japan sea a pull apart basin abstract recent field work in the hokkaido central belt and marine geology studies along the eastern margin of japan sea in addition to previously published data lead us to propose a new model of opening of the japan sea the synthesis of both on land and offshore structural data gives new constraints about the structural evolution of the system the rhombohedral shape of the japan basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early eo oligocene rifting of a pull apart basin accommodated along two large right lateral shear zones east of korea and west of northeast japan and sakhalin it is followed during upper oligocene lower miocene by the main opening of the japan basin as a mega pull apart then a back arc spreading probably related to the subduction process induced the creation of the yamato and tsushima basins at the end of lower miocene and in middle miocene clockwise rotation of southwest japan larger than 20 or major bending of honshu mainland deduced from paleomagnetic studies is unlikely at this time since 1 or 2 my b p to present compression prevails along the eastern margin of the japan sea the generation of marginal basins as pull apart basins along intracontinental strike slip faults is a mechanism which has been proposed by other authors concerning the south china sea the question then is whether the fragmentation of the asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one

controls on back arc basin formation the relationship between subduction and back arc spreading has been well known since the early days of plate tectonics however the reasons why back arc basins are associated with some subduction systems but not all has remained elusive we examine the kinematic controls on subduction and back arc basins for both the present day and cenozoic to differentiate between the major competing hypotheses for back arc basin formation and to explain their temporal and spatial distribution our new data set of subduction and back arc basin parameters uses a new set of paleo oceanic age grids muller et al 2005 associated with a moving atlantic indian ocean hot spot reference frame o neill et al 2005 the plate model includes detailed reconstructed spreading histories of back arc basins based on marine geophysical and satellite gravity data our combined rotation and oceanic paleo age model provides the age distribution of subducting lithosphere through space and time convergence rates and the absolute motion of the downgoing and overriding plates we find that back arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years additionally we establish an age dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30 with back arc spreading our results suggest that back arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge thereby creating accommodation space between the overriding and subducting plates once back arc extension is established it continues regardless of overriding plate motion indicating back arc spreading is not a simple consequence of overriding plate behaviour the landward migration of the overriding plate as a precursor to back arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle however once back arc extension is established rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space our analysis indicates the driving mechanism for back arc extension is a combination of surface kinematics properties of the downgoing slab the effect of lateral mantle flow on the slab and mantle wedge dynamics

50 ma initiation of hawaiian emperor bend records major change in pacific plate motion the hawaiian emperor bend has played a prominent yet controversial role in deciphering past pacific plate motions and the tempo of plate motion change new ages for volcanoes of the central and southern emperor chain define large changes in volcanic migration rate with little associated change in the chain s trend which suggests that the bend did not form by slowing of the hawaiian hot spot initiation of the bend near kimmei seamount about 50 million years ago ma was coincident with realignment of pacific spreading centers and early magmatism in western pacific arcs consistent with formation of the bend by changed pacific plate motion

deep shallow coupling response of the cenozoic bohai bay basin to plate interactions around the eurasian plate abstract the bohai bay basin bbb is a meso cenozoic intracontinental petroliferous basin where four pre existing continental scale fault zones intersect in east china the bbb has experienced complex deformational and evolutionary history that records significant information about how the lithosphere there has responded to the coeval plate interactions around the eurasian plate and or their resulting deep crust mantle processes in the cenozoic now both deep and shallow deformational and evolutionary processes of the bbb have been well studied but many geodynamic mechanisms previously proposed for those processes are too general to explain them well based on various data and principles we first summarized both deep and shallow responses and processes of the bbb in the cenozoic and then matched reasonable geodynamic mechanisms for each of them the results show as follows the cenozoic differential reactivation of pre existing continental scale weak zones controlled the coeval deep shallow differential coupling evolution of the bbb the paleogene extension in the bbb was mainly caused by crust mantle processes triggered by the stagnant izanagi slab the cenozoic strike slip faulting was influenced by various plate interactions in which the oblique subduction and anticlockwise rotation of young pacific plate resulted in the complex pre oligocene strike slip history of the tan lu fault zone to the south of the zhang peng fault zone while the india eurasia collision has caused the intense and synchronous strike slip faulting of various faults there since 35 ma which was then weakened by the oblique subduction and clockwise rotation of young philippine sea plate in the neogene the compression resulting from both the india eurasia collision and the philippine sea plate s subduction contributed to the latest paleogene tectonic inversion in the bbb the arrival of mantle flow triggered by both the india eurasia collision and the stagnant slab of the pacific plate resulted in the tectonic reactivation there in the late neogene

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

global tectonic significance of the solomon islands and ontong java plateau convergent zone abstract oceanic plateaus areas of anomalously thick oceanic crust cover about 3 of the earth s seafloor and are thought to mark the surface location of mantle plume heads hotspot tracks represent continuing magmatism associated with the remaining plume conduit or tail it is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones and therefore 1 influences the eventual composition of continental crust and 2 is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs the ontong java plateau ojp of the southwestern pacific ocean is the largest and thickest oceanic plateau on earth and the largest plateau currently converging on an island arc solomon islands for this reason this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones this volume consists of a series of four papers that summarize the results of joint us japan marine geophysical studies in 1995 and 1998 of the solomon islands ontong java plateau convergent zone marine geophysical data include single and multi channel seismic reflection ocean bottom seismometer obs refraction gravity magnetic sidescan sonar and earthquake studies objectives of this introductory paper include 1 review of the significance of oceanic plateaus as potential contributors to continental crust 2 review of the current theories on the fate of oceanic plateaus at subduction zones 3 establish the present day and neogene tectonic setting of the solomon islands ontong java plateau convergent zone 4 discuss the controversial sequence and timing of tectonic events surrounding ontong java plateau solomon arc convergence 5 present a series of tectonic reconstructions for the period 20 ma early miocene to the present day in support of our proposed timing of major tectonic events affecting the ontong java plateau solomon islands convergent zone and 6 compare the structural and deformational pattern observed in the solomon islands to ancient oceanic plateaus preserved in precambrian and phanerozoic orogenic belts our main conclusion of this study is that 80 of the crustal thickness of the ontong java plateau is subducted beneath the solomon island arc only the uppermost basaltic and sedimentary part of the crust 7 km is preserved on the overriding plate by subduction accretion processes this observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both precambrian and phanerozoic orogenic belts

predicting plate velocities with mantle circulation models 1 we predict plate motions from a comprehensive inversion of theoretical estimates of tectonic forces in order to evaluate the relative importance of these and the uncertainties of such models plate driving forces from the mantle are calculated using global flow models that are driven by tomography and subduction derived density fields observed and predicted plate velocities agree well for a variety of models leading to varied conclusions about the relative importance of forces the dominance of the subduction related density pattern in the mantle is confirmed it appears that p wave models do not satisfactorily image all of the slab associated anomalies in the upper mantle furthermore lower mantle structure always improves the plate motion fit with respect to models that are based on upper mantle anomalies and lithospheric thickening only we show that the average torques from the lower mantle scale with the radial flow through the 660 km phase transition the amplitude of the lower mantle torques will be significant for a range of models if there is mass flux through 660 km we also evaluate parameterized edge forces and find that the additional inclusion of such torques does not significantly improve the model fit the main reason for the nonuniqueness of the inversions is plate boundary geometry since all plate motions are dominated by the trench ridge system and plates move from ridges to trenches

pacific plate motion change at the time of the hawaiian emperor bend constrains the viscosity of earth s asthenosphere important constraints on asthenospheric viscosity come primarily from modeling the glacial rebound of the past 20 kyr but remain somewhat loose because of the intrinsic resolving power of these models we obtain narrower bounds by building on the notion that the asthenosphere also controls the ability to change plate motions over myr we focus on the pacific kinematic change at the time of the hawaiian emperor bend event which is linked to the coeval inception of subduction in the western pacific we sample plausible asthenospheric viscosity and thickness values by requiring the rate at which torque varied to generate the observed kinematics consistent with the nature of subduction initiation uncertainties on the bend event duration and the occurrence of pacific hot spots drift do not hamper our results that suggest that the asthenosphere viscous response to vertical shear over kyr is consistent with that to horizontal shear over myr

on the role of slab pull in the cenozoic motion of the pacific plate we analyze the role of slab pull acting on the pacific plate during its early tertiary change in motion slab pull forces are estimated by integrating the negative buoyancy of a 700 km long slab along a revised subduction boundary model adopting the muller et al 2008 seafloor age reconstructions our results indicate that torques predicted from a simple slab pull model match the pacific plate euler vectors during the tertiary fairly well the change of the pacific motion at similar to 50 40 ma appears to be driven by the onset of the izu bonin mariana system and soon afterwards by the tonga kermadec subduction zones

surface bidirectional reflectance distribution function observed at global scale by polder adeos the spaceborne polder instrument presents the unique capability of sampling the surface bidirectional reflectance distribution function brdf up to about 60 viewing angle for the full azimuth range of every point on earth at 6 km resolution when atmospheric conditions are favorable this paper presents examples of brdf signatures acquired at this resolution on several terrestrial biomes desert steppe grassland boreal forest savanna wetland well identified directional signatures for all azimuths are obtained and shown to be different for each biome specific directional effects in the hot spot and specular directions are well observed in the data

slabs in the lower mantle results of dynamic modelling compared with tomographic images and the geoid abstract the recent increase in resolution of tomographic images of the earth s interior has enabled us to see slabs in the lower mantle on the other hand the distribution of slabs can be inferred from subduction history using a dynamical model of mantle flow comparison of tomographic images with model results can help to distinguish between alternative models of subduction history tomographic models and mantle flow models and thus improve our understanding of the earth here a simple dynamic model of subduction is used and some results are presented amounts and locations of subduction are inferred from published models of plate motion and plate boundaries for the past 120 ma the latter have been interpolated on 2 ma time intervals mantle flow driven by the density anomalies corresponding to subducted slabs is calculated with the method of hager and o connell for a viscosity structure that features an increase in viscosity from 4 10 20 pa below the lithosphere to 4 10 22 pa in the lower part of the lower mantle slabs are advected in the flow field in the model slabs sink on average about 1700 km through the mantle during 100 ma however the calculated average horizontal motion of slabs throughout most of the mantle is only about 600 700 km for slabs that have sunk to the lowermost mantle it is about 1000 km this is in accordance with the previously observed good correlation between subduction locations and lowermost mantle heterogeneities slabs sink fastest in regions with abundant subduction and little trench migration e g below east asia in the lowermost mantle predicted slab locations tend to lie in areas with high seismic velocities however there are large areas of fast seismic velocities where no slabs are predicted and which therefore presumably correspond to earlier subduction in some regions e g below japan our model approximately reproduces the observed shape of the slab in other regions where the agreement is poor the results can help to further constrain models of subduction history and associated mantle flow additionally the predicted geoid is computed and compared with the actual geoid predicted and observed geoid have similar magnitude and a number of features in common however an optimization of the fit is not attempted here since in order to do this also the hot upwellings from the lower boundary layer presumably in the form of plumes would have to be included

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

pacific absolute plate motion since 145 ma an assessment of the fixed hot spot hypothesis 1 using the geometry and ages from 12 pacific seamount chains we have determined two new absolute plate motion models that now extend our self consistent and high resolution models with covariance estimates back to 145 ma the wk08 a model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles yielding a relatively smooth plate motion model the wk08 g model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many coregistered chains both models have been used to assess the viability of the fixed hot spot hypothesis in the pacific in determining the models we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends we were able to connect plate motions for pre and post emperor age intervals by including the ratak gilbert ellice and musicians trails in our analysis however as no active hot spot locations exist for the older chains their inclusion adds additional model parameters both age and geometry misfits increase with age reflecting the observed increase in age uncertainties and the general widening of trails secondary and short lived changes in absolute plate motion mapped in wk08 g appear to correlate with the timing and sense of motion of known pacific rim tectonic events analysis of interchain distances between coeval samples from the hawaii and louisville chains suggests possible discrepancies during the older emperor stage that are compatible with predictions of hot spot drift we computed a new apparent polar wander path for the pacific and found a high degree of correspondence with paleomagnetically derived paths as long as solutions allowing for anomalous skewness were included in the latter our polar wander path suggests that there might have been some true polar wander during the emperor stage complemented by a smaller amount of hot spot drift than otherwise required we show that chain geometries and ages combined with future paleolatitude determinations from additional sites and chains could enable an observation based description of both hot spot and plate motions without relying on predictions of hot spot drift derived from mantle flow calculations

reconciling late neogene pacific absolute and relative plate motion changes new models of pacific absolute plate motion relative to hot spots and models of relative plate motion involving the pacific plate all agree there was a significant change in the late neogene chron 3a 5 89 ma reflecting a more northerly absolute motion than previously determined as pacific absolute plate motion became slightly more northerly left stepping transform segments came under compression some left stepping segments became microplates with clockwise rotation others show clear evidence of compressional deformation conversely right stepping transforms came under tension and many developed intratransform spreading centers or show similar evidence for transform magmatism several large left stepping transform offsets represent portions of the nazca plate protruding into the pacific and as such act as obstacles to the more northerly pacific absolute plate motion we suggest these obstructions act to enhance the generally tensile equatorial pacific stress regime caused by distant slab pull as a consequence the greater french polynesia region has experienced diffuse volcanism that increased considerably following the chron 3a plate motion change we propose that since the hawaii emperor bend time the distant pacific slab pull and the friction between the large buoyant ontong java plateau and the northern margin of the australia plate have produced episodes of increased tensile stresses in the equatorial pacific we believe these stress excursions are responsible for much of the intraplate volcanism observed in a wide triangular region from samoa to the east pacific and pacific antarctic rises

earth science palaeo altimetry of tibet reply molnar et al 1 question our conclusion on the role of convective destabilization of thickened mantle lithosphere in determining the surface elevation history of the tibetan plateau the primary argument depends on our interpretation2 3 of oxygen isotope based estimates of palaeo elevation of the lunpola basin a locality in the centre of the plateau

a general method to normalize landsat reflectance data to nadir brdf adjusted reflectance abstract the landsat satellites have been providing spectacular imagery of the earth s surface for over 40 years however they acquire images at view angles 7 5 from nadir that cause small directional effects in the surface reflectance there are also variations with solar zenith angle over the year that can cause apparent change in reflectance even if the surface properties remain constant when landsat data from adjoining paths or from long time series are used a model of the surface anisotropy is required to adjust all landsat observations to a uniform nadir view primarily for visual consistency vegetation monitoring or detection of subtle surface changes here a generalized approach is developed to provide consistent view angle corrections across the landsat archive while this approach is not applicable for generation of landsat surface albedo which requires a full characterization of the surface bidirectional reflectance distribution function brdf or for correction to a constant solar illumination angle across a wide range of sun angles it provides landsat nadir brdf adjusted reflectance nbar for a range of terrestrial monitoring applications the landsat nbar is derived as the product of the observed landsat reflectance and the ratio of the reflectances modeled using modis brdf spectral model parameters for the observed landsat and for a nadir view and fixed solar zenith geometry in this study a total of 567 conterminous united states conus january and july 2010 landsat 5 thematic mapper tm and landsat 7 enhanced thematic mapper etm images that have swath edge overlapping paths sensed in alternating backscatter and forward scattering orientations were used the average difference between landsat 5 tm and landsat 7 etm surface reflectance in the forward and backward scatter directions at the overlapping landsat scan edges was quantified the conus july view zenith brdf effects were about 0 02 in the landsat visible bands and about 0 03 0 05 and 0 06 in the 2 1 m 1 6 m and near infrared bands respectively comparisons of landsat 5 tm and landsat 7 etm nbar derived using modis brdf spectral model parameters defined with respect to different spatial and temporal scales and defined with respect to different land cover types were undertaken the results suggest that because the brdf shapes of different terrestrial surfaces are sufficiently similar over the narrow 15 landsat field of view a fixed set of modis brdf spectral model parameters may be adequate for landsat nbar derivation with little sensitivity to the land cover type condition or surface disturbance a fixed set of brdf spectral model parameters derived from a global year of highest quality snow free modis brdf product values are provided so users may implement the described landsat nbar generation method

a geodynamical view on the steadiness of geodetically derived rigid plate motions over geological time 1 the ability to map ocean floor magnetization is key to infer past plate motions the advent of geodesy in the earth sciences offered an independent snapshot of contemporary plate kinematics averaged over decades early studies suggested plate motions steadiness through geological time because contemporary rates were similar to past 3 myr averages recent data however show that geodetic and paleo magnetic motions exhibit differences beyond confidence ranges which might suggest geodesy samples time scales shorter than a few centuries these differences pose important questions on the character of plate kinematic variability through time here i derive inferences on the steadiness of geodetically derived plate motions by combining geodynamical arguments with kinematic data sets i exploit data sets to build scenarios for the recent evolution of most of the major plates i compare the minimum rate at which torque needs to vary to generate these scenarios with the maximum rate at which geological processes can contribute torque this allows assessing the geodynamical plausibility of each scenario results indicate that plate motion changes recorded since 3 ma must have taken at least 1 myr to occur two exceptions are the pacific and australian plates whose motions changed by less than 5 and therefore required torque variations that might be built over periods as short as 0 1 myr it remains unresolved for how long geodetically derived plate motions kept steady in the geological past however results indicate it is indeed plausible that they did over the past 1 2 myr these inferences call for a shift in the way we regard the figure of geodetic plate motions

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

the driving mechanism of plate tectonics relation to age of the lithosphere at trenches sea floor age depth and age trench depth relations suggest that the oceanic lithosphere continues to thicken and subside with age beyond 80 ma if so slab pull fs and ridge push fr forces can be calculated from the age of the sea floor at trenches t and if the shear stress acting on the base of the plate increases with absolute velocity a the approximate force balance equation is dva2 svat32 rt where d s and r are constants related to drag slab pull and ridge push respectively the relation between velocity and age is va2 s vat12 r we have tested this model by linear regression using rate and age data for 15 trenches va mm a 2 9 20 32 vat12 26 250 the strength of this correlation r 0 98 is strong evidence in favor of the validity of this simple model these results suggest that ridge push is just sufficient to overcome drag at the base of the plate and does not contribute significantly to the motions of oceanic plates though the value of r is consistent with the motions of plates not attached to subducted slabs

subduction zone infancy examples from the eocene izu bonin mariana and jurassic california arcs a new model for the earliest stages in the evolution of subduction zones is developed from recent geologic studies of the izu bonin mariana ibm arc system and then applied to late jurassic ophiolites of cailfornia the model accounts for several key observations about the earliest stages in the evolution of the ibm system 1 subduction nucleated along an active transform boundary which separated younger less dense lithosphere in the west from older more dense lithosphere to the east 2 initial arc magmatic activity occupied a much broader zone than existed later 3 initial magmatism extended up to the modern trench over a region now characterized by subnormal heat flow 4 early are magmatism was characterized by depleted tholeiitic and ultra depleted boninitic magmas indicating that melting was more extensive and involved more depleted mantle than is found anywhere else on earth 5 early arc magmatism was strongly extensional with crust forming in a manner similar to slow spreading ridges and 6 crust production rates were 120 to 180 km 3 km ma several times greater than for mature arc systems these observations require that the earliest stages of subduction involve rapid retreat of the trench we infer that this resulted from continuous subsidence of denser lithosphere along the transform fault this resulted in strong extension and thinning of younger more buoyant lithosphere to the west this extension was accompanied by the flow of water from the sinking oceanic lithosphere to the base of the extending lithosphere and the underlying asthenosphere addition of water and asthenospheric upwelling led to catastrophic melting which continued until lithosphere subsidence was replaced by lithospheric subduction application of the subduction zone infancy model to the late jurassic ophiolites of california provides a framework in which to understand the rapid formation of oceanic crust with strong arc affinities between the younger sierran magmatic arc and the franciscan subduction complex provides a mechanism for the formation and subsidence of the great valley forearc basin and explains the limited duration of high t high p metamorphism experienced by franciscan melanges

the latest cretaceous early paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern pacific margin episodic growth of accretionary complexes along the northwestern pacific margin is well documented from detailed biostratigraphy and radiometric dating of metamorphic rocks the latest cretaceous to early paleogene rapid growth of the accretionary complexes observed in hokkaido and sakhalin islands was caused by the supply of a large amount of terrigenous sediments from an intracontinent collision zone the mongolia okhotsk zone in the northern asian continent rapid growth of the accretionary prism resulted in episodic tectonic events in the forearc and magmatic arc rapid underplating caused uplift and exhumation of previously accreted complexes along with high pressure series metamorphic rocks now exposed as the kamuikotan complex in hokkaido and the susunai complex in sakhalin the forearc basin shallowed as a result of the uplift the uplift collapsed the old accretionary complex and supplied olistoliths onto the forearc region magmatic activity along the continental margin was also active at the same time subduction of a large amount of terrigenous sediments into the mantle may have contributed to active magmatism at that time a large supply of water trapped in the subducted sediments entered the mantle and increased partial melting of the mantle wedge

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

control of seafloor aging on the migration of the izu bonin mariana trench article i nfo recent global kinematic studies reveal that most of the trenches roll back but a significant number of them advance toward the upper plate those advancing trenches are mostly located in the western pacific and correspond to the subduction of very old mesozoic oceanic lithosphere while retreating trenches are commonly explained by the slab pull action of the descending lithosphere the origin of advancing trenches is still debated since this relationship is dependent upon the adopted reference frame we select region where geological studies show the variability of trench migration style with time the izu bonin mariana ibm region represents a key example the detailed reconstruction of the trench migration of the ibm subducting system reveals that after a long episode of asymmetric rollback the ibm trench recently started advancing we propose that this change from retreating to advancing trench mode results from the subduction of progressively older and stiffer lithospheric material we test this hypothesis by means of two dimensional 2 d numerical models reproducing the effects of the lithospheric aging during subduction the result of our numerical tests shows that the entrance of old and stiff lithosphere forces the trench to advance because the increasing stiffness of the slab prevents the slab to unbend once it has subducted we adapt this physical result to the ibm evolution showing that the switch from trench retreat to trench advance can reconcile the shape of ibm slab as previously suggested finally we discuss the possibility that the subduction of the cretaceous lithosphere might have triggered the change of the motion of the pacific plate around 5 ma

forced subduction initiation recorded in the sole and crust of the semail ophiolite of oman subduction zones are unique to earth and fundamental in its evolution yet we still know little about the causes and mechanisms of their initiation numerical models show that far field forcing may cause subduction initiation at weak pre existing structures while inferences from modern subduction zones suggest initiation through spontaneous lithospheric gravitational collapse for both endmembers the timing of subduction inception corresponds with initial lower plate burial whereas coeval or delayed extension in the upper plate are diagnostic of spontaneous or forced subduction initiation respectively in modern systems the earliest extension related upper plate rocks are found in forearcs but lower plate rocks that recorded initial burial have been subducted and are inaccessible here we investigate a fossil system the archetypal semail ophiolite of oman which exposes both lower and upper plate relics of incipient subduction stages we show with lu hf and u pb geochronology of the lower and upper plate material that initial burial of the lower plate occurred before 104 million years ago predating upper plate extension and the formation of semail oceanic crust by at least 8 myr such a time lag reveals far field forced subduction initiation and provides unequivocal direct evidence for a subduction initiation mechanism in the geological record

earth science palaeo altimetry of tibet arising from d b rowley b s currie nature 439 677 681 2006 rowley currie reply the determination of palaeo elevation has emerged in the past 15 years as an important tool for constraining physical processes that govern the formation of mountain belts rowley and currie1 report palaeo elevations for the lunpola basin within the tibetan plateau and claim that these elevations are incompatible with mantle thickening models for mountain formation we show here that their data do not support this conclusion and indeed are consistent with its opposite the tibetan plateau could have risen by a kilometre or more as its dense lower lithosphere sank into the underlying mantle

on the emergence of plate tectonics at present young oceanic lithosphere is positively buoyant and it does not become negatively buoyant until it is older than about 20 m y if in the past the mantle was hotter the oceanic crust would have been thicker and the lithosphere9s age of neutral buoyancy greater on the other hand the hotter mantle would have had a lower viscosity and convected faster so the average age of oceanic plates at subduction would have been less than the present 100 m y at some time in the past average oceanic lithosphere would have only just become negatively buoyant as it reached a subduction zone it is estimated here that this condition occurred when the mantle was only about 50 c hotter than at present and as recently as 0 9 1 4 b y ago transformation of basaltic crust to eclogite might have enhanced the vigor of the plates but possibly only modestly and intermittently in earlier times plate tectonics could have operated but more slowly so that it could not by itself have accomplished the necessary rate of heat removal from the earth a different tectonic mode must also have operated perhaps subcrustal delamination or dripping plate tectonics would have gradually taken over from the earlier mode plumes are a omplementary mode of mantle convection driven by a lower thermal boundary layer and so they could have operated in conjunction with both regimes of the upper boundary layer

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

the west philippine basin an eocene to early oligocene back arc basin opened between two opposed subduction zones 1 based on geological and geophysical data collected from the west philippine basin and its boundaries we propose a comprehensive cenozoic history of the basin our model shows that it is a back arc basin that developed between two opposed subduction zones rifting started around 55 ma and spreading ended at 33 30 ma the initial spreading axis was parallel to the paleo philippine arc but became inactive when a new spreading ridge propagated from the eastern part of the basin reaching the former one at an r r r triple junction spreading occurred mainly from this second axis with a quasi continuous counter clockwise rotation of the spreading direction the gagua and palau kyushu ridges acted as transform margins accommodating the opening arc volcanism occurred along the palau kyushu ridge eastern margin during the whole opening of the basin whereas the paleo philippine arc decreased its activity between 43 and 36 ma the western margin underwent a compressive event in late eocene early oligocene time leading to the rising of the gagua ridge and to a short subduction episode along eastern luzon in the western part of the basin the spreading system was highly disorganized due to the presence of a mantle plume overlapping spreading centers and ridge jumps occurred toward the hot region and a microplate developed shortly after the end of the spreading a late stage of amagmatic extension occurred between 30 and 26 ma in the central part of the basin being responsible for the deep rift valley that cut across the older spreading fabric

non lambertian effects on remote sensing of surface reflectance and vegetation index this paper discusses the effects of non lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite remote measurement of the surface characteristics is perturbed by atmospheric scattering of sun light this scattering tends to smooth the angular dependence of non lambertian surface reflectances an effect that is not present in the case of lambertian surfaces this effect is calculated to test the validity of a lambertian assumption used in remote sensing for the three types of vegetations considered in this study the assumption of lambertian surface can be used satisfactorily in the derivation of surface reflectance from remotely measured radiance for a view angle outside the backscattering region within the backscattering region however the use of the assumption can result in a considerable error in the derived surface reflectance accuracy also deteriorates with increasing solar zenith angle the angular distribution of the surface reflectance derived from remote measurements is smoother than that at the surface the effect of surface non lambertianity on remote sensing of vegetation index is very weak since the effect is similar in the visible and near infrared part of the solar spectrum for the vegetations treated in this study it is canceled in deriving the vegetation index the effect of the diffuse skylight on surface reflectance measurements at ground level is also discussed

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

reconstructing the cenozoic evolution of the mantle implications for mantle plume dynamics under the pacific and indian plates article history the lack of knowledge of the initial thermal state of the mantle in the geological past is an outstanding problem in mantle convection the resolution of this problem also requires the modelling of 3 d mantle evolution that yields maximum consistency with a wide suite of geophysical constraints quantifying the robustness of the reconstructed thermal evolution is another major concern to solve and estimate the robustness of the time reversed inverse problem of mantle convection we analyse two different numerical techniques the quasi reversible qrv and the backward advection bad methods our investigation extends over the 65 myr interval encompassing the cenozoic era using a pseudo spectral solution for compressible flow thermal convection in 3 d spherical geometry we find that the two dominant issues for solving the inverse problem of mantle convection are the choice of horizontally averaged temperature i e geotherm and mechanical surface boundary conditions we find in particular that the inclusion of thermal boundary layers that yield earth like heat flux at the top and bottom of the mantle has a critical impact on the reconstruction of mantle evolution we have developed a new regularisation scheme for the qrv method using a time dependent regularisation function this revised implementation of the qrv method delivers time dependent reconstructions of mantle heterogeneity that reveal 1 the stability of pacific and african large low shear velocity provinces llsvp over the last 65 myr 2 strong upward deflections of the cmb topography at 65 ma beneath the north atlantic the south central pacific the east pacific rise epr and the eastern antarctica 3 an anchored deep mantle plume ascending directly under the epr easter and pitcairn hotspots throughout the cenozoic era and 4 the appearance of the transient reunion plume head beneath the western edge of the deccan plateau at 65 ma our reconstructions of cenozoic mantle evolution thus suggest that mantle plumes play a key role in driving surface tectonic processes and large scale volcanism 2014 elsevier b v all rights reserved

evolving viscous anisotropy in the upper mantle and its geodynamic implications asthenospheric shear causes some minerals particularly olivine to develop anisotropic textures that can be detected seismically in laboratory experiments these textures are also associated with

southwest pacific absolute plate kinematic reconstruction reveals major cenozoic tonga kermadec slab dragging tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench parallel slab motion through the mantle recently defined as a form of slab dragging we investigate here long term slab dragging components of the tonga kermadec subduction system driven by absolute pacific plate motion to this end we develop a kinematic restoration of tonga kermadec trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle estimating tonga kermadec subduction initiation is challenging because another new caledonia subduction zone existed during the paleogene between the australia and pacific plates we test partitioning of plate convergence across the paleogene new caledonia and tonga kermadec subduction zones against resulting mantle structure and show that most if not all tonga kermadec subduction occurred after ca 30 ma since then tonga kermadec subduction has accommodated 1 700 to 3 500 km of subduction along the southern and northern ends of the trench respectively when placed in a mantle reference frame the predominantly westward directed subduction evolved while the tonga kermadec trench underwent 1 200 km of northward absolute motion we infer that the entire tonga kermadec slab was laterally transported through the mantle over 1 200 km such slab dragging by the pacific plate may explain observed deep slab deformation and may also have significant effects on surface tectonics both resulting from the resistance to slab dragging by the viscous mantle

plate tectonic reconstructions predict part of the hawaiian hotspot track to be preserved in the bering sea we use plate reconstructions to show that parts of the hawaiian hotspot track of ca 80 90 ma age could be preserved in the bering sea based on these reconstructions the hawaiian hotspot was beneath the izanagi plate before ca 83 ma around that time the part of the plate carrying the hotspot track was transferred to the kula plate after 75 80 ma the hawaiian hotspot underlay the pacifi c plate circa 40 55 ma subduction initiated in the aleutian trench part of the kula plate was attached to the north american plate and is preserved as the oceanic part of the bering sea we show that for a number of different plate reconstructions and a variety of assumptions covering hotspot motion part of the hotspot track should be preserved in the bering sea the predicted age of the track depends on the age of aleutian subduction initiation we speculate that bowers and shirshov ridges were formed by paleohawaiian hotspot magmatism

how mantle slabs drive plate tectonics the gravitational pull of subducted slabs is thought to drive the motions of earth s tectonic plates but the coupling between slabs and plates is not well established if a slab is mechanically attached to a subducting plate it can exert a direct pull on the plate alternatively a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate from the geologic history of subduction we estimated the relative importance of pull versus suction for the present day plates observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction

ontong java plateau and late neogene changes in pacific plate motion aided by a new geometrical technique called hot spotting we recently proposed a new model for the absolute motion of the pacific plate this model called wk97 assumed the hawaiian hotspot is under loihi and that there was a change in plate motion at 3 6 ma the model located the louisville hotspot close to the hollister ridge a shallow volcanic ridge associated with a geoid high seismicity and recent volcanism most of the tectonic implications of wk97 however were not addressed furthermore although several recent studies suggest that the geochemistry of hollister lavas may indicate a mixture between louisville melt material and pacific antarctic ridge mid ocean ridge basalt these studies strongly disagree with wk97 and consider it seriously flawed here we discuss numerous tectonic predictions of wk97 and present a large amount of observational evidence in support of it we find that a late neogene collision between the ontong java plateau and the northern margin of the australia plate appears to have altered the motion of the pacific plate as inferred from hotspot volcanism by forcing it to rotate counter clockwise this rotation about a low latitude pole appears to have induced right lateral shear stress along the entire pacific plate divergent boundary which resulted in the formation of extensional transform faults microplates and propagating ridges this change in motion also appears to have triggered concomitant circum pacific tectonism including trench migration and back arc rifting the wk97 suggests that long lived plume fed volcanism on the pacific plate appears very limited perhaps only to five to six hotspots hawaii louisville cobb caroline and perhaps marquesas and bowie the geometry of these chains are consistent with our model despite some evidence for volcanic age progressions most other pacific neogene hotspots are most likely crack spots i e sites of extensional volcanism at preexisting zones of weakness reactivated by plate stresses indeed several volcanic ridges such as hollister ridge near the louisville hotspot appear to have formed in response to stresses following the change in absolute plate motion wk97 also obviates the need for simultaneous different directions of mantle flow in the south central pacific transpression at the san andreas and alpine strike slip faults and aleutian arc explosivity since 6 ma also appear to be consequences of the changes in pacific plate motion furthermore both the wk97 model and observed relative plate motions suggest that adjoining plates have changed their absolute motions as well and that large changes in absolute plate motion do not necessarily imply large changes in relative plate motion our findings support slab pull as the dominant plate tectonic driving force highlight the rheological difference between strong oceanic lithosphere and weak continental crust and suggest that wk97 presently provides a unifying albeit preliminary framework for relating both intraplate and circum pacific tectonism and volcanism in the late neogene

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

possible manifestations of slab window magmatisms in cretaceous southwest japan abstract the slab window system related to ridge subduction is studied to explain the conspicuous activity and the along arc migration of the magmatisms in the eastern margin of eurasian continent in the late mesozoic the trend of the granite ages is scrutinized with systems approach and analyzed by the statistical method in cretaceous southwest japan a reference field of the eurasian eastern margin the magmatic distribution of simultaneous activity was determined to be the v shape of the slab window excluding dating errors from the located age data the slab window magmatism has the most dominant zone of the acidic rocks at or near the centerline of the window the spreading center of two plates and also has the subdominant zone of the acidic to intermediate rocks on either side of the window as the slab window opens due to the plate motions the upwelling current is adiabatically induced in the asthenosphere to fill the window gap the partial melt is generated in the upwelling flux and transports heat to the lower crust to make greater granitic magma chambers by heat conduction to and assimilation with the crustal matter the younger and hotter slabs outside the window also play a role in partial slab melting and or dehydration to the asthenosphere and generate the subdominant granodioritic and adakitic and or high magnesian andesitic magmatisms as the pre and post activities of the main granite genesis the slab window formed by the subducted ridge between the kula and pacific plates was the strong heat source of the active magmatisms and migrated at the rate of 2 8 cm year from southwest to northeast about 8000 km along the continental margin the growth of the continent associated with the active acidic to intermediate magmatisms including the adakitic and or high magnesian andesitic activities is modeled by the slab window system

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

fluid circulation in the depths of accretionary prisms an example of the shimanto belt kyushu japan accretionary prisms constitute ideal targets to study fluid circulation and fluid rock interactions at depths beyond the reach of active margin deep drilling the highest grade rocks from the shimanto belt on kyushu were buried under 3 5 kbars at 300 c toriumi and teruya 1988 they contain abundant quartz veins formed throughout burial and exhumation and variably affected by brittle and ductile deformation cathodoluminescence cl reveals the existence of two distinct types of quartz characterized by a blue and brown color respectively cl blue quartz fills macro veins width 10 m while cl brown quartz is present in micro veins width 1 10 m and ductilely recrystallized domains on the basis of microstructures the fluids associated with the cl blue and cl brown quartz are interpreted as external and local respectively quartz growth rims of alternating cl colors as well as mutually cross cutting veins show that the two fluids cyclically wetted the host rock from fluid inclusions analysis the fluid associated with cl blue quartz has a salinity similar to seawater while the fluid associated with cl brown quartz is less saline in addition cl blue quartz is richer in aluminum than the cl brown one in contrast to the salinity aluminum signature the 18o isotopic signature of both quartz types is similar and buffered by host rock the difference between the preservation of the salinity signature of the fluid and the loss of its 18o signature is explained by quicker exchange kinetics and larger host rock buffering capacity for isotopic reequilibration the local fluid associated with cl brown quartz reflects the dilution of pore water by the pure water produced by prograde dehydration reactions of clay minerals the external fluid associated with cl blue quartz is interpreted as seawater or pore water from shallow depth 1 2 km below seafloor sediments we propose that downward percolation of shallow water to depths 10km is a transient process associated with mega earthquakes

uniqueness of multiangular measurements i an indicator of subpixel surface heterogeneity from misr the recent availability of quasi simultaneous multispectral and multidirectional measurements from space as provided by the multi angle imaging spectroradiometer misr on board the terra platform offers new and unique opportunities to document the anisotropy of land surfaces at critical solar wavelengths this paper presents simple physical principles supporting the interpretation of the anisotropy of spectral radiances exiting terrestrial surfaces in terms of a signature of surface heterogeneity the shape of the anisotropy function is represented with two model parameter values which may be mapped and interpreted in their own right the value of one of these parameters also permits identifying geophysical conditions where the surface heterogeneity becomes significant and where three dimensional 3d radiation transfer effects have to be explicitly accounted for this paper documents these findings on the basis of results from a number of 3d radiation transfer model simulations the latter are used to perform an extensive sensitivity study which includes issues related to the scale of investigation a preliminary validation of these results conducted with a dataset collected by the airmisr instrument over the konza prairie is also discussed

examination of sentinel 2a multi spectral instrument msi reflectance anisotropy and the suitability of a general method to normalize msi reflectance to nadir brdf adjusted reflectance abstract the sentinel 2a multi spectral instrument msi acquires multi spectral reflective wavelength observations with directional effects due to surface reflectance anisotropy and changes in the solar and viewing geometry directional effects were examined by considering two ten day periods of sentinel 2a data acquired close to the solar principal and orthogonal planes over approximately 20 10 of southern africa more than 6 6 million january 2016 and 10 6 million april 2016 pairs of reflectance observations sensed 3 or 7 days apart in the forward and backscatter directions in overlapping sentinel 2a orbit swaths were considered the sentinel 2a data were projected into the modis sinusoidal projection but first had to be registered due to a misregistration issue evident in the overlapping orbits the top of atmosphere reflectance data were corrected to surface reflectance using the sen2cor atmospheric correction software only pairs of forward and backward reflectance values that were cloud and snow free unsaturated and had no significant change in their 3 or 7 day separation were considered the maximum observed sentinel 2a view zenith angle was 11 93 greater brdf effects were apparent in the january data acquired close to the solar principal plane than the april data acquired close to the orthogonal plane and at higher view zenith angle for the january data the average difference between the surface reflectance in the forward and backward scatter directions at the sentinel 2a scan edges increased with wavelength from 0 035 blue 0 047 green 0 057 red 0 078 nir to about 0 1 swir these differences may constitute a significant source of noise for certain applications the suitability of a recently published methodology developed to generate landsat nadir brdf adjusted reflectance nbar was examined for sentinel 2a application the methodology uses fixed modis brdf spectral parameters and is attractive because it has little sensitivity to the land cover type condition or surface disturbance and can be derived in a computationally efficient manner globally it was applied to the southern africa sentinel 2a data and shown to reduce sentinel 2a brdf effects the average difference between the reflectance in the forward and backward scatter directions at the sentinel 2a scan edges was smaller in the nbar data than in the corresponding surface reflectance data residual brdf effects in the sentinel 2a nbar data occurred likely because of atmospheric correction and sensor calibration errors and inadequacies in the nbar derivation approach these issues are discussed with recommendations for future research including global and red edge sentinel 2a nbar derivation that were not considered in this study

origin and motion history of the philippine sea plate abstract the philippine sea plate is the one major plate whose tertiary motion is poorly constrained and whose origin is problematical its southern boundary is the sorong fault system which is part of a major left lateral fault system at the northern margin of the australian plate the southern part of the plate in eastern indonesia has been neglected in most syntheses but includes some of the oldest rocks within the plate which are separated from remnant arcs of the daito ridge province of the northern philippine sea by the west philippine central basin the east indonesian islands of the halmahera waigeo region contain a good mesozoic and tertiary stratigraphic record indicating a long arc history for the southern part of the plate new palaeomagnetic data from these islands define two sub areas an area forming part of the philippine sea plate north of the sorong fault and an area within the sorong fault system the area north of the fault records a long term clockwise rotation history whereas that within the fault zone records local rotations interpreted as due to deformation at the plate edge rocks of philippine sea plate origin within both areas record similar latitudinal shifts the rotation of the area north of the sorong fault is considered to represent the motion of the southern part of the philippine sea plate the new data indicate large tertiary clockwise rotations similar to earlier suggestions for other parts of the plate but record a discontinuous and more complex motion history than previously suggested for the southern part of the plate there was 40 rotation with northward translation between 0 and 25 ma no significant rotation between 25 and 40 ma and there was 50 rotation with southward translation between 40 and 50 ma we show that the new palaeomagnetic data form part of a single set with earlier palaeomagnetic data from elsewhere in the plate the translation history of the southern part of the plate in eastern indonesia can be reconciled with northward motions recorded elsewhere and can be used to determine rotation poles for the plate 15 n 160 e for the interval 5 25 ma and 10 n 150 e for the interval 40 50 ma reconstructions based on these poles predict that at 45 ma the palau kyushu ridge had a wnw ese orientation which is very different from that postulated by many models used to explain the widespread boninite volcanism in the izu bonin marians forearc at this time the long arc history of the southern part of the plate and the reconstructions based on the rotation poles calculated from the palaeomagnetic data favour an origin for the west philippine basin by spreading in a backarc basin

palaeo altimetry of the late eocene to miocene lunpola basin central tibet the elevation history of the tibetan plateau provides direct insight into the tectonic processes associated with continent continent collisions here we present oxygen isotope based estimates of the palaeo altimetry of late eocene and younger deposits of the lunpola basin in the centre of the plateau which indicate that the surface of tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years we conclude that crustal but not mantle thickening models combined with plate kinematic solutions of india asia convergence are compatible with palaeo elevation estimates across the tibetan plateau

episodic formation of neotethyan ophiolites tibetan plateau snapshots of abrupt global plate reorganizations during major episodes of supercontinent breakup abstract neotethyan ophiolites along the bangong nujiang and yarlung tsangpo sutures tibetan plateau consist of mantle peridotite cumulates isotropic gabbro diabase plagiogranite and basaltic lava they comprise morb iab oib and boninitic rocks and mostly belong to supra subduction zone ssz type compositionally different rocks crystallized synchronously over a distance of 2000 km along the bangong nujiang and yarlung tsangpo sutures during the short periods of 190 182 and 132 120 ma respectively resembling the izu bonin mariana ibm proto arc the early jurassic bangong nujiang ophiolites formed in forearc settings during subduction initiation while the middle jurassic early cretaceous bangong nujiang ophiolites and the early cretaceous yarlung tsangpo ophiolites formed in forearc settings at pre existing subduction zones crystallization of the neotethyan ssz ophiolites from the eastern mediterranean middle east tibetan plateau to southeast asia and formation of the associated metamorphic rocks temporally coincided with major supercontinent breakup events 1 initial breakup of pangea in central atlantic and westernmost tethys 190 ma 2 separation of west and east gondwana 170 160 ma and initial opening of piemont ligurian tethys 175 164 ma 3 initial breakups of east and west gondwana 135 125 ma and 4 final breakup of gondwana 104 96 ma far field forces associated with abrupt global plate reorganizations may have triggered subduction initiation or transient interplate coupling decoupling at pre existing subduction zones leading to episodic formation of the neotethyan ssz ophiolites and rapid exhumation of metamorphic rocks in subduction zones the formation events of neotethyan ssz ophiolites and associated metamorphic rocks represent snapshots of global plate reorganizations during the major episodes of supercontinent breakup

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

indian and african plate motions driven by the push force of the reunion plume head mantle plumes are thought to play an important part in the earth s tectonics yet it has been difficult to isolate the effect that plumes have on plate motions here we analyse the plate motions involved in two apparently disparate events the unusually rapid motion of india between 67 and 52 million years ago and a contemporaneous transitory slowing of africa s motion and show that the events are coupled with the common element being the position of the indian and african plates relative to the location of the reunion plume head the synchroneity of these events suggests that they were both driven by the force of the reunion plume head the recognition of this plume force has substantial tectonic implications the speed up and slowdown of india the possible cessation of convergence between africa and eurasia in the palaeocene epoch and the enigmatic bends of the fracture zones on the southwest indian ridge can all be attributed to the reunion plume an analysis of the plate motions involved in two apparently disparate tectonic events the unusually rapid motion of india between 67 million and 52 million years ago and a transitory slowing of africa s motion at around the same time has uncovered a possible common cause for the two the reunion volcanic hotspot beneath the indian ocean has been active for about 67 million years and the close coupling of the motion of india and africa strongly suggests that it is the waxing and waning of the reunion plume head that is driving these motions

arc continent collision and subduction reversal in the cenozoic evolution of the northwest pacific an example from kamchatka ne russia abstract the principal new feature in the cenozoic evolution of the northwest pacific is based on the fact that two arc terranes of upper cretaceous paleogene age were incorporated in the kamchatka orogen during the early tertiary and at the end of the miocene respectively these two arc terranes so called achaivayam valaginskaya campanian lower paleocene and kronotskaya coniacian eocene arcs are separated by a suture zone that contains deformed slices of young paleocene lower eocene oceanic crust paleomagnetic data on the original paleolatitudes of the arc positions as well as geochemical data characterized the arcs as intraoceanic originated in the northwest pacific the arcs were separated by the vetlovka oceanic plate suggested to be a trapped fragment of the kula plate in which a new spreading zone developed in the early tertiary the principal event in the reconstructed evolution is the eocene collision of the extended achaivayam valaginskaya arc terrane with the continental margin of asia the margin is interpreted as the southeastern facing the pacific cretaceous accretionary boundary of the okhotsk microplate docked against the asian continent at 55 65 ma the arc continent collision developed progressively northward from the end of the paleocene early eocene in southern kamchatka to the middle eocene in the olutorka region the different stages of the collision occurred simultaneously along strike of the achaivayam valaginskaya arc according to the geodynamic model based on geological data for southern kamchatka collision included 1 the entrance of the continental margin in the subduction zone deformation of the overriding plate and subduction of fore arc block 2 arc obduction on the continental margin blocking of continental margin subduction and 3 subduction reversal with onset of oceanic subduction at the eastern side of the deformed arc this subduction reversal produced deformation and reverse faulting along the eastern side of the arc thus allowing accretion of tectonic slices of young oceanic crust of the vetlovka plate which began to subduct during the subduction reversal the subducted plate dipping to the southeast was broken off and detached at depth under the arc area the subduction polarity reversal the most characteristic feature of the collision model is strongly supported by structural and geologic data of southern kamchatka and explains the main tectonic metamorphic and magmatic events related to and postdating the collision

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

quantifying the forces needed for the rapid change of pacific plate motion at 6 ma studies have documented several rapid changes along the pacific north american pacific antarctic and pacific australian plate boundaries in latest miocene to earliest pliocene time consistent with a sudden clockwise rotation of pacific plate velocity relative to hotspots during this period we test the hypothesis that this change in plate motion was initiated by cessation of subduction along the northern melanesian arc due to the collision between the arc and the ontong java plateau this hypothesis has long been formulated but never tested quantitatively we use a geomechanical model of the lithosphere to determine the changes in plate boundary forces that are necessary to obtain the observed change in the pacific plate motion our model results show that the change in motion can be explained by a clockwise rotation of the slab related basal strength component of plate driving force the change of slab related force from a post 6 ma to a pre 6 ma setting is perpendicular to the arc and points towards the australian plate the force per unit length is in the range of currently accepted values for subduction zones since there have been no other relevant changes at subduction zones along the pacific plate boundary during the latest miocene we relate this change in slab related force to the former southward dipping pacific plate slab along the northern melanesian arc system which is now detached our model results suggest that rapid changes in plate motion can be triggered by slab detachment with consequences for plate boundary processes even at great distances from the event

reconstruction of subduction and back arc spreading in the nw pacific and aleutian basin clues to causes of cretaceous and eocene plate reorganizations the eocene 50 45 ma major absolute plate motion change of the pacific plate forming the hawaii emperor bend is thought to result from inception of pacific plate subduction along one of its modern western trenches subduction is suggested to have started either spontaneously or result from subduction of the izanagi pacific mid ocean ridge or from subduction polarity reversal after collision of the olyutorsky arc that was built on the pacific plate with ne asia here we provide a detailed plate kinematic reconstruction of back arc basins and accreted terranes in the northwest pacific region from japan to the bering sea since the late cretaceous we present a new tectonic reconstruction of the intraoceanic olyutorsky and kronotsky arcs which formed above two adjacent oppositely dipping subduction zones at 85 ma within the north pacific region during another pacific wide plate reorganization we use our reconstruction to explain the formation of the submarine shirshov and bowers ridges and show that if marine magnetic anomalies reported from the aleutian basin represent magnetic polarity reversals its crust most likely formed in an 85 to 60 ma back arc basin behind the olyutorsky arc the olyutorsky arc was then separated from the pacific plate by a spreading ridge so that the 55 to 50 ma subduction polarity reversal that followed upon olyutorsky ne asia collision initiated subduction of a plate that was not the pacific hence this polarity reversal may not be a straightforward driver of the eocene pacific plate motion change whose causes remain enigmatic

cretaceous tertiary shortening basin development and volcanism in central tibet the geologic map pattern of the qiangtang terrane in central tibet defines a 600 km long and up to 270 km wide east plunging structural culmination it is characterized by early mesozoic blueschist bearing melange and upper paleozoic strata in the core and mainly triassic jurassic strata along the limbs in the western qiangtang terrane 84 e the culmination is unconformably overlain by weakly deformed mid cretaceous volcanic flows and tuffs along the bangong suture to the south 32 n 84 e mid cretaceous nonmarine red beds and volcanic rocks lie unconformably on jurassic suture zone rocks these relationships demonstrate that west central tibet was above sea level during the mid cretaceous and experienced significant denudation prior to mid cretaceous time growth of the qiangtang culmination is inferred to have initiated during southward emplacement of a thrust sheet of early mesozoic melange and upper paleozoic strata during the early cretaceous lhasa qiangtang collision the north south width of the inferred thrust sheet provides a minimum slip estimate of 150 km at 84 e decreasing eastward to 70 km at 87 e paleogene deformation in the qiangtang terrane is characterized by widely distributed mainly north dipping thrust faults that cut eocene oligocene red beds and volcanic rocks in their footwall along the bangong suture the north dipping shiquanhe gaize amdo thrust system cuts 64 and 43 m y old volcanic tuffs in its footwall and accommodated 40 km of post mid cretaceous shortening the tertiary south dipping gaize siling co backthrust bounds the southern margin of the bangong suture and marks the northernmost limit of mid cretaceous marine strata in central tibet cretaceous deformation and denudation in central tibet is attributed to northward underthrusting of the lhasa terrane beneath the qiangtang terrane along the bangong suture this model implies that 1 cretaceous strata along the bangong suture and in the northern lhasa terrane were deposited in a flexural foreland basin system and derived at least in part from the qiangtang terrane and 2 the central tibetan crust was thickened substantially prior to the indo asian collision although its magnitude is poorly known tertiary shortening in the qiangtang terrane is more prevalent than in the lhasa terrane this difference may be attributed to the presence of underthrust melange in the deeper central tibetan crust which would have made it weaker than the lhasa terrane during the indo asian collision

on the effect of temperature and strain rate dependent viscosity on global mantle flow net rotation and plate driving forces summary global circulation models are analysed using a temperature and strain rate dependent rheology in order to refine previous estimates of the nature of mantle flow and plate driving forces based on temperature inferred from a tectonic model and seismic tomography the suboceanic viscosity is lower than underneath continents by one order of magnitude if net rotations of the lithosphere with respect to a stable lower mantle reference frame are accounted for the patterns of flow in the upper mantle are similar between models with layered and those with laterally varying viscosity the excited net rotations scale with the viscosity contrast of continental roots to the ambient mantle this contrast is dynamically limited by the power law rheology surface net rotations match the orientation of hotspot reference frame euler poles well and amplitudes are of the right order of magnitude i compare prescribed surface velocity models with free slip computations with imposed weak zones at the plate boundaries velocity fields are generally consistent models based on laboratory creep laws for dry olivine are shown to be compatible with average radial viscosity profiles plate velocities in terms of orientation and amplitudes plateness of surface velocities toroidal poloidal partitioning and fabric anisotropy formation under dislocation creep in the upper mantle including temperature dependent variations increases the relative speeds of oceanic versus continental lithosphere makes surface velocities more plate like and improves the general fit to observed plate motions these findings imply that plate driving force studies which are based on simpler mantle rheologies may need to be revisited

modeling the behavior of the continental mantle lithosphere during plate convergence in studying orogenic processes the mechanism of viscous rayleigh taylor type removal of gravitationally unstable lithosphere is often invoked to explain the behavior of the mantle lithosphere using numerical models we consider this mechanism and explore alternate styles of deep lithospheric deformation during tectonic convergence the numerical experiments incorporate a mix of viscous and plastic rheologies to model the mechanical evolution of the lithosphere asthenosphere system our results suggest that there are a number of deformational modes of the model mantle lithosphere 1 a dripping or rayleigh taylor type instability 2 an asymmetric underthrusting or subduction 3 symmetric ablative plate consumption 4 slab breakoff the failure and detachment of the strong lithosphere and 5 mixed modes with combinations of these processes the development of the modes is controlled by the rate of convergence associated with the background tectonic regime the density field and the rheology of the mantle lithosphere it is important to determine whether these modes occur in the earth beneath collisional orogens

mountain building and mantle dynamics 1 mountain building at convergent margins requires tectonic forces that can overcome frictional resistance along large scale thrust faults and support the gravitational potential energy stored within the thickened crust of the orogen a general dynamic model for this process is still lacking here we propose that mountain belts can be classified between two end members first those of slab pull type where subduction is mainly confined to the upper mantle and rollback trench motion lead to moderately thick crustal stacks such as in the mediterranean second those of slab suction type where whole mantle convection cells conveyor belts lead to the more extreme expressions of orogeny such as the largely thickened crust and high plateaus of present day tibet and the altiplano for the slab suction type deep mantle convection produces the unique conditions to drag plates toward each other irrespective of their nature and other boundary conditions we support this hypothesis by analyzing the orogenic volcanic and convective history associated with the tertiary formation of the andes after 40 ma and himalayas after collision at 55 ma based on mantle circulation modeling and tectonic reconstructions we surmise that the forces necessary to sustain slab suction mountain building in those orogens derive after transient slab ponding from the mantle drag induced upon slab penetration into the lower mantle and from an associated surge of mantle upwelling beneath africa this process started at 65 55 ma for tibet himalaya when the tethyan slab penetrated into the lower mantle and 10 myr later in the andes when the nazca slab did this surge of mantle convection drags plates against each other generating the necessary compressional forces to create and sustain these two orogenic belts if our model is correct the available geological records of orogeny can be used to decipher time dependent mantle convection with implications for the supercontinental cycle

plate motion changes the hawaiian emperor bend and the apparent success and failure of geodynamic models abstract geodynamic models explain present day plate motions in terms of mantle buoyancy forces arising from subducted lithosphere and lithospheric thickening or from velocity anomalies mapped by seismic tomography however such models do not account for sudden plate tectonic reorganizations such as the dramatic change in pacific plate motion implied by the sharp bend in the hawaiian emperor seamount chain about 43 million years ago candidate mechanisms for the hawaiian emperor bend such as subduction initiation ridge subduction or the possibly time coincident collision between india and asia remain weakly formulated and largely untested we test the india asia collision hypothesis using a model for cenozoic plate motions driven mainly by buoyancy forces introduced at paleo subduction zones and we show that pacific plate motion is virtually unaffected by the development of compressional stresses along the india asia margin geologic evidence suggests subduction initiation at about 43 48 ma along a transform boundary on the western pacific plate margin but this mechanism is difficult to test we speculate that transform boundaries may guide plate motions for long periods of time and that rapid plate motion changes may result from the creation or destruction of major transform faults speculations aside our results show that the character of global plate motion changes is not adequately explained by current geodynamic models