mechanical interactions between rigid particles in a deforming ductile matrix analogue experiments in simple shear flow abstract the mechanical interaction between two or more particles is investigated in newtonian simple shear flow the experimental models allow observation of both the particle rotation and the deformation pattern around the particles the finite and instantaneous strain patterns around rigid particles are strongly heterogeneous and asymmetric with high finite strain zones aligned to the direction of maximum finite stretch these correspond to local flow with low vorticity number heterogeneous strain patterns around rigid particles spread over a distance of 1 2 times the particle length and this distance increases with increasing bulk strain where rigid particles are more concentrated these patterns coalesce and the overall pattern is then strongly controlled by the particles and cannot be simply related to the external boundary conditions in rocks the characteristic asymmetric strain pattern around rigid isolated particles is a reliable shear criterion which becomes unreliable with high concentrations of rigid particles particle rotation is significantly disturbed when the distance between adjacent particles of equal size is shorter than their length that is only in very concentrated suspensions of rigid particles in a composite shape fabric the development of the sub fabric corresponding to the smaller minerals will be more disturbed

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

new seismogenic source and deep structures revealed by the 1999 chia yi earthquake sequence in southwestern taiwan summary in a tectonically active setting large earthquakes are always threats however they may also be useful in elucidating the subsurface geology instrumentally recorded seismicity is therefore widely utilized to extend our knowledge into the deeper crust especially where basement is involved it is because the earthquakes are triggered by underground stress changes that usually corresponding to the framework of geological structures hidden faults therefore can be recognized and their extension as well as orientation can be estimated both above are of relevance for assessment on seismic hazard of a region since the active faults are supposed to be re activated and cause large earthquakes in this study we analysed the 1999 october 22 earthquake sequence that occurred in southwestern taiwan two major seismicity clusters were identified with spatial distribution between depths of 10 and 16 km one cluster is nearly vertical and striking 032 corresponding to the strike slip meishan fault msf that generated the 1906 surface rupture another cluster strikes 190 and dips 64 to the west which is interpreted as west vergent reverse fault in contrast to previous expectation of east vergence our analysis of the focal solutions of all the larger earthquakes in the 1999 sequence with the 3 d distribution of all the earthquakes over the period 1990 2004 allows us reinterpret the structural framework and suggest previously unreognized seismogenic sources in this area we accordingly suggest 1 multiple detachment faults are present in southwestern taiwan coastal plain and 2 additional seismogenic sources consist of tear faults and backthrust faults in addition to sources associated with west vergent fold and thrust belt

kinematic vorticity analysis and evolving strength of mylonitic shear zones new data and numerical results the kinematic vorticity number is an important quantity in structural geology and tecton ics giving a nonlinear ratio of simple shear to pure shear deformation we use natural obser vations and numerical models to show how rigid clast methods for determining the kinematic vorticity number w k are compromised where strain localization occurs at the matrix clast interface our numerical results show that the critical shape factor cutoff between perma nently rotating and stable clasts used to determine w k is highly sensitive to coupling between the clast and the matrix this fi nding provides an elegant explanation for the fact that rigid clast methods tend to underestimate w k relative to other methods we present numerically determined envelopes for clast behavior across a range of kinematic vorticity numbers clast shape factors and matrix clast coupling our numerical models show that the shape pre ferred orientations of feldspar clasts trend toward the positions of mica fi sh with increasing localization at the clast boundary suggesting that mica fi sh behave as highly lubricated clasts our data and numerical results show that the clast matrix interface may be several orders of magnitude weaker than the surrounding matrix and that weak interfaces can lead to a marked drop in the bulk shear strength of faults and shear zones

strain analysis in deformation experiments with pattern matching or a stereoscope abstract the subject of this paper is the analysis of planar deformation in deformation experiments where the specimen can be observed throughout deformation or at regular intervals the critical step in the analysis of deformation is the determination of displacements of material points over a deformation increment pattern matching is a useful and accurate method to perform this task this method is most suited for the measurement of strain over small deformation increments where it can produce better results than strain measurements with strain markers or inscribed grids it is well suited for geological deformation experiments with for instance sand or clay boxes or transparent deformation cells the distribution of strain can be made visible with a stereoscope and two images of the deforming specimen taken at different stages of deformation the differences in relative displacement of features on the images are translated by the brain to apparent elevation the gradient of the slope depends on the magnitude of finite strain a stereoscope is thus a cheap and simple tool to quickly and qualitatively assess strain distribution in a deforming specimen

viscous inclusions in anisotropic materials theoretical development and perspective applications abstract theories and numerical solutions for a viscous ellipsoid in an infinite anisotropic viscous medium subjected to far field homogeneous deformation lie at the heart of self consistent homogenization models and multiscale simulations of texture and fabric development in earth s lithosphere there is considerable literature on ellipsoid inclusions focused on anisotropic elastic materials published in multi disciplinary fields to make this body of work more accessible as well as to advance viscous inclusion studies an effort is made here to summarize recent advances and to further develop formally more explicit and where possible analytic solutions for incompressible viscous materials the point force concept and equivalent inclusion method of eshelby are used together with the green function approach this leads to generalized equations for ellipsoid inclusion behaviors in anisotropic materials in the particular case of isotropic materials the new mathematical development here enables the use of existing methods for elastic materials to get solutions for corresponding viscous inclusion problems efficiently and accurately a 2d formulation is also presented for elliptic cylinders in plane straining flows of anisotropic materials using the same green function method that is adopted for 3d inclusions the 2d formulation is benchmarked with existing analytic solutions a reconnaissance investigation to compare the behaviors of 2d elliptic inclusions and triaxial ellipsoids in a matrix of planar anisotropy undergoing far field plane straining flows suggests that conclusions drawn from 2d cannot be applied to 3d in anisotropic cases the application of the viscous inclusion theory to the rheologically heterogeneous and non linear lithosphere is discussed by regarding a heterogeneous element as an ellipsoidal inclusion embedded in a hypothetical homogeneous equivalent matrix whose effective rheology is obtained through micromechanical homogenization and assuming that the conditions of scale separation are satisfied the viscous inclusion theory forms the backbone of multiscale models for natural deformation and the accompanying texture and fabric development

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

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

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

microstructures and petro fabrics of lawsonite blueschist in the north qilian suture zone nw china implications for seismic anisotropy of subducting oceanic crust abstract we conducted a detailed study on the microstructures and petro fabrics of massive and foliated lawsonite blueschist lbs in north qilian suture zone nw china the lattice preferred orientation lpo of glaucophane and lawsonite in foliated lawsonite blueschist lbs is considered to be dominantly formed by the deformation mechanism of dislocation creep and rigid body rotation respectively the lpo of glaucophane is mainly characterized by the 001 axis aligning parallel to lineation and the 100 axis and 110 pole plunging perpendicular to foliation in contrast the lpo of lawsonite features the maximum 010 axis concentrated close to lineation and the 001 axis strongly clustered normal to foliation the preferred orientation of 010 axis of lawsonite parallel to lineation is supported by a two dimensional numerical modeling using the finite volume method fvm the mineral lpos are much stronger in foliated lbs than in massive lbs in addition a kinematic vorticity analysis suggests that both pure shear dominant wm 0 18 0 26 and simple shear dominant wm 0 86 0 93 deformation regimes are present in foliated lbs the 001 axis and 010 pole of glaucophane and the 100 and 010 axes of lawsonite tend to distribute in a foliation parallel girdle in the pure shear dominant samples but simple shear dominant samples display more lineation parallel concentrations of a 001 axis of glaucophane and a 010 axis of lawsonite because the whole rock seismic anisotropies in foliated lbs are significantly higher than those in massive lbs and a counteracting effect on seismic anisotropies occurs between glaucophane and lawsonite the delay time of fast s wave polarization anisotropy induced by an actual subducting oceanic crust with a high subducting angle 45 60 is expected to range from 0 03 to 0 09 s lower bound for massive lbs and from 0 1 to 0 3 s upper bound for foliated epidote blueschist

strain partitioning in banded and or anisotropic rocks implications for inferring tectonic regimes abstract among the many concepts that have contributed to the development of structural geology in the last half century two are particularly important these are i the link between the symmetry of the structure the vorticity of the associated deformation process and the tectonic regime and ii the widespread partitioning of strain however a clear understanding of these concepts and the links between them are not always apparent in structural analyses carried out to determine the prevailing tectonic regime of an area through the use of structural symmetries and kinematic indicators this contribution based on field studies from cap de creus experimental data and theoretical concepts highlights some of the problems encountered when attempting to deduce the type of strain and associated regional tectonic regime from field structures the relation between the symmetry of a structure and its associated kinematics is not unique for example it is demonstrated that in mechanically anisotropic materials symmetry variations do not necessarily reflect marked vorticity variations but rather the angular variations between the kinematic framework and the anisotropy planes because of widespread strain partitioning local and general kinematics do not generally match this mismatch is especially accentuated in rheologically heterogeneous rocks nevertheless correct interpretations are possible by performing continuous multi scale structural analyses in which the impact of strain partitioning and of the presence of material anisotropies and heterogeneities are considered

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

strain and flow in the metamorphic core complex of ios island cyclades greece we have analysed strain and flow kinematics in the footwall of the south cyclades shear zone scsz an important tectonic boundary within the attic cycladic crystalline complex exposed on ios island cyclades aegean sea coarse grained augen gneisses in the basement unit flooring the scsz and forming a metamorphic core complex are excellently suited to measure finite strain using the fry method and estimate the vorticity number wk of flow with the blocked object method the results show that oligo miocene exhumation of the basement unit during extension brought approximately 70 n s crustal stretching and up to 40 subvertical shortening in a plane strain environment k 0 99 linear down section strain decrease constrains a zone of contact deformation of the scsz of about 1 5 km thick kinematic vorticity number estimates suggest little deviation from pure shear wk 0 26 finite strain and wk are not correlated indicating that the ios basement and the overlying cover units were stretched compatibly while the scsz is a localized zone of high strain net displacement however may be restricted to about ten kilometres this has important repercussions on large scale tectonic models for extension in the aegean

an estimate of kinematic vorticity from rotated elongate porphyroblasts internal fabric in strain shadows around elongate rutile porphyroblasts indicates rotation of porphyroblasts relative to the incremental stretching direction during deformation within a regional scale shear zone in south central alaska for porphyroblasts of various aspect ratios and initial orientations this fabric is used to assess the sense of rotation relative to the direction of maximum incremental stretching the total rotation and the vorticity the total rotation of porphyroblasts relative to the external fabric based on these parameters varies as a function of porphyroblast orientation all 111 porphyroblasts regardless of orientation have rotated in a clockwise sense relative to the external fabric comparison of these results with previous models suggests that the deformation which affected the porphyroblasts took place in the field of continuous forward rotation with a maximum ratio of the rate of pure shearing to the rate of simple shearing sr of 0 21 or a kinematic vorticity number wk 0 92 the model curves showing rotation vs final orientation do not vary significantly over the range of sr and r that is relevant to this study the data have significant scatter yet there is remarkable agreement between the data and the model for a of 1 5 these results illustrate how strain shadows around porphyroblasts with large aspect ratios and variable initial orientations provide a more complete assessment of kinematics than inclusion trails within more equant porphyroblasts

holocene uplift and subsidence along an active tectonic margin southwestern taiwan abstract taiwan is located along a convergent plate boundary where the luzon arc collides with the eurasia continental margin the tainan plain of southwestern taiwan is incorporated into and deformed by a regional fold and thrust belt associated with this convergent plate margin in this study we establish a tentative regional holocene relative sea level curve that allows us to analyze crustal uplift and subsidence rates of the tainan plain the maximum holocene uplift rates on the tainan plain occur on the tainan tableland and the chungchou terrace these two areas have experienced long term holocene uplift rates of 5 and 7 mm yr respectively the tawan lowland located between these two areas is subsiding at a long term rate of about 1 mm yr based on this pattern of the crustal movement the tainan tableland is interpreted as a mud diapiric dome and the chungchou terrace as the product of a blind thrust fault the holocene reference sea level curve proposed in this study can be used to determine the pattern of crustal movements elsewhere in taiwan it also can suggest that the holocene terrace development does not occur in area where the uplift rate exceeds 8 mm yr while late holocene regression the general trend around the western pacific is not recorded where the rate of subsidence is lower than 1 mm yr

shape fabrics of particles in low concentration suspensions 2d analogue experiments and application to tiling in magma abstract jeffery s equations ascribe a theoretical cyclic nature to the shape fabric of non interacting rigid particles immersed in a viscous fluid undergoing simple shear flow this theoretical behaviour is confirmed at low shear strains 5 first experiment 134 identical particles or 1 second experiment 178 particles with two size classes then become stable at 17 first experiment and at more than 50 second experiment of the population of particles due to the contribution of the tiled particles the shape fabric becomes asymmetrical in its orientation distribution with a maximum lying above the shear plane the latter result provides a new shear sense indicator in addition to the statistical determination of the tiled features the study also suggests that crystalline fabrics in magmas could be acquired at high melt fractions i e early in the crystallization history of the magma

characteristics of surface ruptures associated with the chi chi earthquake of september 21 1999 abstract the chi chi earthquake which reactivated the chelungpu fault in central taiwan generated surface ruptures over 100 km long surface ruptures of the chi chi earthquake can be divided into the north south and the east west sections the north south section extends for about 84 km and the northern e w section 16 km the north south section consists of a continuous main rupture and some branches these are characterized by thrust motion with some strike slip components topographic surveys indicate that the ground commonly uplifted as a single continuous ramp step surface and deformation is mainly concentrated on the hanging wall fault slip data and gps measurements show that the hanging wall along the northern segment of the chelungpu fault moved northwest but that along the southern segment of the fault the hanging wall shifted to the southwest sandbox models suggest that the above dissimilarity in hanging wall movement direction is mainly due to the presence of the peikang basement high in the east west section the ruptures comprise a series of en echelon steep faults with right step or left step geometry and trend ene wsw to e w near the ta an river the surface rupture orientation shifts from ne sw to nw se and terminates at the shuangtung fault here the ruptures appear to be controlled by the 10 15 km wide nw trending sanyi puli shear zone clay modeling displays the development of e w trending ruptures when a n s trending fault meets a n30 w trending weak zone

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

along strike variations of morphotectonic features in the western foothills of taiwan tectonic implications based on stream gradient and hypsometric analysis abstract the taiwan mountain belt provides a key example for analyzing the relation between morphology and tectonics in an active compressional environment there is a striking geometrical relationship between the location of salients and reentrants of the mountain belt and the presence of major crustal inhomogeneities such as structural highs in the foreland basin major along strike variations of structural styles occur in range front rock units of the fold thrust belt stream gradient and hypsometric analysis has been carried out to highlight the along strike variations of morphotectonic features and to illustrate the relative activities in different tectonic regimes of the western foothills the normalized stream length gradient index sl index and the hack profile are two of the stream gradient indices that effectively reflect the tectonic uplift in a region de trending and residual analysis of the hypsometric integral hi eliminates the spatial dependency of small drainage basins and the residual hypsometric integral corresponds to differential uplift activity integration of stream gradient indices and hypsometry provides more robust tectonic interpretation five morphotectonic provinces have been identified in the western foothills based on stream gradient indices and hypsometry each province is bounded by a series of n140 e trending transfer fault zones either inherited from the eurasian passive margin and or newly formed in the sedimentary cover in response to the presence of basement highs within the foreland basin the peikang and kuanyin highs the morphotectonic features as well as deformation styles vary within each province a high uplift but low shortening rate typifies the crustal deformation style in the transpressional regime north of the peikang basement high on the contrary a low uplift but high shortening rate characterizes the crustal deformation style in the transtensional regime south of the peikang basement high the higher geomorphic indices suggest that greater tectonic activity occurs in central than in southwestern taiwan this inference is also supported by the coseismic deformation of the 1999 chi chi earthquake

fabric evolution of rigid inclusions during mixed coaxial and simple shear flows abstract in a slowly moving viscous fluid a population of non interacting rigid inclusions evolves in an oscillatory fashion or creates a stable fabric depending on the flow geometry and the shape of the inclusions using jeffery s equations for the motion of a rigid ellipsoidal inclusion a mixed coaxial and simple shear flow was investigated both analytically and by numerical modeling exact results were obtained for spheroidal inclusions depending on the axial ratio of the inclusion and the amount of the coaxial component of flow individual inclusions can move cyclically or rotate to a stable orientation in one of two mutually orthogonal directions equations were found which allow us to distinguish between these types of motion and to determine the stable inclusion orientation the relative motions of individual inclusions determine the preferred orientation in a population of inclusions in a heterogeneous population with diverse axial ratios the fabric evolves as the superposition of subfabrics corresponding to subsets with different axial ratios the orientations of stable subfabrics depend on axial ratios and could thus be used as kinematic indicators in cases of a sufficiently large coaxial component of flow the fabric created by a heterogeneous population may comprise two stable mutually orthogonal subfabrics no exact results are available for general i e non spheroidal ellipsoidal inclusions and numerical modeling must be used if the coaxial component of flow is sufficiently strong the non spheroidal inclusions move much like the spheroidal ones orthogonal subfabrics may appear as transient features in the evolution of a homogeneous population of non spheroidal ellipsoidal inclusions

the behavior of shape preferred orientations in metamorphic rocks amphiboles and jadeites from the monte mucrone area sesia lanzo zone italian western alps abstract in the eclogitic micaschists of the monte mucrone area sesia lanzo zone italian western alps we have measured in detail the eclogitic lineation at several outcrops we present observations at the markers scale this scale allowing the whole range of progressive deformations to be described populations of glaucophanes and jadeites show different statistical features which must be at least for a part produced by the distinct mechanical behavior for these markers during the alpine history the glaucophanes show a positive correlation between the intensity of preferred orientation and their aspect ratio due to a mainly rigid behavior the observed differences in shape and orientation of jadeites also show different behavior related to different retromorphic overprints we briefly discuss the implications of these observations on the significance of metamorphic lineations

clast based kinematic vorticity gauges the effects of slip at matrix clast interfaces clast based methods for estimating the mean kinematic vorticity number wm are compromised by strain localization at the clast margins localization increases with modal matrix mica content as determined with samples from the sandhill corner mylonite zone a crustal scale high strain strike slip shear zone in maine using these samples we estimate wm with the oblique quartz shape preferred orientation and rigid clast rotation methods the rigid clast rotation method yields much lower values for wm than the quartz method to investigate whether or not slip at the matrix clast interface can explain the discrepancy in calculated wm we conducted numerical modeling of rigid clasts enveloped by a low viscosity layer both embedded within a shearing viscous matrix within this dynamic framework we carried out numerical sensitivity analyses in which we varied the viscosity ratio between the lubricating layer and the surrounding matrix the thickness of the lubricating layer and the kinematic vorticity number of the bulk flow our data and numerical results succeed in explaining why wm estimates from clast based rotational methods are typically lower than estimates from other methods and this has implications for testing hypotheses related for example to vorticity partitioning in oblique convergent settings crustal scale extrusion or channel flow and exhumation of ultra high pressure rocks all of which rely on robust estimates of wm the relation between the shape preferred orientations of clasts and modal mica content lead to the hypothesis that mica is the cause of the lubrication at clast matrix interfaces if so then we surmise that mica fish should be self lubricating and would therefore form an end member shape preferred orientation regardless of matrix modal mica content the unique role of mica allows us to speculate about the bounds on viscosity contrast between the matrix and lubricated clast interfaces

evolution of zircon deformation mechanisms in a shear zone lanzo massif western alps abstract magmatic zircons within two sheared gabbroic dykes from the peridotitic massif of lanzo western alps italy revealed evolution of deformation from crystal plasticity to rigid body rotation during shear zone evolution this is the first time that multiple zircon grains have been analysed in a kinematic context in a shear zone zircon grains recorded crystal plastic deformation activating the commonly inferred 001 and 100 glide systems to the newly identified 110 glide system the exact selection of glide system could be dependant of deformation conditions such as pressure temperature and strain rate moreover the activation of one or several glide systems within a single grain could be favoured by the primary orientation of the grains combined with a high strain rate in these sheared gabbros the deformation mechanisms evolve from plastic deformation at low strain rate conditions to increase strain strain softening and localisation of deformation the progressive shear zone development and the softening of the matrix relative to the zircon has lead to a switch from crystal plasticity to rigid body rotation of zircon the zircon grains rigid body rotation involved that their long axes became parallel to the lineation of the shear zone causing reorientation and dispersion of the misorientation axes away from kinematic y

asymmetric quartz c axis fabrics and flow vorticity a study using rotated garnets abstract the development of a type i crossed girdle c axis fabric with an asymmetric density distribution and an internally asymmetrical skeletal outline is examined in a specimen of garnet bearing mylonitic quartzite from the betic movement zone in southern spain the garnets are pre mylonitic skeletal porphyroblasts that rotated during mylonitic deformation but preserved a strain free equilibrium microstructure and a random c axis fabric it follows that the asymmetry of the density distribution must result from the deformation history itself the sense of asymmetry of the c axis population and that of the skeletal outline are consistent with the sense of vorticity inferred from extensional crenulations and asymmetric microboudinage and also with the sense of rotation of the garnets analysis of the rotation angles with aspect ratio of the garnet porphyroblasts demonstrates that a pure shear component was involved in an essentially non coaxial flow this may explain the internal asymmetry of the fabric skeleton and confirms the idea that a spectrum exists of type i fabrics intermediate between the theoretically predicted fabrics for pure and simple shear a tentative reconstruction of the kinematic framework suggests that the central segment of the fabric skeleton is linked to the extensional apophysis of the flow

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

uplift of tainan tableland sw taiwan revealed by sar interferometry interferometric processing of five sar ers images reveals uplift of the tainan tableland sw of taiwan during the period 1996 1998 the maximum measured ground motion for these two years is 2 8 cm along the radar line of sight towards the satellite indicating for the displacement vector a vertical component of 3 2 cm and a horizontal component of 1 6 cm towards the wsw considering additional information from gps data the reconstructed displacement field is consistent with the geological interpretation of the tainan tableland as an actively growing anticline connected to the taiwan fold and thrust belt this implies that the deformation front is located farther west than usually assumed in the tainan area the large tainan city is thus located in an active deformation zone seismic hazard assessment is however difficult because the mechanisms and kinematics are not known in detail

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

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

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

vorticity decomposition and its application to sectional flow characterization abstract great insights have been gained by applying the concept of vorticity to the study of the natural flow of rocks geologists have used various schemes of vorticity decomposition depending on the purpose of their studies the fundamental decomposition divides the overall vorticity into that of the material with respect to the instantaneous stretching axes and the spin of these axes in an external reference frame in which the flow is defined this represents a new contribution to continuum mechanics material science and structural geology its implications for the kinematic analysis of geological structures and fabrics are more significant than have been realized in virtually every geological situation the flow has a spin component and therefore vorticity decomposition needs to be considered the decomposition of vorticity is applied to the characterization of the two dimensional flow on a material plane sectional flow in a general three dimensional flow field the analysis of the sectional flow and sectional non coaxiality is a precondition for a determination of the initial orientation of structural elements such as the orientation of a fold developed in a competent layer that is embedded in a high strain zone and their temporal evolution theoretically it may also be possible to derive the symmetry of a natural deformation path by examining fabric symmetries on differently oriented sections from deformed rock samples

are isolated stable rigid clasts in shear zones equivalent to voids abstract particles in shear enclose important information about a rock s past and can potentially be used to decipher the kinematic history and mechanical behavior of a certain outcrop or region isolated rigid clasts in shear zones often exhibit systematic inclinations with respect to the shear plane at small angles tending towards the instantaneous stretching direction of the shear zone this shape preferred orientation cannot be easily explained by any of the analytical theories used in geology it was recently recognized that a weak mantle surrounding the clast or a slipping clast matrix interface might be responsible for the development of the observed inclinations physical considerations lead us to conjecture that such mantled rigid clasts can be effectively treated as voids that are not allowed to change their shape the resulting equivalent void conjecture agrees well with numerical and field data and has the following important geological implications i clasts in shear zones can have stable positions in simple shear without the requirement of an additional pure shear component ii the stable orientation can be approached either syn or antithetically hence the clast can rotate against the applied shear sense iii the strain needed to develop a strong shape preferred orientation is small 1 and therefore evaluations based on other theories may overestimate strain by orders of magnitude iv the reconstruction of far field shear flow conditions and kinematic vorticity analysis must be modified to incorporate these new findings

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

active structures as deduced from geomorphic features a case in hsinchu area northwestern taiwan abstract two previously documented active faults in northwestern taiwan the hsinchu and hsincheng faults are evaluated for their earthquake hazard potential by using a digital elevation model dem aerial photos and field mapping both of these thrust faults contain active anticlines in their hanging walls based on folding of young alluvial deposits mapping of the hsinchu fault suggests the presence of numerous scarps oriented sub parallel to the fault trace that was previously defined by projection of subsurface geology we interpret the geometry of the surface scarps to be mainly produced by the thrust component but in part by a lateral component of fault slip the scarps associated with the hsincheng fault system are less complex and offset a flight of terraces including the modern flood plain a back thrust exposed 1 2 km east of the hsincheng fault is interpreted as linked with the main thrust surface deformation is only apparent south of the touchien river and becomes less obvious across another wrench fault system which is linked to hsinchu fault in the west and extends southeastward parallel to the touchien river the wrench fault system mentioned above not only offsets the hsinchu fault but also divides the hsincheng fault into segments the supporting evidence found for this includes pressure ridges and pull apart sags two associated hanging wall anticlines are both recently active based on deformed geomorphic surfaces two major ne striking thrusts and one nw wrench fault system are identified reflecting the compression stress is partitioned in this area which might be resulted from recently influenced extension tectonics i e okinawa back arc rifting

middle late holocene river terraces in the erhjen river basin southwestern taiwan implications of river response to climate change and active tectonic uplift abstract we reconstruct the holocene river history of the erhjen river area 140 km 2 by correlating river terraces aided by 28 radiocarbon dates multiple terraces developed in the lower erhjen river since the middle holocene they converge downstream to the coastal plain the rates of channel incision into bedrock calculated from these terraces at yuehshihchieh are 7 8 mm year during ca 5 7 2 5 ka 5 cm year during 1 5 1 3 ka and 1 cm year since 1 ka the last is close to the average incision rate since middle holocene meanwhile only a single but wide middle late holocene paleo floodplain was developed in the upper erhjen river it was completely abandoned only after 0 8 ka likely following an episode of base level fall starting from the coastal plain based on the apparent downstream and upstream convergence of these dated terraces we identify a doming structure or anticline within the basin which results in a tilt rate of 10 6 to 10 7 per year in the lower erhjen river valley the major terraces here had different initial long profiles which implies that a critical graded long profile may not be a prerequisite for formation of a wide erosional terrace surface instead we propose that these terraces were initiated by a series of catastrophic rainfall events probably climatic related which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high discharge runoff we find that not only terrace surface formation but also channel incision can be strongly controlled by climatic driven discharge and bedload conditions as suggested by the contrast of bedrock incision rates we observe at yuehshihchieh apparently the climate and its effects on the landscape cannot be regarded as constant during the holocene even in a humid tropical area like taiwan however such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created the lower erhjen river that is characterized by active tectonic tilting is an example of this setting

incremental deformation and fabric development in a kcl mica mixture abstract the history of deformation and of mica reorientation is described in a kcl mica mixture in the middle of a kink like experimental shear zone the history was reconstructed by deforming several specimens to successively greater total strains and assuming the more deformed specimens passed through the states of strain and fabric exhibited by the less deformed specimens a pseudo differentiated layering is described which arises from the original network distribution of the mica grains without benefit of any differentiation process a comparison is made between the observed mica fabrics at various strains and those predicted by the march model taking the measured initial preferred orientation of the micas into account the actual reorientation processes in the material are found to be more efficient than the march transformation at shortening strains less than about 70 but less efficient at higher strains these departures from marchian behavior are explaned qualitatively comparison is also made between observed and predicted intensities of mica preferred orientation assuming a hypothetical random orientation of micas in the starting material for the march calculation

the autocorrelation function an image processing tool for fabric analysis abstract the use of the autocorrelation function acf is proposed as a method for fabric and or strain analysis its chief purpose is to extend fabric analysis to fine grained materials such as clays micrites etc or to materials where the determination of individual grain shapes is tedious or impossible the main advantage of the method is that no segmentation of the image prior to analysis is necessary in other words any bias associated with identifying grain boundaries and the like is avoided in as much as the recognition of grains or grain boundaries is a matter of scale the acf can be used without loss of generality whenever the grain size is small in comparison with the size of the analysed area the method is computer based it requires a scanner for the digitization of the images and sufficient storage space and computing power for digital image processing the method uses half tone images as input these can be obtained from thin sections acetate peels polished surfaces photographic negatives or positives etc the acf is a two dimensional function that is related to the average shape that occurs in the fabric it is scaled with respect to the original image and allows simultaneous analysis of small and large features the acf enables a a quantitative description of the fabric in general terms b an efficient grain size determination and c if strain is a valid interpretation of the fabric the derivation of the finite strains in the plane of observation in the first part of the paper the acf method is introduced by way of a few numerically generated fabrics and compared to other methods of fabric and strain analysis in the second part an application to three samples of experimentally deformed solnhofen limestone is demonstrated

the chiuhsiungken fault a candidate to trigger a hazardous earthquake in western taiwan abstract the chiuhsiungken fault located along the boundary between the western foothills fold and thrust belt and the coastal plain in the chiayi yunlin area of taiwan has been identified as an active thrust through geological and geomorphic investigations young geomorphic features provided by shortening across the chiuhsiungken fault are well preserved and provide excellent examples to illustrate features provided by active thrust faulting historic seismicity records show that the deformation front in the chiayi yunlin area is very active and the fault slips at a rate of mm yr based on tectonic geomorphic investigation the chiuhsiungken fault has the potential to produce large earthquakes in the future the fault with a length about 15 km can be traced northward to the sinistral kuken transfer fault and southward to near the sinistral chuchi transfer fault the maximum potential magnitude of an earthquake triggered by the chiuhsiungken fault is estimated to be a m w 6 4 however the magnitude of the earthquake could be larger than expected if the adjacent faults rupture together with the chiuhsiungken fault

detection of a recent earthquake fault by the shallow reflection seismic method the 1999 chi chi earthquake in taiwan was a relatively unique seismic event which activated the chelungpu thrust fault with extraordinarily large surface ruptures up to 9 8 m horizontally and 5 6 m vertically the fault is 80 km long lying mostly in a north south direction and with a reverse thrust dipping shallowly to the east for this paper we used the shallow reflection seismic method a small scale method to map this active fault a large scale structure and provide evidence in support of the thin skinned thrust model for this earthquake fault the investigation is comprised of two parts the first concentrates on the northern portion of the fault where the fault trace was bent 70 to the northeast and was accompanied by abnormally large ground displacements and damage the seismic sections obtained are of good quality and can be used to explore the detailed faulting mechanism the second part aims to find the gross features of the 60 20 km fault surface using limited shallow seismic measurement

kinematic behaviour of an interface and competence contrast analogue models with different degrees of bonding between deformable inclusions and their matrix abstract in a system composed of a ductile matrix with a particle included in it the deformation of the matrix the displacement field and the rotation and the deformation of the block are related to the viscosity ratio between block and matrix and also to the degree of bonding between the matrix and the block in this paper belemnites from the lower lias of the alps provide a natural example of moderately deformed objects included in a slaty matrix they are compared with analogue models made of paraffin in which a long block of a more competent paraffin is included depending on the degree of bonding between matrix and object the same block appears to be deformable or quite rigid with a high degree of bonding the strain refraction observed corresponds to the viscosity ratio between the block and the matrix when the degree of bonding is weak the block is quite undeformed its rotation is great and the deviation of the strain in the matrix is analogous to that observed around a fault the kinematic conditions appear to have a greater effect on the finite strain than the viscosity ratio of the materials

porphyroblast inclusion trail orientation data eppure non son girate extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non coaxial ductile deformation of the matrix subsequent to their growth this has been demonstrated for all tectonic environments so far investigated the work also has provided new insights and data on metamorphic structural and tectonic processes including 1 the intimate control of deformation partitioning on metamorphic reactions 2 solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones and relative plate motion and 3 a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens

biases in three dimensional vorticity analysis using porphyroclast system limits and application to natural examples a description of the systematic errors associated with the measurement of the vorticity number from poryhroclasts in natural systems is presented and discussed we show that strong biases and systematic errors could derive both from some erroneous physical i e no slip across clast matrix boundary homogeneity within the matrix as well as geometrical assumptions i e the radius ratio and angular measurements carried out in two dimensions on outcrop surfaces and thin section by comparing natural datasets of porphyroclast shape preferred orientation spo with different theoretical curves plots we suggest that at least one of the jeffery physical assumptions can be tested when applying vorticity techniques the comparison of different possible sources of systematic errors indicates that for medium to low vorticity numbers wm 0 8 vorticity data are strongly biased and that a minimum systematic error of 0 2 should be taken into account finally we use data from natural shear zones from the southern variscan belt in sardinia to test and discuss the starting assumptions of the jeffery model one of the main challenges of modern structural geology is to try to obtain information about the rheology and kinematics of flow occurring in the deepest crust and upper mantle several microstructure fabrics e g fabric asymmetry associated with mylonites represent potentially important sources of information to obtain kinematic data as well as for estimation of deformation parameters see passchier trouw 2005 for a review in particular porphyroclast systems have been shown to be a sensitive indicator of flow parameters and can be used to constrain the relative ratio of combined pure and simple shear i e the vorticity of the flow several theoretical and practical studies indicate that syn kinematic recrystallization of mantles sor d shaped tails around porphyroclasts and shape preferred orientation spo of porphyroclasts may store information on the amount of shear strain with the aim of developing a vorticity gauge theoretical and experimental models for study of the rotation and behaviour of elliptical porphyroclasts in a fluid have been proposed and developed the first attempt began with the pioneering works of jeffery 1922 and eshelby 1957 that found solutions for rigid objects immersed in a viscous and linear elastics fluid respectively bretherton 1962 ghosh ramberg 1976 and bilby kolbuszewski 1977 further adapted the basic jeffery analytical solution to material science and structural geology subsequent investigations used the previous theoretical calculation to develop efficient strain and vorticity gauge techniques capable of quantifying the flow parameters within shear zones passchier 1987 wallis 1992 simpson de paor 1993 holcombe little 2001 three main analytical techniques passchier 1987 wallis 1995 holcombe little 2001 are commonly employed to characterize flow within shear zones using rigid porphyroclats jessup et al 2007 all these techniques use the measurement of the axial ratio of porphyroclast r the shape factor fig 1 and the angle of long axis porphyroclast with respect to foliation or stretching direction h fig 1 and the distribution of the cross plotted curves to define the mean vorticity number wm these curves define a threshold number rc below which the porphyroclasts continuously rotate and above which they record stable sink position however as many authors passchier 1987 marques coelho 2001 have already noted the jeffery model assumes 1 rigid particles immersed in a non confined viscous flow 2 a perfect coupling on matrix particle interface and 3 no interference between particles during deformation use of the jeffery model implies that these physical assumptions are met and or need to be at least preliminarily tested although techniques to estimate the vorticity of flow have become routinely used on sheared rocks in a variety of tectonic settings e g klepeis et al 1999 xypolias doutsos 2000 xypolias koukouvelas 2001 bailey eyster 2003 law et al 2004 carosi et al 2006 2007 iacopini et al 2008 sarkarinejad et al 2008 2010 frassi et al 2009 larson godin 2009 relatively few detailed analysis of error sources have been proposed and a critical discussion from prior d j rutter e h tatham d j eds deformation mechanisms rheology and tectonics microstructures mechanics and anisotropy geological society london special publications 360 301 318 doi 10 1144 sp360 17 the geological society of london 2011 publishing disclaimer www geolsoc org uk pub ethics at university of aberdeen on november 19 2012 http sp lyellcollection org downloaded from

shape fabric development in rigid clast populations under pure shear the influence of no slip versus slip boundary conditions abstract shape fabrics of elliptical objects in rocks are usually assumed to develop by passive behavior of inclusions with respect to the surrounding material leading to shape based strain analysis methods belonging to the rf family a probability density function is derived for the orientational characteristics of populations of rigid ellipses deforming in a pure shear 2d deformation with both no slip and slip boundary conditions using maximum likelihood a numerical method is developed for estimating finite strain in natural populations deforming for both mechanisms application to a natural example indicates the importance of the slip mechanism in explaining clast shape fabrics in deformed sediments

long term crustal movement caused by the chiuchiungkeng fault in southwestern taiwan constraints from luminescence dating abstract to investigate the long term crustal movement of the chiuchiungkeng fault cckf a proposed active fault located in the southwestern coastal plain of taiwan two boreholes and dissected alluvial fans were selected for determination of depositional ages using luminescence the standard single aliquot regenerative dose sar protocol was applied to large aliquots of 90 150 m quartz with dose rates based mainly on high resolution gamma spectrometry the laboratory growth curves show a relatively large saturation value which should allow reliable ages to be determined back to 150 ka to test whether a significant sensitivity change occurred during natural measurement the single aliquot regeneration and added dose sara method was also used to estimate equivalent dose this showed that a sensitivity change of 4 may be introduced during the routine sar procedure the age results unaffected by significant sensitivity change all lie within 60 105 ka and an 80 ka synchronous surface is used to evaluate the long term fault behaviour based on the offset across the hanging wall and footwall a long term fault slip rate of 1 5 m ka 1 is estimated for the near surface cckf from the anomalously steep slope of an 80 ka abandoned fan surface observed in the hanging wall a long term tilt rate of 42 m km 1 can be also derived based on the assumption that the initial slope is given by the modern river bed finally it is deduced that the slip rate of the cckf along its deeper part must be greater than 1 5 m ka 1 since the apparent rate is reduced by folding of the hanging wall

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities

chemical stratification in the silicate earth abstract the largest density contrast between magmas and common ferromagnesian minerals in the mantle occurs at two locations these are nearest the earth s surface and at about 650 700 km depth where the lower mantle mineral assemblage becomes stable at solidus temperatures the large density contrast between magmas and olivine nearest the surface diminishes to zero somewhere between the middle and lower stratigraphic sections of the upper mantle it is also here where the composition of all anhydrous magmas is most similar to that of an undepleted garnet iherzolite composition for an earth that has differentiated by fractional crystallization and melting processes which depend on the separation of crystalline phases from silicate liquids having different densities the 650 km discontinuity could represent a chemical boundary layer the chemical change in the early archean could have been from primordial upper mantle compositions above the boundary layer to differentiated lower mantle compositions below a primary stratigraphic model is offered for the distribution of depleted enriched and primordial isotopic mantle components formed by the transport fate of magmas in the beginning of earth history depleted morb source regions were established in the uppermost part of the upper mantle primordial mantle was located at the middle to the deepest regions of an upper mantle which was processed by anhydrous melting and crystallization enriched and depleted components could have been formed at these levels also by igneous processing in the presence of h 2 o or co 2 and involving highly compressible magmas the lower mantle became heterogeneous with enrichments at the top and depletions elsewhere it is suggested that the present day isotopic structure of the mantle has inherited elements of this primary stratification primordial 143 nd 144 nd and 87 sr 86 sr observed in oceanic islands basalts are located in the middle of upper mantle convection cells enriched ratios found in both oceanic islands basalt and kimberlite could have originated near and on either side of the 650 km chemical boundary layer

mineral lineation produced by 3 d rotation of rigid inclusions in confined viscous simple shear abstract the solid state flow of rocks commonly produces a parallel arrangement of elongate minerals with their longest axes coincident with the direction of flow a mineral lineation however this does not conform to jeffery s theory of the rotation of rigid ellipsoidal inclusions reis in viscous simple shear because rigid inclusions rotate continuously with applied shear in 2 dimensional 2 d flow the rei s greatest axis e1 is already in the shear direction therefore the problem is to find mechanisms that can prevent the rotation of the rei about one axis the vorticity axis in 3 d flow the problem is to find a mechanism that can make e1 rotate towards the shear direction and so generate a mineral lineation by rigid rotation about two axes 3 d analogue and numerical modelling was used to test the effects of confinement on rei rotation and for narrow channels shear zone thickness over inclusion s least axis wr 1 can rotate backwards from an initial orientation w e1 parallel to the shear plane in great contrast to jeffery s model 3 back rotation is limited because inclusions reach a stable equilibrium orientation 4 most importantly and in contrast to jeffery s model and to the 2 d simulations in 3 d the confined rei gradually rotated about an axis orthogonal to the shear plane towards an orientation with e1 parallel to the shear direction thus producing a lineation parallel to the shear direction the modelling results lead to the conclusion that confined simple shear can be responsible for the mineral alignment lineation observed in ductile shear zones

garnet porphyroblast timing and behaviour during fold evolution implications from a 3 d geometric analysis of a hand sample scale fold in a schist detailed 3 d analysis of inclusion trails in garnet porphyroblasts and matrix foliations preserved around a hand sample scale tight upright fold has revealed a complex deformation history the fold dominated by interlayered quartz mica schist and quartz rich veins preserves a crenulation cleavage that has a synthetic bulk shear sense to that of the macroscopic fold and transects the axis in mica rich layers garnet porphyroblasts with asymmetric inclusion trails occur on both limbs of the fold and display two stages of growth shown by textural discontinuities garnet porphyroblast cores and rims pre date the macroscopic fold and preserve successive foliation inflection intersection axes fias which have the same trend but opposing plunges on each limb of the fold and trend nne ssw and ne sw respectively the fias are oblique to the main fold which plunges gently to the wsw inclusion trail surfaces in the cores of idioblastic porphyroblasts within mica rich layers define an apparent fold with an axis oblique to the macroscopic fold axis by 32 whereas equivalent surfaces in tabular garnet adjacent to quartz rich layers define a tighter apparent fold with an axis oblique to the main fold axis by 17 this potentially could be explained by garnet porphyroblasts that grew over a pre existing gentle fold and did not rotate during fold formation but is more easily explained by rotation of the porphyroblasts during folding tabular porphyroblasts adjacent to quartz rich layers rotated more relative to the fold axis than those within mica rich layers due to less effective deformation partitioning around the porphyroblasts and through quartz rich layers this work highlights the importance of 3 d geometry and relative timing relationships in studies of inclusion trails in porphyroblasts and microstructures in the matrix

morphotectonic evidence from lateral propagation of an active frontal fold pakuashan anticline foothills of taiwan abstract the pakuashan anticline is uniquely suited for study of the forward and lateral growth of fault related folds the pakuashan ridge development arises from the late quaternary uplift of the most external thrust zone of the western foothills of taiwan from kaoshiung to taichung recent and active westward thrusting occurs at the front of the foothills the pakuashan anticline trending n 150 e in the northern part to n 000 in the southern part has been active throughout the quaternary period this activity is marked by geological structures tectonic geomorphology and seismicity a multisource and multiscale approach to study of the continental collision setting has been undertaken to combine tectonics sedimentology and geomorphology studies of fracture patterns allow identification of two main features of stress orientations a wnw ese compression direction and e w and n s extension directions quantitative geomorphic parameters have been used to define the morphotectonic evolution and to infer tectonic style along the mountain front geomorphic evidence provides significant information on the processes that govern lateral propagation of an active anticline quaternary terraces are uplifted tilted and folded over the pakuashan ridge drainage systems in areas of active compression give information on the thrust zone structures and their development steep drainage and high local relief indicate that the pakuashan anticline forms a well defined zone of high uplift especially in the southern part the two main controls on drainage in that area are rock strength in the hanging wall and propagation of the deformation towards the south

active deformation of taiwan from gps measurements and numerical simulations using a two dimensional distinct element model we evaluate the relationships between plate kinematics and present day deformation in taiwan where active collision occurs in particular the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data gps obtained in taiwan and the surrounding islands of the philippine sea plate and the eurasian shelf the main aim of this paper is to produce a mechanically consistent 2 d model that accounts for the observed velocity field taken as whole within the limits of acceptable rheological parameters and reasonable boundary displacement conditions we evaluate how the active deformation of taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms respectively major mechanical discontinuities such as the main fault zones in the mountain belt and the opening of the okinawa trough particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns we show that despite parameter uncertainties several tectonic factors the presence of the strong kuanyin and peikang highs in contrast to the weak subduction zone to the south the weak active regional shear zones and the opening of the back arc okinawa trough concur to provide an acceptable mechanical model for this regional deformation these sources are related not only to the geometry of the plate boundary the direction of plate convergence and the shape of the chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the longitudinal valley fault zone and the western thrust belt of taiwan

preferred orientation developed by rigid markers in two dimensional simple shear strain a theoretical and experimental study abstract in a homogeneous two dimensional deformation linear markers embedded in a viscous matrix develop a preferred orientation along the principal axis of the strain ellipse theoretical analysis of marker rotation under two dimensional simple shear is used to derive an orientation distribution function this function shows that the relative density maximum increases with progressive strain its value being equal to the major minor strain ellipse axis ratio moreover the density is equal to the unity along the lines of no finite longitudinal strain experimentally observed preferred orientation is in good agreement with the expected theoretical distribution

a statistical approach to determination of a mineral lineation abstract a statistical model of the bipolar von mises type was applied to the analysis of mineral lineation defined by the preferred dimensional orientation of inequant grains on a foliation surface orientation data of 203 258 grains from each of four rock specimens fit the model well suggesting a useful analytical technique with three advantages 1 confidence in whether a metamorphic tectonite has a mineral lineation can be determined using a 2 test 2 the orientation of the mineral lineation can be represented by the mean direction with a specified confidence interval and 3 the degree of preferred dimensional orientation of grains can be quantified by the concentration parameter

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow

on the geometric relationship between deformation microstructures in zircon and the kinematic framework of the shear zone abstract we present novel microstructural analyses of zircon from a variety of strained rocks for the first time multiple plastically deformed zircon crystals were analyzed in a kinematic context of the respective host shear zones our aim was to derive how the orientation of zircon grains in a shear zone affects their deformation based on careful in situ observations for sampling we selected zircon bearing rocks that were deformed by simple shear samples covered a range of p t conditions and lithologies including various meta igneous and meta sedimentary gneisses microstructural analyses of zircon crystals in situ with scanning electron backscatter diffraction mapping show strong geometrical relationships between orientations of i the long axes of plastically deformed zircon crystals ii the crystallographic orientation of misorientation axes in plastically deformed zircon crystals and iii the foliation and lineation directions of the respective samples we assume that zircon crystals did not experience post deformation rigid body rotation and thus the true geometric link can be observed the relationships are the following a plastically deformed zircon crystals usually have long axes parallel to the mylonitic foliation plane b crystals with axes oriented at an angle 15 to the foliation plane are undeformed or fractured zircon crystals that have axes aligned parallel or normal to the stretching lineation within the foliation plane develop misorientation and rotation axes parallel to the 001 crystallographic direction zircon grains with the axis aligned at 30 60 to the lineation within the foliation plane often develop either two low miller indices misorientation axes or one high miller indices misorientation axis host phases have a significant influence on deformation mechanisms in a relatively soft matrix zircon is more likely to develop low miller indices misorientation axes than in a relatively strong matrix these relationships are independent of zircon s grain size and shape and reflect the strong geometric control of the macroscopic kinematic rotation axis on the crystal plastic deformation behavior of zircon and on the geometry of its slip systems we describe previously unknown rheological and crystallographic properties of zircon which suggest a tool for deriving an orientation of the plastically deformed zircon crystals with respect to the associated foliation and stretching lineation additionally relationships between zircon deformation microstructures and the macroscopic kinematic framework have implications for zircon geochronology if deformation events result in zircon distortion and as a consequence partial or complete resetting of the zircon isotopic system the age of deformation can be accurately dated