seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

rate of strike slip motion on the amanos fault karasu valley southern turkey constrained by k ar dating and geochemical analysis of quaternary basalts the left lateral amanos fault follows a 200 km long and up to 2 km high escarpment that bounds the eastern margin of the amanos mountain range and the western margin of the karasu valley in southern turkey just east of the northeastern corner of the mediterranean sea regional kinematic models have reached diverse conclusions as to the role of this fault in accommodating relative motion between either the african and arabian turkish and african or turkish and arabian plates local studies have tried to estimate its slip rate by k ar dating quaternary basalts that erupted within the amanos mountains flowed across it into the karasu valley and have since become offset however these studies have yielded a wide range of results ranging from 0 3 to 15 mm a 1 which do not allow the overall role and significance of this fault in accommodating crustal deformation to be determined we have used the cassignol k ar method to date nine quaternary basalt samples from the vicinity of the southern part of the amanos fault these basalts exhibit a diverse chemistry which we interpret as a consequence varying degrees of partial melting of their source combined with variable crustal contamination this dating allows us to constrain the quaternary slip rate on the amanos fault to 1 0 to 1 6 mm a 1 the dramatic discrepancies between past estimates of this slip rate are partly due to technical difficulties in k ar dating of young basalts by isotope dilution in addition previous studies at the key locality of hacilar have unwittingly dated different chemically distinct flow units of different ages that are juxtaposed this low slip rate indicates that at present the amanos fault takes up a small proportion of the relative motion between the african and arabian plates which is transferred southward to the dead sea fault zone it also provides strong evidence against the long standing view that its slip continues offshore to the southwest along a hypothetical left lateral fault zone located south of cyprus

dating of faults and estimation of surface uplift and erosion rates in the northern margin of dabie mountains china abstract absolute timing of fault movement provides information about tectonic deformation history the k ar dating method has been applied to determine the absolute timing of fault movement the key to k ar dating of fault gouge is to verify that the illite is of authigenic origin here we show effective and convincing evidences for authigenic illite in fault gouge the characteristics of the authigenic illite reveal that the host rocks were under near surface environment during fault activities the result indicates fault movement in late cretaceous in the northern margin of dabie mountains orogenic belt according to the absolute timing the uplift and erosion rates of the northern margin of dabie mountains are also estimated

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

evolutionary aspects of lithosphere discontinuity structure in the western u s 1 we have produced common conversion point ccp stacked ps and sp receiver function image volumes of the moho and lithosphere asthenosphere boundary lab beneath the western united states using transportable array data the large image volumes and the diversity of tectonic environments they encompass allow us to investigate evolution of these structural discontinuities the moho is a nearly continuous topographic surface whereas the lab is not and the seismic images show a more complex expression the first order change in lab depth in the western u s occurs along the cordilleran hingeline the former laurasian passive margin along the southwestern precambrian north american terranes the lab is about 50 deeper to the east of the hingeline than to the west with most of the increase in lab thickness being in the mantle lithosphere we infer that the moho and the lab are late mesozoic or cenozoic everywhere west of the hingeline modified during farallon subduction and its aftermath between the hingeline and the rocky mountain front the lab and to a lesser extent the moho have been partially reset during the cenozoic by processes that continue today seismicity and recent volcanism in the interior of the western u s are concentrated along gradients in crustal and or lithospheric thickness for example the hingeline and the eastern edge of the coastal volcanic magmatic terranes to us this suggests that lateral gradients in integrated lithospheric strength focus deformation similarly areas conjectured to be the sites of convective downwellings and associated volcanism are located along gradients in regional lithosphere thickness

formation of cratonic mantle keels by arc accretion evidence from s receiver functions 1 delineating mantle interfaces can provide important clues for understanding the formation of continents we use s wave receiver functions to investigate lithospheric structure along a transect extending from vancouver island to baffin island observed sp converted waves allow for interpretation of boundaries in the depth range expected for tectonic plates receiver functions show a distinct negative amplitude feature interpreted as the lithosphere astbenosphere boundary at shallow depths beneath british columbia 85km deepening abruptly at the eastern edge of the cordillera to 260km beneath the canadian shield dipping mid lithospheric discontinuities extend beneath several giant ca 1 8 ga epicontinental magmatic arcs consistent with formation of cratonic lithosphere by arc accretion this model provides a plausible explanation for global mid lithospheric discontinuities within cratons and aids in understanding their formation

thermal uplift and erosion across the continent ocean transform boundary of the southern exmouth plateau thermal evolution of the continental lithosphere at a continent ocean transform margin is examined using a two dimensional heat conduction model all heating is assumed to result from the emplacement of new oceanic ridge against the continent the assumed initial continental temperature gradient is probably best applied to regions having experienced finite duration periods of rifting lasting tens of millions of years a deep seismic reflection profile across the southern paleo transform margin of the exmouth plateau northwest australia tests the predictions of the model using this reflection profile it is estimated that up to 3 5 km of sediments have been eroded from the continental rim diminishing to almost no erosion at 60 km from the continent ocean transform boundary this trend and these values for erosion can be matched approximately using the model under the condition of local isostasy a finite difference scheme is employed where the surface elevation is the result of the competing 1 thermal uplift up 2 surficial erosion down and 3 local isostatic rebound up in response to the erosion the model predicts that most of the erosion ceases by 40 ma after ridge emplacement and that of the order of 1000 km3 eroded sediments are shed for every 10 km of transform length

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

apatite fission track thermochronological constraints on the pattern of late mesozoic cenozoic uplift and exhumation of the qinling orogen central china abstract the qinling orogen of central china was formed by intracontinental collision between the north and south china blocks the orogen comprises several micro blocks bounded by sutures and faults and has undergone long term intracontinental deformation since the late triassic the micro blocks include the southern margin of the north china block s ncb the northern qinling belt nqb the southern qinling belt sqb and the northern margin of the south china block n scb under a uniform tectonic setting in late mesozoic cenozoic these micro blocks have been subjected to a range of deformation styles as demonstrated by their structural deformation history of magmatism and the development of sedimentary basins to investigate the differences among the micro blocks and to quantify their uplift and exhumation we obtained 45 rock samples from eight mesozoic granites in these micro blocks and conducted apatite fission track aft thermochronological modeling the results reveal that the qinling orogen underwent four distinct stages of rapid cooling histories during the late mesozoic cenozoic and showed variation in uplift and exhumation whereby the intracontinental deformation started in the south the n scb and propagated to the north s ncb in the first stage during the late jurassic early cretaceous ca 160 120 ma rock cooling occurred mainly in the n scb attributed to the clockwise rotation and northward subduction of the south china block beneath the qinling orogen in the second stage compression and extension related uplift was initiated during the late early cretaceous early late cretaceous ca 120 90 ma in the sqb consistent with the southward subduction of the north china block and broadly extensional deformation in the eastern china continent in the third stage a gentle regional scale cooling event that occurred during the latest cretaceous paleocene ca 90 50 ma started in the nqb and became widespread in the qinling orogen this regional scale uplift and exhumation event was probably a response to the opposite polarity subduction beneath the qinling orogen combined with the effects of subduction of the pacific plate from the southeast the fourth stage eocene oligocene ca 50 20 ma was marked by another phase of rapid cooling in the s ncb the nqb and the nw sqb and is interpreted as being cause by the eastward tectonic escape of tibetan plateau related to india asia collision furthermore the record of variable timings and rates of cooling of these micro blocks together with regional structural analysis indicates that the late mesozoic cenozoic intracontinental deformation in the qinling orogen was characterized by a spatiotemporally variable and propagating style uplift and exhumation of the micro blocks and the predominant deformation was through displacement across various boundary sutures and faults

k ar dating of fault gouge in the northern sydney basin nsw australia implications for the breakup of gondwana abstract the occurrence of synkinematic and authigenic clay minerals is a common feature in fault gouges few attempts have been made to date fault gouges we present the first age data in australia for synkinematic illite smectite growth in two fault zones of the northern sydney basin nsw the faults occur at burwood beach nsw in the northern part of the sydney basin and are hosted by early permian siltstones tuffs and coals of the lambton formation newcastle coal measures the faults are 1 5 m apart show normal displacement and trend n s with steep easterly dips foliated gouge zones comminution and dilational breccias are developed along both fault surfaces k ar ages extracted from samples in the gouge and tuffs in the damage zones are 172 6 10 m to 119 ma 2 m 237 245 ma for the

gravity waves in the troposphere and stratosphere during the macwave midas summer rocket program 1 combining data taken during the macwave summer rocket campaign at the andoya rocket range 69 3 n 16 0 e with a lidar radiosondes falling spheres and vhf radars at andoya and at the esrange the gravity wave content of the troposphere and stratosphere during the campaign nights was analyzed the lidar yielded vertical wavelengths and periods of gravity waves in the stratosphere a stokes parameter analysis was performed for the radiosonde and falling sphere data to estimate propagation directions of the gravity waves the wave content in the troposphere was inferred by applying wavelet and cross spectral methods to the radar data we found propagation conditions and spectra of the waves to vary with height following the change in the background wind the waves were excited both at the ground and in the tropopause lower stratosphere region

holocene mean uplift rates across an active plate collision boundary in taiwan samples of holocene fossil coral from uplifted reefs of three tectonically distinct yet geographically proximal regions of taiwan have been dated by uranium series and 14c isotopes applying corrections for altitude change caused by sea level fluctuations enables evaluation of long term average holocene uplift rates for three areas across an active convergent margin i the hengchun peninsula of the eurasian tectonic plate ii the eastern coastal range of taiwan a plate boundary and iii two offshore islands lanyu and lutao both situated on the leading edge of the adjoining philippine plate the data indicate that while all three areas have experienced uplift through the holocene plate collision has caused significantly higher uplift rates in the region directly along the plate boundary

recent subsidence of the venice lagoon from continuous gps and interferometric synthetic aperture radar 1 coastal regions are increasingly affected by larger storms and rising sea level predicted by global warming models aggravating the situation in the city of venice where tidal induced seasonal flooding coupled with natural and anthropogenic subsidence have been perennial problems in light of accelerated efforts to protect venice from the rise in sea level we assess land subsidence in the venice lagoon over the last decade through a combined analysis of gps position time series from 2001 55 to 2011 00 for four stations installed by the magistrato alle acque di venezia and thousands of observations of insar permanent scatterers using radarsat 1 images from 2003 3 to 2007 85 we determine that the northern lagoon subsides at a rate of 2 3 mm yr whereas the southern lagoon subsides at 3 4 mm yr the city of venice continues to subside at a rate of 1 2 mm yr in contrast to geodetic studies in the last decade of the 20th century suggesting that subsidence has been stabilized the gps results indicate a general eastward tilt in subsidence and that the natural subsidence rate related to the retreat of the adriatic plate subducting beneath the apennines is at least 0 4 0 6 mm yr our combined gps and insar analysis demonstrates high spatial resolution in the vertical direction with a precision of 0 1 0 2 mm yr with respect to a global reference frame continued efforts to secure the city of venice from flooding must also take into account the significant local and regional subsidence rates as well as the expected rise in sea level

lithosphere asthenosphere interaction beneath the western united states from the joint inversion of body wave traveltimes and surface wave phase velocities summary the relation between the complex geological history of the western margin of the north american plate and the processes in the mantle is still not fully documented and understood several pre usarray local seismic studies showed how the characteristics of key geological features such as the colorado plateau and the yellowstone snake river plains are linked to their deep mantle structure recent body wave models based on the deployment of the high density large aperture usarray have provided far more details on the mantle structure while surface wave tomography ballistic waves and noise correlations informs us on the shallow structure here we combine constraints from these two data sets to image and study the link between the geology of the western united states the shallow structure of the earth and the convective processes in mantle our multiphase dna10 s model provides new constraints on the extent of the archean lithosphere imaged as a large deeply rooted fast body that encompasses the stable great plains and a large portion of the northern and central rocky mountains widespread slow anomalies are found in the lower crust and upper mantle suggesting that low density rocks isostatically sustain part of the high topography of the western united states the yellowstone anomaly is imaged as a large slow body rising from the lower mantle intruding the overlying lithosphere and controlling locally the seismicity and the topography the large e w extent of the usarray used in this study allows imaging the slab graveyard a sequence of farallon fragments aligned with the currently subducting juan de fuca slab north of the mendocino triple junction the lithospheric root of the colorado plateau has apparently been weakened and partly removed through dripping the distribution of the slower regions around the colorado plateau and other rigid blocks follows closely the trend of cenozoic volcanic fields and ancient lithospheric sutures suggesting that the later exert a control on the locus of magmato tectonic activity today the dna velocity models are available for download and slicing at http dna berkeley edu

imaging crustal and upper mantle structure beneath the colorado plateau using finite frequency rayleigh wave tomography a new 3 d shear velocity model of the crust and upper mantle beneath the colorado plateau and surrounding regions of the southwestern united states was made with finite frequency rayleigh wave tomography using earthscope usarray data the goal of our study is to examine the colorado plateau lithospheric modification that has resulted from cenozoic tectonism and magmatism we have inverted for the isotropic vs model from a grid of rayleigh wave dispersion curves obtained by a modified two plane wave method for periods from 20 to 167 s we map the lithosphere asthenosphere boundary under the colorado plateau by identifying the middle of the shallowest upper mantle negative vs gradient the depths of the lithosphere asthenosphere boundary inferred here agree well with receiver function estimates made independently the strong lateral heterogeneity of shear velocity can be mainly attributed to 200 400 k variations in temperature together with 1 partial melt fraction in the shallow upper mantle the resulting vs structures clearly image the upper mantle low velocity zones under the colorado plateau margins that are associated with magmatic encroachment these upper mantle low velocity zones resulted from the convective removal of the colorado plateau lithosphere that had been rehydrated by subduction released water refertilizing and destabilizing it this convective erosion by the asthenosphere at the low viscosity part of the lithosphere is driven by the large step in lithospheric thickness and the thermal gradient across the boundary between the plateau and the extended basin and range since the mid cenozoic at a rate similar to that of magmatic migration into the plateau from the southeast south and northwest moreover the rayleigh wave tomography model images parts of a high velocity drip in the western colorado plateau and thus provides additional seismic evidence for ongoing convective downwelling of the lithosphere that was initially suggested by receiver functions and body wave tomography the widespread edge convective erosion which the regional delamination style downwelling processes are a 3 d manifestation of could provide additional buoyancy sources to support the excess uplift at the margins of the plateau

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

how the crust meets the mantle lithoprobe perspectives on the mohorovicic discontinuity and crust mantle transition application of regional geophysical and geological methods throughout two decades of canada s lithoprobe project provides new opportunities to analyze the mohorovicic discontinuity moho and crust mantle transition the transect format employed during lithoprobe in which 10 specified regions of canada were targeted for approximately a decade each between 1984 and 2003 permitted teams of scientists to focus on geological geophysical and tectonic issues for each transect as a primary objective was to enhance knowledge of the structure of the crust and lithosphere an obvious target in each transect was the nature and origin of the moho and crust mantle transition accordingly the combined results provide new perspectives on the moho and the relationship of the moho to the crust mantle transition perhaps the most important result is that the continental geophysical moho is a deceptively simple feature it has a variety of signatures at different scales that preclude a single universally applicable interpretation in methods that provide large scale information such as regional seismic studies it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity however its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical moho which are complex and varied in some areas within canada it appears that the geophysical moho may be old and perhaps remains from the time the crust formed in other areas it appears to be a relatively young feature that was superimposed onto older crustal fabrics

deep probe imaging the roots of western north america analysis of the lithoprobe deep probe and southern alberta refraction experiment data sets focusing on the region between deep probe shots 43 and 55 has resulted in a continental scale velocity structural model of the lithosphere of platformal western laurentia reaching depths of 150 km three major lithospheric blocks were investigated i the hearne province a typical continental archean cratonic province lying beneath the western canada sedimentary basin ii the wyoming province an even older block of phanerozoic modified archean crust with an enigmatic lower lithosphere and iii the yavapai mazatzal province proterozoic terranes underlying the colorado plateau and southern rocky mountains in this study the northern two of these regions are investigated with a modified ray theoretical traveltime inversion routine that respects the spherical geometry of the earth the resulting crustal velocity structure combined with supporting geological and geophysical data reveals that the medicine hat block mhb lying between the hearne and wyoming provinces is a third independent archean crustal block the subcrustal lithosphere along the profile is homogeneous in velocity structure but two significant northward dipping reflectors are apparent and interpreted as relic subduction zones associated with sutures between the three archean blocks the hearne crust is typical of an archean shield or platform both in its thickness of 34 50 km and its seismic velocity structure the crust of the archean mhb and wyoming province which ranges in thickness from 49 to 60 km includes a 10 30 km thick high velocity layer interpreted to be proterozoic in age such a feature is unexpected beneath archean crustal provinces but if the region is considered to be the remanent marginal portion of a larger archean continent then the interpreted proterozoic underplating and lack of an archean lithospheric root can be explained the variable topography along the reflective upper and lower boundaries of this layer especially within the mhb suggests considerable variability in its emplacement and subsequent tectonic history

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

what brought them up exhumation of the dabie shan ultrahigh pressure rocks metamorphic coesite and diamond in the dabie shan eastern china testify to subduction of continental crust to 100 km depth exhumation of these ultrahigh pressure rocks through the crust encompassed two stages 1 south dipping foliation southeast plunging stretching lineation lineation parallel isoclinal folds and boudins indicate extreme subhorizontal shortening and subvertical extension during top to northwest shearing at 200 180 ma syntectonic recrystallization occurred at eclogite and amphibolite facies temperatures and at pressures below coesite stability 2 northwest southeast subhorizontal extension from 133 to 122 ma was concentrated within an asymmetric structural dome in a magmatic complex that forms the northern half of the dabie shan pluton cores at deep structural levels have weak hypersolidus fabrics and pluton carapaces are mylonitic gneisses formed at upper amphibolite facies conditions deformation is concentrated in greenschist facies mylonites and ultramylonites along the xiaotian mozitang detachment fault at the northern topographic limit of the dabie shan our preferred exhumation model involves two stages triassic indentation vertical extrusion and erosion followed by cretaceous plate margin transtension

hydrocarbon charge history of the silurian bituminous sandstone reservoirs in the tazhong uplift tarim basin china the tarim basin is the largest inland basin in china the hydrocarbon charge history of the silurian bituminous sandstone reservoirs in the tazhong uplift was investigated using an integrated approach combining detailed petrographic analysis thin section scanning electron microscopy and transmission electron microscopy clay mineral x ray diffraction characterization and modeling of authigenic clay minerals and subsequent potassium argon k ar dating of authigenic illite the timing of the hydrocarbon charges of the reservoirs in the tazhong uplift area is compared with that of the kongquehe area within the basin the authigenic illite ages in the tazhong uplift area and the kongquehe area range from 383 ma to 204 ma indicating a unique age distribution pattern in the basin the silurian oil accumulations were primarily formed in the late caledonian through the late hercynian the reservoirs within wells qiao 1 kongque 1 longkou 1 and yingnan 2 located in the western area and the eastern area of the basin were charged around 383 to 271 ma in the late caledonian to the early hercynian the reservoirs in wells tazhong 37 tazhong 67 tazhong 12 and tazhong 32 located in the center of the basin were charged at around 235 to 204 ma in the late hercynian a correlation between the authigenic illite ages and the thickness of the silurian bituminous sandstones suggests that the paleostructural framework is a key controlling factor the paleo oil pool located in and around the sedimentary centers such as wells qiao 1 and kongque 1 was formed relatively early 383 ma the k ar dating results were consistent with the results of conventional hydrocarbon accumulation history analysis and highlight the differences in the accumulation timing between various oil pools in different parts of the basin

rates of continental erosion and mountain building the first objective of this work was to obtain values for the rates at which continental erosion can smooth out or remove the topographic expression produced by orogeny the dominant part is played by mechanical erosion which acts most strongly in regions of large topographic expression chemical erosion depends strongly on precipitation or runoff in individual river drainage basins but because most continents have very similar average rainfall chemical erosion is fairly uniform for continental sized areas and will succeed in planing down all continents to a level peneplain if given enough time the exception to this rule is australia which has a very low chemical erosion rate because of its dryness the time constants for mechanical and chemical erosion so obtained vary between about 30 and 300 my depending on the continent and the assumptions made mountain building occurs throughout the geological time scale but at a non uniform rate although there will not be a balance between erosion and mountain building over a short time scale due to the non uniform rate of mountain building the long term situation must be that the two phenomena should balance out it is shown that the freeboard of continents will respond to the long term balance between mountain building and erosion an expression has been derived for the average continental elevation in which the rate of mountain building depends on the rate of radiogenic heat production within the earth it is shown that relatively small changes in average elevation above sea level of a few hundred metres are predicted to have occurred since the beginning of the proterozoic as mountain building is predicted to decrease on average with time because of the reduction in internal heat generation and as erosion is dependent on the average elevation this average elevation will decrease slowly through time the opposite of what some workers have predicted a more complicated model of mountain building is then investigated in which one component of mountain building has a sinusoidal signal the oscillations in average elevation depend on the period of the sinusoid being smaller for shorter periods finally an average continental elevation is derived using a list of real orogenic events although this list of orogenies is incomplete there is some indication that the actual continental elevation as seen in the flooding history of the continents is similar to that derived in this paper

timing of brittle deformation within the nojima fault zone japan abstract k ar ages from clay fault gouges of outcrop and core samples ug500 well from the nojima fault zone awaji island japan are consistent internally with established field constraints and with apatite and zircon fission track ages demonstrating the suitability of this method for dating of brittle deformation six unspiked and thirty conventional k ar data of clay minerals separated from gouge zones were analysed characterized by protoliths of high grade metamorphic and magmatic rocks the samples from the nojima fault zone offer the opportunity to distinct identify newly grown illite in the fault planes all dated sample fractions were characterized by xrd sem and tem k ar ages of 29 separates have an age range from 63 4 1 3 ma early palaeocene danian to 42 2 1 0 palaeogene middle eocene lutetian some

kar systematics of illite smectite in argillaceous rocks from the ordos basin china abstract conventional k ar dating x ray diffraction analyses illite crystallinity determinations and quantitative infrared spectroscopy mineral analyses were carried out on clay materials of the mesozoic and paleozoic argillaceous rocks from the ordos basin china in order to date the illite smectite diagenesis and to evaluate the influence of detrital contamination on the k ar ages a clay mineral assemblage of illite i s chlorite kaolinite was determined two different stages of illite diagenesis were distinctly identifiable which can be correlated to two thermal and or fluid flow events accompanying well known major tectonic movements in china a jurassic diagenetic event 170 160 ma is related to the early yanshanian movement whereas a silurian devonian diagenetic age 420 370 ma corresponds to the late caledonian movement no influence of the jurassic event is evident on the silurian devonian diagenetic illite attesting to the good retentivity of diagenetic illite for argon principles for estimating any influence on the k ar data of a size fraction by detrital contamination are discussed decreasing illite crystallinity and increasing or constant k ar data with increasing depth indicate that authigenic illite predominates and that the k ar data are diagenetic with little detrital influence furthermore the correlation between k ar ages and depth can reveal the temperature controlled mechanisms of the diagenetic illitization process increasing k ar ages with depth reflects burial diagenesis while constant k ar ages with depth indicates a diagenetic event caused by a short lived thermal event as shown in our study