heat flow anomaly in the middle okinawa trough heat flow measurements in the okinawa trough were carried out on three cruises in 1984 and 48 new values were obtained non linear temperature depth profiles were obtained at some stations and interpreted as showing the results of hydrothermal circulation in the southwestern part of the trough heat flow appears to be lower in the central rift zone than in the surrounding area a high heat flow area around 126 e exists an extremely high and localized heat flow anomaly was observed in the central rift zone of the middle okinawa trough it is probably caused by present or recent igneous activity if the anomaly is due to an intrusion the maximum depth and age of the intrusive body can be assessed by the amplitude and horizontal extent of the heat flow anomaly assuming conductive cooling the age is younger than 3 105 yrs and the depth is shallower than 3 5 km when advective heat transfer is taken into account the age must be much younger

late cenozoic evolution of the east china continental margin insights from seismic gravity and magnetic analyses abstract seismic reflection profiles reveal the structural characteristics beneath the east china sea shelf margin and the okinawa trough and provide new constraints on the late cenozoic evolution of the east china continental margin the frontal shelf basin between the taiwan sinzi uplift and the trough axis occupies the western half of the northern middle okinawa trough in this basin the middle late miocene sediments are confined to grabens or half grabens dominated by listric faults whereas the overlying pliocene quaternary sequence is characterized by a uniform thickness and dense planar type faults suggesting that rifting of the northern middle okinawa trough initiated during the middle miocene but slowed down during the earliest pliocene since that time the opening of the okinawa trough has been dominated by diffuse rifting the southern okinawa trough is predominately filled by quaternary sediments indicating that its back arc rifting began during the earliest pleistocene contractional structures identified in the pre quaternary sequence beneath the continental slope along with an erosional pleistocene pre pleistocene unconformity in the southern okinawa trough demonstrate the existence of pre rifting compression and uplifting in this region we use this evidence and previously published results to propose an evolutionary model of the east china continental margin during the late cenozoic the northern middle okinawa trough began rifting during the middle miocene on a paleo uplift the luzon arc initially impinged upon the eurasian continental margin during the late miocene near the southeastern end of the miyako fault belt and activated the proto taiwan orogeny in today s southern okinawa trough and adjacent regions during the late miocene pliocene the orogeny quickly propagated southwestward along with the west northwest moving philippine sea plate subsequently the rifting of the southern okinawa trough was initiated during the earliest pleistocene and propagated southwestward following the post collisional collapse of the proto taiwan orogen this geodynamic scenario resembles that of present day northern taiwan

slab horizontal subduction and slab tearing beneath east asia the present day architecture of subducted slabs in the mantle as inferred from seismic tomography is a record of plate tectonics through geological time the unusually large slab that lies nearly horizontally above the 660 km mantle discontinuity beneath east asia is presumably from subduction of the pacific plate numerical models have been used to explore the mechanical and geophysical factors that contribute to slab stagnation but the evolution of this horizontal structure is not fully understood because of uncertainties in the plate tectonic history and mantle heterogeneity here we show that forward mantle flow models constrained by updated tectonic reconstructions can essentially fit major features in the seismic tomography beneath east asia specifically significant tearing propagated through the subducted western pacific slab as the philippine sea plate rotated clockwise during the miocene leading to internal slab segmentation we believe this tearing associated with philippine sea plate rotation also affects the horizontal configuration of slabs

is taiwan the result of arc continent or arc arc collision abstract conventionally it has been accepted that the formation of taiwan results from the collision of the luzon arc with the eurasian continental margin we suggest that taiwan results from the collision of the luzon arc with the former ryukyu subduction zone before the collision the latter extended a few hundred kilometres southwest of its present day termination in the early to middle miocene the subduction became inactive in its southwest portion and the manila trench migrated northeastward giving rise to the formation of the luzon arc the collision started in the late miocene by closing the oceanic domain located between the luzon arc and the former ryukyu arc because the luzon arc moved northwestward with respect to the former ne sw trending ryukyu arc the oblique collision first resulted in the indentation on the south ryukyu arc west of 123 5 e and the narrowing of the corresponding portion of the okinawa trough prior to the uplift of taiwan today the hsuehshan and backbone ranges represent the uplifted portion of the backarc basin and the longitudinal valley corresponds to the suture zone between the former ryukyu and the luzon arcs in this model we propose to link although they are not of the same age two truncated backarc basins the active okinawa trough to the northeast and the former active tainan backarc basin to the southwest the former backarc basin extended from southwest of taiwan to southern japan and could have been initiated near the paleo location of taiwan as early as the eocene oligocene the result of the collision is the truncation of the ancient backarc basin associated with the shortening deformation and uplift of the ancient outer arc and related backarc region which provides the fundamental mechanism of the taiwan mountain building this model is in agreement with a counterclockwise rotation of the portion of taiwan located west of the coastal range belonging to the luzon arc and a clockwise rotation of the south ryukyu arc earthquake focal mechanisms geodetic observations and the distribution of the petrologic and structural features are also consistent with the proposed arc arc collision model

opening mode of the okinawa trough paleomagnetic evidence from the south ryukyu arc more than 250 samples of volcanics and sedimentary rocks were collected from the south ryukyu arc for paleomagnetic study and k ar dating stable primary components of magnetization were isolated from 18 sites after thermal demagnetization the mean paleomagnetic direction for 15 eocene volcanic sites d 30 1 i 40 3 95 10 3 indicates a direction which is deflected 18 6 11 6 clockwise from the expected field direction calculated from the 40 ma pole of eurasia the clockwise deflection is observed also in the dike rock d 144 0 i 32 1 the age of which is determined to be 9 6 0 8 ma by the conventional k ar dating method these results indicate that with respect to eurasia the southern part of the ryukyu arc has rotated clockwise 19 during the past 10 m y we attribute this rotation to the back arc opening of the southern part of the okinawa trough which occurred by means of the wedge mode later than 10 ma

the formation and evolution of the east china sea shelf basin a new view abstract back arc basins and the related subduction systems have been extensively studied however back arc basins exhibiting episodic jumps of extension centers by the subduction of different ocean slabs are poorly known the east china sea shelf basin ecssb comprises two eastward younging subparallel depression zones and its formation and evolution is accompanied by a complicated subduction history and regional tectonic events offer an excellent opportunity to decipher the various geological features of back arc basins here we review the tectonic and sedimentary features of the subbasins in the ecssb and its adjacent regions and then reconstruct the evolution of the sedimentary paleogeography the west depression zone wdz of the ecssb experienced rifting in the late cretaceous during the subduction of the izanagi plate at the eastern continental boundary in the northern wdz the changjiang depression was mainly dominated by fluvial to lacustrine deposits this depression experienced strong compression characterized by folds and erosion during the transition from a synrift to postrift setting at the end of the paleocene then another compression event occurred that resulted in extensive folds and uplift accompanied by a large scale alluvial fan in the eastern changjiang depression coinciding with the subparallel subduction of the izanagi pacific ridge in the early eocene however the lishui jiaojiang sag characterized by diffuse extension rather than focused rifting in its late rifting period this sag was mainly covered by paralic to marine deposits and experienced extensive erosion caused by tilted sequences from the late eocene to oligocene which shared the same characteristics as basins around the taiwan region it is widely accepted that the formation and evolution of basins around taiwan were controlled by the evolving of the south china sea scs and the related regional tectonics considering the eastward extent of scs it would seem that the southern ecssb was part of the passive margin of scs accordingly the southern ecssb might be significantly influenced by the scs the east depression zone edz commenced rifting in approximately the middle eocene as inferred from the absence of the compressional event that occurred in the early eocene and the existence of a thick layer reflection below the pinghu fm late eocene due to the subduction of the pacific plate the depocenters of the ecssb and the okinawa trough jumped eastward successively triggered by the three oceanic slabs of the izanagi plate at 72 ma the pacific plate at 50 ma and the philippine sea plate at 15 ma thus a new model for the formation and evolution of the ecssb is suggested in which a back arc basin of episodic extension with jumping depocenters in respond to subduction of three oceanic slabs meanwhile its differences between northern and southern part are caused by the dominant subduction and opening of scs respectively the ecssb and okinawa trough might formed mainly by rollback of the oceanic slab possibly due to slab stagnation and toroidal flow related to the subduction however the effects of large scale mantle flow cannot be exclusively identified in this research in addition further research in this region will give new insights into both the formation and evolution of the scs and the continental breakup process

evolution of the southern taiwan sinzi folded zone and opening of the southern okinawa trough abstract recent interpretation of seismic sections and free air gravity anomalies in offshore northern taiwan reveals that the southern taiwan sinzi folded zone began to form in late middle miocene though it was mainly constructed in the late pliocene with strong reverse faulting and folding two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern taiwan sinzi folded zone and the southern ryukyu arc these two structures are displaced by several northwest striking dextral strike slip faults that were active in the early quaternary when the clockwise rotated southern ryukyu arc and the folded southern taiwan sinzi folded zone were broken it is believed that recent extension in the southern okinawa trough started in the early quaternary because uplift on the southern taiwan sinzi folded zone continued to latest pliocene early quaternary paleogene miocene sediments of the east china sea shelf in the western part of the southern okinawa trough basin are interpreted to indicate that the east china sea shelf basin extended to the east of the southern taiwan sinzi folded zone

basement structures of east and south china seas and adjacent regions from gravity inversion abstract the satellite derived gravity gives us an opportunity to investigate the basement structures of the east and south china seas since the satellite gravimetry could provide large scale gravity data with high resolution of 1 arc min by 1 arc min we isolate the residual gravity anomaly corresponding to the basement by subtracting the gravity anomalies of sediments and moho undulations from satellite derived free air gravity anomalies two methods namely gravity inversion method and convolution method based on flexure isostasy model are used to calculate the moho undulations in order to guarantee the accuracy of the moho undulations since it occupies large percentages of the gravity anomalies we invert the isolated gravity anomaly for the basement depths of east and south china seas and adjacent areas with resolution of 1 arc min by 1 arc min the basement depths of east and south china seas range from 0 5 km to 12 km and the moho depths vary between 6 km and 32 km the basement topography reveals many tectonic depressions and two spreading axes concealed by the sediments which are unseen in the bathymetry the two spreading axes correspond to the spreading ridges derived from magnetic anomaly and the sw ne oriented spreading axis extends sw much farther than that identified from magnetic anomaly almost reaching to the nam con son basin we also find that the faults constrain the distributions of basement depressions since the faults usually lie along the places where large changes of basement depth take place reversely the basement map could be used to identify the unknown faults besides according to the four profiles in the east and south china seas the mirror image relation was found between the basement topography and the underlying moho undulations that when the basement depth increases or decreases the corresponding moho depth decreases or increases

the okinawa trough genesis of a back arc basin developing along a continental margin abstract the okinawa trough is the only example of a marginal back arc basin type at a young stage of evolution that developed along a continental margin the first phase of crustal stretching and subsidence occurred during late miocene early pliocene times a second major phase occurred after the latest pliocene or early pleistocene with en echelon rift axes along the axes of the okinawa trough oblique to the general trend of the arc and trench crustal separation and active spreading has occurred in the central and southern okinawa trough but the north okinawa trough is only in a rifting stage the development of the basin has several correlations with the general tectonism of the arc system 1 1 there was a synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the fore arc terrace 2 2 back arc rifting was initiated in the volcanic arc and propagated along it during the neogene remnants of a volcanic arc are found on the continental side of the basin the beginning of the back arc spreading observed in the central and southern okinawa trough correspond to a relative minimum in the activity of the volcanic arc 3 3 the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events such a collision lateral back arc opening model could explain the initiation of the opening of back arc basins but additional phenomena such as thermal convection retreating trench model or anchored slab model are indispensable to maintain extension in the back arc basin

neogene subsidence pattern in the multi episodic extension systems insights from backstripping modelling of the okinawa trough abstract extensional systems of back arc basins have been widely recognized and studied in se asia however the interactions between extensional tectonics and spatial temporal distributions of tectonic subsidence in an active back arc basin are poorly known using a backstripping technique we analysed 33 multichannel seismic profiles to calculate the neogene tectonic subsidence across the entire okinawa trough ot for the first time reconstruction of the tectonic subsidence shows that the ot can be roughly divided into four subsidence stages with variable rate by comparing the temporal spatial distribution of the intensive subsidence area we confirmed that rifting events first occurred in the northern segment not and middle segment mot from the miocene to late pliocene and then propagated to the southern segment sot after the late pliocene the factors controlling the rapid tectonic subsidence over the entire ot can be classified into two categories 1 ne to nne trending normal faulting related to extension of the ot and nw to nww trending strike slip faulting i e the tokara fault and the miyako fault related to subduction of the philippine sea plate under the eurasian plate 2 the anomalous rapid subsidence occurred in the southernmost part of the sot is likely related to the subducted gagua ridge which caused magma intrusion resulting from partial melting we suggest that magmatic bodies produced by partial melting of subducted materials intruded into the crust and created a dense lithosphere causing this rapid tectonic subsidence

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

polyphasic origin of salinity in the senegal delta and middle valley saline areas are a major obstacle to the development of sustainable irrigated agriculture in the senegal valley they have been attributed to the incorporation of marine salts in the sediments during the last marine transgression however this does not explain their geomorphological situation and geochemical features they are distributed as strips about 100 200 m wide and several kilometers long which are composed of two parallel substrips one located in the depressions of former creek beds and the other on higher ground on the southern bank in these two substrips the chemical composition of salinity and its distribution in the soil suggest that it arises from more than one source comparison of saline areas of the middle valley with present day salt accumulation in the delta suggests a four stagesalinization process which involves evaporation from a shallow watertable aeolian salt accumulation as clay dunes deep transformation of shell beds into gypseous layers under temporary acid conditions inducedby oxidation of pyrite under the mangrove vegetation and secondary salinization by runoff the four stage model agrees with a regional salinity chemical database and the geomorphology of the saline areas in the senegal valley the lower middle valley and the delta can therefore be regarded as a chrono sequence the recent salinity features occurring in the delta and the more developed ones upriver at the limit of the marine transgression

the southwest ryukyu arc is a migrating microplate forearc sliver abstract we propose a new interpretation for the tectonism of the southwest ryukyu arc based on inland stress field analyses and the interpretation of seismic reflection profiles the recent stress field in the southwest ryukyu arc is under tension the axial direction of which is parallel to the trench axis but an e w dextral slip shear zone is developing at its western extremity yonaguni and westwards to taiwan these features are closely related to the degree of the oblique subduction of the philippine sea plate and the strength of coupling between it and southwest ryukyu arc we regard the southwest ryukyu arc as a migrating microplate the neotectonics of the southwest ryukyu arc are attributed to the westward migration of the microplate which is bounded by the miyako depression to the east and by taiwan to the west the microplate obducting onto the eurasian plate at taiwan started to migrate westward at about 4 ma when the relative motion between two plates philippine sea and eurasian changed direction from s n to se nw in region

the origin of vertisols and their relationship to acid sulfate soils in the senegal valley in the senegal valley it is commonly considered that the acid sulfate soils of the delta are fossil soils overlain by more recent sediments and that the vertisols which abruptly overlie a thick sandy horizon result from a change in the sedimentation mode of the river however we show that both soils belong to the same pedological system extending from the delta to the limit of the last marine transgression this conclusion is based on 1 the study of soil profiles intermediate between acid sulfate soils and vertisols along a 100 m sequence in the delta 2 the mineralogy of the clay fraction 2 am in a 200 km transect along the river and 3 the similarity of the sand size distribution across the textural discontinuity between the horizons the following processes are involved in the pedological transformations 1 development of acidity by oxidation of pyrite 2 neutralization of acidity initially by the carbonate in shell beds and later by the hydrolysis of easily weatherable silicate clays the slightly alkaline river water precipitates kaolinite and later smectite at the contact between the strongly acidic and slightly alkaline environments this results in the formation of a superficial vertic clay horizon surmounting a sandy horizon therefore we emphasize that the soil morphology results from development and control of acidity and not from changes in past climates

structural characteristics of the northern okinawa trough and adjacent areas from regional seismic reflection data geologic and tectonic implications abstract analysis of regional multi channel seismic data from the northern okinawa trough and adjacent shelf provides some important constraints on the structural development of the area the sedimentary strata in the northern east china sea shelf basin separated from the okinawa trough by the taiwan sinzi belt are affected by the miocene compressional tectonism and truncated by the late miocene unconformity in contrast those in the western margin of the northern okinawa trough are cut by numerous normal faults and the late miocene horizon forms a conformable surface this suggests that the taiwan sinzi belt acted as a buttress for the northern okinawa trough against the compressional tectonism our data also reveal the ho basin in the western margin of the northern okinawa trough previously known only from proprietary industry data the longwan ridge lying between the ho basin and the northern okinawa trough may be the youngest of the relict arcs or buried ridges in the area the abrupt along strike change in the fault polarity near the northern margin of the depocenter of the ho basin suggests a nw trending left lateral transfer zone or fault the western boundary of the northern okinawa trough is characterized by the gently deepening seafloor whereas that of the southern okinawa trough is marked by steep border faults suggesting more rapid subsidence in the south this together with the well developed symmetric axial faults in the south and the greater width and the lack of well developed axial zone in the north may suggest focused rifting extension in the southern okinawa trough and diffuse rifting extension in the northern okinawa trough we postulate that the diffuse rifting extension in the northern okinawa trough is due to the tectonic perturbation caused by the convergence or subduction of the topographically high and buoyant amami plateau at the northern ryukyu arc

formation of arcs and backarc basins inferred from the tectonic evolution of southeast asia since the late cretaceous abstract results of the geological and geophysical surveys in the daito ridges and basin in the northern west philippine basin suggest that the daito ridge was an arc facing toward the south from the late cretaceous to the early tertiary the late cretaceous and tertiary history of southeast asia is evaluated based on these data in the daito ridges and basins and reconstructed based on overall plate kinematics that have operated in this area during the late cretaceous the daito ridge and the east philippine islands were positioned along the boundary between the indian and pacific plates the western half of the philippines setting on the indian plate approached from the south and collided with the east philippine daito arc either during the latest paleocene or the earliest eocene it is inferred that the bulk of the philippine archipelago rotated clockwise and borneo spun counterclockwise during the tertiary from the reconstruction the formation of backarc basins and their spreading direction are assessed as a result some primary causes and significant characteristics are suggested for the opening of backarc basins in southeast asia first opening of some backarc basins commenced with or was triggered by collisions second backarc basins opened approximately parallel to oceanic plate motion third the formation of some backarc basins was triggered by the approach of a hot spreading center fourth the spreading mode or direction of backarc basins was greatly affected by the configuration of the surrounding continent and was also rearranged to spread approximately parallel to oceanic plate motion the formation of backarc basins and their spreading direction can be reasonably explained by plate kinematics however the generative force responsible for their formation is possibly within the subduction system particularly to form horizontal tensional force in backarc side

cenozoic tectonic evolution of the east china sea shelf basin and its coupling relationships with the pacific plate subduction abstract the east china sea shelf basin is one of the mesozoic cenozoic basins located in the edge of eastern china continent whose formation and evolution are closely related to the subduction of the pacific plate however the underlying correlations between the tectonic evolution of the east china sea shelf basin and the pacific plate subduction 65 ma to present remain poorly understood in this paper the basin is divided into western and eastern depression groups to further study its tectonic evolution in combination with the characteristics of pacific plate subduction this paper performs a coupling analysis of the basin evolution regarding its migration direction and evolution rate the results of balanced section and deformation rate analyses reveal that the east china sea shelf basin experienced different regional activities during the cenozoic which could be summarized as four geologic periods and three tectonic evolution stages in this interpretation it is recognized that tectonic activity occurred in the western depression group and then shifted to depocenters of the eastern group in contrast the pacific plate subducted westwards beneath the eurasian plate over the same geologic time span surprisingly a slightly negative correlation between the intensity of the tectonic deformation of the east china sea shelf basin and the subduction rate of the pacific plate is demonstrated when the subduction rate is no more than 75 mm a however the basin deformation intensity increases with the plate subduction rate after 75 mm a the results of this work have implications for explaining the major role that the subduction of the pacific plate played in the formation and evolution of the eastern china basins

saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils variability and implications the saturated hydraulic conductivity ks of sulfuric horizons exerts a fundamental control on the connectivity between shallow groundwater and drains in coastal acid sulfate soils cass strongly influencing rates of lateral seepage towards or from field drains the ks of sulfuric horizons was assessed on seven major coastal floodplains of eastern australia using an in situ recovery technique conducted in 0 4 0 65 m deep pits duplicate recovery tests were conducted in a total of 148 pits located in 32 separate geomorphic units across the seven coastal floodplains most pits were constructed in clay soils with acidic ph 500 m day 1 data are log normally distributed and the median ks was 15 4 m day 1 over 40 of the pits had values 20 m day 1 challenging the assumption that ks in sulfuric horizons in cass landscapes is generally low visual observations confirm that high ks values were strongly associated with macropore flow these data demonstrate that ks in coastal floodplain sulfuric horizons can be very high and is extremely variable within individual floodplains these findings highlight the need for site specific assessments of soil hydraulic properties in cass in order to ensure appropriate design and application of acid management techniques

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

the relationship between topography and gravity on earth and venus abstract the measurement of the admittance between the topography and the gravity of a planet as a function of wavelength provides important constraints on its interior processes a detailed discussion of the influence of noise on such measurements shows that at long wavelengths the admittance is best determined in the frequency domain using gravity as input and topography as output this procedure is used to estimate the admittance in the pacific and indian oceans the observed values are reduced by volcanism above plumes which produces a contribution to the long wavelength compensated topography when this effect is taken into account there is little evidence that the admittance is reduced by the presence of a low viscosity zone in the upper mantle a similar study of venus shows an excellent correlation between gravity g and topography h for wavelengths greater than 700 km with an admittance of about 50 mgal km 1 this value agrees well with that expected from numerical axisymmetric models of plumes and can be used to construct maps of residual topography by calculating h g 50 where h is in kilometers and g in milligals the power spectrum of the gravity field and its skewness with positive anomalies covering a smaller area but being larger than the negative ones are also in agreement with those of the numerical models of the major topographic features only aphrodite and ishtar terrae behave differently with a value of admittance of about one third of other large structures this difference requires their topography to be partly supported by variations in crustal thickness by analogy with similar structures on earth both are likely to be supported by volcanically thickened crust on top of rising plumes though the observed relationships do not rule out other models the behavior of the admittance at long wavelengths is important because it can constrain the thickness of the convecting layer at wavelengths of more than 3000 km the gravity data provides some evidence that the layer depth is about 1000 km over the center of beta and phoebe regiones there are short wavelength anomalies of residual topography produced by crust that is thinner than that elsewhere flanked by positive anomalies of thicker crust the regions of thin crust occur beneath rift zones this behavior can be explained if crust flows down the flanks of elevated regions above plumes and can generate coronae when the plume support disappears

tidally induced melting events as the origin of south pole activity on enceladus abstract the intense activity at the south pole of enceladus hints at an internal water reservoir however there is no direct evidence of liquid water at present and its long term stability in the interior remains problematic by modeling heat production and transfer in the ice shell in a spherical geometry we show that tidal heating naturally leads to a concentration of convective hot upwellings in the south polar region favoring the preservation of liquid water at depth we show that large volumes of water are produced within the ice shell at the south pole during periods of elevated orbital eccentricity 3 5 times the present day value strong lateral variations in the melt production and crystallization rates result in stress concentration in the south polar region thus providing an explanation for the tectonic activity observed today we predict that an internal ocean may be sustained over the long term as the consequence of repeated periods with elevated orbital eccentricity leading to episodic melting and resurfacing events

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

a tear fault boundary between the taiwan orogen and the ryukyu subduction zone more than twenty seismic lines were analysed across the intersection of the taiwan orogen and the ryukyu arc forearc system the main results of this study concern the recognition of two superposed sedimentary basins that were previously unknown we have named the recent one the hoping basin and the older tectonized one the suao basin the suao basin containing sediments more than 3 km thick records subsidence of about 3 km on its southwestern portion after being shortened in the direction of plate convergence on the basis of seismicity gravity present day plate kinematics as well as seismic reflection data we relate the dramatic subsidence of the suao basin to the initiation of a wnw trending tear fault within the philippine sea plate this tear fault decouples the subducting philippine sea plate to the northeast and the apparent overthrusting philippine sea plate in the coastal range to the southwest back arc rifting may thus occur in the westernmost section of the okinawa trough above the sinking philippine sea slab while lithospheric shortening prevails south of hualien as a consequence the triangular area located southwest of the tear fault between the taiwan coastline and the toe of the yaeyama ridge no longer belongs to the ryukyu forearc it is now passively transported with the non subducting portion of the philippine sea plate we propose an evolutionary model for the relative chronology of tectono sedimentary events in this region over the last 5 m y

two phase opening model for the okinawa trough inferred from paleomagnetic study of the ryukyu arc tertiary volcanic and sedimentary rocks were collected at 50 sites of both the central ryukyu arc and the southern ryukyu arc for a paleomagnetic and geochronological study in an attempt to understand the opening of the okinawa trough back arc basin stable primary components of remanent magnetization were isolated through both thermal and alternating field demagnetization experiments from 12 sites of three geological units of the central ryukyu arc and from 12 sites of two geological units of the southern ryukyu arc the paleomagnetic results were compared with the tertiary apparent pole wander path of eurasia in order to investigate the tectonic movement of the ryukyu arc with respect to the asian continent the comparison and the radiometric ages indicate that the southern ryukyu arc rotated clockwise through 25 between 10 ma and 6 ma in contrast the central ryukyu arc experienced little rotational motion since 17 ma we propose the following two phase opening model for the okinawa trough opening the first stage took place between 10 ma and 6 ma the southern part of the trough opened by means of a wedge mode to cause the clockwise rotation of the southern ryukyu arc in the central part the parallel opening occurred and the ryukyu arc drifted without any rotation the second phase started recently in the whole okinawa trough it is observed as the present activities in the trough

present day lunette sediment cycling at witpan in the arid southwestern kalahari desert abstract witpan is a pan depression in the southwestern kalahari desert the pan fringing lunette dune has a number of notable characteristics a highly active crest the lower lunette pediment is cemented and the lower lunette supports a highly developed and active gully system geomorphological and sedimentological considerations are used to evaluate the interaction of wind and water in shaping contemporary lunette processes it is considered that like other pans in the area groundwater activity influences pan floor sediment availability and transport that the present highly sea sonal climatic regime permits the interaction of aeolian transport of sediment to the dune and its return to the pan floor by water during storm events creating a cycling process favoured by sedimentary properties that promote surface runoff

size and shape of saturn s moon titan cassini observations show that saturn s moon titan is slightly oblate a fourth order spherical harmonic expansion yields north polar south polar and mean equatorial radii of 2574 32 0 05 kilometers km 2574 36 0 03 km and 2574 91 0 11 km respectively its mean radius is 2574 73 0 09 km titan s shape approximates a hydrostatic synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to saturn than titan presently does titan s lack of high relief implies that most but not all of the surface features observed with the cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation titan s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes

origin of marginal basins of the nw pacific and their plate tectonic reconstructions abstract geometry of basins can indicate their tectonic origin whether they are small or large the basins of bohai gulf south china sea east china sea japan sea andaman sea okhotsk sea and bering sea have typical geometry of dextral pull apart the java makassar celebes and sulu seas basins together with grabens in borneo also comprise a local dextral transform margin type basin system similar to the central and southern parts of the shanxi basin in geometry the overall configuration of the philippine sea resembles a typical sinistral transpressional pop up structure these marginal basins except the philippine sea basin generally have similar or compatible rift history in the cenozoic but there do be some differences in the rifting history between major basins or their sub basins due to local differences in tectonic settings rifting kinematics of each of these marginal basins can be explained by dextral pull apart or transtension these marginal basins except the philippine sea basin constitute a gigantic linked dextral pull apart basin system formation of the gigantic linked dextral pull apart basin system in the nw pacific is due to nne to ene ward motion of east eurasia this mainly was a response to the indo asia collision which started about 50 ma ago the displacement of east eurasia can be estimated using three aspects 1 the magnitude of pull apart of the dextral pull apart basin system 2 paleomagnetic data from eastern eurasia and the region around the arctic and 3 the shortening deficits in the large tibetan plateau all the three aspects indicate that there was a large amount 1000 to 1200 km of northward motion of the south china block and compatible movements of other blocks in eastern eurasia during the rifting period of the basin system such a large amount of motion of the eastern eurasia region contradicts any traditional rigid plate tectonic reconstruction but agrees with the more recent concepts of non rigidity of both continental and oceanic lithosphere over geological times based on these three estimates the method developed for restoration of diffuse deformation of the eurasian plate and the region around the arctic and the related kinematics of the marginal basins we present plate tectonic reconstructions of these marginal basins in global plate tectonic settings at the four key times 50 35 15 and 5 ma the plate tectonic reconstructions show that the first order rift stage and post rift stage of the marginal basins are correlated with the first order slow uplift stage and the rapid uplift stage of the tibetan plateau respectively the proto philippine sea basin was trapped as a sinistral transpressional pop up structure at a position that was 20 south of its present position at about 50 ma ago or earlier while the japan arc migrated eastward during the rifting period of the japan sea basin the shikoku basin opened and the parece vela basin widened

a rigid and weathered ice shell on titan a strong inverse correlation between gravity and topography leads to the conclusion that saturn s largest moon titan must have a rigid ice shell with an elastic thickness exceeding 40 kilometres titan saturn s largest moon may have a stronger ice shell than previously thought several lines of evidence suggest that titan has a global subsurface ocean beneath an outer ice shell 50 200 km thick with a rigid portion that is thin and weak here hemingway et al report a strong inverse correlation between gravity and topography at long wavelengths that are not dominated by tides and rotation this finding is not compatible with a geologically active low rigidity ice shell suggesting that titan s ice shell must be substantially rigid with an elastic thickness of greater than 40 km several lines of evidence suggest that saturn s largest moon titan has a global subsurface ocean beneath an outer ice shell 50 to 200 kilometres thick1 2 3 4 if convection5 6 is occurring the rigid portion of the shell is expected to be thin similarly a weak isostatically compensated shell has been proposed7 8 to explain the observed topography here we report a strong inverse correlation between gravity3 and topography9 at long wavelengths that are not dominated by tides and rotation we argue that negative gravity anomalies mass deficits produced by crustal thickening at the base of the ice shell overwhelm positive gravity anomalies mass excesses produced by the small surface topography giving rise to this inverse correlation we show that this situation requires a substantially rigid ice shell with an elastic thickness exceeding 40 kilometres and hundreds of metres of surface erosion and deposition consistent with recent estimates from local features10 11 our results are therefore not compatible with a geologically active low rigidity ice shell after extrapolating to wavelengths that are controlled by tides and rotation we suggest that titan s moment of inertia may be even higher that is titan may be even less centrally condensed than is currently thought12

east asia plate tectonics since 15 ma constraints from the taiwan region abstract 15 ma ago a major plate reorganization occurred in east asia seafloor spreading ceased in the south china sea japan sea taiwan sea sulu sea and shikoku and parece vela basins simultaneously shear motions also ceased along the taiwan sinzi zone the gagua ridge and the luzon ryukyu transform plate boundary the complex system of thirteen plates suddenly evolved in a simple three plate system eu ph and pa beneath the manila accretionary prism and in the huatung basin we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations these two patterns are rotated by 15 they were formed by seafloor spreading before 15 ma and belonged to the same ocean named the taiwan sea half spreading rate in the taiwan sea was 2 cm year from chron 23 to 20 51 to 43 ma and 1 cm year from chron 20 43 ma to 5b 15 ma five plate kinematic reconstructions spanning from 15 ma to present show implications concerning the geodynamic evolution of east asia amongst them the 1000 km long linear gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the ph sea plate the formation of taiwan was driven by two simple lithospheric motions i the subduction of the ph sea plate beneath eurasia with a relative westward motion of the western end a of the ryukyu subduction zone ii the subduction of eurasia beneath the philippine sea plate with a relative southwestward motion of the northern end b of the manila subduction zone the luzon arc only formed south of b the collision of the luzon arc with eurasia occurred between a and b east of a the luzon arc probably accreted against the ryukyu forearc

estimating erosional exhumation on titan from drainage network morphology 1 drainage networks on titan earth and mars provide the only known examples of non volcanic fluvial activity in our solar system the drainage networks on titan are apparently the result of a methane ethane cycle similar to earth s water cycle the scarcity of impact craters and the uneven distribution of fluvial dissection on titan suggest that the surface may be relatively young the purpose of this study is to assess the importance of erosion relative to other plausible mechanisms of resurfacing such as tectonic deformation cryovolcanism or deposition of aerosols we present a new method based on a measure of drainage network shape known as the width function to estimate cumulative erosion into an initially rough surface we calibrate this method with a numerical landscape evolution model and successfully test the method by applying it to river networks on earth with different exhumation histories to estimate erosional exhumation on titan we mapped fluvial networks in all synthetic aperture radar swaths obtained by the cassini spacecraft through t71 application of our method to the most completely imaged drainage networks indicates that for two of four regions analyzed titan s fluvial networks have produced only minor erosional modification of the surface for the best constrained region in the northern high latitudes we find that fluvial networks reflect spatially averaged erosion of more than 0 4 but less than 9 of the initial topographic relief this result implies either a recent non fluvial resurfacing event or long term fluvial incision rates that are slow relative to the rate of resurfacing

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques