evolution of mesozoic sandstone compositions southern junggar northern tarim and western turpan basins northwest china a detrital record of the ancestral tian shan abstract sandstone compositional data can be a powerful tool in the interpretation of tectonic and climatologic influences on sedimentary basin fill in addition to yielding important information about porosity in sandstone petroleum reservoirs in order to explore these relationships a modified gazzi dickinson point counting technique was used to analyze the composition of 143 mesozoic sandstone samples from the southern junggar northern tarim and western turpan basins of northwestern china results indicate that a mesozoic ancestral version of the tian shan physiographically separated the junggar and tarim basins and provided sand of very different composition to each basin mesozoic sandstone from the northern tarim basin is diverse in composition and lithic rich qm41f14l45 qp42lvm26lsm32 is locally micaceous and contains common radiolarian chert grains and few dense accessory minerals inferred source rocks include upper paleozoic alkali granite and metamorphic complexes thick silurian bedded chert sequences and lower paleozoic strata of a passive continental margin in contrast sandstone from the southern junggar and western turpan basins is uniformly volcanic rich qm21f21lt58 qp13lvm68lsm19 and contains abundant dense accessory minerals and only local radiolarian chert and mica inferred principal source rocks are devonian carboniferous andesitic arc volcanics the effect of sampling scale on sandstone composition outweighs that of plate tectonic setting samples were derived mostly from medium and coarse grained fluvial systems that likely drained only portions of the ancestral tian shan and hence preserve local source rock signatures rather than an integrated compositional signal that can be directly compared to plate tectonic petrofacies models in addition though mesozoic basins of western china were most akin to broken foreland basins mesozoic sandstone is considerably more compositionally diverse and lithic rich than that of modern or ancient broken foreland basins because of the variety of accreted terranes constituting the ancestral tian shan temporal changes in sandstone composition are consistent with episodes of mesozoic deformation in the tian shan each deformational episode increased physiographic relief of the ancestral range produced renewed downcutting and erosion of source rocks and resulted in the deposition of compositionally very immature sandstone in adjacent basins although a regional early mesozoic megamonsoon and an early cretaceous rain shadow cast across the northern tarim basin are interpreted from regional facies and paleontologic data neither paleoclimatic phenomenon appears to have significantly modified sandstone composition in the study area calculations of intergranular volume porosity cement indicate that porosity in sandstone from the tarim and junggar basin depocenters was reduced principally by burial compaction and that the rate of porosity reduction was highest for lithic rich samples

late cenozoic tectonic evolution of the northwestern tien shan new age estimates for the initiation of mountain building the tien shan are the quintessential intracontinental range situated more than 1000 km north of the suture between india and asia their initiation and growth in the cenozoic however remain poorly understood in this study we present stratigraphic detrital fission track and magnetostratigraphic results that provide a basis for reconstructing the cenozoic tectonic evolution of the kyrgyz range and adjacent chu basin in the northwestern tien shan detrital fission track thermochronology indicates that the northwestern tien shan was tectonically quiescent for much of the cenozoic prior to uplift and exhumation in the late miocene the kyrgyz range was buried by sediments shed from highlands to the south and or east paired bedrock fission track and u th he ages from a sampling transect of 2 4 km relief demonstrate that rapid exhumation commenced at ca 11 ma initial thrusting in the hinterland was followed by evaporite accumulation 0 4 km m y which coincided with erosion of the pre 11 ma strata that mantled the kyrgyz range between 10 and 3 ma bedrockexhumation rates decreased to 0 3 km m y while sedimentation rates decelerated initially to 0 25 km m y before accelerating to 0 4 km m y at 4 5 ma detrital fission track results indicate that by 4 5 ma

on the inference of denudation rates from cooling ages of minerals abstract the inference of denudation rates from the temperature time histories of rocks is not straightforward because the geothermal gradient evolves with time as denudation advects heat towards the land surface we show that the curvature in the temperature time path recorded by an exhumed rock is strongly dependent upon denudation rate and upon the temperature of the rock before denudation began but only weakly dependent upon the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation for the case in which denudation rate is constant a systematic search of parameter space yields robust estimates of denudation rate and of the initial temperature if there is prior knowledge of the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation this may be used further to limit the acceptable ranges of the other two parameters application of this procedure to two geological examples suggests that denudation rates in the nanga parbat massif are lower and less variable than previously suggested and that the inference drawn from accelerated cooling rates of accelerating denudation in the andes is incorrect

formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

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

tectono thermal evolution of the southwestern alxa tectonic belt nw china constrained by apatite u pb and fission track thermochronology abstract the central asian orogenic belt caob is regarded to have undergone multiple phases of intracontinental deformation during the meso cenozoic located in a key position along the southern caob the alxa tectonic belt atb connects the northernmost tibetan plateau with the mongolian plateau in this paper we apply apatite u pb and fission track thermochronological studies on varieties of samples from the southwestern atb in order to constrain its thermal evolution precambrian bedrock samples yield late ordovician early silurian 430 450 ma and late permian 257 ma apatite u pb ages the late paleozoic magmatic sedimentary samples yield relatively consistent early permian ages from 276 to 290 ma these data reveal that the atb experienced multiple paleozoic tectono thermal events as the samples passed through the apatite u pb closure temperature 350 550 c we interpret these tectonic events to record the long lived subduction accretion processes of the paleo asian ocean during the formation of the southern caob with possible thermal influence of the permian tarim mantle plume apatite fission track aft data and thermal history modelling reveal discrete low temperature thermal events for the atb inducing cooling reheating through the aft partial annealing zone 120 60 c during the permian the samples underwent rapid cooling via exhumation or denudation from deep crustal levels to temperatures

the thermo tectonic history of the song kul plateau kyrgyz tien shan constraints by apatite and titanite thermochronometry and zircon u pb dating abstract the song kul basin sits on a plateau at the northern and middle kyrgyz tien shan junction it is a lacustrine basin occupied by lake song kul and predominantly developed on igneous basement this basement was targeted for a multi method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present day morphology zircon u pb dating by la icp ms revealed four different magmatic episodes a late cambrian 500 ma island arc system a late ordovician 450 ma subduction related intrusion an early permian 290 ma collisional stage and a middle to late permian 260 ma post collisional magmatic pulse middle to late triassic 200 230 ma titanite fission track ages and late triassic early jurassic 180 210 ma apatite fission track ages and thermal history modeling indicate the song kul basement was already emplaced in the shallow crust at that time an exhumed fossil apatite fission track partial annealing zone is recognized in the bordering song kul mountain ranges the area experienced only minor post early mesozoic denudation the igneous basement was slowly brought to apatite u th he retention temperatures in the late cretaceous palaeogene miocene to present reactivation of the tien shan does not manifestly affect this part of the orogen

denudation and cooling of the lake teletskoye region in the altai mountains south siberia as revealed by apatite fission track thermochronology abstract lake teletskoye occupies a narrow graben located in the northwestern sector of the altai fold belt in south siberia the lake basin is thought to have formed during the pleistocene as a distant result of the cenozoic collision of india and eurasia that caused a tectonic reactivation of the palaeozoic gorny altai ga and west sayan ws blocks the present work reports of a pilot fission track study performed on 13 apatite separates collected from rocks that were sampled along two profiles in close proximity of the lake the age length data and aft thermochronological modelling reveal two important phases of cooling in the altai mountains a first one during the late jurassic early cretaceous and a second one that started in the miocene pliocene and that persists until today the first event is interpreted to result from uplift induced denudation probably related to the closure of the mongol okhotsk ocean the second event can be linked to the young cenozoic movements that lie at the origin of the formation of the lake teletskoye basin

fault reactivation in the junggar region northwest china the role of basement structures during mesozoic cenozoic compression basement structures exposed at the margins of the junggar basin were created during the altaid orogeny in the late palaeozoic the most prominent structures are backstops to subduction accretion complexes north tien shan fault or major thrusts within these complexes dalabute and kelameili faults both types of basement structure are far more common in accretionary turkic type orogens such as the altaids than true sutures probably the only suture sensu stricto in the junggar area is cryptic and lies under the junggar basin s thick mesozoic cenozoic cover the exposed palaeozoic fault zones have been reactivated by mesozoic cenozoic compressional events which are the long distance expression of orogenies at the southern margin of asia latest palaeozoic and mesozoic events reactivated a larger number of fault zones than have been affected by the cenozoic india asia collision possibly because of an increase in the strength of the junggar basement over time following late permian rifting cenozoic strain is partitioned between strike slip motion on basement structures within the palaeozoic orogenic belts around the junggar basin and numerous thrusts and transpressive faults in regions marginal to and within the basin itself most major strike slip faults are reactivated structures and occupy narrower zones than their palaeozoic precursors thrust zones follow the palaeozoic basement grain but active faults have propagated into the mesozoic cenozoic cover

early cretaceous denudation related to convergent tectonics in the baikal region se siberia we present 24 new apatite fission track aft ages and 18 track length measurements from the baikal region se siberia most samples have aft ages between 140 and 100 ma with relatively high mean track lengths c 13 2 m the relationship between aft ages elevation and mean track lengths indicate that the samples record rapid cooling during the early cretaceous 140 120 ma as also shown by thermal history inversion of track length distributions cooling took place during a late jurassic early cretaceous orogenic phase related to closure of the mongol okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting basin inversion and large vertical motions the variation in aft ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role minimum amounts of early cretaceous denudation are estimated at 2 3 km

tectonic history of the kyrgyz south tien shan atbashi inylchek suture zone the role of inherited structures during deformation propagation 1 multimethod chronology was applied on intrusives bordering the kyrgyz south tien shan suture stss to decipher the timing of 1 formation and amalgamation of the suturing units and 2 intracontinental deformation that built the bordering mountain ranges zircon u pb data indicate similarities between the tien shan and tarim precambrian crust caledonian 440 410 ma and hercynian 310 280 ma zircon u pb ages were found at the edge of the stss related to subduction and closure of the turkestan ocean and the formation of the suture itself permian triassic 280 210 ma titanite fission track and zircon u th he data record the first signs of exhumation when the stss evolved into a shear zone and the adjacent tarim basin started to subside low temperature thermochronological apatite fission track zircon and apatite u th he analyses reveal three distinct cooling phases becoming younger toward the stss center 1 jurassic cretaceous cooling ages provide evidence that a mesozoic south tien shan orogen formed as a response to the cimmerian orogeny 2 early paleogene 60 45 ma data indicate a renewed pulse of stss reactivation during the early cenozoic 3 neogene ages constrain the onset of the modern tien shan mountain building to the late oligocene 30 25 ma which intensified during the miocene 10 8 ma and pliocene 3 2 ma the cenozoic signals may reflect renewed responses to collisions at the southern eurasian border i e the kohistan dras and india eurasia collisions this progressive rejuvenation of the stss demonstrates that deformation has not migrated steadily into the forelands but was focused on pre existing basement structures

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

a mid cretaceous change from fast to slow exhumation of the western chinese altai mountains a climate driven exhumation signal abstract the chinese altai mountains in western china are bound by cenozoic transpressional strike slip faults many of which show quaternary activity to better understand how mesozoic cenozoic deformation has affected the history of exhumation and uplift of the chinese altai mountains we collected paleozoic granitoid samples for apatite fission track and apatite u th sm he thermochronology central apatite fission track ages for n 6 samples range from 68 to 104 ma whereas apatite u th sm he ages range from 56 to 272 ma for n 23 samples n 80 individual analyses across four transects in the western chinese altai our results indicate fast cooling during the late early cretaceous followed by slow cooling since thermal modeling results suggests

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

episodic exhumation and related tectonic controlling during mesozoic in the eastern tian shan xinjiang northwestern china abstract the eastern tian shan ets which is located in the southern margin of the central asian orogenic belt experienced multiple cooling episodes during the mesozoic however the topography and cooling pattern of the region have been extensively affected by complex structural deformations here we combined a detailed structural analysis with new and existing low temperature thermochronological data from the eastern ets moqingwula range to constrain the process of deformation and exhumation during the mesozoic our results indicate that two phases deformation occurred in the late jurassic and the late cretaceous to the paleocene that transformed the landscape of the moqingwula range the first phase tilted the northern moqingwula range coinciding with folding and thrusting the second phase of deformation disrupted planation surfaces which dominantly formed in the early cretaceous and were preserved on the summit of the ranges our new data reveals three prominent cooling episodes during the 222 ma 138 113 ma and 68 57 ma as well as another subdued cooling phase during 113 92 ma in addition through integration of the regional cooling history and topographic evolution we discuss the geodynamics of the deformations and exhumations associated with tectonism within the central asian orogenic belt

tertiary strike slip faulting in southeastern mongolia and implications for asian tectonics abstract geologic maps have long portrayed the late cretaceous recent geologic history of southeastern mongolia as tectonically quiescent we present new data based on outcrop observations that indicate the northeast trending east gobi fault zone egfz was reactivated in the cenozoic as a sinistral strike slip fault system inversions of cenozoic fault slip data imply that faulting was associated with north northwest subhorizontal shortening and east northeast subhorizontal extension we propose that faulting is tertiary in age based on published interpretations of seismic reflection data which reveal that the mid cretaceous 100 95 ma unconformity is deformed by strike slip faults and based on field observation of strike slip faults and fracture sets that cut upper cretaceous and cenozoic strata but lack evidence for neotectonic activity published seismicity maps also appear to argue against significant quaternary faulting within the egfz these new data may lend credence to published models proposing a middle miocene or older kinematic linkage between the egfz and the altyn tagh fault in china the recognition that the egfz has a history of left lateral displacement in both the early mesozoic and cenozoic means that currently available estimates of offset based on displaced paleozoic rocks constrain total offset only this reactivation history supports the notion that inherited lithospheric structures are important in controlling the location and thus modes of intracontinental deformation in asia as a function of collisional far field effects and evolving boundary conditions of the pacific margin

combined apatite fission track and single grain apatite u th he ages from basement rocks of central dronning maud land east antarctica possible identification of thermally overprinted crustal segments abstract apatite fission track ft and single grain u th he ages from four vertical profiles in central dronning maud land east antarctica range from 312 20 ma to 135 11 ma and 304 28 ma to 104 8 ma respectively the combined age data allows to discriminate between undisturbed cooled due to exhumation and thermally overprinted crustal blocks profiles at the zwieselhohe and the conradgebirge revealed unusual apatite ft vs elevation relationships and u th he ages older than the corresponding central apatite ft ages possibly providing evidence for a jurassic thermal overprint most probably jurassic magmatism and associated advective heating led to total annealing of the apatite fission tracks but helium only partially diffused the model developed in this paper suggests that the u th he ages from the zwieselhohe and conradgebirge profiles are in part relicts of the pre jurassic cooling history two thermally undisturbed vertical profiles are used to record the long term cooling history of central dronning maud land time temperature paths derived from modelled apatite ft data of these profiles revealed two phases of accelerated cooling during the late carboniferous and the early jurassic both phases are followed by slow cooling which is also documented by the spread in apatite u th he single grain ages the cooling at the end of the carboniferous is most probably related to far field effects associated to the prevailing convergent tectonics during the initial separation between east antarctica and mozambique erosion along an evolving rift shoulder caused the jurassic cooling denudation of the basement was simultaneous with volcanism with both pre dating c 20 10 ma sea floor spreading in the riser larsen sea c 155 ma post jurassic cooling was restricted to the lowest temperature sensitivity of both methods combined inverse modelled apatite ft data and forward modelled u th he data suggest an eocene oligocene cooling step possibly related to the flexural isostatic response to the development of ice sheets

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

deposition in the kuznetsk basin siberia insights into the permian triassic transition and the mesozoic evolution of central asia abstract this paper describes the permian mesozoic stratigraphy of the kuznetsk basin southern siberia which is adjacent to the vast and hydrocarbon rich west siberian basin and on the edge of the siberian flood basalts the basin fill is permian to cretaceous in age and is dominated by non marine siliciclastics up to 7 km thick palaeocurrent indicators show dominant flow to the north northeast during the permian to jurassic fourteen lithofacies are grouped in three facies associations fluvial channel belt overbank and floodplain floodplain pond coal bearing permian siliciclastics are interpreted as meandering river deposits in a foreland basin with subsidence generated by thrust sheet loading from at least three basin margins these sediments pass abruptly but conformably upwards into coal barren sandstones and conglomerates and siltstones interpreted as braided river deposits two basalt flows occur within the coal barren succession a recently published precise ar ar age of 250 3 0 7 ma for the lower of these basalts

backstacking apatite fission track stratigraphy a method for resolving the erosional and isostatic rebound components of tectonic uplift histories measuring tectonic uplift of the mean surface of earth using thermochronological data to document uplift histories is often plagued by confusion arising from the independent nature of the thermal and sea level frames of reference the technique of backstacking apatite fission track stratigraphy differentiates between vertical movement of rocks toward earth9s surface due to erosional or tectonic denudation and tectonic uplift of earth9s surface apatite fission track analysis can also be used to identify episodes of erosion where no other evidence for the erosional event exists in addition to providing information about the timing magnitude and geographic distribution of erosion

paleomagnetic study of cenozoic sediments from the zaisan basin se kazakhstan and the chuya depression siberian altai tectonic implications for central asia abstract this paper presents new paleomagnetic results on cenozoic rocks from northern central asia eighteen sites were sampled in pliocene to miocene clays and sandy clays of the zaisan basin southeastern kazakhstan and 12 sites in the upper oligocene to pleistocene clays and sandstones of the chuya depression siberian altai thermal demagnetization of isothermal remanent magnetization irm showed that hematite and magnetite are the main ferromagnetic minerals in the deposits of the zaisan basin stepwise thermal demagnetization up to 640 660 c isolated a characteristic chrm component of either normal or reverse polarity at nine sites at two other sites the great circles convergence method yielded a definite direction measurements of the anisotropy of magnetic susceptibility showed that the hematite bearing sediments preserved their depositional fabric these results suggest a primary origin of the chrm and were substantiated by positive fold and reversal tests the mean paleomagnetic direction for the zaisan basin d 9 i 59 k 19 95 11 is close to the expected direction derived from the apw path of eurasia j geophys res 96 1991 4029 and shows that the basin did not rotated relative to stable asia during the tertiary in the upper pliocene pleistocene sandstones of the chuya depression a very stable chrm carried by hematite was found its mean direction d 9 i 46 k 25 95 7 is characterized by declination close to the one excepted for early quaternary whereas inclination is lower in the middle miocene to lower pliocene clays and sandstones a stable chrm of both normal and reverse polarities carried by magnetite was isolated its mean direction d 332 i 63 k 31 95 4 is deviated with respect to the reference direction and implies a neogene 39 8 counterclockwise rotation of the chuya depression relative to stable asia these results and those from the literature suggest that the different amount of rotation found in the two basins is related to a sharp variation in their tectonic style predominantly compressive in the zaisan basin and transpressive in the siberian altai at a larger scale the pattern of vertical axis rotations deduced from paleomagnetic data in northern central asia is consistent with the hypothesis of a large left lateral shear zone running from the pamirs to the baikal heterogeneous rotations however indicate changes in style of faulting along the shear zone and local effect for the domains with the largest rotations

organic carbon production and preservation in response to sea level changes in the turonian carlile formation u s western interior basin abstract a primary sea level control over the distribution of total organic and carbonate carbon and organic matter type can be inferred in the early to middle turonian carlile formation fm western interior basin united states the conceptual model relies on chemo and lithostratigraphic correlations of lower to mid turonian strata in the central kwis supported by ammonite biostratigraphy and is based primarily on lithologic gamma ray spectrometric and geochemical facies analysis of the usgs portland no 1 core from central colorado the amoco rebecca bounds no 1 core from western kansas and the hawarden core from northwestern iowa sedimentation in the central marine axial basin of the cretaceous western interior seaway kwis during the turonian mostly reflects deposition by pelagic settling and from nepheloid layers with winnowing by bottom currents relatively high total organic carbon toc carbonate caco3 and rock eval pyrolysis hydrogen index hi values correspond to transgressive or highstand episodes within the overall regressive sequence whereas low values of these parameters characterize regressive intervals the lower fairport shale member of the carlile fm and coeval strata in iowa were deposited during a second order sea level highstand the waning stages of the greenhorn cyclothem an overall shallowing and coarsening upward sequence characterizes the overlying majority of the carlile fm this trend is punctuated by a short term transgressive episode with associated retrograde facies and a disconformity earlier studies document relatively high productivity during the turonian nutrient input to the seaway required to sustain water column productivity is difficult to account for solely by riverine inputs thus a model of transgressive flooding of preconditioned oxygen deficient nutrient rich water from the global ocean into the kwis is invoked this advection of nutrients and low oxygen water also helped to create broadly distributed dysoxic to anoxic conditions in the seaway which would otherwise have been difficult to maintain in a relatively well mixed shallow sea as the seaway regressed river supplied sea surface nepheloid layers provided sufficient nutrient inputs and occasionally established temporary stratification of the water column and thus contributed to maintaining an environment poised to produce and preserve organic matter

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

vertical axis rotation or lack thereof of the eastern mongolian altay mountains implications for far field transpressional mountain building abstract the altay mountains of western mongolia accommodate 10 20 of the current shortening of the india asia collision in a transpressive regime kinematic models of the altay require faults to rotate anticlockwise about a vertical axis in order to accommodate compressional deformation on the major strike slip faults that cross the region such rotations should be detectable by palaeomagnetic data previous estimates from the one existing palaeomagnetic study from the altay on oligocene and younger sediments from the chuya basin in the siberian altay indicate that at least some parts of the altay have experienced up to 39 8 of anticlockwise rotation here we present new palaeomagnetic results from samples collected in cretaceous and younger sediments in the zereg basin along the har us nuur fault in the eastern altay mountains mongolia our new palaeomagnetic results from the zereg basin provide reliable declinations with palaeomagnetic directions from 10 sites that pass a fold test and include magnetic reversals the declinations are not significantly rotated with respect to the directions expected from cretaceous and younger virtual geomagnetic poles suggesting that faults in the eastern altay have not experienced a large degree of vertical axis rotation and cannot have rotated 7 in the past 5 m y the lack of rotation along the har us nuur fault combined with a large amount of rotation in the northern altay fits with a kinematic model for transpressional deformation in which faults in the altay have rotated to an orientation that favours the development of flower structures and building of mountainous topography while at the same time the range widens at the edges as strain is transferred to better oriented structures thus the har us nuur fault is a relatively young fault in the altay and has not yet accommodated significant rotation

conservation and redistribution of crust during the indo asian collision we evaluate the mass balance of the indo asian orogen by reconstructing the indian and asian margins prior to collision using recently published paleomagnetic and surface shortening constraints and subtracting modern crustal volumes derived from gravity inversions and deep seismic soundings results show a 30 deficit between original and modern orogen volumes if the average global crustal thickness of 41 km is assumed prior to collision even once eastward extrusion and crustal flow are considered such a large discrepancy requires crustal recycling of a magnitude that is greater than one half of the modern orogenic mass as others have previously suggested proposals for extensive high elevations prior to or soon after the collision further exacerbate this mismatch and dramatically increase the volume of material necessary to be placed into the mantle however we show that this discrepancy can be eliminated with a 23 29 km thick crust within the orogen prior to collision along with a thick southern tibet margin the lhasa and qiangtang terranes because of the relatively low magnitude of surface shortening in asia an initially thin crust would require underplating of indian crust in southern tibet and displacement of a highly mobile lower crust to the north and east in order to explain modern crustal thicknesses the contrast between a proposed thinner asian interior and older and thicker lithosphere of the north china block may have defined the distal extent of deformation at the time of collision and since

the evolution of hydroclimate in asia over the cenozoic a stable isotope perspective abstract links between tectonics and regional climate have been extensively studied in asia however despite decades of research the relative roles of tectonics and global climate in pacing the long term evolution of climate in asia remain disputed today climate in asia is characterized by large scale monsoonal circulation over india and southern china and exceptionally arid deserts across much of central asia that to the north yield to the wetter conditions of the steppe and taiga how why and if these boundaries have changed during the cenozoic has been limited by the lack of paleoclimate proxy data that can be broadly applied over space and time we use a large compilation of pedogenic and lacustrine carbonate stable oxygen 18o and carbon 13c isotope data 7 700 samples which record large scale atmospheric circulation and primary productivity respectively to reconstruct cenozoic hydroclimate in asia and delineate the boundaries through time of monsoonal and mid latitude westerly moisture the 18o data indicate that atmospheric circulation has remained similar to today for at least 55 million years southern tibet has always received southerly likely monsoonal moisture and this southerly moisture has likely rarely extended northward of the central tibetan plateau in contrast northern tibet and central asia have received moisture dominantly via the mid latitude westerlies which have maintained a semi arid to arid climate in central asia since the early eocene thus the spatial extent of large scale atmospheric circulation appears largely unperturbed by contemporaneous changes in india asia collisional tectonics extent of the paratethys and in global climate the 13c data support this interpretation but yield additional details particularly low 13c across a wide swath of eastern china during the eocene suggests greater primary productivity due to a strengthened east asia monsoon perhaps driven by high atmospheric pco2 and globally warm temperatures consistently higher 13c in central asia indicates that central asia has remained more arid than surrounding regions such as northern india and southern china which have received abundant precipitation due to the presence of monsoonal moisture however increases in 13c across much of central asia throughout the cenozoic including particularly pronounced increases in mongolia and kazakhstan during the neogene imply that primary productivity has declined across much of asia this large scale de greening is attributable to the combined effects of cenozoic global cooling and the late cenozoic uplift of the tian shan and altai mountains which block westerly moisture the uplift of these ranges in the late miocene is supported by decreasing neogene 18o in eastern kazakhstan and sharply increasing 13c in the lee of the altai these regional data demonstrate that the tian shan and altai reached sufficient elevations to interact with the westerly jet by the late miocene establishing a substantial rain shadow and shifting the seasonality of precipitation in western central asia we conclude that paleoclimatic changes during the cenozoic in central asia are more tightly controlled by global climate and by the interaction of the mid latitude westerlies with the tian shan and altai rather than by changes in the height or extent of the tibetan plateau or paratethys

geomorphic mesozoic and cenozoic evolution in the oka jombolok region east sayan ranges siberia the east sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far field effects of the india asia collision and the extension linked to the opening of the baikal rift system the active deformation that affects this range is very recent around 5 ma but occurs in a very complex morphotectonic setting and the understanding of the tertiary deformation relies entirely on a detailed knowledge of the pre deformation situation using apatite fission track thermochronology cosmogenic 10be and morphological study on tertiary lava flows we demonstrate that prior to the oligocene the morphology of the east sayan area was characterized by a wide constantly rejuvenated erosion surface apatite fission track thermal modelling indicates that this surface started to form at least in late jurassic early cretaceous 140 120 ma the long term exhumation rates several tens of million years derived from apatite fission track data 17 5 m ma and the short term erosion rates over a few hundred thousand years derived from cosmogenic 10be data 12 20 m ma are coherent implying a near constant mean erosion rate since late jurassic this constant slow erosion prevented the formation of a lateritic kaolinic weathering crust on the planation surface by oligocene early miocene times a long wavelength uplift that remains to be explained induced incision that created shallow valleys later filled by basaltic lava flows finally the present short wavelength topography initiated during the pliocene

anomalous mesozoic thermal regime central appalachian piedmont evidence from sphene and zircon fission track dating a total of 17 sphene and 45 zircon fission track ages fta are reported from the piedmont province of pennsylvania delaware and maryland the reading prong of new jersey and the newark basin of pennsylvania with the exception of one sphene sample fta fall within a relatively restricted age range sphene 190 217 ma average 199 ma and zircon 143 218 ma average 184 ma near concordance of fta over a large tract of crystalline basement sim20 000 km 2 and within upper triassic sediments in the newark basin indicates late triassic early jurassic total resetting of the fission track clocks followed by regional cooling between sphene sim275 pm 25 circ c to zircon sim 220 pm 40 circ c closure temperatures at rates of 4 8 c ma fourteen rb sr whole rock mica ages together with previously reported 40 ar 39 ar biotite and hornblende ages generally indicate no regional mesozoic resetting thus the maximum temperature experienced by the samples was 300 c sphene fta clo

late paleozoic to early triassic multiple roll back and oroclinal bending of the mongolia collage in central asia abstract the architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined because of unavailable data the central asian orogenic belt caob provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage in this paper we review several lines of available evidence which enable us to propose a new tectonic model of huge roll back in the formation of the accretionary tectonics of the mongolian collage in central asia in the early paleozoic the mongolia collage comprised the southern siberian and the tuva mongol oroclines the siberia craton and the mongolia collage jointly formed a giant tadpole shape within the paleo asian and panthanlassic oceans its head siberia was to the south and the tail tuva mongol to the northwest the structures and tectonic zonation of the mongolia collage are characteristic of multiple arcs which have been separately described in detail in different segments southwards from the southern siberia east sayan west sayan gorny altai chara via the lake zone junggar tianshan gobi altai beishan alxa to the manlay hegenshan baolidao solonker segments almost all segments underwent early paleozoic to permian or even triassic frontal subduction and accretion while rifting in the late carboniferous to permian or triassic occurred in the outward oceanward westward advancing mongolian collage therefore we suggest that a huge complex roll back active from the carboniferous to permian or even to late triassic facilitated the formation of the mongolian collage the outward multiple roll back process was compatible and almost coeval with the start of the tuva mongol orocline and rotation of the siberian craton as confirmed by paleomagnetic and structural data during the roll back processes an archipelago paleogeography was formed behind the frontal subduction and accretion in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times the roll back process was affected by the collision of the kazakhstan collage along the chara and karamay zones in the early permian the collision of the tarim craton along the south tianshan zone in the early permian the collision of the dunhuang block along the liuyuan zone in the early permian triassic the collision of the alxa block along the qugan qulu zone in the permian and the collision of the north china craton along the solonker zone in the middle late triassic the tectonic styles and architecture of accretionary orogenic belts like the caob are characterized both by the amalgamation of multiple terranes and by oroclinal bending the systematic anatomy of the multiple roll back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens

geometry of the fault zone of the 2003 ms 7 5 chuya earthquake and associated stress fields gorny altai abstract the co seismic deformations produced during the september 27 2003 chuya earthquake ms 7 5 that affected the gorny altai russia are described and discussed along a 30 km long segment the co seismic deformations have manifested themselves both in unconsolidated sediments as r and r shears extension fractures and contraction structures and in bedrock as the reactivation of preexisting schistosity zones and individual fractures as well as development of new ruptures and coarse crushing zones it has been established that the pattern of earthquake ruptures represents a typical fault zone trending nw se with a width reaching 4 5 km and a dextral strike slip kinematics the initial stress field that produced the whole structural pattern of co seismic deformations during the chuya earthquake is associated with a transcurrent regime with a nnw sse almost n s trending of compressional stress axis 1 and a ene wsw almost e w trending of tensional stress axis 3 the state of stress in the newly formed fault zone is relatively uniform the local stress variations are expressed in insignificant deviation of 1 from n s to nw se or ne sw in short term fluctuations of relative stress values in keeping their spatial orientations or in a local increase of the plunge angle of the 1 the geometry of the fault zone associated with the chuya earthquake has been compared with the mechanical model of fracturing in large continental fault zones with dextral strike slip kinematics it is apparent that the observed fracture pattern corresponds to the late disjunctive stage of faulting when the master fault is not fully developed but its segments are already clearly defined it has been shown that fracturing in widely different rocks follows the common laws of the deformation of solid bodies even close to the earth surface and with high rates of movements

multi method chronometry of the teletskoye graben and its basement siberian altai mountains new insights on its thermo tectonic evolution

outcrop versus core and geophysical log interpretation of mid cretaceous paleosols from the dakota formation of kansas abstract paleosols of the mid cretaceous late albian to early cenomanian dakota formation in kansas and nebraska are well exposed in road river and clay pit exposures but show systematic overprinting by modern weathering examination of deep drill cores reveals that modern weathering effects include 1 oxidation of pyrite to jarosite 2 reaction of jarosite and calcite to clear selenite and 3 oxidation of sphaerosiderite and siderite nodules to hematite surface oxidation in this region extends no deeper than 2 m from the surface hematite nodules and coatings of leaves are found in core only at one stratigraphic horizon which was not as appears in outcrop a laterite transformed matrix density and photoelectric absorption logs of cores reveal that kaolinite clays are most abundant within deeply weathered paleosols sayela pedotype at this stratigraphic level near the albian cenomanian boundary when angiosperm forests were especially diverse and lived in a subtropical humid climate other paleosols of the early cenomanian were less deeply weathered and fossil plants of this age included temperate humid angiosperm mangal and swamp woodland but conifer dominated floodplain forests this short lived mid cretaceous warm wet spike has also been recognized in other paleosols of minnesota utah nevada and new mexico and coincides with marine black shale of the breitstroffer event midcontinental marine transgression a sequence stratigraphic boundary and a marked increase in early angiosperm diversity

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

pliocene to quaternary deformation in south east sayan siberia initiation of the tertiary compressive phase in the southern termination of the baikal rift system the south east sayan area wof the lake baikal is subjected to a very complex tectonic setting where the extensional stress field of the baikal rift system meets the compressional stress field generated by the india asia collision further south using satellite images aerial photographs srtm dem field mapping of geomorphological structures and published neotectonics and geological data we show that most of the relief in the se sayan initiated during late pliocene pleistocene through compressive reactivation of inherited structures by late quaternary clockwise rotation of the compressive field generated strike slip faulting and local secondary extension still within a general compressional stress field we demonstrate that the formation of the small scale extensional basins within the east sayan range is not linked to general the extension in the baikal rift system nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression

counter clockwise rotation of the eastern part of the mongolia block early cretaceous palaeomagnetic results from bikin far eastern russia summary we present palaeomagnetic results from lower cretaceous rocks in bikin area of the alchan basin 46 5 n 134 7 e sikhote alin orogenic belt far eastern russia a high temperature magnetization component with maximum unblocking temperatures at about 590 c was isolated from six sites of dacite welded tuffs in the albian alchanskaya formation the fold tests for these six sites are positive suggesting that primary magnetization is preserved in the studied rocks the tilt corrected mean direction of d 309 3 i 68 7 95 10 1 with a corresponding palaeopole position at 57 0 n 76 8 e a95 15 1 indicates a counter clockwise ccw rotation for the studied area ccw rotation is also indicated from west directed declinations d 249 1 i 64 1 95 11 2 obtained from secondary magnetization of the berriasian kultukha formation combining with the previously reported studies the west directed cretaceous palaeomagnetic directions cover widely the eastern part of the mongolia block comparison with 100 ma palaeomagnetic pole for eurasia shows that the eastern part of the mongolia block experienced a ccw rotation of over 36 with respect to the eurasian continent later than late cretaceous this rotation is ascribed to post late cretaceous extension that affected the continental basins the middle amur sanjiang razdolnian amur zeya and songliao basins of the northeast chinese plain along the eastern margin of the mongolia block contemporaneous with this ccw rotation similar extension resulted in clockwise rotation of the eastern part of the north china block

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history ii application to the french western alps abstract thermochronologic data collected along age elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates however thermochronologic age elevation relationships are known to be perturbed by topographic effects and potential changes in relief which are neglected in the inherently 1 d interpretation commonly applied such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging in a companion paper we develop a methodology for rigorously interpreting thermochronologic age elevation profiles in terms of exhumation rates and relief development through time and to independently quantify the resolution of these constraints here we test this approach using a thermochronological dataset consisting of apatite and zircon fission track and u th he data collected at la meije peak in the pelvoux ecrins massif french western alps our data and models suggest a three phase exhumation history in the pelvoux ecrins massif including a pulse of rapid exhumation at 6 5 5 ma preceded and followed by more moderate rates of denudation in the order of 0 3 0 4 km myr 1 this rapid exhumation event appears to occur coevally in other external crystalline massifs in the alps but is not detected by qualitative inspection of the age elevation relationships both our synthetic results and inversion of the la meije data strongly suggest that apatite fission track age elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required combining apatite fission track and u th he ages and particularly including fission track length data greatly improves the resolution of the inferred exhumation histories although denudation rates through time and the timing of rate changes are generally well resolved our data have insufficient resolution to satisfactorily constrain the relief history synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data

tectonic history of the irtysh shear zone ne kazakhstan new constraints from zircon u pb dating apatite fission track dating and palaeostress analysis abstract the irtysh shear zone isz is an important structure in the framework of the central asian orogenic belt caob it represents the site of final collision of kazakhstan with siberia during hercynian times and records up to 1000 km of lateral displacement during subsequent reorganization in the caob edifice we present new zircon u pb apatite fission track and fault kinematic data along the isz and consequently derived its tectonic history with emphasis on its formation and reactivation episodes carboniferous 340 320 ma zircon u pb ages were obtained for the syn and post collisional kalba narym intrusives dating their emplacement in the framework of the siberia kazakhstan collision during this period the isz experienced an early brittle left lateral mainly transtensional stress regime late carboniferous early permian post collisional intrusives were emplaced and the stress regime changed to a late brittle regime characterized by more compressional conditions indicating rheological strengthening as a response to cessation of ductile shearing and cooling of the isz crust apatite fission track data and thermal history modeling reveal late cretaceous 100 70 ma cooling of the isz basement rocks as a response to denudation of a bordering late mesozoic altai orogen after this denudation event the tectonic activity ceased during the late mesozoic early cenozoic a final step of cooling from 25 ma exhibited by some of the thermal history models may reflect reactivation of the isz and initiation of cenozoic altai mountain building the late plio pleistocene phase of mountain building coincides with a new change in the palaeostress field characterized by minor transpressional right lateral shear conditions

uplift and erosion of the san bernardino mountains associated with transpression along the san andreas fault california as constrained by radiogenic helium thermochronometry apatite helium thermochronometry provides new constraints on the tectonic history of a recently uplifted crystalline mass adjacent to the san andreas fault by documenting aspects of the low temperature 40 100 c thermal history of the tectonic blocks of the san bernardino mountains in southern california we have placed new constraints on the magnitude and timing of uplift old helium ages 64 21 ma from the large big bear plateau predate the recent uplift of the range and show that only several kilometers of exhumation has taken place since the late cretaceous period these ages imply that the surface of the plateau may have been exposed in the late miocene and was uplifted only 1 km above the mojave desert in the last few myr by thrusting on the north and south a similar range in helium ages 56 14 ma from the higher san gorgonio block to the south suggests that its crest was once contiguous with that of the big bear block and that its greater elevation represents a localized uplift that the big bear plateau did not experience the structure of the san gorgonio block appears to be a gentle antiform based on the geometry of helium isochrons and geologic constraints young ages 0 7 1 6 ma from crustal slices within the san andreas fault zone indicate uplift of a greater magnitude than blocks to the north these smaller blocks probably experienced 3 4 km of uplift at rates 1 5 mm yr in the past few myr and would stand 2 5 km higher than the big bear plateau if erosion had not occurred the greater uplift of tectonic blocks adjacent to and within the san andreas fault zone is more likely the result of oblique displacement along high angle faults than motion along the thrust fault that bounds the north side of the range we speculate that this uplift is the result of convergence and slip partitioning associated with local geometric complexities along this strike slip system transpression thus appears to have been accommodated by both vertical displacement within the san andreas fault zone and thrusting on adjacent structures

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

tracking the multi stage exhumation history of the western chinese tianshan by apatite fission track aft dating implication for the preservation of epithermal deposits in the ancient orogenic belt abstract the western chinese tianshan located in the southern domain of the central asian orogenic belt caob was originally established by multiple accretion collision processes in the paleozoic and was modified by complicated intracontinental tectonic evolution in the mesozoic to cenozoic understanding the timing and mechanism of the latter geological processes is critical to unravel the preservation conditions of the epithermal deposits in the western chinese tianshan this work presents new apatite fission track aft data for three mountain ranges keguqinshan wusunshan and nalatishan of the western chinese tianshan to track their exhumation history our aft data gave a wide range of ages from 76 8 5 5 ma to 182 3 9 9 ma and the mean confined fission track lengths are between 9 8 0 5 m and 12 3 0 2 m the new data in combination with the thermal history modeling results allow us to summary three main episodes of exhumation in the western chinese tianshan including the early permian 300 280 ma late triassic late jurassic 230 140 ma and late oligocene early miocene 30 20 ma the first episode may have been caused by terrane accretion collision in the late paleozoic leading to uplift of the keguqinshan that supplied abundant sediments to form a critical cover of ca 4 km thick on these epithermal deposits the second episode was likely related to closure of the mongol okhotsk ocean in the mesozoic and an extremely slow exhumation rate ca 0 0083 mm y as well as a moderate erosion of ca 0 8 km thick are estimated the last episode is regarded to be the result of collision between the indian plate and the eurasia plate in the cenozoic and this significant tectonic event triggered rapid exhumation up to ca 0 1 mm y of the whole region in the western chinese tianshan which removed more than ca 3 2 km pre cenozoic sedimentary cover and sent the epithermal deposits to the subsurface level

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

late jurassic early cretaceous closure of the mongol okhotsk ocean demonstrated by new mesozoic palaeomagnetic results from the trans baikal area se siberia summary we present new palaeomagnetic results from the transba ikal area se siberia from the mongol okhotsk suture zone the boundary between the amuria and siberia blocks in order to better constrain the time of closure of the mongol okhotsk ocean in the mesozoic we col lected 532 rock samples at 68 sites in six localities of basalts trachy basalts and andesites from both sides of the mongol okhotsk suture at unda river j 3 51 7 n 117 4 e kremljevka peak k1 51 8 n 117 5 e and torey lakes k 1 50 1 n 115 9 e on the southern side of the suture and at monostoy river j 1 51 1 n 106 8 e ingoda river k 1 51 2 n 112 2 e and bichura town k 1 50 6 n 107 6 e on the northern side progressive thermal demagnetization enabled us to resolve low ltc and high htc temperature components of magnetization at most sites jurassic palaeopoles computed from the htcs show a large discrepancy with respect to the apparent polar wander path of eurasia which we interpret in terms of 1700 2700 km of post late jurassic northward movement of amuria with respect to siberia although ge ological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data give evidence of a large remaining palaeolatitude difference between the amuria and siberia blocks in contrast early cretaceous sites cluster remarkably well along a small circle which is centred on the average site location this implies the absence of post early cretaceous northward motion of amuria relative to siberia and demonstrates the pre early cretaceous closure of the mongol okhotsk ocean finally we interpret the very large tectonic rotations about local vertical axes evidenced by the small circle distribution of poles as arising both from collision processes and from left lateral shear movement along the suture zone due to the eastward extrusion of amuria under the effect of the collision of india into asia

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

uplift age and rates of the gurvan bogd system gobi altay by apatite fission track analysis abstract the dating of the uplift onset of the mongolian mountain ranges the northernmost relief associated with the india eurasia convergence is a fundamental issue to better understand the mechanisms of propagation of the cenozoic transpressive deformation in central asia using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the gurvan bogd system in the gobi altay since the middle mesozoic to the late cenozoic the region was firstly affected by a lower middle jurassic tectonic phase characterized by a vertical crustal movement larger than 2 km then followed a protracted period without major crustal vertical movements until the last uplift phase the peneplanation of the jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 ma this same surface corresponds to the present summit plateaux of the massifs standing about 2000 m above the surrounding region which corresponds to the vertical movement produced by the ongoing uplift modelling of fission track data from the massifs of ih bogd and baga bogd shows that this uplift phase probably started at 5 3 ma the gobi altay mountain range appears therefore as one of the youngest mountain ranges in central asia which is consistent with the idea of a northward propagation of the transpressional deformation from the himalayan front to the siberian craton the cenozoic uplift rate of the massifs is estimated to be between 0 25 and 1 mm yr which is slightly higher than the upper pleistocene vertical slip rates of the bordering faults this suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

emplacement and exhumation of the kuznetsk alatau basement siberia implications for the tectonic evolution of the central asian orogenic belt and sediment supply to the kuznetsk minusa and west siberian basins terra nova 23 248 256 2011 abstract new geochronological data zircon u pb titanite fission track tft and apatite fission track aft dating and apatite u th sm he thermochronology and thermal history modelling yield constraints on the development of the granitoid basement of the kuznetsk alatau mountains southern siberia the final stages of magmatism in the kuznetsk alatau palaeo island arc are late cambrian and collision of the arc with siberia occurred in the early ordovician the basement was exhumed by the early devonian continuous devonian early triassic sedimentation filled the adjoining kuznetsk and minusa basins and buried and re heated the kuznetsk alatau basement after initial pangaea break up and siberian flood basalt magmatism the basement reached tft and aft retention temperatures in the middle triassic and early cretaceous respectively during denudation induced cooling terra nova 00 1 9 2011

structural evolution of the teletsk graben russian altai abstract lake teletskoye in the northeastern part of the altai mountain range has attracted the attention of geo scientists for a long time because it fills an impressive tectonic depression the lake is 77 km long and 4 km wide and it has a maximum water depth of 325 m the vertical offset of the basement surface is up to 3000 m a multidisciplinary study of the teletsk graben was carried out during the last few years including satellite image and air photo analysis bathymetric structural and geomorphological mapping high resolution seismic profiling and seismic refraction the structural study revealed that reactivation of preexisting weak basement zones is important in controlling the basin formation these zones separate different tectonic terranes at the contact of which the teletsk graben developed this study identifies the significance of the basin in the regional neotectonic context it shows that the major vertical movements are restricted to the basin itself but do not characterize the whole region outside of the basin recent tectonic structures have the same pattern as adjacent areas of northeast altai and west sayan quaternary glaciations have had no major influence on the basin formation two stages of faulting are identified first transpressive movements restricted to discrete reactivated fault zones controlled the opening of the basin in the second stage normal faulting is dominant and is responsible for the modern basin outline an echo sounding survey led to the recognition of several morphological characteristics of the lake bottom in the southern part the uppermost sediments seem slightly disturbed whereas further north transverse ridges and slope breaks are increasingly common the deepest part of the lake is located in a highly disturbed zone of normal fault bounded blocks the structural difference between the southern and northern subbasins is supported by the interpretation of a deep seismic refraction profile which indicates a substantial increase of basement isochores in the area where the reactivated teletsk paleozoic shear zone crosses the lake correlation of high resolution seismic profiles suggests that the teletsk graben started to evolve during the pleistocene and that its present shape was formed in two stages the first stage was responsible for the opening of the southern basin it probably started in the middle pleistocene a second kinematic stage induced by a sinistral reactivation of the ne striking west sayan fault initiated the opening of the different segments of the northern subbasin due to opposite movements between the reactivated teletsk and west sayan faults this second stage was active after the end of late pleistocene glaciations and during the holocene the recent lateral extension and the related n s trending normal faults result from a change in tectonic regime with related extensional movements along the main reactivated fault zones these recent movements result in the lateral escape of the lake borders and the collapse of the area between them

mesozoic tertiary exhumation history of the altai mountains northern xinjiang china new constraints from apatite fission track data abstract this study uses apatite fission track ft analysis to constrain the exhumation history of bedrock samples collected from the altai mountains in northern xinjiang china samples were collected as transects across the main structures related to palaeozoic crustal accretion events ft results and modeling identify three stages in sample cooling history spanning the mesozoic and tertiary stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 10 c stage two records a period of relative stability with little if any cooling taking place between 75 and 25 20 ma suggesting the altai region had been reduced to an area of low relief support for this can be found in the adjacent junngar basin that received little if any sediment during this interval final stage cooling took place in the miocene at an accelerated rate bringing the sampled rocks to the earth s surface this last stage linked to the far field effects of the himalayan collision most likely generated the surface uplift and relief that define the present day altai mountains

a vendian cambrian island arc system of the siberian continent in gorny altai russia central asia an extended vendian cambrian island arc system similar to the izu bonin mariana type is described in the gorny altai terrane at the margin of the siberian continent three different tectonic stages in the terrane are recognized 1 a set of ensimatic active margins including subducted oceanic crust of the paleo asian ocean the uimen lebed primitive island arc oceanic islands and seamounts the set of rocks is assumed to be formed in the vendian 2 a more evolved island arc comprising calc alkaline volcanics and granites a fore arc trough in middle late cambrian time was filled with disrupted products of pre middle cambrian accretionary wedges and island arcs 3 collision of the more evolved island arc with the siberian continent folding metamorphism and intrusion of granites occurred in late cambrian early ordovician time in the late paleozoic the above mentioned caledonian accretion collision structure of the siberian continent was broken by large scale strike slip faults into several segments this resulted in the formation of a typical mosaic block structure

interpretation of lithologies and depositional environments of cretaceous and lower permian rocks by using a diverse suite of logs from a borehole in central kansas as part of an extensive research program a borehole was drilled to extend sedimentary facies models of the cretaceous into the subsurface on the eastern side of the western interior cretaceous basin in kansas lithodensity neutron and spectral gamma ray logging runs were completed to facilitate interpretation of rocks penetrated by the borehole th k th u and composition profile logs based on apparent grain density and photoelectric absorption index were prepared and used to show vertical changes in geochemical facies and clay mineralogy these logs were compared with the gamma ray log and drill cuttings to interpret depositional environments the th k log sharply defines the cretaceous permian boundary and together with the th u log emphasizes the contrast between marine upper cretaceous rocks of the greenhorn depositional cycle and nonmarine to transitional rocks of the lower cretaceous the long term cyclic pattern of the th u log is an excellent indicator of a broad transgression regression during the greenhorn cycle on an open marine shelf whereas extreme fluctuations of th u in the lower cretaceous rocks suggest a high degree of short term environmental variability interpretation of the rhomaa umaa compositional profile in the dakota formation indicates several pulses of marine transgression and regression prior to the initiation of the greenhorn cycle in central kansas

large earthquakes in the katun fault zone gorny altai paleoseismological and archaeoseismological evidence abstract paleoseismological and archaeoseismological research in the katun fault zone in gorny altai reveals soft sediment deformation structures ssds in late quaternary sediments that fill the yaloman graben ssds seismites were produced by large paleoearthquakes m 5 5 5 along the katun fault that occurred about 150 and 90 ka in the 38 19 and 19 12 5 ka intervals and after 12 5 ka the event after 12 5 ka within the graben had a magnitude of ms 7 2 7 6 traces of another event shaking intensity i v esi 2007 intensity scale timed in the range from the 3rd century bc to the 1st century ad were discovered during studies of a scythian necropolis at the chultukov log 1 site located within the manzherok graben in the northern end of the katun fault burial mounds near a mountain slope at the site are damaged by colluvium rocks of the same colluvium are scattered over 25 m off the slope and deform burial structures cairns and stone rings and inner stone walls of grave chambers as well as the primary anatomical position of buried bodies including those in burials not damaged by colluvium from outside thus the katun fault was an active structure generating large earthquakes from the middle pleistocene through the holocene

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

accommodating large scale intracontinental extension and compression in a single stress field a key example from the baikal rift system the baikal rift system in southern siberia is one of the main intracontinental extensional features on earth the rift system represents the northwestern boundary of the amuria plate and in that respect can be considered as an evolving plate boundary the baikal rift system has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution however the age of the initiation of deformation and the mechanism driving this deformation are still largely debated while major extension has occurred since the late miocene pliocene the onset of extension seems older than the india asia collision implying that several driving mechanisms may have acted together or in relay through time in this work we review the available data and models for deformation in an area encompassing the baikal rift system the sayan ranges to the west and the transbaikal to the east using a synthesis of this data and our own field and mapping observations we show that the baikal rift system along with transpressional deformation in the sayan ranges and transtension in the transbaikal area can be explained through major left lateral strike slip systems the deformation is strongly controlled by inherited crustal and lithospheric structures and is distributed over a wide area within the western amuria plate that consequently cannot be considered as a rigid block such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust

tectonic implications of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china 1 a paleomagnetic study has been carried out in the east of the tan lu fault in liaoning province ne china to understand the timing of tan lu fault activity samples aging from early paleozoic to late mesozoic from 51 sites have been analyzed paleozoic and late permian early triassic rocks are remagnetized by the recent geomagnetic field however late cretaceous between 118 and 83 ma red tuffaceous sandstone passes a positive fold test shows no present earth field characteristic remanent magnetization carried by both magnetite and hematite presents a solo normal polarity and thus provides the only reliable paleomagnetic data in this study the paleomagnetic pole calculated from these rocks p 59 4 n p 205 5 e and a95 7 3 is statistically undistinguishable from all available cretaceous paleomagnetic data from eastern liaoning korean peninsula indicating that these areas may belong to a single tectonic unit here named the east liaoning korea elk block at least since the late cretaceous conversely a significant discrepancy between the elk block and chinese block i e north and south china blocks characterized by a differential rotation 22 5 10 2 with a negligible latitudinal displacement 0 8 6 1 is demonstrated this result indicates first that the left lateral displacement along the tan lu fault if any must have occurred before the late cretaceous and second that the korean block can not be considered as a rigid part of north china block sedimentological and structural evidence show that the meso cenozoic triangle shaped plain consisting of songliao xialiaohe sanjiang zeya and other smaller basins developing in northeast china and southeast russia south of the mongol okhotsk belt experienced a heterogeneous rifting from the late jurassic to tertiary the variable amount of extension larger in the northeast 300 km than in the southwest 80 km is probably related to the clockwise rotation of the elk block centered at the south of the bohai bay basin this result shows that a significant segment of the east eurasian margin more than 1000 km long experienced differential rotation in cenozoic times

interpreting data dispersion and inverted dates in apatite u th he and fission track datasets an example from the us midcontinent abstract new apatite u th he ahe and apatite fission track aft data were acquired for cratonic basement samples from an 80 m span of drillcore in northeastern kansas the short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques individual ahe dates from four samples range from 99 to 464 ma three samples yield dates 300 ma higher eu 39 113 ppm and substantial data dispersion uncorrelated with eu and grain size these apatites have strong and variable eu zonation aft dates for five samples range from 242 to 291 ma the sample with the highest eu apatites and oldest ahe dates yields the youngest aft results these results are inverted with ahe dates distinctly older than the corresponding aft date we explore both the causes of data dispersion and the overall compatibility of this cratonic dataset we find that geologically reasonable thermal histories can 1 explain the distribution of the moderate eu ahe data when accounting for the influence of radiation damage grain size and eu zonation on apatite he diffusivity 2 reproduce the observed dispersion in the high eu ahe data when using a viable range of eu zonation and grain size and 3 explain the aft data for the same samples the ahe and aft data are mutually consistent and viable thermal histories successfully predict the observed pattern of older ahe than aft dates for the high eu apatites together these results suggest that appropriately accounting for the known controls on apatite he diffusivity can explain the observed dispersion and inverted ahe and aft results in some thermochronometry datasets a range of ahe dates should be especially common in cratonic data because small differences in apatite he diffusivity are amplified by the thermal histories that typify cratonic settings we use these results to develop some guidelines for interpreting dispersed ahe datasets first date eu and date grain size correlations should be evaluated and if these patterns occur they can be used to better resolve the thermal history second for samples that yield inexplicably large dispersion of ahe dates uncorrelated with eu and crystal size the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution

structural control on meso cenozoic tectonic reactivation and denudation in the siberian altai insights from multi method thermochronometry abstract the siberian altai forms part of the central asian orogenic belt and currently is an active intracontinental mountain belt this siberian altai orogen was shaped during multiple phases of intense mountain building and associated denudation throughout the mesozoic and cenozoic we performed a multi method thermochronometric study on the altai basement in siberia in order to distinguish these denudation episodes and to place them in an absolute time frame our data shows that inherited suture zones such as the charysh terekta ulagan sayan suture played a dominant role during this episodic deformation in the altai titanite fission track results reveal late triassic early jurassic cooling which is best expressed in intrusions close to the suture zone apatite fission track aft results reveal a second phase of steady basement cooling during the late jurassic and cretaceous in the suture aft and additional apatite u th sm he ahe data reveal a consistent late cretaceous early palaeogene phase of fast cooling we interpret the mesozoic cooling signals as far field effects of the mongol okhotsk orogeny the intense late cretaceous palaeogene basement cooling signal in the suture zone can be explained as a result of fault reactivation during the collapse of this orogen and the subsequent re organization of crustal blocks during most of the palaeogene and early neogene basement cooling stagnated indicating tectonic quiescence neogene ahe ages for the kurai range directly adjacent to the suture may reflect renewed rapid cooling as a result of denudation of the present day altai mountains we interpret this most recent cooling as an indirect consequence of stress propagation from the india eurasia collision into the caob interior which thus reached as far as southern siberia this study further demonstrates the importance of thermochrological studies on intrusions along major fault zones in order to date and distinguish fault reactivation episodes

evolution of mesozoic fluvial systems along the se flank of the west siberian basin russia abstract the mesozoic stratigraphy in the subsurface of the west siberian basin contains prolific hydrocarbon accumulations and thus the depositional environments of marine and marginal marine jurassic and cretaceous age sediments are well established however no information is currently available on strata of equivalent age that crop out along the se basin margin in the mariinsk krasnoyarsk region despite the potential of these exposures to supply important information on the sediment supply routes into the main basin detailed sedimentological analysis of jurassic cretaceous clastic sediments in conjunction with palaeo botanical data reveals five facies associations that reflect deposition in a range of continental environments these include sediments that were deposited in braided river systems which were best developed in the early jurassic these early river systems infilled the relics of a topography that was possibly inherited from earlier triassic rifting more mature fluvial land systems evolved in the mid to late jurassic by the mid jurassic well defined overbank areas had become established channel abandonment was commonplace and mudrocks were deposited on floodplains coal deposition occurred in mires which were subject to periodic incursions by crevasse splay processes cretaceous sedimentation saw a renewed influx of sand grade sediment into the region it is proposed that landscape evolution throughout the jurassic was driven simply by peneplanation rather than tectonic processes by contrast the influx of sandstones in the cretaceous is tentatively linked to hinterland rejuvenation tectonic uplift possibly coeval with the growth of large deltaic clinoform complexes of the neocomian in the basin subsurface