timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

geodetic and model data reveal different spatio temporal patterns of transient mass changes over greenland from 2007 to 2017 abstract much of the research to understand the ice mass changes of greenland ice sheet gris has focused on detecting linear rates and accelerations at decadal or longer periods the transient short term non secular mass changes show large variability and if not properly accounted for can introduce significant biases into estimates of long term ice mass loss rates and accelerations despite the growing number of geodetic observations in terms of spatial coverage types of observables and the extent of the time series studies of the transient mass changes over gris are lacking to address this limitation we apply multi channel singular spectral analysis to the gravity recovery and climate experiment grace mass concentrations mascon surface mass balance smb model output and ice discharge data to determine the transient mass changes over greenland over the decade 2007 to 2017 the goal of this analysis is to elucidate the spatio temporal variability of the ice mass change for the entire gris both the mascon and smb transient mass changes are characterized by a sustained mass gain from late 2007 to early 2010 a sustained mass loss from early 2010 to early 2013 and a mass gain from early 2013 to mid 2015 global positioning system sites deployed along the coast of greenland showed uplift from early 2010 to early 2013 and subsidence from early 2013 to 2015 consistent with the corresponding ice mass loss and gain of the entire gris the peak to peak amplitude of the transient mass change was estimated to be 294 27 gt from grace mascons and 252 16 gt from the smb where the latter value includes the effect of ice discharge the transient mass change due to ice discharge accounted for less than 10 of the total transient mass change our regional assessment reveals that the central west southwest northeast and southeast regions display similar time varying patterns as we found for the entire gris but the north and northwest regions show different patterns atmospheric circulation anomalies as measured by the greenland blocking index gbi are able to explain most of these transient anomalies more specifically high gbi associated high temperature was one of the main reasons for the transient mass loss of the entire gris during 2010 2012 while low gbi can explain the transient mass gain during 2013 2015 contrasting behaviors of precipitation anomalies in east and west greenland under abnormally high or low gbi conditions may explain the different patterns of the transient mass change in the northwest and the rest of greenland

effect of lithospheric thickness on the formation of high and low angle normal faults it is accepted that extension of a homogeneous brittle layer should produce high angle normal faults the rotation of the upper parts of such a fault to a low dip requires fault offset that is greater than the local lithospheric thickness new model calculations indicate that a fault cutting lithosphere thicker than 10 20 km can build up only a few kilometres horizontal throw before a new fault replaces it such a small offset leaves the fault little rotated from its initial high dip angle for thinner lithosphere the fault offset may be much larger leading to rotation of the upper inactive parts of a high angle fault to a low dip angle in continents this can happen where thin upper crustal lithosphere is decoupled from mantle lithosphere by weak lower crust the calculations suggest that normal faults begin with high dip angles and only in areas of very thin lithosphere can they be offset enough to produce low angle fault structures this prediction is consistent with the occurrence of low angle faults in areas with higher than normal heat flow

seasonal and interannual global surface mass variations from multisatellite geodetic data 1 monthly global surface mass distribution changes are estimated in the spherical harmonic domain with a complete spectrum up to degree and order 50 the estimates are derived by inverting gps displacement series measured at roughly 450 continuously tracking sites and ocean bottom pressure obp estimates of a data assimilated ocean circulation model from 1993 to 2004 the inversion uses a hybrid estimator after singular value decomposition of the normalized measurement equations with reduced reliance on a priori spectral information the results are then compared and combined with gravity recovery and climate experiment grace gravity data to provide enhanced spectral and geographic coverage high fidelity degree 1 surface mass variation coefficients are recovered corresponding to equivalent geocenter motion with better than 0 5 mm annual amplitude precisions in all three components a clear annual surface mass cycle occurs in both gps obp and grace derived results there is very good agreement among the low degree spherical harmonic coefficients and in global geographic pattern but with significant regional differences in amplitudes annual variations of average mass over the global oceans antarctica and greenland are then derived total surface mass over both antarctica and greenland peak in their respective summers due to increased atmospheric mass large interannual variations have also been found involving several continents in the 11 year gps obp solution the patterns of variation suggest that the recent satellite laser ranging slr observation of a reversal in trend of the earth s oblateness may be largely an interannual surface mass cycle with considerable contribution from the northern continents

structural style formation of low angle normal fault and its controls on the evolution of baiyun rift northern margin of the south china sea abstract recent studies of high resolution seismic reflection profiles in the northern rifted margin of the south china sea revealed that low angle normal faults dominated the structural evolution of deepwater basins rather than high angle normal faults solely as was previously assumed however none of the studies proposed kinematic restorations of the fault system and the relationship to continental margin formation the baiyun rift is located in the slope of the northern margin of the south china sea underlain by extremely thinned continental crust it is filled with a relatively complete sequence of cenozoic sediments up to 10 km and has been considered the best documented deepwater basin basin wide 3d seismic data together with the available deepwater well data have allowed the structural framework to be built and tectono stratigraphic history of the baiyun rift to be traced in detailed from the rift stage a quantitative study of the primary geometry and kinematics of the major faults can be performed consequently results show the inception of the rift is characterized by faults slipped at high angles the later stage mid eocene of intensive extension is dominated by a fault system with large horizontal displacements 10 km and initial low dips

contourite drifts on early passive margins as an indicator of established lithospheric breakup the albian cenomanian breakup sequence bs offshore northwest iberia is mapped described and characterised for the first time in terms of its seismic and depositional facies the interpreted dataset comprises a large grid of regional 2d seismic reflection profiles complemented by industry and odp dsdp borehole data within the bs are observed distinct seismic facies that reflect the presence of a black shales and fine grained turbidites b mass transport deposits mtds and coarse grained turbidites and c contourite drifts borehole data show that these depositional systems developed as mixed carbonate siliciclastic sediments proximally and as organic carbon rich mudstones black shales distally on the northwest iberia margin mtds and turbidites tend to occur on the continental slope frequently in association with large scale olistostromes distally these change into interbedded fine grained turbidites and black shales showing widespread evidence of deep water current activity towards the top of the bs current activity is expressed by intra bs erosional surfaces and sediment drifts the results in this paper are important as they demonstrate that contourite drifts are ubiquitous features in the study area after aptian albian lithospheric breakup therefore we interpret the recognition of contourite drifts in northwest iberia as having significant palaeogeographic implications contourite drifts materialise the onset of important deep water circulation marking the establishment of oceanic gateways between two fully separated continental margins as a corollary we postulate the generation of deep water geostrophic currents to have had significant impact on north atlantic climate and ocean circulation during the albian cenomanian with the record of such impacts being preserved in the contourite drifts analysed in this work

the use of gps horizontals for loading studies with applications to northern california and southeast greenland received 23 august 2012 revised 15 january 2013 accepted 20 january 2013 published 25 april 2013 1 we describe how gps measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements to improve and extend gps studies of surface loading we show that the ratio of the vertical displacement to the horizontal displacement combined with the direction of the horizontal motion can help determine whether nearby loading is concentrated in a small region for example in a single lake or glacier and where that region is we illustrate this method by applying it to two specific cases an analysis of gps data from northern california to monitor the level of lake shasta and the analysis of data from a single gps site in southeast greenland to determine mass variability of two large nearby outletglaciers helheim glacier and midgaard glacier the californiaexampleserves largely as a proof of concept where the results can be assessed by comparing with independent observations lake shasta tide gauge data in this case our greenland results show that both helheim and midgaard have experienced notable interannual variations in mass loss rate over the last decade helheim sm ass loss accelerated rapidly in mid 2003 decelerated in late 2005 and increased again in 2008 2009 before returning to about its pre 2003 rate in late 2010 midgaard s mass loss accelerated in mid 2004 and remained more or less constant before returning to its pre 2003 rate in late 2008

the widespread occurrence of low angle normal faults in a rift setting review of examples from thailand and implications for their origin and evolution abstract at least 31 low angle 1 km cenozoic normal faults are identified on seismic reflection data onshore and offshore thailand although some faults have been moderately rotated to lower angles pre rotation dips still indicate formation at low angles about 25 and 35 the dominant east dip of low initial fault dips suggest that pre existing fabrics controlled the fault dip direction in the mergui basin patches of gently dipping basement reflections on seismic reflection data support this observation well data points to a pre rift basement with a widespread component of slaty phyllitic and chlorite schist lithologies that are associated with significant strength anisotropy the subduction zone setting of se asia with a high fluid flux into the crust associated with high levels of co2 has parallels with the setting for lanfs in italy where it is suggested high pore fluid pressures played an important role in lanf reactivation in cross section most lanfs curve from a high angle in sedimentary section to planar or stepped in basement until they reach the brittle ductile transition zone in a few cases lanfs have a convex up geometry some long segmented faults are composed of mixed regions of high and low angle segments the local mix of high and low angle faults indicates that the principal stresses probably were vertical and horizontal during fault formation any rotation of stresses would have to be local not regional lanfs in the mergui basin have very high displacement gradients as low as 2 1 indicating the same fault segments some 20 30 km long have repeatedly slipped while displacements can decline dramatically at key discontinuities the lanf segments are inferred to be very weak and probably slipped mostly aseismically while adjacent lower displacement high angle segments were probably seismically active hence in areas of mixed high and low angle fault segments seismicity may erroneously suggest that high angle normal faults are the dominant fault type the presence of such a high concentration of low and high displacement lanfs in a non metamorphic core complex setting demonstrates that lanfs can form initially at a low angle that isostatic rotation of initially high angle faults to a low angle is not necessary or appropriate to explain the faults and that low angle normal faults are not just features associated with orogenic collapse

structural and thermal constraints on the initiation angle of detachment faulting in the southern basin and range the chemehuevi mountains case study the cenozoic normal fault system exposed in the chemehuevi mountains of the southern cordillera provides constraints on the initiation angle and geometry of an extensional fault system that has accommodated extreme crustal stretching there three stacked brittle low angle normal faults that formed at depths as great as 10 12 km cut gently down section northeastward through deformed proterozoic and mesozoic crystalline basement hanging wall blocks are displaced relatively northeastward the upper crust above the chemehuevi detachment fault was pulled apart along high angle normal faults that rotated to more gentle dips through time in contrast rocks of originally mid crustal affinity in the footwall were only gently rotated and accommodated minor extension application of 40 ar 39 ar and fission track thermochronology to rocks in the footwall of the chemehuevi detachment fault system provides further constraints on the timing and initiation angle of regional detachment faulting at the onset of extension between 22 and 24 ma granitic rocks exposed in the southwestern and northeastern portions of the footwall were at 200 c and 350 400 c respectively separated by a distance of some 23 km down the known slip direction this gradual increase in temperature with original depth is attributed to the gentle southwest tilting of broadly planar pre extension isothermal surfaces and constrains the exposed part of the chemehuevi detachment fault to have had a regional dip initially of about 15 to 30 the fault system apparently cut gently down through the upper crust to a minimum depth of 10 12 km the deepest exposed parts of the system today and was domed from midcrustal depths and locally denuded during continued slip together the structural and thermochronologic data confirm the suggestion that faults accommodating large magnitude slip can be initiated and move within the seismogenic regime at moderate to low angles that is 30

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

extension discrepancy at north atlantic nonvolcanic rifted margins depth dependent stretching or unrecognized faulting rifted margins show an apparent discrepancy between the amount of extension measurable from faults and the amount of crustal or lithospheric thinning determined from wide angle data or subsidence this extension discrepancy has been interpreted in terms of depth dependent stretching in which the upper crust is extended and thinned far less than the rest of the lithosphere here i show that at those nonvolcanic margins where the velocity structure is well known the upper and lower crust appear to thin equally toward the margin implying that the discrepancy is not due to depth dependent stretching but more likely due to unrecognized polyphase and top basement faulting

the extreme melt across the greenland ice sheet in 2012 1 the discovery of the 2012 extreme melt event across almost the entire surface of the greenland ice sheet is presented data from three different satellite sensors including the oceansat 2 scatterometer the moderate resolution imaging spectroradiometer and the special sensor microwave imager sounder are combined to obtain composite melt maps representing the most complete melt conditions detectable across the ice sheet satellite observations reveal that melt occurred at or near the surface of the greenland ice sheet across 98 6 of its entire extent on 12 july 2012 including the usually cold polar areas at high altitudes like summit in the dry snow facies of the ice sheet this melt event coincided with an anomalous ridge of warm air that became stagnant over greenland as seen in melt occurrences from multiple ice core records at summit reported in the published literature such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the medieval warm period given its rarity the 2012 extreme melt across greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research

improved methods for observing earth s time variable mass distribution with grace using spherical cap mascons we discuss several classes of improvements to gravity solutions from the gravity recovery and climate experiment grace mission these include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution jpl rl05 and an alternate jpl rl05m mass concentration mascon solution benefitting from those same improvements but derived in surface spherical cap mascons the mascon basis functions allow for convenient application of a priori information derived from near global geophysical models to prevent striping in the solutions the resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions and do not necessitate empirical filters to remove north south stripes lowering the dependence on using scale factors the global mean scale factor decreases by 0 17 to gain accurate mass estimates ocean bottom pressure obp time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions increase in correlation coefficient of 0 08 globally particularly in low latitude regions with small signal power increase in correlation coefficient of 0 35 regionally in addition to reducing the error rms with respect to the in situ data reduction of 0 37 cm globally and as much as 1 cm regionally greenland and antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins however mascon solutions typically have greater resolution for smaller spatial regions in particular when studying secular signals

interannual variability of greenland ice losses from satellite gravimetry 1 using extended satellite gravity measurements from the gravity recovery and climate experiment grace here we show that ice losses in southeast greenland appear to have slowed down dramatically since late 2007 while those in the west especially northwest greenland show continued accelerations in recent years over the period april 2002 to november 2009 averaged ice loss rates in eastern greenland 120 31 gt yr are still significantly larger than those in the west 86 3 22 gt yr however the estimated ice loss rate from glaciers in northwest greenland has increased from 30 9 8 gt yr over the first few years 2002 2005 to 128 2 33 gt yr for the more recent period 2007 2009 while the loss rate in southeast greenland for the more recent period has become almost negligible down from 109 28 gt yr of just a few years ago the rapid change in the nature of the regional ice mass in southeast and northwest greenland in the course of only several years further reinforces the idea that the greenland ice sheet mass balance is very vulnerable to regional climate conditions the dramatic slow down of ice loss in southeast greenland observed by grace provides an independent verification of similar reports from other remote sensing data the observed significant interannual variability of greenland ice mass change suggests that it is very challenging to quantify greenland s long term ice mass change rates and some observed apparent accelerations might simply be a reflection of the interannual variability

the tectono sedimentary evolution of a hyper extended rift basin the example of the arzacq mauleon rift system western pyrenees sw france in this paper we present a sedimentary and structural analysis that together with maps sections and new ar ar data enable to describe the tectono sedimentary evolution of the mauleon hyper extended rift basin exposed in the w pyrenees hyper extension processes that ultimately resulted in exhuming mantle rocks are the result of the subsequent development of two diachronous detachment systems related to two evolutional stages of rifting an initial late aptian early albian crustal thinning phase is first recorded by the development of a crustal necking zone controlled by the north vergent southern mauleon detachment system during a subsequent exhumation phase active faulting migrates to the north with the emplacement of the northern mauleon detachment system that exhumed north section thinned continental crust and mantle rocks this diachronous crustal thinning and exhumation processes are also recorded by the diachronous deposition of syn tectonic sedimentary tracts above the two supra detachment sub basins syn tectonic sedimentary tracts record the progressive exhumation of footwall rocks along detachment systems tectonic migration from the southern to the northern mauleon detachment system is recorded by the coeval deposition of sag deposits above the necking zone basin and of syn tectonic tracts above exhumed rocks north section located on a hanging wall situation related to the mauleon hyper extension structures the arzacq basin also records a major crustal thinning phase as shown by its subsidence evolution so as by deep seismic images the absence of major top basement structures and its overall sag morphology suggest that crustal thinning processes occurred by decoupled extension of lower crustal levels contrasting with the southern mauleon detachment system reconciling observations from the mauleon and arzacq basins we finally propose in this paper that they were the result of one and the same asymmetric crustal thinning and exhumation processes where extension is accommodated into the upper crust in the mauleon basin lower plate basin and relayed in ductile lower crust below the arzacq basin upper plate basin

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

data adaptive detection of transient deformation in geodetic networks author s walwer d calais e ghil m abstract 2016 american geophysical union all rights reserved the recent development of dense and continuously operating global navigation satellite system gnss networks worldwide has led to a significant increase in geodetic data sets that sometimes capture transient deformation signals it is challenging however to extract such transients of geophysical origin from the background noise inherent to gnss time series and even more so to separate them from other signals such as seasonal redistributions of geophysical fluid mass loads in addition because of the very large number of continuously recording gnss stations now available it has become impossible to systematically inspect each time series and visually compare them at all neighboring sites here we show that multichannel singular spectrum analysis m ssa a method derived from the analysis of dynamical systems can be used to extract transient deformations seasonal oscillations and background noise present in gnss time series m ssa is a multivariate nonparametric statistical method that simultaneously exploits the spatial and temporal correlations of geophysical fields the method allows for the extraction of common modes of variability such as trends with nonconstant slopes and oscillations shared across time series without a priori hypotheses about their spatiotemporal structure or their noise characteristics we illustrate this method using synthetic examples and show applications to actual gps data from alaska to detect seasonal signals and microdeformation at the akutan active volcano the geophysically coherent spatiotemporal patterns of uplift and subsidence thus detected are compared to the results of an idealized model of such processes in the presence of a magma chamber source

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

the structure and formation of diapirs in the yinggehai song hong basin south china sea abstract the occurrence of shale diapirs in the yinggehai song hong ygh sh basin is well documented as is their association with big petroleum fields in order to better understand how and why the diapirs form we performed a detailed geophysical analysis using a new regional compilation of high resolution two and three dimensional seismic reflection data as well as drilling data that cover the diapirs in ygh sh basin as many as 18 diapirs were identified and are arranged in six n s striking vertical en echelon zones on seismic reflection sections gas chimney structures diapiric faults and palaeo craters are genetically linked with the process of diapirism here we use geophysical and geological observations to propose a three stage model for diapirism initiation emplacement and collapse during these three stages different diapiric structure styles are formed which we describe in detail these include buried diapirs piercing diapirs and collapsed diapirs we link the diapirism to activity on the offshore continuation of the red river fault as shown on our high resolution seismic reflection data which is also related to a high paleogeothermal gradient caused by crustal thinning we also recognize the role of loading by the very large volume of sediment eroded from the edges of the tibetan plateau and delivered by the red river to the basin

seismic reflectivity of detachment faults of the iberian and tethyan distal continental margins based on geological and petrophysical data abstract low angle detachment faults are key to our understanding of the tectonic evolution of magma poor rifted continental margins in seismic images of present day rifted margins the identification and interpretation of such features is however notoriously difficult and ambiguous we address this problem by studying the structure and seismic response of such faults through a synoptic interpretation of petrophysical data and geological evidence from the distal segments of the present day west iberian and the ancient tethyan margins on the basis of the geologically well constrained remnants of the tethyan margins which are spectacularly preserved and exposed in the alps of eastern switzerland vertical profiles at four key geological settings of a typical magma poor rifted margin are constructed and their synthetic seismic responses are compared to the observed seismic data from corresponding locations in the present day iberian margin the seismic structure of these profiles is considered as the sum of deterministic large scale and the stochastic small scale components both components are analyzed for all pertinent lithologies the large scale structures are derived from laboratory measurements on samples from both the west iberian and tethyan margins whereas the small scale fluctuations are constrained predominantly on the basis of well log data from the iberian margin different realizations of the simulated stochastic small scale velocity fluctuations illustrate the potential variability of impedance contrasts and its impact on the seismic response from lithological interfaces and fault structures our results indicate that the nature of the seismic response from low angle detachment faults is largely determined through the fracture healing behavior of the surrounding rocks geological evidence from the exposed fragments of the tethyan margins indicate that fracture healing is generally well developed in crustal lithologies but largely absent in mantle lithologies it is for this reason that low angle intra crustal detachment faults tend to be seismically undetectable conversely crust mantle detachments have a complex and variable seismic response depending on the nature of the damaged zone and on the frequency content of the seismic data these model based inferences are consistent with the available evidence from the present day iberian passive margin and thus open new perspectives for the interpretation of the corresponding seismic images

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

antarctica greenland and gulf of alaska land ice evolution from an iterated grace global mascon solution we have determined the ice mass evolution of the antarctica and greenland ice sheets ais and gis and gulf of alaska goa glaciers from a new grace global solution of equal area surface mass concentration parcels mascons in equivalent height of water the mascons were estimated directly from the reduction of the inter satellite k band range rate kbrr observations taking into account the full noise covariance and formally iterating the solution the new solution increases signal recovery while reducing the grace kbrr observation residuals the mascons were estimated with 10 day and 1 arc degree equal area sampling applying anisotropic constraints an ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances the details and causes of the spatial and temporal variability of the land ice regions studied are discussed the estimated mass trend over the total gis ais and goa glaciers for the time period 1 december 2003 to 1 december 2010 is 380 plus or minus 31 gt a exp 1 equivalent to 1 05 plus or minus 0 09 mma exp 1 sea level rise over the same time period we estimate the mass acceleration to be 41 plus or minus 27 gt a exp 2 equivalent to a 0 11 plus or minus 0 08 mm a exp 2 rate of change in sea level the trends and accelerations are dependent on significant seasonal and annual balance anomalies

the depositional characteristics and oil potential of paleo pearl river delta systems in the pearl river mouth basin south china sea abstract delta systems in the zhuhai zhujiang and hanjiang formations are interpreted as having formed during periods of sea level rise from the late oligocene to mid miocene 30 10 5 my b p deltas in the zhuhai formation were developed in a shallow water environment on a sandy wave or fluvial dominated coasts thick and blanket like sandstones are common but mudstones are infrequent oil bearing zones have been found only in the upper part of the systems overlain by mudstone of the zhujiang formation deltas in the zhujiang formation are interpreted as having formed in a deeper water environment on sandy wave or fluvial dominated coasts carbonate platforms started growing on the dongsha massif as the sea level slowly rose the moderate sandstone mudstone ratio in the delta systems and a zone of secondary porosity in the carbonate rocks provide an excellent reservoir rock and seal rock for the basin deltas in the lower hanjiang formation are similar to those of the zhujiang formation but the upper part of the formation is interpreted as having formed in a shelf environment the thick shelf mudstone interbedded with offshore bar sandstones would be one of the better regional seal rocks in the study area no carbonate rock developed on the dongsha massif due to the rapid rise in sea level all delta systems from the zhuhai to the zhujiang formation are stacked in an onlap pattern indicating a more and more expanding marine transgression which was caused by eustatic sea level rise this marine transgression is almost unique and contrasts to the progradational offlap pattern of cenozoic delta systems in the gulf of mexico it resulted in thick sandstone deposits immature or poorly mature source rock and no ductile mudstones with no growth faults or rollover structures hydrocarbons generated from eocene oligocene lacustrine source rocks are trapped by drape structures related to local basement highs or by carbonate rock with secondary porosity most of the remaining undiscovered reserves in the basin will be found in non structural subtle traps especially stratigraphic traps

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

different expressions of rifting on the south china sea margins abstract rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin being opened quite recently in the tertiary in a scissor shape manner the south china sea scs offers an image of the rifting structures which varies along strike the basin margins the scs has a long history of extension which dates back from the late cretaceous and allows us to observe an early stretching on the northern margin onshore and offshore south china with large low angle faults which detach the mesozoic sediments either over triassic to early cretaceous granites or along the short limbs of broad folds affecting palaeozoic to early cretaceous series these early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone because these low angle faults reactivate older trends they vary in geometry according to the direction of the folds or the granite boundaries a later set of faults characterized by generally e w low and high angle normal faults was dominant during the eocene associated half graben basement deepened as the basins were filling with continental or very shallow marine sediments this subsequent direction is well expressed both in the north and the sw of the south china sea and often reactivated earlier detachments at places the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the phu khanh basin east of the vietnam fault a third direction of faults which rarely reactivates the detachments is ne sw and well developed near the oceanic crust in the southern and southwestern part of the basin this direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part and ended by the late miocene after the onset of the regional mid miocene unconformity known as mmu and dated around 15 5 ma latest miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast the se margin of the south china sea does not show the extensional features as well as the northern margin detachments are common in the dangerous grounds and reed bank area and may occasionally lead to mantle exhumation the sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the late miocene when it suddenly deepened this period also corresponds to the cessation of the shortening of the nw borneo wedge in palawan sabah and sarawak we correlate the variation of margin structure and composition of the margin mainly the occurrence of granitic batholiths and mesozoic broad folds with the location of the detachments and major normal faults which condition the style of rifting the crustal boudinage and therefore the crustal thickness

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

seismic stratigraphy and tectonic structure from a composite multi channel seismic profile across the entire dangerous grounds south china sea abstract we interpret a more than 500 km long composite multi channel seismic reflection profile across the entire dangerous grounds the south china sea five tectonostratigraphic units are determined together with seven sequence boundaries detailed analysis of extensional features based on measurements of fault heaves revealed two major phases of extension separated by a distinct unconformity which likely correspond with the beginning of sea floor spreading in the south china sea early extension occurred during continental rifting late cretaceous early oligocene and resulted in formation of half grabens and rotated blocks controlled by a deeply rooted detachment system extension continued in our study area during the drifting phase of the east subbasin of the south china sea late oligocene early miocene until the subsequent opening of the southwest subbasin at about 25 ma but its intensity decreased markedly thereafter deeply rooted detachment systems evolved possibly during this second phase of extension at the continent ocean transition area from a coincidence of the lowermost reflections and moho depth as derived from gravity inversion we tentatively interpret the flattened part of this detachment system as the crust mantle boundary it is suggested that the dangerous grounds reflect a magma poor rift system at the initial stage of mantle unroofing we suggest that a widespread carbonate platform developed across the dangerous grounds concurrent with the period of seafloor spreading in the southwest subbasin of the south china sea fault related stretching factors f along the line show discrepancies with the whole crustal stretching factors c the continental crust of the dangerous grounds may have experienced nonuniform thinning

a deep seismic investigation of the flemish cap margin implications for the origin of deep reflectivity and evidence for asymmetric break up between newfoundland and iberia summary seismic reflection and refraction data were acquired along the southeast margin of flemish cap at a position conjugate to drilling and geophysical surveys across the galicia bank margin the data document first order asymmetry during final break up between newfoundland and iberia an abrupt necking profile of continental crust observed off flemish cap contrasts strongly with gradual tapering on the conjugate margin there is no evidence beneath flemish cap for a final phase of continental extension that resulted in thin continental crust underlain by a strong s like reflection which indicates that this mode of extension occurred only on the galicia bank margin compelling evidence for a broad zone of exhumed mantle or for peridotite ridges is also lacking along the flemish cap margin instead anomalously thin 3 4 km thick oceanic crust is observed this crust is highly tectonized and broken up by high angle normal faulting the thin crust and rift structures that resemble the abandoned spreading centre in the labrador sea suggest that initial seafloor spreading was affected by processes observed in present day ultra slow spreading environments landwards flemish cap is underlain by a highly reflective lower crust the reflectivity most likely originates from older palaeozoic orogenic structures that are unrelated to extension and break up tectonics

the breakup sequence and associated lithospheric breakup surface their significance in the context of rifted continental margins west iberia and newfoundland margins north atlantic regional 2d seismic reflection profiles and borehole data are used to characterise the syn to post rift transition in the shallow offshore porto basin and in deep offshore regions of west iberia and newfoundland east canada the interpreted data highlight the development of a regional stratigraphic surface at the time of complete lithospheric breakup between west iberia and newfoundland this surface usually called breakup unconformity is renamed in this work as lithospheric breakup surface lbs on the basis that 1 it is not always developed as an unconformity and 2 all lithosphere is involved on the breakup process not only the continental crust depositional changes occur across the lbs in association with late aptian lithospheric breakup which is marked by the deposition of a breakup sequence bs rather than a single stratigraphic surface stratigraphic correlations between strata in shallow and deeper parts of the two margins lead us to propose the breakup sequence bs as representing the transitional period between lithospheric breakup and the establishment of thermal relaxation as the main process controlling subsidence on divergent continental margins the results in this work are important for other continental margins as they demonstrate that during lithospheric breakup significant quantities of sediment bypassed the inner proximal margins of west iberia and newfoundland on their way to the outer proximal margin in addition the interpreted data show that complete lithospheric breakup between conjugate margins is recorded by similar tectono stratigraphic events in iberia and newfoundland these events are associated with reservoir successions in sediment overfilled basins and with carbon rich strata black shales in sediment starved basins

annual variations in gps measured vertical displacements near upernavik isstrom greenland and contributions from surface mass loading in response to present day ice mass loss on and near the greenland ice sheet steady crustal uplifts have been observed from the network of global positioning system gps stations mounted on bedrock in addition to the secular uplift trends the gps time series also show prominent annual variability here we examine the annual changes of the vertical displacements measured at two gps stations srmp and upvk near upernavik isstrom in western greenland we model elastic loading displacements due to various surface mass loading including three non ice components atmospheric pressure ocean bottom pressure continental water storage and one ice component i e surface mass balance smb we find that the contribution from atmospheric pressure changes can explain 46 and 78 of the annual amplitude observed in the gps verticals at srmp and upvk respectively we also show that removing the predicted loading displacements due to smb adversely increases the annual variance of the gps residuals however using the gps data alone we cannot identify the exact cause s of this discrepancy because the annual loading displacements are sensitive to the smb changes from over 85 of the ice sheet area alternatively by differencing vertical displacements between the two stations we find a good agreement between the modeled differential smb loading displacements and the gps residuals after removing non ice components our study highlights the necessity of correcting for non ice loading contributions in the gps measurements of crustal deformation to infer ice mass changes in greenland at annual periods

greenland ice sheet mass balance distribution of increased mass loss with climate warming 2003 07 versus 1992 2002 we derive mass changes of the greenland ice sheet gis for 2003 07 from icesat laser altimetry and compare them with results for 1992 2002 from ers radar and airborne laser altimetry the gis continued to grow inland and thin at the margins during 2003 07 but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s the net balance changed from a small loss of 7 3g t a 1 in the 1990s to 171 4g t a 1 for 2003 07 contributing 0 5 mm a 1 to recent global sea level rise we divide the derived mass changes into two components 1 from changes in melting and ice dynamics and 2 from changes in precipitation and accumulation rate we use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation driven changes to mass changes increased losses from melting and ice dynamics 17 206 gt a 1 are over seven times larger than increased gains from precipitation 10 35 gt a 1 during a warming period of 2 k 10 a 1 over the gis above 2000 m elevation the rate of gain decreased from 44 to 28 gt a 1 while below 2000 m the rate of loss increased from 51 to 198 gt a 1 enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers as well as accelerating ice flow increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

the c 32 alkane 1 15 diol as a tracer for riverine input in coastal seas long chain alkyl diols are lipids that occur ubiquitously in marine sediments and are used as a proxy for sea surface temperature sst using the long chain diol index ldi and for upwelling intensity high nutrient conditions the distribution of 1 13 and 1 15 diols has been documented in open marine and lacustrine sediments and suspended particulate matter but rarely in coastal seas receiving a significant riverine and thus continental organic matter input here we studied the distribution of diols in four shelf seas with major river outflows the gulf of lion the kara sea the amazon shelf and the berau delta covering a wide range of climate conditions the relative abundance of the c32 1 15 diol is consistently higher close to the river mouth and particularly in the suspended particulate matter of the rivers suggesting a terrigenous source this is supported by statistical analysis which points out a significant positive correlation between the c32 1 15 diol and the branched and isoprenoid tetraether index a proxy reflecting soil and riverine input in marine environments however the c32 1 15 diol was not detected in soils and is unlikely to be derived from vegetation suggesting that the c32 1 15 diol is mainly produced in rivers this agrees with the observation that it is a dominant diol in most cultivated freshwater eustigmatophyte algae we therefore suggest that the relative abundance of the c32 1 15 diol can potentially be used as a proxy for riverine organic matter input in shelf seas our results also show that long chain alkyl diols delivered by rivers can substantially affect ldi reconstructed ssts in coastal regions close to river mouths

improving the estimate of the secular variation of greenland ice mass in the recent decades by incorporating a stochastic process abstract the irregular interannual variations observed in the greenland ice sheet gris mass balance can be interpreted as stochastic these variations often have large amplitudes and if not accounted for correctly in the mass change model parameterization could have profound impacts on the estimate of the secular trend and acceleration here we propose a new mass trajectory model that includes both the conventional deterministic components and a stochastic component this new model simultaneously estimates the secular rate and acceleration seasonal components and the stochastic component of mass changes simulations show that this new model improves estimates of model parameters especially accelerations over the conventional model without stochastic component using this new model we estimate an acceleration of 1 6 1 3 gt yr2 in mass change minus means mass loss for 2003 2017 using the gravity recovery and climate experiment grace data and an acceleration of 1 1 1 3 gt yr2 using the modeled surface mass balance plus observed ice discharge the corresponding rates are estimated to be 288 2 12 7 gt yr and 274 9 13 0 gt yr the greatest discrepancies between the new and the conventional model parameter determinations are found in the acceleration estimates 1 6 gt yr2 vs 7 5 gt yr2 from the grace data the estimated accelerations using the new method are apparently smaller than those estimated by other studies in terms of mass loss our quantitative analysis elucidates that the acceleration estimate using the conventional method is the lower bound i e 7 5 gt yr2 for 2003 2017 while the acceleration estimated by the new method lies in the middle of the possible ranges it is also found that these discrepancies between the new and the conventional methods diminish with sufficiently long 20 yr observation records

grace observes small scale mass loss in greenland using satellite gravity data between february 2003 and january 2008 we examine changes in greenland s mass distribution on a regional scale during this period greenland lost mass at a mean rate of 179 25 gt yr equivalent to a global mean sea level change of 0 5 0 1 mm yr rates increase over time suggesting an acceleration of the mass loss driven by mass loss during summer the largest mass losses occurred along the southeastern and northwestern coast in the summers of 2005 and 2007 when the ice sheet lost 279 gt and 328 gt of ice respectively within 2 months in 2007 a strong mass loss is observed during summer at elevations above 2000 m for the first time since the start of the observations

the peridotite ridge province in the southern iberia abyssal plain seismic constraints revisited the west iberia margin has become the type example of a magma starved margin in which extension during breakup led to the exhumation of mantle rocks apparently over a broad area much of our understanding of this process is based on geophysical and drilling data from the southern iberia abyssal plain where the seaward part of the region of exhumed mantle is comprised of a series of margin parallel basement ridges here we analyse wide angle and normal incidence seismic data from a series of intersecting profiles across this peridotite ridge province and develop a three dimensional picture of its structure using these seismic data we infer a location and age magnetic anomaly m1 125 127 ma of first formed oceanic crust in this region that are consistent with ocean drilling program data and data from the conjugate margin we infer that the peridotite ridge province is about 70 km wide with strong serpentinization 75 at the top of basement reducing to much lower degrees 25 around 2 km below we map the geometry of some prominent reflectors on the landward margin of the peridotite ridge province that likely represent detachment faults and show that one of these has a domal structure similar to that of detachment faults at slow to ultra slow spreading mid ocean ridges

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

mass transport waves amplified by intense greenland melt and detected in solid earth deformation the annual cycle and secular trend of greenland mass loading are well recorded in measurements of solid earth deformation horizontal crustal displacements can potentially track the spatiotemporal detail of mass changes with great fidelity our analysis of greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense melt years we discover that solitary seasonal waves of substantial mass transport 1 67 0 54 gt month traveled at an average speed of 7 1 km month through rink glacier in 2012 we deduce that intense surface melting enhanced either basal lubrication or softening of shear margins or both causing the glacier to thin dynamically in summer the newly routed upstream subglacial water was likely to be both retarded and inefficient thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months as the climate continues to produce increasingly warmer spring and summer amplified seasonal waves of mass transport may become ever more present with important ramifications for the future sea level rise

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

polyphase faulting during the development of the west galicia rifted margin rifted margins are commonly characterised by an extension discrepancy the amount of extension measurable from the observed faulting is far less than that required to explain the crustal thinning it is shown here that polyphase faulting may provide a simple explanation for this paradox but can be very hard to recognise on seismic sections however at the west galicia rifted margin the galicia interior basin between the galicia bank and the mainland and the deep galicia margin to the west of the galicia bank a combination of high quality depth images seismic velocity information and stratigraphic control through odp drilling and submersible sampling provide complementary evidence for polyphase faulting berriasian hauterivian rifting in the galicia interior basin occurred along two sets of faults the first unroofed deep crustal rocks evidenced by high seismic velocities close to top basement the second cut and dismembered these early faults further rifting up until the aptian then focussed west of the galicia bank where two further phases of faulting can be inferred from the diachronous nature of seismostratigraphic units tilted within fault blocks removal of the latest phase of faulting aligns discontinuous reflections within the fault blocks into an anastomosing network of earlier faults restoration along these brings the crust back to its early hauterivian state similar to the present structure of the interior basin

paleomagnetic evidence of large footwall rotations associated with low angle faults at the mid atlantic ridge exposures of gabbros and mantle derived peridotites at slow spreading oceanic ridges have been attributed to extension on long lived low angle detachment faults similar to those described in continental metamorphic core complexes in continental settings such detachments have been interpreted as having originated and remained active at shallow dips alternatively currently shallow dipping fault surfaces may have originated at moderate to steep dips and been fl attened by subsequent fl exure and isostatic uplift while the latter interpretation would be more con sistent with andersonian faulting theory it predicts large footwall tilts that have not been observed in continental detachment faults here we use the magnetization of oceanic gabbro and peridotite samples exposed near the fifteen twenty fracture zone on the mid atlantic ridge to demonstrate that substantial footwall rotations have occurred widespread rotations ranging from 50 to 80 indicate that original fault orientations dipped steeply toward the spreading axis

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

models of the development of the west iberia rifted continental margin at 40 30 n deduced from surface and deep tow magnetic anomalies the ocean continent transition oct on nonvolcanic rifted continental margins is important in that it contains evidence concerning the breakup of the continents and the onset of seafloor spreading the nature of the oct off western lberia has recently been attracting attention following seismic and other geophysical studies there and drilling of acoustic basement by leg 149 of the ocean drilling program here we concentrate on the interpretation of a new digital magnetic anomaly chart for the iberia abyssal plain between 39 5 o and 42 2 o n the most striking anomaly is a trough which exists immediately east of and locally parallel to anomaly j and is closely coincident with a basement peridotite ridge we conclude from modeling surface magnetic anomalies and a deep tow magnetometer profile that seafloor spreading began about 129 9 m y ago barremian at a rate of 10 0 mm yr consistent with drilling and seismostratigraphic results from the southern lberia abyssal plain a second feature is the existence of linear low amplitude isochron parallel magnetic anomalies east of the peridotite ridge trough and a clear change in the trend of these anomalies east of about 11 o 15 w it is possible to model these anomalies by a series of 7 to 30 km wide weakly magnetized crustal blocks of about the same thickness as the oceanic crust the west to east anticlockwise change in trend at 11 o 15 w suggests either a major change in stress regime and or in the type of magnetic anomaly source we speculate that the region between the peridotite ridge and 11 o 15 w represents a transitional crust whose formation was dominated by the same stress regime which accompanied eventual seafloor spreading we explain the change in trend at 11 o 15 w by a model featuring a rift which propagated through continental crust from south to north we consider three scenarios for the formation of the transitional zone crust first continental crust is surrounded and impregnated by intrusive and extrusive material formed from passive upwelling of magma created by the limited adiabatic decompression partial melting which occurs as the two continental lithospheric plates first begin to separate second such crust is surrounded by unroofed upper mantle material or third the zone is the product of ultraslow seafloor spreading present evidence tends to support the first scenario in this scenario the top of the asthenosphere eventually becomes shallow enough to enable magma to penetrate the thinnest continental crust fill the space caused by additional extension and form the transitional crust already described over a broad zone at least several tens of kilometers wide at breakup upper mantle rocks become exposed on the seafloor and undergo extensive serpentinization in a final stage we envisage focusing of the igneous activity leading to the onset of seafloor spreading initially producing thin oceanic crust because of a restricted melt supply the width of continuous tectonically extended continental crust in the southern iberia abyssal plain is less than was previously supposed

extreme crustal thinning in the south porcupine basin and the nature of the porcupine median high implications for the formation of non volcanic rifted margins the southern porcupine basin is characterized by axial stretching factors that are greater than six and typical of rifted margins as such the basin can be regarded as a natural laboratory to investigate the evolution and symmetry of rifting leading towards continental separation and breakup a bright reflection here named p cuts down to the west from the base of the sedimentary section is overlain by small fault blocks and appears to represent a detachment fault p may in part follow the top of partially serpentinized mantle this interpretation is consistent with gravity modelling and with numerical models of crustal embrittlement and mantle serpentinization during extension furthermore p closely resembles the s reflection west of iberia where such serpentinites are well documented although overall the basin remains symmetrical the consistent westward structural dip of the detachment implies that at high stretching factors extension became asymmetric farther south the porcupine median high appearing lens shaped in cross section overlies the tilted fault blocks and is onlapped by postrift sediment despite no evidence for synrift magmatism this high has previously been interpreted as a basaltic structure however it develops above the line of intersection of the crust mantle boundary with the p detachment and hence may be related to the spatial limit of serpentinization the median high may represent a serpentinite mud volcano or diapir we suggest that such structures produce the serpentinite breccias found within the rifted continent ocean transition of nonvolcanic margins

geodetic measurements reveal short term changes of glacial mass near jakobshavn isbrae greenland from 2007 to 2017 abstract the global positioning system gps and gravity recovery and climate experiment grace provide important geodetic datasets to study glacial mass change applying the multichannel singular spectral analysis to the gps measured vertical and horizonal crustal displacement and grace derived vertical displacement near jakobshavn isbrae ji in western greenland from 2007 to 2017 we reconstruct the short term loading displacements due to ice mass changes both the vertical and east displacements show strong seasonal variability they also reveal three episodes of transient displacements downward and eastward motion from late 2007 to around 2010 sustained upward and westward motion from 2010 to early 2013 and downward and eastward motion till late 2016 we also forward model the seasonal and transient displacements caused by surface mass balance smb and glacier dynamics our model agrees well with the geodetic observations and provides quantitative insights into the contribution from smb and ice dynamics to the ice mass changes we find that smb is the dominant contributor to the seasonal and transient displacements at three out of four gps sites aasi ilul and qeqe while at the fourth gps site kaga that is closest to the glacier the contributions to the transient displacements from smb and glacier dynamics are comparable the forward modeling also suggests that the dynamic mass change in the ji catchment underwent strong seasonal variations and these variations correlated more with the seasonal retreat and advance of the calving front than with the changes of glacial velocities our altimetry results reveal that the frontal portion of ji catchment lost 34 gt in 2012 and this loss of ice declined to only 11 gt in 2016 due to widespread thickening along the main flowline

the continent ocean transition at the southeastern margin of the south china sea abstract the south china sea formed by magma poor or intermediate volcanic rifting in the paleogene we investigate the structure of the continent ocean transition cot at its southern margin off nw palawan between the continental blocks of reed bank and the islands of palawan and calamian several surveys recorded by the bgr from 1979 to 2008 established a comprehensive database of regional seismic lines accompanied with magnetic and gravity profiles we interpret two major rifted basins extending in the ne direction across the shelf and slope separated by a structural high of non volcanic origin the continent ocean transition is interpreted at the seaward limit of the continental crust when magnetic spreading anomalies terminate some 80 100 km farther north the area in between displays extensive volcanism as manifest by extrusions that occasionally reach and cut the seafloor by dykes and by presumed basaltic lava flows occurring after break up the cot is highly variable along the nw palawan slope one type shows a distinct outer ridge at the cot with a steep modern seafloor relief the other type is characterised by rotated fault blocks bounded by listric normal faults ramping down to a common detachment surface half grabens developed above a strongly eroded pre rift basement the seafloor relief is smooth across this other type of cot we suggest the pre rift lithospheric configuration had major influence on the formation of the cot besides transfer zones volcanic domains confined to the north of competent crustal blocks correlate with the style of the cot gravity modelling revealed an extremely thinned crust across the shelf we propose a depth dependent extension model with crust being decoupled from mantle lithosphere explaining the discrepancy of subsidence observed across the south china sea region

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

ages and magnetic structures of the south china sea constrained by deep tow magnetic surveys and iodp expedition 349 combined analyses of deep tow magnetic anomalies and international ocean discovery program expedition 349 cores show that initial seafloor spreading started around 33 ma in the northeastern south china sea scs but varied slightly by 1 2 myr along the northern continent ocean boundary cob a southward ridge jump of approximate to 20 km occurred around 23 6 ma in the east subbasin this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the southwest subbasin which propagated for about 400 km southwestward from approximate to 23 6 to approximate to 21 5 ma the terminal age of seafloor spreading is approximate to 15 ma in the east subbasin and approximate to 16 ma in the southwest subbasin the full spreading rate in the east subbasin varied largely from approximate to 20 to approximate to 80 km myr but mostly decreased with time except for the period between approximate to 26 0 ma and the ridge jump approximate to 23 6 ma within which the rate was the fastest at approximate to 70 km myr on average the spreading rates are not correlated in most cases to magnetic anomaly amplitudes that reflect basement magnetization contrasts shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers in addition to large vertical intensity variations these complexities are caused by late stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0 5 which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization the primary contribution to magnetic anomalies of the scs is not in the top 100 m of the igneous basement

structure and sediment budget of yinggehai song hong basin south china sea implications for cenozoic tectonics and river basin reorganization in southeast asia the temporal link between offshore stratigraphy and onshore topography is of key importance for understanding the long term surface evolution of continental margins here we present a grid of regional high quality reflection seismic and well data to characterize the basin structure we identify fast subsidence of the basin basement and a lack of brittle faulting of the offshore red river fault in the yinggehai song hong basin since 5 5 ma despite dextral strike slip movement on the onshore red river fault we calculate the upper crustal whole crustal and whole lithospheric stretching factors for the yinggehai song hong basin which show that the overall extension observed in the upper crust is substantially less than that observed for the whole crust or whole lithosphere we suggest that fast basement subsidence after 5 5 ma may arise from crustal to lithospheric stretching by the regional dynamic lower crustal mantle flow originated by collision between india eurasia and indian oceanic subduction below the eurasian margin in addition we present a basin wide sediment budget in the yinggehai song hong basin to reconstruct the sedimentary flux from the red river drainage constrained by high resolution age and seismic stratigraphic data the sediment accumulation rates show a sharp increase at 5 5 ma which suggests enhanced onshore erosion rates despite a slowing of tectonic processes this high sediment supply filled the accommodation space produced by the fast subsidence since 5 5 ma our data further highlight two prominent sharp decreases of the sediment accumulation at 23 3 ma and 12 5 ma which could reflect a loss of drainage area following headwater capture from the paleo red river however the low accumulation rate at 12 5 ma also correlates with drier and therefore less erosive climatic conditions

symmetric and asymmetric lithospheric extension relative effects of frictional plastic and viscous strain softening 1 strain dependent rheologies may play a critical role in the deformation of the lithosphere and particularly in the development of focused shear zones we investigate the effects of strain softening on lithospheric extension using plane strain thermomechanical finite element model experiments parametric softening is specified as a linear decrease of the effective internal angle of friction the effective viscosity or both in the model rheologies the sensitivity of deformation to the choice of softening parameters is investigated in cases where the crust is either strongly or weakly coupled to the mantle lithosphere results are classified according to the symmetry s or asymmetry a of the deformation of the upper and lower lithosphere during rifting strain softening is required for rifting asymmetry but is not always sufficient a range of model tectonic styles occurs including pure and simple shear modes with focused shear zones mode selection is mostly determined by the feedback between two primary controls the dominant rheology and the parametric strain softening mechanisms listed above softening of the dominant rheology promotes asymmetric extension of that part of the lithosphere controlled by the dominant rheology model results are consistent with the proposed primary controls and the factors that contribute to these controls in particular decreasing and increasing the rifting velocity can change the mode by changing the dominant rheology asymmetry is strongest in coupled models which include a decrease in the internal angle of friction and have low rifting velocities

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

complex rifted continental margins explained by dynamical models of depth dependent lithospheric extension observations from a number of rifted margins e g south atlantic salt basin mid norwegian margin exmouth plateau reveal wide regions of extremely attenuated crust and depositional environments that indicate depth dependent lithospheric extension although the one dimensional thermal kinematic consequences of depth dependent extension are understood no comprehensive process based explanation for the complex style of these margins exists here we present self consistent numerical models of passive margin formation that explain the depth dependent extension the width of the margin its characteristic tripartite nature and why such margins are prone to deposition of evaporites under appropriate climatic conditions some features that are important to reproducing the observed characteristics include decoupling between upper and lower parts of the lithosphere during stretching contrasting wide and narrow extensional styles above and below the decoupling level and progressive focusing of crustal extension toward the rift axis

origin of regional rooted low angle normal faults a mechanical model and its tectonic implications rooted listric low angle normal faults 20 of regional extent have been recognized widely in the past few years in the north american cordillera and elsewhere the low angle geometry of these crustal scale normal faults conflicts with anderson s 1942 classic theory of faulting in that theory the orientations of principal stresses are assumed to be vertical and horizontal the predicted dip angle of normal faults is about 60 rather than 20 or less recent geological and geophysical studies in the mid tertiary extensional terrane of southeastern california and western arizona suggest that thick mylonitic gneisses in the lower plates of low angle detachment faults may represent unidirectionally sheared laminar flow in and below the midcrust directed ductile flow possibly related to the gravitational spreading of thickened lower crust may induce a shearing traction on the horizontal or subhorizontal base of the brittle upper crust thus the orientations of the principal stresses can no longer be vertical and horizontal at this interface a simple elastic model incorporates the effect of basal shearing due to gravitational spreading on stress distributions in an elastic upper crust this model shows that parallel belts of compression and extension can be produced if a shearing traction acting on the base of the elastic upper crust is considered in particular appropriate stress conditions for the formation of regional low angle normal faults 20 can be produced by the superposition of two stress fields a basal shear stress field induced by the basal shear traction and a contractional stress field in which the horizontal deviatoric stress is compressional and the vertical gradient of the horizontal normal stress component is constant this superposed stress field may represent a tectonic setting where a stress field with compressional deviatoric stress induced by plate subduction or convergence is superposed on a basal shear stress field induced by gravitational spreading of thickened lower crust these results may explain both puzzling parallel belts of extension and compression and the occurrence of major low angle normal faults in some orogenic systems

movement along a low angle normal fault the s reflector west of spain 1 the existence of normal faults that moved at low angles less than 20 has long been debated one possible low angle fault is the s detachment at the west galicia spain margin and thought to occur at the top of serpentinized mantle it is unlikely that s was a large submarine slide as it was probably active over several million years without the development of any compressional features such as toe thrusts it appears to have rooted beneath the conjugate flemish cap margin and it is similar to structures elsewhere that also appear to be rooted detachments here we analyze depth images to identify synrift sediment packages above s and use the geometry of these synrift packages to constrain the angle at which s both formed and remained active we find that s must have remained active at angles below 15 too low to be explained simply by the low friction coefficient of partially serpentinized peridotites instead we suggest that transient high fluid pressures must have developed within the serpentinites and propose a model in which anastomosing fault strands are alternately active and sealed enabling moderately high fluid pressures to develop