how does venus lose heat the tectonics and volcanism of the terrestrial planets are controlled by the loss of heat from the planetary interior on the earth about 70 of the heat flow through the mantle is attributed to the subduction of cold lithosphere in order to understand the tectonic and volcanic processes on venus it is necessary to understand how heat is transported through its mantle in this paper three alternative end member hypotheses are considered the first is the steady state loss of heat through the mantle to the surface in analogy to the earth however without plate tectonics and subduction on venus a steady state requires either a very high plume flux or very rapid rates of lithospheric delamination the required plume flux would be equivalent to about 80 plumes with the strength of the hawaiian plume the required delamination flux implies a 50 delamination of the entire venus lithosphere every 10 m y neither appears possible so that it is concluded that venus cannot transport heat through its mantle to its surface on a steady state basis the second hypothesis is that there has been a strong upward concentration of the heat producing elements into the crust of venus the heat generated is then lost by conduction surface measurements of the concentrations of the heat producing elements place constraints on this model if everything is favorable this hypothesis might be marginally acceptable but it is considered to be highly unlikely the third hypothesis is that heat is lost by episodic global subduction events followed by long periods of surface quiescence the near random distribution of craters suggests that the last subduction event occurred about 500 ma this model implies a thick thermal lithosphere 300 km at the present time which is consistent with a variety of surface observations lava lakes on the earth are considered as analogies to plate tectonics they also exhibit episodic subduction events

tectonic and kinematic study of a strike slip zone along the southern margin of central ovda regio venus geodynamical implications for crustal plateaux formation and evolution the tectonic system of the southern margin of central ovda regio a crustal plateau which straddles venus equator has been interpreted as a dextral strike slip array on the basis of evidence clearly identifiable as are riedel fracture patterns of different scales en echelon folds and brittle strike slip faults this transcurrent regime developed two main shear belts inner and outer on respectively thicker and thinner crust whose minimum dextral displacement has been estimated in 30 50 km since the up or downwelling models for plateau formation cannot easily explain tectonic shears of this magnitude along their margins an alternative hypothesis has been built which stands on the proposed collisional belt which could form ovda northern border king et al 1998 lunar planet sci conf 29 abstract 1209 tuckwell and ghail 2002 lunar planet sci conf 33 abstract 1566 within this framework the shear would represent a transcollisional transcurrent zone similar to the strike slip zones produced in the foreland of the himalayas tibet collision front eastern ovda would be an independent area of thickened crust pushed to the sse by the northern collision with the deformation concentrated at its margins and experiencing a shear strain on its southern margin none of the data however either supports nor helps to discard theoretical subduction events as a cause of the collision on the contrary image relationships could be interpreted as evidence that the main shear deformation took place during the last global resurfacing event on the planet

structural analysis of a sampling of tesserae implications for venus geodynamics abstract understanding the nature and timing of tessera formation is fundamental to venus tectonic and geodynamic models tesserae are commonly considered to exhibit complex deformation histories to represent the oldest global stratigraphic unit to have formed during a global phase of tesserization and to require weak lithosphere for their formation although these characterizations of tesserae are gaining widespread mention in the literature they are essentially unsupported by an assemblage of data yet they figure prominently in the way we frame and address questions about venus tectonics thus they are quickly becoming accepted paradigms despite a lack of scientific foundation open discussion of these hypotheses or assumptions is crucial because of their implications concerning geodynamic models of the surface evolution and planetary dynamics of venus we examined tessera terrain in ishtar terra crustal plateaus and as inliers within the plains using high resolution magellan radar imagery we describe several types of tessera terrain that record a wide range of structural histories fold and s c terrains are found only in ishtar terra ribbon lava flow and basin and dome terrains reside within the interior of crustal plateaus whereas folded ribbon terrain and extended folded terrain comprise margins of crustal plateaus inliers are divisible into fracture dominated and graben dominated tesserae although some inliers host early contractional fabrics the range of deformation histories recorded by the various tessera types indicates that tesserae should not be considered a single map unit tessera deformation records local to regional surface strain patterns and reflects near surface rheology at the time of deformation progressive deformation fabrics in some tessera terrain record changes in shallow crustal rheology through time thus structural analysis of individual tessera types and tessera provinces will allow us to better understand the tectonic processes responsible for tessera formation tesserae likely formed in several tectonic environments including 1 as a result of subsurface flow in ishtar terra 2 as sequences of surface layer extension and contraction in crustal plateaus 3 as flooded crustal plateaus and 4 as densely fractured surface layers fractured as a result of corona and chasma formation

lithospheric scale folding numerical modelling and application to the himalayan syntaxes we describe the eastern and western himalayan syntaxes which are large scale antiforms situated at geodynamically similar locations and the metamorphic evolution of which is coeval in the india asia collisional history to understand the mechanical plausibility of the structural interpretation we present two dimensional finite element modelling of lithospheric folding the models reveal the coeval development of adjacent synformal basins analogous to the peshawar and kashmir basins on both sides of the western syntaxis similarities between geological data and calculated models indicate that lithospheric buckling is a basic response to large scale continental shortening and an efficient mountain building process

mesoscale strike slip faults and damage zones at marsalforn gozo island malta well exposed strike slip faults in limestones in the north western part of gozo show damage zones that can be grouped into three categories based on their location along faults tip damage linking damage and distributed damage the predominant fracture types within damage zones include extension fractures and secondary faults tip damage zones usually show wedge shaped patterns formed by antithetic faults and extension fractures commonly accompanied by block rotation several fractures are combined at linking damage zones typically with the concentration of a high intensity of fractures structures in distributed damage zones are typically similar to the classical riedel shear pattern evolutionary and 3d models are proposed in terms of the geometries of damage zones for small displacement strike slip fault zones different evolutionary routes depend on fault tip modes and locations

determining heights and slopes of fault scarps and other surfaces on venus using magellan stereo radar this report presents relationships and techniques for determining the heights and slopes of discretely dipping surfaces such as normal fault scarps on the surface of venus from measurements of their widths in magellan stereo synthetic aperture radar sar images these surfaces are clearly recognizable as distinct bands of increased or decreased radar backscatter relative to flat lying areas in the 120 to 280 m resolution magellan sar images but are not generally imaged in the 10 km resolution magellan altimetry our methods take into account radar distortion effects and allow one to determine whether a slope is foreshortened laid over elongated or in radar shadow the techniques make use of graphs constructed for the magellan incidence angle profiles so that investigators can determine the local height and slope of an individual surface in a straightforward manner but the techniques are applicable to any stereo radar data set if the radar incidence angles are known additionally the techniques can be used to improve digital elevation models constructed using radar stereoscopy in areas that have steep local terrain where stereoscopic fusion may be impossible due to the effects of layover or radar shadow using these techniques we show that there are normal fault scarps on venus with heights in the 700 m range that have remarkable topographic slopes of close to 60 something unheard of on earth and which suggests a high effective cohesive strength of the venusian crust

tectonic evolution of the high himalaya in upper lahul nw himalaya india the upper lahul region in the nw himalaya is located in the transition zone between the high himalayan crystalline hhc to the sw and the tethyan zone sedimentary series to the ne the tectonic evolution of these domains during the himalayan orogeny is the consequence of a succession of five deformation events an early dl phase corresponds to synmetamorphic ne verging folding this deformation created the tandi syncline which consists of permian to jurassic tethyan metasediments cropping out in the core of a large scale synformal fold within the hhc paragneiss this tectonic event is interpreted as related to a ne directed nappe stacking shikar beh nappe probably during the late eocene to the early oligocene a subsequent d2a phase caused sw verging folding in the hhc this deformation is interpreted as contemporaneous with late oligocene to early miocene sw directed thrusting along the main central thrust in the tethyan zone a d2b phase is marked by a decollement thrust a system of reverse faults and gentle folds associated with sw directed tectonic movements this deformation is related to an imbricate structure characteristic of a shallow structural level and developed in the frontal part of a nappe affecting the tethyan zone units of se zanskar nyimaling tsarap nappe a later d3 phase generated the chandra dextral shear zone cdsz a large scale ductile dextral strike slip shear zone located in the transition zone between the hhc and the tethyan himalaya the cdsz most likely represents a part of a system of early miocene extensional and or dextral strike slip shear zones observed at the hhc tethyan zone contact along the entire himalaya a final d4 phase induced large scale doming and ne verging back folding

evidence for large scale strike slip faulting on venus radar images obtained from the magellan mapping mission reveal that much of the surface of venus has undergone tectonic deformation though normal and thrust faults are common there has been little evidence of discrete large offset strike slip faults on venus we present a clear example of large scale strike slip faulting in lavinia planitia venus our observations of the spatial and temporal relationships between the molpadia linea deformation belt and an associated fracture system indicate that the fractures were formed as the result of strike slip faulting localized along the belt global tectonism on venus is dominated by vertical deformation we attribute this example of horizontal deformation to a reorientation of the regional stress field associated with mantle downwelling

an alternative kinematic interpretation of thetis boundary shear zone venus evidence for strike slip ductile duplexes 1 on venus a 1000 km long 50 to 200 km wide anastomosing shear zone system thetis boundary shear zone tbsz separates the eastern ovda and northwestern thetis regiones previous workers mapped a part of this shear zone and interpreted it as a sinistral strike slip shear zone containing an extensional jog in the present study it is reexamined for a detailed structural and kinematic analysis and an alternative kinematic interpretation is provided the tbsz is divided into western central and eastern segments the western segment is narrow and is oriented in a ene wsw direction along its northern boundary the preexisting folds of tessera are cut by the shear zone and the folds are dragged into parallelism with the shear zone in response to dextral strike slip motion both the western and central segments contain a pair of conjugate deformation bands sigmoidal folds and linear ridges which appear similar to s c like structures of large scale ductile shear zones the acute angle between the s and c bands suggests dextral sense of displacement the eastern segment forms the northeastern restraining bend of the tbsz where the shear zone is characterized by a wide branching fan like anastomosing shear zone system with well developed contractional strike slip ductile duplexes the internal fabric defined by the sigmoidal folds consistently shows dextral sense of displacement therefore the tbsz is a dextral strike slip shear zone showing s c like structures and contractional strike slip duplexes similar to the continental scale ductile shear zones on earth

early to middle jurassic vegetation and climatic events in the qaidam basin northwest china abstract jurassic deposits are well exposed in the qaidam basin qinghai province northwest china and are regarded as one of the most completely developed early middle jurassic plant bearing sequences in northern china the early to middle jurassic palynoflora in this basin shows a high diversity of spores and pollen grains which are characterized by four palynological assemblage zones corresponding to the pliensbachian toarcian aalenian bajocian and bathonian in age vegetation reconstruction demonstrates four vegetation types upland coniferous forest in the pliensbachian coastal cheirolepidiacean forest in the toarcian lowland fern forest in the aalenian bajocian and a mixed forest in the bathonian nearest living relative analysis of the major plant groups shows that the early to middle jurassic vegetation in the qaidam basin not only consists of plants with tropical subtropical climate requirements but also those indicating temperate climatic conditions in addition bryophytes and fungi as well as cheirolepidiaceae which are generally considered to indicate warmer and or drier conditions are also documented in the palynofloras it is suggested that a temperate to subtropical climate generally prevailed during the early to middle jurassic in this basin however the vegetation features and the sedimentary data signify that an overall humid to semi humid phase was punctuated by warmer and locally dry and or arid episodes the two higher temperature and aridity events occurred in the toarcian and bathonian callovian periods in the qaidam basin these climatic events can be inferred by increase of relative abundance of classopollis pollen some tropical subtropical fern spores and the occurrences of variegated red beds and evaporite rocks these events may either be associated in some way with a transient global warming phenomenon due to an enhanced greenhouse effect or be linked with intensification of a potential monsoonal circulation such events finally caused a weakening and even arrested coal accumulation in the qaidam basin during the toarcian and the bathonian callovian intervals

catastrophic resurfacing and episodic subduction on venus abstract there is clear evidence that a catastrophic resurfacing event occurred on venus in the relatively recent past a primary data source for this resurfacing event is the spatial distribution of impact craters in this paper we apply the pair correlation technique to the observed crater distribution and find that the result is identical to that for a random distribution in order to test the sensitivity of the technique we also apply it to the spatial distribution of coronae on venus for the coronae we find substantial deviations from a random distribution one explanation for the catastrophic resurfacing is the episodic subduction hypothesis we model episodic subduction using a thermal boundary layer stability analysis we find that episodic subduction events with intervals of 500 to 700 myr can transport only 15 25 of the radiogenic heat produced within the planet we suggest that the remainder of the heat must be lost to the surface during a period of vigorous tectonic activity following the subduction event but prior to the subsequent stabilization of a global lithosphere

boudinage in multilayered rocks under layer normal compression a theoretical analysis abstract this paper presents a dynamic analysis of boudinage in multilayers of alternate brittle and ductile layers under layer normal compression based on the mode of fracturing of individual brittle layers boudinage is classified into three types tensile fracture boudinage type 1 shear fracture boudinage type 2a and extensional shear fracture boudinage type 2b the layer thickness ratio t r t b t d and the strength ratio f t 2 e between the brittle and the ductile units are the principal physical factors determining the type of boudinage type 1 boudinage develops rectangular boudins and occurs when t r is low f is high 0 8 in contrast type 2a boudinage takes place when t r is high 8 5 or f is low a r of all the types of boudins is inversely proportional to layer thickness ratio t r however type 1 and type 2 boudins have contrasting aspect ratios which are generally greater and less than 1 respectively

formation and suppression of strike slip fault systems strike slip faults are a defining feature of plate tectonics yet many aspects of their development and evolution remain unresolved for intact materials and or regions a standard sequence of shear development is predicted from physical models and field studies commencing with the formation of riedel shears and culminating with the development of a throughgoing fault however for materials and or regions that contain crustal heterogeneities normal and or thrust faults joints etc that predate shear deformation kinematic evolution of strike slip faulting is poorly constrained we present a new plane stress finite strain physical analog model developed to investigate primary deformation zone evolution in simple shear pure strike slip fault systems in which faults or joints are present before shear initiation experimental results suggest that preexisting mechanical discontinuities faults and or joints have a marked effect on the geometry of such systems causing deflection lateral distribution and suppression of shears a lower limit is placed on shear offset necessary to produce a throughgoing fault in systems containing preexisting structures fault zone development observed in these experiments provides new insight for kinematic interpretation of structural data from strike slip fault zones on earth venus and other terrestrial bodies

playa lake and sheetflood deposits of the upper cretaceous jindong formation korea occurrences and palaeoenvironments abstract lake model of the upper cretaceous jindong formation in korea was established on the basis of sedimentological and palaeobiological records of the playa lake and sheetflood deposits and their palaeoenvironmental implications the playa lake and sheetflood deposits of the jindong formation are characterized by the common presence of traces of vanished evaporites complicated polygonal desiccation cracks and rainprints the pedogenic carbonate development and the preservation of invertebrate traces and dinosaur and bird tracks the traces of vanished evaporites including halite and sulphate evaporite occur as evaporite pseudopmorphs and moulds the occurrence of all of the evaporite minerals as traces suggests that flooding stages persisted much longer than evaporation and desiccation stages invertebrates birds and dinosaurs inhabited the playa lake environment of the upper cretaceous jindong lake the jindong lake formed by the combination of humid source area and arid depositional site due to an orographic effect in fault bounded basin extensive development of the playa lake and sheetflood deposits with evaporite mineral casts and very limited association of shoreline deposits in the jindong formation are characteristic of closed lake and the jindong lake is compared to a lake formed in partly drained closed basin the aggradation of mudflat deposits indicates continued subsidence of the basin and continuation of an underfilled lake basin the jindong lake expanded and stabilized as a playa lake surrounded by dry to saline mudflats and palaeoclimate and subsidence rates changed little throughout the period of the jindong lake development

effects of crustal heterogeneity on the morphology of chasmata venus 1 the ix chel kuanja and vir ava chasmata ikvc are a 7000 km long collection of discontinuous topographic troughs and deformation suites collectively they account for approximately 12 5 of the 55 000 linear km of chasmata on venus however morphologically the ikvc differs significantly from the majority 75 of venusian chasmata because it lacks corona features coronae represent notable volumes of material both erupted onto the surface and intruded into the crust together with chasmata coronae may also be important indicators of venus s interior convective processes as well as significant contributors to venus s heat loss although ikvc lacks coronae detailed geologic and structural mapping along its length highlights previously unrecognized structural and volcanic relationships indicative of local uplift collapse and volcanism we call pseudocoronae in light of this mapping previous corona formation models theoretical and numerical are evaluated and an amended hypothesis diapir stagnation is presented for pseudocorona formation the diapir stagnation model proposes that variations of the crustal thickness perturb corona formation and thus affect their resultant surface morphology chasmata are accompanied by corona development when forming in regions of relatively thin or normal plains type crust 20 km but lack corona features when influenced by crustal heterogeneities mechanical and chemical at depth associated with thick crustal plateau roots 35 80 km e g ovda thetis and phoebe regios beneath crustal plateaus diapiric rise is inhibited by 1 the presence of a low density crustal keel that creates a deep seated density trap and 2 a composition dependent mechanically weak crust mantle boundary layer diapir stagnation can be characterized or accompanied by minimal broad doming of the surface formation of radial and concentric extension structures lateral dike propagation and collapse all of which may be accompanied by limited volume surface eruptions of the lowest density melt phases through time the crust mantle boundary layer may repeatedly lift and subside through conductive heating and viscous flow which may allow more voluminous melt migration and eruption however true coronae fail to develop

geological evolution of venus rises plains plumes and plateaus crustal plateaus and volcanic rises major physiographic features on venus both formed over mantle plumes crustal plateaus were produced by large degrees of plume melting beneath thin lithosphere the oldest tectonic features in crustal plateaus are ribbon like troughs indicating early uplift and tensile stretching their shallow depths suggest that surface temperature there was higher in the past widespread volcanic plains derived from the broad upwellings of internally heated mantle convection were continually erupted during the time of crustal plateau formation discrete volcanic rises younger than crustal plateaus formed over a thicker lithosphere with less plume partial melting the presence of only one transitional form indicates that the lithosphere thickened rapidly thermal and magmatic models show that the formation of these major features can be tied to an expected change in mantle convective style about 1 billion years ago

crustal structure of southwest japan revealed by the integrated seismic experiment southwest japan 2002 abstract a multi purpose seismic experiment named the 2002 integrated seismic experiment southwest japan was conducted in 2002 along a more than 240 km long line across southwest japan from the pacific coast to the japan sea coast its profile provides the first crustal scale cross section across the japanese island arc which highlights a number of significant points related to the structural development of the arc major outstanding points are that the japanese island arc is composed of two completely different crusts juxtaposed by the median tectonic line mtl and that the mtl started its activity associated with lower crustal thinning and formation of an upper crustal scale half graben in late cretaceous

traces of evaporites in upper cretaceous lacustrine deposits of korea origin and paleoenvironmental implications abstract diverse types of halite and sulfate evaporite traces occur in the upper cretaceous lacustrine deposits of the jindong formation and the jangdong tuff in korea in which dinosaur tracks are common the halite traces usually occur as casts or moulds and they include traces of primary halite hoppers primary and intrasedimentary skeletal halite and intrasedimentary tiny halite the sulfate traces occur as intrasedimentary and displacive casts filled with sediments and sparry calcite and the casts occur as diverse modes from single crystal casts through nodular aggregates to massive aggregates some aggregates of the sulfate casts are aligned in crack pattern and selective occurrence of the laths in ripple troughs are observed soluble sulfate evaporite minerals such as gypsum glauberite or mirabilite are probable for the precursors of these traces these halite and sulfate traces are interpreted to have been formed in a saline lake and mudflats it is interpreted that meteoric water was responsible for the evaporite precipitation in the jindong lake and jangdong lake recycled brine produced by the repeated dissolution of evaporites might contribute to the evaporite precipitation in the paleo jindong lake and the paleo jangdong lake the development of saline lake deposits in the jindong formation and the jangdong tuff suggests that the southern part of the korean peninsula remained an inland continental area during the cretaceous resulting in semi arid paleoclimatic condition due to an orographic effect by the location of the korean peninsula on continental margin in mid latitude with topographic barriers during the cretaceous the occurrence of dinosaur tracks in the lake margin deposits of saline lake with frequent inflow of dilute meteoric water suggests that upper cretaceous dinosaurs inhabiting lakes on the korean peninsula might have drunken brackish water

magellan and comparative planetology magellan data have been widely used to provide explanations for the tectonics and volcanism on venus however it is also important to compare our understanding of these processes on venus with the earth moon and mars one essential question concerning the behavior of these bodies is how does the heat get out internal heat generation and planetary cooling are the energy sources responsible for planetary tectonics and volcanism on the earth the plates of plate tectonics are the thermal boundary layers of mantle convection cells the subduction of these cold plates at ocean trenches contributes about 75 of the mantle heat flux it is now quite clear that active plate tectonics is not occurring on venus the surface of venus is a single rigid plate as is the case for the moon mars and mercury prior to magellan the general consensus was that venus was in a near uniformatarian state with conductive heat losses through the lithosphere balancing internal heat generation and secular cooling of the planet however crater studies from magellan images provide direct evidence for a catastrophic or episodic evolution of venus one explanation is that venus died tectonically 500 m y ago plate tectonics occurred during the early evolution of the planet but ceased as the radioactive heat production decreased an alternative explanation is that venus experiences episodic global subduction events two major questions concerning the earth remain largely unanswered particularly when compared with venus 1 why does the earth have continents 2 why does the earth have plate tectonics a major difference between the earth and venus is the presence of liquid water oceans during much of the evolution of the earth it has been hypothesized that water is an essential ingredient for the silicic volcanism that produces continental rocks on the earth and the absence of well defined continental masses on venus supports this hypothesis it has long been recognized that plate tectonics cannot evolve in time without internal deformation of plates plate evolution in time results in geometrical incompatibilities that require overlaps or gaps on the earth these incompatibilities lead to broad zones of continental deformation i e the western united states and china the absence of plate tectonics on venus suggests that rheologically soft continents are necessary for plate tectonics a reasonable conclusion is that the earth is the remarkable planet in terms of tectonics and volcanism not venus

global tectonic evolution of venus from exogenic to endogenic over time and implications for early earth processes venus provides a rich arena in which to stretch one s tectonic imagination with respect to non plate tectonic processes of heat transfer on an earth like planet venus is similar to earth in density size inferred composition and heat budget however venus lack of plate tectonics and terrestrial surficial processes results in the preservation of a unique surface geologic record of non plate tectonomagmatic processes in this paper i explore three global tectonic domains that represent changes in global conditions and tectonic regimes through time divided respectively into temporal eras impactors played a prominent role in the ancient era characterized by thin global lithosphere the artemis superstructure era highlights sublithospheric flow processes related to a uniquely large super plume the fracture zone complex era marked by broad zones of tectonomagmatic activity witnessed coupled spreading and underthrusting since arrested these three tectonic regimes provide possible analogue models for terrestrial archaean craton formation continent formation without plate tectonics and mechanisms underlying the emergence of plate tectonics a bolide impact model for craton formation addresses the apparent paradox of both undepleted mantle and growth of archaean crust and recycling of significant archaean crust to the mantle this article is part of a discussion meeting issue earth dynamics and the development of plate tectonics

tessera terrain and crustal plateaus venus many workers assume that tessera terrain marked by multiple tectonic lineaments and exposed in crustal plateaus comprises a global onion skin on venus a growing body of structural mechanical magmatic gravitational topographic and geologic evidence indicates that tesserae record the local interaction of individual deep mantle plumes with an ancient globally thin venusian lithosphere resulting in local regions of thickened crust

a 400 km scale strike slip zone near the boundary of thetis regio venus we present a structural analysis of an area of venus surface centred on 3 s 116 e the area is dominated by a wide zone of deformation striking 050 n distinguished from the terrain on either side of it by markedly different structural and morphological characteristics the deformation zone contains two principal fault sets defined by form position and orientation members of the first set are present along the length of the deformation zone they are discontinuous consistently right stepping and are interpreted as riedel shears in a sinistral strike slip regime members of the second fault set are interpreted as normal faults and are often seen in pairs forming extensional grabens these faults are most prominent in the central region of the deformation zone and coincide with a deflection in strike of both the first fault set and the boundaries of the deformation zone a detailed kinematic analysis of all fault orientations and the boundaries of the deformation zone fit the predictions of transtensional theory supporting the hypothesis that this sinistral strike slip zone contains an extensional jog this interpretation is further supported by analysis of the interaction between faults belonging to the two sets variation in intercept geometry kinematic linking of the two fault sets and rotation of fault strike between the two fault sets all strongly suggest simultaneous development of these structures and therefore a common tectonic origin a driving mechanism for such large scale horizontal deformation on venus has yet to be established

characteristics of jurassic continental arc magmatism in south korea tectonic implications abstract study of whole rock geochemical and isotope sr nd characteristics of jurassic plutons from south korea shows differences in chemical compositions that might reflect the jurassic tectonic environments of east asia these plutons are dominated by granites and granodiorites with subordinate intermediate monzodiorite to diorite phases all analyzed samples show depletions in ta nb p and ti and enrichment in large ion lithophile elements characteristic of high k calc alkaline i type granitoids of the active continental margin early jurassic plutons fall into two groups documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontc

system of tectonic features common to earth mars and venus investigations of landforms on the terrestrial planets have revealed a system of tectonic features consisting of long narrow regularly spaced folds and or thrust faults referred to as wrinkle ridges and conjugate sets of cross trending strike slip faults these are observed in the yakima fold belt of the columbia plateau earth the ridged plains of the tharsis province mars and the lowland plains of lavinia planitia venus the wrinkle ridges and strike slip faults reflect a relatively small amount of crustal shortening in these regions of distributed deformation the observed geometric relations between the structures are consistent with those predicted by the coulomb anderson model although the tectonic settings of the provinces studied on the three planets are very different the crustal materials appear to have deformed in a similar manner

measurements of transience and downward fluid flow near episodic methane gas vents hydrate ridge cascadia aqueous flux measurements within cold seep regions on northern hydrate ridge cascadia indicate a high degree of variability with extended periods of downflow and reversals of flow direction over periods of weeks to months local episodic venting of free methane gas was also observed the instruments recorded similar changes in hydrologic flow patterns both on and off clam fields the magnitude of the flow rates decreasing away from the clam field the coincidence of episodic gas venting with nearby highly variable aqueous fluid flow suggests that they may be coupled we propose that these observations are consistent with the action of a gas driven pump that operates somewhat like a geyser the hypothesis of gas driven pumping of seawater through northern hydrate ridge has important ramifications for the mass fluxes through this region

magma emplacement in transpression the santa olalla igneous complex ossa morena zone sw iberia the santa olalla igneous complex a late variscan group of intrusions located in the ossa morena zone sw iberia has been the focus of a gravity and structural study the structure outlined by the foliation map is complex showing two different structural domains one characterized by vertical and the other by horizontal magmatic foliations the vertical fabrics are restricted to the ne half of the complex which is in direct contact with a variscan sinistral strike slip fault cherneca fault whereas the horizontal fabrics are developed in the sw half of the complex which is characterized by a horizontal tabular geometry gravity modeling indicates that the deeper floor of the plutons is closely related to the ne margin and the cherneca fault an emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results 1 magma ascent was favored by releasing bends in the trace of the cherneca fault 2 when magma reached the present level it intruded to the sw with a horizontal sheet geometry generating the subhorizontal foliation domain 3 after emplacement the ne half of the complex suffered the external tectonic stress field provoked by sinistral motion along the cherneca fault subsequently generating the subvertical magmatic foliation domain

geologic constraints on crustal plateau surface histories venus the lava pond and bolide impact hypotheses 1 venusian crustal plateau formation is hotly debated crustal plateaus are large 1500 2500 km quasi circular 0 5 to 4 km high plateaus that host distinctive tectonic fabrics called ribbon tessera debate centers on plateau support and fabric formation detailed geologic mapping of an 360 000 km2 region eastern ovda regio provides critical clues for plateau evolution ribbon tessera fabrics record broadly synchronous layer contraction extension and flooding as an initially strong thin layer 100 m developed across ovda as the layer underwent ductile shortening and brittle extension subsurface lava flooded structural lows with progressive deformation the layer thickened leading to formation of progressively longer wavelength structures early formed shorter wavelength structures and lava filled valleys were carried piggyback on longer wavelength folds this history indicates an extremely large strength contrast that is inconsistent with a conductive geotherm reflecting instead the presence of a near surface molten layer i propose the lava pond hypothesis ribbon tessera fabrics represent progressively solidified scum of a huge lava pond leading to crustal plateau formation i further propose that individual lava ponds formed as a result of large bolide 20 30 km diameter impact with ancient thin lithosphere causing massive partial melting in the upper mantle melt rose buoyantly to form huge 1500 2000 km diameter lava ponds completely resurfacing the local area in the upper mantle depleted residuum would be compositionally more buoyant and stronger than adjacent undepleted mantle isostatic adjustment resulted in pond uplift and plateau formation subsequent secular cooling could freeze a plateau in place or mantle convection could strip away the residuum root leading to plateau collapse

structural evolution of lavinia planitia venus implications for the tectonics of the lowland plains this work shows the results of a detailed structural analysis of the deformation belts of lavinia planitia ridge belts and graben and groove belts can be observed at the studied area while wrinkle ridges and large individual grooves predominate in the smooth plains transcurrent components of displacement are commonly observed and transpression and transtension zones are the rule rather than the exception at most of the studied belts along strike azimuth changes of deformation belts are accommodated by internal variations in the predominance of contractional transcurrent or extensional structures the material of the surrounding plains embays most of these deformation belts the kinematic analysis of this complex network of tectonic structures suggests a broadly synchronous activity of contractional transcurrent and extensional structures the maximum horizontal shortening axis determined in this work describes a steady semicircular pattern centered at alpha regio this deformation continued although with subdued activity after embayment of the deformation belts by the material of the plains future study of the tectonic evolution of the lowland plains should take into account the importance of the coeval history of neighboring uplands and lowlands

opening mode of the japan sea inferred from the palaeomagnetism of the japan arc the western edge of the pacific plate is marked by a chain of back arc basins stretching from the aleutians through japan and the philippines to new zealand most of the basins lie behind volcanic island arcs far from continents and are the result of extension of the oceanic lithosphere1 but the japan sea is bounded on one side by continental crust the sikhote alin and korean peninsula of the asian continent and on the other by an active arc with continental fragments it can thus be said to be associated more with continental rifting1 4 than with oceanic processes we report here palaeomagnetic data from the japan arc which indicate that since the early miocene north east japan has rotated counter clockwise through 47 around a vertical axis while south west japan has rotated clockwise through 56 refs 5 8 we attribute this differential rotation which took place concurrently between 21 and 11 myr ago to the back arc opening of the japan sea8 with a double door mode that is there are two fan shaped spreading basins facing each other such a fan shaped opening is probably peculiar to the geological phenomenon of rifting of a continental fragment from thick continental lithosphere

mesozoic terrane accretion in northeast china sikhote alin and japan regions abstract the nadanhada range in northeast china is composed of upper paleozoic limestone greenstone middle to late triassic bedded chert and middle jurassic siliceous shale these rocks are enclosed in post middle jurassic clastic rocks the lithologic association ages radiolarian assemblages and geologic structure of the nadanhada range are very similar to those of the tamba mino ashio terrane in southwest japan this indicates that the nadanhada range is the northern extension of the tamba mino ashio terrane mesozoic tectonostratigraphic terranes identified in northeast china sikhote alin and southwest japan are the khanka terrane a micro continent composed of precambrian metamorhic rocks and paleozoic to mesozoic sedimentary and volcanic covers the nadanhada western sikhote alin terrane a disrupted terrane composed of upper paleozoic to jurassic sedimentary rocks the eastern sikhote alin terrane a terrane composed mainly of early cretaceous clastics the tetyukhe terrane a disrupted terrane composed of upper paleozoic to early cretaceous sedimentary rocks the hida terrane a continent type stratigraphic terrane composed of precambrian and upper paleozoic basement covered with jurassic to cretaceous coarse clastics and the tamba mino ashio terrane a disrupted terrane composed of upper paleozoic to earliest cretaceous sedimentary rocks accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data

evidences for a noachian hesperian orogeny in mars a number of tectonic structures have been located at the thaumasia plateau daedalia planum and aonia terra mars they include isolated folds with axial traces up to 200 km long trains of tightly folded structures tens of km long and thrusts their size and geometry are similar to those on earth and the direction of compression seems to have varied amply with time suggesting a complex tectonic evolution crater counts on the deformed terrain point to noachian to early hesperian ages on the basis of the geometry and geological relations of these structures we propose that they form part of an old martian orogen the thaumasia aonia orogen which embraced not only the thaumasia plateau but areas of daedalia planum aonia terra and nereidum montes as well a regional coherent layering is previous to the deformation and could represent the trace of even older stresses on the martian lithosphere

tessera terrain ribbon fabrics on venus reviewed could they be dyke swarms abstract endogenic and exogenic models have been developed over the past 25 years to explain the development of extensive pervasive high aspect ratio troughs and graben like structures ribbons and short to long wavelength folds in tessera terrains commonly associated with crustal plateaus on venus many of the models are complex and appear to be both internally contradictory and inconsistent with well established geological principles they are based on what amount to assumptions regarding i the secular evolution of crustal thickness ii crustal mechanical homogeneity and isotropy iii the mechanics of ribbon formation and iv the relative timing of ribbons in the structural geological sequence of tessera terrains on the basis of both theoretical and observational considerations this contribution will suggest that coupling the formation of tessera ribbons to the emplacement of dyke swarms relatively late in the structural development of tessera terrains may provide a resolution for the apparent inconsistencies in those published models

geology and distribution of impact craters on venus what are they telling us magellan has revealed an ensemble of impact craters on venus that is unique in many important ways we have compiled a data base describing the 842 craters on 89 of venus surface mapped through orbit 2578 the craters range in diameter from 1 5 to 280 km we have studied the distribution size density morphology geology and associated surface properties of these craters both in the aggregate and for some craters in greater detail we find that 1 the spatial distribution of craters is highly uniform 2 the size density distribution of large craters diameters 35 km is similar to the young crater populations on other terrestrial planets but at a much lower density that indicates an average age of only about 0 5 ga based on the estimated population of venus crossing asteroids 3 unlike the case on other planets the density of small craters diameters 35 km declines rapidly with decreasing diameters because of atmospheric filtering 4 the spectrum of crater modification differs greatly from that on other planets 62 of all craters are pristine only 4 are embayed by lavas and the remainder are affected by tectonism but none are severely and progressively depleted as extrapolated from the size density distribution of larger craters 5 large craters have a progression of morphologies generally similar to those on other planets but small craters are typically irregular or multiple rather than bowl shaped 6 diffuse radar bright or dark features surround some craters and 367 similar diffuse splotches with no central crater are observed and 7 other crater features unique to venus include radar bright or dark parabolic arcs opening westward and extensive outflows originating in crater ejecta the first three of these observations are entirely unexpected we interpret them as indicating that the planet s cratering record was erased by a global resurfacing event or events the latest ending about 0 5 ga after which volcanic activity declined but did not cease entirely since the last resurfacing event a maximum of 10 of the planet has been resurfaced and only about 4 of the craters have been obliterated convective thermal evolution models support this interpretation arkani hamed and toksoz 1984 observations 3 7 confirm quantitatively the expectation that the dense atmosphere of venus has strongly affected the production of craters large impactors have been relatively unaffected intermediate sized ones have been fragmented and have produced overlapping or multiple craters a narrow size range has produced shock induced splotches but no craters and the smallest bodies have had no observable effect on the surface the number of craters eliminated by the atmospheric filter is enormous about 98 of the craters between 2 and 35 km in diameter that magellan might have observed on a hypothetical airless venus unique crater related features such as parabolas and outflow deposits demonstrate the roles of venus high atmospheric density and temperature in modifying the crater formation process finally heavily fractured craters and lava embayed craters are found to have higher than average densities along the major fracture belts and rifted uplands connecting aphrodite terra and atla beta themis and phoebe regiones these craters thus provide physical evidence for recent volcanic and tectonic activity at a low level

fossil wood diversity gradient and far east asia palaeoclimatology during the late triassic cretaceous interval abstract mesozoic fossil floras are distributed over eastern asia china mongolia siberia korea and japan according to a regular latitudinal pattern two floras are usually distinguished a northern type and a southern type the distribution of which oscillated during the mesozoic in japan this regular pattern is disrupted by a sharp inflexion of the boundary between the two floras two competing hypotheses have been proposed to explain this disruption one hypothesis advocates later tectonic motion clouding the original pattern while the other hypothesis proposes that a warm oceanic current allowed the southern flora to grow much further north in coastal areas we used fossil wood a biotic component that has not previously been used for a palaeobiogeographical study of the region the observed fossil wood diversity at the generic level does not fit with the hypothesis of a warm oceanic current unless this hypothesis is modified to include alternating warm northbound and cold southbound oceanic currents our results provide new evidence for the palaeoecology of the mesozoic continental biota in far east asia

ribbon terrain formation southwestern fortuna tessera venus implications for lithosphere evolution abstract the term tessera has been used to describe regions of deformed venusian crust exhibiting two or more intersecting sets of structural elements however tessera includes terrains formed by a variety of spatially and temporally discrete tectonic processes tessera fabric characterizes highland plateau structure and thus understanding the nature of this deformation is critical to understanding the mode of highland plateau formation many tessera fabrics include ribbons folds and late graben in this paper we refine the geometry of ribbons through geologic mapping and radargrammetric analysis of type ribbon structures at southwestern fortuna tessera we extend our findings to ribbon fabrics at thetis regio any model of ribbon formation must account for the following constraints on ribbon geometry a ribbon forming lineaments exhibit sharp contrasts relative to adjacent materials b ribbon bounding lineaments form a distinct pattern alternating between radar dark and radar bright which represent trough walls oriented away from and toward the satellite respectively c ribbons form long narrow troughs that alternate with parallel narrow ridges ridges and troughs display extreme length width aspect ratios d trough walls are near vertical e troughs are shallow with consistent shallow depth along individual troughs and in adjacent troughs f in some cases e g southwest fortuna tessera trough walls are parallel and matched and would exhibit a close fit if the trough was closed in these cases trough walls merge laterally forming v shaped terminations trough floors are smooth and flat lacking small scale interior lineaments g in other cases e g thetis regio ribbons display a d but trough walls are defined by a series of subparallel lineaments including local interior lineaments and trough floors ramp up to join trough walls displaying parallel rather than v shaped terminations trough walls would not display a close fit if closed we propose two member types of ribbons tensile fracture ribbons and shear fracture ribbons tensile fracture ribbons display features a f and formed by the opening of tensile fractures of a thin brittle layer above a ductile substrate they require a near fracture free shallow crust and very shallow depth to the brittle ductile transition bdt the presence of ribbon structures within highland plateaus favors an upwelling model for highland plateau formation in which crustal thickening results from magmatic underplating related to a mantle upwelling or mantle plume in order for the plume to be able to anneal mechanically the crust as required by ribbon formation the lithosphere would likely have to be quite thin these implications are consistent with highland plateaus as an ancient signature of mantle plumes on thin lithosphere whereas volcanic rises which are presently thermally supported reflect thick lithosphere phoebe regio represents a transitional lithospheric thickness

venus records a rich early history the distribution and character of venus s impact craters led to the widely accepted idea that venus underwent global catastrophic resurfacing ca 500 ma and thus venus records only a short history encompassing surface evolution since postulated catastrophic resurfacing ribbon tessera terrain rtt a structurally distinctive unit represents some of venus s old est surfaces and is widely accepted as forming prior to postulated global catastrophic resur facing we constructed a global geologic map of rtt unit exposures and structural trends using national aeronautics and space administration nasa magellan data map relations illustrate that rtt displays planet scale patterns that together with altimetry record a rich geologic history that predates proposed global catastrophic resurfacing

style and sequence of extensional structures in tessera terrain venus recent studies have focused on the question of the stratigraphic sequence and thus the stages of tessera formation specifically if tessera are formed by contractional deformation followed by extensional deformation or vice versa a major question centers on the interpretation of specific lineaments within tesserae as graben bounded by faults 60 or alternatively open tension fractures dipping 90 we document and assess the origin of extensional structures in tesserae at several locations on venus noting the morphology continuity along strike parallelism of walls stratigraphic position and interaction with other structures and variability due to radar viewing geometry in each study area our analyses demonstrate that 1 the extensional structures have variable widths interior subparallel lineaments and ramp terminations 2 ridges and lineaments are continuous across the troughs where the floors of many of these structures contain the lowered sections of preexisting structures and 3 intratessera plains are seen to embay ridges and an impact crater is superposed on a ridge and in both cases these features are subsequently deformed by the extensional structures we conclude that the morphology of these extensional structures is consistent with an origin as graben not open tension fractures and that these graben postdate the ridges in each study area both the graben and the ridges of the sizes found in our survey can be formed when the brittle crust is of the order of 1 to 10 km thick to further test the tension fracture model we examine the conditions of a venus that could produce tension fractures of the dimension 1 km width of extensional structures found in tessera terrain and find that thermal gradients of a minimum of 400 to 1500 k km 1 heat flows of 800 to 3000 mw m 2 are required for a range of diabase rheologies and strain rates thought typical of venus during tessera formation such a thermal structure would favor partial melting at depths 1 km dike propagation from this region of shallow melting within the tensile stress field would produce vast quantities of volcanism mitigating against the preservation of the closely associated tension fractures this volcanism is not observed both the amplitude and sign of changes in surface temperature induced by atmospheric warming due to massive outpourings of lava are not consistent with the hotspot model on the basis of our analysis of tesserae we conclude that the ridges formed first in response to large scale contraction of the crust and that the graben formed contemporaneously and largely following this phase as the thickened crust relaxed in a manner to what is predicted and observed for plateau regions on earth such as tibet and the altiplano

quench textures in altered spherules from the cretaceous tertiary boundary layer at agost and caravaca se spain abstract abundant spherules are observed in a well preserved cretaceous tertiary boundary ktb layer at the agost and caravaca sections betic cordilleras se spain these spherules have been diagenetically altered to goethite or k feldspar different morphologies are observed ranging from perfect spheres to droplet shapes this is the first time that dendritic and fibroradial textures are reported in goethite spherules with clearly splash form morphology this morphology suggests that they originated from melt in the hot vapour plume and not as condensate as unaltered ktb spherules are composed of clinopyroxene this could be the probable precursor of part of the altered spherules at agost and caravaca which may have been derived from an expanding vapour plume with a significant contribution of extraterrestrial material in addition c rich cores have been detected in k feldspar which are enriched in ir pt pd and ni although postdepositional processes and microbial activity could have led to severe modification of the original element concentrations the high content of noble metals and ni suggests extraterrestrial contamination

structural and kinematic analysis of eastern ovda regio venus implications for crustal plateau formation crustal plateaus on venus constitute one of that planet s most intriguing tectonic features they host so called tessera terrain or deformed crust exhibiting two or more sets of intersecting tectonic lineaments which comprises 8 of venus surface major questions surrounding crustal plateaus and tessera terrain include 1 what is the nature of crustal plateau deformation what structures are present and what are their spatial and temporal relations 2 what is the global distribution of tessera terrain does it form a global layer under the regional plains cropping out in crustal plateaus or is it confined to crustal plateaus and 3 what are the implications of 1 and 2 for understanding the processes responsible for formation and deformation of crustal plateaus structural and kinematic analyses reveal that deformation at ovda regio venus largest crustal plateau is characterized by linear shallow steep sided troughs ribbons long arcuate long wavelength folds short mid wavelength folds and wide complex graben temporal relations between structures lead to a three phase regional strain history consisting of 1 layer normal flattening of a thin competent membrane resulting in radially oriented distributed extension ribbon formation 2 modest contraction of a thicker layer concentric folding at plateau margins interference folding in the plateau interior and 3 limited extension localized at fold crests graben formation wavelength analysis of ribbons and folds places limits on the thickness of the competent layer during each stage of deformation and reflects an early shallow brittle ductile transition bdt that deepened with time ovda s deformation topography and gravity are all spatially correlated strongly suggesting a genetic relationship between surface deformation and processes causing crustal thickening and plateau uplift thus tessera terrain at ovda regio is likely confined to the topographically high plateau and does not extend beneath the surrounding regional plains similar patterns persist at other crustal plateaus indicating that tessera terrain is in general confined to crustal plateaus and does not form a globally continuous layer ovda s structures their spatial and temporal relations the resulting strain history and the behavior of the bdt through time support a model of mantle plume upwelling in a thin lithospheric regime for crustal plateau formation and contradict previous downwelling models similarities between structural and kinematic trends at ovda regio and other crustal plateaus lend support to this idea c 1999 academic press

gravel bearing radiolaria as tracers for erosional events a review of the status of recent research in sw japan and korea abstract the authors introduce a case study of research on the provenance of radiolaria bearing gravels and clasts of the monomictic chert pebble conglomerates in the lower cretaceous monobegawa group a paralic molasse in the outer zone of southwest japan reconstruction of oceanic plate stratigraphy from gravels and clasts in monomictic chert pebble conglomerates based on their lithology and radiolarian ages is possible and effective for the provenance research in the case of the monobegawa group a review of provenance studies of radiolaria bearing gravels in mesozoic orogenic sediments in sw japan and korea is included the paper concludes with the discussion of the erosional events of the jurassic and pre jurassic accretionary complexes in sw japan with reference to the late mesozoic geological history in the eastern margin of asian continent

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels

pulsating continents on venus an explanation for crustal plateaus and tessera terrains we propose that tessera terrains on venus represent continental crust that does not participate in the periodic recycling of the lithosphere through global subduction events we have studied the force balance on the boundary of a continental area that survives a global subduction event using an analytical model in the proposed model the ratio between the crustal and lithospheric mantle thicknesses controls the force balance if the crust thickness is less than 2 5 of the lithospheric mantle thickness the continental area will be compressed but if the crustal thickness is higher than 2 5 of the lithospheric mantle thickness the continental area will spread out and collapse consequently if the lithospheric mantle beneath a continental region is delaminated during a global subduction event the continent will collapse generating tessera inliers dominated by extensional tectonics but if a significant portion of lithospheric mantle remains then the continental area will be compressed generating a plateau by crustal shortening the observed plateau heights can be explained by this model a 2 km height plateau can be generated by a lithospheric mantle thickness of 40 km while a 4 km height plateau can be generated by a 90 km thick lithospheric mantle we have modelled this crustal thickening of a continental area by tectonic contraction using a thin viscous sheet approach with a newtonian viscosity for the crust the force from a hot mantle elevated during a global subduction event is enough to build up a plateau by compression in 50 ma using a viscosity for the continental crust of 1021 pa s and 200 ma for 5 1021 pa s during this compressional stage concentric fold and thrust belts are generated in the plateau continent erasing any impact craters that were present the subsequent stabilization of a new crust and lithosphere in the surrounding mantle changes the force balance allowing a moderate gravitational collapse of the plateau continent accommodated by radial grabens the pulsating continent model links for the first time the generation of crustal plateaus and the origin of the volcanic plains predicting the observed equivalent effective crater density for both terrains