accuracy assessment of ocean tide models around antarctica 1 accurate ocean tide models for the circum antarctic seas are required to remove unwanted signals from floating ice elevation and space borne time variable gravity measurements e g grace we present accuracy assessments for several global csr4 fes2004 fes99 got00 2 nao 99b tpxo6 2 and antarctic cada00 10 and cats02 01 ocean tide models using coastal and pelagic tide gauges gravimetric data and gps records of ice shelf surface elevation the accuracies of csr4 and nao 99b are poor in the ice shelf regions the optimum model for the entire circum antarctic seas is tpxo6 2 with a root mean square deviation of 5 7 cm 40 lower than the next best model fes2004 the main exception is the filchner ronne ice shelf where cada00 10 and cats02 01 most accurately represent observations from two sites near the rutford ice stream grounding line

dwindling groundwater resources in northern india from satellite gravity observations 1 northern india and its surroundings home to roughly 600 million people is probably the most heavily irrigated region in the world temporal changes in earth s gravity field in this region as recorded by the grace satellite mission reveal a steady large scale mass loss that we attribute to excessive extraction of groundwater combining the grace data with hydrological models to remove natural variability we conclude the region lost groundwater at a rate of 54 9 km3 yr between april 2002 the start of the grace mission and june 2008 this is probably the largest rate of groundwater loss in any comparable sized region on earth its likely contribution to sea level rise is roughly equivalent to that from melting alaskan glaciers this trend if sustained will lead to a major water crisis in this region when this non renewable resource is exhausted

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

evolution of the archean and paleoproterozoic lower crust beneath the trans north china orogen and the western block of the north china craton abstract we report u pb ages and hf isotopes of zircons in granulites from two continental suture zones in the north china craton ncc from granulite xenoliths entrained in the cenozoic hannuoba basalts within the trans north china orogen tnco that amalgamates the western and eastern blocks and from a mafic granulite associated with ultrahigh temperature uht granulites within the inner mongolia suture zone imsz that welds the yinshan and ordos blocks the zircons in these rocks together with the inherited zircons from mesozoic subalkalic intrusives of these regions show several distinct u pb age populations and provide constraints on the evolution of the lower crust beneath the ncc parts of the older zircons from the tnco yield discordant data that project to ages of about 2 5 to 2 7 ga these old zircons show hf tdm model ages of 2 6 2 9 ga suggesting the existence of archean lower crust beneath the tnco which is coupled with the neoarchean metamorphic basement and greenstone belt a major zircon population grew at 1 75 2 0 ga consistent with the timing of the paleoproterozoic collision between the various crustal blocks within the ncc suggesting that this event had a significant effect on the archean lower crust the older inherited zircons from the western block also yield discordant data that project to younger ages of about 1 8 to 1 9 ga this age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the uht rocks in the khondalite belt within the imsz these older zircons yield hf tdm model ages of 2 0 2 5 ga suggesting that the lower crust beneath the western block in the ncc to be dominantly paleoproterozoic and decoupled with the archean metamorphic basement of the region yet another population of zircons from the hannuoba banded granulite xenoliths garnet bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of phanerozoic concordant ages ranging from 470 ma to 40 ma with peaks at 315 ma 220 230 ma 120 ma and 46 ma the late paleozoic zircons predominantly occur in the garnet bearing pyroxenite xenoliths and yield variable ehf t values of 24 to 18 triassic cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable ehf t values ranging from 48 to 16 the tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted ehf t with a dominant range from 0 to 18 these data suggest episodic magmatic underplating in the ancient lower crust of the ncc lasting continuously throughout phanerozoic producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust our data clearly demonstrate the important events of phanerozoic magmatic underplating beneath the neoarchean paleoproterozoic crust of the ncc

palaeoproterozoic crustal accretion and collision in the southern capricorn orogen the glenburgh orogeny abstract the capricorn orogen in central western australia records the palaeoproterozoic collision of the archaean pilbara and yilgarn cratons until recently only one orogenic event was thought to be the cause of this collision the 1830 1780 ma capricorn orogeny however recent work has uncovered an older event the glenburgh orogeny that occurred between 2000 and 1960 ma the glenburgh orogeny reflects the collision of a late archaean to palaeoproterozoic microcontinent the glenburgh terrane with the archaean yilgarn craton and is therefore tectonically distinct as well as significantly older than the widespread 1900 1800 ma tectonothermal events recorded in northern australia the glenburgh terrane preserves a different history from either the yilgarn or pilbara cratons granitic gneiss protoliths dated at ca 2550 ma were intruded by widespread granite magmatism dated at 2005 1970 ma accompanied by high grade metamorphism and deformation throughout the terrane at ca 1960 ma silicic granite of the bertibubba supersuite intruded the northern margin of the yilgarn craton along the errabiddy shear zone a crustal scale shear zone that today marks the contact of the glenburgh terrane and yilgarn craton at ca 1950 ma silicic dykes intruded the southernmost part of the glenburgh terrane marking the end of the glenburgh orogeny east of the glenburgh terrane the glenburgh orogeny resulted in the cessation of mafic volcanism in the bryah basin and the basin s eventual closure siliciclastic carbonate and chemical sedimentary rocks were deposited in the padbury basin that formed a retro arc foreland basin on top of the bryah basin and probably records the later stages of the glenburgh orogeny collision

on land ice loss and glacial isostatic adjustment at the drake passage 2003 2009 1 land glacier extent and volume at the northern and southern margins of the drake passage have been in a state of dramatic demise since the early 1990s here time varying space gravity observations from the gravity recovery and climate experiment grace are combined with global positioning system gps bedrock uplift data to simultaneously solve for ice loss and for solid earth glacial isostatic adjustment gia to little ice age lia cryospheric loading the present day ice loss rates are determined to be 26 6 gt yr and 41 5 9 gt yr in the southern and northern patagonia ice fields npi spi and antarctic peninsula ap respectively these are consistent with estimates based upon thickness and flux changes bounds are recovered for elastic lithosphere thicknesses of 35 h 70 km and 20 h 45 km and for upper mantle viscosities of 4 8 1018 pa s and 3 10 1019 pa s using a half space approximation for npi spi and ap respectively using an iterative forward model strategy antarctic peninsula ice models with a prolonged lia extending to a d 1930 are favored in all 2 fits to the gps uplift data this result is largely decoupled from earth structure assumptions the gia corrections account for roughly 20 60 of the space determined secular gravity change collectively the on land ice losses correspond to volume increases of the oceans equivalent to 0 19 0 045 mm yr of sea level rise for the last 15 years

40ar 39ar constraints on the tectonic history and architecture of the ultrahigh pressure sulu orogen new 40ar 39ar ages are presented from the giant sulu ultrahigh pressure uhp terrane and surrounding areas combined with u pb ages sm nd ages rb sr ages inclusion relationships and geological relationships they help define the orogenic events before during and after the triassic collision between the sino korean and yangtze cratons in the qinling microcontinent tectonism occurred between 2 0 and 1 4 ga the uhp metamorphism occurred in the yangtze craton between 240 and 222 ma its thermal effect on the qinling microcontinent was limited to partial resetting of k feldspar 40ar 39ar ages subsequent unroofing at rates of 5 25 km myr 1 brought the uhp terrane to crustal levels where it underwent a relatively short amphibolite facies metamorphism the end of that metamorphism is marked by 40ar 39ar ages in the 219 210 ma range implying cooling at crustal depths at rates of 50 200 c myr 1 ages in the 210 170 ma range may reflect protracted cooling or partial resetting by jurassic or cretaceous magmatism jurassic 166 149 ma plutonism was followed by cooling at rates of c 15 c myr 1 suggesting relatively deep crustal conditions whereas cretaceous 129 118 ma plutonism was succeeded by cooling at rates of c 50 c myr 1 suggesting relatively shallow crustal depths

residual ocean tide signals from satellite altimetry grace gravity fields and hydrodynamic modelling summary improvements of a global state of the art ocean tide model are identified and quantified by applying three independent approaches namely i empirical ocean tide analysis of multimission altimeter data ii evaluation of grace data and gravity field models and iii high resolution hydrodynamic modelling although these approaches have different capabilities to sense ocean tides they obtain results which are basically consistent one with each other the analysis of altimeter data clearly identifies significant residual amplitudes over shallow water for all major diurnal and semidiurnal constituents and the non linear tide m4 grace data and the time series of monthly gravity field models exhibit on a larger scale residual ocean tide signals over much the same areas the analysis of dynamic residuals of hydrodynamic modelling with data assimilation proves the validity of linear dynamics in the deep ocean and shows correlation of dynamic residuals with energy dissipation in these areas

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

structure of the crust and uppermost mantle of the yanshan belt and adjacent regions at the northeastern boundary of the north china craton from rayleigh wave dispersion analysis abstract we have used rayleigh wave dispersion analysis and inversion to produce a high resolution s wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the north china craton ncc using waveform data from 45 broadband ncisp stations rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the s wave velocity structure from 15 km down to 120 km depth the inverted lower crust and uppermost mantle velocities about 3 75 km s and 4 3 km s on average are low compared with the global average the moho was constrained in the depth range of 30 40 km indicating a typical crustal thickness along the profile however a thin lithosphere of no more than 100 km was imaged under a large part of the profile decreasing to only 60 km under the inner mongolian axis ima where an abnormally slow anomaly was observed below 60 km depth the overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern ncc during mesozoic cenozoic time distinctly high velocities up to 4 6 km s were found immediately to the south of the ima beneath the northern yanshan belt ysb extending down to 100 km depth the anomalous velocities are interpreted as the cratonic lithospheric lid of the region which may have not been affected by the mesozoic cenozoic deformation process as strongly as other regions in the eastern ncc based on our s wave velocity structural image and other geophysical observations we propose a possible lithosphere asthenosphere interaction scenario at the northeastern boundary of the ncc we speculate that significant undulations of the base of the lithosphere which might have resulted from the uneven mesozoic cenozoic lithospheric thinning may induce mantle flows concentrating beneath the weak ima zone the relatively thick lithospheric lid in the northern ysb may serve as a tectonic barrier separating the on craton and off craton regions into different upper mantle convection systems at the present time

a new model for the dynamic evolution of chinese lithosphere continental roots plume tectonics abstract chinese continental lithosphere comprises three tectonic domains 1 eastern china a region characterized by rifting extensional basins and voluminous basaltic volcanism 2 central china a plexus of cratonic terrains with low heat flow 40 50 mw m2 including the tarim erdos and yangtze blocks welded by pre cenozoic orogenic belts and 3 western china a region comprising the qinghai tibet himalaya orogen the relatively thin crust 35 km and lithosphere 70 km of eastern china is believed to reflect mantle upwelling while near normal crust 45 km and thickened lithosphere 200 km in central china suggest a mantle lithosphere root resembling those inferred for the kaapvaal and siberian cratons thickened crust 70 km and lithosphere 150 km in western china reflect the advanced development of an orogen root the lower density and relative buoyancy of central cratonic mantle roots appear to have contributed to the long term tectonic stability of the central chinese lithospheric blocks in contrast gravitational instability produced by thickening of the denser western chinese lithosphere and the resulting subsidence and eventual delamination of orogenic roots are believed to have led to postorogenic extensional collapse although the geological relationships suggest compressional forces caused both mountain building and orogen root development extensional stress resulting from gravitational collapse is believed to have induced lithospheric and crustal thinning with concomitant reduction of topography the term continental roots plume tectonics has been adopted to describe the configuration and dynamic condition of subcontinental lithosphere and upper mantle beneath china accordingly it is proposed that supracrustal tectonic forms represent the surface expressions of and responses to deep continental roots plume tectonics while the prevailing view is that the western orogenic belt is not genetically related to eastern continental rifting such a relationship is inherent to the continental roots plume tectonics model it is further proposed that the formation of orogenic lithosphere roots triggered eastward extrusion of the asthenosphere along the 400 km depth mantle interface and in response to subduction at the eastern margin produces plume like upwelling beneath eastern china we suggest that processes involved in continental roots plume tectonics are directly responsible for the formation and evolution of the eurasian supercontinent

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

age constraints on recycled crustal and supracrustal sources of archaean metasedimentary sequences eastern goldfields province western australia evidence from shrimp zircon dating abstract shrimp u pb zircon dating of sedimentary volcanic and subvolcanic intrusive rocks from unconformity bounded sequences in the eastern goldfields province defines maximum depositional ages for those sequences the kambalda sequence which records a backarc basin was deposited prior to 2700 ma and from at least 2715 ma the spargoville sequence which records an arc adjacent volcano bound basin was deposited between 2700 and 2683 ma the kalgoorlie sequence which records an intra arc rift basin comprises two tectonic stages with depositional ages of 2681 2670 and 2661 2655 ma deposition of the spargoville and kalgoorlie sequences overlapped with the intrusion of granitoids and subvolcanic porphyries thereby indicating that those granitoids were emplaced during crustal extension younger submarine fan kurrawang sequence and braided fluvial merougil and jones creek sequences deposits of a remnant ocean basin were deposited at when coupled to palaeocurrent data provenance dating of detrital zircon suites fingerprints southeast oriented amalgamation of felsic detritus from multiple sources within longitudinal depositional systems and longitudinal reworking of felsic detritus from single sourced transverse systems most felsic detritus was recycled from coeval volcanoplutonic arcs and the orogen to the remnant ocean basin sequences with zircon ages ranging from 2730 to 2660 ma older felsic sources with age ranges of 3570 3130 3030 2900 2870 2770 and 2760 ma could have been structural enclaves within the volcanoplutonic arcs or orogen but were more likely within a distant cratonic basement when coupled with stratigraphic data it is concluded that detrital zircon age distributions preserve evidence for the sedimentary recycling of coeval volcanoplutonic arc or orogenic sources uplifted basin floor and dissected arc successions and cratonic basement virtually all source terrains have apparently vanished presumably through the combination of tectonic and sedimentary recycling and tectonic severance increased use of detrital zircon suites from archaean sedimentary sequences is advocated in order to quantify the balance between sedimentary recycling of felsic rocks from contemporaneous volcanoplutonic sources which themselves document crustal growth in arc environments and from relict volcanoplutonic and crustal basement sources which document the degree of crustal recycling

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

tectono stratigraphy of late archaean greenstone terranes in the southern eastern goldfields western australia abstract late archaean greenstone terranes in the southern part of the eastern goldfields are regionally extensive faultbounded entities defined on the basis of small but distinct differences in stratigraphy and structure the greenstones comprise volcano sedimentary successions that were all deposited at the same time c 2720 2675 ma on sialic crust hence the terranes are interpreted to represent contemporaneous probably adjacent basins these basins were affected by the same history of granite plutonism and regional deformation c 2675 2620 ma early subhorizontal deformation is poorly understood but includes at least locally significant thrust stacking d1 with a south to north movement direction this was followed by regional east west extension affecting all supracrustal successions above a province wide detachment now lying at depths between 4 and 7 km this detachment may have evolved from the greenstone basement contact but only after extensive reworking clastic basins developed along or above major extensional faults but no volcanism is associated with this extension subsequent east west d2 shortening resulted in regional scale thrusting folding and associated late stage transcurrent fault movements the d2 event is contemporaneous with a major thermal event represented by voluminous granite emplacement c 2660 ma and associated peak regional metamorphism in the greenstone succession predominantly monzo granite derived from older sialic crust was emplaced throughout the period of basin formation and deformation early synvolcanic granite c 2719 2710 ma is a minor component late synvolcanic granite c 2685 2675 ma is widespread and syn d2 granite c 2660 ma is abundant there are a few small late tectonic intrusions c 2640 ma to 2600 ma the lateral lithostratigraphic persistence of the contemporaneous basins the syn d2 low pressure regional metamorphism and the province wide monzo granite magmatism suggest that the greenstone basins possibly developed in a tectonic setting similar to that of failed rifts above aborted spreading centres the basins closed in response to far field compressional stresses

spatial distribution of 1950 1800 ma metamorphic events in the north china craton implications for tectonic subdivision of the craton abstract great progress has been made in the last twenty years in understanding the unification of the north china craton according to a prevailing model it developed by amalgamation of four sub blocks by three spatially and temporally separate orogenic belts the first at 1950 ma formed the western block the second at 1900 ma created the eastern block and the third at 1850 ma unified the eastern and western blocks however new data show that the 1950 ma orogen was affected by granulite facies reequilibration at 1800 ma and parts of the 1850 ma orogen have evidence of metamorphism at 1950 1900 ma new zircon u pb ages enable the paleoproterozoic metamorphic events to be statistically sub divided into four at 1955 ma m 1 1920 ma m 2 1885 ma m 3 and 1850 ma m 4 the m 1 2 events always appear together mainly in two belt areas including the helanshan qianlishan northern ordos yinshan liangcheng huai an lushan jiaobei and liaodong regions whereas the m 3 4 events are distributed over larger areas and were superimposed on the m 1 2 activities this age distribution is inconsistent with previous models of three separate orogens it should also be noted that the igneous rocks contemporary with the regional ultra high temperature high pressure granulite facies metamorphisms m 1 2 were previously described as arc related series i e the gabbro norites i s type granites and trimodal volcanics based on the spatial distribution of the paleoproterozoic metamorphic events m 1 4 and of the coeval igneous rocks we speculate that the assembly of the ncc was created by one orogen which formed between the eastern and western cratons in two tectonic stages two marginal arcs the korean and xuwujia developed against both eastern sides of the two sub cratons and were both accreted and deformed at 1965 1900 ma m 1 2 subsequently the amalgamation of the two sub cratons resulted in metamorphism on the western side of the eastern craton and in metamorphism that was superimposed on both accreted arcs at 1900 1790 ma m 3 4

expected improvements in determining continental hydrology ice mass variations ocean bottom pressure signals and earthquakes using two pairs of dedicated satellites for temporal gravity recovery 1 the gravity recovery and climate experiment mission has demonstrated the ability to quantify global mass variations at large spatial scales with monthly to sub monthly temporal resolution future missions of this type taking advantage of improved measurement technologies will be limited by temporal aliasing errors we suggest the addition of a second pair of satellites to reduce these errors using an optimized mission architecture consisting of a polar pair of satellites coupled with a lower inclined pair of satellites 72 both in 13 day repeating orbits we quantify the expected scientific improvements that having two pairs of satellites will provide over one pair numerical simulations to spherical harmonic degree 100 are run over one full year analysis using empirical orthogonal functions reveals that two satellite pairs determine annual mass variations in small basins which are undetected using one pair of satellites averaging kernels are used to show that two satellite pairs offer an 80 reduction in the level of error in determining mass variations in 53 hydrological basins and 12 greenland basins over the year after standard grace post processing techniques have been applied to the one pair solutions it is seen that two satellite pairs with no post processing still offer a 25 75 improvement in determining the mass variations spatiospectral localization analysis is used to show increased spatial resolution and higher signal to noise ratios in recovering hydrology in the amazon river basin ocean bottom pressure signals in the southeast pacific basin and a simulated earthquake signal representative of the 2010 maule chile earthquake

proterozoic evolution and tectonic setting of the northwest paterson orogen western australia abstract the proterozoic igneous deformation and metamorphic histories of the palaeoproterozoic rudall complex in the northwestern paterson orogen can be linked to those of the arunta inlier in central australia and in part with the capricorn orogen in central western australia the similarities in deformation and metamorphic histories for these widely separated regions indicate a palaeoproterozoic continent continent collisional event between the palaeoproterozoic west australian and north australian cratons between c 1830 and 1765 ma in the paterson orogen this palaeoproterozoic collisional event resulted in the yapungku orogeny which included thrust stacking of clastic sedimentary and volcanic rocks deposition of the protoliths for the c 1790 ma siliciclastic paragneiss succession contemporaneous with granitic intrusion and metamorphism up to granulite facies during this 65 million year period the arunta inlier and capricorn orogen were deformed metamorphosed at medium to high grades and intruded by granitoids during the strangways orogeny in the arunta inlier and the capricorn orogeny in the capricorn orogen the neoproterozoic tarcunyah throssell and lamil groups are clastic sedimentary sequences that were deposited after 1070 ma in the northwestern paterson orogen and deformed by the miles orogeny before 678 ma the miles orogeny produced a northwesterly trending fold and fault system of tight to isoclinal upright and overturned folds and thrust faults the orogeny may have been coincident with the c 750 720 ma areyonga tectonic movement affecting the arunta inlier and the lower neoproterozoic part of the amadeus basin in central australia at c 550 ma the paterson orogeny which is most likely equivalent to the petermann orogeny in the musgrave complex of central australia deformed the northwestern paterson orogen and was preceded by local intrusion of granites the similarities of styles and timing of deformation in the northwestern paterson orogen arunta inlier and capricorn orogen indicate that these three regions were probably linked during most of the proterozoic

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

dynamic cause of marginal lithospheric thinning and implications for craton destruction a comparison of the north china superior and yilgarn cratons we present a comparative tectonic analysis of the north china craton ncc which has lost parts of its root with the yilgarn and superior cratons which preserve their roots we compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots while others retain them based on the comparison and analysis of geological geophysical and geochemical data it is clear that the lithospheric thinning beneath craton margins is a common phenomenon which may be caused by convergence between plates however craton destruction is not always accompanied by lithospheric thinning except for cratons that suffered subduction and collision from multiple sides the western block also known as the ordos block of the ncc yilgarn and superior cratons have not experienced craton destruction the common ground among them is that they are surrounded by weak zones e g mobile belts or orogens that sheltered the cratons from deformation which contribute

lower crustal processes leading to mesozoic lithospheric thinning beneath eastern north china underplating replacement and delamination abstract our recent studies show that the lower crust and lithospheric mantle in the eastern north china craton ncc was thinned in the mesozoic the lower crust played a key role in the tectonic mechanism that led to lithospheric thinning geochemical data from volcanic rocks and xenoliths support the idea that delamination of the lower crust and lithospheric mantle took place only along the northern and perhaps the southern margins of the ncc and this was linked to post collisional orogenic processes however it is difficult for the delamination process to act on the whole eastern ncc and remove 80 120 km of the lithosphere lower crustal xenoliths in mesozoic and cenozoic basalts within the ncc are of two kinds one is granulite facies metamorphosed two pyroxene gabbros and eclogite facies metamorphosed garnet pyroxenites formed at 140 120 ma the other is precambrian granulites that were strongly overprinted by mesozoic metamorphism large scale lower crustal replacement took place in the mesozoic beneath the ncc in other words some or perhaps most part of the present lower crust of the ncc is not precambrian the present lowermost crust is mostly composed of mesozoic meta gabbros and pyroxenites abundant late jurassic high sr granites in the ncc which are compositionally similar to a dakite probably formed by partial melting of the lowermost crust leaving a residue of eclogite or garnet amphibolite a hot upwelling mantle was necessary to partially melt the pre existing lowermost crust and underplate magma in order to form the present lower crust although eclogites could sink into the mantle it is hard to imagine that there was a thick enough eclogite layer that could drag 80 120 km of the lithosphere into the asthenosphere beneath the ncc magmatic underplating seems to be a better alternative mechanism thus the formation of the present lower crust through the underplating and replacement of the pre existing one was closely related to lithospheric thinning and represented a continuation of the same geodynamic process

rayleigh wave phase velocity heterogeneity and multilayered azimuthal anisotropy of the superior craton ontario summary we study the azimuthally anisotropic upper mantle structure of the superior craton and grenville province in ontario canada using rayleigh wave phase velocity data in the period range 40 160 s 152 two station dispersion measurements are combined in a tomographic inversion that solves simultaneously for isotropic and anisotropic terms using a least squares technique we perform a series of tests to derive optimal regularization smoothing and damping and to assess the resolution of and trade offs between isotropic and anisotropic anomalies the tomographic inversion is able to resolve isotropic phase velocity anomalies on a scale of 200 300 km and to distinguish between different anisotropic regimes on a 500 km scale across the study region isotropic phase velocity anomalies in the tomographic model span a range of up to 2 per cent around a regional average which is similar to the canadian shield dispersion curve of brune dorman 1963 with phase velocities up to 3 per cent above global reference models the amplitude of azimuthal phase velocity anisotropy reaches a maximum of 1 2 per cent a clear east west division of the study area based on both isotropic phasevelocity anomalies and azimuthal anisotropy is apparent in the western superior isotropic phase velocities are generally higher than the regional average anisotropy is observed at all periods with ene wsw to ne sw fast propagation directions at periods 120 s the anisotropy likely results from frozen lithospheric fabric aligned with tectonic boundaries whereas the anisotropy at longer periods is interpreted to arise from present day sublithospheric flow the fast directions from published sks measurements are close to the fast rayleigh wave propagation directions throughout the period range sampled and the large sks splitting times may be accounted for by this near coincidence of fast propagation directions across most of eastern ontario phase velocities are lower than the regional average fast propagation directions rotate from nw se at 40 130 s period to wnw ese at periods 140 160 s the results suggest a difference in fast propagation directions between the anisotropic fabric frozen into the lithosphere and the fabric due to current and recent sublithospheric flow the superior craton and grenville province are characterized by large scale structural variations that reflect the complex tectonic history of the region this study highlights differences between the characteristics of eastern and western ontario and indicates the occurrence of multiple layers of anisotropy in the subcratonic upper mantle

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

subprovince accretion tectonics in the south central superior province development of tectonic subprovinces as shear bounded granite greenstone and sediment dominated terranes during the late archaean is reviewed and interpreted from relationships between portions of

updated gondwana permian cretaceous earth history of australia abstract permo carboniferous glaciation confined to icecaps and mountain glaciers was followed by permian coal measures and early triassic barren measures and redbeds in the east terminally deformed in the mid triassic coal deposition resumed during the late triassic and tholeiite was erupted in the southeast after rifting the western margin was formed by the opening of the indian ocean at 156 and 132 ma at 140 ma a brief glaciation affected central australia by the 99 ma mid cretaceous the southern margin was finally shaped by the opening of the southeastern indian ocean the shoreline retreated to the present coast from the maximum aptian shoreline of an epeiric sea and the eastern highlands were uplifted to produce the present morphology of australia new data relate to the permo carboniferous and early cretaceous glaciations the kiaman reversed paleomagnetic interval events about the permian triassic boundary including possible impact craters advances in palynology invertebrate paleontology macrofloral paleontology and paleobiogeography the provenance of sediments by u pb ages and host rock affinity of zircons stable isotopes and biomarkers in petroleum systems coal environments calibrating the time scale with u pb ages of zircons fission track thermotectonic imaging geothermal energy and terranes split off the western margin

the role of mobile belts for the longevity of deep cratonic lithosphere the crumple zone model many archean cratons are surrounded by proterozoic mobile belts that have experienced episodes of tectonic re activation over their lifetimes this suggests that mobile belt lithosphere may be associated with long lived inherited weakness it is proposed that the proximity of this weakness can increase the longevity of deep archean lithosphere by buffering archean cratons from mantle derived stresses the physical plausibility of this idea is explored through numerical simulations of mantle convection that include continents and allow for material rheologies that model the combined brittle and ductile behavior of the lithosphere within the simulations the longevity of deep cratonic lithosphere does increase if it is buffered by mobile belts that can fail at relatively low stress levels

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

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

source parameter inversion for recent great earthquakes from a decade long observation of global gravity fields we quantify gravity changes after great earthquakes present within the 10 year long time series of monthly gravity recovery and climate experiment grace gravity fields using spherical harmonic normal mode formulation the respective source parameters of moment tensor and double couple were estimated for the 2004 sumatra andaman earthquake the gravity data indicate a composite moment of 1 2 1023 n m with a dip of 10 in agreement with the estimate obtained at ultralong seismic periods for the 2010 maule earthquake the grace solutions range from 2 0 to 2 7 1022 n m for dips of 12 24 and centroid depths within the lower crust for the 2011 tohoku oki earthquake the estimated scalar moments range from 4 1 to 6 1 1022 n m with dips of 9 19 and centroid depths within the lower crust for the 2012 indian ocean strike slip earthquakes the gravity data delineate a composite moment of 1 9 1022 n m regardless of the centroid depth comparing favorably with the total moment of the main ruptures and aftershocks the smallest event we successfully analyzed with grace was the 2007 bengkulu earthquake with m0 5 0 1021 n m we found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events deeper sources i e in the upper mantle could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume thus reducing the negative gravity component focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum

an integrated multi scale 3d seismic model of the archaean yilgarn craton australia abstract the collection of a range of different seismic data types has greatly improved our understanding of the crustal architecture of australia s archaean yilgarn craton over the last few years these seismic data include broadband seismic studies seismic receiver functions wide angle recordings and mine scale to deep seismic reflection transects each data set provides information on the three dimensional 3d tectonic model of the yilgarn craton from the craton scale through to the mine scale this paper demonstrates that the integration and rationalisation of these different seismic data sets into a multi scale 3d geological seismic model that can be visualised at once in a single software package and incorporating all available data sets significantly enhances this understanding this enhanced understanding occurred because the integrated 3d model allowed easy and accurate comparison of one result against another and facilitated the integrated questioning and interrogation across scales and seismic method as a result there are feedback questions regarding understanding of the individual seismic data sets themselves as well as the yilgarn craton as a whole the methodology used including all the data sets in the model range had to allow for the wide range of data sets frequencies and seismic modes at the craton scale p wave s wave and surface wave variations constrained the 3d lithospheric velocity model revealing noticeable large scale velocity variations within and across the craton an interesting feature of the data easily identified in 3d is the presence of a fast s wave velocity anomaly 4 8 km s 1 within the upper mantle this velocity anomaly dips east and has a series of step down offsets that coincide approximately with province and terrane boundaries of the yilgarn craton one dimensional receiver function profiles show variations in their crustal velocity across the craton these crustal velocity variations are consistent with the larger scale geological subdivision of the craton and provide characteristic profiles for provinces and terranes the receiver function results and the deep seismic reflection data both agree on the depth to the moho and both indicate an increase in moho depth to the east the 2d seismic refraction results in the south west of the craton provide crustal thickness information an indication of middle and lower crustal compositions and information regarding the broad scale architectural framework at the province and terrane scale the deep seismic reflection data and the mine scale seismic data provide geometric constraints on crustal architecture in particular the orientation of the region s fault systems as well as variations in the thickness of the granite greenstone succession integration of the results from wide angle seismic refraction data coincident with the deep seismic reflection data provided additional constraints on likely upper crustal lithologies the integrated 3d seismic model implies the dominant geodynamic process involved the development of an orogenic belt that developed with a series of contractional folding and thrusting events separated by equally important extensional events the seismic reflection data in particular suggests that extensional movement on many shear zones was more common than previously thought the seismic reflection data suggest that the dominant mineral systems involved deeply sourced fluid flowing up crustal penetrating shear zones these deeply sourced fluids were further focussed into sites located above fault breached domal regions in the upper crust

the panthalassa a cerium rich atlantic type ocean sedimentary environments of the tamba group southwest japan abstract the oceanic sediments of the tamba group a part of the japanese paleozoic mesozoic accretionary prism were studied geochemically these oceanic sediments have various ree patterns which correspond to specific ocean floor environments the type ii suite of the tamba group contains the following changes in sedimentary environment pelagic sedimentation under the influence of hydrothermal activity or diagenetic metal accumulation negative ce anomaly pelagic sedimentation in ce poor seawater or diagenesis under less oxic conditions lree hree or mree lree hree pattern and slow pelagic sedimentation under oxic conditions where authigenic metal flux from seawater resulted in a positive ce anomaly different from the type ii suite lower pelagic sediments of the type i suite show a lree hree pattern which indicates the inflow of very fine terrigenous or volcanic materials cherts and siliceous shales with positive ce anomaly are exclusively present in the upper part of chert siliceous shale sequences in all successions of the tamba group this suggests that seawater of the panthalassa ocean was at least partially enriched in ce resembling the modern atlantic more than the modern pacific ocean the following reasons for this enrichment are considered 1 1 fluvial input from surrounding continents was substantial 2 2 reductive regeneration of ce from continental shelves was active or 3 3 ce depleted seawater did not enter from the other ocean

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

some new measurements of heat flow in the superior province of the canadian shield borehole heat flow measurements are reported from six new sites in the superior province of the canadian shield values adjusted for glaciation effects but not for holocene climatic variations range from 42 to 56 mw m2 when these new values are combined with 21 previously published borehole values the mean is 42 mw m2 with a standard deviation of 11 mw m2 the data for a site on the lac du bonnet batholith suggest that the batholith has a thin veneer less than 3 km of rock of high radiogenic heat production at the surface

dynamics of intracontinental extension in the north baikal rift from two dimensional numerical deformation modeling we model the recent deformation along a lithospheric scale cross section perpendicular to the northern part of the baikal rift zone brz with two dimensional finite element models using realistic lithospheric structure and rheological properties and imposing extension as a far field boundary condition we find a model that matches reasonably well the topography observed deformation pattern gravity anomalies and age of formation of the northern brz our results suggest that 1 extensional strain can occur away from the main rift basin in the sayan baikal range and create depending on the rheological properties of the lithosphere a large off rift basin analogous to the barguzin basin or a series of basins and ranges as observed in the southern part of the sayan baikal range 2 anelasticity plays a major role by participating in the uplift of rift shoulders and hanging wall deformation and allowing the subsidence and tilting of the hanging wall along high angle planar normal faults 3 the lower crust accommodates differential strain between the brittle upper crust and upper mantle by horizontal shear and lateral flow towards the regions of crustal and mantle thinning 4 far field extensional stress and a lithospheric discontinuity inherited from paleozoic tectonic events are sufficient to initiate rifting and basin subsidence and 5 there is no or very little dynamic contribution of a hypothetic asthenospheric plume under the brz at least in the recent phase of its evolution fast rifting stage 3 5 myr

anomalous lithosphere beneath the proterozoic of western and central australia a record of continental collision and intraplate deformation a new surface wave seismic tomography model of australia is presented which provides a means of investigating the lithospheric structure beneath the proterozoic regions in the west north and centre of the continent with improved resolution and reliability the dominant feature of the model is a region of low seismic wavespeeds in the uppermost mantle at approximately 75 km depth beneath central australia the zone of slow wavespeeds is underlain by a region of fast wavespeeds more typical of continental lithosphere this layered velocity structure and strong positive wavespeed gradient makes the shallow anomaly hard to explain in terms of high mantle temperatures and typical steady state continental geotherms a possible thermal explanation requires the impact of the redistribution of high heat producing elements within the crust alternatively a mineral or minerals with low seismic velocities such as amphibole in the shallowest part of the lithosphere with a more conventional lithology in the deep continental root below could explain the seismic wavespeeds the anomaly is located directly beneath the zone where the australian cratons amalgamated in the proterozoic and where subsequently there have been periods of intraplate tectonic activity suggesting a correlation between the prolonged history of deformation and a highly unusual lithospheric structure in western australia the capricorn orogen and pilbara craton have a similar lithospheric thickness whereas a thicker lithosphere is observed beneath the yilgarn to the south in northern australia large regions appear to be underlain by fast wavespeeds similar to those observed beneath the yilgarn craton variations in the shear wavespeeds beneath the arunta also indicate that there is not always an obvious correlation between the overlying surface geology and seismic structures observed in the upper mantle

high resolution body wave tomography models of the upper mantle beneath eastern china and the adjacent areas 1 we present new 3 d tomographic models of vp vs and vp vsratio anomalies in the upper mantle beneath ec and adjacent areas this data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout eastern china ec during mesozoic to cenozoic time the tomographic images were constructed by inverting body wave travel times recorded at 1300 stations within the upgraded china national seismic network and 9 temporary arrays resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km the salient features of vp vs and vp vsratio anomalies can be clearly identified these include strong multiscale heterogeneities occupying the upper mantle beneath ec and differences in the spatial scale of anomalies found beneath northern and southern areas of ec these features demonstrate a degree of spatial variability in the geodynamic evolution of ec we propose two mechanisms to explain these patterns first the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into ec these areas would experience stronger convection and an altered stress regime in the upper mantle creating significant thermal anomalies beneath the south china block scb relative to the eastern north china craton ncc second differing thermal states and viscosities for the eastern ncc and the cathaysia block cab resulted in differing responses to regional deformation the archean hinterland of the eastern ncc specifically has a colder thermal state and higher viscosity and therefore exhibits only small scale heterogeneities due to the effect of shear localization the neoproterozoic cab has a relatively warm thermal state with lower viscosity and thus deformed more continuously

ocean tidal solutions in antarctica from grace inter satellite tracking data 1 long wavelength components of the oceanic tides surrounding antarctica are estimated directly from three years of grace satellite to satellite ranging measurements an inversion is performed for the major constituents m2 o1 and s2 with k1 excluded because of inadequate phase sampling the tides are parameterized as localized average mass anomalies over areas approximately 3002 km2 other parameters including satellite state adjustments are estimated simultaneously with the tides qualitative comparison of our solutions with in situ tide measurements shows agreement in spatial pattern clearly indicating regions where our adopted prior model is inadequate to exploit these solutions follow on work must assimilate these long wavelength components into a high resolution numerical tidal model

regional acceleration in ice mass loss from greenland and antarctica using grace time variable gravity data we use gravity recovery and climate experiment grace monthly gravity fields to determine the regional acceleration in ice mass loss in greenland and antarctica for 2003 2013 we find that the total mass loss is controlled by only a few regions in greenland the southeast and northwest generate 70 of the loss 280 58 gt yr mostly from ice dynamics the southwest accounts for 54 of the total acceleration in loss 25 4 1 2 gt yr 2 from a decrease in surface mass balance smb followed by the northwest 34 and we find no significant acceleration in the northeast in antarctica the amundsen sea as sector and the antarctic peninsula account for 64 and 17 respectively of the total loss 180 10 gt yr mainly from ice dynamics the as sector contributes most of the acceleration in loss 11 4 gt yr 2 and queen maud land east antarctica is the only sector with a significant mass gain due to a local increase in smb 63 5 gt yr

geodynamics of the eastern yilgarn craton abstract over the last decade there have been significant advances in our understanding of the stratigraphy magmatism deformation metamorphism and timing of mineralisation in the eastern yilgarn craton eyc of western australia the integration of these disciplines has enabled a holistic review of the tectonic history of the eyc which favours a paraautochthonous tectonic model a significant advance has been the recognition of a 2810 ma rifting event off the eastern margin of the youanmi terrane which set up the north northwest trending architecture of the eyc rifting was followed by a 100 myr long phase of tectonic activity initiated by the establishment of a convergent margin at 2715 ma characterised by a west dipping subduction zone to the east of the eyc subduction was associated with the deposition of 2715 2670 ma volcanic stratigraphy and the emplacement of voluminous tonalite trondhjemite granodiorite magmatism which resulted in magmatic thickening of the crust volcanism was terminated by a 5 myr pulse of east northeast contraction followed by mid orogenic extension possibly linked to lithospheric and lower crustal delamination the lack of ultra high pressure metamorphism and the presence of high geothermal gradients preclude this contractional event from recording continent continent collision mid orogenic extension at 2665 ma resulted in the introduction of metasomatised mantle melts mafic granites and syenites deposition of siliciclastic basins which record metamorphic anticlockwise ptt paths and the start of significant economic gold mineralisation in the eyc high stretching factors and or delamination associated with this extension event resulted in significant heat input into the base of the crust which eventually led to the emplacement of low ca crustal melt granites and cratonisation of the eyc major gold mineralisation postdates mid orogenic extension and was associated with renewed compression transpression 2650 ma and the development of steep predominantly north northwest striking sinistral and later north to north northeast striking dextral strike slip faults during low ca granite emplacement

correcting grace gravity fields for ocean tide effects 1 the grace mission will be launch in early 2002 and will map the earth s gravity fields and its variations with unprecedented accuracy during its 5 year lifetime unless ocean tide signals and their load upon the solid earth are removed from the grace data their long period aliases obscure more subtle climate signals which grace aims at the difference between two existing ocean tide models can be used as an estimate of current tidal model error for the m2 s2 k1 and o1 constituents when compared with the expected accuracy of the grace system both expressed as spherical harmonic degree variances we find that the current ocean tide models are not accurate enough to correct grace data at harmonic degrees lower that 35 the accumulated tidal errors may affect the grace data up to harmonic degree 56 furthermore the atmospheric radiation tides may cause significant errors in the ocean tide model if altimetry corrected for inverted barometer effects was used in its derivation to study the temporal characteristics of the ocean tidal constituents when sampled by grace approximate alias frequencies were derived assuming a sampling of half a sidereal day those results show that the ocean tide errors will not cancel in the grace monthly averaged temporal gravity fields the s2 and the k2 terms have alias frequencies much longer than 30 days so they remain almost unreduced in the monthly averages

gravity recovery and climate experiment grace alias error from ocean tides 1 gravity recovery and climate experiment grace is able to observe interannual and longer period mass redistribution driven by climate changes however alias errors due to inaccurate ocean tide models may contaminate these signals to quantify this problem we estimate alias contamination due to expected errors in eight tidal constituents q1 o1 p1 k1 n2 m2 s2 and k2 for the period august 2002 to february 2006 differences between got00 2 and tpxo6 2 tide models are used as estimates of tide model errors the alias estimate is based on an approximate method employing least squares fits of spherical harmonics to potential differences between the two grace satellites results from this method are similar to previous estimates confirming this is a useful and efficient way to study the alias problem new findings are 1 the period of the m2 tide alias is about 140 d much longer than the predicted period 13 5 d because of monthly sampling of the 13 5 d period 2 there are two alias periods for k1 one about 90 d and one longer than 7 years and 3 the slow decay in the grace orbit causes tide component aliases to differ from pure frequencies as the orbit evolves we also find that aliases can contaminate in both space and time and thus may affect estimates of mass changes over land finally we compare the simulated s2 alias with the estimated s2 alias in grace data they are similar but our approximate method appears to overestimate alias error over high latitude oceans and along certain coastlines while underestimating error over low latitude oceans

the lithosphere of north china craton from surface wave tomography abstract fundamental mode rayleigh wave group velocity dispersion data were used in a tomographic study to reconstruct the crust and upper mantle shear velocity structure in east asia this article expounds the features of lithosphere structure in different sub regions of north china and discusses their implications for the tectonic evolution and present tectonics of north china craton ncc the study revealed that strong earthquakes took place in the low velocity zones and along the boundaries between high and low velocities in the middle and lower crust the active nw trending zhangjiakou bohai seismic belt corresponds to a prominent low velocity zone in the crust and upper mantle lid in addition to the well known structural difference between western and eastern ncc we are able to resolve clearly the lithospheric features of sub regions in eastern ncc the southern north china basin and north yellow sea are characterized by a high velocity crust and upper mantle lid down to 70 80 km depth while the northern north china basin has a low velocity crust and the velocity below moho to about 130 km is rather uniform and low there is also a general trend of velocity decrease in the upper mantle from west to east the velocity images bear the imprints of subduction and collision that took place in the periphery of ncc since mesozoic and shed some light on the mechanism of mesozoic lithospheric thinning of eastern ncc

continental collision and accretion recorded in the deep lithosphere of central china abstract basaltic andesitic volcaniclastic diatremes erupted in the mesozoic 160 ma in the xinyang area henan province of central china the locality lies on the western margin of the eastern block of the north china craton and the southern margin of this craton the diatremes carry a suite of xenoliths including lower crustal mafic to felsic granulites eclogites meta gabbros pyroxenites and mantle peridotites the petrological and geochemical data show that the crust in the area is temporally and compositionally zoned exposed rocks up to ca 2 85 ga old underlain by felsic granulites and rare pyroxenites with zircon ages of 3 6 3 4 ga to ca 30 km depth deeper ca 30 45 km parts of the lower crust consist of high pressure mafic to felsic granulites and meta gabbro which give paleoproterozoic 2 0 1 8 ga zircon ages our data show the significance of underplating vertical crustal growth in the paleoproterozoic which was related to the amalgamation of the eastern and western block of this craton and a global columbia supercontinent assembly hf isotope data indicate that both juvenile material and remelting of older 3 8 3 0 ga crustal rocks were involved in this important event paleozoic 440 260 ma and early mesozoic 228 219 ma zircons are also found in xenoliths from the deeper part of the lower crust and the uppermost mantle i e eclogite and peridotite they are interpreted as reflecting geodynamic processes related to the continental collision between this craton and the yangtze craton respectively the xenoliths from xinyang diatremes thus record the growth and modification of the old paleo mesoarchean continental lithosphere by magma underplating during several tectonic events assembly of the southern and northern parts of the eastern block in neoarchean time collision of the western and eastern blocks along the trans china orogen in the paleoproterozoic and subduction and collision of the yangtze craton with the north china craton in early paleozoic and triassic times respectively

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

autochthonous development of superior province greenstone belts abstract models for superior province greenstone belt development have changed over the last 30 years from ensimatic generally autochthonous models to suspect allochthonous terrane models based on the plate tectonic paradigm models intermediate between these end members such as autochthonous terrane models have not been prominent within the superior province there is a secular variation from early ca 3 ga platformal assemblages with overlying rift related komatiite tholeiite units representing breakup of ca 3 ga continental fragments to late ca 2 7 ga pull apart basins autochthonous terranes should demonstrate some sort of logical order such as that described above whereas allochthonous terranes will be largely oceanic in character and should be essentially random in their occurrence rather than exhibiting secular order in the face of this situation this paper reviews evidence from throughout the superior province that suggests many but not all greenstone assemblages developed autochthonously or parautochthonously the earliest greenstone assemblages in the superior province are generally quartzite and carbonate bearing platform sequences in the north caribou terrane and the marmion terrane deposited unconformably upon granitoid or greenstone basement the evidence for autochthonous parautochthonous development includes the presence of unconformities between keewatin type greenstone units such as 1 basal unconformities between ca 3 ga granitoid or volcanic basement and slightly younger platformal assemblages 2 between ca 2 9 ga platformal assemblages and younger platformal and andean arc assemblages stratigraphic patterns such as adjacent greenstone belt assemblages representing sharply differing geodynamic settings with some indication of palinspastic order or progression in the northern central and southern superior province are considered suggestive of orderly autochthonous progression from platforms through rifting of continental fragments and late assembly during the kenoran orogeny petrogenetic data indicating involvement of older granitoid crust in genesis of greenstone assemblages of a variety of ages throughout the superior province suggests the presence of older basement implying autochthonous or parautochthonous development of many assemblages younger greenstone assemblages in the abitibi wawa subprovince and the north caribou terrane contain xenocrystic zircons similar in age to stratigraphically underlying greenstone assemblages this pattern has been interpreted to represent autochthonous greenstone development the current above enumerated evidence for autochthonous development of greenstone assemblages is generally indirect few actual unconformities between keewatin type greenstone assemblages have been recognized in the superior province to aid in future recognition of unconformities in keewatin type greenstone assemblages examples of unconformities of varying degrees of subtlety in archean sequences are reviewed archean unconformities ranging from sharp angular discordances in the northern superior province to subtle stratigraphic patterns to weathering related geochemical mobilization along inter formational contacts are described these styles of unconformity in archean sequences suggest previously unrecognized major disconformities and unconformities may well exist between keewatin type assemblages in the superior province generally and the abitibi wawa subprovince specifically the most important disconformity suggested in the abitibi wawa subprovince is between the ca 2726 ma deloro and the ca 2708 ma tisdale assemblages the presence of unconformities and disconformities coupled with the indirect lines of evidence cited above suggest an autochthonous origin for many superior province greenstone belts this autochthonous origin involves either autochthonous or parautochthonous evolution of assemblages at least in part in place that is development of ca 3 ga platform sequences in selected locales followed by in place evolution of a succession of plume oceanic and arc assemblages culminating in late pull apart basin sequences implications of the autochthonous model for greenstone belts of the superior province particularly the abitibi wawa subprovince include the future ability to recognize unconformity bounded sequences potentially improving regional scale correlation

microfabric characteristics and rheological significance of ultra high pressure metamorphosed jadeite quartzite and eclogite from shuanghe dabie mountains china quantitative analysis of the structural evolution of jadeite quartzite a rare ultra high pressure uhp rock type from the dabie mountains of eastern china sheds light on the formation and evolution of uhp orogenic belts worldwide geological mapping of the shuanghe area where jadeite quartzites crop out was carried out to determine the spatial relationships between different uhp rocks within this orogen the deformation mechanisms of jadeite quartzite geodynamical parameters stress strain strain rate and microstructure including lattice preferred orientation lpo were determined from six jadeite quartzite samples from the shuanghe area lpos of clinopyroxene jadeite and omphacite garnet rutile and quartz from these jadeite quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the shuanghe area microstructural lpos of jadeite omphacite garnet rutile and quartz were determined using electron backscattered diffraction ebsd analysis quartz fabrics were largely recrystallized during late low grade stages of deformation whereas garnet shows no strong lpo patterns rutile fabrics show a weak ls fabric along 001 jadeite and omphacite show the strongest eclogite facies lpo patterns suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust microstructural data show that the jadeite lpo patterns are similar to those of omphacite and vary between l and s types which correlate with prolate and oblate grain shape fabrics spo quartz lpos are monoclinic microstructural analysis using tem shows that the dominant slip systems of jadeite in one sample are 100 001 110 001 and 1 1 0 1 2 110 while in another sample no dislocations are observed abundant dislocations in quartz were accommodated by the dominant slip system 0001 1120 indicating basal glide and represents regional shearing during the exhumation process this suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under uhp conditions the protoliths of jadeite quartzite metasedimentary rocks from the northern passive continental margin of the yangtze craton experienced the same deep subduction and were deformed under similar rheological conditions as other uhp eclogite marble and paragneiss experimental uhp deformation of quartzo feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths the resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km 24 gpa thus processes of deep continental subduction may be better understood through understanding the rheology and mechanical behaviour of jadeite jadeite quartzites such as those from the shuanghe may be exhumed remnants of deeply subducted slabs of continental crust other parts of which subducted past thedepth of no return and remain in the deep mantle

cratonic reactivation and orogeny an example from the northern margin of the north china craton abstract reactivation of cratonic basement involves a number of processes including extension compression and or lithospheric delamination the northern margin of the north china craton ncc adjacent to the inner mongolian orogenic belt was reactivated in the late paleozoic to early mesozoic during this period the northern margin of the ncc underwent magmatism n s compression regional exhumation and uplift including the formation of e w trending thick skinned and thin skinned south verging folds and south verging ductile shear zones zircon u pb shrimp ages for mylonite protoliths in shear zones which show ages of 310 290 ma mid carboniferous early permian constraining the earliest possible age of deformation muscovite within carbonate and quartz feldspar muscovite mylonites from the kangbao weichang and fengning longhua shear zones defines a stretching lineation and gives 40ar 39ar ages of 270 250 ma 250 230 ma 230 210 ma and 210 190 ma deformation developed progressively from north to south between the late paleozoic and triassic exhumation of lower crustal gneisses high pressure granulites and granites occurred at the cratonic margin during post ductile shearing 220 210 ma an undeformed early jurassic 190 180 ma conglomerate overlies the deformed rocks and provides an upper age limit for reactivation and orogenesis deformation was induced by convergence between the southern mongolia and north china cratonic blocks and the location of this convergent belt controlled later deformation in the yanshan tectonic province this province formed as older e w trending archean proterozoic sequences were reactivated along the northern margin of the ncc this reactivation has features typical of cratonic basement reactivation compression crustal thickening remelting of the mid to lower crust and subsequent orogenesis adjacent to the orogenic belt

space borne gravimetric satellite constellations and ocean tides aliasing effects summary ocean tides redistribute mass at high temporal frequencies satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest this paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology including temporal filtering of time series of gravity solutions spatial smoothing and the use of satellite constellations for this purpose an earth system model esm was constructed which included state of the art time varying components for ocean atmosphere solid earth hydrology ice sheets and ocean tides using the esm we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations we find that 1 the ocean tide aliasing strongly depends on the satellite constellation the choice of orbital parameters and the length of the data span 2 the aliasing effect manifests itself differently for different geographical regions 3 the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits 4 optimizing the choice of orbital parameters of a single grace type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems finally we corroborate the experiences with grace data analysis that appropriate post processing techniques can significantly improve the quality of the retrieved gravity changes

lithospheric structure of the ordos block and its boundary areas inferred from rayleigh wave dispersion abstract we have measured rayleigh wave phase velocities of the ordos block and its southern and western boundary areas and inverted these data to describe the upper mantle structure the ordos block was found to be characterized by distinctly high seismic velocities at depths commonly associated with a low velocity asthenosphere to the south abnormally slow velocity anomalies appeared in the weihe rift probably indicating subsolidus grain boundary weakening effect under high temperatures near solidus instead of partial melt in the asthenosphere an intermediate seismic velocity structure was observed beneath the northern qinling orogen nql to the south of the weihe rift a thin high velocity lid which was probably a cratonic relic was found under the haiyuan arcuate tectonic region hatr west of the ordos block a thick lithosphere was present beneath the ordos block 200 km and the nql 140 km while a thinner lithosphere 100 km was found beneath the hatr and the weihe rift the observed structural differences were likely associated with different lithospheric tectonics in the study region whereas the weihe rift and the hatr had been strongly affected by cenozoic lithospheric modification and thinning the ordos block and the nql appeared to have been much less influenced combined with previous studies our results suggested that the far field effect of the indo asia collision may have played an important role in the unique lithospheric process in the study region such as the extension of the weihe rift the preservation of a cratonic relic under the hatr and the localized intense lithospheric modification of these two regions the substantial variations of deep structure and thus contrasting rheological properties between the ordos block and the surrounding notable seismic belts the hatr and weihe rift may be a candidate mechanism for the contrasting seismicity of the region the lateral variations in the lithospheric structure estimated here generally agreed with changes in upper mantle deformation patterns previously derived from sks splitting measurements

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

low temperature phanerozoic history of the northern yilgarn craton western australia abstract the phanerozoic cooling history of the western australian shield has been investigated using apatite fission track aft thermochronology aft ages from the northern part of the archaean yilgarn craton western australia primarily range between 200 and 280 ma with mean confined horizontal track lengths varying between 11 5 and 14 3 m time temperature modelling of the aft data together with geological information suggest the onset of a regional cooling episode in the late carboniferous early permian which continued into late jurassic early cretaceous time present day heat flow measurements on the western australian shield fall in the range of 40 50 mw m 2 if the present day geothermal gradient of 18 2 c km 1 is representative of average phanerozoic gradients then this implies a minimum of 50 c of late palaeozoic to mesozoic cooling assuming that cooling resulted from denudation the data suggest the removal of at least 3 km of rock section from the northern yilgarn craton over this interval the perth basin located west of the yilgarn craton contains up to 15 km of mostly permian to lower cretaceous clastic sediment however published u pb data of detrital zircons from permian and lower triassic basin strata show relatively few or no grains of archaean age this suggests that the recorded cooling can probably be attributed to the removal of a sedimentary cover rather than by denudation of material from the underlying craton itself the onset of cooling is linked to tectonism related to either the waning stages of the alice springs orogeny or to the early stages of gondwana breakup

flat mantle reflectors in eastern china possible evidence of lithospheric thinning abstract recent 24 s deep seismic reflection records revealed five flat reflectors in the lithospheric mantle in eastern china with increasing depth they are named m1 to m5 and can be seen on both field single shot and stacked records reflector m1 corresponds to the moho discontinuity whereas m5 may be the reflection from the bottom of the current lithosphere which is about 78 km deep according to geothermal measurements the other three reflectors seem peculiar and might result from interactions between the lithosphere and deeper mantle based on lithological and geochemical data it is suggested that the lithosphere has been thinned from about 150 km to about 60 km in the late mesozoic and then has been thickened to about 78 km during the cenozoic the thinning process produced a granulite layer in the old lower crust caused by magmatic underplating whereas an eclogite layer formed beneath owing to the subduction of the paleo tethys and yangtze craton during the permian and early mesozoic reflector m2 at about 12 s two way traveltime twt might result from the paleozoic moho which represents the boundary between the previous granulite and eclogite facies reflector m3 at about 14 s might correspond to the bottom of the eclogite layer beneath which the old lithospheric mantle remained the old and the newly developed mantle may have different compositions resulting in reflector m4 the multi layered mantle reflectors demonstrate a mantle structure that possibly correlates with the lithospheric thinning process that occurred in eastern china during the late mesozoic the discovery of multi layered mantle reflectors in the studied areas indicates a high heterogeneity of the upper mantle reflection seismology with improved technology together with velocity and resistivity imaging and rock physics measurements can provide more details of the heterogeneity and related dynamic processes that occurred in the lithospheric mantle

greenland mass variation from time variable gravity in the absence of grace 1 in a recent paper the authors succeeded in the inference of time variable gravity from orbit analysis of the champ satellite the authors demonstrated the potential of the adopted methods by validation against grace data and surface height changes from gps ground stations this paper presents the capability of orbit analysis for the spatiotemporal quantification of greenland mass change trends based on champ time variable gravity fields from january 2003 to december 2009 we estimated the ice mass loss over the entire of greenland to 246 10 gt yr this result is in line with the findings from grace data analysis 223 10 gt yr over the same period the trend estimates differ by only 10 moreover for some areas the spatial mass variation patterns are in good agreement pinpointing dominant deglaciation along the greenland coastline we conclude that orbit analysis of low earth orbiting spacecraft is suitable to assess greenland mass balance in the absence of the grace satellites

grace observations of m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica 1 by processing the grace satellite to satellite tracking data and estimating the temporal gravity fields regionally over the southern polar region with a 5 day interval we observed m2 and s2 ocean tides underneath the filchner ronne and larsen ice shelves antarctica based on the predicted aliased periods we extracted the m2 and s2 signals from the time series of 5 daily mean grace regional gravity estimates the grace observations agreed well with the predicted tides from the fes2004 and cats02 01 models after smoothing the models to the commensurate spatial resolution as grace overall the grace and the models agreed within 10 20 difference in the tidal amplitude and 20 in phase for both m2 and s2 our results suggest that grace provides valuable observations of ocean tides with a spatial resolution as short as 300 km over the remote area lacking of quality observations such as the antarctica ice shelves

is the ordos basin floored by a trapped oceanic plateau abstract the ordos basin in china has about 10 km of neoarchean to quaternary sediments covering an enigmatic basement of uncertain origin the basement is tectonically stable has a thick mantle root low heat flow few earthquakes and has been slowly subsiding for billions of years the basement has geophysical signatures that indicate it is dominantly intermediate to mafic in composition and is similar to some other cratons world wide and also to several major oceanic plateaus it was accreted to the amalgamated eastern block and central orogenic belt of the north china craton ncc in the paleoproterozoic then involved in several proterozoic tectonic events including being over thrust by an accretionary orogen and intruded by andean arc related magmas and then involved in a continent continent collision during amalgamation with the columbia supercontinent thus the basement rocks are deformed metamorphosed to granulite facies and determining their initial origin is difficult we suggest that the data is consistent with an origin as an oceanic plateau that accreted to the ncc and later experienced different episodes of differentiation associated with later subduction and collisions formation of cratonic lithosphere by accretion of oceanic plateaus may be one mechanism to create stable cratons other cratons that apparently formed by partial melting of underplated and imbricated oceanic slabs are stable in some cases but also re activated and de cratonized in some cases in asia where they have been affected by younger subduction hydration slab roll back and melt peridotite reactions this suggests that the initial mode of craton formation may be a factor in the preservation of stable cratons and de cratonization is not only influenced by younger tectonic activity

arctic ocean tides from grace satellite accelerations 1 models are routinely used to remove the effects of global ocean tides from grace data during processing to reduce temporal aliasing into monthly grace solutions these models have typically been derived using data from satellite altimeters such as topex poseidon therefore the arctic ocean components of tide models are not constrained by altimetry data potentially resulting in errors that are likely to alias into monthly grace gravity fields at all latitudes seven years of grace inter satellite accelerations are inverted to solve for corrections to the amplitude and phase of major solar and lunar ocean tides at latitudes north of 50 n using a mascon approach the tide model originally applied to our data was fes2004 truncated to maximum degree lmax 90 simulations are performed to verify that our inversion algorithm works as designed uncertainty estimates are derived from tidal solutions on land and by subtracting two independent solutions that each use 3 5 years of data features above the noise floor in the m2 k1 s2 and o1 solutions likely represent errors in fes2004 errors due to truncating the spherical harmonic expansion of fes2004 are too small and errors in the land mask model needed to transform sea surface heights into mass only affect coastal areas and do not produce similar relative amplitudes for any examined tides in the oceans north of 50 n these residuals tend to reduce the fes2004 amplitudes for m2 k1 s2 and o1 reductions in the variance of accelerations not used in our inversion suggest that our results can be used to improve grace processing

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

lateral variation of crustal structure in the ordos block and surrounding regions north china and its tectonic implications abstract crustal thicknesses and poisson s ratios in the ordos block and surrounding regions were estimated by the use of the h k stacking method on teleseismic receiver functions the data came from 353 temporary and permanent seismic stations in 2006 2011 results show that the crustal thickness and poisson s ratio gently vary within the ordos block with an average of 41 3 km and 0 265 respectively consistent with a felsic composition of the crust crustal thicknesses predicted on the basis of airy isostasy are consistent with the estimated thicknesses implying that the topography is approximately compensated the reactivated portion of the north china craton that has undergone mesozoic cenzoic lithospheric thinning is also characterized by the thinning crust while the ordos block maintains normal crustal thickness and average crustal velocity inferred higher densities in the lower crust and the anti correlation between poisson s ratio and crustal thickness in the ordos block may be the result from underplating of mafic magmas in the precambrian around the ordos block the paleoproterozoic khondalite zone in the northern edge has higher poisson s ratio and thickened crust which is consistent with the lower crust being of more mafic composition the weihe shanxi graben in the southeastern edge has mid high poisson s ratio high heat flow and thinning crust which is consistent with the known transtensional tectonic setting in the liupanshan thrust belt along the southwestern edge of the ordos plateau significant variations in crustal thicknesses and poisson s ratios occur on two sides besides a thickened crust a concaved moho implies horizontal shortening of this edge of the ordos block due to its collision with the northeastern tibetan plateau the structural differences between the eastern and western edges of the ordos block reflect that the ordos block is in tectonic stress environment of the western compression and the eastern extension

flat slab subduction trench suction and craton destruction comparison of the north china wyoming and brazilian cratons abstract the mechanisms of growth and destruction of continental lithosphere have been long debated we define and test a unifying plate tectonic driving mechanism that explains the numerous petrological geophysical and geological features that characterize the destruction of cratonic lithospheric roots data from three archean cratons demonstrate that loss of their roots is related to rollback of subducted flat slabs some along the mantle transition zone beneath the cratons during flat slab subduction dehydration reactions add water to the overlying mantle wedge as the subducting slabs roll back they suck in mantle material to infill the void space created by the slab roll back and this fertile mantle becomes hydrated the roll back causes concomitant lithospheric thinning of the overlying craton so the flux of newly hydrated mantle material inevitably rises causing adiabatic melting generating new magmas that gradually destroy the roots of the overlying craton through melt peridotite reactions calculated fluxes of new mantle material beneath cratons that have lost their roots range from 2 7 trillion to 70 million cubic kilometers which is sufficient to generate enough melt to completely replace the affected parts of the destroyed cratons cratonic lithosphere may be destroyed in massive quantities through this mechanism warranting a re evaluation of continental growth rates with time

ocean tides in the weddell sea new observations on the filchner ronne and larsen c ice shelves and model validation 1 ocean tides under the large weddell sea ice shelves are among the least well observed on earth here we present new spatially extensive observations of the vertical tidal motion of the filchner ronne and larsen c ice shelves using global positioning system gps data spanning a few weeks to years we pay particular attention to the major tidal constituents m2 s2 o1 k1 as well as important grace aliasing periods k2 and s1 we compare the estimated constituents with recent global and regional tide models and find that no single model is the most accurate across all constituents or ice shelves the root sum square errors are 7 8 cm cats2008a and tpxo7 2 and 11 12 cm got4 7 and fes2004 with the energetic m2 rmse 4 8 cm and s2 4 5 cm generally dominating these statistics the fes2004 k1 is particularly inaccurate near the larsen c ice shelf with errors approaching 20 cm meaning that grace release 4 estimates of mass change in the northern antarctic peninsula will be biased we find tidal energy at 3 4 5 6 and weakly at 7 cycles per day at all of our sites the largest amplitudes within these bands are at m4 mo3 and sp3 and approach 30 mm although significant spatial variations exist we show that they generally do not appear to originate in areas of reduced water column in ice shelf grounding zones comparing model estimates with our m4 ms4 and mn4 values shows that models do not accurately represent these terms

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material