the roles of vortex rossby waves in hurricane secondary eyewall formation abstract a high resolution full physics model initiated with an idealized tropical cyclone like vortex is used to simulate and investigate the secondary eyewall formation the beta skirt axisymmetrization bsa hypothesis previously proposed is examined and the roles of axisymmetrizing vortex rossby waves vrws in the secondary eyewall formation are further investigated during the formation period convection outside the inner core region is organized into an outer spiral rainband the pv dipoles that are persistently generated by convective updrafts through tilting effect move along the rainband and inward toward inner core region and are finally axisymmetrized in the preexisting beta skirt region the formation of the secondary eyewall is preceded by a rapid intensification period during which vortical hot towers discrete vrws and sheared vrws dominate the inner core asymmetric structures sheared vrws are repeatedly emanated from the outer edge of the eyewall and become more concentric when propa

flow vorticity in zhangbaling transpressional attachment zone se china abstract plagioclase porphyroclasts with well preserved idiomorphic shapes and zoning and showing limited clast interaction are ubiquitous in the flat lying zhangbaling schist that is exposed east of the tan lu fault in southeast china plagioclase porphyroclasts define rigid particles whose distribution be related to the kinematic vorticity of the schist using the methods of porphyroclast hyperbolic distribution phd and modified rf passchier wallis plot the kinematic vorticity numbers calculated from this approach range from wk 0 72 to 0 82 increasing progressively from south to north along the zhangbaling belt such a wk distribution indicates that the zhangbaling schist was deformed uniformly under simple shear dominated general shear and that the zhangbaling ductile crust experienced relatively even crustal thinning deformation the subhorizontal zhangbaling schist is considered a mid crustal attachment zone that coupled the rigid upper crust to a subvertical wrench shear zone in the lower crust

deformation volume and cleavage development in metasedimentary rocks from the ballarat slate belt psammites from the ballarat slate belt in se australia exhibit well developed differentiated or spaced cleavage defined by alternating phyllosilicate and quartz rich domains termed p and q domains respectively strain estimates derived from independent microstructural and chemical observations suggest that the p q fabrics developed in response to plane strain deformation dominated by solution transfer with the principal finite shortening in the p domains approximately twice that in the adjacent q domains significant finite extensions are indicated by ubiquitous quartz albite chlorite overgrowths in both p and q domains while pressure shadow development around syntectonic pyrite porphyroblasts suggest finite extension of at least 100 this estimate is comparable with the extension predicted for constant volume deformation and consequently there appears to have been no significant bulk material loss or gain on the hand specimen scale these observations are consistent with solute transfer scales as little as a few centimetres via diffusion in a stationary fluid and do not require although do not necessarily preclude large scale advective fluid transport through the slate belt during cleavage formation as suggested in previous studies

triassic polyphase deformation in the feidong zhangbaling massif eastern china and its place in the collision between the north china and south china blocks the feidong zhangbaling massif is located between the dabieshan and sulu areas along the tan lu fault in eastern china five tectonic metamorphic events are distinguished there the earliest deformation d1 corresponds to a southward compression that occurred during subduction of the south china block below the north china block top to the south shearing is coeval with late permian early triassic blueschist facies metamorphism and possibly with the development of south verging recumbent folds in the neoproterozoic paleozoic sedimentary cover of the south china foreland the main ductile deformation d2 is an extensional one characterized by top to the north shearing coeval with the early stage of exhumation of the high pressure rocks a top to the nw ductile shearing and microfolds overturned to the northwest belong to a second deformational phase of exhumation d3 which is distinct from the main event d2 previous 40ar 39ar mica dates ranging between 245 and 212 ma suggest late permian early triassic ages for the d1 to d3 events the d4 event produced ne sw trending folds in the sedimentary cover interpreted as gravity collapse structures a late cretaceous brittle extensional event d5 controls the opening and infill of continental half grabens in the study area the tan lu fault is a cretaceous brittle normal fault the lack of ductile deformation presented along the tan lu fault suggests that it did not play a significant role in the exhumation of high pressure metamorphic rocks

mantled porphyroclast gauges we investigate the behavior of the isolated mantled porphyroclast in a shear zone the method employed is a finite element model three distinct phases clast mantle and matrix are present the rheologies are power law with exponents ranging from 1 to 5 and the far field boundary condition is simple shear the effective viscosity of the mantle is assumed to be less than those of the clast and the matrix we show for which parameter sets mantled porphyroclasts reach super horizontal stabilization with respect to the shear plane and sense clasts in natural mylonites frequently exhibit similar orientations which are interpreted as stable inclinations the systematic examination of the matrix mantle clast system allows for the construction of attractor maps that can be directly used as gauges for i the effective viscosity contrast between matrix and mantle ii the production rate of mantle material around the clast as a function of the bulk shear strain and iii for the total shear strain the necessary data required to use the attractor maps are simple geometrical parameters that can be measured in the field i e clast aspect ratio clast inclination versus the shear plane mantle thickness and mantle and clast area this new method successfully reproduces the characteristics of natural porphyroclasts and is in good agreement with data from natural shear zones q 2005 elsevier ltd all rights reserved

upper mantle structure beneath the siberian craton and surrounding areas based on regional tomographic inversion of p and pp travel times abstract we present a model of 3d seismic anomalies in the upper mantle beneath a part of northern asia that includes the siberian craton the west siberian plate the mountains framing siberia altai sayan and baikal and mongolia we used the differential travel times of pp and p phases to investigate the deep seismic structure beneath a large part of the siberian region where neither stations nor earthquake distributions are sufficient to apply other body wave tomographic schemes to show the reliability of the results based on inversion if the pp p residuals we performed various tests including 1 tests with odd even data 2 synthetic tests with checkerboard and realistic patterns and 3 inversions in other areas with clear structures furthermore for the southern part of the study area we present another model based on the inverse tomographic scheme its which uses travel times recorded by worldwide stations from events located in the study area in the overlapping areas these two independent models are generally consistent the main model of this study is obtained by merging the results of the pp p and its schemes this model shows a clear differentiation between the high velocity siberian craton and low velocity structures beneath the mountains framing siberia the area of cenozoic magmatism in western sayan is clearly associated with a low velocity anomaly at a depth of 600 700 km this low velocity pattern is located beneath the cratonic area while at shallower depths it seems to flow around the bottom of the thick craton lithosphere to the sw margin of the craton

testing the utility of the porphyroclast hyperbolic distribution method of kinematic vorticity analysis kinematic vorticity wk is a dimensionless measure of rotation relative to finite stretching and is essential for complete understanding of flow in ductile shear zones the porphyroclast hyperbolic distribution phd method is a widely used technique for estimating wk based on the acute angle between the flow eigenvectors determined from the orientations of back rotated s porphyroclasts the utility of the phd was tested with tertiary ultramylonites from the santa catalina mountains arizona proterozoic ultramylonites from the virgin mountains nevada and a paleozoic ultramylonite from the hylas zone in the virginia piedmont bootstrapping statistics and a computational sieving process were used to analyze the phd data set average standard deviations of the bootstrapped data sets yield a 1s standard error of 9 for a wk value measured as a simple shear sieving results imply that back rotated porphyroclasts may not orient parallel to the extensional eigenvector the phd method is useful for discerning between deformations that are pure shear dominated general shear or simple shear dominated but is not accurate enough to report precise wk values when performed on multiple sections the phd method can identify zones of monoclinic versus triclinic shear 2007 elsevier ltd all rights reserved

life of a six hour hurricane hurricane claudette developed from a weak vortex in 6 h as deep convection shifted from downshear into the vortex center despite ambient vertical wind shear exceeding 10 m s 1 six hours later it weakened to a tropical storm and 12 h after the hurricane stage a circulation center could not be found at 850 hpa by aircraft reconnaissance at hurricane strength the vortex contained classic structure seen in intensifying hurricanes with the exception of 7 12 c dewpoint depressions in the lower troposphere upshear of the center these extended from the 100 km radius to immediately adjacent to the eyewall where equivalent potential temperature gradients reached 6 k km 1 the dry air was not present prior to intensification suggesting that it was associated with vertical shear induced subsidence upshear of the developing storm it is argued that weakening of the vortex was driven by cooling associated with the mixing of dry air into the core and subsequent evaporation and cold downdrafts evidence suggests that this mixing might have been enhanced by eyewall instabilities after the period of rapid deepening the existence of a fragile small but genuinely hurricane strength vortex at the surface for 6 h presents difficult problems for forecasters such a temporary hurricane in strongly sheared flow might require a different warning protocol than longer lasting hurricane vortices in weaker shear

application of the rfφ technique to ellipitical markers deformed by pressure solution abstract the applicability of the r f technique of finite strain analysis to elliptical markers whose shape is modified by pressure solution is investigated variably oriented elliptical markers shortened by removing material from one or both sides in open and closed systems are compared to markers shortened homogeneously by the same amount for the models examined it was found that the r f technique correctly predicts the principal directions the initial marker axial ratio and the axial ratio of a circle deformed in a like manner interpretation of strain ratios in terms of percent shortening requires knowing how much volume was lost equations relating the strain ratio to percent shortening are given for both constant volume and volume loss deformation

simultaneous pure and simple shear the unifying deformation matrix abstract any simultaneous combination of finite simple shear and finite pure shear is a linear transformation which can be expressed as a single transformation matrix for two dimensions the matrix is upper triangular with an off diagonal term called the effective shear strain is a simple function of the pure and simple shear components for three dimensions a simultaneous combination of thrusting in the x direction thrusting in the y direction and a wrench in the x direction in addition to 3 orthogonal components of coaxial strain can also be represented by a 3 3 upper triangular matrix here three off diagonal terms xy x y and y z occur xy is a simple function of the horizontal coaxial strain values and thrusting in the x direction yz depends on the coaxial strain components in the y and z directions and the thrusting in the y direction while xz is related to all six strain components the matrix also allows for volume change either homogeneously or preferentially in a single direction a method of decomposing the deformation matrix into a series of incremental deformation matrices where each incremental deformation records the same kinematic vorticity number as the finite deformation is shown the orientation and magnitude of the finite strain ellipsoid ellipse is easily and accurately found at any increment during the deformation

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

finite strain analysis of the zhangbaling metamorphic belt se china crustal thinning in transpression abstract finite strain analysis of pebbles in the metatillite and phyllite shows that the deformation of the metatillite phyllite zone is flattening to plane strain dominated results of spo analysis of the rigid plagioclase porphyroclasts in three perpendicular planes indicate monoclinic strain symmetry of the zhangbaling schist and oblate geometry of the clast forward strain modeling of rigid clasts is performed based on the shape fabric of the clast population integrated results of finite strain modeling and finite strain analysis indicate that this midcrustal section experienced at least 18 36 thinning in the oblique convergence between north and south china blocks

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

a numerical study of the genesis of concentric eyewalls in hurricanes we use two axisymmetric numerical models to explore the dynamics of concentric eyewalls in hurricanes the first is a simple two layer model using balanced dynamics and parametrized convection while the second is a cloud resolving non hydrostatic model in the case of the balanced model infinitesimal disturbances amplify into secondary eyewalls provided the lower troposphere is sufficiently moist otherwise finite amplitude perturbations are necessary to initiate amplifying structures but experiments with the full physics model show that finite amplitude disturbances are always necessary to initiate secondary eyewalls regardless of the initial humidity of the lower troposphere experiments with both models in which the surface wind is held constant in the surface flux formulations fail to develop secondary eyewalls demonstrating that in these models the disturbances once initiated grow through the wind induced surface heat exchange wishe mechanism based on this work we hypothesize that real secondary eyewalls result from a finite amplitude wishe instability triggered by external forcing such as interaction of the tropical cyclone with baroclinic eddies topography or local perturbations in sea surface temperature copyright 2003 royal meteorological society

the dilemma of asymmetric porphyroclast systems and sense of shear abstract asymmetric porphyroclast systems have long been used as independent shear sense indicators based on their clast tail asymmetry and or stair stepping tail geometry over the last two decades advances in exploring the mechanical behavior of rigid clasts in a viscous flow has shed new light on understanding the formation of porphyroclast systems embedded in noncoaxial viscous flow and subsequently quantifying many aspects of flow kinematics using examples from naturally deformed rocks combined with results from recent advances our study indicates that 1 in general only porphyroclast systems composed of equant shaped clasts can be treated as independent shear sense indicators 2 special attention should be given to type porphyroclast systems composed of high angle intermediate aspect ratio clasts which may contain meaningful information on bulk flow kinematics 3 bookshelf structures cannot serve as independent shear sense indicators multi criteria and thorough three dimensional shape analyses are suggested for a proper interpretation of flow kinematics in ductile shear zones

thermochronologic constraints on deformation and cooling history of high and ultrahigh pressure rocks in the qinling dabie orogen eastern china the hong an block is the best place to study the exhumation of high pressure hp and ultrahigh pressure uhp metamorphic rocks in the qinling dabie orogen of eastern china because it lacks the extensive cretaceous tectonic and thermal overprint observed in the dabie shan we measured timing of deformation and rate of cooling of the hp uhp rocks by 40ar 39ar analyses of synkinematic minerals from tectonites of key structural zones in the hong an and tongbai shan normal sense shear along the north dipping huwan detachment at the northern edge of the hong an block occurred between 237 and 231 ma this detachment facilitated the bulk of the exhumation of the hp uhp rocks our new 40ar 39ar ages combined with u pb zircon and sm nd ages of 245 240 ma suggest that exhumation of uhp rocks from mantle depths occurred at rates of 5 25 mm yr from 245 to 230 ma the mountain range is a warped extensional footwall within which white mica cooled from 225 to 205 ma locally younger extension is recorded by white mica recrystallization at 198 194 ma after which the entire block had cooled to below 300 c early cretaceous 40ar 39ar ages from the tongbai shear zone indicate that dextral shear along the southwest boundary of the orogen was contemporaneous with normal to sinistral oblique slip along the xiaotian mozitan fault along the northern boundary coeval dextral and sinistral shear zones along the northern and southwestern margins of the hong an and dabie shan would have caused eastward lateral extrusion of these two blocks perhaps driven by collision of the lhasa block with eurasia

dynamical and physical processes leading to tropical cyclone intensification under upper level trough forcing abstractthe rapid intensification of tropical cyclone tc dora 2007 southwest indian ocean under upper level trough forcing is investigated tc trough interaction is simulated using a limited area operational numerical weather prediction model the interaction between the storm and the trough involves a coupled evolution of vertical wind shear and binary vortex interaction in the horizontal and vertical dimensions the three dimensional potential vorticity structure associated with the trough undergoes strong deformation as it approaches the storm potential vorticity pv is advected toward the tropical cyclone core over a thick layer from 200 to 500 hpa while the tc upper level flow turns cyclonic from the continuous import of angular momentum it is found that vortex intensification first occurs inside the eyewall and results from pv superposition in the thick aforementioned layer the main pathway to further storm intensification is associated with secondary eyewall formation triggered by external

observations of wave mean flow interaction in the southern hemisphere abstract variations of zonal mean and eddy properties in the southern hemisphere during the winter of 1979 are studied several periods of enhanced wave activity and rapid zonal mean changes are observed during these periods of rapid change both the actual zonal wind tendency and the eliassen palm flux divergence have a dipole pattern in the upper stratosphere with positive values in high latitudes and negative values in middle and low latitudes the positive values of e p flux divergence near the pole are particularly interesting since they suggest a possible source of wave activity in this region the stationary component of wavenumber 1 and the eastward traveling component of wavenumber 2 contribute most to the dipole pattern of wave driving in the stratosphere a nearly uniform deceleration of the mean flow in the troposphere is contributed to by all zonal wavenumbers from 1 to 10 the lower wavenumbers contribute most to the driving in high latitudes while the driving in lower latitudes is contri

ar ar geochronology of ultrahigh pressure metamorphism in central china the dabie shan of china contain the largest areal exposure of ultrahigh pressure regional metamorphic rock known on earth the thermal history of these unusual rocks is central to understanding the tectonic processes responsible for their creation preservation and exhumation published ages of ultrahigh pressure metamorphism and subsequent cooling range from archean to jurassic by analyzing 21 dabie hornblende phengite and biotite samples by the 40ar 39ar method we find that 1 cooling from peak metamorphic temperatures to 300 c occurred between about 206 and 178 ma 2 widespread cretaceous ages reflect reheating by a postultrahigh pressure magmatic extensional episode 3 40ar 39ar and k ar ages older than 230 ma and perhaps 210 ma are geologically meaningless due to the incorporation of excess 40ar and 4 dabie ultrahigh pressure metamorphic rocks are temporally related to blueschist facies rocks farther west in the suture zone

external influences on hurricane intensity part iii potential vorticity structure abstract the interaction of hurricane elena 1985 with a baroclinic wave was reexamined using both potential vorticity pv and a formulation for eliassen palm fluxes in cylindrical coordinates the hurricane began to deepen rapidly as a narrow upper level positive pv anomaly became nearly superposed over the low level center the intensification appeared to represent an evaporation wind feedback activated by constructive interference of the pv anomalies enhanced convection associated with this process eroded the upper pv anomaly and prevented it from crossing the hurricane and reversing the intensification the eliassen palm flux divergence showed that maximum eddy activity remained in the upper troposphere prior to the reintensification this activity was produced in part because the action of the outflow anticyclone of the hurricane contributed to synoptic scale wave breaking the upper level pv anomaly that approached the center was much narrower in extent than the original synoptic scale trough th

effect of shape and orientation on rigid particle rotation and matrix deformation in simple shear flow the rotation behaviour of rigid particles from a wide range of symmetry classes was analysed in a series of three dimensional analogue experiments in which the particles were embedded in a transparent linear viscous matrix deformed to large shear strains comparison of the measured trajectories with theoretical periodic paths for rigid ellipsoids shows that quadratic slightly orthorhombic and monoclinic particles have trajectory paths and rotation rates closest to theory orthorhombic and monoclinic particles with a minimum aspect ratio 1 5 develop non periodic trajectories the results establish that the simplified theoretical model for ellipsoidal forms is a good approximation for a wide range of natural particle shapes the relationship between the rotation of a rigid particle and deformation of the adjacent matrix was also determined in a series of experiments by placing the particle at different depths relative to an imprinted grid the results are well illustrated by the surface passing through the centre of the particle and initially parallel to the shear plane two deformed regions in the matrix are recognised in the first region the matrix rotates with the particle together forming an approximately ellipsoidal object the second region is dominated by folds of limited extent along the rotation axis and greatest extent in a direction that rotates asymptotically toward the shear direction the folds rotate more slowly than the principal direction of maximum finite stretch

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

40ar 39ar dating of strike slip motion on the tan lu fault zone east china abstract ne trending sinistral ductile shear belts in the southern part of the tan lu fault zone east china are exposed along the eastern edge of the northern dabie belt and southern zhangbaling belt three hornblende three phengite and 12 biotite separates from greenschist facies mylonites in the shear belts were dated by the 40ar 39ar method in this study a hornblende plateau age of 143 3 ma is interpreted as representing the time of sinistral motion on the zhangbaling part of the tan lu fault zone seven biotite samples from the same part yield 40ar 39ar cooling ages from 137 to 125 ma a phengite plateau age of 138 8 ma from the eastern edge of the dabie belt is considered as being close to the time of deformation in the tan lu strike slip zone five biotite 40ar 39ar ages from 120 to 110 ma and one phengite age of 121 ma from the same area represent cooling ages after the sinistral faulting it is concluded on the basis of these 40ar 39ar ages that the sinistral ductile shear belts in the southern part of the tan lu fault zone were produced in earliest early cretaceous this sinistral motion on the tan lu fault zone is considered to be related to high speed highly oblique subduction of the pacific plate at this time

finite strain heterogeneity and volume loss in slates of the taconic allochthon vermont u s a abstract slates of the taconic allochthon have ellipsoidal reduction spots which have been used to determine the finite state of strain at seven sites the strain is highly heterogeneous at all scales ranging from several centimeters to many kilometers variations in x y ratios is small but variations in y z ratios is large and this pattern is seen at all scales the heterogeneity can be used to determine a strain path which is nearly horizontal on a flinn diagram we propose that uniaxial flattening associated with late stage cleavage development was accommodated by volume loss and that the most highly strained sites have experienced an average 55 volume loss at a minimum explaining our results without volume loss requires a subhorizontal extension and creates strain compatibility problems consideration of the strain history of these rocks suggests that folding related strains have been modified by later cleavage related events the last of which was uniaxial flattening accommodated by volume loss the finite strains are reflective almost exclusively of the latest cleavage producing strains

strain insensitive preferred orientation of porphyroclasts in mont mary mylonites abstract the shape preferred orientation spo of porphyroclasts was determined in high temperature mylonites the porphyroclasts approach rhomboidal sillimanite or elliptical garnet plagioclase sillimanite shapes and exhibit aspect ratios r as high as 11 particles with r 3 are dominantly rhomboidal the long axis of the best fit ellipse defines a very strong spo inclined at 5 10 to the mylonitic foliation in an antithetic sense with respect to the shear direction this angle is independent of r the inclination of the long sides of rhomboidal sillimanite increases from 10 to 20 with decreasing r in contrast the short sides have a constant orientation of 15 to 17 irrespective of r and are parallel to extensional crenulation cleavage low aspect ratio mainly elliptical objects show low intensity spo close to the shear plane the two spos appear strain insensitive in the case of r r 3 a stable position is acquired this is not explained by any of the current theoretical and experimental models of spo

monoclinic model shear zones abstract although many ductile shear zones are supposed to have developed by approximately simple shear flow some must have formed under different conditions a few types of such non simple shear zones have been proposed in the literature such as transpression transtension and stretching shear zones this paper presents a full three dimensional kinematic model of shear zones with monoclinic flow geometry monoclinic shear zone types can be classified according to flow parameters and according to the geometry and orientation of accumulating finite strain modelling of finite strain accumulation shows that a number of unusual and potentially problematic structural features may develop in monoclinic shear zones these include stretching lineations normal to the displacement direction foliations normal to the shear zone boundary switching of the position of principal finite strain axes x y and z during progressive deformation and strain gradients along shear zones that may give rise to obliqueness of fabric elements of the same age in adjacent rock volumes

external influences on hurricane intensity part i outflow layer eddy angular momentum fluxes abstract outflow layer winds were objectively analyzed every 12 h for 6 days during the life cycle of hurricane elena 1985 a high correlation was found between angular momentum fluxes by azimuthal eddies at large radii and central pressure changes in the storm 27 33 h later momentum flux by eddies exceeded that by the azimuthal mean outside the 800 km radius while vortex spinup by the eddies reached instantaneous magnitudes as large as 25 m s 1 day outflow maxima and minima repeatedly appeared more than 1000 km from the hurricane center and tracked inward with time the results provide evidence of significant environmental control on the behavior of the storm after reaching hurricane strength elena experienced a major secondary intensification associated with a large inward cyclonic eddy momentum flux produced by the passage of a middle latitude trough north of the hurricane an outflow maximum appeared radially inside of the eddy momentum source consistent with balanced vortex theory and tracke

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

petrology and zircon u pb geochronology of metamorphic massifs around the middle segment of the tan lu fault to define the boundary between the north and south china blocks abstract the tan lu fault tlf is a significant linear structure of eastern china the middle segment of the tlf in the northern anhui province separates the north china block ncb and south china block scb lack of geological work makes the plate boundary here ambiguous detailed field survey and laboratory analyses have been conducted to constrain the formation and evolution of the tlf to the west of the tlf the wuhe massif underwent a granulite facies metamorphism with t 778 836 c p 1 0 1 2 gpa during 2 41 2 43 ga according to la icp ms u pb zircon dating on the contrary to the east of the tlf the zhangbaling massif suffered a greenschist to lower amphibolite facies metamorphism with the average metamorphic temperature at around 340 440 c with the protolith igneous ages of ca 750 ma these differences indicate that the two massifs belong to the different blocks furthermore the granitic gneiss in the central part of tlf gives three populations of zircon u pb age at 667 504 ma 228 2 ma and 211 2 ma respectively the later two groups of spectra correspond to the periods of subduction and exhumation of the dabie massif 245 200 ma combined with previous study the precise plate boundary between ncb and scb has been delineated as the zhuding shimenshan fault and the initial time of the motion for the tlf is also discussed

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

deformation around rigid particles the influence of slip at the particle matrix interface abstract theoretical and previous experimental studies of rigid particle structures have only considered the behaviour of rigid particles for which the interface between particle and matrix is coherent in natural rocks the boundary behaviour may cover the whole range from free slip to complete coherence examples where slip may be promoted include crack seal deformation during the development of pressure shadows core mantle structures where the mantle is composed of much weaker fine recrystallized material and crystallizing magmas or partially molten rocks where grain boundaries are lubricated by the melt phase analogue scale model experiments have been performed under pure shear and simple shear conditions to compare the particle rotation and the flow in the matrix for both slipping and non slipping particle matrix interfaces when slip does occur particles rotate faster in pure shear and slower in simple shear than for non slip leading to the more rapid development of a shape preferred orientation the preferred orientation tends to be bimodal in simple shear flow the flow and finite strain patterns in the matrix are also strongly influenced by slip at the interface and porphyroclast systems can develop geometries with ambiguous or contradictory shear senses dependent on the original particle orientation in multi particle experiments slip on the interfaces enhances strong strain localization in non linear viscous material to produce patterns very similar to natural s c fabrics

analogue modelling of the influence of shape and particle matrix interface lubrication on the rotational behaviour of rigid particles in simple shear abstract the rotational behaviour of a rigid particle embedded in a linear viscous matrix undergoing cylindrical simple shear couette flow was studied in 2d rock analogue experiments the influence of particle shape elliptical vs monoclinic aspect ratio and the nature of the matrix particle interface lubricated vs unlubricated was investigated both matrix pdms and lubricant liquid soap were linear viscous with a viscosity ratio of ca 10 4 without lubricant the rotational behaviour of all particles closely approximates the jeffery theory lubricated monoclinic particles with the long diagonal initially parallel to the shear direction show back rotation and approach a stable position lubricated elliptical particles initially parallel to the shear direction also show back rotation but only transiently stabilize weak planar zones in the matrix adjacent to unlubricated elliptical particles do not induce backward rotation in general for elliptical particles rotation rate as a function of orientation depends on axial ratio and thickness of the lubricant mantle for thick mantles initially 10 of the volume of the particle rotation rates are faster than jeffery theory for very thin mantles they are markedly slower compared with thick mantles particularly when the long axis is nearly parallel to the shear direction rotation rates are never strictly zero so true stabilization does not occur however for more elongate particles axial ratio 6 rotation rates are so slow that a very strong shape preferred orientation would develop in a lubricated elliptical particle population in experiments the volume of lubricant is constant and the thickness adjacent to the long side of the particle progressively decreases with increasing strain in natural examples of porphyroclast systems the weak mantle continually develops by recrystallization and or cataclasis of the rigid clast core and a steady state between production and thinning could be attained potentially leading to true stabilization for particles with a high axial ratio

2 d shape preferred orientations of rigid particles in transtensional viscous flow ghosh and ramberg tectonophysics 34 1976 1 70 studied the two dimensional 2 d rotational behaviour of individual rigid particles embedded in a viscous medium subject to simple shear and transpression sr 0 at low medium shear strains we now extend this theoretical study to transtension sr 0 by deriving a new analytical solution to non interacting populations of rigid particles and to high shear strains we used different initial orientations of particles in the same graph to simulate populations of particles in an originally isotropic rock our results show that 1 shape preferred orientations spos developed in viscous simple shear flow are transient and cyclical except for particles with aspect ratio or material lines which tend to the shear direction 2 stable spos can develop in transpression they dip towards the shear sense but when defining an s c structure with the shear foliation this composite fabric is always antithetic and thus indicates the wrong sense of shear 3 stable spos can also develop in transtension they dip opposite to the shear sense but when defining an s c structure with the shear foliation this composite fabric is always synthetic and thus indicates the correct sense of shear 4 spos produced in transpression or transtension can be used as vorticity gauges only when they represent stable orientations which must be demonstrated a priori

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

mid crustal partitioning and attachment during oblique convergence in an arc system palaeoproterozoic ketilidian orogen southern greenland abstract the ketilidian orogen in se greenland contains a continental magmatic arc julianehab batholith and forearc which formed in the overriding plate of a palaeoproterozoic oblique subduction boundary between c 1854 and 1795 ma during uplift and deformation of the forearc between c 1795 and 1780 ma its sedimentary sequences were invaded by arc type magmas and metamorphosed at ht lp upper amphibolite facies conditions which led to widespread anatexis and generation of abundant s type granites transpression during early deformation d 1 was partitioned into arc parallel sinistral strike slip in the magmatic arc rocks of the batholith and arc normal contraction in the sedimentary and volcaniclastic sequences of the proximal forearc psammite zone subsequently d 1 fabrics in the psammite zone were overprinted and transposed in an intense flat lying d 2 ductile shear zone with arc parallel stretching lineations and top ne kinematic indicators the kinematic significance of the d 2 shear zone is that it accommodated vertical differences in strain and displacement and permitted deformation to be partitioned differently at different levels in the crust as such it is an attachment or coupling zone that provided kinematic linkage between deformation at different crustal levels during ne transport of a forearc sliver overprinting of the upper crustal domain of d 1 strike slip partitioned transpression in the forearc during d 2 is attributed to migration of the attachment zone to a higher crustal level this migration was a consequence of an enhanced geothermal gradient in the proximal part of the forearc due to the emplacement of batholith related plutonic suites during d 2

rapid intensification of a sheared fast moving hurricane over the gulf stream abstracthurricane irene 1999 rapidly intensified from 65 to 95 kt 33 4 to 48 9 m s 1 in 18 h during the rapid intensification ri period the northeastward storm motion increased from 10 to 18 m s 1 the ambient southwesterly vertical wind shear increased from 6 7 to 10 13 m s 1 and the downshear tilt of the inner core vortex increased the azimuthal wavenumber 1 asymmetric convection that developed was consistent with a superposition of shear induced and storm motion induced forcing for vertical motion downshear and ahead of the center although the diabatic heating remained strongly asymmetric it was of sufficient intensity to dramatically increase the azimuthally averaged heating this heating occurred almost entirely inside the radius of maximum winds a region known to favor rapid warm core development and spinup of the vortex it is hypothesized that asymmetric forcing from the large vertical wind shear and rapid storm motion were responsible for ri an unanswered question is what determin

the influence of matrix rheology and vorticity on fabric development of populations of rigid objects during plane strain deformation abstract the influence of vorticity and rheology of matrix material on the development of shape preferred orientation spo of populations of rigid objects was experimentally studied experiments in plane strain monoclinic flow were performed to model the fabric development of two populations of rectangular rigid objects with object aspect ratios rob 2 and 3 the density of the rigid object populations was 14 of the total area objects were dispersed in a newtonian and a non newtonian power law matrix material with a power law exponent n of 1 2 the kinematic vorticity number wn of the plane strain monoclinic flow was 1 0 8 and 0 6 with finite simple shear strain of 4 6 3 0 and 0 9 respectively in experiments with rob 3 the spo is strongly influenced by wn and the material properties of the matrix deformation of a power law matrix material and low wn resulted in a stronger spo than deformation of a linear viscous matrix and high wn strain localization coupled with particle interaction plays a significant role in the development of a shape preferred orientation high strain simple shear zones separate trains of rigid objects that are surrounded by low strain zones with wn lower than the bulk wn in fabrics involving populations of objects with rob 2 rheology of the matrix materials does not systematically influence the intensity of the spo

the effect of non passive clast behaviour in the estimation of finite strain in sedimentary rocks abstract existing methodologies that use ellipsoidal objects for the analysis of geological strain typically assume that these objects acted passively during deformation this assumption when not valid can lead to significant underestimates of strain in rocks deformed under low grade conditions in orogenic forelands this is especially true when clastic sedimentary rocks are utilized to measure strain the competency contrast between clasts and matrix possibly leading to marked non passive behaviour the systematic nature of this finite strain underestimation may allow for a correction of strain estimates when this type of behaviour is evident

the interaction of supertyphoon maemi 2003 with a warm ocean eddy understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change here an investigation is presented of the interaction between supertyphoon maemi the most intense tropical cyclone in 2003 and a warm ocean eddy in the western north pacific in september 2003 maemi passed directly over a prominent 700 km 500 km warm ocean eddy when passing over the 22 n eddy rich zone in the northwest pacific ocean analyses of satellite altimetry and the best track data from the joint typhoon warning center show that during the 36 h of the maemi eddy encounter maemi s intensity in 1 min sustained wind shot up from 41 ms 1 to its peak of 77 m s 1 maemi subsequently devastated the southern korean peninsula based on results from the coupled hurricane intensity prediction system and satellite microwave sea surface temperature observations it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water the typhoon s self induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper ocean mixed layer in the warm eddy which prevents the deeper cold water from being entrained into the upper ocean mixed layer as simulated using the coupled hurricane intensity prediction system the incorporation of the eddy information yields an evident improvement on maemi s intensity evolution with its peak intensity increased by one category and maintained at category 5 strength for a longer period 36 h of time without the presence of the warm ocean eddy the intensification is less rapid this study can serve as a starting point in the largely speculative and unexplored field of typhoon warm ocean eddy interaction in the western north pacific given the abundance of ocean eddies and intense typhoons in the western north pacific these results highlight the importance of a systematic and in depth investigation of the interaction between typhoons and western north pacific eddies

concentric eye walls secondary wind maxima and the evolution of the hurricane vortex abstract research aircraft observations in recent hurricanes support the model of shapiro and willoughby 1982 for the tropical cyclone s response to circularly symmetric convective heat sources convective rings in both nature and the numerical model the tangential wind commonly increases rapidly just inside the radius of maximum wind and decreases inside the eye near the central axis of the vortex thus both secondary outer wind maxima and eyewall wind maxima often contract as they intensify this response is independent of the horizontal spatial scale of the maximum an outer maximum is frequently observed to constrict about a pre existing eye and replace it this chain of events often coincides with a weakening or at least a pause in intensification of the vortex as a whole the concentric eye phenomenon is a common but by no means universal feature of tropical cyclones it is most frequently observed in intense highly symmetric systems

experimental observations on the effect of interface slip on rotation and stabilisation of rigid particles in simple shear and a comparison with natural mylonites for axial ratios r not vert similar3 porphyroclasts from three mylonites all show a very strong spo with the long axis of the best fit ellipse at an antithetic angle of 5 10 to the shear direction this is more consistent with a stable end orientation than with the transient fabrics predicted by theory for elliptical rigid particles in simple shear the cause of this divergence is investigated in a series of high simple shear strain 15 analogue experiments performed in a ring shear machine couette flow using a linear viscous matrix pdms the rotational behaviour of elongate r not vert similar5 rigid particles with elliptical and rhomboidal shapes comparable with the natural examples is modelled for both coherent and slipping particle matrix interfaces interface slip causes a dramatic reduction in the rotation rate of the elliptical particle compared with theory when the long axis is close to the shear direction but not stabilisation interface slip does result in stabilisation of the rhomboidal particle with the long diagonal oriented at a small antithetic angle to the shear direction for monoclinic particles mirror image shapes referred to here as types 1 and 2 show different rotational behaviour for the type 1 particle with a shape comparable to porphyroclast systems and mica fish the long side rotates asymptotically into parallelism with the shear direction natural examples of type 1 particles such as hornblende and olivine porphyroclasts measured from the finero mylonites southern alps show a very strong preferred orientation for r not vert similar3 with the long side parallel or at a small 5 antithetic angle to the mylonitic foliation for type 2 particles the short side stabilises close to the shear direction or at a small synthetic angle as also observed for sillimanite porphyroclasts from the mont mary mylonites western alps in this natural case stabilisation of the short sides is against an extensional crenulation cleavage rather than the mylonitic foliation the analogue experiments establish that interface slip is one mechanism for stabilisation of elongate rhomboidal particles in natural examples decoupling from the matrix may be affected by extensional crenulation cleavage or c planes in s c fabrics

attachment formation during partitioning of oblique convergence in the ketilidian orogen south greenland subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts a mid crustal attachment zone is exposed in the palaeoproterozoic ketilidian orogen south greenland which formed as a result of north directed oblique convergence at a cordilleran type margin rifting c 2 1 ga and compressional deformation and magmatism 1850 ma on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 ma now separated into three episodes or peaks of activity the first episode was focused on the back arc region and was followed by the main arc construction phase during which transpression was partitioned into strike slip and contraction components despite the longevity of this active margin system individual tectonic events took place rapidly e g development of fore arc d1 d3 and accompanying high temperature low pressure metamorphism took place over c 12 ma we explain the fore arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks this migration may be attributed to an increase in the geothermal gradient accompanied by or followed by exhumation of the mid crust the partially molten hence weak attachment zone solidified and strengthened during cooling before emplacement of the post orogenic rapakivi suite during the third distinct phase of mild sinistral transpression