a simple multicloud parameterization for convectively coupled tropical waves part i linear analysis abstract recent observational analysis reveals the central role of three multicloud types congestus stratiform and deep convective cumulus clouds in the dynamics of large scale convectively coupled kelvin waves westward propagating two day waves and the madden julian oscillation a systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds a systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation a nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere in particular a dry troposphere

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

planetary scale selection of the madden julian oscillation in an air sea coupled dynamic moisture model the authors present an air sea coupled dynamic moisture asdm model to explore the mechanism of preferred planetary scale of the madden julian oscillation mjo this asdm model extended from the original frictionally coupled dynamic moisture model and a mixed layer model can present a good simulation of planetary scale characteristics of the mjo including a slow eastward propagation of 5 m s 1 coupled rossby kelvin wave like structure and phase leading of convective center by warm sea surface temperature sst it is interesting that the planetary scale selection in terms of instability is only found in the nonlinear asdm model with the assumption of positive only heating such a scale selection however cannot be found in the asdm model with linear heating or in an uncoupled atmosphere model the essential mechanism for the scale selection is nonlinear positive only heating and the air sea interaction primarily provides an instability source to support this scale selection this scale selection is attributed to different phase speeds of coupled moist rossby kelvin waves and dry kelvin waves from short wave initial perturbations the easterly wind anomalies of eastward propagating dry kelvin waves from a stronger wave component will catch up with other weaker moist components and suppress their westerly wind anomalies resulting in weak sst gradient as well as reduced moisture convergence and precipitation for these suppressed components as a result the wavenumber one structure is selected the warm pool like mean state will select the stronger component among the initial short wave perturbations and accelerate this scale selection process these results provide new insight into mjo mechanism in terms of air sea interaction

practical estimation of compression behavior of clayey silty sands using equivalent void ratio concept abstractclayey silty sands are widespread as naturally sedimentary soils such as marine deposits in estuaries and offshore locations they belong to a unique class of gap graded soils featuring a d

reply to comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault abstract in the eastern part of ladakh the right lateral karakoram fault zone kfz bifurcates into two strands called the pangong strand and the tangtse strand these two strands bound a region called the pangong transpression zone ptz which consists of migmatitic dioritic gneiss calc silicates and the durbuk pluton a pluton of two mica leucogranite outcrop scale observations suggest pervasive migration of leucogranitic melt through the existing tectonic structures of the gneiss magnetic fabric from both the tectonized and undeformed parts of the durbuk pluton show parallelism with the tectonic fabric of the host gneiss which along with pervasive melt migration indicates syn kinematic relationship between deformation along the kfz leucogranite magmatism and emplacement of the durbuk pluton u pb geochronology of zircons from the dioritic gneiss yields a crystallization age of 63 6 1 5 ma and also shows younger zircon growth down to 13 ma which suggest arc magmatism at 65 ma followed by partial melting and leucogranite magmatism in the kfz till 13 ma one two mica leucogranite sample from the durbuk pluton gives a crystallization age of 22 7 0 5 ma as the durbuk pluton is syn tectonic with deformation along kfz it is inferred that the kfz initiated at least 23 ma ago

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

quartz fabrics in the alpine fault mylonites influence of pre existing preferred orientations on fabric development during progressive uplift strong quartz crystallographic preferred orientations cpos were developed during dislocation creep in the mylonite zone exposed in the hanging wall of the dextral reverse alpine fault zone new zealand the cpos have a consistent asymmetry indicating a high ratio of simple to pure shear strain with a shear sense of dextral up to the nw consistent with the mesoscopic shear sense indicators and with slip on the active fault there is a transition from y maxima and asymmetric single girdles in mylonites and ultramylonites within 300 m of the present fault trace to cross girdle fabrics in the protomylonites further from the fault the strong y maxima or single girdle cpos are ascribed to high ductile shear strains under amphibolite facies conditions while the cross girdle patterns found in the protomylonites are interpreted to represent deformation under lower temperature conditions however the observed fabric transition cannot logically be attributed to variations in temperature during the last increment of deformation the highly oriented y maximum fabrics formed at high temperature contain very few grains suitably oriented for basal slip so that the slip systems activated during subsequent shear at lower temperatures during exhumation were prism or rhomb further from the fault where shear strains under high temperature conditions were lower weaker fabrics developed under these conditions were modified at higher levels in the crust into crossed girdle patterns this interpretation implies that intense localisation of shear strain along the fault zone within the lower crust must have occurred in order for the high temperature fabrics to become sufficiently intense to be preserved this in turn implies that deep seated localised shear was taking place early during the evolution of the current oblique slip plate boundary fault the results of this study also indicate that the current model that operation of certain slip systems in quartz is mostly a function of temperature is incorrect future work should consider the effects of deformation history total strain and the presence of other mineral phases

microstructures and quartz lattice preferred orientations in the eclogite bearing migmatitic gneisses of the d entrecasteaux islands papua new guinea 1 lattice preferred orientations lpo of quartz in gneiss domes of the d entrecasteaux islands woodlark rift shed insight into exhumation of the world s youngest 5 7 ma eclogite bearing terrane at cm yr rates we focus on deformation that affected the terrane as it transited between lower crustal depths and the surface including 1 grain scale deformation mechanisms and 2 style of flow and mode of emplacement of the domes electron backscatter diffraction was used to analyze microstructure and lpos of 37 quartzofeldspathic gneiss samples that enclose meter scale mafic blocks preserving original eclogite facies assemblages during exhumation of the ultrahigh pressure uhp terrane gneisses were retrogressed in the amphibolite facies at lower crustal depths the lpos change from dome cores to carapaces consistent with decreasing deformational temperatures in the relatively chilled outer carapaces of the domes the quartz lpos consist of mostly crossed girdle c axis patterns with some cleft girdle and small circle lpos and record dislocation creep accommodated by mixed slip in the cores of the migmatitic domes a chessboard pattern of subgrains is common and quartz lpos primarily record prism c slip probably at 630 c other microstructures indicate recovery by high temperature grain boundary migration grain boundary mobility was anisotropic leading to strong grain shape fabrics oblique to foliation but not obviously relatable to shear sense evidence for melt present deformation is abundant and microstructures including partially dissolved feldspar grains indicate some deformation by fluid assisted grain boundary diffusion creep lpos in carapace rocks are symmetrical recording flow that was dominantly coaxial we interpret the gneiss domes to have been emplaced into the rift as partially molten diapirs

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

experiments on tropical circulation with a simple moist model a simple model of the circulation of the tropical atmosphere is constructed where the circulation is determined entirely by the sea surface temperature s s t pattern or rather by a forcing field which is closely related to s s t it is an equatorial beta plane model with an assumed simple baroclinic vertical structure the moisture and precipitation fields are allowed to evolve freely so there are feedbacks between the latent heating which contributes to driving the motion and the low level velocity field which produces the moisture convergence required to generate precipitation experiments with idealized pacific s s t distributions produce qualitatively realistic precipitation patterns for january a patch in the west pacific over the equator and july a zonal strip north of the equator analytic solutions for zonally symmetric flow are given to illustrate the basic dynamics and to study the parameter dependence of the precipitation an analysis of zonal variations shows that a good simplifying approximation for this component is to neglect rayleigh friction while retaining newtonian cooling the effect of changing the zonal contrast in the prescribed forcing is to gradually alter the circulation from hadley like to walker like the model suggests that along the equator a relatively small contrast is needed to break a zonal band of precipitation

kinematic evolution of the ama drime detachment insights into orogen parallel extension and exhumation of the ama drime massif tibet nepal abstract the ama drime massif is a north south trending antiformal structure located on the southern margin of the tibetan plateau that is bound by the ama drime and nyonno ri detachments on the western and eastern sides respectively detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the ama drime detachment to document spatial and temporal patterns of deformation deformation temperatures estimated from quartz and feldspar microstructures quartz c axis fabrics and two feldspar geothermometry of asymmetric strain induced myrmekite range between 400 and 650 c micro and macro kinematic indicators suggest west directed displacement dominated over this temperature range mean kinematic vorticity estimates record early pure shear dominated flow 49 66 pure shear overprinted by later simple shear 1 57 pure shear high strain 36 50 shortening and 57 99 down dip extension dominated flow during the later increments of ductile deformation exhumation of the massif was accommodated by at least 21 42 km of displacement on the ama drime detachment samples from the nyonno ri detachment were exhumed from similar depths we propose that exhumation on the nyonno ri detachment during initiation of orogen parallel extension 11 13 ma resulted in a west dipping structural weakness in the footwall that reactivated as the ama drime detachment

temperature and strain gradients through lesser himalayan rocks and across the main central thrust south central bhutan implications for transport parallel stretching and inverted metamorphism in order to understand mass and heat transfer processes that operated during himalayan orogenesis we collected temperature finite and incremental strain and kinematic vorticity data through a 5 km thickness of lesser and greater himalayan rocks in southern bhutan this transect crosses two major shear zones the main central thrust mct and shumar thrust st raman spectroscopy on carbonaceous material and garnet biotite thermometry are integrated with deformation temperatures from quartz petrofabrics these data define inverted field gradients that correspond in structural position with the mct and st which are separated by sections in which temperatures remain essentially constant temperatures increase from 400 500 c to 700 750 c between 675 m below and 200 m above the mct this defines a 269 44 c km inverted gradient interpreted to have formed via high magnitude 100 250 km shearing on a discrete mct zone delineated by the limits of inverted metamorphism temperatures increase from 300 400 c to 400 530 c across the st which is attributed to differences in maximum burial depth of hanging wall and footwall rocks strain and vorticity data indicate that lesser and greater himalayan rocks were deformed by layer normal flattening transport parallel lengthening and foliation normal shortening increase from 38 71 and 36 49 respectively between 2 3 1 0 km below the mct the mct acted as a stretching fault with translation on the order of 100 s of km accompanied by transport parallel stretching of footwall and hanging wall rocks on the order of 10 s of km this demonstrates that stretching accommodated between major shear zones can make a significant contribution to cumulative mass transfer

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

a new empirical calibration of the quartz c axis fabric opening angle deformation thermometer abstract the opening angle of quartz c axis fabrics oa is strongly temperature dependent and has proven to be a powerful deformation thermometer for natural metamorphic rocks previous considerations of empirical data have identified a linear correlation between oa and temperature between 250 and 650 c and no correlation above 650 c however possible effects of pressure have not been investigated we expanded the data set of oa versus temperature including data from rocks deformed over 300 1050 c and 2 5 15 kbar disregarding possible effects of pressure the oa temperature relationship can be described by two linear correlations for the intervals 250 650 c and 650 1050 c t c 6 9 o a degrees 48 250 c t 650 c and o a 87 t c 4 6 o a degrees 258 650 c t 1050 c and o a 87 the change on the curve slope of the oa temperature relationship correlates approximately to the low to high quartz transition and to changes in the dynamic recrystallization mechanism from subgrain rotation to grain boundary migration the available data suggest that pressure has a secondary effect accompanying the major temperature dependence of oa which is particularly important for temperatures above 650 c where the correlation between oa and temperature is less pronounced for fixed pressures the oa has logarithmic relationships with temperature over the range 250 1050 c the following thermometer equation is formulated from a multiple regression t c 410 44 ln oa degrees 14 22 p kbar 1272 an uncertainty of 50 c is inherited from the petrological temperature estimates of the natural samples the data suggest the gradual increasing importance of prism c slip relative to slip in quartz with rising temperature under conditions of average geological strain rate and water weakening prism c slip dominates for deformation above 700 c

oriented grain growth and modification of frozen anisotropy in the lithospheric mantle abstract seismic anisotropy throughout the oceanic lithosphere is often assumed to be generated by fossilized texture formed during deformation at asthenospheric temperatures close to the ridge here we investigate the effect of high temperature and high pressure static annealing on the texture of previously deformed olivine aggregates to simulate residence of deformed peridotite in the lithosphere our experiments indicate that the orientation and magnitude of crystallographic preferred orientation cpo will evolve due to the preferential growth of grains with low dislocation densities these observations suggest that texture and stored elastic strain energy promote a style of grain growth that modifies the cpo of a deformed aggregate we demonstrate that these microstructural changes alter the orientation distributions and magnitudes of seismic wave velocities and anisotropy therefore static annealing may complicate the inference of past deformation kinematics from seismic anisotropy in the lithosphere

dem modeling of large scale triaxial test of rock clasts considering realistic particle shapes and flexible membrane boundary abstract this paper presents a novel framework for the discrete modeling of the large scale triaxial test of rock clasts considering both the realistic particle shapes and veritable flexible boundary condition first real shaped particle models for the tested rock clasts are precisely reconstructed using the close range photogrammetry technique the rubber membrane was modeled by a series of bonded particles then the laboratory procedures of the triaxial test i e sample preparation isotropic compression and shearing are reproduced in the dem simulations with consideration of the veritable confining boundary to ensure more reliable numerical results a systematic dem calibration framework is established to determine the modeling parameters based on a series of calibration experiments including tensile test suspension test clast membrane sliding test and large scale triaxial test finally the proposed method is applied to investigate the effects of confining pressure on the macro and micro mechanical behaviors of rock clasts the presented works lay a foundation for further studies on revealing the mechanisms of the conventional triaxial test e g the effect of end restraint and rubber membrane moreover the proposed systematic framework for calibration of modeling parameters can be applied to precisely capture the real mechanical properties of various types of granular rock like materials in dem simulations

impact of air sea coupling on the madden julian oscillation in a general circulation model abstract the impact of air sea coupling on the dynamics of the tropical madden julian oscillation mjo is investigated with an atmospheric general circulation model gcm coupled to an ocean mixed layer model in the uncoupled gcm where climatological sea surface temperature sst is specified realistic space time spectra of near equatorial zonal wind and precipitation are produced with power concentrated at eastward wavenumbers 1 3 with periods of 35 90 days however the simulated mjo is roughly 50 stronger than observed largely resulting from enormous activity during northern summer furthermore during southern summer when the observed mjo is most dominant across the indian and western pacific oceans intraseasonal variance in the uncoupled model is overly concentrated to the north and east of australia with little activity extending into the equatorial indian ocean contrary to other recent modeling studies coupling did not alleviate either of these problems nor did it have any other apprecia

atmospheric convergence feedback in a simple model for el nino abstract a parameterization is developed for the feedback between dynamics and heating associated with moisture convergence in the tropical atmospheric boundary layer the feedback improves the ability of a simple model to simulate observed anomalies of the tropical atmosphere during el nino events in particular two features of the observations are reproduced by including the feedback process the smaller scale of atmospheric anomalies as compared to sst anomalies and the focusing of the anomalies in the vicinity of the mean convergence zones the principal remaining shortcomings of the model are discussed

comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault by k sen b k mukherjee and a s collins journal of structural geology 62 2014 13 24

orogen parallel deformation of the himalayan midcrust insights from structural and magnetic fabric analyses of the greater himalayan sequence annapurna dhaulagiri himalaya central nepal the metamorphic core of the himalaya greater himalayan sequence ghs in the annapurna dhaulagiri region central nepal recorded orogen parallel stretching during mid crustal evolution anisotropy of magnetic susceptibility ams and field based structural analyses suggest that mid crustal deformation of the amphibolite facies core of the ghs occurred under an oblate sub oblate strain regime with associated formation of low angle northward dipping foliation magnetic and mineral stretching lineations lying within this foliation from the top of the ghs record right lateral orogen parallel stretching we propose that oblate strain within a mid crustal flow accommodated oblique convergence between india and the arcuate orogenic front without need for strain partitioning in the upper crust oblate flattening may have also promoted orogen parallel melt migration and development of melt depleted regions between km3 scale leucogranite culminations at 50 100 km intervals along orogen strike following cessation of flow continued oblique convergence led to upper crustal strain partitioning between orogen perpendicular convergence on thrust faults and orogen parallel extension on normal and strike slip faults in the annapurna dhaulagiri himalaya orogen parallel stretching lineations are interpreted as a record of transition from mid crustal orogen perpendicular extrusion to upper crustal orogen parallel stretching our findings suggest that mid crustal flow and upper crustal extension could not be maintained simultaneously and support other studies from across the himalaya which propose an orogen wide transition from mid crustal orogen perpendicular extrusion to upper crustal orogen parallel extension during the mid miocene the 3d nature of oblate strain and orogen parallel stretching cannot be replicated by 2d numerical simulations of the himalayan orogen

multiscale atmosphere ocean interactions and the low frequency variability in the equatorial region abstractin the present study a simplified multiscale atmosphere ocean coupled model for the tropical interactions among synoptic intraseasonal and interannual scales is developed two nonlinear equatorial plane shallow water equations are considered one for the ocean and the other for the atmosphere the nonlinear terms are the intrinsic advective nonlinearity and the air sea coupling fluxes to mimic the main differences between the fast atmosphere and the slow ocean suitable anisotropic multispace multitime scalings are applied yielding a balanced synoptic intraseasonal interannual el nino sinen regime in this distinguished balanced regime the synoptic scale is the fastest atmospheric time scale the intraseasonal scale is the intermediate air sea coupling time scale common to both fluid flows and el nino refers to the slowest interannual ocean time scale the asymptotic sinen equations reveal that the slow wave amplitude evolution depends on both types of nonlinearities analytic solution

fabric transitions in quartz via viscoplastic self consistent modeling part i axial compression and simple shear under constant strain quartz is a common crustal mineral that deforms plastically in a wide range of temperatures and pressures leading to the development of different types of crystallographic preferred orientation cpo patterns in this contribution we present the results of an extensive modeling of quartz fabric transitions via a viscoplastic self consistent vpsc approach for that we have performed systematic simulations using different sets of relative critical resolved shear stress of the main quartz slip systems we have performed these simulations in axial compression and simple shear regimes under constant von mises equivalent strain of 100 1 73 assuming that the aggregates deformed exclusively by dislocation glide some of the predicted cpos patterns are similar to those observed in naturally and experimentally deformed quartz nevertheless some classical cpo patterns usually interpreted as result from dislocation glide e g y maxima due to prism slip are clearly not developed in the simulated conditions in addition we reported new potential preferred orientation patterns that might happen in high temperature conditions both in axial compression and simple shear we have demonstrated that cpos generated under axial compression are usually stronger that those predicted under simple shear due to the continuous rotation observed in the later simulations the fabric strength depends essentially on the dominant active slip system and normally the stronger cpos result from dominant basal slip in followed by rhomb and prism c slip whereas prism slip does not produce strong fabrics the opening angle of quartz 0001 fabric used as a proxy of temperature seems to be reliable for deformation temperatures of 400 c when the main slip systems have similar behaviors

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

prism c slip in the quartzites of the oakhurst mylonite belt california abstract quartz c axis fabrics from 21 amphibolite facies quartzites of the oakhurst mylonite belt california suggest that prism c prism a and basal a slip systems were activated during deformation qualitative two dimensional kinematic models consistent with meso and microscopic shear criteria are constructed based on a regime of combined pure and simple shear in this kinematic framework most of the observed c axis fabric patterns of the oakhurst mylonite belt can be explained if prism c slip was dominant during the early increments of deformation until a transition to dominant basal a slip occurred an apparent relationship between grain size and type of crystallographic fabric is interpreted as resulting from some quartz syntectonic vein quartz having recorded only the latest increments of deformation comparison with the metamorphic evolution of fault zones of similar tectonic origin in california suggests that prism c slip was enhanced by the circulation of hot fluids which hydrolytically weakened quartz and allowed prism c slip to occur at relatively low temperature

dynamic recrystallization processes in plagioclase porphyroclasts abstract recrystallization processes in plagioclase porpyroclasts were studied in samples from an anorthositic gabbro of the jotun complex south norwegian caledonides the deformation took place at a temperature of approximately 700 c and at pressures below 900 mpa two populations of plagioclase porphyroclasts can be distinguished based on microstructural observations the crystallographic orientation and grain shapes for the two populations are interpreted as soft and hard orientations of the dominant slip system 010 001 with respect to the kinematic reference system the orientations of porphyroclasts and recrystallized grains were measured with a u stage microscope analysis of misorientations between porphyroclasts and adjacent recrystallized grains yields different results for the two types of porphyroclasts in type 1 porphyroclasts soft orientation the misorientation is inferred to be caused by subgrain rotation due to the activation of the 010 001 slip system resulting in a host control orientation relationship whereas in type 2 porphyroclasts hard orientation no dominant misorientation relationship could be identified the slip systems of the dislocations inferred from transmission electron microscopy tem analysis correspond well with the results of the u stage misorientation analysis in type 2 porphyroclasts hard orientation micro fracturing was observed in the tem whereas microfractures are absent in type 1 porphyroclasts soft orientation micro fracturing is likely to be the mechanism for nucleation of new grains in type 2 porphyroclasts resulting in a no host control orientation relationship between porphyroclasts and recrystallized grains

plastic anisotropy and fabric evolution in sheared and recrystallized quartz single crystals 1 the effect of a lattice preferred orientation on the flow strength of quartz aggregates dynamically recrystallized from single crystals of synthetic quartz was investigated using general shear experiments in a griggs apparatus experiments were conducted at shear strains up to 5 at a temperature of 900 c confining pressure of 1 5 gpa and shear strain rate of 10 5 s 1 three starting orientations of crystal were used to activate three slip systems basal a prism c and prism a although slip induced rotation of the crystal axes in the first two orientations led to the activation of additional slip systems for crystals with higher water contents basal a and prism a orientations are relatively weak and prism c orientations are stronger all three initial crystal orientations undergo dynamic recrystallization with increasing shear strain although the strain required for 100 recrystallization varies 2 for prism c slip 3 8 for basal a slip and 5 for prism a slip for all three starting orientations distinct domains of recrystallized grains develop with c axes parallel to y of the strain ellipsoid ymax replacing recrystallized grains of other orientations the ymax domains increase in size with increasing strain in addition strain markers show that strain is highly localized within the ymax domains indicating geometrical softening of up to an order of magnitude in effective viscosity

an air sea coupled skeleton model for the madden julian oscillation this work is an extension and improvement of the minimal madden julian oscillation mjo skeleton model developed by majda and stechmann which can capture some important features of the mjo slow eastward propagation quadrupole vortex structure and independence of frequency on wavelength but is unable to produce unstable growth and selection of eastward propagating planetary waves with the addition of planetary boundary layer frictional moisture convergence these deficiencies can be remedied the frictional boundary layer selects the planetary scale eastward propagation as the most unstable mode but the dynamics remains confined to atmospheric processes only here the authors study the role of air sea interaction by implementing an oceanic mixed layer ml model of wang and xie into the mjo skeleton model in this new air sea coupled skeleton model the features of the original skeleton model remain additionally the air sea interaction under mean westerly winds is shown to produce a strong instability that selectively destabilizes the eastward propagating planetary scale waves although the cloud shortwave radiation seasurfacetemperature crs feedbackdestabilizesbotheastwardand westward modes theair sea feedback associated with the evaporation and oceanic entrainment favors planetary scale eastward modes over the western hemisphere where easterly background winds prevail the evaporation and entrainment feedbacks yield damped modes indicating that longitudinal variation of the mean surface winds plays an important role in regulation of the mjo intensity in addition to the longitudinal variation of the mean sea surface temperature or mean moist static stability this theoretical analysis suggests that accurate simulation of the climatological mean state is critical for capturing the realistic air sea interaction and thus the mjo

thermo kinematic evolution of the annapurna dhaulagiri himalaya central nepal the composite orogenic system the himalayan orogen represents a composite orogenic system in which channel flow wedge extrusion and thrust stacking operate in separate orogenic domains with distinct rheologies and crustal positions we analyze 104 samples from the metamorphic core greater himalayan sequence ghs and bounding units of the annapurna dhaulagiri himalaya central nepal optical microscopy and electron backscatter diffraction ebsd analyses provide a record of deformation microstructures and an indication of active crystal slip systems strain geometries and deformation temperatures these data combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the ghs the profiles define a three stage thermokinematic evolution from midcrustal channel flow stage 1 7008c to 550 6508c to rigid wedge extrusion stage 2 400 6008c and duplexing stage 3 280 4008c these tectonic processes are not mutually exclusive but are confined to separate rheologically distinct orogenic domains that form the modular components of a composite orogenic system these orogenic domains may be active at the same time at different depths positions within the orogen the thermokinematic evolution of the annapurna dhaulagiri himalaya describes the migration of the ghs through these orogenic domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems

antecedents and self induction of active break south asian monsoon unraveled by satellites 1 understanding the origin and perpetuation of the monsoon cycle has eluded scientists for decades using a suite of unprecedented satellite measurements we show that the antecedents of the active break monsoon emerge in the western equatorial indian ocean eio the initiation of a new rainy phase in the western eio is preceded by in situ surface wind convergence and central eio warming both are induced by the subdued condition over the eastern eio set up in the previous cycle thus a self induction mechanism appears to be operating in maintenance of the indian monsoon intraseasonal oscillation the finding here offers a focus for prediction of the active break indian monsoon with potential predictability about four weeks in advance

simulation of the madden julian oscillation in a coupled general circulation model part ii the role of the basic state abstract in part i of this study it was shown that air sea coupling had a positive impact on some aspects of the simulation of the madden julian oscillation mjo by a gcm however errors in the basic state climate of that gcm appeared to be preventing the mjo related convection from propagating into the west pacific in this paper the actual impact of these errors will be addressed an integration of a flux adjusted version of the coupled model has been performed which has reduced basic state errors in the west pacific in this version of the coupled gcm the mjo does propagate into the west pacific the simulation of the mjo by a coupled model with the same atmospheric component but a different ocean gcm is also analyzed this coupled gcm has similar systematic errors in low level zonal wind and precipitation to the model studied in part i but with warmer ssts results from this experiment together with the other available evidence suggest that it is the errors in the low level zonal wind component

seasonality in the madden julian oscillation abstract this study using observational data and global reanalysis products synthesizes existing knowledge on the seasonality in the madden julian oscillation mjo and discusses its possible dependence on the mean background state the seasonality in the mjo is documented in terms of its components in low level zonal wind and precipitation a single peak season boreal winter exists near the equator in the indian and western pacific oceans for the broad tropical region however the seasonality in the mjo is featured by a latitudinal migration across the equator between two peak seasons the primary peak season is in boreal winter december march during which mjo signals are mainly confined to the indian and western pacific ocean and reach their maxima in the south pacific convergence zone the secondary peak season is boreal summer june september during which the strongest mjo occurs north of the equator from the bay of bengal to the south china sea and another separated region of strong mjo

ebsd microfabric study of pre cambrian deformations recorded in quartz pebbles from the sierra de la demanda n spain abstract we describe a new method for the reorientation of lattice preferred orientation data in the absence of a pre constrained kinematic reference frame the method enables us to present conventional quartz fabric diagrams after measurements taken from rock sections with a general orientation with respect to foliation and lineation a microstructural and electron back scattered diffraction ebsd study of quartz pebbles in early cambrian conglomerates following this method permit us to recognize a variety of fabrics that resulted from syn metamorphic ductile deformation under variable temperatures up to 650 c the likely source area of the conglomerates was a proterozoic basement candidates for source rock correlations include neoproterozoic units similar to those outcropping in the northern iberian massif neoproterozoic medium to high grade metamorphic rocks as those outcropping in sw iberia or a neoarchean to mesoproterozoic concealed basement

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

a frictional skeleton model for the madden julian oscillation abstractthe madden julian oscillation mjo is a multiscale system a skeleton model developed by majda and stechmann can capture some of planetary scale aspects of observed features such as slow eastward propagation nondispersive behavior and quadrupole vortex structure however the majda stechmann model cannot explain the source of instability and the preferred planetary scale of the mjo since the mjo major convection region is leaded by its planetary boundary layer pbl moisture convergence here a frictional skeleton model is built by implementing a slab pbl into the neutral skeleton model as a skeleton model allowing the scale interaction this model is only valid for large scale waves this study shows that the pbl frictional convergence provides a strong instability source for the long eastward modes although it also destabilizes very short westward modes for the long waves wavenumber less than 5 the pbl ekman pumping moistens the low troposphere to the east of the mjo convective envel

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

midcrustal discontinuities and the assembly of the himalayan midcrust detailed quartz lattice preferred orientation lpo data define two structural discontinuities in the exhumed high grade metamorphic core of the himalaya exposed in the upper tama kosi region of east central nepal the structures are marked by abrupt breaks in a general trend of up structural section increasing quartz lpo defined deformation temperatures deformation associated with the upper structural discontinuity which occurs within sillimanite grade rocks is postpeak metamorphism in both the hanging wall and the footwall new geochronologic data constrain the timing of metamorphism in the hanging wall of the upper discontinuity to between 24 and 16 ma indistinguishable from previously published ages for the footwall movement across this structure represents early miocene strain localization and thickening in the himalayan midcrust movement across the lower discontinuity which occurs between staurolite and kyanite grade rocks appears to be synmetamorphic with material in its footwall at approximately 10 ma but postpeak metamorphism for material in its hanging wall this movement is interpreted to reflect the underplating and incorporation of material into the metamorphic core the recognition of two thrust sense discontinuities in the exhumed himalayan core in the tama kosi region is consistent with other similar structures recognized along the himalaya the widespread nature of these structures reinforces that they are important to our understanding of the evolution of the kinematics of large hot orogens

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

convection over the pacific warm pool in relation to the atmospheric kelvin rossby wave abstract deep convection over the western tropical pacific warm pool is analyzed in terms of its relation to the atmospheric kelvin rossby wave which dominates the large scale flow during the austral summer the study uses doppler radar data collected by aircraft and ship radars during different time periods in the tropical ocean global atmosphere coupled ocean atmosphere response experiment to characterize the mesoscale circulations of organized convective cloud systems occurring throughout the season the study focuses on convection in two contrasting phases of the wave the westerly onset region just west of the point within the wave where low level easterlies change to westerlies and the strong westerly region or westerly wind burst lying between the large scale counterrotating gyres of the kelvin rossby wave in the westerly onset region the zonal wind component had midlevel easterlies overlying low level westerlies in the strong westerly region a deep layer of westerlies extended from the

provenance of quartz rich metamorphic tectonite pebbles from the black flysch w pyrenees n spain an ebsd and detrital zircon la icp ms study abstract metasandstone and quartz tectonite conglomerate pebbles from the albian black flysch encapsulate evidence of pre mesozoic igneous and metamorphic events quartz deformation microstructures and crystallographic fabrics characterize plastic flow under sub greenschists 250 300 c to high grade metamorphic conditions above 550 600 c detrital zircon grains from the pebbles provide concordant 206pb 238u radiometric ages ranging from 473 26 ma to 2261 59 ma with four major populations clustered in the intervals 1 96 1 80 ga paleoproterozoic 1 11 0 93 ga stenian tonian 765 571 ma neoproterozoic and 500 475 ma cambro ordovician the youngest zircons and the probability distribution of the studied population permit us to establish an early ordovician maximum depositional age for tectonite pebble protoliths and relate them with the armorican quartzite detrital zircon signature we identify the currently submerged landes massif of the armorican platform as the most likely candidate to being the source of black flysch metamorphic conglomerate pebbles

analytic representation of the large scale organization of tropical convection the pivotal role of mesoscale organization on the large scale coherence of tropical convection is represented by a nonlinear dynamical model the general model consists of two interlocked systems a mesoscale parameterization of organized convection and a two layer model of large scale equatorial dynamics the lower layer dynamics is rossby gyre like whereas outflow from organized convection maintains the upper layer circulation the transports of zonal momentum in the vertical and meridional directions are key processes an archetype of the general model in spite of being brutally simplified represents the convective organization momentum transport and equatorial superrotation realized by the cloud resolving convection parameterization or superparameterization explicit approach developed by grabowski the mesoscale parameterization is an analytic equivalent of the cloud system resolving models used in this computational approach finally issues in parameterizing convective organization are discussed

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

the impact of water on slip system activity in olivine and the formation of bimodal crystallographic preferred orientations abstract crystallographic preferred orientations cpos in olivine are widely used to infer the mechanisms conditions and kinematics of deformation of mantle rocks recent experiments on water saturated olivine were the first to produce a complex cpo characterised by bimodal orientation distributions of both 100 and 001 axes and inferred to form by combined activity of 001 100 100 001 and 010 100 slip this result potentially provides a new microstructural indicator of deformation in the presence of elevated concentrations of intracrystalline hydrous point defects and has implications for the interpretation of seismic anisotropy here we document a previously unexplained natural example of this cpo type in a xenolith from lesotho and demonstrate that it too may be explained by elevated concentrations of hydrous point defects we test and confirm the hypothesis that combined 001 100 100 001 and 010 100 slip were responsible for formation of this cpo by 1 using high angular resolution electron backscatter diffraction to precisely characterise the dislocation types present in both the experimental and natural samples and 2 employing visco plastic self consistent simulations of cpo evolution to assess the ability of these slip systems to generate the observed cpo finally we utilise calculations based on effective medium theory to predict the anisotropy of seismic wave velocities arising from the cpo of the xenolith maxima in s wave velocities and anisotropy are parallel to both the shear direction and shear plane normal whereas maxima in p wave velocities are oblique to both adding complexity to interpretation of deformation kinematics from seismic anisotropy

effects of curvature related dem contact model on the macro and micro mechanical behaviours of granular soils a comprehensive comparison between the hertz mindlin model and the linear spring model in true triaxial shear simulations of granular soils was conducted using the discrete element method dem th

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

quantifying geometrically necessary dislocations in quartz using hr ebsd application to chessboard subgrain boundaries abstract this study presents the first use of high angular resolution electron backscatter diffraction hr ebsd to quantitatively characterise geometrically necessary dislocations in quartz subgrain structures hr ebsd exploits cross correlation of diffraction patterns to measure intragranular misorientations with precision on the order of 0 01 with well constrained misorientation axes we investigate the dislocation structures of chessboard subgrains in quartz within samples from the greater himalayan sequence nepal our results demonstrate that chessboard subgrains are formed primarily from two sets of subgrain boundaries one set consists primarily of m c edge dislocations the other consists primarily of dislocations with a burgers vectors apparent densities of geometrically necessary dislocations vary from 10 13 m 2 within some subgrain boundaries to 12 m 2 within subgrain interiors the results suggest that at pressures above approximately 10 kbar chessboard subgrains may form within the quartz stability field most importantly this study demonstrates the potential of hr ebsd as an improved method for analysis of intragranular microstructures in quartz that are used as indicators of deformation conditions

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

stability analysis of rock wedge slide subjected to groundwater dynamic evolution abstract heavy rainfall may increase the infiltration rate raising the groundwater table after a short period time variation in the hydrostatic pressure on potential sliding surfaces and trailing edges of fissures in a rock slope may contribute to slope failure the failure mechanisms of rainfall triggered rock wedge slides have been widely studied in the literature however studies on the dynamic evolution of groundwater in rock failure are still limited in this study a typical rock wedge slide that occurred in chengkou county chongqing china is selected as a case study to analyze the stability of rock wedge with double planes and tension crack subjected to groundwater dynamic evolution model tests were designed and performed to reproduce the dynamic evolution of groundwater in the rock slope and analyze its role in wedge failure development and distribution characteristics of water pressure are investigated through monitoring the water pressure distributed along the surfaces of wedge failures from the experimental study it is found that the initial formation process of water pressure along the sliding surface consists of four types of distribution patterns i e triangular distribution type i trapezoidal distribution type ii trapezoidal distribution and type iii trapezoidal distribution based on the model tests and theoretical analysis the order of the calculated safety factors of the chengkou rock wedge slide are triangle type i trapezoid type ii trapezoid type iii trapezoid the existence of inflection points in the trapezoidal distribution mode significantly increases water pressure on both sides of rock wedge which contributes instability the new approach for investigation of the effect of dynamic evolution groundwater on stability of rock wedge slide is developed based on fundamental mechanism and experimental study it can be adopted for stability assessment of similar rock wedge slides in other areas

metamorphic history of the central himalaya annapurna region nepal and implications for tectonic models pressure temperature time p t t conditions of metamorphism have been determined in the annapurna region of central nepal that place new constraints on the structural and tectonic evolution of the himalayan orogenic wedge peak p t conditions increase structurally upward 525 c and 8 kbar in the lesser himalayan sequence 650 c and 12 kbar at the base of the greater himalayan sequence across the main central thrust 750 c and 12 kbar in the middle of the greater himalayan sequence and 775 c and 13 kbar near the top of the greater himalayan sequence metamorphic monazite ages in the greater himalayan sequence also increase structurally upward 16 21 ma for subsolidus growth at the base of the greater himalayan sequence to 25 ma for peak t metamorphism and anatexis near the top of the greater himalayan sequence these ages are several million years older than at equivalent structural levels at langtang 200 km to the east the p t t data recommend reinterpretation of the bhanuwa fault within the greater himalayan sequence as a thrust and the presence of a different thrust structurally above the bhanuwa thrust here named the sinuwa thrust the new data are consistent with progressive stacking of tectonic slices with calculated overthrust rates that are consistent with some but not all models that presume 2 cm yr convergence across the himalaya since 25 ma despite differences in absolute ages similarities among the chemical systematics of monazite peak p t conditions and overthrust rates calculated for annapurna when compared to langtang imply that the broad geodynamics in one part of an orogen can be realistically extrapolated within a few hundred kilometers although the timing and duration of movement on discrete thrust surfaces may differ