microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

chronology and tectonic significance of cenozoic faults in the liupanshan arcuate tectonic belt at the northeastern margin of the qinghai tibet plateau abstract the liupanshan arcuate tectonic belt latb is located at the northeastern margin of the qinghai tibet plateau major strike slip and thrust faults in the liupanshan area are prominent cenozoic structures which are critical in understanding and reconstructing the tectonic deformation history this paper not only provides detailed investigations on geometric and kinematic characteristics of these faults in the latb but also dates the faults movements by electron spin resonance esr the latb underwent a succession of compression extension and again compression tectonic deformation processes since the cenozoic the liupanshan curved faults first experienced sinistral strike slip shear during 57 61 ma the liupanshan curved faults responded to the deformation caused by the eastward escape of the qinghai tibet plateau and acted as the northeastern boundary of the deformation timing for the formation of the liupanshan curved faults shows that the collision of the indian and eurasian plates must have occurred earlier than these faults activity because the latter is reflected the far field effect of the collision

direct ion microprobe u pb dating of fossil tooth of a permian shark abstract we report here direct ion microprobe dating of fossil tooth dentine of a permian fresh water shark orthacanthus senckenbergianus using the shrimp instrument recently installed at hiroshima university fifteen spots on the small sample approximately 2 mm 1 mm indicate a 238 u 206 pb isochron age of 266 18 ma and a tera wasserburg concordia intercept age of 266 24 ma in a three dimensional 238 u 206 pb 207 pb 206 pb 204 pb 206 pb diagram these permian ages are consistent with a 235 u 207 pb age of 453 170 ma and a 232 th 208 pb age of 235 310 ma suggesting indistinguishable depositional and early diagenetic ages of the fossil in its sedimentary sequences the success of the method depends on the chemical fractionation of uranium from lead in a specimen a few hundred microns in size and the consequent variations in lead isotopic compositions due to radioactive decay

natural hydraulic fractures in the wessex basin sw england widespread distribution composition and history bedding parallel veins of fibrous calcite beef are historical in the wessex basin the veins are common in mesozoic mudstones and shales especially of liassic to mid cretaceous ages cone in cone structures which consist of multiple nested cones are also well developed within the beef to investigate the distribution and the context of formation of beef in the basin we have made several field studies and analysed numerous samples the veins are widespread vertically and horizontally in the sedimentary sequence but they are especially common near or within potential source rocks for petroleum or near major tectonic faults the internal structures of some beef veins have revealed that they formed during late cretaceous to tertiary compressional inversion of the basin the typical composition for beef is of calcite with some pyrite and fragments of shale however inclusions or patches of hydrocarbons liquid or solid occur within calcite crystals or between fibres respectively according to some previous studies as well as ours beef veins of the wessex basin represent natural hydraulic fractures which formed as a result of fluid overpressure this may have resulted in part from chemical compaction of petroleum source rocks during late cretaceous to tertiary times indeed source rocks at outcrop in the wessex basin could be more mature than previously thought and the beef veins may be good markers of maturation

a revised chronology for tertiary sedimentation in the sikouzi basin implications for the tectonic evolution of the northeastern corner of the tibetan plateau abstract the space time pattern of development of high topography associated with the tibetan plateau remains incomplete due in large part to sparse proxy data that allow estimates of the growth of individual mountain ranges here we present the results of a stratigraphic investigation of a 3100 m section of tertiary fluvio lacustrine strata in the sikouzi basin located at the northeastern most corner of the tibetan plateau results of magnetostratigraphic analysis coupled with a newly discovered miocene in situ fossil assemblage suggest that the section preserves a nearly complete record extending from initial basin formation at 29 myr until 0 5 myr sediment accumulation rates increase from relatively slow accumulation during the oligocene miocene 9 cm kyr to rapid accumulation in the pliocene 22 cm kyr apparently occurring in two sustained pulses at 10 5 ma and 5 ma respectively the increase in accumulation rates starting at 10 5 ma is interpreted as heralding the initial uplift of the liupan shan consistent with cooling and exhumation of the range zheng et al 2006 the pliocene increase in accumulation rate is accompanied by a distinct change in lithofacies the appearance of coarse detritus with provenance from the madong shan and up section changes in bedding orientation that are interpreted as growth strata collectively our data suggest that the generation of relief in the madong shan began at 5 4 ma moreover analysis of paleomagnetic declinations from the sikouzi section reveals a clockwise rotation of the sikouzi basin during the time period 24 5 4 ma that was followed by a subsequent counterclockwise rotation 5 4 0 5 ma our study suggests that activity along the liupan shan haiyuan fault system probably initiated at 10 5 ma but that the present day configuration of the fault system and associated ranges near the fault tip dates to pliocene time

methods for determining deformation history for chocolate tablet boudinage with fibrous crystals abstract chocolate tablet boudinage with fibrous crystal growths between the boudinaged plates from two localities were studied in one from leytron valais switzerland the deformation history was found to be a succession of plane strain increments with the shortening direction perpendicular to the boudinaged sheet and the extension direction showing a progressive change in orientation within the sheet the incremental and finite strains were evaluated the other specimen from parys mountain anglesey great britain was found to have a more complex history with diachronous break up of the competent layer and flattening strain increments it was found that under these circumstances the direct graphical methods of determining finite and incremental strains gave inconsistent results a numerical model was developed which allowed the simulation of chocolate tablet structure with a complex deformation history the model was applied to the anglesey specimen and three possible strain histories for this structure were tried

the use of syntectonic fibres to determine strain estimates and deformation paths an appraisal abstract fibrous pressure shadows developed adjacent to rigid brittle inclusions are familiar features in many tectonites belief that these structures reflect the deformation path as once adjacent grains move apart has led to the derivation of a variety of techniques to determine both incremental and finite strain estimates these methods which can be divided into rigid fibre models e g durney and ramsay and deformable fibre models e g ellis display potentially serious problems when applied to field examples recent studies of microstructures within veins and pressure shadows support the concept that syntectonic fibre complexes can reflect deformation paths and are therefore useful markers of incremental and finite strain the problems mentioned therefore stem directly from the application of the techniques worked examples using these techniques give a variety of strain values dependent upon the extent to which a particular technique allows for volume change or fibre deformation this is useful locally however if the results are to be meaningful on a regional scale then it is imperative that the same technique be applied in the analysis of all fibres regardless of the local deformation path in such studies the merits of a particular technique in determining a correct strain value come second to allowing the spatial distribution of strain to be determined semi quantitatively and thus allowing comparison of similarly derived results with one another

ion microprobe u pb dating of apatite abstract to illustrate in situ sensitive high resolution ion microprobe shrimp analysis of apatites pb isotopes and pb u ratios of five apatite samples with different ages have been measured using shrimp ii ion microprobe at hiroshima university the prap apatite from a carbonatite complex at prairie lake ontario with a 207 pb 206 pb age of 1156 45 ma 2 was used as the standard for 206 pb 238 u 238 u 16 o 238 u calibration apatites from the poohbah lake alkaline complex give 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages of 2726 145 ma 2 and 2701 86 ma 2 in agreement with a conventional tims 207 pb 206 pb age of 2667 10 ma 2 and a k ar isochron age of 2706 46 ma 2 for the remaining three apatite samples the 204 pb 206 pb 238 u 206 pb and 204 pb 206 pb 207 pb 206 pb isochron ages obtained by shrimp are consistent with radiometric and geological ages in the literature

commencing uplift of the liupan shan since 9 5 ma evidences from the sikouzi section at its east side abstract the cenozoic evolution of the liupan shan situated at the northeast of the tibetan plateau will provide constraints to test the models and mechanisms of the evolution of the plateau in this contribution the sikouzi section at the east of the liupan shan has been selected to study liupan shan s uplift history at around 9 5 ma constrained by the magnetostratigraphy the sediment and depositing architecture characteristics obviously changed synchronously flow direction changed from e w to w e and accumulation rate increased to more than double all these evidences suggest that the liupan shan initiated uplifting at around 9 5 ma subsequently a stage of intense uplift happened during 8 2 7 3 ma indicated by the apatite fission track aft data across the liupan shan regional comparison indicates that this stage of uplift is not only with local but also regional significance the miocene uplift of the tibetan plateau triggered the intensification of the east asian monsoon and asian intercontinental aridity which has been implied by the pollen results of the sikouzi section

cenozoic tectonic evolution of the south ningxia region northeastern tibetan plateau inferred from new structural investigations and fault kinematic analyses abstract the northeastward growth process of the tibetan plateau has been a key issue to be long termly debated which is well documented by the south ningxia region at the northeasternmost periphery of the tibetan plateau due to its cenozoic convex to the northeast arcuate range and basin structures here new structural measurements and fault kinematic analysis together with new geochronological results delineate a two stage cenozoic tectonic evolution in the region providing the new structural evidences to decipher the northeastward growth process of the tibetan plateau the first stage is marked by widespread sedimentary basin formation during the oligocene to late miocene ca 30 10 5 ma under nw se extensional regime and subsequent basin inversion triggered by nw se compression in the late miocene ca 10 5 9 5 ma these events were probably associated mainly with the far field effect of the northwestward subduction of the pacific plate a little related to the plateau growth the second stage largely presents an intensive mountain building process and following re deformation since the late miocene ca 9 5 ma which was predominantly a result of the far field responses to the northeastward growth of the tibetan plateau and partially to the pacific subduction the second stage further comprises three alternating episodes of shortening and extension events the earliest episode of ne sw compression caused intensive crustal shortening in a long period from the late miocene to early pleistocene ca 9 5 1 8 ma leading to a significant mountain building process in this region a gentle ne sw extension subsequently dominated here in the late pleistocene ca 18 ka as manifested by the widespread appearance of paleo lakes along the nw striking boundary faults since the end of the late pleistocene ca 18 ka a youngest tectonic regime affected this region characteristic of a tectonic transpression causing evidently strike slip activities on the primary faults and the development of small scale pull apart basins along the haiyuan fault

sedimentary characteristics of cenozoic strata in central southern ningxia nw china implications for the evolution of the ne qinghai tibetan plateau abstract cenozoic sedimentary deposits in central southern ningxia province nw china are an important record of tertiary tectonic events along the evolving qinghai tibetan plateau s northeast margin shortly after the onset of the indo eurasia collision to the south a thrust belt and adjoining foreland basin began to form during 40 30 ma the eocene sikouzi formation developed in a distal setting to this basin in normal fault bound basins that may have formed in a forebulge setting subsequent deposition of the oligocene qingshuiying formation occurred during a phase of apparently less intense tectonism and the previous underfilled foreland basin became overfilled during the early miocene contractional deformation was mainly distributed to the west of the liupan shan this resulted in deformation of the qingshuiying formation as indicated by an unconformity with the overlying miocene hongliugou formation the unconformity occurs proximal to the haiyuan fault suggesting that the haiyuan fault may have begun movement in the early miocene in the late miocene thrusting occurred west of the southern helan shan and an unconformity developed between the hongliugou and qingshuiying formations proximal to the the cha gu fault relationships between the miocene stratigraphy and major faults in the region imply that during the late miocene the deformation front of the qinghai tibetan plateau had migrated to the cha gu fault along the western ordos margin and the xiang shan was uplifted central southern ningxia was then incorporated into the northeast propagating thrust wedge the driving force for ne propagation of the thrust wedge was most likely pronounced uplift of the northeastern plateau at the same time analysis of the sedimentary record coupled with consideration of the topographic evolution of the region suggests that the evolving fold and thrust belt experienced both forward breaking fold and thrust belt development and out of sequence fault displacements as the thrust wedge evolved and the foreland basin became compartmentalised the documented sedimentary facies and structural relationship also place constraints on the miocene recent evolution of the yellow river and its tributaries

petrography and isotopic geochemistry of bedding parallel fibrous gypsum veins in the neogene qingshuiying formation of the ningnan basin north china insights for growth model of antitaxial fibrous veins abstract bedding parallel fibrous gypsum veins which are widely developed in the neogene qingshuiying formation of the ningnan basin a tertiary basin located in the northeastern margin of the tibetan plateau provide valuable information on stress field fluid origin and host rock deformation during their formation the systematic petrographic observation and isotope analysis of both of veins and wall rocks were carried out to investigate the formation mechanism of bedding parallel fibrous gypsum veins the distribution of fibrous gypsum veins shows vertical heterogeneity and mainly occurs in the middle and lower part of the qingshuiying formation with relatively high gypsum content single fibrous gypsum veins consist of a median zone and two fibrous zones the median zone is characterized by blocky gypsum crystals and multiple host rock fragments formed by crack seal events the fibrous zone is composed of parallel gypsum fibres a high angle to the vein walls indicating shear component vein opening is considered to be the result of fluid overpressure caused by horizontal compression in low permeability mudstone during basin inversion fibrous gypsum crystals grow continuously without obvious growth competition between adjacent crystals this indicates that growth of gypsum fibres occurs in limited space even without fractures the main driving force for vein dilation is force of crystallization of gypsum fibre growth and fluid pressure also has a certain contribution the sulfur and strontium isotopes of gypsum veins exhibit a high degree of consistency with wall rocks which indicates the material of the fibrous gypsum veins is derived from the wall rock a suitable growth model of bedding parallel fibrous gypsum veins in the ningnan basin is established which explains the process of vein interaction and the formation of v shaped or u shaped solid inclusions

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

tectonically driven organic fluid migration in the dabashan foreland belt evidenced by geochemistry and geothermometry of vein filling fibrous calcite with organic inclusions abstract fibrous calcite veins with organic inclusions have been widely considered as indicators of oil and gas generation and migration under overpressure abundant fibrous calcite veins containing organic bearing inclusions occur in faulted lower paleozoic through triassic hydrocarbon source rocks in the dabashan foreland belt dbf 13cpdb and 18opdb values of the fibrous calcite range from 4 8 to 1 9 and 12 8 to 8 4 respectively which is lighter than that of associated carbonate host rocks ranging from 1 7 to 3 1 and 8 7 to 4 5 a linear relationship between 13cpdb and 18opdb indicates that the calcite veins were precipitated from a mixture of basinal and surface fluids the fibrous calcite contains a variety of inclusions such as solid bitumen methane bearing all liquid inclusions and vapor liquid aqueous inclusions homogenization temperatures of aqueous inclusions range from 140 to 196 c with an average of 179 c salinities of aqueous inclusions average 9 7 wt nacl independent temperatures from bitumen reflectance and inclusion phase relationships of aqueous and methane bearing inclusions were used to determine fluid pressures results indicate high pressures elevated above typical lithostatic confining pressure from 150 to 200 mpa the elevated salinity and high temperature and pressure conditions of the fibrous calcite veins argue against an origin solely from burial overpressure resulting from clay transformation and dehydration reactions instead fluid inclusion p t data and geochemistry results and regional geology indicate abnormally high pressures during fluid migration these findings indicate that tectonic stress generated fracture and fault fluid pathways and caused migration of organic bearing fluids from the dbf during the yanshan orogeny

in situ ion microprobe u pb dating and ree abundances of a carboniferous conodont we report here in situ ion microprobe u pb dating of a conodont micro fossil using an ion microprobe method thirteen spots on the single fragment of the carboniferous conodont size approximately 800 m 100 m yield a 238u 206pb isochron age of 323 36 ma and a tera wasserburg concordia intercept age of 332 44 ma in a three dimensional 238u 206pb 207pb 206 pb 204pb 206pb diagram these ages are consistent with the depositional and early diagenetic ages of the fossil in its host mississippian sedimentary sequence within experimental error the success of the method depends on the chemical fractionation of u from pb within a hundred m length scale and the consequent variations in pb isotopic compositions due to radioactive decay shale normalized rare earth element ree abundances of two spots on the same sample show flat patterns from light ree to middle ree and decreases from middle ree to heavy ree with negative anomalies of both ce and eu the ree characteristics are significantly different from those of devonian conodonts reported by other workers suggesting discrepant redox states and or formation environments

fibrous calcite veins overpressures and primary oil migration the fibrous calcite veins found parallel to the bedding of certain shales may have been formed during burial as a consequence of overpressuring their presence could even be indicative of former overpressures this suggestion if it can be upheld carries implications for theories of primary oil migration

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

quaternary fans and terraces in the khumbu himal south of mount everest their characteristics age and formation large fans and terraces are frequent in the khumbu himal within the high himalayan valleys south of mt everest these features are composed of massive matrix and clast supported diamicts that were formed from both hyperconcentrated flows and coarse grained debris flows cosmogenic radionuclide crn exposure ages for boulders on fans and terraces indicate that periods of fan and terrace formation occurred at c 16 c 12 c 8 c 4 and c 1 5 ka and are broadly coincident with the timing of glaciation in the region the dating precision is insufficient to resolve whether the surfaces formed before during or after the correlated glacial advance however the sedimentology and morphostratigraphic and geomorphological relationships suggest that fan and terrace sedimentation in this part of the himalaya primarily occurs during glacier retreat and is thus paraglacial in origin furthermore modern glacial lake outburst floods and their associated deposits are common in the khumbu himal as the result of glacial retreat during historical times we therefore suggest that late quaternary and holocene fan and terrace formation and sediment transfer are probably linked to temporal changes in discharge and sediment load caused by glacier oscillations responding to climate change the timing of major sedimentation events in this region can be correlated with fans and terraces in other parts of the himalaya suggesting that major sedimentation throughout the himalaya is synchronous and tied to regional climatic oscillations bedrock incision rates calculated from strath terrace ages average c 3 9 mm a 1 suggesting that the overall rate of incision is set by regional uplift

on the crystallisation pressure of gypsum we estimate the crystallisation pressure of gypsum quantitatively with reference to the geological context of the gypsum keuper formation the formation contains sulphatic claystones which have the property of swelling in the presence of water and have caused substantial structural damage to the linings of several tunnels in switzerland and germany the swelling of these rocks is attributed to the transformation of anhydrite into gypsum which occurs via the dissolution of anhydrite in pore water and the precipitation of gypsum from the solution this simultaneous dissolution precipitation process happens because the solubility of gypsum is lower than that of anhydrite under the conditions prevailing after tunnelling and it does not cease until all of the anhydrite has been transformed the elementary mechanism behind the development of the macroscopically observed swelling pressure is the growth of gypsum crystals inside the rock matrix if a crystal is in contact with a supersaturated solution but its growth is prevented by the surrounding matrix it then exerts a so called crystallisation pressure upon the pore walls in the present paper the crystallisation pressure is calculated by means of a thermodynamic model that takes coherent account of all relevant parameters including the chemical composition of the pore water and pore size variations in these parameters lead to a very wide range of crystallisation pressures from zero to several tens of megapascals by using the results of mercury intrusion porosimetry and chemical analyses of samples from three swiss tunnels however we show that the range of predicted values can be reduced significantly with the help of standard project specific investigations