buried but preserved the proterozoic arubiddy ophiolite madura province western australia abstract we describe a previously unidentified proterozoic ophiolite complex situated in the madura province in southeastern western australia the madura province is almost entirely covered by mesozoic to cenozoic basin rocks but new basement drillcores have revealed oceanic crustal assemblages that record continental marginal basin formation followed by oceanic subduction and basin closure the pinto basalt has e morb oib chemical affinity and nd 1600 ma from 2 54 to 3 3 it formed by mantle upwelling beneath extending crust in an ocean continent transition zone and must be considerably older than c 1389 ma adakite that intrudes it the sleeper camp formation comprises mafic metavolcaniclastic schist intruded by metadolerite and plagiogranite veins zircon crystals from the metavolcaniclastic schist yield a dominant age component and maximum depositional age of 1536 13 ma the metadolerite and plagiogranite veins have zircon crystallization ages of 1479 8 ma and 1471 5 ma respectively interlayered basalt and sediments of the malcolm metamorphics have a maximum depositional age of c 1470 ma and were metamorphosed at 1315 11 ma the mafic rocks from both units are tholeiitic with morb like hfse ratios that point to a depleted mantle source similar to n morb but with trace element patterns that indicate subduction enrichment v ti ratio trends suggest the sleeper camp formation marks oceanic subduction initiation at c 1479 ma the progression to oceanic arc formation is recorded by the malcolm metamorphics after c 1470 ma and the haig cave supersuite from 1415 to 1389 ma the majority of these rocks occur within the hanging wall of the rodona shear zone and were structurally emplaced above the continental margin of the west australian craton between 1389 and 1330 ma during oceanic arc continent collision forming the arubiddy ophiolite complex the occurrence of oceanic crustal assemblages behind the accreted ophiolite complex frozen by the emplacement of voluminous 1192 1125 ma moodini supersuite ferrogabbros and granites demonstrates that continental collision did not occur between the west australian and south australian cratons the preservation of rocks of oceanic affinity behind ophiolites could be a hallmark of other proterozoic terranes that have escaped full continent continent collision

anatomy of a meltwater drainage system beneath the ancestral east antarctic ice sheet the east antarctic ice sheet was larger than present during past cold periods seafloor geophysical data show that in the ross sea the extended ice sheet was underlain by an active hydrologic system during the glacial termination

polythermal three dimensional modelling of the greenland ice sheet with varied geothermal heat flux computations over 50 000 years into steady state with greve s polythermal ice sheet model and its numerical code are performed for the greenland ice sheet with today s climatological input surface temperature and accumulation function and three values of the geothermal heat flux 42 54 6 29 4 mw m 2 it is shown that through the thermomechanical coupling the geometry as well as the thermal regime in particular that close to the bed respond surprisingly strongly to the basal thermal heat input the most sensitive variable is the basal temperature field but the maximum height of the summit also varies by more than 100m furthermore some intercomparison of the model outputs with the real ice sheet is carried out showing that the model provides reasonable results for the ice sheet geometry as well as for the englacial temperatures

heat flow heat production and lithospheric thermal regime in the iberian peninsula abstract the first heat flow and heat production maps of the iberian peninsula and its margins using previously acquired data are presented the surface heat flow map includes 553 determinations carried out on water and mining exploration wells oil exploration wells and on the seafloor the surface heat flow varies noticeably from the iberian mainland 65 10 mw m 2 to the atlantic and the mediterranean margins where the heat flow reaches values of about 40 50 mw m 2 and 80 100 mw m 2 respectively the heat production map consists of 664 determinations carried out on rock samples from the variscan iberian massif and the betics the higher values are obtained for granitic rocks 2 5 3 5 w m 3 whereas metasediments and basic rocks reach values of 1 2 5 w m 3 and nearly zero respectively the lithospheric structure deduced for the iberian peninsula by combining heat flow heat production and elevation data indicates that most of the iberian mainland is characterized by a lithospheric thickness of 110 5 km this value is maintained across the west atlantic margin whereas towards the mediterranean margin the lithospheric thickness decreases down to 60 40 km this study also suggests that the heat production in the southern variscan iberian massif must be noticeably higher 3 7 0 5 w m 3 than in the rest of the areas in order to fit the measured heat flow crustal thickness and elevation data

heat flow from the west african shield the heat flow over precambrian shields is generally lower than over other continental provinces previous observations at 9 sites of the west african shield have shown that heat flow ranges from 20 mw m sup 2 in niger to 38 42 mw m sup 2 in liberia ghana and nigeria since some of these values are lower than expected for precambrian shields it is important to find out whether or not they are representative of the entire shield before trying to derive its thermal structure in this paper we present new heat flow determinations from seven sites of the west african shield these indicate that the surface heat flow is comparable with that of other precambrian shields in the world

gplates building a virtual earth through deep time gplates is an open source cross platform plate tectonic geographic information system enabling the interactive manipulation of plate tectonic reconstructions and the visualization of geodata through geological time gplates allows the building of topological plate models representing the mosaic of evolving plate boundary networks through time useful for computing plate velocity fields as surface boundary conditions for mantle convection models and for investigating physical and chemical exchanges of material between the surface and the deep earth along tectonic plate boundaries the ability of gplates to visualize subsurface 3 d scalar fields together with traditional geological surface data enables researchers to analyze their relationships through geological time in a common plate tectonic reference frame to achieve this a hierarchical cube map framework is used for rendering reconstructed surface raster data to support the rendering of subsurface 3 d scalar fields using graphics hardware accelerated ray tracing techniques gplates enables the construction of plate deformation zones regions combining extension compression and shearing that accommodate the relative motion between rigid blocks users can explore how strain rates stretching shortening factors and crustal thickness evolve through space and time and interactively update the kinematics associated with deformation where data sets described by geometries points lines or polygons fall within deformation regions the deformation can be applied to these geometries together these tools allow users to build virtual earth models that quantitatively describe continental assembly fragmentation and dispersal and are interoperable with many other mapping and modeling tools enabling applications in tectonics geodynamics basin evolution orogenesis deep earth resource exploration paleobiology paleoceanography and paleoclimate

paleoclimatic evidence for future ice sheet instability and rapid sea level rise sea level rise from melting of polar ice sheets is one of the largest potential threats of future climate change polar warming by the year 2100 may reach levels similar to those of 130 000 to 127 000 years ago that were associated with sea levels several meters above modern levels both the greenland ice sheet and portions of the antarctic ice sheet may be vulnerable the record of past ice sheet melting indicates that the rate of future melting and related sea level rise could be faster than widely thought

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

proterozoic crustal evolution of the eucla basement australia implications for destruction of oceanic crust during emergence of nuna abstract the crystalline basement beneath the cretaceous to cenozoic bight and eucla basins in western australia has received comparatively little attention even though it lies on the eastern margin of one of the most mineral resource endowed regions on the planet this basement is characterized by a complex geological evolution spanning c 2 billion years but paucity of outcrop and younger basin cover present a daunting challenge to understand the basement geology in this work the composition of the unexposed proterozoic crystalline basement to the bight and eucla basins is investigated through zircon hf isotopes and whole rock geochemistry from new drillcore samples this region includes two geophysically defined basement entities the madura province containing 1 c 1478 ma sleeper camp formation which has variable isotopic signatures including evolved values interpreted to reflect reworking of rare slivers of hyperextended archean crust 2 1415 1389 ma haig cave supersuite with mantle like isotope values interpreted as melting of subduction modified n morb source and 3 1181 1125 ma moodini supersuite with juvenile isotopic signatures interpreted to reflect mixed mafic lower crustal and asthenospheric melts produced at the base of thinned crust the coompana province to the east of the madura province has three major magmatic components 1 c 1610 ma toolgana supersuite with chemical and isotopic characteristics of primitive arc rock 2 c 1490 ma undawidgi supersuite with juvenile isotope values consistent with extensional processes involving asthenospheric input and 3 1192 1140 ma moodini supersuite with strong isotopic similarity to moodini supersuite rocks in the madura province this new isotopic and geochemical data shows that the madura and coompana regions together represent a huge tract of predominantly juvenile material magma sources recognised include 1 depleted mantle producing morb like crust at c 1950 ma but also contributing to younger magmatism 2 recycled c 1950 ma crust reworked in primitive arcs and in intra plate settings and 3 minor evolved material representing fragments of hyperextended continent the observed isotopic evolution pattern is comparable to that of other central australian proterozoic provinces including the musgrave province the northern margin of the gawler craton and components within the rudall province linking these isotopic signatures defines the mirning ocean and its subducted and underplated equivalents in a global context we suggest c 1950 ma crust production reflects the onset of ordered oceanic spreading centres which swept juvenile crustal fragments into nuna

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

non mare silicic volcanism on the lunar farside at compton belkovich non basaltic volcanism is rare on the moon and has been found predominantly on the lunar nearside analysis of lunar reconnaissance orbiter camera images and spectral data reveal the presence of compositionally evolved non basaltic volcanism on the lunar farside

evidence of a hydrological connection between the ice divide and ice sheet margin in the aurora subglacial basin east antarctica subglacial hydrology in east antarctica is poorly understood yet may be critical to the manner in which ice flows data from a new regional airborne geophysical survey icecap have transformed our understanding of the topography and glaciology associated with the 287 000 km2 aurora subglacial basin in east antarctica using these data in conjunction with numerical ice sheet modeling we present a suite of analyses that demonstrate the potential of the 1000 km long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin we present results from our analysis of basal topography bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures although no clear cut subglacial lakes are found within the aurora basin itself dozens of lake like reflectors are observed that in conjunction with other results reported here support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the dome c ice divide to reach the coast via the totten glacier

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

what controls the location of ice streams ice streams influence ice sheet mass balance and stability but key aspects of their behaviour remain poorly understood this paper reviews and discusses one very important aspect what controls their location in an ice sheet seven potential controls on ice stream location are identified from the literature topographic focusing topographic steps macro scale bed roughness calving margins subglacial geology geothermal heat flux and subglacial meltwater routing for each control the theoretical basis for its link to rapid ice flow is introduced followed by discussion of the evidence of its influence on the location of both contemporary and palaeo ice streams based on this new synthesis topographic focusing subglacial geology meltwater routing and calving margins appear to be most commonly associated with fast ice flow it is clear that rather than a single control however there exist a number of potential controls of varying influence we propose a hierarchy of factors with those occurring at the top of the hierarchy exerting a stronger influence on ice stream location and where present beneath an ice sheet are very likely to be associated with fast flow those factors occurring lower down the hierarchy are less commonly associated with ice streaming but appear to be influential in the absence of more common controls in such a hierarchy topographic focusing in the presence of a calving margin is the primary control in the absence of this ice streams will preferentially occur in areas with favourable subglacial meltwater routing and subglacial geology in the absence of these bed roughness geothermal heat flux and topographic steps may promote ice streaming significantly the primary controls on a given ice stream location are likely to influence its spatial and temporal dynamics ice streams governed by the presence of meltwater routing and or calving processes might exhibit more variable behaviour because these controls can vary over relatively short time scales compared to controls that vary over longer time scales e g geothermal heat flux subglacial roughness geology and topography identifying the controls on ice stream location is therefore of paramount importance when understanding ice stream longevity and their past and future activity

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

basal mechanics of ice stream b west antarctica 2 undrained plastic bed model based on the results of our studies of the physical conditions beneath ice stream b we formulate a new analytical ice stream model the undrained plastic bed model henceforth the upb model mathematically the upb model is represented by a non linear system of four coupled equations which express the relationships among ice sliding velocity till strength water storage in till and basal melt rate we examine this system of equations for conditions of ice stream stability over short timescales that permit holding ice stream geometry constant less than hundreds of years temporal variability is introduced into the upb model only by the direct dependence of till void ratio changes e t on the basal melting rate m r since till strength b e and ice stream velocity u b b change as long as till void ratio varies the first condition for ice stream stability is that of constant till water storage 0 the second condition for ice stream stability arises from the feedback between ice stream velocity till strength and the basal melting rate which depends on shear heating m r u b b this is the weak till condition which requires that in a steady state till strength is a small fraction of the gravitational driving stress b n 1 1 d the salient feature of the upb model is its ability to produce two thermo mechanically controlled equilibrium states one with a strong bed and slow ice velocities ice sheet mode and one with a weak bed and fast ice velocities ice stream mode this bimodality of basal conditions is consistent with the available observations of subglacial conditions beneath slow and fast moving ice in west antarctica basal conditions that do not correspond to these two steady states may occur transiently during switches between the two stable modes the upb model demonstrates that ice streams may be prone to thermally triggered instabilities during which small perturbations in the basal thermal energy balance grow leading to generation or elimination of the basal conditions which cause ice streaming

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

hansteen mons an lroc geological perspective abstract mons hansteen is a relatively high albedo well known lunar red spot located on the southern margin of oceanus procellarum 2 3 s 50 2 w it is an arrowhead shaped 25 km on a side two layer mesa with a small cone shaped massif on its north edge formed by three morphologically and compositionally distinct geologic units these units were emplaced in three phases over nearly 200 million years the oldest 3 74 ga hilly dissected unit composed of high silica and low feo content materials formed a low steep sided mesa the materials of this unit erupted mainly from vents along northeast and northwest trending sets of fractures the pitted unit which comprises the upper tier mesa is composed of high silica and even lower feo content materials this material was erupted at 3 5 ga from numerous closely spaced vents i e pits formed along closely spaced northeast southwest trending sets of fractures at nearly the same time eruptions of lower silica and higher feo materials occurred on the north flank of mons hansteen at the intersection of two major fractures to produce the north massif unit the eruptions that created the north massif units also produced materials that thinly blanketed small areas of the hilly dissected and pitted units on the north flank of mons hansteen also at nearly the same time i e 3 5 ga basalt flows formed the surrounding mare each unit of mons hansteen appears to be mantled by locally derived ash which only modestly contaminated the other units the morphology of mons hansteen especially the pitted unit suggests a style of volcanism where only a relatively small amount of material is explosively erupted from numerous closely spaced vents

antarctic subglacial conditions inferred from a hybrid ice sheet ice stream model abstract subglacial conditions of large polar ice sheets remain poorly understood despite recent advances in satellite observation major uncertainties related to basal conditions such as the temperature field are due to an insufficient knowledge of geothermal heat flow here a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots as well as the distribution of subglacial lakes in this way geothermal heat flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available results of the sensitivity experiments show that 55 of the grounded part of the antarctic ice sheet is at pressure melting point calculated basal melt rates are approximately 65 gt year 1 which is 3 of the total surface accumulation although these sensitivity experiments exhibit small variations in basal melt rates the impact on the ice age of basal layers is quite important in areas that are characterized by relatively low melt rates this may lead to standard deviations up to 50 in a model run over a period of 10 6 years subglacial water flow is concentrated underneath the large outlet glaciers of antarctica the larger subglacial lakes are perched at the head of these subglacial water systems an exception however is the lake system of the recovery ice stream catchment that receives a substantial amount of subglacial melt water from the upstream catchment

spatial analysis of temperature bht dst data and consequences for heat flow determination in sedimentary basins large numbers of bottom hole temperatures bhts and temperatures measured during drill stem tests dsts are available in areas explored for hydrocarbons but their usefulness for estimating geothermal gradients and heat flow density is limited we investigated a large data set of bht and dst measurements taken in boreholes in the american midcontinent a geologically uniform stable cratonic area and propose an empirical correction for bhts based on relationships between bhts dsts and thermal logs this empirical correction is compared with similar approaches determined for other areas the data were analyzed by multivariate statistics prior to the bht correction to identify anomalous measurements and quantify external influences spatial patterns in temperature measurements for major stratigraphic units outline relations to regional structure comparision of temperature and structure trend surface residuals reveals a relationship between temperature highs and local structure highs the anticlines developed by continuous but intermittent movement of basement fault blocks in the late paleozoic are subtle features having closures of 10 30 m and contain relatively small hydrocarbon reservoirs the temperature anomalies of the order of 5 7 c may reflect fluids moving upward along fractures and faults rather than changes in thermal conductivity resulting from different pore fluids

dependence of century scale projections of the greenland ice sheet on its thermal regime observations show that the greenland ice sheet has been losing mass at an increasing rate over the past few decades which makes it a major contributor to sea level rise here we use a threedimensional higher order ice flow model adaptive mesh refinement and inverse methods to accurately reproduce the present day ice flow of the greenland ice sheet we investigate the effect of the ice thermal regime on 1 basal sliding inversion and 2 projections over the next 100 years we show that steady state temperatures based on present day conditions allow a reasonable representation of the thermal regime and that both basal conditions and century scale projections are weakly sensitive to small changes in the initial temperature field compared with changes in atmospheric conditions or basal sliding we conclude that although more englacial temperature measurements should be acquired to validate the models and a better estimation of geothermal heat flux is needed it is reasonable to use steady state temperature profiles for short term projections as external forcings remain the main drivers of the changes occurring in greenland 2014 publishing technology

a detailed study of the distribution of heat flow and radioactivity in new hampshire u s a abstract we present a set of 39 new determinations of heat flow and radiogenic heat production for several different geological environments in the state of new hampshire u s a with the extensive data set now available for the state the linear relation of heat flow and heat production appears as a very useful generalization for the study of the heat flow field of a geological province our measurements indicate that the vertical distribution of radiogenic heat production is similar in plutonic and metasedimentary rocks our data are compatible with the linear relationship established earlier by f birch and his co workers in 1968 young granites are markedly enriched in radioactive elements and those which do not outcrop are revealed by anomalies in the general relation of heat flow versus radioactivity heat flow is high for plutons by low elsewhere the mean heat flow through metasedimentary formations is 1 15 cal cm2 s 48 mw m2 a value near the mean heat flow for old cratons the lowest heat flow measured is 0 76 cal cm2 s 32 mw m2 for a unit poor in radioactivity the heat flow field grades smoothly into the low heat flow regions of the canadian shield the new hampshire region is in thermal equilibrium its heat flow is in secular equilibrium with the heat generated by crustal sources and that supplied from the mantle in this area the thermal perturbations due to orogenic events decrease below the detection level in less than 200 275 ma the thickness of the layer which is thermally affected during continent continent collision type orogenies cannot be greater than about 190 km

spatial variations in heat at the base of the antarctic ice sheet from analysis of the thermal regime above subglacial lakes antarctic subglacial lakes provide an important boundary condition for thermal analysis of the ice sheet in that the basal ice temperature over lakes may be assumed to be at the pressure melting point we have used a one dimensional vertical heat transfer equation to determine theoretical temperature values for the ice sheet base above 77 subglacial lakes identified from airborne radio echo sounding data covering 50 of antarctica variations in our temperature results to below the pressure melting temperature over lakes are due to either our estimate of the geothermal heat flux or a neglect of heat derived from a internal ice deformation and b basal sliding in the thermal model our results indicate that when the geothermal heat flux is set at 54 mw m 2 the ice sheet base above 70 of the known antarctic subglacial lakes is calculated to be at the pressure melting value these lakes are located mainly around dome c ridge b and vostok station for the ice sheet above subglacial lakes located hundreds of kilometres from the ice divide using the same thermal model loss of heat due to vertical advection is calculated to be relatively high in such regions if the ice sheet base is at the pressure melting point heat lost due to vertical advection must be supplemented by heat from other sources for the three lakes beneath terre adelie and george v land for instance the basal thermal gradient calculated to produce pressure melting at the ice sheet base is equivalent to 1 5 2 times the value obtained when 54 mw m 2 of geothermal heat is used as the sole basal thermal component we suggest that as distance from the ice divide increases so too does the amount of heat due to internal ice deformation and basal sliding moreover by considering the ice sheet basal thermal characteristics above subglacial lakes which lie on the same ice flowline we demonstrate empirically that the heat due to these horizontal ice motion terms varies pseudo exponentially with distance from the ice divide the location along a flowline where a rapid increase in the basal heat gradient is calculated may correspond to the onset of large scale basal sliding

high geothermal heat flow basal melt and the origin of rapid ice flow in central greenland age depth relations from internal layering reveal a large region of rapid basal melting in greenland melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet locally high melt rates indicate geothermal fluxes 15 to 30 times continental background the southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin

organization of ice flow by localized regions of elevated geothermal heat flux the impact of localized regions of elevated geothermal heat flux on ice sheet dynamics is largely unknown simulations of ice dynamics are produced using poorly resolved and low resolution estimates of geothermal heat flux observations of crustal heat production within the continental crust underneath the lambert amery glacial system in east antarctica indicate that high heat flux regions of at least 120 mw m 2 exist here we investigate the influence of simulated but plausible localized regions of elevated geothermal heat flux on ice dynamics using a numerical ice sheet model of the lambert amery glacial system we find that high heat flux regions have a significant effect across areas of slow moving ice with the influence extending both upstream and downstream of the geothermal anomaly while fast moving ice is relatively unaffected our results suggest that localized regions of elevated geothermal heat flux may play an important role in the organization of ice sheet flow

the mairan domes silicic volcanic constructs on the moon 1 the mairan domes are four features located in northern oceanus procellarum at 312 3e 41 4n on the moon high resolution visible imagery visible to mid ir spectra and lunar prospector th abundance data all indicate that these four domes have a composition that is consistent with derivation from a si rich highly evolved magma

the thermal blanketing effect of sediments on the rate and amount of subsidence in sedimentary basins formed by extension abstract the thermal blanketing effect of sediments with finite thermal conductivity on the rate and amount of subsidence in rift basins is presented in contrast with mckenzie s 1978 model which assumed infinite thermal conductivity of the sedimentary covers the post rift cooling of the lithosphere is shown to be very slow owing to the blanketing effect even 200 m y after extension ceases there is still an enormous amount of residual heat in the lithosphere with moderate thermal conductivity of the sediments k s 2 0 w mk the maximum discrepancy in subsidence predicted by the two models i e the present model and that of mckenzie are 2 km 2 6 km and 3 2 km for thinning factors of 1 5 2 and 3 respectively subsidence is moderately sensitive to k s when k s is greater than 2 0 w mk becoming more sensitive to k s when k s is less than 2 0 w mk the presence of mudstone would further slow down the cooling the thermal conductivity of the sediment is shown to govern the temperature gradient of rift basins although it has little influence on heat flow the heat production of the upper crust and sediment comprises an important component of heat flow unless heat absorption in rift basins is unusually high subsidence is insensitive to the heat production of sediments when the thinning factor is less than 2 the mean temperature gradient of rift basins is shown to decrease quickly over a few million years and as a result such basins are not favourable as regards hydrocarbon maturity the central graben of the north sea is chosen to test the model the model satisfactorily predicts the subsidence history and thermal evolution with the base zechstein as the basement and the cenozoic subsidence as the thermal subsidence the best fit value of the mean thermal conductivity of the sediments in the graben is 1 67 w mk and the thinning factor is about 2

repeated large scale retreat and advance of totten glacier indicated by inland bed erosion climate variations cause ice sheets to retreat and advance raising or lowering sea level by metres to decametres the basic relationship is unambiguous but the timing magnitude and sources of sea level change remain unclear in particular the contribution of the east antarctic ice sheet eais is ill defined restricting our appreciation of potential future change several lines of evidence suggest possible collapse of the totten glacier into interior basins during past warm periods most notably the pliocene epoch causing several metres of sea level rise however the structure and long term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice sheet extents here we show that deep ice sheet erosion enough to expose basement rocks has occurred in two regions the head of the totten glacier within 150 kilometres of today s grounding line and deep within the sabrina subglacial basin 350 550 kilometres from this grounding line our results based on icecap aerogeophysical data demarcate the marginal zones of two distinct quasi stable eais configurations corresponding to the modern scale ice sheet with a marginal zone near the present ice sheet margin and the retreated ice sheet with the marginal zone located far inland the transitional region of 200 250 kilometres in width is less eroded suggesting shorter lived exposure to eroding conditions during repeated retreat advance events which are probably driven by ocean forced instabilities representative ice sheet models indicate that the global sea level increase resulting from retreat in this sector can be up to 0 9 metres in the modern scale configuration and exceeds 2 metres in the retreated configuration

heat flow in southern australia and connections with east antarctica viscosity and melt generation at the base of ice sheets are critically dependent upon heat flow yet subglacial heat flow is poorly constrained due to the logistical challenges of obtaining boreholes that intersect the bedrock beneath thick ice cover currently continental estimates of antarctic heat flow are derived from geophysical methods that provide ambiguous constraints of crustal heat sources despite their demonstrated importance for accurate predictions of future ice sheet behavior this study pursues an alternative approach by using heat flow measurements from rock units in the coompana province of southern australia which represent the geological counterparts of those beneath wilkes land in east antarctica we present nine new surface heat flow estimates from this previously uncharacterized region ranging from 40 to 70 mw m2 with an average of 57 3 mw m2 these values compare favorably to recent geophysically derived estimates of 50 75 mw m2 for the totten glacier catchment of east antarctica and to the single in situ measurement of 75 mw m2 from the law dome deep ice borehole however they are appreciably lower than the range of 56 120 mw m2 83 13 mw m2 average for the abnormally enriched proterozoic terranes of the central australian heat flow province this study provides the first regional heat flow map of geological provinces formerly contiguous with east antarctica through the application of continent scale heat flow data sets tied to a jurassic plate tectonic reconstruction for gondwana our approach reveals several discrepancies with current heat flow models derived from geophysical methods and provides a more robust analysis of subglacial heat flow using this plate tectonic synthesis as a proxy for east antarctica

heat flow and heat production in the namaqua mobile belt south africa results of heat flow and heat production surveys at 13 localities in the namaqua mobile belt southern africa are presented twelve stations traverse the 1200 1100 m y old gneissic and metamorphic bushmanland and gordonia subprovinces one station is situated in the richtersveld subprovince a 2000 1730 m y old volcano sedimentary domain mildly affected by the 1200 1100 m y old orogeny surface heat flow in the mobile belt ranges from 39 to 81 mw m 2 and averages at 61 11 mw m 2 surface heat production ranges from 0 8 w m 3 in mafic rocks to extreme values of 6 9 12 3 w m 3 in the springbok district western namaqualand high heat production in the springbok district is associated with a thin tabular granitic intrusive and is not representative of the basement the mean heat production of the remaining stations in the mobile belt is 2 3 1 1 w m 3 linear regression analysis of the heat flow heat production data yields a poor fit correlation coefficient 0 62 and imprecise estimates for the intercept 34 6 mw m 2 and slope 11 3 km the eastern margin of the mobile belt has relatively low heat flow and heat production geothermal geological and gravity data suggest a relative depletion of crustal radiogenic heat production in the region however the average namaqua heat flow is higher than worldwide averages for proterozoic terrains there is no geological or geophysical evidence for recent mantle heating below the namaqua mobile belt suggesting that an elevated crustal radioactive component is largely responsible for the elevated heat flow in this respect the mobile belt is similar to several mid late proterozoic heat flow provinces that are characterized by high average surface heat flow and probably have elevated crustal radiogenic heat input these observations and seismic data suggest that the namaqua crust consists of an upper layer that contributes 40 50 on average to the heat flow and a depleted lower layer the inferred heat flow at midcrustal levels is 50 60 of the average surface heat flow the mobile belt s average surface heat flow is 40 85 higher than that from the basement of the adjacent archaean kaapvaal craton and its inferred midcrustal heat flow is similar to the lowest surface values in the craton heat production data from the kaapvaal craton indicate that its upper crust is not depleted of heat sources while enhanced radiogenic heat input from the namaqua upper crust may account for part of the higher than craton heat flow it cannot account for the full excess consequently a larger equilibrium mantle heat flow related to a reduced lithospheric thickness below namaqualand seems to be required by the new data

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

mafic rocks of the southern appalachians a review subaerially erupted metabasalts of tholeiitic affinity which occur as conformable units in late precambrian stratified sequences intrusive equivalents late precambrian volcanism related to a divergent plate tectonic setting devonian hillabee greenstone complex talladega belt at the southwestern fringe of the blue ridge belt shows tholeiitic and calc alkaline affinities suggestive of a volcanic arc or actively developing continental margin environment metabasalts of tholeiitic affinity and probable late precambrian age are also abundant in the inner piedmont belt some of these for example the dadeville complex are associated with younger but pre metamorphic mafic intrusives mafic rocks of the kings mountain charlotte and carolina slate belts include metamorphosed late precambrian to cambrian basaltic flows and tuffs deposited in submarine environments and a large number of gabbroic complexes modified journal abstract

hot rocks in a cold place high sub glacial heat flow in east antarctica numerical models are the primary predictive tools for understanding the dynamic behaviour of the antarctic ice sheet however a key boundary parameter sub glacial heat flow remains poorly constrained we show that variations in abundance and distribution of heat producing elements within the antarctic continental crust result in greater and more variable regional sub glacial heat flows than currently assumed in ice modelling studies such elevated heat flows would have a fundamental effect on ice sheet behaviour and highlight that geological controls on heat flow must be considered to obtain more accurate and refined predictions of ice mass balance and sea level change supplementary materials heat flow and heat production definitions heat production data and details of the 2d model of the gross geometry of the continental lithosphere for a section through prydz bay are available at www geolsoc org uk sup18690

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

a multiproxy provenance approach to uncovering the assembly of east gondwana in antarctica east gondwana is generally thought to have assembled through the amalgamation of indo antarctica and australo antarctica along the ediacaran cambrian kuunga orogen the location of a boundary between indo antarctica and australo antarctica within this key gondwana forming orogen remains controversial because extensive ice cover in east antarctica precludes traditional characterization of terranes here we integrated pb isotope analysis of detrital feldspar grains with u pb dating of detrital monazite and zircon grains from offshore sediments to infer the location of the onshore boundary between indo antarctica and australo antarctica new and compiled data from onshore basement exposures highlight the different age and pb isotope signatures of indo antarctica and australo antarctica holocene sediments offshore from mirny station queen mary land east antarctica have detrital feldspar pb isotope signatures and detrital monazite and zircon u pb ages that reflect contributions from both indo antarctica and australo antarctica the presence of both indo antarctic and australo antarctic crust beneath ice cover near mirny station implies proximity to a fundamental terrane boundary within the kuunga orogen which could coincide with a geophysical lineament at 94 e mirny fault the geophysical expression of this boundary extends into the subglacial interior of east antarctica where prior to more recent rifting it may have connected with one or more previously inferred gondwana forming sutures the revised geometry of the kuunga orogen suggests that the assembly of east gondwana involved dominantly strike slip motion in the mirny region coupled with high angle convergence between indo antarctica and australo antarctica to the west

tectonic framework and evolution of the gawler craton southern australia the gawler craton is the major crustal province in the southern australian proterozoic and is pivotal in models seeking to describe the evolution of proterozoic australia the craton is host to the olympic dam iron oxide cu au u ree deposit as well as a number of other iron oxide copper gold iocg au and iron ore deposits the evolution of the gawler craton is dominated by two major phases of tectonic activity late archean and late paleoproterozoic early mesoproterozoic in total spanning ca 1 billion years the late archean 2560 2500 ma basin development was coeval with arclike felsic magmatism and mafic ultramafic magmas including komatiites collisional deformation between 2480 and 2420 ma led to ca 400 m y of tectonic quiescence conceivably within an early paleoproterozoic continental interior the second major phase of tectonic activity was in the middle to late paleoproterozoic and early mesoproterozoic 2000 1450 ma paleoproterozoic tectonism was initially dominated by rift related events which produced a series of basins over the interval ca 1900 to 1730 ma some of which contain significant iron ore reserves transient contractional deformation at ca 1850 ma led to batholith scale granitic magmatism in part derived from melting of the late archean basement major basin development was finally terminated by the 1730 to 1690 ma kimban orogeny the effects of which are widespread and include the formation of crustal scale shear systems granitic magmatism and low to high grade metamorphism the kimban orogeny was followed by a renewed period of extension between ca 1680 and 1640 ma leading to local magmatism and sedimentation which appears in part to have been coeval with the high grade ca 1650 ma ooldean event in the western gawler craton at ca 1620 to 1615 ma the generation of the arc related st peter suite in the southern gawler craton implies that craton components were located at an active plate margin the arc environment was superseded by a transition to a continental interior regime which coincided with the voluminous gawler range volcanics 1595 1590 ma and hiltaba suite granitoids 1595 1575 ma the hiltaba suite is dominated by high t fractionated felsic rocks with coeval mafic magmatism confirming a mantle involvement emplacement of the hiltaba suite coincided with the major mineralizing interval in the gawler craton regionally two distinct mineral systems have been recognized the olympic iocg province in the eastern part of the craton and the gold dominated systems within the central gawler gold province the spatial distribution of iocg versus au dominated mineral systems appears to reflect regional variations in crustal composition and hiltaba suite petrogeneses hiltaba aged granites in the olympic iocg province are isotopically more evolved richer in u and th and oxidized compared to similar aged granites in the au dominated province modern day heat flow in the iocg province is significantly higher 90 10 mwm 2 compared to the au dominated province 54 5 mwm 2 suggesting there are important lithospheric compositional differences between the two metallogenic provinces which may reflect an older phase of craton assembly widespread northwest southeast contractional deformation coeval with the emplacement of the hiltaba suite is expressed by the formation and or reactivation of shear zones ranging up to crustal scale within this regime northwest trending structures such as those in the vicinity of the olympic dam deposit are likely to have accommodated dilation associated with strike slip movements intersection between these structures and northeast trending contractional faults may have formed suitable structural traps for 1590 to 1580 ma mineralization the timing of syn hiltaba deformation overlaps with transpression and medium to high grade metamorphism associated with the ca 1570 to 1540 ma kararan orogeny which dominates the geophysical architecture of the central northern part of the craton the youngest phase of deformation in the craton is expressed by reactivation of shear zones between ca 1470 and 1450 ma and regional cooling

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years