the mount hay block central australia another puzzle piece for paleo mesoproterozoic tectonic history abstract the 100 km 2 mount hay block arunta region central australia is a 15 km thick crustal cross section comprised of granulite facies tectonites containing a tectonothermal record from ca 1803 to ca 1552 ma as demonstrated by the combination of prior work and new monazite geochronology and thermobarometry igneous and sedimentary protoliths formed ca 1803 1798 ma during 1810 1790 ma stafford tanami time between ca 1790 and 1740 ma nearly continuous magmatism in the aileron province and possibly ages of recrystallized zircon and monazite in the mount hay block record subduction along the southern margin of the proterozoic australia mawson continent geologic mapping and zircon and monazite geochronology demonstrate that the mount hay block was penetratively deformed between ca 1720 ma and 1700 ma during 1735 1690 ma strangways time this includes the 8 km thick mount hay sheath fold which records ne sw subhorizontal shear once paleozoic tilting of the mount hay block is removed while still in the deeper crust 798 33 c 7 6 0 7 kbar fabrics along the northern edge of the mount hay block were transposed by the cross cutting 7 km thick capricorn ridge shear zone at ca 1551 7 5 5 ma during chewings time once restored the capricorn ridge shear zone records ne sw extension a jump in strain rate while at high temperatures 725 c initiated severe localization accommodated initially by pseudotachylite formation and cataclasis then mylonitization during fe rich fluid flux shearing may have continued to pressure temperature conditions as low as

initial tectonothermal evolution within the scandinavian caledonide accretionary prism constraints from40ar 39ar mineral ages within the seve nappe complex sarek mountains sweden in the caledonide orogen of northern sweden the seve nappe complex is dominated by rift facies sedimentary and mafic rocks derived from the late proterozoic baltoscandian miogeocline and offshore continent iapetus transition metamorphic breaks and structural inversions characterize the nappe complex within the sarek mountains the sarektjakka nappe is composed of c 600 ma old dolerites with subordinate screens of sedimentary rocks these lithological elements preserve parageneses which record contact metamorphism at shallow crustal levels the sarektjakka nappe is situated between eclogite bearing nappes mikka and tsakkok nappes which underwent high p metamorphism at c 500 ma during westward subduction of the baltoscandian margin 40ar 39ar mineral ages of c 520 500 ma are recorded by hornblende within variably foliated amphibolite derived from mafic dyke protoliths within the sarektjakka nappe plateau ages of 500 ma are displayed by muscovite within the basal thrust of the nappe and are consistent with metamorphic evidence which indicates that the nappe escaped crustal depression as a result of detachment at an early stage of subduction cooling ages recorded by hornblende from variably retrogressed eclogites in the entire region are in the range of c 510 490 ma and suggest that imbrication of the subducting miogeocline was followed by differential exhumation of the various imbricate sheets hornblende cooling ages of 470 460 ma are recorded from massive dyke protoliths within the sarektjakka nappe these are similar to ages reported from the seve nappe complex in the central scandinavian caledonides probably these date imbrication and uplift related to early ordovician arrival of outboard terranes e g island arc sequences represented by structurally lower horizons of the koli nappes metamorphic contrasts and the distinct grouping of mineral cooling ages suggest that the various seve structural units are themselves internally imbricated and were individually tectonically uplifted through argon closure temperatures during assembly of the seve nappe complex the cooling ages of 520 500 ma recorded within seve terranes and along terrane boundaries of the sarek mountains provide evidence of significant accretionary activity in the northern scandinavian caledonides in the late cambrian early ordovician

interstadial records of the last glacial period at pantai remis malaysia two eustatic high sea stands during the last glacial period are recognised at pantai remis these highstands lower than present day sea level are tropical manifestations of the ameliorating interstadial climate during the weichselian devensian wisconsin glaciation in the northern hemisphere the earlier highstand corresponds to a sea level of 14 6 m below mean sea level msl it is interpreted as synchronous with oyxgen isotope stage 5a and is correlated with other known sea level curves in other parts of the world the younger high sea stand dated 55810 1140 to 53870 1400 yr bp indicates sea level of 4 3 m below msl it represents an interstadial equivalent that lasted for at least 2000 yr whereas the earlier interstadial period indicates a minimum duration of twice this amount or very likely even longer as reflected from the thickness of the accumulated deposits the palynological records indicate that during interstadial times climatic stability in the tropics is attained and was sufficiently long for vegetation to thrive and develop the palynofloral constituents of the earlier interstadial phase at pantai remis showed the establishment of vegetation in a coastal setting initiated by pandanus swamp forests simultaneously mangrove swamp flourished in the lower lying parts of the area hence the presence of direct tidal influence is evident both the pandanus and mangrove swamps were succeeded by mixed freshwater swamp forests of a campnosperma calophyllum assemblage subsequently a slightly open and somewhat drier mixed swamp forest prevailed marked by the increase in fern spore representation the later interstadial phase showed shorter vegetation successions which commenced on the landward edge of a mangrove swamp forest the mangrove was successively replaced by strand forest as indicated by domination of casuarina equisetifolia the palynological assemblages in both the interstadial periods indicate similarity to the present day coastal vegetation this implies that during the interstadials the climate in the lowlands of peninsular malaysia and presumably throughout the equatorial region was as that prevailing today 1997 john wiley sons ltd

state of strain in a quartzite mylonite central australia abstract the finite strain due to mylonitization of a quartzite has been determined using measurements of deformed quartz grains and ribbons developed from quartz grains equant before the deformation the mylonites are developed in long narrow steeply dipping mylonite zones within the chewings range quartzite of central australia this quartzite is very pure 98 quartz the quartzite surrounding the mylonite zones appears unstrained the samples examined exhibit severe flattening strains k values of between 0 01 and 0 12 and r values of between 5 and 30 have been determined application of formulae to calculate volume change assuming the model of an ideal ductile deformation band structure indicate significant apparent volume losses with values between 0 69 and 0 95 such values seem unreasonably high as no geological evidence for large volume loss is seen the band structure model is considered inapplicable for these mylonite zones the observed structural features can best be explained by a deformation history involving severe bulk shortening normal to the zones

two dimensional strain determination by the inverse surfor wheel abstract a simple method of two dimensional strain determination from the preferred orientation of deformed lines is presented it is based on the change of probability of intersecting lines on a given traverse as a function of traverse orientation the method can be applied to real lines such as grain boundary outlines or to virtual lines such as the tie lines between centre points of neighbouring grains in this manner estimates for the strain of surfaces i e of the particles enclosed by the surfaces and of bulk strain can be obtained

calculation of volume change in ductile band structures abstract volume changes incurred during the development of ideal band structures infinite shear zones can be readily calculated if one knows the principal directions and principal ratios of total strain within and adjacent to the ideal band structures the calculation is greatly simplified if one knows the directions and ratios of the strain that generated the band structures or if the total strain of the host rocks is zero in some natural deformation zones apparent volume losses according to the band model exceed 30 and may be unreasonably high further determinations of apparent volume change will help to judge the physical viability of the band model and its strict geometrical requirements for example the propagation of embryonic deformation zones may lead to total strain patterns that differ greatly from those of band structures

a holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at batulicin south kalimantan indonesia abstract pollen analysis of a coastal peat swamp core representing 9100 bp from batulicin south kalimantan indonesia shows that mangrove forest with rhizophora as its main element has been established since the early holocene vegetation development in general and particularly mangrove forest was influenced by holocene environmental changes the highest value of rhizophora at ca 8200 bp indicates an early holocene sea level drop and implies sea level at ca 9 m subsequently mangrove forest was severely disrupted by rapid sea level rise at ca 6400 bp prior to the holocene maximum however it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca 6000 bp and flourished until ca 1000 bp from ca 6000 bp the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation human influence is recognized from ca 1600 bp

strain and vorticity analysis in the zagros suture zone w iran implications for neo tethys post collision events abstract shear zone development in the zagros orogenic belt is a result of the oblique collision of the arabian plate with the iranian plateau to distinguish areas deformed during the collisional phase from those deformed by post collisional events the coaxiality of deformation and the shape of the strain ellipsoid ses have been analyzed the variation of strain intensity in each shear zone has been evaluated by calculating the strain ratio in the principal strain planes the angle and the kinematic vorticity number wk in the post collisional shear zones wk varies from 0 80 to 0 99 and from 16 7 to 44 01 the strain component is mostly simple shear though in some shear zones it is sub simple shear outside of the shear zones wk is extremely low varying from 0 00 to 0 26 and values are under 5 a coaxial deformation regime is dominant and the strain component is pure shear in most of the shear zones ses is constricted and prolate indicating that deformation occurred under transtensional conditions however in some regions ses is flattened and oblate as is common in transpressional zones shear zones that have evolved under dual deformation conditions suggest that transtensional events can be superimposed on transpressional structures

control of the geometry of precursor brittle structures on the type of ductile shear zone in the adamello tonalites southern alps italy abstract amphibolite facies ductile shear zones developed during the immediate post intrusive cooling history of the adamello tonalites southern alps italy shear zones include i thin a few mm s thick fault like shear zones that accommodate shear strain values up to several 100 s the dominant type ii mylonitic horizons dm s thick in sharp contact with the undeformed wall rock iii continuous shear zones with sigmoidal shaped s or composite s c foliations a transition between the different types occurs along strike over short distances discontinuous shear zones are also localized on pegmatite dykes and quartz veins and both i and ii are discontinuously outlined by quartz layers detailed surface mapping reveals that most fault like shear zones are arranged en echelon mainly forming contractional steps markers crosscut by shear zones allow the displacement to be measured at several positions along shear zones and this reveals very steep displacement gradients close to the shear zone tips differential displacement is mainly accommodated at contractional steps by the development of foliated domains geochemical analyses of major and trace elements show that there is no compositional change along strain gradients the overall features are consistent with nucleation of shear zones on former sets of en echelon joints in many cases intruded by pegmatite dykes or filled with quartz reactivation of joints produced strongly localized shear zones whereas broader foliated zones evolved from the contractional jogs between adjacent stepped joint terminations during progressive shearing these jogs were progressively involved in the accommodation of shear displacement and overall shear zone development

development of cassiterite bearing sediments and their relation to late pleistocene sea level changes in the straits of malacca abstract cassiterite bearing sediments were surveyed in the central parts of the straits of malacca by high resolution seismic profiling and vibrocoring placer deposits of cassiterite were found in the tidal scour channel of cape rachado and a pleistocene river valley according to sedimentological parameters the cassiterite derived from a local primary mineralization of granite and from long distance fluvial transport the basement consisting of granites and metamorphites is covered by four sedimentary sequences which are separated by major erosional unconformities the last two unconformities were attributed to the regressional periods of the last and previous glaciations based on the distribution of the sequences deposited during periods of high sea level the malaysian peninsula is subsiding

implications of strain and vorticity of flow analyses to interpret the kinematics of an oblique convergence event zagros mountains iran abstract finite strain and vorticity of flow analyses were carried out within the deh vazir deformed conglomerates in the sanandaj sirjan metamorphic belt zagros mountains iran this belt is in a sequence of tectono metamorphic complexes made of low to high grade metamorphic rocks affected by a polyphase deformation history using rf technique for two dimensional strain analysis showed that the finite strain of xz plane is rs 3 7 0 70 the calculation of the harmonic mean from the axial ratios of the extracted pebbles and plotting these data in the flinn diagram resulted in k 0 7 0 38 i e oblate strain ellipsoid kinematic vorticity analysis of deformed pebbles showed that wk parameter is 0 59 0 10 i e pure shear dominated non coaxial flow the results quantitatively support the recognition of a partitioned dextral inclined transpressive regime with bulk triclinic symmetry along the sanandaj sirjan metamorphic belt resulted from the oblique collision between the african arabian continent and the iranian microcontinents

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

microstructural and crystal fabric evolution during shear zone formation abstract the microstructures and crystal fabrics associated with the development of an amphibolite facies quartzo feldspathic mylonitic shear zone torridon nw scotland have been investigated using sem electron channelling our results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history microstructural variation is particularly pronounced at low shear strains significant intragranular deformation occurs via a domino faulting style process whilst mechanical incompatibilities between individual grains result in characteristic grain boundary deformation accommodation microstructures a sudden reduction in grain size defines the transition to medium shear strains but many of the boundaries inherited from the original and low shear strain regions can still be recognized and define distinctive bands oriented at low angles to the shear zone margin grains within these bands have somewhat steeper preferred dimensional orientations these domains persist into the high shear strain mylonitic region where they are oriented subparallel to the shear zone margin and consist of sub 20 m grains the microstructures suggest that the principal deformation mechanism was intracrystalline plasticity with contributions from grain size reduction via dynamic recrystallization grain boundary migration and grain boundary sliding crystal fabrics measured from the shear zone vary with position depending on the shear strain involved and are consistent with the operation of several crystal slip systems e g prism basal rhomb and acute rhomb planes in a consistent direction probably parallel to a and or m they also reveal the presence of dauphine twinning and suggest that this may be a significant process in quartz deformation a single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed rather the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation the mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which develop during shear zone evolution the stability of some microstructures to higher shear strains the exploitation of others at lower shear strains and a continuously evolving crystal fabric mean that the strain gradient observed across many shear zones is unlikely to be equivalent to a time gradient

complex flow in lowest crustal anastomosing mylonites strain gradients in a kohistan gabbro northern pakistan 1 strain localization in near paleo moho metagabbros of the kohistan arc northern pakistan produced anastomosing shear zones the two dimensional 2 d analysis of strain gradients in planes parallel to the general flow direction reveals simple shear strain 7 combined with about 50 surface loss the pargasite garnet assemblage of the mylonite has a density 2 8 higher than the protolith which is insufficient to account for the measured surface loss furthermore major and trace element compositions of the gabbro and the mylonite indicate isochemical deformation average vp and acoustic impedance measured at room temperature and up to 300 mpa increase from gabbro through the gradient zone to mylonite they are consistent with density measurements the three dimensional analysis of shape preferred orientation and lattice preferred orientation of sheared and synkinematic minerals indicates that the 2 d surface loss reflects sideways and lengthwise material transfer sideways and lengthwise material transfers take place in widening and lengthening mylonites respectively the anastomosing shear zone pattern impels this complexity of the regional flow we conclude that shear zones with a thinning component are likely representative of deep crustal flow in other tectonic environments

brittle ductile brittle deformation during cooling of tonalite adamello southern italian alps abstract late to post magmatic deformation in slightly diachronous contiguous intrusions of the north western adamello batholith southern alps italy is recorded as from oldest to youngest i joints ii solid state ductile shear zones iii faults associated with epidote k feldspar veins and iv zeolite veins and faults structures ii to iv are localized on the pervasive precursory network of joints i which developed during the earliest stages of pluton cooling high temperature 500 c ductile overprinting of joints produced lineations defined by aligned biotite and hornblende on the joint surfaces and highly localized mylonites the main phase of faulting producing cataclasites and pseudotachylytes occurred at 250 c and was associated with extensive fluid infiltration cataclasites and pseudotachylytes are clustered along different e w striking dextral strike slip fault zones correlated with the activity of the tonale fault a major tectonic structure that bounds the adamello batholith to the north ductile deformation and cataclastic veining episodes occurred at p 0 25 0 3 gpa during rapid cooling of the batholith to the ambient temperatures 250 c that preceded the exhumation of the batholith timing of the sequence of deformation can be constrained by 39 ar 40 ar ages of 30 ma on pseudotachylytes and various existing mineral ages in the whole composite adamello batholith multiple magma pulses were intruded over the time span 42 30 ma and each intrusive body shows the same ductile to brittle structural sequence localized on the early joint sets this deformation sequence of the adamello might be typical of intrusions undergoing cooling at depths close to the brittle ductile transition

mangrove pollen of indonesia and its suitability as a sea level indicator we investigated the mangroves of southeast sulawesi indonesia to assess their potential as proxies for reconstructing sea level during the holocene initial investigations confirmed that the mangrove species demonstrate zonations parallel to the shoreline and are dominated by the family rhizophoraceae with avicennia heritiera and sonneratia also important constituents of the mangroves we investigated the vertical distributions of pollen assemblages at three sites partial cca analysis demonstrated that at all three sites elevation was a significant control on the distribution of pollen assemblages in surface samples we combined the three contemporary transects to develop a regional transfer function to explain the relationship between the surface assemblages and elevations using the maximum likelihood ml method the developed transfer function indicated mangrove pollen can be used as a precise indicator of past sea levels with an error of 0 22 m the transfer function was applied to two fossil cores from the wakatobi marine national park and evaluated using the modern analogue technique both cores showed similar patterns in changes of palaeo mangrove elevation and had modern analogues in the contemporary training set we conclude that mangrove pollen is a suitable proxy for reconstructing sea level in tropical environments

strain and shape fabric variations associated with ductile shear zones abstract the foliated and compositionally banded granitic orthogneisses in the central core of the maggia nappe a lower pennine basement nappe of the central swiss alps are shown to be the sheared equivalent of late hercynian age granitic intrusions these ductile shear zones show mineral assemblages in amphibolite facies are alpine in age and form an anastomosing network enclosing remnant lozenge shaped pods of relatively undeformed rock the foliation developed within the shear zones concomitantly with a change in shape of quartz grain aggregates from initially equidimensional through tear drop shapes to ribbon like aggregates these shape changes occurred by intracrystalline glide together with intercrystalline slip on deformation induced planar surfaces

stratigraphic record of holocene coseismic subsidence padang west sumatra 1 stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of padang west sumatra along the mentawai segment 0 5 s 0 3 s of the sunda subduction zone each earthquake is marked by a sharp soil mud contact that represents a sudden change from mangrove to tidal flat the earthquakes occurred about 4000 and 3000 cal years b p based on radiocarbon ages of detrital plant fragments and seeds the absence of younger paleoseismic evidence suggests that late holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone our results point to a brief few thousand year window of preservation of subsidence events in tidal wetland stratigraphic sequences a result that is generally applicable to other emergent coastlines of west sumatra

a mohr circle method for 3d strain measurement using the geometry of no finite longitudinal strain and the rxz strain ratio abstract this paper proposes a new method for 3d finite strain analysis this method utilizes a mohr circle construction combined with stereographic projection of the geometry of no finite longitudinal strain and with the strain ratio on the xz plane of the finite strain ellipsoid the method is described using numerical examples and then it is tested by applying it to the deformed deh vazir conglomerate in the southwestern part of the sanandaj sirjan hp lt metamorphic belt within the zagros orogenic belt in iran the results of this method compare well with previous finite strain measurements using strain ratios on three principal planes of finite strain calculation of finite strain from strain ratios on the xy and yz principal planes is advantageous when preparation of 3 perpendicular sections is difficult or impossible

quaternary sea level changes relative changes of the land sea interface have occurred throughout geologic time although these changes can be caused by several factors alternating global events such as glaciation deglaciation are the most effective in the quaternary period other causes e g volumetric changes in the mid oceanic ridge system have been proposed to explain sea level changes from the upper cretaceous to the mid miocene pitman 1978 however the evidence available suggests that no uniform response can be expected worldwide as a result of global glacio eustatic events this is due to tectonics glacial isostasy hydroisostasy and geoidal configuration of the ocean surface among other variables all these factors have been operative at various timescaies and have been subject to local and regional variations this explains why sea level curves for the holocene fail to provide a uniform global trend instead several local curves have been derived from many areas the variability of postglacial sea levels has been explained by different models considering glacial isostasy clark et al 1978 the redistribution of ice and water loads from antarctic deglaciation peltier 1988 and future sea level rise due to the melting of the greenland and antarctic ice sheets has been predicted by clark and primus 1987 as will be discussed more fully later a global warming is expected to take place due to the increasing accumulation of co2 and other

strain pattern in the aar granite central alps orthogneiss developed by bulk inhomogeneous flattening the central part of the aar granite aar valley shows lens shaped domains of low strain separated by anastomosing domains of high strain a comparable pattern is found on all scales of observation deformation gradients are outlined by a gradual change from isotropic granite to orthogneiss and locally ultramylonites ultramylonites are concentrated within conjugate ductile shear zones where moderate the strain is concentrated in very narrow small scale faults which affect relatively undeformed granite within foliated domains finite strain measurements on deformed xenoliths indicate that i strain intensity increases gradually with grain size reduction and ii finite strain ellipsoids are of flattening type irrespective of the degree of mylonitization the pattern of small scale faulting the trends of the regional foliation and the orientation of ductile shear zones are consistent with a bulk strain field of flattening type throughout progressive deformation

the initiation and evolution of the transpressional straight river shear zone central fiordland new zealand abstract structural data and u pb geochronology on zircon from central fiordland new zealand show the role of pre existing structural heterogeneities in the kinematic evolution of a newly discovered zone of transpression the straight river shear zone consists of steep zones of high strain that are superimposed onto older fabrics across a 10 80 km region the older foliation formed during two periods of tectonism contraction and magmatism of mostly carboniferous 312 306 ma age and early cretaceous batholith emplacement ending by 113 4 1 7 ma followed by extension that ceased by 88 4 1 2 ma the primary mechanism for the formation of steep shear zone foliations was the folding of these older fabrics conjugate crenulation cleavages associated with the folding record shortening at high angles to the shear zone boundaries fold axial surfaces and axial planar cleavages strike parallel to the shear zone with increasing strain as they progressively steepened to subvertical in most areas shear sense flips from oblique sinistral east side down component to oblique dextral west side down across zones of intermediate and high strain high strain zones display subvertical mineral lineations steep strike slip faults and shear sense indicators that record strike slip motion across the steep lineations these patterns reflect triclinic transpression characterized by narrow zones of mostly strike slip deformation and wide zones of mostly contraction zones of high strain align with offshore traces of late tertiary strike slip faults suggesting that a previously undocumented component of late tertiary shortening and strike slip motion is accommodated within fiordland

strain pattern and vorticity analysis of deformed conglomerates in the heneshk area within the sanandaj sirjan metamorphic belt zagros mountains iran strain measurements have been carried out using the rf method on a jurassic deformed conglomerate in the sanandaj sirjan metamorphic belt zagros mountain of iran estimated finite strain ellipsoids range from general flattening to near plane strain flinn parameter k 0 6 0 9 with strain ratios in the x z plane with rxz 5 4 quantitative kinematic analyses were performed on the conglomerates using the rigid clast method estimated kinematic vorticity numbers wk varied between 0 43 and 0 63 implying a general shear flow 30 simple shear 42 and 58 pure shear 70 i e pure shear dominated non coaxial flow combining strain and vorticity data we estimated a horizontal shortening of 42 55 measured normal to the walls of the deformation zone we discuss this pure shear dominated deformation in terms of convergence between the afro arabian continent and the central iranian microcontinents

stratigraphic evidence for an early holocene earthquake in aceh indonesia abstract the holocene stratigraphy of the coastal plain of the aceh province of sumatra contains 6 m of sediment with three regionally consistent buried soils above pre quaternary bedrock or pre holocene unconsolidated sediment litho bio and chronostratigraphic analyses of the lower buried soil reveals a rapid change in relative sea level caused by coseismic subsidence during an early holocene megathrust earthquake evidence for paleoseismic subsidence is preserved as a buried mangrove soil dominated by a pollen assemblage of rhizophora and or bruguiera ceriops taxa the soil is abruptly overlain by a thin tsunami sand the sand contains mixed pollen and abraded foraminiferal assemblages of both offshore and onshore environments the tsunami sand grades upward into mud that contains both well preserved foraminifera of intertidal origin and individuals of the gastropod cerithidea cingulata radiocarbon ages from the pre and post seismic sedimentary sequences constrain the paleoearthquake to 6500 7000 cal yrs bp we use micro and macrofossil data to determine the local paleoenvironment before and after the earthquake we estimate coseismic subsidence to be 0 45 0 30 m which is comparable to the 0 6 m of subsidence observed during the 2004 aceh andaman earthquake on aceh s west coast

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

the changing mangrove shorelines in kuala kurau peninsular malaysia abstract a considerable extent of the shoreline along the west coast of peninsular malaysia is vegetated by mangrove forests typically one observes frequent change of position of the mangrove outer shore limit the kuala kurau coastline in northwest perak which provides a good example is selected for this study the geological evidence indicates that marine sediments prevail throughout the kuala kurau coastal plain greenish gray clay predominates with varying amounts of silt and sand underlying the basically flat topography the present shoreline has prograded from its initial position within a time span of about 5000 years similarly from 1914 to 1969 a prograding shoreline trend is indicated however from 1969 to 1986 there was widespread erosion although both accreting and retreating situations were indicated erosion in the mangrove fringes in the later years is related to sediment budget freshwater supply over exploitation and utilisation of mangrove forest and the effects indirect of the fishing industry

holocene sea levels and palaeoenvironments malay thai peninsula southeast asia sedimentological and palynological investigations of great songkhla lakes east coast of the malay thai peninsula southeast asia reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps compared with other regions in southeast asia the assemblages are of relatively low diversity geochronological data indicate that the great songkhla lakes record one of the earliest mangrove environments in southeast asia 8420 8190 cal yr bp which are subsequently replaced by a freshwater swamp at 7880 7680 cal yr bp owing to the decline of marine influence sea level observations from great songkhla lakes and other areas of the malay thai peninsula reveal an upward trend of holocene relative sea level from a minimum of 22 m at 9700 9250 cal yr bp to a mid holocene high stand of 4850 4450 cal yr bp which equates to a rise of c 5 5 mm yr the sea level fall from the high stand is steady at c 1 1 mm yr geophysical modelling shows that hydroisostasy

mineral fish their morphological classification usefulness as shear sense indicators and genesis mineral fish are sheared and commonly asymmetric mineral grains or clusters of grains this work reports 11 sub types of mineral fish showing a top to se sense of ductile shearing in the karakoram metamorphic complex kmc the mineral fish are of three broad geometries sigmoid lenticular and parallelogram reliable senses of shear are indicated by the overall asymmetry and inclination of mineral fish on the other hand the true shear sense is not always indicated by either the orientations of their cleavage planes or those of the individual grains in composite mineral fish the ranges of local orientations of single sigmoid mineral fish that include the lower values 23 in the kmc indicate their extensive ductile shearing the studied mineral fish were products of a range of deformation mechanisms including homogeneous deformation simple shear intra granular slip crystal plastic deformation fracturing and synthetic shearing additionally some examples might have undergone duplex slips and a few nucleated and grew either prior to or during the top to se shearing

structural analysis of high pressure shear zones bacariza formation cabo ortegal nw spain abstract high pressure granulites of the bacariza formation cabo ortegal complex nw spain exhibit spectacular examples of ductile shear zones developed at different scales in rocks containing pre existing foliations a detailed structural analysis was carried out on these shear zones in order to unravel and compare the role of various parameters controlling the deformation process i e heterogeneous simple shear components of homogeneous deformation heterogeneous volume change and degree of non coaxiality although heterogeneous simple shear largely dominated negligible deviations from the ideal simple shear model were detected involving shortening along the structural directions perpendicular to the stretching axis within the foliation plane of the finite strain ellipsoid the relationship between displacement parallel to a half shear zone and the normal distance from its boundary provided the basis for the estimation of the stress exponent in the power law constitutive flow equation associated with each shear zone which is interpreted as a rheological indicator these geometric and rheological results and the thermobaric conditions of high pressure shear zone deformation indicate that these shear zones accommodated dominant plastic rock flow coeval with high pressure and high temperature deformations under moderate stress levels concomitant with elevated strain rates

strain compatibility and shear zones is there a problem in analyzing deformation in rocks it is important to ensure that the solutions obtained satisfy strain compatibility this creates a challenge to understanding patterns of strain associated with shear zones in which measured strain may appear incompatible with the strain in the shear zone walls flattening strains are common in natural shear zones with locally straight and parallel boundaries to satisfy compatibility conditions such strains require volume loss across the shear zone or deviations from plane strain with or without discontinuities between the shear zone and the wall rock in the case of shear zones for which there is no evidence of volume loss or discontinuities along the shear zone walls problems of strain compatibility may be resolved if individual shear zones are linked together in an appropriate fashion shear zones commonly occur in anastomosing arrays and simple configurations of such arrays and the strains associated with them are examined it is shown that local transpression with strain compatibility can be accounted for in this way quite complex local strain patterns can develop in simple arrays

strain partitioning in ductile shear zones an example from a lower pennine nappe of switzerland abstract the rocks of the maggia nappe a lower pennine nappe of the swiss alps were deformed in at least three phases during alpine orogeny hercynian granites in the core of the nappe developed ductile shear zones during the early phases of deformation but between shear zones they remained almost undeformed both heterogeneous simple shear and heterogeneous volume change played an important role in the formation of the ductile shear zones partitioning of different strain components indicates a volume loss of nearly 80 90 towards the centres of some of the shear zones such a large amount of volume loss is also corroborated by strain analysis of deformed xenoliths in other shear zones of the same region a comparative study of theoretical strain paths and the natural results indicates constant shear strain rate but changing dilation rate during deformation

constraints on deformation path from finite strain gradients we present a methodology for analyzing finite strain gradients in high strain zones in order to place constraints on the zone s possible deformation path to accomplish this the high strain zone is divided into several sub zones within each of which finite strain is described by a single ellipsoid based on knowledge of the spatial and temporal evolution of deformation strain observed in less deformed sub zones is then mathematically removed from more deformed sub zones to calculate incremental finite strains the mean kinematic vorticity number of each of these increments must be constant if deformation was steady state we use the methodology to analyze two natural examples of high strain zones at different scales both natural examples have non steady state likely deformation paths which may be a common characteristic of high strain zones although results of the methodology are not unique identification of likely paths considerably narrows the range of possible deformation paths consequently useful kinematic information can be extracted from finite strain data even in instances where the detailed spatial and temporal evolution of a high strain zone cannot be determined conclusively

radiocarbon and thermoluminescence dating of the old alluvium from a coastal site in perak malaysia abstract exposures of the old alluvium in pantai mine and sinar manjung mine in perak peninsular malaysia reveal woody peat layers interbedded with angular sands and gravels eight samples from peat within the pantai mine were dated using accelerator mass spectrometry ams radiocarbon dating together with a near surface shell sample five samples of quartz sand from the pantai mine and three samples of similar sand from sinar manjung mine were dated by thermoluminescence tl dating while for several samples both dating techniques were at the limits of their detection results from the upper strata of the northwestern face of the pantai mine indicate agreement between the two independent dating techniques the age of the old alluvium known as the simpang formation in perak is confirmed as late pleistocene at this site the measured ages range from 28 000 years b p to 67 000 years b p but the lower units are older than this and appear at this site to be beyond the range of both dating techniques

average properties of ellipsoidal fabrics implications for two and three dimensional methods of strain analysis abstract many rocks contain ellipsoidal objects such as pebbles or reduction zones which display a variety of shapes and orientations in deformed rocks such objects may be used for strain analysis by using the concept of an average ellipsoid here called the fabric ellipsoid two fabric ellipsoids are defined which are the results of two different algebraic averaging processes during deformation of ellipsoidal distributions the fabric ellipsoids change as if they were themselves material ellipsoids and are therefore of fundamental importance in strain analysis in most studies to date such 3 d fabric ellipsoids have been obtained from 2 d average ellipses determined on section planes cut through the rock sample previous work has assumed that the average ellipses will approximate to section through a single fabric ellipsoid i show here that this is not the case as sectioning introduces a systematic bias into the section ellipse data this bias is distinct from the statistical errors due to finite sample size and measurement errors discussed in other work and must be considered in any method of strain analysis using section planes

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

strain distribution within a km scale mid crustal shear zone the kuckaus mylonite zone namibia the subvertical kuckaus mylonite zone kmz is a km wide crustal scale proterozoic dextral strike slip shear zone in the aus granulite terrain sw namibia the kmz was active under retrograde amphibolite to greenschist facies conditions and deformed felsic and minor mafic gneisses which had previously experienced granulite facies metamorphism during the namaqua orogeny lenses of pre to syn tectonic leucogranite bodies are also deformed in the shear zone pre kmz deformation d1 is preserved as moderately dipping gneissic foliations and tightly folded migmatitic layering shear strain within the kmz is heterogeneous and the shear zone comprises anastomosing high strain ultramylonite zones wrapping around less deformed to nearly undeformed lozenges strain is localized along the edge of leucogranites and between gneissic lozenges preserving d1 migmatitic foliations strain localization appears controlled by pre existing foliations grain size and compositional anisotropy between leucogranite and granulite the local presence of retrograde minerals indicate that fluid infiltration occurred in places but most ultramylonite in the kmz is free of retrograde minerals in particular rock composition and d1 fabric heterogeneity are highlighted as major contributors to the strain distribution in time and space with deformation localization along planes of rheological contrast and along pre existing foliations therefore the spatial distribution of strain in crustal scale ductile shear zones may be highly dependent on lithology and the orientation of pre existing fabric elements in addition foliation development and grain size reduction in high strain zones further localizes strain during progressive shear maintaining the anastomosing shear zone network established by the pre existing heterogeneity

strain in ductile shear zones in the caledonides of northern sweden a three dimensional puzzle small scale ductile shear zones are well developed in amphibolites of caledonian nappes of the swedish lapland strain in the shear zones is recorded by the shapes of originally sub equant aggregates of plagioclase feldspar classical strain analysis on two dimensional xz profiles across the shear zones leads to results that indicate large volume losses associated with the shear strain large volume losses are however incompatible with geochemical analysis which shows little chemical variation across the shear zones by including data from xy and yz sections information on the three dimensional state of strain can be obtained these data indicate that deformation is not confined to a two dimensional plane particle extension within the shear zone parallel to the shear plane and perpendicular to the shear direction has also occurred the state of strain and strain path in the shear zone can be modeled in a general way by combining stretches in x y and z with simple shearing and volume loss end member models correspond to plane strain with volume loss kx ky 1 kz 1 transpression kx 1 ky 1 kz and pure shear kx 1 kz ky 1 these models produce identical strain ratios and orientations on the xz section but differ in stretch in y and in area of the strain ellipse on the xz section extension in y or x allows for reconciliation of the geometrical and geochemical data for part of an individual shear zone but poses a problem of strain compatibility at the edges and terminations of the shear zones the shear zones show a complex anastomosing pattern in three dimensions and their connectivity provides a way in which strain compatibility is maintained

on stress and strain in a continuous discontinuous shear zone undergoing simple shear and volume loss i summarise observations within a continuous discontinuous shear zone to discuss the local stress and strain conditions experienced within a mixed rheology shear zone undergoing volume loss and deformation approximating simple shear the chrystalls beach complex new zealand comprises phacoids formed from dismembered beds by layer parallel extension enclosed within a relatively incompetent matrix local extension is generally subparallel to the regional direction of shortening and overall it appears that layer parallel extension is a geometrical necessity in low angle shear zones where significant flattening occurs in response to simple shear accompanied by volume loss preferential stress loading of phacoids is predicted by fibre loading theory and the failure of phacoids by brittle fracture is thereby governed by fibre stresses transferred from the matrix the principal stress orientations in a phacoid are likely rotated relative to the matrix and either parallel or perpendicular to the phacoid matrix interface as preferential loading of phacoids decreases the stress level in the matrix an increased volume fraction of phacoids increases the strength of the shear zone as a whole however only small matrix volume fractions are required for the composite to act nearly as weak as the matrix 2012 elsevier ltd all rights reserved

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

antarctic summer sea ice trend in the context of high latitude atmospheric circulation changes abstractthe potential mechanisms underlying the observed increasing trend in antarctic summertime sea ice cover for the 1979 2017 period have been investigated using a relatively novel method called the self organizing map som among the nine nodes generated to explain the variability of antarctic sea ice cover two nodes 3 and 7 exhibit a statistically significant linear trend in the time series of the frequency of the som pattern occurrence that together explain 40 of the total trend in the sea ice cover these two nodes have completely opposite spatial patterns and directions of trend and are associated with different atmospheric circulation patterns node 3 which represents an increase in sea ice over the weddell sea and the eastern ross sea and a decrease over the other coastal seas of west antarctica appears to be related to the positive phase of the southern annular mode sam linked with the la nina pattern of sea surface temperature sst over the tropical pacific ocean the opposite spati

structural pattern and emplacement mechanism of the neka valley nappe complex eastern alborz iran the neka valley nappe complex is exposed in the south of gorgan county in the eastern alborz fold and thrust belt we use the results of a regional survey of the structural data and their patterns to interpret the mechanisms that emplaced the unmetamorphosed nappes in the foreland fold and thrust belt of the alborz mountains most of the strain magnitudes are low in the study area but increase slightly towards what are probably their proximal ends strain ellipsoid is dominantly oblate with xy aligned along and across the belt or the nappe complex the average kinematic vorticity number w k 0 6 which indicates most of the strain partitioning resulted in a general shear most of flinn s k values and the stretch along the shear plane values are lower than 1 structural indicators such as orthogonal extensional joints pinch and swell structures anastomosing cleavages and listric normal and growth faults developed by push from the rear large scale thrust complexes with opposed dips such as triangle zones as well as k and values 1 are compatible with the shear flow diverging distally and streamlines expected of the rear compression emplacement mechanism together with a later minor brittle deformation these major ductile strains appears to provide a general model suitable for the emplacement of the nappes studied in a thin skinned fold and thrust belt where the sedimentary cover strata shortened and imbricated in the upper crust

shear band formation and strain localization on a regional scale evidence from anisotropic rocks below a major detachment betic cordilleras spain regional scale deformation taking place in a strongly anisotropic yet homogeneous metapelitic protolith during an apparently single tectonic event was systematically investigated as a function of the distance to the main tectonic contact i e the filabres shear zone a major detachment in the betic cordilleras spain the density of c3 shear bands or extensional crenulation cleavage reworking the earlier s2 schistosity increases exponentially towards the contact in parallel with the decrease in the size of the shear domains systematic variations in angles and shape ratios are also reported deformation and age patterns however suggest that this spectacular trend at least partly results from a progressive localization of the deformation through time this fossilized shear strain gradient was thus produced somewhat diachronously such shear strain patterns nevertheless provide a mean to constrain the rheological properties for such weak lithologies and a mean to better understand crustal deformation

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

kinematics stress deformation and material behavior abstract a compact review is given of some fundamentals of the theory of flow in materials and of the bulk behavior of experimentally deformed rocks kinematics is discussed first because it provides an easy introduction to second order tensor quantities these are explained as quantities linking the components of pairs of vectors to one another for example velocity vectors to position vectors the velocity gradient tensor or stress vectors to plane normal vectors the stress tensor the fundamental theorem of stress theory is derived from the requirement of force balance at a point here and elsewhere the treatment is mostly two dimensional this saves space yet provides an introduction to principles that are important again in three dimensions mohr circles are used extensively to represent two dimensional tensor quantities geometrically including asymmetric velocity gradient and deformation tensors the decomposition of a general deformation into components of translation rotation and strain is explained and this may lead to greater appreciation of such unfamiliar possibilities as coaxial accumulation of a simple shear deformation the section on experimental deformation is concerned mainly with the measured strengths of rocks and how these can be extrapolated to strengths at geological strain rates the text is followed by a glossary

late holocene depositional environments and coastal evolution of the mekong river delta southern vietnam abstract the mekong river delta in southern vietnam is a tide dominated delta and has been formed by the mekong river system the sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre existing deposits in the south china sea and gulf of thailand around 6000 to 5000 yr bp maximum holocene transgression occurred and seawaves surrounded uplands of the late pleistocene terrace basement rock and weathered land in the northern parts of the delta double notches were undercut by seawaves on the limestone hill in hatien at about 4 5 and 2 5 m above present sea level marine deposits prevailed throughout the delta during the highstand and regressions of relative sea level over the last 4550 yr bp delta progradation has produced a great flat plain of 62 520 km 2 this extremely fast progradation could be due to a very high sediment supply depositing in the slight inclination of the receiving basin b neotectonic movements and relative sea level changes c widespread mangrove forests playing an important role to enhance sediment accumulation former mangrove marshy deposits were significantly developed in the plain of reeds and longxuyen quadrangle mangrove marshes have also been developing well in the camau peninsula and present coastlines moreover regressions over the last 4550 yr bp have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta

modeling the influence of tectonic extrusion and volume loss on the geometry displacement vorticity and strain compatibility of ductile shear zones oblate strains are often observed in meso scale ductile shear zones and this is generally taken to indicate narrowing across the shear zone during formation volume loss is one mechanism that could produce shear zone narrowing however not all shear zones display characteristics consistent with volume loss and in such cases the narrowing must be accomplished by the extrusion of material from within the shear zone to explore the relationship between shear zone geometry volume loss and extrusion shear zones were mathematically modeled results demonstrate the important influence of pure shear and volume loss on controlling the geometry displacement and vorticity of ductile shear zones further volume loss does not preclude extrusion unless for a given volume loss the strain is of a specific geometry extrusion is a likely mechanism important in shear zone development even if volume loss occurs extrusion presents strain compatibility problems because unlike crustal scale shear zones meso scale ductile shear zones do not possess a free surface if extrusion occurs bulk strain compatibility can be maintained if shear zones interlink in anastomosing arrays or change in thickness though not all shear zone systems display such characteristics modeling results elucidate the deformation style of shear zone in the northwest adirondacks in ny and in the kebnekaise region in northern sweden

structure and development of an anastomosing network of ductile shear zones a detailed structural analysis of an anastomosing shear zone network in metagabbros from the archean rainy lake zone canada revealed the existence of prevalent dextral and minor sinistral conjugate shear zones with the obtuse angle 130 facing the main shortening direction a typology of shear zone intersections confluences and other features shows that all shears formed during a single deformation event with dextral and sinistral shears being active together or in an alternating fashion in spite of the difficulty of establishing a complete kinematic sequence early and late shears can be distinguished the final angular pattern between dextral and sinistral shears is not an original feature dextral and sinistral shears formed at nearly right angles and the angles progressively opened towards the extension direction as a result of increasing strain the obtuse angles were achieved by the combined effects of continued shearing on newly forming shears and internal deformation of the lozenge shaped domains of lesser deformed rock bounded by the shears through time there was an increasing prevalence of dextral shears over sinistral ones the studied pattern and sequential analysis indicate that the bulk deformation was noncoaxial with a deformation regime evolving from a pure shear dominated dextral transpression to a higher vorticity dextral transpression

strain and possible volume loss in a high grade ductile shear zone small scale ductile shear zones in high grade metagabbros from the caledonides of northern sweden provide a good opportunity for examining the development of fabric and strain in rocks undergoing progressive non coaxial deformation the rocks contain strain markers in the form of aggregates of plagioclase feldspar a selected shear zone is analyzed assuming monoclinic symmetry which requires for the zone as a whole variable simple shear variable volume change or variable simple shear and volume change plus a homogeneous deformation both size of the feldspar aggregates and aspect ratio of the aggregates plotted against orientation indicate significant volume decrease in excess of 50 and perhaps as much as 80 towards the centers of the zones the data are broadly consistent with a deformation path involving constant shear strain across the zone followed by variable volume change or by a path of progressive loss of volume with increasing shear strain followed by a homogeneous strain they are not consistent with a single path involving rates of shear strain and volume loss that are in constant proportions there is little difference in chemical composition between the shear zone and the surrounding rock an analysis of the concentrations of elements in the shear zone and wall rock suggests that volume changes were slight 15 the discrepancy between the values of volume change estimated from strain analysis and geochemical analysis may be resolved either by geochemical equilibration being attained after deformation or by a departure from the geometric constraints of the monoclinic band model for shear zones modification of marker particle size and shape during dynamic recrystallization may also partly account for the apparent volume loss