anisotropy but contributes indirectly in the fact that this network controls the microcrack orientations comparison between seismic measurements of peridotite and gabbro in the same conditions suggest that p and s waves anisotropies are a possible discriminating factor between the two lithologies in the suboceanic lithosphere c 2003 published by elsevier b v

the earliest mantle fabrics formed during subduction zone infancy harzburgites obtained from the oldest crust mantle section in the philippine sea plate 52 ma along the landward slope of the southern izu ogasawara trench preserve mantle fabrics formed during the infancy of the subduction zone that is during the initial stages of pacific plate subduction beneath the philippine sea plate the harzburgites have relatively fresh primary minerals despite of their heavy serpentinizations and show inequigranular interlobate textures and crystal preferred orientation patterns in olivine 001 100 and opx 100 001 the harzburgites have the characteristics of residual peridotites whereas the dunites obtained from the same location as the harzburgites provide evidence for the earliest stages of arc volcanism during the inception of subduction we propose that the 001 100 olivine patterns began forming in immature fore arc mantle with an increase in slab derived hydrous fluids during the initial stages of subduction in in situ oceanic island arc

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

the early middle miocene subduction complex of the louisiade archipelago southern margin of the woodlark rift field microstructural and 40ar 39ar thermochronologic data from the louisiade archipelago the southern rifted margin of the woodlark basin in se papua new guinea document an accretionary wedge that formed during early middle miocene n dipping subduction of the australian margin and transpression along the australian pacific plate boundary metasedimentary rocks of the calvados schist and the metagabbros that intrude them were metamorphosed at up to greenschist facies conditions three tectonic foliations s1 s3 are present and f1 f3 fold hinges plunge ese or wnw parallel to mineral stretching and intersection lineations fold vergence is dominantly to the sw and top to the sw thrusting of ultramafic rocks over the calvados schist is documented locally on rossel island the data suggest progressive deformation associated with nne ssw shortening and ese wnw extension via dissolution precipitation creep and more locally dislocation creep 40ar 39ar step heating analyses of three white mica separates yield middle miocene plateau or plateau like segments that are affected by variable pliocene argon loss and are interpreted as syntectonic mica growth during metamorphism and deformation followed by partial resetting just prior to the onset of seafloor spreading in the woodlark basin a 12 ma 40ar 39ar age from a dacite sill of the panarora volcanics provides a minimum age constraint for the termination of northward subduction and a maximum age for crosscutting brittle strike slip faults these data are critical to constraining the subduction exhumation history of the world s youngest high ultrahigh pressure terrane and further support analogies between se papua new guinea and the early oligocene western alps

textural evolution during high pressure dehydration of serpentinite to peridotite and its relation to stress orientations and kinematics of subducting slabs insights from the almirez ultramafic massif abstract the almirez ultramafic massif se spain preserves the transformation of high p antigorite atg serpentinite to chlorite chl harzburgite 1 6 1 9 gpa 680 710 c a metamorphic reaction that is the primary source of water at the intermediate depth of subducting slabs we present a detailed ct and ebsd study of oriented samples across the atg serpentinite dehydration isograd to investigate the textural evolution during serpentinite dehydration to peridotite and its relation to stress orientations and the kinematics of subducting slabs above the atg out isograd atg serpentinite shows a prograde mylonitic foliation and a weak shape preferred orientation spo of oxide aggregates defining a n s stretching lineation the antigorite crystal preferred orientation cpo is characterized by 001 atg perpendicular to the foliation and the poles to 100 atg and 010 atg distributed in a girdle like symmetry with 100 atg nearly parallel to the stretching lineation the antigorite microstructure and cpo are consistent with deformation by dislocation creep twinning and dissolution precipitation creep these textures record the long term shear deformation near the slab interface where the main compressive stress 1 was at an acute angle to the foliation below the atg out isograd atg serpentinite dehydrated to unfoliated coarse grainedchl harzburgite with granofels or spinifex textures distributed in alternating decameter sized lenses crystallization of granofels and spinifex chl harzburgite records respectively a sequence of slow and fast fluid draining events during serpentinite dehydration under the same orientation of the principal stresses that resulted in the shear deformation of the atg serpentinite both textural types exhibit coarse grained textures with systematic mineral cpos and spos and microstructures without evidence of major ductile deformation the texture of the granofels chl harzburgite formed by a topotactic dehydration reaction after atg serpentinite coupled to compaction leading to an olivine layering subparallel to the atg serpentinite foliation the olivines of granofels chl harzburgite are rounded and display a weak cpo that can be accounted for by the topotactic reaction 100 atg 100 ol and 001 atg 010 ol after atg serpentinite similarly orthopyroxene shows a marked cpo consistent with the topotactic reaction 100 opx 001 atg and 001 opx 100 atg spinifex chl harzburgite displays systematic mineral spo and cpo spinifex olivines are tabular on 100 ol and elongated along 001 ol c b a and define a ese wnw platelet lineation the average texture is characterized by 001 ol opx subparallel to a strong ese wnw oxide aggregate lineation and 100 ol opx and 001 ol opx within a plane of similar orientation to the atg serpentinite foliation the spos and cpos of spinifex chl harzburgites are composed of up to four orientation populations of tabular olivines where one population is volumetrically dominant in all samples relative to the main orientation population the cpo of olivine shows clustered distribution of 100 ol and 010 ol maxima rotated at systematic angles around 001 ol these clustered cpos and spos show a remarkable correlation with the orientation of the principal paleostresses the preponderant orientation population of tabular olivines lies on the plane of maximum compression 2 3 plane and has 010 ol and its 100 ol tabular faces nearly perpendicular to the atg serpentinite foliation this population can be accounted for by oriented growth of platy crystals perpendicular to 1 the other populations lie in the plane perpendicular to the least compressive stress 3 and the planes of maximum shear the driving force and causes for the oriented crystallization of tabular olivine in these planes is uncertain but their correlation with paleostresses suggests a cause effect relationship spinifex and granofels chl harzburgites show a marked ese wnw oxide aggregate lineation that differs in orientation from that of atg serpentinite and is approximately parallel to the intermediate compressive stress 2 these lineations and the platelet lineation of spinifex chl harzburgite may be due to along strike fluid flow below the permeability barrier that constituted the atg out dehydration isograd our study shows that the kinematics of the slab paleostresses and fluid flow exert a dynamic control on the textures of atg serpentinite dehydrating to peridotite in subducting slabs

volatiles nitrogen noble gases in recently discovered snc meteorites extinct radioactivities and evolution abstract we report noble gas and nitrogen analyses of newly discovered snc meteorites one nakhlite nwa817 and four shergottites nwa480 nwa856 nwa1068 and sau 005 the k ar age 1 3 ga as well as the cosmic ray exposure cre age 10 0 1 3 ma of nakhlite nwa817 agree with data of nakhla the cre ages of nwa480 nwa856 and nwa1068 2 35 0 20 2 60 0 21 and 2 01 0 65 ma respectively are consistent within uncertainties with other basaltic shergottites but the cre age of sau 005 1 25 0 07 ma is distinct and indicates a different ejection event bulk k ar ages of all shergottites exceed the reported radiometric ages and reveal the presence of inherited radiogenic 40 ar in basaltic lavas the isotopic composition of nitrogen trapped in these snc meteorites is not homogeneous since 15 n values of either 15 to 20 or 45 indicate different nitrogen reservoirs all shergottites contain fission xenon from 238 u and fission xe of extinct t 1 2 82 ma 244 pu previously identified in alh84001 in chassigny and in nakhla is also present in at least one shergottite nwa856 the shergottites contain less fissiogenic xe than other snc suggesting that either their source was more degassed or that the magma source region closed at a later time in nakhlites fission xenon from 244 pu correlates with uranium a geochemical proxy of plutonium thus it is possible that fissiogenic xe was not inherited during magma differentiation but rather was produced in situ and retained in refractory mineral assemblages in this interpretation the magma evolution that settled the mineralogy and geochemistry of nakhlites took place at a time when 244 pu was alive and pre dated the late events recorded in their radiometric ages alternatively fissiogenic xenon was trapped from a mantle source during closed system evolution of the parent magmas in which case such evolution might have taken place at considerable depth pressure in order to inhibit magma degassing during the course of differentiation

mesozoic history of the fairway aotea basin implications for the early stages of gondwana fragmentation the fairway ridge is a buried continental structure that separates the fairway basin from the new caledonia basin the proposed cretaceous age of the fairway basin has remained highly hypothetical to date deep offshore petroleum exploration wells revealed well dated mesozoic carbonaceous sedimentary rocks in the taranaki basin at the southern end of the aotea basin in this paper we use geophysical data to confirm the continuity of the 2000 km long fairway aotea basin connecting new caledonia to new zealand and prove its early late cretaceous age analysis of seismic reflection profiles together with newly compiled gravity and magnetic maps reveals late cretaceous ne sw trending lineaments projecting northeastward from major tasman sea fracture zones and the bellona trough which demonstrate that the opening of the fairway aotea basin predates the opening of the tasman sea this result combined with observations of the mesozoic regional geology suggests that the lord howe fairway and norfolk ridges are part of a remnant late early cretaceous continental arc which was fragmented into three pieces by the late early to early late cretaceous this event might be contemporaneous with a plate motion change between the gondwana and pacific plates and or the arrival of the hikurangi plateau in the subduction zone around 105 ma which caused the cessation of subduction along this plate boundary we interpret either of those two events as being possible trigger events for the post early cretaceous fragmentation of the eastern gondwana margin in a slab retreat process

deformation zone jumps in a young convergent setting the lengguru fold and thrust belt new guinea island abstract the lengguru fold and thrust belt in west papua indonesia has all the characteristics of a young orogen involved in a rapidly changing tectonic setting the analysis of the young wedge shows however that its internal shortening has ceased recently and that it is nowadays suffering severe extension recent topographic data marine industrial seismic lines and drilling were used with field observations and measurements to create detailed cross sections and a new structural map the study allows us to distinguish two superimposed prisms composed of stacked mesozoic marine sediments of the australian margin against a crustal buttress the construction of these two wedges is younger than 11 myr the structures of the lengguru belt external zones are sealed by an unconformable clastic series indicating that the construction of the lengguru prism had aborted suddenly due to a change in the way the australian and pacific plate convergence was accommodated at that time the internal zones probably started to exhume and the tectonic regime became extensional nowadays the internal part of the lengguru fold and thrust belt is undergoing an active east west extension we believe that the extension observed in the lengguru wedge is coeval with a transition from a compressive to a transtensional regime illustrated in the central range of papua and the onset of the tarera aiduna and paniai left lateral faults the structure of the lengguru belt therefore results from events occurring over a very short time span a previous late miocene northeast southwest compression linked to the subduction process a second from middle miocene to early pliocene and a late pliocene quaternary global extension in the whole range the evolution is compared with that of the seram wedge and the misool onin kumawa continental ridge to the west where deformation is accommodated at a localized zone which jumps as convergence between australian and pacific plate proceeds this evolution of the belt reflects rapid changes in the accommodation oblique shortening with the isolated orogenic wedge of lengguru fold and thrust belt left to collapse this example illustrates the way a long lasting subduction terminates at the lithospheric scale the deformation remains rooted at the suture zone however at the surface the shortening is suddenly widespread over a large area during a very short time span formation of the lengguru belt prior to being transferred to another plate boundary

geological evolution regional perspectives and hydrocarbon potential of the northwest phu khanh basin offshore central vietnam abstract seismic stratigraphic and structural analyses of the northwest phu khanh basin offshore central vietnam based on 2 d seismic data indicate that the initial rifting began during the latest cretaceous or palaeogene controlled by left lateral transtension along the east vietnam boundary fault zone evbfz and northwest southeast directed extension east of the evbfz rifting stopped due to transpression during middle oligocene times but resumed by left lateral transtension during the late oligocene thick sequences of lacustrine and alluvial sediments were deposited during the palaeogene rift periods the late oligocene rifting ended due to inversion triggered by right lateral wrenching near the palaeogene neogene boundary following the onset of this inversion regional uplift and volcanism took place in the southern half of the study area and contemporaneous subsidence and transgression took place farther north leading to widespread carbonate deposition as the right lateral wrenching decreased during the early neogene thermal subsidence and siliciclastic sedimentation became dominant resulting in the buildup and southward propagation of the shelf slope sediment accumulation and subsidence rates increased after the middle miocene times due to eastward tilting of central vietnam and the adjacent offshore area potential direct hydrocarbon indicators dhis in the phu khanh basin include common amplitude anomalies gas chimney like features and seafloor gas seeps in addition oil seeps are found at dam thi nai immediately landward of the basin geochemical analyses of the oil seeps indicate the existence of at least two early to peak mature source rocks maturation modelling combined with the seismic analysis suggests the likely presence of oil kitchens 40 50 km downdip in the basin and a fairly simple oil migration route the basin is probably charged from lacustrine syn rift mudstones humic coals and fore reef marls potential reservoirs are turbidite lowstand delta shelf and coastal sandstones as well as platform and reef carbonates and fractured basement various structural and stratigraphic traps formed during the palaeogene and early neogene prior to the main stage of petroleum generation

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

successive rifting events in marginal basins the example of the coral sea region papua new guinea reactivation of extensional structures is commonly inferred during rift evolution in that context we present original seismic interpretation to explore the geometry and interactions of three successive rifting events in the coral sea region papua new guinea the first event r 1 poorly documented occurred during the triassic along an older n s permian structural fabric during the jurassic extensional faults were reactivated through a second extensional episode r 2 which formed small 10 20 km basins bounded by n s ne sw and e w listric faults extension prolonged during the lower cretaceous with seafloor spreading in the owen stanley oceanic basin now incorporated in the papuan fold and thrust belts a third late cretaceous extensional phase r 3 gently reactivated some of the faults with very limited landward tilt in most basins and deformation located along the present continent ocean transition seafloor spreading in the coral sea followed from danian to ypresian this extensional system is sealed by unequally preserved eocene strata that mark the onset of postrift thermal subsidence prior to the margin inversion from oligocene onward this overall evolution suggests various extensional systems that are geographically and temporarily defined the one another the early rifting of the crust is controlled by preexisting continental features resulting in the local pangaea breakup in contrast the coral sea propagator cuts through the rifted margin and is controlled by a subduction complex in accordance with the tasman sea opening this evolution underlines the interactions existing between two extension modes in agreement with variations of the regional geodynamical setting around australia

arc continent collision in papua guinea constraints from fission track thermochronology the papua new guinea png mobile belt adjacent to the finisterre arc was formerly the leading ne corner of the australian plate that converged obliquely with the pacific plate forty new apatite and zircon fission track analyses of mobile belt rocks previously dated by k ar and rb sr analyses constrain neogene time temperature paths and tectonic models the paleogene arc along the southern margin of the caroline plate was juxtaposed against png in the early miocene coeval with locking up of the west dipping solomon subduction zone by the ontong java plateau these events initiated wrenching along the northern png margin and increased westward subduction of the solomon sea plate beneath the eastern margin the mobile belt underwent extension above the downgoing slab with rapid cooling of metamorphic rocks at 17 ma immediately prior to emplacement of the maramuni arc from 17 to 12 ma a change in plate motion at 12 10 ma terminated the arc and caused png caroline plate convergence creating the orogenic belt in new guinea from 12 to 4 ma this resulted in 4 5 km of uplift and 3 km of denudation and cooling of the entire mobile belt in the late miocene propagating westward along the mobile belt at 8 5 ma and southward into the fold belt at 5 4 ma the compression caused thrusting of miocene strata within the mesozoic type section a further change in plate motion at 4 3 ma returned the margin to transpression with local compression along strike slip faults and ongoing collision of the finisterre arc terrane