strain localization at the margins of strong lithospheric domains insights from analog models the lateral variation of the mechanical properties of continental lithosphere is an important factor controlling the localization of deformation and thus the deformation history and geometry of intraplate mountain belts a series of three layer lithospheric scale analog models with a strong domain sd embedded at various depths are presented to investigate the development of topography and deformation patterns by having lateral heterogeneities within a weak continental lithosphere the experiments performed at a constant velocity and under normal gravity indicate that the presence or absence of the sd controls whether deformation is localized or distributed at a lithospheric scale deformation and topography localize above the edges of the sd while the sd region itself is characterized by minor amounts of surficial deformation and topography the depth of the sd within the ductile crust ductile mantle lithosphere or both controls the pattern of deformation and thus the topography the presence of a sd in the ductile crust or in the mantle results in limited surficial topographic effects but large variations in the moho topography strong moho deflection occurs when the sd is in the ductile crust while the moho remains almost flat when the sd is in the mantle when the sd occupies the ductile lithosphere the sd is tilted these analog experiments provide insights into intraplate strain localization and could in particular explain the topography around the tarim basin a lithospheric scale heterogeneity north of the india asia collision zone

constraints on the evolution of crustal flow beneath northern tibet crustal flow is an important tectonic process active in continent continent collisions and which may be significant in the development of convergent plate boundaries in this study the results from multidimensional electrical conductivity modeling have been combined with laboratory studies of the rheology of partially molten rocks to characterize the rheological behavior of the middle to lower crust of both the songpan ganzi and kunlun terranes in the northern tibetan plateau two different methods are adopted to develop constraints on melt fraction temperature and crustal flow velocity in the study area the estimates of these parameters are then used to evaluate whether crustal flow can occur on the northern margin of the tibetan plateau in the songpan ganzi crust all conditions are satisfied for topography driven channel flow to be dominant with partial melt not being required for flow at temperature above 1000 c further north the kunlun fault defines the southern boundary of a transition zone between the tibetan plateau and the qaidam basin constrained by the estimated melt fractions it is shown that channel injection across the fault requires temperatures close to 900 c the composition of igneous rocks found at the surface confirm those conditions are met for the southern kunlun ranges to the north the qaidam basin is characterized by colder crust that may reflect an earlier stage in the channel injection process in the study area at least 10 of the eastward directed tibetan crustal flow could be deflected northward across the kunlun fault and injected into the transition zone defining the northern margin of the tibetan plateau

dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the tibetan plateau summary dynamic stresses developed in the deep crust as a consequence of flow of weak lower crust may explain anomalously high topography and extensional structures localized along orogenic plateau margins with lubrication equations commonly used to describe viscous flow in a thin gap geometry we model dynamic stresses associated with the obstruction of lower crustal channel flow due to rheological heterogeneity dynamic stresses depend on the mean velocity u viscosity and channel thickness h uniquely through the term u h 2 these stresses are then applied to the base of an elastic upper crust and the deflection of the elastic layer is computed to yield the predicted dynamic topography we compare model calculations with observed topography of the eastern tibetan plateau margin where we interpret channel flow of the deep crust to be inhibited by the rigid sichuan basin model results suggest that as much 1500 m of dynamic topography across a region of several tens to a hundred kilometres wide may be produced for lower crustal material with a viscosity of 2 10 18 p asfl owing in a 15 km thick channel around a rigid cylindrical block at an average rate of 80 mm yr 1

the effects of a lateral variation in lithospheric strength on foredeep evolution implications for the east carpathian foredeep abstract lateral variations in lithospheric strength have been adopted often in flexural modeling both 2d and 3d to better fit the observed basement deflections typically supported by gravity data this approach provides essentially a snap shot of the role of lithosphere strength in determining the present day geometry in contrast we investigate and quantify the effects of a lateral change in lithospheric strength on the evolution of the foredeep in front of an advancing orogen transitions in lithospheric strength are common in the foreland of orogens and show large variations in the width of the transition zone and the strength difference former passive margins for instance will display strength changes distributed over several tens to hundreds of kilometers other transitions may originate from juxtaposition or accretion of pieces of lithosphere with different properties and may be characterized by a much smaller width than former passive margins in our modeling a constant load representing an advancing orogenic belt is displaced towards and across a transition from a weak to a strong plate in a 2d elastic thin plate model the effect of different transition widths and strength contrasts on foredeep geometry and bending stress is investigated interference of flexural wavelengths across the transition affects foredeep geometry by causing rapid basin widening oscillation of the bulge and volume increase the bending stresses are found to concentrate and amplify around the strength transition large transition gradients i e large strength contrast or small transition width cause the highest rates of change basin widening caused by the orogenic load advancing towards the transition between the east european craton and the moesian platform appears to control the sarmatian transgression over the east carpathian foreland in romania

northward channel flow in northern tibet revealed from 3d magnetotelluric modelling abstract the kunlun fault defines one of the major northern tectonic boundaries of the tibetan plateau previous geophysical studies have detected a major change in rheology across this boundary but it is not clear how this is related to models that have invoked crustal flow the lithospheric resistivity structure of the kunlun fault has been investigated by both the indepth iii and iv magnetotelluric mt transects all the mt data were processed using modern statistically robust methods and have been analysed for directionality and dimensionality in order to improve understanding of the anisotropic distribution of melt previously revealed by our remodelling of the indepth iii mt data a variant approach on 3d inversion of 2d profiles was investigated to explore and improve lateral resolution in addition to the apparent surficial deformation associated with the sinistral strike slip kunlun fault the 3d modelling of the indepth mt data reveals that complex deformation processes are occurring at mid crustal depths in northern tibet the 3d mt inversion results supported by synthetic modelling particularly confirm and highlight the presence of separate north south intrusions of conductive material crossing the kunlun fault into the more resistive kunlun qaidam block these north south intrusions are interpreted to be associated with the horizontal channel flow of partially molten songpan ganzi crust into two or more separated channels moving northwards and crossing the surficial trace of the kunlun fault at mid to lower crustal depths

present day deformation of the qaidam basin with implications for intra continental tectonics abstract the qaidam basin is a plateau of low relief about 3 km in elevation and covering a large area of 1 2 105 km2 physiographically the basin marks a transitional region between the northeastern tibetan plateau 5 0 5 km in elevation and the surrounding low lying areas the northeastern and southwestern edges of the basin are bounded by the qilian shan nan shan and qimantag eastern kunlun shan mountain belts respectively at present the entire region is under northeast southwest compression based on a synthesis of recent geological and geophysical results we propose that each flanking mountain belt consists of a sequence of crustal nappes originating from ramp thrusts at mid crustal levels 15 km deep over a distance range of 700 km these two broad fold and thrust belts operating in tandem and with some uniform shortening in the intervening qaidam basin successively raised the surface elevation from below 2 km to 5 km at depth the crust is correspondingly thickened from 40 km beneath the foreland of the qilian shan to approximately 55 km under the interior of the qaidam basin and then to nearly 70 km beneath tibet in contrast to the himalayan front where earthquake faulting occurs down to a depth of 50 km in the foreland but the zone of active thrust faulting is less than 200 km in width plateau building in the qaidam region illustrates how a wide orogen is developing along northeastern tibet in the interior of eurasia

control of detachment geometry on lateral variations in exhumation rates in the himalaya insights from low temperature thermochronology and numerical modeling 1 the himalayan range is commonly presented as largely laterally uniform from west to east however geological structures topography precipitation rate convergence rates and low temperature thermochronological ages all vary significantly along strike here we focus on the interpretation of thermochronological data sets in terms of along strike variations in geometry and kinematics of the main crustal detachment underlying the himalaya the main himalayan thrust mht we report new apatite fission track aft ages collected along north south transects in western and eastern central nepal at the latitudes of the annapurna and langtang massifs respectively aft ages are consistently young 3 ma along both n s transects in the high relief zone of the higher himalaya and increase 4 to 6 ma toward the south in the lesser himalaya we compare our new data to published low temperature thermochronological data sets for nepal and the bhutan himalaya we use the full data set to perform both forward and inverse thermal kinematic modeling with a modified version of the pecube code in order to constrain potential along strike variations in the kinematics of the himalayan range our results show that lateral variations in the geometry of the mht in particular the presence or absence of a major crustal scale ramp strongly control the kinematics and exhumation history of the orogen

3 d electrical structure across the yadong gulu rift revealed by magnetotelluric data new insights on the extension of the upper crust and the geometry of the underthrusting indian lithospheric slab in southern tibet abstract the approximately north south trending cenozoic yadong gulu rift ygr in the eastern lhasa block is an ideal location to investigate the extensional kinematic mechanism of the upper crust and the deformation characteristics of the indian lithospheric slab in southern tibet the magnetotelluric mt method has been widely used in probing subsurface structures at lithospheric scale and is sensitive to high electrically conductive body conductor a three dimensional 3 d inversion of mt data was conducted to derive the east west electrical structures across the northern segment of the ygr the result reveals that the conductors in the middle crust are not continuous in the east west direction the deep conductor underneath the ygr is interpreted to result from the tearing of the indian lithospheric slab the upper crust to the east of the ygr is significantly intruded by underlying conductors based on the features of the 3 d inversion result from this study and other geophysical observations the formation of the ygr is most likely caused by tearing of the indian lithospheric slab through the pull of mid lower crustal conductors that have locally weak strength beneath the ygr

rheology and strength of the lithosphere abstract mechanical properties of lithosphere are of primary importance for interpretation of deformation at all spatial and time scales from local scale to large scale geodynamics and from seismic time scale to billions of years depending on loading conditions and time scale lithosphere exhibits elastic brittle plastic or viscous ductile properties as can be inferred from rock mechanics data a large part of the long term lithospheric strength is supported in the ductile or ductile elastic regime while it also maintains important brittle strength yet at short seismic time scale s the entire lithosphere responds in elastic brittle elastic regime even though rock mechanics experiments provide important insights into the rheological properties of the lithosphere their conditions e g time scales strain rates temperature and loading conditions are too far from those of real earth therefore these data cannot be reliably extended to geological time and spatial scales strain rates 10 17 to 10 13 s 1 without additional parameterization or validation based on geological time scale observations of large scale deformation for the oceanic lithosphere the goetze and evan s brittle elastic ductile yield strength envelopes yses were validated by geodynamic scale observations such as the observations of plate flexure however oceanic lithosphere behavior in subduction zones and passive continental margins is strongly conditioned by the properties of the continental counterpart whose rheology is less well understood for continents and continental margins the uncertainties of available data sources are greater due to the complex structure and history of continental plates for example in a common continental rheology model dubbed jelly sandwich the strength mainly resides in crust and mantle while in some alternative models the mantle is weak and the strength is limited to the upper crust we address the problems related to lithosphere rheology and mechanics by first reviewing the rock mechanics data te flexure and ts earthquake data and long term observations such as folding and subsidence data and then by examining the physical plausibility of various rheological models for the latter we review the results of thermo mechanical numerical experiments aimed at testing the possible tectonic implications of different rheology models in particular it appears that irrespective of the actual crustal strength the models implying weak mantle are unable to explain either the persistence of mountain ranges for long periods of time or the integrity of the subducting slabs although there is certainly no single rheology model for continents the jelly sandwich is a useful first order model with which to parameterize the long term strength of the lithosphere it is concluded that dry olivine rheology laws seem to represent well the long term behavior of mantle lithosphere in oceans margins and continents as to the continent and margin crust rheology analysis of the results of thermo mechanical models and of te data based on the most robust variants of flexural models suggests that continental plates with te 30 50 smaller than their theoretical mechanical thickness hm i e te 20 60 km should be characterized by a weak lower or intermediate crustal rheology enabling mechanical decoupling between crust and mantle older plates such as cratons are strong due to crust mantle coupling and specific properties of the cratonic mantle lithosphere

lithospheric heterogeneity in the kyrgyz tien shan imaged by magnetotelluric studies 1 a 450 km long north south magnetotelluric profile spanning the tien shan from kazakhstan to western china reveals lateral variations in the resistivity of the mantle lithosphere to depths of 140 km minimum changes of one order of magnitude in this depth range result from variations in temperature or composition or both higher resistivities beneath a central portion of the range where the moho is half as deep as elsewhere in the tien shan indicate a strong lithospheric block we propose that this block protects this region of thin crust from appreciable deformation and instead transmits stresses due to india asia plate convergence from the southern to the northern parts of the range

building a training image with digital outcrop models summary current standard geostatistical approaches to characterizing subsurface heterogeneity may not capture realistic facies geometries and fluid flow paths multiple point statistics mps has shown promise in portraying complex geometries realistically however realizations are limited by the reliability of the model of heterogeneity upon which mps relies that is the training image ti attempting to increase realism captured in tis a quantitative outcrop analog based approach utilizing terrestrial lidar and high resolution calibrated digital photography is combined with lithofacies analysis to produce tis terrestrial lidar scans and high resolution digital imagery were acquired of a westwater canyon member morrison formation outcrop in ojito wilderness new mexico usa the resulting point cloud was used to develop a cm scale mesh digital images of the outcrop were processed through a combination of photogrammetric techniques and manual digitizing to delineate different facies and sedimentary structures the classified images were projected onto the high resolution mesh creating a physically plausible digital outcrop model dom portions of which were used to build mps tis the resulting mps realization appears to capture realistic geometries of the deposit and empirically honors facies distributions

crustal and upper mantle structure of northern tibet imaged with magnetotelluric data 1 magnetotelluric mt data were collected in northern tibet along the amdo to golmud highway during the 1995 and 1999 project indepth international deep profiling of tibet and the himalaya surveys broadband and long period mt data were collected and the te mode tm mode and vertical magnetic field data were inverted to yield a minimum structure two dimensional resistivity model the model obtained from inverting all responses simultaneously shows that a pervasive midcrustal conductor extends from the kunlun shan to the bangong nuijiang suture the vertically integrated conductivity conductance of this crustal layer is greatest in the northern qiangtang terrane at latitude 34 n the electrical resistivity of the upper mantle is constrained by the mt data to be in the range of 10 30 m across the songpan ganze and qiangtang terranes this is lower than would be expected if asian lithosphere underthrusts northern tibet as far as the qiangtang terrane the mt responses are more consistent with a model in which asian lithosphere extends as far south as the kunlun shan and the upper mantle beneath the songpan ganze and qiangtang terranes is sufficiently hot to contain a small fraction of interconnected partial melt

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

3d digital outcrop modelling of the lower cretaceous los santos formation sandstones mesa de los santos region colombia implications for structural analysis abstract the increasing development of the geological data acquisition and processing techniques for outcrops from photographs acquired with the unmanned aerial vehicles has had a great impact on various branches of geology such as structural geology when approaching structural analysis one of the main inputs is given by the fracture orientations therefore the use of unmanned aerial vehicles is a great benefit for acquiring in a very short time a large georeferenced dataset for fractures distribution and orientation even in normally non accessible outcrops access during the fieldwork as well as the ease of data processing and visualization constitute great advantages provided by the use of unmanned aerial vehicles in structural analysis and modelling in this study data were acquired from two outcrops from the lower cretaceous los santos formation sandstones mesa de los santos region colombia el duende and la mojarra outcrops the data was processed in photogrammetry software based on the structure from motion technique with which a dense point cloud was obtained for each outcrop the dense point cloud was processed with the discontinuity set extractor software obtaining the main families of discontinuities and their associated clusters later as a validation these orientations which obtained in a digital way were contrasted with field data previously acquired in the area obtaining a good consistency between both datasets finally the data was associated with the regional structural trends evidenced in the field data generating more data to improve the structural models of the area

unlocking the spatial dimension digital technologies and the future of geoscience fieldwork the development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field based geoscientific study since the invention of the geological map digital methods make it easier to re use pre existing data e g previous field data geophysical survey satellite images during renewed phases of fieldwork increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork high resolution geomatic surveys including laser scanning methods allow 3d photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods in addition better data management on projects is possible using geospatially referenced databases that match agreed international data standards collectively the new techniques allow 3d models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists this development will permit explicit information on uncertainty to be carried forward from field data to the final product current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output

penetration of crustal melt beyond the kunlun fault into northern tibet the transition between the weak lithosphere of the tibetan plateau and the surrounding rigid crustal blocks has a key role in the ongoing collision between india and asia a reanalysis of existing magnetotelluric data suggests that crustal melt penetrates north from the tibetan plateau beyond the kunlun fault and weakens the crust beneath the kunlun shan

rheology of the northern apennines lateral variations of lithospheric strength abstract a thermorheological wsw ene profile along the northern apennines is presented the variations in rheology are estimated using two different models the conventional model in which only frictional sliding and power law creep are taken into account and a new model in which in addition to the previous two mechanisms a high pressure brittle fracture mechanism is included upper and lower bounds for the rheology are considered a hard case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite and a soft case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite important differences in lithospheric rheological structure are inferred between the western and the eastern sectors of the chain in the former a creme brulee structure generally applies in the latter a jelly sandwich structure applies these rheological models therefore are not alternative but end members of a continuous spectrum of rheological behaviours

structure of the central altyn tagh fault revealed by magnetotelluric data new insights into the structure of the northern margin of the india asia collision abstract the altyn tagh fault atf is a left lateral strike slip fault that forms the northern margin of the tibetan plateau and plays a significant role in accommodating the convergence between the colliding indian and eurasian plates as a part of the fourth phase of the indepth project magnetotelluric mt data were collected across the central segment of the atf to determine the lithospheric scale structure of the fault system dimensionality analyses demonstrated that the mt data can be interpreted using two dimensional approaches but some localized 3 d effects are seen consequently both 2 d and 3 d inversions were carried out and a joint interpretation was made on the basis of these two types of models inversion models revealed two major conductors beneath the qaidam basin qb and altyn tagh range atr respectively the conductive region beneath the qb was interpreted as a ductile layer in the lower crust to upper mantle that might represent flow beneath the western margin of the qb whereas the large scale south dipping conductor beneath the atr is interpreted as a region with high fluid content formed by metamorphism associated with the oblique underthrusting of the tarim block beneath the northern tibetan plateau these fluids migrate upwards through the fault system and have formed serpentinized zones in the crust combining these interpretations a structural model compatible with diverse geophysical observations is proposed in which we suggest the competing end member rigid block model and continuum model are reconcilable with the continuum model locally dominant for the study region as evidenced by a thickened crust

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

a comprehensive rocket and radar study of midlatitude spread f 1 an instrumented sounding rocket launched from wallops island virginia has flown through a midlatitude spread f msf event in conjunction with simultaneous ionosonde hf radar and 244 mhz scintillation observations from the ground the in situ measurements include the electric field horizontal neutral wind and plasma density within the spread f region the ground based hf radar measurements of wave signatures in the bottomside f region ledge reveal the presence of waves propagating to the north and northwest prior to and during the spreading event the periods of these bottomside waves range from 16 to 60 min and they are shown to be associated with a strong tropical storm located 2000 km southeast of the launch site enhancements in the auroral current system occur about an hour before the msf first appears but none of the observed waves can be attributed to this source the new phase sensitive ionosonde system operated at wallops island during the experiment confirms the long standing hypothesis that this particular spread f event arises from multipath echoes distributed over a wide field of view in the bottomside f region evidence of vertically displaced plasma that could produce such multipath echoes is observed in the rocket data at and above the f region peak over spatial scales smaller than the wavelengths observed on the bottomside ledge by the hf radar but similar to the range separation given by the high resolution ionosonde echoes when the scale lengths of the structures are interpreted in magnetic coordinates no significant plasma density structures smaller than a few kilometers are observed in the rocket data and no unusual scintillation is observed along a path coincident with the rocket trajectory

ionospheric frequency spread and its relationship with range spread in mid latitude regions the distinction between range spread and frequency spread as seen on mid latitude ionograms is discussed a classification of these two types of spread f is proposed in terms of different arrangements of the duplicate traces which provide the basic trace structures of mid latitude spread f ionograms experimental results are presented to support the idea that frequency spread results from multiple ray paths associated with a shallow ripple structure in the isoionic contours close to the direction of the zenith position so that each ray path has a range approximately equal to that of its neighbor furthermore a horizontal gradient of maximum electron density is an additional requirement to create frequency spread atmospheric conditions involving ionospheric f2 region heights and upper atmosphere neutral particle densities which seem to favor the generation of frequency spread are discussed

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

electrical resistivity structures between the northern qilian mountains and beishan block nw china and tectonic implications abstract controversies exist on the tectonic models at the northern margin of the qinghai tibetan plateau new magnetotelluric mt data with a bandwidth of 0 001 5827 5 s were collected along one profile starting from the northern qilian mountains in the southern end crossing the hexi corridor the kuantan shan hei shan uplift the huahai basin and coming into the beishan block two dimensional 2d and three dimensional 3d resistivity models of the data are derived using magnetotelluric inversion codes the 2d models and the electrical structures along the profile extracted from the 3d models are comparable and complementary in defining reliable scales and shapes of anomalies in electrical resistivity the crust upper mantle structures beneath the northern plateau are characterized by two imbricated southward underthrusted blocks of continental crust or lithosphere the northern qilian fault is interpreted as a gently south dipping decollement in the upper crust along the top of a high resistivity body below the northern qilian mountains the two high resistivity bodies below the kuantan shan hei shan uplift are disconnected the upper crustal one may connect with the high resistivity basement below the northern qilian mountains in that the attitudes and deformations of the strata at these areas are coherent whereas the lower crust upper mantle one may be the cold lithospheric materials of the block north to the hexi corridor and that forms a south dipping boundary between the hexi corridor and its northern neighbors the observed high electrical resistivity beneath the beishan block provides further support for the notion that the beishan block should be rigid as a whole only in this manner could it transfer stress from south to north the northern boundary of the qinghai tibetan plateau is below the kuantan shan hei shan fault and underthrusting of continental crust or lithosphere is the main cause for the thickening of the plateau crust in the north

deriving fault slip histories to test for secular variation in slip with examples from the kunlun and awatere faults abstract although offset and age data from displaced landforms are essential for identifying earthquake clusters and thus testing whether faults slip at uniform or secularly varying rates it is not clear how the uncertainties in such measurements should be propagated so as to yield a robust fault slip history i e record of fault displacement over time here we develop a monte carlo approach for estimating the distribution of geologically reasonable fault slip histories that fit the offset and age data from a population of dated and displaced landforms the model assumes that the landforms share common faulting histories the offset and age constraints are correct and the fault has not reversed shear sense analysis of the model results yields both a precise average slip rate in the case where a linear fit is applied to the data and a best fit fault slip history in the case where the linear constraint is removed the method can be used to test for secular variation in slip because the uncertainty on this best fit history is quantified by applying the method to previously published morphochronologic data from faulted late quaternary terrace risers along the kunlun fault in china and the awatere fault in new zealand we have assessed the extent to which our modeled average slip rates match previously reported values and the data support previous interpretations of uniform slip rate the kunlun data set yields average slip rates of 8 7 3 6 2 1 mm yr and 5 1 1 6 1 2 mm yr 68 27 confidence for the central and eastern reaches of the fault respectively both of which match previously published slip rates our analysis further indicates that these fault reaches have both slipped uniformly over the latest quaternary in contrast analysis of data from the saxton river site along the awatere fault reveals a mid holocene deceleration in slip rate from 6 2 1 6 1 4 mm yr to 2 8 1 0 0 6 mm yr this result contradicts previous interpretations of uniform slip along the awatere fault the monte carlo method we present here for quantifying fault slip histories using the offset and age data from a population of faulted landforms provides an important tool for distinguishing temporally uniform from secularly varying fault slip

cenozoic deformation history of the qaidam basin nw china results from cross section restoration and implications for qinghai tibet plateau tectonics abstract the deformation and uplifting history of the qinghai tibet plateau is a controversial issue and so far there has been insufficient evidence for interpretation investigations of the cenozoic deformation in the northeastern edge of this plateau may provide some relevant information in this paper the cenozoic deformation history of the qaidam basin has been studied based on results from the balanced cross section restoration of six geological sections they indicate that 1 the qaidam basin has been undergoing continuous shortening since the beginning of cenozoic with two relatively fast shortening phases the first during 42 8 40 5 ma and the second during 2 8 ma present 2 the shortening rate of the qaidam basin reached its maximum value since 2 8 ma and approximately 32 of the average total cenozoic shortening took place in this period and 3 the shortening of all sections reached approximately 50 of their respective total shortening by miocene the cenozoic deformation history of the qaidam basin shows good synchroneity with uplifting history of the qinghai tibet plateau it is therefore proposed that the deformation and uplifting in the south and north edges of the qinghai tibet plateau was almost synchronous with the altyn tagh fault formed at the beginning of india asia collision accordingly it is postulated that since the india asia collision at the beginning of cenozoic the indian plate moved northward continuously with two relatively fast phases the first during 42 8 40 5 ma and the second during 2 8 ma present approximately 50 of the total cenozoic northward displacement of the indian plate of the total amount of crustal shortening and uplifting of the qinghai tibet plateau and of the total cenozoic strike slip displacement of the altyn tagh fault were probably reached by the early miocene moreover another 30 40 might have taken place during 2 8 ma present the periods during 42 8 40 5 ma and during 2 8 ma present may also be the two fast phases for crustal shortening and uplifting of the qinghai tibet plateau and strike slip displacement of the altyn tagh fault

structure and geometry of the aksay restraining double bend along the altyn tagh fault northern tibet imaged using magnetotelluric method large restraining bends along active strike slip faults locally enhance the accumulation of clamping tectonic normal stresses that may limit the size of major earthquakes in such settings uncertain fault geometry at depth limits understanding of how effectively a bend arrests earthquake ruptures here we demonstrate fault imaging within a major restraining bend along the altyn tagh fault of western china using the magnetotelluric mt method the new mt data were collected along two profiles across the aksay restraining double bend which is bounded by two subparallel strands of the altyn tagh fault northern natf and southern satf both two dimensional 2d and three dimensional 3d inversion models show that the aksay bend may be the center of a positive flower structure imaged as a high resistivity body extending to a 40 km depth and bounded by subvertical resistivity discontinuities corresponding to the natf and satf in the western section of the aksay bend both the natf and satf show similar low resistivity structure whereas in the eastern part of the bend the low resistivity anomaly below the satf is wider and more prominent than that below the natf this observation indicates that the satf shear zone may be wider and host more fluid than the natf lending structural support to the contention that fault slip at depth is asymmetrically focused on the satf even though surface slip is focused on the natf a south dipping low resistivity interface branching upward from the satf towards the natf indicates a fault link between these strands at depth

implications of crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

cenozoic tectonic evolution of the qaidam basin and its surrounding regions part 3 structural geology sedimentation and regional tectonic reconstruction the qaidam basin is the largest topographic depression inside the tibetan plateau because of its central position understanding the tectonic origin of the qaidam basin has important implications for unraveling the formation mechanism and growth history of the tibetan plateau in order to achieve this goal we analyzed regional seismic reflection profiles across the basin and a series of thickness distribution patterns of cenozoic strata at different time slices the first order structure of the basin is a broad cenozoic synclinorium which has an amplitude ranging from 16 km in the west to 48 in the west to 15 s 1 to 1 3 10 17 s 1 the eastward decrease in upper crustal shortening requires a progressive shift in crustal thickening mechanisms across qaidam basin from dominantly upper crustal shortening in the west to dominantly lower crustal shortening in the east although sedimentation began synchronously at 65 50 ma across the entire basin the initiation ages of the southern and northern basin bounding structures are significantly different deformation started at 65 50 ma in the north and at 29 24 ma in the south this information and the existing inference that the uplift of the eastern kunlun range south of qaidam basin began after 30 20 ma imply that the paleogene 65 24 ma qaidam and hoh xil basins on both sides of the eastern kunlun range may have been parts of a single topographic depression 500 km wide in the north south direction between the qilian shan and fenghuo shan thrust belts in the north and south the development of this large paleogene basin in central tibet and its subsequent destruction and partitioning by the neogene uplift of the eastern kunlun range requires a highly irregular sequence of deformation possibly controlled by preexist ing weakness in the tibetan lithosphere

the viscosity structure of the mantle during 1991 1994 the four year period covered by this report there has been a shift in emphasis away from one dimensional radial mantle viscosity models and toward an understanding of the three dimensional radial and lateral structure of mantle viscosity our understanding of mantle viscosity comes primarily from two sources studying the creep properties of mantle minerals under appropriate pressures and temperatures and using theoretical flow models to predict surface observables such as plate velocities gravity geoid and heat flow laboratory measurements of deformation indicate that the rheology of upper mantle minerals such as olivine mg fe 2sio4 is a strong function of temperatue grain size and stress cf karato and wu 1993 the deformation of minerals under mantle conditions generally follows a flow law of the form e a nd mexp q qrt 1 where is the deformation rate is the deviatoric stress is the shear modulus d is the grain size of the rock q is the activation energy for the deformation mechanism t is the temperature in kelvin r is the gas constant and a is a constant viscosity is defined as e 2 therefore deformation is directly related to viscosity substituting equation 1 into equation 2 an effective viscosity eff a n 1dmexp qrt 3 can be defined for temperature changes of 100 degrees k the viscosity changes by an order of magnitude at constant stress cf karato and wu 1993 changes of deviatoric stress by a factor of 2 change the viscosity by an order of magnitude cf karato and wu 1993 other factors such as partial pressure of oxygen and water content may also have important effects

crustal structure across the altyn tagh range at the northern margin of the tibetan plateau and tectonic implications wepresentnewseismicrefraction wide angle reflection dataacrossthealtyntaghrangeanditsadjacentbasins wefindthatthe crustal velocity structure and by inference the composition of the crust changes abruptly beneath the cherchen fault i e 100 km north of the northern margin of the tibetan plateau north of the cherchen fault beneath the tarim basin a platform type crust is evident in contrast south the cherchen fault the crust is characterized by a missing high velocity lower crustal layer our seismic model indicates that the high topography 3 km of the altyn tagh range is supported by a wedge shaped region with a seismic velocity of 7 6 7 8 km s that we interpret as a zone of crust mantle mix we infer that the altyn tagh range formed by crustal scale strike slip motion along the north altyn tagh fault and northeast southwest contraction over the range the contraction is accommodated by 1 crustal thickening via upper crustal thrusting and lower crustal flow i e creep and 2 slip parallel swdirected underthrusting of only the lower crust and mantle of the eastern tarim basin beneath the altyn tagh range d 2005 elsevier b v all rights reserved

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

evaluation of a workflow to derive terrestrial light detection and ranging fracture statistics of a tight gas sandstone reservoir analog understanding natural fracture networks in the subsurface is highly challenging as direct one dimensional borehole data are unable to reflect their spatial complexity and three dimensional seismic data are limited in spatial resolution to resolve individual meter scale fractures here we present a prototype workflow for automated fracture detection along horizontal scan lines using terrestrial light detection and ranging t lidar data are derived from a kilometer scale pennsylvanian locally upper carboniferous reservoir outcrop analog in the lower saxony basin northwestern germany the workflow allows the t lidar data to be integrated into conventional reservoir modeling software for characterizing natural fracture networks with regard to orientation and spatial distribution the analysis outlines the lateral reorientation of fractures from a west southwest east northeast strike near a normal fault with approximately 600 m 1970 ft displacement toward an east west strike away from the fault fracture corridors 10 20 m 33 66 ft wide are present in unfaulted rocks with an average fracture density of 3 4 3 9 m 1 11 2 12 8 ft 1 a reservoir scale digital outcrop model was constructed as a basis for data integration the fracture detection and analysis serve as input for a stochastically modeled discrete fracture network demonstrating the transferability of the derived data into standard hydrocarbon exploration and production industry approaches the presented t lidar workflow provides a powerful tool for quantitative spatial analysis of outcrop analogs in terms of natural fracture network characterization and enriches classical outcrop investigation techniques this study may contribute to a better application of outcrop analog data to naturally fractured reservoirs in the subsurface reducing uncertainties in the characterization of this reservoir type at depth

a model of the crust and mantle structure down to 700 km depth beneath the lhasa to golmud transect across the tibetan plateau as derived from seismological data abstract a 700 km deep seismic velocity cross section beneath the lhasa to golmud transect across the tibetan plateau is presented in contrast to the first version of this cross section which comprised an 800 km wide swath centred on the lhasa to golmud transect due to the recent proliferation of publications concerning the mantle structure beneath tibet this study is based only on seismic profiles which either run along or cross the transect and arrays or studies which at least partly cover the transect the results from the recent indepth iv project indicate that the crustal thickness change from 70 km beneath the songpan ganzi terrane and kunlun mountains to 54 km beneath the qaidam basin is located about 100 km north of the kunlun fault and almost 45 km north of the north kunlun thrust the qaidam basin moho is underlain by crustal velocity material for almost 45 km and the apparently overlapping crustal material may represent songpan ganzi lower crust underthrusting or flowing northward beneath the qaidam basin moho thus the high tibetan plateau may be thickening northward into south qaidam as its weak thickened lower crust is injected beneath the stronger qaidam crust beneath the crust high velocity dense cold indian lithospheric mantle extends northwards until about the banggong nujiang suture northwards asian lithospheric mantle is overlain by a low velocity less dense warm tibetan plate consisting of an upper lithospheric and a lower asthenospheric part the apparent northwards deepening of the 410 and 660 km discontinuities by about 20 km implies that the upper mantle beneath north tibet is slower less dense and warmer than under south tibet in agreement with the observed uppermost mantle velocities this in turn could provide some of the isostatic support for the high elevations in the north where the crust is somewhat thinner than in the southern plateau

lidar based digital outcrops for sedimentological analysis workflows and techniques f rarity x m t van lanen d hodgetts r l gawthorpe p wilson i fabuel perez j redfern

complex geometry and kinematics of subsidiary faults within a carbonate hosted relay ramp abstract minor fault geometry and kinematics within relay ramps is strongly related to the stress field perturbations that can be produced when two major fault segments overlap and interact here we integrate classical fieldwork and interpretation of a virtual outcrop to investigate the geometry and kinematics of subsidiary faults within a relay ramp along the tre monti normal fault in the central apennines although the tre monti fault strikes parallel to the regional extension ne sw it shows predominant dip slip kinematics suggesting a nw se oriented extension acting at sub regional scale 1 10 km conversely the slickenlines collected on the front segment of the relay ramp highlight right lateral kinematics the subsidiary faults in the relay ramp show a complex geometry variable attitudes and slickenlines describe multiple kinematics left lateral dip slip right lateral independently of their orientation our fault slip analysis indicates that a local stress field retrieved from the kinematic inversion of the slickenlines collected on the front segment and likely promoted by the interaction between the overlapping fault segments that bound the relay zone can explain most of the geometry and kinematics of the subsidiary faults further complexity is added by the temporal interaction with both the regional and sub regional stress fields

is the asian lithosphere underthrusting beneath northeastern tibetan plateau insights from seismic receiver functions abstract whether or not the asian lithosphere has underthrusted beneath the tibetan plateau is important for understanding the mechanisms of the plateau s growth using data from the permanent seismic stations in northeastern tibetan plateau we studied seismic structures of the lithosphere and upper mantle across the plateau s northeastern margin using p and s receiver functions the migrated p and s receiver function images reveal a thick crust and a diffuse lithosphere asthenosphere boundary lab beneath the tibetan plateau contrasting sharply with the relatively thin crust and clear sharp lab under the bounding asian blocks the well defined lab under the asian blocks tilts toward but does not extend significantly under the tibetan plateau this is inconsistent with the model of asian mantle lithosphere underthrusting beneath the tibet plateau instead our results indicate limited passive deformation of the bounding asian lithosphere as it encounters the growing tibetan plateau

turbulent upwelling of the mid latitude ionosphere 2 theoretical framework in a companion paper data from the mu radar have been presented which show that during sunspot minimum conditions in japan the mid latitude ionosphere is sometimes characterized by regions of rapid and turbulent upwelling in this paper we explore possible mechanisms for these events the most likely process seems to be the instability of the equilibrium which occurs when the mid latitude plasma is supported against gravity either by an eastward electric field component or by a southward neutral wind as was proposed by perkins 1973 we show for example that the growth rate determined by perkins is considerably higher in sunspot minimum conditions than at sunspot maximum for comparable altitudes of the ionospheric f layer the growth rate is not very large however and we argue here that the observed structures must evolve from preexisting undulations of the bottomside of the f region which are generated by gravity waves that is the gravity waves create finite amplitude structures which are amplified by the plasma instability an intriguing feature of the gravity wave role in this process is that the echoing patches detected by the mu radar and the height bands detected by the arecibo radar which we believe to be related phenomena all seem to propagate to the west this is the same direction reported for the angle of arrival measurements of classic mid latitude spread f by a number of researchers using ionosonde techniques since the mu radar detects the upwelling regions from nonthermal 3 m irregularities there must be mechanism to create such tracers we propose that secondary structures are created at intermediate scales via the e b instability operating on the dome of the upwelling structure and by the neutral wind driven process on either the west or the east wall of the structure depending on the direction of the zonal wind the 3 m waves are then created in a cascade process which brings energy into a range of k space in which the structures are linearly damped finally we discuss the fine structure of the echoing patches and suggest several plausible mechanisms two of which involve e region coupling and one which deals with the vertical structure of the gravity wave seeding process

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

electrical resistivity structures of the kunlun qaidam qilian system at the northern tibet and their tectonic implications abstract the northern tibetan plateau is characterized by northwest southeast trending basin range systems such as the kunlun shan ranges qaidam basin qilian shan ranges the cenozoic evolution and deformation of the qaidam basin and its neighboring ranges are important indications for the northward growth of the tibetan plateau the latest magnetotelluric data were collected along a profile in n16 5 e from the songpan ganzi block across the kunlun shan ranges east section of the qaidam basin and ending in the qilian shan ranges both two dimensional and three dimensional inversions of the data along the profile were performed and the results provided new evidence for lithospheric structures in the northern tibetan plateau with three dimensional isotropic inversion codes we are able to model the phase roll out of quadrant proq magnetotelluric data which exist at low frequencies in a number of continuous sites at the northern qaidam basin sensitivity studies of the three dimensional models indicate that the qaidam basin with low resistivity upper crust is the major contributor for the proq effect while a south north striking low resistivity gap intersecting with the qaidam basin at its northern part affects the range of the proq effect in the magnetotelluric resistivity models the qaidam basin is not in symmetric structure at upper crust level with its depocenter near the northern qaidam fault at mid lower crust level the compositions of both the kunlun shan ranges and the southern qaidam basin are of generally high resistivity which does not support large scale lower crust materials of the songpan ganzi block flow below the kunlun shan ranges or the qaidam basin instead the unsymmetrical qaidam basin and the shovel shape high resistivity anomalies in crust below the kunlun shan ranges and the southern qiadam basin indicate the regional northward push from the songpan ganzi block the south deepening low resistivity anomalies in the crust of the qilian shan ranges support the existence of an intracrustal detachment which controls the thrusts in northern qaidam basin and the qilian shan ranges the crustal deformation in northern tibetan plateau is consistent with mantle convergence or collision between the kunlun qaidam lithospheric mantle and the asian lithospheric mantle

lithospheric and upper mantle structure of the northeastern tibetan plateau 1 we use receiver functions calculated for data collected by the indepth iv seismic array to image the three dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern tibet our results indicate an average crustal thickness of 65 to 70 km in northern tibet in addition we observe a 20 km moho offset beneath the northern margin of the kunlun mountains a 10 km moho offset across the jinsha river suture and gently northward dipping moho beneath the qaidam basin a region in the central qiangtang terrane with higher than normal crustal vp vs ratio of 1 83 can be the result of the eocene magmatic event in the qiangtang terrane we observe a significant lithospheric mantle discontinuity beneath the bangong nujiang suture at 80 km depth which dips 10 to the north reaching 120 km depth we interpret this feature as either a piece of lhasa terrane or remnant oceanic slab underthrust below northern tibet we detect a 20 km depression of the 660 km discontinuity in the mantle transition zone beneath the northern lhasa terrane in central tibet which suggests this phase transition has been influenced by a dense and or cold oceanic slab a modest 10 km depression of the 410 km discontinuity located beneath the northern qiangtang terrane may be the result of localized warm upwelling associated with small scale convection induced by the penetration of the sinking indian continental lithosphere into the transition zone beneath the central tibetan plateau

from outcrop to flow simulation constructing discrete fracture models from a lidar survey terrestrial light detection and ranging lidar surveys offer potential enrichment of outcrop based research efforts to characterize fracture networks and assess their impact on subsurface fluid flow here we explore two methods to extract the three dimensional 3 d positions of natural fractures from a lidar survey collected at a roadcut through the cretaceous austin chalk 1 a manual method using the university of california davis keck center for active visualization in the earth sciences and 2 a semiautomated method based on mean normal and gaussian curvature surface classification each extraction method captures the characteristic frequencies and orientations of the primary fracture sets that we identified in the field yet they extract secondary fracture sets with varying ability after making assumptions regarding fracture lengths and apertures the extracted fractures served as a basis to construct a discrete fracture network dfn that agrees with field observations and a priori knowledge of fracture network systems using this dfn we performed flow simulations for two hypothetical scenarios with and without secondary fracture sets the results of these two scenarios indicate that for this particular fracture network secondary fracture sets marginally impact 10 change the breakthrough time of water injected into an oil filled reservoir our work provides a prototype workflow that links outcrop fracture observations to 3 d dfn model flow simulations using lidar data an approach that offers some improvement over traditional field based dfn constructions in addition the techniques we used to extract fractures may prove applicable to other outcrop studies with different research goals

electrical resistivity variations of lithospheric mantle beneath the northern tibetan plateau with tectonic implications abstract the northern tibetan plateau including the areas north of kunlun shan is characterised by a strapped basin range system and major strike slip faults however the surficial deformation differs laterally the collection of magnetotelluric mt data covering the northern tibetan plateau has made it possible to apply a three dimensional isotropic inversion of these data for the entire study area the plane area covered by mt sites is more than 700 700 km2 and the longest periods of most of these sites approximate or exceed 10 000 s all of these aid in distinguishing the weak responses generated by deep anomalies in the lithospheric mantle the three dimensional inversion is applied to a subset of mt data and it is observed that the full impedance data of most mt sites well fit the responses of the final three dimensional model two modes of relationship among the lithospheric mantles in the northern tibetan plateau are proposed the moderate low resistivity corridor indicates that the lithospheric mantle has a low viscosity which is favourable for shortening at shallow crustal levels under a regional compression environment furthermore the low resistivity anomalies in the west qaidam basin and southwest qilian shan form a passage that may connect with weak materials in the lower crust of songpan ganzi terrane through the qiman tagh range the high resistivity lithospheric mantle of east kunlun shan east qaidam basin and alashan is dislocated according to the surface boundaries indicating a face to face subduction below qilian shan this represents the major dynamic model in the northern tibetan plateau

lidar intensity as a remote sensor of rock properties abstract lidar collects high resolution spatial data making it a popular tool for outcrop investigations however few of these studies utilize lidar s spectral capability lidar scanners commonly collect intensity returns power returned power emitted that are influenced primarily by distance and target reflectivity with lesser influence from angle of incidence roughness and environmental conditions application of distance normalization results in values that approximate target reflectivity at the near infrared wavelength of lidar quartz rich sandstones are more reflective than clay rich mudstones scans of unweathered core and weathered outcrop were collected to investigate the relationship between lithology and lidar intensity in unweathered laboratory samples intensity shows an inverse relationship to wt clay and are positively correlated to wt combined quartz plagioclase and k feldspar a similar relationship was also observed in scans of lightly weathered outcrop although weathering and moisture diminished intensity contrast between sand rich and shale rich intervals thus lidar intensity is a possible remote sensor of lithology particularly in remotely located and inaccessible outcrops

parameterizing parasequences importance of shelf gradient shoreline trajectory sediment supply and autoretreat the basic reservoir flow unit in shallow marine depositional systems is the parasequence since it is bounded top and base by regionally extensive shales that can form barriers to fluid flow as a result it is the key stratigraphic unit requiring parameterization for both exploration and development purposes a database comprising 3385 measurement points from 385 parasequences from 28 locations and 16 different passive margin and foreland basins was compiled from outcrop and subsurface data analysis of the data suggests that a mean value for parasequence thickness is 17 m 56 ft mean parasequence sandstone fraction is 0 60 and mean shoreface sand body thickness is 8 m 26 ft the mean maximum parasequence progradation distance is 23 km 14 mi the results indicate that there are two critical controls that can significantly vary the parameter values stated above 1 stacked shoreline trajectory or systems tract and 2 shelf gradient the analyses indicate that shelf gradient is the most important parameter that has a first order control on parasequence properties shelf gradient in the ancient can be approximated to high gradient or low to moderate gradient categories via analysis of parasequence thickness change versus progradation distance from wells mean parasequence thickness or mean progradation distance from seismic attribute data parasequence progradation distance is to some degree predictable if stacked shoreline trajectory shelf gradient category and mean parasequence thickness are known the data suggest that there are two types of parasequences accommodation dominated and supply dominated parasequences the progradation distance of these parasequences are controlled by delta autoretreat mechanisms modulated by the combination of fifth and fourth order milankovitch scale orbitally forced climate change driven sediment supply cycles interacting with eustatically and tectonically driven accommodation cycles

magnetotelluric image of the fluid cycle in the costa rican subduction zone fluids entering the subduction zone play a key role in the subduction process they cause changes in the dynamics and thermal structure of the subduction zone1 and trigger earthquakes when released from the subducting plate during metamorphism fluids are delivered to the subduction zone by the oceanic crust and also enter as the oceanic plate bends downwards at the plate boundary however the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions4 or transfer to the deep mantle implying possible storage of fluids in the crust here we use magnetotelluric data to map the entire hydration and dehydration cycle of the costa rican subduction zone to 120 km depth along the incoming plate bend we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle along the subducting plate interface we document the dehydration of sediments the crust and mantle we identify an accumulation of fluids at 20 30 km depth at a distance of 30 km seaward from the volcanic arc comparison with other subduction zones5 14 indicates that such fluid accumulation is a global phenomenon although we are unable to test whether these fluid reservoirs grow with time we suggest that they can account for some of the missing outflow of fluid at subduction zones

distinct lateral contrast of the crustal and upper mantle structure beneath northeast tibetan plateau from receiver function analysis abstract we investigate the crustal thickness poisson s ratio and the thickness variation of the mantle transition zone using the p receiver function technique on data recorded by the 68 seismic station of the ascent experiment beneath the northeast tibetan plateau our results reveal a distinct crustal and upper mantle structure contrast between the western and eastern part of the northeast tibetan plateau along two migrated profiles in the eastern region the moho is relatively smooth and continuous and varies in depth between 80 and 51 km whereas the depth of the moho beneath the western region varies between 77 and 52 km and is offset 20 km beneath the boundary between the kunlun fault and qaidam basin the delay times for the ps phases from both the 410 km and 660 km discontinuities in the western region are 1 2 s later than that in the eastern region indicating that the average velocities of the upper mantle in the western region are lower than that in the eastern region crustal rocks with low to moderate poisson s ratios are interpreted to be dominated by felsic to intermediate compositions implying that large scale middle lower crustal flow does not occur easily the nearly constant thickness of the mantle transition zone with an average value of 255 km 24 4 s from south to north implies that no lithospheric fragments correlating to the india asia collision have entered into the mantle transition zone

eastern termination of the altyn tagh fault western china constraints from a magnetotelluric survey the left lateral altyn tagh fault forms the northern boundary of the tibetan plateau the strike slip rate of the active altyn tagh fault decreases northeastward and reduces close to zero as it passes north of the qilian shan this geometry raises controversies on whether and how the fault terminates or extends further east to address these controversies wide band magnetotelluric data were collected along four profiles across the altyn tagh fault ranging from 135 to 261 km in length all four profiles are located in the foreland of the qilian shan ranges and are oriented perpendicular to the inferred fault zone that could be the continuation of altyn tagh fault both the two dimensional and three dimensional electrical resistivity models derived from our magnetotelluric data show that the hexi corridor crust is generally of low resistivity whereas the crust of the huahai jinta basin is in general of high resistivity with a local and isolated low resistivity anomaly within the mid lower crust the generally high resistivity crust of the huahai jinta basin may be rheologically unfavorable for the altyn tagh fault passing through the basin toward the northeast the entirely different electrical structure between the hexi corridor and its northern neighbors indicates the existence of a tectonic boundary that coincides with the altyn tagh fault in the west and reverse faults in the east the two dimensional electrical conductivity models suggest that the altyn tagh fault transfers from a single fault in the west to a branching set of mainly dip slip faults in the east

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

analogue modelling of continental collision influence of plate coupling on mantle lithosphere subduction crustal deformation and surface topography abstract the role of the plate boundary in a continental collisional setting is investigated by lithospheric scale analogue models key variables in this study are the degree of coupling at the plate interface and along the moho of the lower plate as well as the geometry of the plate contact they control the onset of intra plate deformation orogenic architecture amount of mantle lithosphere subduction and basin development in all experiments deformation initiates at the plate interface by the formation of a pop up structure a vertical plate boundary with respect to the shortening direction results in buckling of the lithosphere whereas experiments with an inclined plate boundary show underthrusting and foreland basin development without orogenic wedge formation continental collision and coinciding mantle lithosphere subduction may occur only if the lower crust of the foreland plate is weak enough promoting crust mantle decoupling during decoupling the weak lower crust beneath the orogen thickens significantly by ductile flow as it detaches from the down going mantle lithosphere this lower crustal thickening effects the distribution of upper crustal deformation and topography subduction of weak lower crust is favored when the weak plate interface has a significant thickness 15 km in nature and a high amount of shortening is applied increasing coupling at the plate interface through time leads to intra plate deformation by thickening and gentle folding and influences surface uplift and subsidence above the plate interface the transition from a mechanically decoupled plate boundary with a significant amount of mantle lithosphere subduction towards stronger plate coupling resulting in intra plate deformation and topography development can be recorded in for instance the caucasus the colombian cordillera the pyrenees and the alps thickening of the lower crust as portrayed for the western alps does not demand a strong frictional type behavior of the lower crust but can also be the consequence of ductile processes

middle and upper atmosphere radar observations of ionospheric density gradients produced by gravity wave packets by observing the ionospheric f region simultaneously in multiple beams with the middle and upper atmosphere mu radar we have been able to track the passage of gravity waves and measure the horizontal electron density gradients that they produce our previous work on this topic on one day of observations verified that the gradient structure and fluctuations were consistent with a gravity wave source the present work 1 looks at several days of observation to confirm the routine existence of these gradient structures 2 identifies individual wave packets 3 finds evidence that long trains of gravity wave fluctuations are composed of several juxtaposed wave packets of one or two cycles each rather than a single wave of many cycles 4 finds that during quiet periods strong waves are present only during the daytime but during disturbed periods they are present day and night and 5 notes several other characterizations

terrestrial laser scanning in geology data acquisition processing and accuracy considerations terrestrial laser scanning or lidar is a recent innovation in spatial information data acquisition which allows geological outcrops to be digitally captured with unprecedented resolution and accuracy with point precisions and spacing of the order of a few centimetres an enhanced quantitative element can now be added to geological fieldwork and analysis opening up new lines of investigation at a variety of scales in all areas of field based geology integration with metric imagery allows 3d photorealistic models to be created for interpretation visualization and education however gaining meaningful results from lidar scans requires more than simply acquiring raw point data surveys require planning and typically a large amount of post processing time the contribution of this paper is to provide a more detailed insight into the technology data collection and utilization techniques than is currently available the paper focuses on the workflow for using lidar data from the choice of field area and survey planning to acquiring and processing data and finally extracting geologically useful data because manufacturer specifications for point precision are often optimistic when applied to real world outcrops the error sources associated with lidar data and the implications of them propagating through the processing chain are also discussed

the electrical structure of the slave craton the slave craton in northwestern canada a relatively small archean craton 600400 km is ideal as a natural laboratory for investigating the formation and evolution of mesoarchean and neoarchean sub continental lithospheric mantle sclm excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available over the last 5 years deep probing electromagnetic surveys were conducted on the slave using the natural source magnetotelluric mt technique as part of a variety of programs to study the craton and determine its regional scale electrical structure two of the four types of surveys involved novel mt data acquisition one through frozen lakes along ice roads during winter and the second using ocean bottom mt instrumentation deployed from float planes the primary initial objective of the mt surveys was to determine the geometry of the topography of the lithosphere asthenosphere boundary lab across the slave craton however the mt responses revealed completely serendipitously a remarkable anomaly in electrical conductivity in the sclm of the central slave craton this central slave mantle conductor csmc anomaly is modelled as a localized region of low resistivity 10 15 v m beginning at depths of f80 120 km and striking ne sw where precisely located it is spatially coincident with the eocene aged kimberlite field in the central part of the craton the so called corridor of hope and also with a geochemically defined ultra depleted harzburgitic layer interpreted as oceanic or arc related lithosphere emplaced during early tectonism the csmc lies wholly within the ne sw

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

early cenozoic faulting of the northern tibetan plateau margin from apatite u th he ages models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary yet a growing body of evidence in the tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen s history and thus our current mechanical understanding of orogenic plateau development is incomplete new apatite u th he ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures accelerated erosion is used as a proxy of fault timing and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins helium results are synthesized with published geologic thermochronometric and sedimentologic data from which a growing picture of regional compressional deformation in middle to late eocene time in northern tibet emerges we relate the early cenozoic period of deformation to the initiation of collision between india and eurasia despite the fact that the plate boundary was located 3000 km to the south regardless of whether or not high topography was built simultaneously as a result of this deformation early cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time

fault growth by linkage observations and implications from analogue models abstract using time sequence analyses of extensional fault models we demonstrate the pivotal role played by fault segmentation in the accumulation of displacement and length during the growth of faults experiments are described in which incremental steps during the development of individual faults have been reconstructed from time lapse photographs taken during model deformation these records confirm the composite segment hierarchy of fault structure a pattern that is frequently recognised in many natural arrays they reveal the progressive enlargement of individual faults to be the product of a repetitive cycle of tip line propagation overlap and linkage between nearest neighbours by contrasting the displacement patterns of successive increments during growth convincing evidence is also presented to suggest that individual segments of faults may remain kinematically independent once they are physically linked this behaviour is shown to be responsible for the characteristic saw tooth patterns often recognised in strike parallel fault displacement profiles such patterns are believed to arise where relict segment boundaries remain preserved as asperities to slip so that displacement is confined to discrete parts of a fault plane surface growth in this way also causes the maximum displacement d and surface length l of faults to continually change by different proportions incremental displacement records presented here corroborate field evidence which shows that linkage between fault segments during growth is responsible for a significant component of the spread of values often recorded in d versus l compilations finally we speculate that linkage between fault segments also accounts for transient irregularities recorded in the frequency distribution of the fault length populations of each model

modeling of grabens extending above evaporites in canyonlands national park utah abstract grabens in canyonlands national park utah began extending above a layer of evaporites when the colorado river cut through the overburden two dimensional finite element models simulate the effects of geometry and rock properties on graben configuration and spacing only those models having a progressively increasing slope or no slope mimicked the natural upslope graben propagation typical rock properties produced the most realistic fault patterns an initial friction angle of 31 a cohesion of 1 mpa and strain weakening comprising cohesion loss and decrease of friction angle to 26 a tensile stress limit narrowed the grabens and reproduced the vertical upper portion of the natural faults the viscous salt resisted overburden spreading and controlled its rate modeled grabens spread at typical rates of 1 2 mm a 1 for a salt viscosity of 1 10 18 pa s and the entire system strained at rates from 6 0 10 14 s 1 to 0 5 10 14 s 1 the faults bounding a graben formed nearly simultaneously at the top surface and propagated downward salt rose beneath the grabens as reactive diapirs overburden adjacent to the canyon flexed as salt was expelled and formed an arching horst and graben a corresponding horst has been found in the field the model results scale to larger dimensions except for the steep upper part of the faults reduced dimensions create vertical or no faults

seismic evidence for the north china plate underthrusting beneath northeastern tibet and its implications for plateau growth abstract lithospheric deformation of the tibetan plateau is caused by subduction of the indian northward and asian southward plates the effects of this interaction on inner reaches of the asian continent between the tibetan plateau and the north china craton ncc for example remain uncertain due to poor geophysical data coverage in northeastern tibet ne tibet we provide here detailed knowledge of the lithospheric structure beneath ne tibet as determined from a dense broadband seismic profile traversing ne tibet to the westernmost ncc receiver function imaging reveals several significant features including a north dipping intracrustal converter nc moho offset overlap beneath major fault zones and a low velocity layer lvl in the middle lower crust the lithosphere asthenosphere boundary lab is clearly defined and appears as a south dipping interface that runs continuously from the alxa interior to the qilian orogen interpretation of these observations combined with other seismic evidence implies that the ncc lithospheric mantle has been persistently underthrust beneath the qilian orogen this process forms the thick skinned crustal accretionary wedges which develop above a middle lower intracrustal decollement our results provide further deep geophysical constraints on the cenozoic post collisional evolution of the convergent boundary between ne tibet and the ncc and help clarify the mechanism of plateau growth in this boundary area

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

stratigraphic evolution of an aeolian erg margin system the permian cedar mesa sandstone se utah usa the permian cedar mesa sandstone of south east utah is a predominantly aeolian succession that exhibits a complex spatial variation in sedimentary architecture which in terms of palaeogeographic setting reflects a transition from a dry erg centre through a water table controlled aeolian dominated erg margin to an outer erg margin subject to periodic fluvial incursion the erg margin succession represents a wet aeolian system accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport variation in the level of the water table relative to the depositional surface determined the nature of interdune sedimentary processes and a range of dry damp and wet flooded interdune elements is recognized variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre locally interconnected damp and or wet interdune ponds in the aeolian dominated erg margin and fully interconnected fluvially flooded interdune corridors in the outer erg margin relationships between aeolian dune and interdune units indicate that dry damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration temporal variation in the rates of water table rise and bedform migration determined the angle of climb of the erg margin succession such that accumulation rates increased during periods of rapidly rising water table whereas sediment bypassing zero angle of climb occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table during these periods in the outer erg margin the expansion of fluvially flooded interdunes in front of non climbing but migrating dunes resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass flood supersurfaces a spectrum of genetic depositional models is envisaged that accounts for the complex spatial and temporal evolution of the cedar mesa erg margin succession

the missing complexity in seismically imaged normal faults what are the implications for geometry and production response the impact of geometric uncertainty on across fault flow behaviour at the scale of individual intra reservoir faults is investigated in this study a high resolution digital elevation model dem of a faulted outcrop is used to construct an outcrop scale geocellular grid capturing high resolution fault geometries 5 m scale seismic forward modelling of this grid allows generation of a 3d synthetic seismic cube which reveals the corresponding seismically resolvable fault geometries 12 5 m scale construction of a second geocellular model based upon the seismically resolvable fault geometries allows comparison with the original outcrop geometries running fluid flow simulations across both models enables us to assess quantitatively the impact of outcrop resolution versus seismic resolution fault geometries upon across fault flow the results suggest that seismically resolvable fault geometries significantly underestimate the area of across fault juxtaposition relative to realistic fault geometries in turn this leads to overestimates in the sealing ability of faults and inaccurate calculation of fault plane properties such as transmissibility multipliers tms

a statistical study of midlatitude spread f at wallops island virginia 1 an ionosonde study using data from wallops island virginia 37 95 n 284 53 e 67 5 dip angle over a full solar cycle from 1996 to 2006 has been conducted a pattern recognition algorithm is used to analyze these ionograms in order to determine the statistics of midlatitude spread f an ionogram displays spread f both horizontally and vertically which are defined as range and frequency spread f respectively range and frequency spreading can occur either simultaneously or separately seasonal and solar cycle variations have been studied using the data set both are significant and are somewhat different for range and frequency spread f correlations of spread f duration with f 10 7 kp and ae are investigated the results provide insights into causative sources for both types of midlatitude spread f

characteristics of the equatorial plasma drifts as obtained by using canadian doppler ionosonde over southern tip of india we present here characteristics of the doppler drift measurements over tirunelveli 8 73 n 77 70 e dip 0 5 n an equatorial site over southern india using doppler interferometry technique of canadian ionosonde three dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic e w and n s directions after having compared with lowell s digisonde drifts at trivandrum we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012 the observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons the comparison of doppler vertical drifts with the drifts obtained from a virtual height and b fejer drift model suggests that doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods further it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread f in the ionograms and gps l band scintillations the zonal drifts on the other hand showed westward during daytime with mean drifts of 150 200 m s and correlated well with equatorial electrojet strength indicating the role of e region dynamo during daytime while they are eastward during nighttime with mean drifts of 100 m s resembling f region dynamo process also zonal drifts showed large westward prior to the spread f onset during autumn equinox than vernal equinox suggesting strong zonal shears which might cause equinoctial asymmetry in spread f

electrical resistivity structures northeast of the eastern kunlun fault in the northeastern tibet tectonic implications abstract only sparse deep geophysical data have been obtained in the region to the north of the eastern kunlun fault eklf in the tibetan plateau which leads to inconsistent and ambiguous descriptions of the area in various geodynamic models the detailed geophysical issues in the region including the northeast boundary of the plateau and the crust mantle coupling mode northeast of the eklf are under dispute to resolve these disputes we have collected magnetotelluric mt data along five profiles in the region to the north of the eklf since 2009 the interpretation of data from the latest profile labeled l5 which starts from the eastern margin of the qaidam basin crosses the qilian mountain and the hexi corridor and finally reaches the southern alashan block is the focus of this paper these new results are comparable with our previously determined structures the two dimensional 2d resistivity model supports three divisions of the qilian mountain a complex northern qilian a relatively simple sandwiched southern qilian and a transitional central qilian in between them our data indicate a relatively low resistivity layer at the middle lower crust below the eastern margin of the qaidam basin and the southern qilian mountain this result indicates a weak crustal zone wcz existing northeast of the eklf and is interpreted as a large north dipping thrust at this depth the presumed imbricated thrust in the crust in the northeastern plateau resulting from the indenting of the mantle wedge from the south is the primary process in the crustal thickening in the region the mt results indicate that the northeastern boundary of the tibetan plateau is not below the eklf instead we suggest that the northeastern boundary of the outgrowth of the tibetan plateau is along and below the northern rim of the hexi corridor

electrical resistivity structure at the northern margin of the tibetan plateau and tectonic implications 1 the ene wsw striking altyn tagh fault atf and the wnw ese trending western qilian mountains define the northern margin of the tibetan plateau new magnetotelluric data were collected along three profiles crossing the eastern section of the atf and the southern qilian mountains the basic sounding bandwidth ranged from 0 003 to 7000 s the transverse electric and transverse magnetic mode data sets were inverted into resistivity sections using a conventional two dimensional 2d inversion code and data at periods of 0 3333 5464 s were inverted using a commonly employed three dimensional 3d code the 3d results constrain the interpretation of the 2d models and the final interpretative resistivity models show that lithospheric structures are spatially variable along the atf and across southern qilian in profiles across the atf the main fault is imaged as a vertical resistivity boundary and the high resistivity body in the western profile extends about 15 km deeper than the corresponding body in the eastern profile positive flower structures are apparent in the western profile but are only weakly visible in the eastern profile these observations suggest that the depth of the atf is spatially variable mantle resistivity images indicate a relatively cold and rigid tarim lithosphere which is consistent with a geodynamic model of oblique subduction of the tarim basin below the atf a high resistivity body in the crust of southernmost qilian indicates a huge thick skinned structure low resistivity bodies at the crust mantle boundary south of the main atf are presumed to form a weak layer beneath northern tibet

tearing of the indian lithospheric slab beneath southern tibet revealed by sks wave splitting measurements a b s t r a c t shear wave birefringence is a direct diagnostic of seismic anisotropy it is often used to infer the northern limit of the underthrusting indian lithosphere based on the seismic anisotropy contrast between the indian and eurasian plates most studies have been made through several near north south trending passive source seismic experiments in southern tibet to investigate the geometry and the nature of the underthrusting indian lithosphere an east west trending seismic array consisting of 48 seismographs was operated in the central lhasa block from september 2009 to november 2010 splitting of sks waves was measured and verified with different methods along the profile the direction of fast wave polarization is about 60 in average with small fluctuations the delay time generally increases from east to west between 0 2 s and 1 0 s and its variation correlates spatially with north south oriented rifts in southern tibet the sks wave arrives 1 0 2 0 s later at stations in the eastern part of the profile than in the west the source of the anisotropy estimated by non overlapped parts of the fresnel zones at stations with different splitting parameters is concentrated above ca 195 km depth all the first order features suggest that the geometry of the underthrusting indian lithospheric slab in the himalayan tibetan collision zone beneath southern tibet is characterized by systematic lateral variations a slab tearing and or breakoff model of indian lithosphere with different subduction angles is likely a good candidate to explain the observations

overlapping faults and their effect on fluid flow in different reservoir types a lidar based outcrop modeling and flow simulation study in this article we focus on the potential of fault overlap zones as conduits for fluid flow in a variety of reservoir types light detection and ranging lidar technology were applied to collect a three dimensional spatially constrained data set from a well exposed fault overlap zone that crops out in the devil s lane area of the canyonlands national park in utah a virtual outcrop was generated and used to extract structural and stratigraphic data that were taken into a reservoir modeling software and reconstructed the outcrop based model was flow simulated and used to test fluid flow through a real world fault overlap zone a structural framework was built based on collected outcrop data and combined with a series of nine different facies models the different facies models included an eolian model based on the outcrop and a range of synthetic fluvial and shallow marine systems results show that for certain depositional models cross fault reservoir communication may be poor despite the geometric connectivity of the relay beds this was the case for low net gross fluvial models and shoreface models conversely high net gross fluvial systems and eolian systems show good communication through the same relay zone overall the results show that in the presence of a fault overlap zone pressure communication across a relay ramp may still be poor depending on the scale of the faults and relay ramp as well as the geometry and volume of the sands

cenozoic tectonic evolution of qaidam basin and its surrounding regions part 1 the southern qilian shan nan shan thrust belt and northern qaidam basin cenozoic qaidam basin the largest active intermountain basin inside tibet figures importantly in the debates on the history and mechanism of tibetan plateau formation during the cenozoic indo asian collision to determine when and how the basin was developed we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern qilian shan nan shan thrust belt and northern qaidam basin our geologic observations provide new constraints on the timing and magnitude of cenozoic crustal thickening in northern tibet specifically our work shows that the southernmost part of the qilian shan nan shan thrust belt and contractional structures along the northern margin of qaidam basin were initiated in the paleocene early eocene 65 50 ma during or immediately after the onset of the indo asian collision this finding implies that stress was transferred rapidly through tibetan lithosphere to northern tibet from the indo asian convergent front located 1000 km to the south the development of the thrust system in northern qaidam basin was driven by motion on the altyn tagh fault as indicated by its eastward propagation away from the altyn tagh fault the eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of qaidam basin suggesting thrust loading was the main control on the basin formation and evolution the dominant structure in northern qaidam basin is a southwest tapering triangle zone which started to develop since the paleocene and early eocene 65 50 ma and was associated with deposition of an overlying southwest thickening growth strata sequence recognition of the triangle zone and its longevity in northern qaidam basin explains a long puzzling observation that cenozoic depocenters have been located consistently along the central axis of the basin this basin configuration is opposite to the prediction of classic foreland basin models that require the thickest part of foreland sediments deposited along basin edges against basin bounding thrusts restoration of balanced cross sections across the southern qilian shan nan shan thrust belt and northern qaidam basin suggests that cenozoic shortening strain is highly inhomogeneous varying from 20 to 60 both vertically in a single section and from section to section across the thrust belt the spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of cenozoic rotations in different parts of qaidam basin the observed crustal shortening strain also implies that no lower crustal injection or thermal events in the mantle are needed to explain the current elevation 3000 3500 m and crustal thickness 45 50 km of northern qaidam basin and the southern qilian shan nan shan thrust belt instead thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern qaidam basin and the southern qilian shan nan shan region

multi scale three dimensional distribution of fracture and igneous intrusion controlled hydrothermal dolomite from digital outcrop model latemar platform dolomites northern italy abstract in recent years fracture controlled hydrothermal dolomitization in association with igneous activity has gained interest in hydrocarbon exploration the geometry and distribution of dolomite bodies in this setting are of major importance for these new plays the latemar platform presents a spectacularly exposed outcrop analogue for carbonate reservoirs affected by igneous activity and dolomitization light detection and ranging lidar scanning and digital outcrop models doms of outcrops offer a great opportunity to derive geometrical information only a few analysis methods exist to quantitatively assess huge amounts of georeferenced three dimensional lithology data this study presents a novel quantitative approach to describe three dimensional spatial variation of lithology derived from doms this approach is applied to the latemar platform to determine dolomite body geometry and distribution in relation to crosscutting dikes a high resolution photorealistic dom of the latemar platform allows description of dolomite occurrences in three dimensions with high precision at platform scale this results in a unique lithology dataset of limestone dolomite and dike positions this dataset is analyzed by true three dimensional variography for the geospatial description of dolomite distribution in most studies three dimensional geostatistics is the combination of two dimensional horizontal and one dimensional vertical variation in this study the dolomite occurrences are extensive in three dimensions and cannot be reduced to a two dimensional one dimensional case therefore the concept of two dimensional variogram maps is expanded to a three dimensional description of lithology variation three dimensional anisotropy detection is used to derive principal directions in the occurrence of dolomite two small scale