the mesozoic and tertiary basins of the bohemian massif and their evolution abstract the bohemian massif is a major positive element within the structural framework of the alpine carpathian foreland its basement became consolidated during the variscan orogeny crustal thicknesses range between 32 5 km and 40 km during the late carboniferous and early permian the bohemian massif became dissected by a conjugate system of wrench faults which controlled the accumulation of a continental coal bearing series late permian red beds were deposited on intramontane topographic depressions in triassic to mid jurassic times the bohemian massif formed a high from which clastics were shed into adjacent basins during the late jurassic and late cretaceous it became transected by nw se trending sedimentary basins the sub hercynian and laramide phases of foreland compression resulted in deformation and uplift of the bohemian massif the eger graben a 350 km long volcanotectonic zone cutting across the bohemian massif in an ene wsw direction came into evidence during the oligocene and is at present inactive the crust of the bohemian massif forms the autochthonous substratum of the outer carpathians which are paralleled by the neogene carpathian foredeep the neogene intramontane neo autochthonous vienna basin is superimposed on the alpine carpathian nappe systems and developed under a tensional setting

reinterpretation of late quaternary sediment chronology of lake biwa japan from correlation with marine glacial interglacial cycles a review of published stratigraphic records of pollen sediment grain size diatoms and organic matter composition from lake biwa japan identifies four pre holocene episodes of milder climate increased surface runoff and enhanced aquatic productivity indicating intervals of warmer and wetter conditions which are interpreted as being interglacial correlation of these episodes to times of marine interglacial periods revises the age scale of the lake biwa sediment sequence which has been based on fission track dating the revised chronostratigraphic scale proposes an age of ca 430 000 yr b p for the base of the 250 m thick t bed instead of the former age of ca 700 000 yr b p

magmatic evolution of the eastern coast plutonic complex bella coola region west central british columbia the eastern coast plutonic complex in west central british columbia 51 54 n consists of a broad belt of jurassic to eocene granitic to dioritic intrusive rocks that collectively represent more than 140 m y of nearly continuous subduction related magmatism seven distinct intrusive suites have been identified in the bella coola region including from oldest to youngest the howe lake stick pass firvale desire fougner big snow and four mile suites pre late cretaceous rocks were produced by episodic subduction related magmatism characterized by partial melting of preexisting lower arc crust with minimal incorporation of evolved continental material the eastern coast plutonic complex experienced a magmatic lull between ca 110 and 95 ma coincident with sinistral transpression potentially linked to translational displacement of the wrangellia alexander composite terranes crustal thickening in late cretaceous time ca 100 90 ma possibly due to underplating of the wrangellia alexander terrane produced a deep crustal root 40 km that likely extended into the eclogite transition zone adakitic magmas ca 95 67 ma were produced by partial melting of an amphibolitic protolith in this thickened lower arc crust adakitic plutons are pre syn and postkinematic with respect to late cretaceous high angle shear zones and they are coeval and spatially associated with postkinematic two mica granites ca 70 75 ma having a hybrid a type geochemistry we suggest that delamination of this dense crustal root led to voluminous magmatism extension and crustal exhumation in paleocene eocene time the successive intrusive events in the eastern coast plutonic complex may reflect a predictable evolutionary progression common to all continental arc systems

dynamic recrystallization mechanisms and their transition in the daling thrust dt zone darjeeling sikkim himalaya abstract the daling thrust dt delineates a zone of intense shear localization in the lesser himalayan sequence lhs of the darjeeling sikkim himalaya from microstructural studies of deformed quartzite samples we show a transition in the dynamic recrystallization mechanism with increasing distance from the dt dominated by grain boundary bulging blg recrystallization closest to the dt and progressively replaced by sub grain rotation sgr recrystallization away from the thrust the transition is marked by a characteristic variation in the fractal dimension d of grain boundaries estimated from the area perimeter method for the blg regime d 1 046 which decreases significantly to a value as low as 1 025 for the sgr regime using the available thermal data for blg and sgr recrystallization we infer increasing deformation temperatures away from the dt in the hanging wall based on the quartz piezometer our estimates reveal strong variations in the flow stress 59 00 mpa to 16 00 mpa over a distance of 1 2 km from the dt deformation mechanism maps constructed for different temperatures indicate that the strain rates 10 12 s 1 to 10 14 s 1 comply with the geologically possible range finally we present a mechanical model to provide a possible explanation for the cause of stress intensification along the dt

time variation in coarse materials from lake bottom sediments and secular paleoclimatic change variations in the percentage of materials coarser than 4 5 phi in sediment from lake biwa are closely related to global climatic change and are indicative of large fluctuations in sediment discharge into the lake coarse materials increased markedly during the interglacials postglacial and last interglacial periods the variations also are linked with solar insolation and have distinct periods of about 20 000 and 40 000 years which correspond to the periods of the obliquitical and processional parameters periods of 60 000 and 120 000 years are major in the variations

crustal evolution of the ktb drill site from oldest relics to the late hercynian granites the crustal unit penetrated during the german continental deep drilling program ktb the zone of erbendorf vohenstrauss zev comprises an association of metabasites and paragneisses and orthogneisses that underwent high and medium pressure metamorphic cycles during the early palaeozoic in this summary of the structural petrological geochemical and geochronological information from borehole and surface rocks we show that geological models proposed prior to drilling have had to be significantly modified features of the zev such as the dominant nw se trending structures devonian 370 ma medium pressure amphibolite facies metamorphism 0 6 0 8 gpa 720 c and earlier eclogite stage are directly comparable with those of the nearby bohemicum unit in western bohemia intervening units in contrast exhibit ne sw trending structures and carboniferous 315 325 ma low pressure metamorphism all units are cut by predominantly posttectonic granites mostly 320 ma earlier models to explain this contrast by means of a nappe emplacement of the zev in the narrow time interval between the younger regional metamorphism and granite intrusion could not be substantiated because contrary to predictions the same rock association was present in the whole of the drilled 9 1 km and therefore no nappe boundary was drilled instead it is interpreted that shallow crustal levels reached by the zev subsequent to the devonian event shielded most of it from the effects of the carboniferous metamorphism a lack of expected thermal and baric gradients within the drilled metamorphic pile is a result of repeated stacking of an original 3 km depth section in mesozoic times an important result of the geological investigations of the ktb project is the recognition that the present day geometry of the zev is a result of cold shallow level thin skinned tectonics that in the absence of the view into the third dimension offered by the drill hole could not have been accurately predicted from the fossil high grade assemblages and structures seen at the surface

quartz microstructures developed during non steady state plastic flow at rapidly decaying stress and strain rate abstract synseismic loading to very high stresses 0 5 gpa and subsequent creep during stress relaxation in the uppermost plastosphere at temperatures of ca 300 350 c near the lower tip of an inferred once seismically active crustal scale fault was proposed based on peculiar microstructures identified in rocks exposed over 100 km 2 in the sesia zone european western alps here we discuss the conspicuous and highly heterogeneous microstructural record of quartz in disseminated small scale shear zones sub basal deformation lamellae and arrays of elongate subgrains on the tem scale indicate an early stage of glide controlled deformation at high stresses distributed brittle failure is indicated by healed microcracks very fine grained recrystallised aggregates with a pronounced crystallographic preferred orientation reflect intense plastic flow by dislocation creep locally a fine grained foam microstructure indicates a final stage of static grain growth at low differential stress for the previously inferred peak stresses of about 0 5 gpa and given temperatures initial strain rates on the order of 10 10 s 1 are predicted by available flow laws for dislocation creep of quartz we emphasise the importance of short term non steady state deformation in the uppermost plastosphere underlying seismically active upper crust the related heterogeneous record of quartz is governed by the local stress history at constant temperature

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

uranium lead dates from the central gneiss complex and ecstall pluton prince rupert map area british columbia uranium lead dates for nine zircon fractions from six rock samples of central gneiss complex cgc are concordant between 65 and 85 ma two fractions from a sample near the eastern edge of the cgc give discordant u pb dates between 108 and 171 ma but analytical uncertainties and geological complexities prohibit meaningful interpretation two fractions from two samples from the ecstall pluton give concordant u pb dates of about 98 4 ma and date the emplacement of the ecstall pluton the concordant cgc dates indicate late cretaceous to early tertiary peak metamorphism granulite and amphibolite facies of the cgc east of work channel lineament this contrasts with a slightly older mid cretaceous peak metamorphism west of work channel lineament inferred from the synmetamorphic nature of the ecstall pluton

structural analysis of a ductile brittle precambrian shear zone in the sierra madre wyoming western extension of the cheyenne belt abstract existing plate tectonic models for the cheyenne belt a proterozoic suture at the southern margin of the archean wyoming craton are based largely on data from the medicine bow mountains southern wyoming this paper tests the hypothesis that a major structural and geochronological discontinuity in the sierra madre of southern wyoming is the western extension of the cheyenne belt the sierra madre shear zone consists of a cataclastic western segment and a mylonitic eastern segment that comprises several mylonite zones the eastern segment records early ductile thrusting ca 1750 ma and later dextral strike slip faulting as revealed by macrostructural microstructural and quartz fabric analysis structures associated with these events are kinematically compatible and coeval with structures within the suture zone in the medicine bow mountains the correlation of shear zones in the two ranges is supported further by lithologic similarity of distinctive rocks north of and within the shear zones and the presence of unusual quartz fabrics documenting c slip in synkinematic granites in both ranges isolated exposures of mylonite along the dominantly cataclastic western segment suggest that the mylonitic shear zone was formerly more extensive the western segment of the sierra madre shear zone is a single zone of intense cataclasis that truncated and dismembered the earlier ductile shear zone kinematic analysis within the cataclastic zone suggests that it formed during north directed thrusting east striking south dipping thrust faults and associated overturned to the north recumbent folds are developed in supracrustal rocks directly north of the cataclastic fault zone this spatial association of north vergent structures and their apparent kinematic compatibility suggests that they are genetically related two major northwest striking cataclastic dextral strike slip in the eastern sierra madre appear to merge with the cataclastic thrust fault these cataclastic faults are interpreted as parts of a north vergent thrust tear system that cut across the original suture zone as rocks in the upper plate of the thrust were transported to the north it is not known whether this deformational event occurred in response to continued post suture convergence to the south or if it represents a separate and distinct precambrian event the prominent bend in the sierra madre shear zone may be an oroclinal flexure produced as a consequence of northward translation along the cataclastic thrust system

correlation between magnetic fabrics strain and biotite microstructure with increasing mylonitisation in the pretectonic wyangala granite australia abstract the wyangala granite is a foliated porphyritic silurian granite from the palaeozoic circum pacific type eastern lachlan orogen elo of australia it is a paramagnetic ilmenite bearing s marginal i type two mica to mainly biotite granite with different biotite contents and local chlorite alteration very highly strained quartz epidote bands are present in this contribution anisotropy of magnetic susceptibility ams is compared with independently measured intensity and 3d style of strain biotite microstructure and degree of mylonitisation for low strain granites with weak s foliations through medium strain protomylonitic granites with moderate s and c foliations to a high strain altered granite with a strong single foliation the samples are further analysed for possible contributions from sample heterogeneity magmatic flow and sub magmatic deformation a good correlation p ams 1 02 0 04 ln p e qtz is obtained between site average degree of ams p ams in the granite and degree of finite strain anisotropy p e qtz from aspect ratios of quartz aggregates in s foliations in hand specimen and outcrop p ams 1 03 1 14 p e qtz 1 4 19 the magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the march model the observed quartz strains however exceed the ams march strains and are near neutral plano linear character the geological factors that may have contributed to these differences include intra and inter crystalline deformation of biotite and bimodality in s and c magmatic fabric is not clearly evident in either the ams or the biotite data new data for synkinematic oligoclase low titanium biotite and low sodium k feldspar show that conditions during deformation were approximately transitional greenschist amphibolite facies i e well below solidus this agrees with published age data that put the granite emplacement in an extensional back arc setting in already deformed country rocks and before later convergent regional deformation in middle devonian tabberabberan event to early carboniferous kanimblan event time

210pb dating of scottish lake sediments afforestation and accelerated soil erosion changes in the rate of soil erosion in lake catchments can be identified from changes in the rate of sediment accumulation in lakes here we compare recently afforested sites with non afforested sites in the galloway area of southwest scotland we show that lakes with non afforested catchments have slow constant sediment accumulation rates whereas lakes with recently afforested catchments have changes in accumulation that parallel the known history of afforestation for loch grannoch the sediment accumulation rate increases from 0 1 cm yr 1 to over 2 cm yr 2 during the disturbance period data from l skerrow however suggest that the rate might decline to predisturbance levels after approximately 10 years as the forest canopy closes and drainage channels stabilize

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

millennial scale stratigraphy of a tide dominated incised valley during the last 14 kyr spatial and quantitative reconstruction in the tokyo lowland central japan spatial and quantitative analysis of infilling processes of the tide dominated incised valleys beneath the tokyo lowland during the last 14 kyr was undertaken by using data from 18 sediment cores 467 radiocarbon dates and 6100 borehole logs the post last glacial maximum valley fills consist of braided river meandering river estuary spit and delta systems in ascending order the boundary between the estuary and delta systems is regarded as the maximum flooding surface the maximum flooding surface beneath the tokyo lowland is dated at 8 ka in the arakawa valley and 7 ka in the nakagawa valley this age difference is due to the migration of the tone river from the arakawa valley to the nakagawa valley at 5 ka and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers the meandering river system is dominated by sheet like sands that were deposited during lateral migration of channels during the younger dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the younger dryas the transition between these channel geometries is controlled by a threshold sea level rise of 4 to 7 mm yr 1 before migration of the tone river at 5 ka the tide dominated bay in the nakagawa valley was filled by upward fining laterally accreting muds the muds accreted from the margin to the axis of the bay such lateral accretion of suspended particles derived from outside the bay has been documented in other tide dominated coastal environments and is probably common in other similar settings after the migration of the tone river the bay was filled by upward coarsening deltaic sediments

brittle deformation events at the western border of the bohemian massif germany investigations of brittle deformation structures present within the crystalline rocks of the bavarian oberpfalz reveal a complex late to post variscan crustal evolution upper carboniferous mainly westphalian granites were emplaced into semibrittle to brittle rocks of the zev zone of erbendorf vohenstraus and the egz erbendorf greenschist unit respectively from both the alignment of the granites and the direction of granite related tension gashes a north east south west extension must be assumed for the period of magmatic activities apart from the granite intrusions rapid crustal uplift about 1 5 km my led to an increase in the geothermal gradient from 40 c km late variscan post granitic the increased geothermal gradient persisted during the succeeding reverse faulting which results from late carboniferous probably stephanian east west and northeast south west compression although not evidenced directly in the area considered strike slip faults seem to have played an important part during the late variscan crustal evolution particularly in the early permian the strike slip events indicate further crustal shortening and indentation under north south compression a similar indentation was present in cretaceous time after a weak phase of early cretaceous reverse faulting which results from north south compression strike slip faults formed under north west south east and north south compression all these faults in particular the strike slip faults seem to be related to the cretaceous and lowermost tertiary convergence of the alpine carpathian orogeny a late stage of crustal extension characterized by a radial stress tensor 2 3 is indicated through high angle normal faults which probably formed during the subsidence of the adjacent neogene eger graben

fabric analysis of quartzites with negative magnetic susceptibility does ams provide information of spo or cpo of quartz abstract we ask the question whether petrofabric data from anisotropy of magnetic susceptibility ams analysis of deformed quartzites gives information about shape preferred orientation spo or crystallographic preferred orientation cpo of quartz since quartz is diamagnetic and has a negative magnetic susceptibility 11 samples of nearly pure quartzites with a negative magnetic susceptibility were chosen for this study after performing ams analysis electron backscatter diffraction ebsd analysis was done in thin sections prepared parallel to the k1k3 plane of the ams ellipsoid results show that in all the samples quartz spo is sub parallel to the orientation of the magnetic foliation however in most samples no clear correspondance is observed between quartz cpo and k1 magnetic lineation direction this is contrary to the parallelism observed between k1 direction and orientation of quartz c axis in the case of undeformed single quartz crystal pole figures of quartz indicate that quartz c axis tends to be parallel to k1 direction only in the case where intracrystalline deformation of quartz is accommodated by prism slip it is therefore established that ams investigation of quartz from deformed rocks gives information of spo thus it is concluded that petrofabric information of quartzite obtained from ams is a manifestation of its shape anisotropy and not crystallographic preferred orientation

statistical analysis of grain size distribution in pleistocene sediments from lake biwa japan abstract time series of grain size distributions from pleistocene sediments deposited in lake biwa during the past 550 millennia show dominant periods of 40 000 and 20 000 yr that are very close to those predicted by the milankovitch theory as well as a period of about 70 000 yr not directly predicted by this theory the 70 000 yr period is strongest followed by the 20 000 yr period the sequences also show that coarser particles were deposited in general during strong solar insolation whereas finer particles were deposited during weak insolation

southern continuation of the coast shear zone and paleocene strain partitioning in british columbia southeast alaska this paper documents the newly recognized southern continuation of the early tertiary coast shear zone extending its known length by 350 km to more than 1200 km three sites along the shear zone in british columbia douglas channel bella coola and machmell river have similar histories during the period ca 65 55 ma the shear zone is 2 11 km thick and is defined by well developed mylonite zones that strike northwest and dip steeply northeast motion on the shear zone was predominantly reverse with the northeast side up synkinematic plutons are common in the shear zone lower plate rocks high grade gneiss derived from an ancient continental margin assemblage show little evidence of the extensive deformation and plutonism in the shear zone north of bella coola high grade gneiss forms the upper plate but to the south weakly metamorphosed rocks of stikinia compose the upper plate geochronologic data show that the shear zone was active between ca 60 and 55 ma at douglas channel ca 62 and 56 ma at bella coola and after 66 and before 56 ma near the machmell river these features match those of the coast shear zone in southeast alaska and adjacent british columbia together the shear zones formed a continental scale reverse ductile fault in paleocene time plate reconstructions show an oblique component to the dominantly dextral transcurrent paleocene margin partitioning of this motion across the continental margin produced a regional system of strike slip faults and contraction on the coast shear zone

orientation and nature of active crustal stresses determined by electromagnetic measurements in the patagonian segment of the south america plate based on electromagnetic measurements we determined the current stress directions in the uppermost continental crust of patagonia between the active plate margin of the chilean pacific coast and the argentinean passive atlantic margin regional variations of the observed stress pattern are giving details onto the acting tectonic processes we distinguish five regional stress domains with different prevailing horizontal stress directions sh 1 southern coastal cordillera and longitudinal valley sh ssw nne 2 chiloe island sh sw ne 3 northern patagonian andes sh wsw ene 4 argentinean pampa and atlantic margin sh wnw ese and 5 southern patagonian andes sh wnw ese these stress regimes can be related to the geometry of the subducting nazca and antarctic plates to the transform fault between the south america and scotia plates and to passive margin processes along the atlantic coast absolute plate motion and rapid relative plate convergence control the subduction geometry and therefore the stress directions along the convergent margin of the south america plate and the structural style within and landward of the magmatic arc the knowledge of current local stress directions permits the characterisation of potential fault kinematics by in situ measuring of electromagnetic emissions from rocks we determined the maximum horizontal stress orientation in the uppermost crust using a new geophysical tool our investigations on the orientation of the stress regimes also allow conclusions about the causative forces of either tectonic or gravitational origin in this part of the south america plate

sheared bedding parallel quartz vein as an indicator of deformation processes abstract monomineralic veins are well known as good recording of filling and precipitation processes however they are also able to register the action of deformation in rocks we used monomineralic quartz veins from quadrilaterro ferrifero brazil to represent how the deformation actuated during the transformation of different structures they were analyzed using a combination of a u stage and ebsd two main types of quartz aggregates are distinguished single crystals with subgrain development and strain free grains of quartz we interpret the microstructures and textures as the result of a combination of concurrent crystal plasticity microfracturing solution transfer and recrystallization the single quartz grains were deformed by dislocation glide however as the c axis orientation of the grain was not favorable for further glide on basal planes the deformation was accommodated by microfracturing new grains were formed along the deformed zones with crystallographic orientations suitable for gliding on basal planes as the deformation proceeded the new grains continue to develop until the vein was completely recrystallized into an aggregate of granular grains

characterization of the crust of the coast mountains batholith british columbia from p to s converted seismic waves and petrologic modeling abstract the late triassic to early tertiary coast mountains batholith cmb of british columbia provides an ideal locale to study the processes whereby accreted terranes and subduction related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals seismic measurements combined with calculated elastic properties of various cmb rock compositions provide a window into the deep crustal lithologies that are key to understanding the processes of continental growth and evolution we use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the cmb then test the viability of these sections via forward modeling with synthetic seismic data the compositions that make up our petrologic forward models are based on calculations using the free energy minimization program perple x to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area seismic data were collected along two transects in west central british columbia a southern line that crossed the cmb near the town of bella coola near 52 n and a northern line centered on the towns of terrace and kitimat near 54 n along both transects seismic receiver functions reveal high vp vs ratios near the insular intermontane terrane boundary and crustal thickness increasing from 26 3 km to 34 3 km at the 1 sigma certainty level from west to east across the coast shear zone csz on the southern line we observe an anomalous region of complex receiver functions and diminished moho signals beneath the central portion of the cmb our petrologic and seismic profiles show that observed seismic data from much of the cmb can be well matched in terms of crustal thickness and structure average vp vs and amplitude of the moho converted phase without including ultramafic residual material in the lower crust

biogenic silica record in lake biwa of central japan over the past 145 000 years abstract the record of the biogenic silica flux bsf g cm 2 103yr 1 in lake biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions the bsf record of lake biwa demonstrates five periods over the past ca 145 000 yr when the bsf values were significantly greater than 7 5 g cm 2 103yr 1 and five intervals when they were lower the data imply that paleoclimatic conditions were warmer and wetter from ca 123 000 to 115 000 103 000 to 95 000 88 000 to 72 000 57 000 to 32 000 yr b p and around ca 6000 yr b p when the bsf values were greater and relatively dry and cold from ca 141 000 to 123 000 yr b p and during intervals between two of the five warm and wet episodes when the bsf values were lower time series of the bsf record can be correlated with the record of biogenic silica content in lake baikal and the marine oxygen isotope stages 1 through 6 furthermore the bsf values varied with much higher amplitude during the last interglaciation than during the last glaciation probably implying that the diatom productivity in lake biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions

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

thermometry of quartz mylonites importance of dynamic recrystallization on ti in quartz reequilibration quartz mylonites from the tonale fault zone in the alps northern italy have been investigated by the ti in quartz geothermometer titaniq in order to test its applicability to measure deformation temperatures the eastern part of the tonale fault zone was contact metamorphosed by the synkinematic intrusion of the adamello pluton forming an 800 m wide mylonitic shear zone with a synkinematic temperature gradient from 280 c at the frictional viscous transition to 700 c at the pluton contact as derived from metamorphic mineral assemblages deformation microstructures from quartz mylonite samples systematically collected across the mylonitic shear zone display the entire range of dynamic recrystallization in quartz which comprise bulging recrystallization blg subgrain rotation recrystallization sgr and grain boundary migration recrystallization gbm titaniq geothermometry yields the near peak deformation temperature for quartz mylonites deformed at metamorphic temperatures above 540 c in the zone of gbm however for mylonites formed under lower temperatures in the zones of sgr and blg the preexisting ti concentrations were not reset it is suggested that this is due to the sluggish ti volume diffusion rates below 500 c and the short duration of contact metamorphism and deformation even in the higher temperature samples the reequilibration of ti in quartz content was achieved by grain boundary migration rather than by volume diffusion hence our results show that gbm is crucial for the reequilibration of ti in quartz while quartz mylonites deformed by either blg or sgr which predominate in natural shear zones at greenschist facies metamorphic conditions most likely yield inherited temperatures

variability of the rebound hardness as a proxy for detecting the levels of continuity and isotropy in archaeological quartz abstract the equotip hardness tester is applied to different types of quartz and other lithic raw materials in order to determine if variations in the rebound hardness measured by this device may serve as a proxy for detecting the levels of continuity and isotropy of toolstones continuity the amount of cracks and other internal defects and isotropy the measure of the directional properties of a raw material are known to have important effects on the level of consistency and predictability of fractures which in turn is traditionally considered a main factor for defining the flaking quality of a given raw material the results demonstrate the existence of differences among the raw materials analysed in both the average value and the variability of the rebound hardness while cryptocrystalline samples show the most homogeneous results quartz and metamorphic rocks display a comparatively higher variance in the specific case of quartz such variability seems to be mainly caused by the presence of internal planes and discontinuities while anisotropy although also active had played a comparatively modest role the results achieved by the equotip hardness tester suggest that this device could be successfully used for a basic or preliminary estimating of some of the physical and mechanical properties of stone raw materials therefore it is a potential index test for complementing other more accurate laboratory methods

a 4000 year record of hydrologic variability from the olympic mountains washington usa sedimentological and geochemical analyses of gravity and piston cores retrieved from lake quinault washington reveal an 4000 year flood dominated depositional record individual flood event laye

theoretical investigation of the time variation of drainage density a theoretical equation was developed to express the time variation of drainage density in a basin or geomorphic surface di t t is the drainage density at time t on the i th basin or geomorphic surface which was formed at time t is a factor related to the erosional force causing the development of the rivers of the basin or surface at time i is the maximum drainage density and di is the initial drainage density on the i th geomorphic surface or basin the equation is based on the assumption that the drainage density increases with time until it reaches a specific upper limit i t the maximum drainage density which is related to certain physical properties of the basin the equations for various dated basins or geomorphic surfaces can be combined into one modified equation if the same relative erosional forces have acted on those basins or surfaces t t and if the basins or surfaces have the same physical properties i t i t di d0 the application of this equation to coastal terraces and glacial tills shows that the model is compatible with observed drainage densities on various dated basins or surfaces

the relationship between ductile shear zone and mineralization in the jiufeng sn deposit northern guangxi south china evidence from structural analysis and cassiterite u pb dating abstract the jiufeng sn deposit is located in the outer contact zone southwest of the neoproterozoic motianling granitic pluton in northern guangxi south china the deposit is characterized by a nne striking 30 200 m wide ductile shear zone named the jiufeng ductile shear zone majority of the sn orebodies including four large ones are hosted by the shear zone field and microstructural observations electron backscatter diffraction measurements and magnetic fabric analyses show that the shear zone is characterized by sinistral thrust shearing the shear zone has also slightly modified the sn orebodies quartz in the shear zone exhibits core mantle structure and undulose extinction quartz has experienced significant sub grain rotation and grain boundary migration recrystallization lattice preferred orientation analysis reveals primarily basal rhomb and prism slips cassiterite grains in the shear zone however demonstrate brittle deformation therefore the deformation temperature during the ductile shearing is estimated lower than 650 c and below u pb closure temperature of cassiterite as such the u pb isotopic composition of the cassiterite was not disturbed by the shearing and the u pb age of the cassiterite could be used for the age of the sn mineralization la icp ms u pb dating of cassiterite grains selected from a cassiterite bearing tourmalinite sample performed in this study yielded a tera wasserburg u pb lower intercept age of 832 3 5 3 ma this age is consistent within error with that of the neighboring neoproterozoic motianling granitic pluton which suggests a close genetic relationship between the sn mineralization and the granitic magmatism studies show that the jiufeng ductile shear zone was produced by a widespread caledonian or kwangsian tectonic event in south china indicating that the shearing was much later than the sn mineralization and has no generic relationship to the sn deposit

contrast of metamorphic and structural histories across the work channel lineament coast plutonic complex british columbia a prominent topographic lineament along the western margin of the coast plutonic complex of southeast alaska and adjacent parts of british columbia separates terranes of contrasting metamorphic histories where it enters british columbia near prince rupert as the work channel lineament the western terrane preserves a regional medium high pressure metamorphic facies series increasing from chlorite grade in the west to kyanite muscovite migmatite near the lineament the metamorphic structural and age relations of the western terrane are consistent with a model of crustal thickening accompanied by westward transport of higher over lower grade metamorphic units during the jurassic this terrane was uplifted and cooled by cretaceous time 85 ma east of work channel lineament high temperature relatively low pressure assemblages are overprinted onto high pressure assemblages the low pressure metamorphic assemblages developed in the eocene during rapid uplift 2 mm yr of rocks which initially may have been metamorphosed at the same time and along the same pt gradient as those of the western terrane structures along the work channel lineament suggest vertical motion during uplift of the eastern terrane and after metamorphism of the western terrane because the metamorphic discontinuity across the lineament is 3 5 kbar at about 700 the lineament in the prince rupert area marks a major crustal break

asian summer monsoon variability during the late glacial and holocene inferred from the stable carbon isotope record of black carbon in the sediments of muge co southeastern tibetan plateau china a sediment core from an alpine lake muge co from the southeastern margin of the tibetan plateau was analyzed for sediment grain size distribution and the carbon isotopic composition of black carb

fabric asymmetry and shear sense in movement zones asymmetry between lattice preferred orientation and shape fabrics is commonly observed in microstructural studies of many deformed mineral aggregates e g ice carbonate rocks peridotites and quartzites theoretical predictions are limited by the nature of the models available and more can be gained by discussion of the mechanisms which give rise to such asymmetry in specific natural and experimental situations

development of microcracks in granites during cooling and uplift examples from the variscan basement in ne bavaria germany abstract microcracks in two late variscan granites in ne bavaria provide information about regional paleostress directions and p t conditions during cooling and uplift in both granites three prominent generations of healed microcracks called ci cii ciii constitute an orthorhombic fabric the orientation of which is closely related to the mesoscopic joint pattern we present a model relating this orthorhombic crack fabric not only to external deviatoric stresses but also to internal stresses on the grain scale resulting from the strong thermal contraction of quartz relative to the feldspar framework at the deepest level 1 subvertical steep ci cracks developed normal to 3 and selectively in the quartz their formation caused a stress uncoupling of quartz aggregates from the external 3 direction so that further contraction of quartz produced steep cii cracks normal to 2 forming bridges between ci cracks at higher levels 2 subvertical the same process reactivated the ci cracks and now formed horizontal crack bridges ciii p t estimates based on fluid inclusion data and inferred geothermal gradients are 250 400 c at 1 5 3 kbar for ci cii cracks and 150 200 c at 1 2 kbar for ciii cracks the orientation of the younger open cracks which formed at higher crustal levels partly corresponds to the present regional stress field

tree ring information and rainfall characteristic for landslide in the kobe district japan heavy rainfall on the south side of the rokko mountains has often caused severe landslides and debris flows analysis of the annual summation of rainfall in excess of 100 mm day shows that the rainfall in this area has dominant periodicities of about 25 30 10 13 and 5 7 years the period of about 25 30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area temporal change in this rainfall may provide a first approximation for erosional force analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25 30 years cross spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25 30 years evidence that variations in the ring width may be used as proxy data for erosional force

fabric development during exhumation from ultrahigh pressure in an eclogite bearing shear zone western gneiss region norway abstract petrofabrics and trace element thermobarometry of deformed quartzofeldspathic gneiss and associated coesite bearing eclogite in the salt mylonite zone western gneiss region norway document a pressure temperature deformation path from ultrahigh pressure to amphibolite facies conditions the salt mylonite zone is dominated by quartzofeldspathic gneiss with a strong foliation and lineation coesite bearing eclogite within the shear zone contains a foliation and lineation defined by elongate omphacite consistent with that of the host gneiss suggesting that gneiss and eclogite were deformed in the same kinematic framework in eclogite omphacite preserves ls to l type crystallographic preferred orientation and quartz preserves prism fabrics that developed in quartz near coesite quartz transition conditions the quartzofeldspathic gneiss in the mylonite zone records prism and rhomb slip in quartz and reverse zoning in plagioclase higher ca rims consistent with re equilibration during decompression the ti concentration in quartz in gneiss is higher than that in quartz in eclogite suggesting that quartz recrystallized at a lower pressure in the gneiss ti in quartz thermobarometry of rutile bearing eclogite and titanite bearing gneiss indicates equilibration at t 750 c and t

protolith relations of the gravina belt and yukon tanana terrane in central southeastern alaska metamorphic rocks west of the coast mountains batholith in central southeastern alaska are divided into the gravina belt taku terrane and newly defined ruth assemblage the ruth assemblage comprises metapelite quartzose metaclastic strata quartzite marble felsic metatuff mafic metavolcanic rocks and orthogneiss depositional and emplacement ages of 367 pm 10 ma and 345 pm 13 ma inferred from discordant u pb zircon analyses on felsic metatuff and granodioritic orthogneiss respectively require that at least portions of the ruth assemblage be late devonian and early mississippian in age the assemblage is similar in age and protolith to and thus correlated with the yukon tanana terrane the gravina belt is characterized by upper jurassic and lower cretaceous mafic volcanic rocks and tuffaceous turbiditic clastic strata that unconformably overlie the alexander terrane metamorphic rocks that structurally underlie the taku terrane and ruth assemblage are included in this assemblage trace

dynamically recrystallised quartz c axis fabrics in greenschist facies quartzites singhbhum shear zone and its footwall eastern india influence of high fluid activity abstract oriented specimens of quartz tectonites from the singhbhum shear zone ssz an important tectonic element in the precambrian eastern indian shield and its footwall have been analysed for c axis fabrics of dynamically recrystallised quartz grains in individual specimens the fabric pattern is either an asymmetric type i cross girdle or an asymmetric kinked single girdle irrespective of whether the fabric is from the ssz or its footwall the asymmetry of the fabric confirms a southward thrust movement of the northern block on a northerly dipping shear zone the measured fabrics are characterised by a concentration near the y axis of the finite strain ellipsoid with an equally or subordinately developed concentration near the z axis although some earlier works suggest the y concentration of the quartz c axis fabric as due to the influence of higher temperature obtained in amphibolite facies the occurrence of a similar concentration in the quartz c axis fabric from quartz tectonites of the ssz and its footwall interpreted to have formed under greenschist facies condition is explained by formation of the fabric under high fluid activity during deformation

recent horizontal stress directions in basement rocks of southern sweden deduced from open microcracks abstract the strike direction of open intragranular microcracks in quartz and feldspar host grains was determined using optical transmission and reflection microscopy on eight oriented samples taken in two study areas in precambrian basement rocks of southern and south central sweden for an area of about 160 km 2 sw of vastervik and two sample locations w of uppsala the vast majority of open microcracks displays a strong preferred nw se strike direction according to the common assumptions that natural cracks in crystalline rocks are predominantly extensional mode i and that open cracks belong to the latest microcrack generation these strike directions should reflect the sub recent main horizontal stress direction h of the recent tectonic stress field this conclusion is supported by corresponding directions known from in situ stress measurements and focal plane solutions in the vicinity of the study areas it is remarkable that even in samples taken close i e a few hundred metres to recently active large scale faults the orientation of microcracks does not deviate from this common direction this may point to slip on already softened faults very local stress reorientations e g m scale or that local stress relief was accomplished by other processes at micro scale e g mechanical twinning in favourably oriented feldspar crystals or slip on grain boundaries

periodic variations of grain size in pleistocene sediments in lake biwa and earth orbital cycles a time sequence of grain size distributions from the pleistocene sediments in lake biwa located in the central part of japan 35 n 136 e has dominant periodicities of 41 000 23 000 and 19 000 years which are very close to those predicted from the astronomical theory of paleoclimate introduced by milankovitch the time variation of the grain size is very similar to that of insolation of caloric summer in the northern hemisphere

upper paleozoic to lower mesozoic strata and their conodonts western coast plutonic complex british columbia six lithologic units including two newly named formations were mapped on randall dunira and nearby islands the islands are characterized by greenschist facies metamorphism and westerly directed thrusting the oldest unit is a late mississippian massive limestone on ducie island the dunira formation composed of thin bedded limestone and siltstone is early and middle pennsylvanian in age it is unconformably overlain by limestone and dolomite of the upper triassic randall formation the randall formation grades upwards into a green phyllitic unit of late triassic age rhyolitic and more mafic volcanic rocks may represent a bimodal volcanic suite of early jurassic age based on a u pb date of 188 ma on zircons these five units correlate with rocks in the alexander terrane in southeastern alaska the sixth and presumed youngest unit consists of flysch like sedimentary rocks of probable middle jurassic to early cretaceous age that may correlate with rocks of the gravina nutzotin belt the three ol

structural model for the saxothuringian moldanubian suture in the variscan basement of the oberpfalz northeastern bavaria f r g interpreted from geophysical data abstract the moldanubian saxothuringian boundary marks a prominent subduction zone in the internal parts of the european variscides in the oberpfalz area deep reflection seismic profiles show a high density of various reflectors mainly in the upper crust indicating a complex polyphase deformation during the collision process seismic structures and related data from surface geology suggest that the moldanubian saxothuringian collision consisted of two main phases the first phase is marked by extensive nw directed overthrusting of moldanubian onto saxothuringian crust along se dipping master decollements some of which can be traced down to the moho during an advanced stage progressive overthrusting led to the development of wedge structures associated with se directed backthrusting and backfolding in the upper structural levels subsequently some of these wedges and their related decollements were folded to form the main ne striking anticlines the first phase of crustal imbrication correlates with a regional low pressure high temperature metamorphism at about 320 ma decreasing in grade northwestward the second phase is characterized by a reorientation of the main direction of crustal shortening from nw se to sw ne which is interpreted as the result of the n directed indentation of the vindelician terrane into the moldanubian this event is recorded by conjugate systems of overthrusting and subsequent strike slip faulting in the oberpfalz and the bavarian forest and the black forest vosges area in the area of the southern german block between these basement outcrops the indentation front is marked by the arc shaped axes of gravimetric and magnetic anomalies and permo carboniferous troughs

large scale transpressive shear zone patterns and displacements within magmatic arcs the coast plutonic complex british columbia the coast plutonic complex is the largest magmatic arc of the north american cordillera extending from northwestern washington state to eastern alaska it forms the transition between two tectonic domains that are suspected to have undergone several phases of large several thousands of kilometers orogen parallel displacement during the mesozoic and early cenozoic a compilation of fabric data published isotopic ages and new structural observations shows that the western coast plutonic complex was affected by subvertical orogen parallel crustal scale shear zones these shear zones mainly reflect sinistral transpression and were sequentially active from 110 to 87 ma during the intrusion of voluminous batholiths sinistral shearing was roughly coeval with the development of the thrust belts flanking the coast plutonic complex between 101 and 85 ma suggesting plate scale transpression was a first order process in the construction of the coast mountains orogen these shear zones separate panels with distinct plutonic and cooling histories suggesting the sinistral displacements between crustal blocks were large greater than tens to hundreds of kilometers this transpressive shear system likely reflects the jurassic to early late cretaceous migration of outboard cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models this example from the coast orogen shows how transpression is partitioned between a thermally weakened magmatic arc and outwardly vergent fold and thrust belts our analysis further shows that the 2000 km long late cretaceous to early tertiary coast shear zone has a minimum extent toward the south to at least 51 30 n

application of lu hf garnet dating to unravel the relationships between deformation metamorphism and plutonism an example from the prince rupert area british columbia abstract the tectonic history of the prince rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal scale shear zones syn tectonic garnet in the prince rupert area has lu hf ages of 102 6 3 7 ma and 108 3 4 1 ma 2 porphyroblast matrix relationships in these samples and samples from the same outcrops indicate syn tectonic garnet growth these relationships imply that the garnet ages directly date the development of the metamorphic foliations a third sample of migmatitic garnet amphibolite from the contact aureole of the 94 90 ma ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode 105 ma similar to the ages obtained from the other samples and a growth or equilibration event at 94 ma during pluton emplacement the data show that the older lu hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement the ecstall pluton was emplaced 10 to 15 m y after regional metamorphism and thrust stacking in the prince rupert area in order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation metamorphism and plutonism throughout the north american cordillera in the time period between 110 and 85 ma contractional and transpressional deformation occurred throughout much of the north american cordillera at this time from southeastern alaska to the baja peninsula in mexico left lateral transpression dominated the canadian cordillera whereas right lateral transpression affected areas south of the idaho salmon river suture zone including the sierra nevada batholith this reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first order feature of the geology of the north american cordillera during the cretaceous

thermobarometry and p t path of garnet aluminosilicate bearing gneisses from the ktb drill core continental deep drilling project germany garnet zoning characteristics reaction microstructures and thermobarometric studies document a multistage p t evolution for the paragneisses of the ktb drill core the prograde heating and burial path led through the sillimanite stability field before it entered the kyanite field close to the p t peak the uppermost paragneiss amphibolite unit 0 560 m reached peak conditions at 650 670 c and 7 8 kbar the units below 560 3574 m show higher peak temperatures of 680 720 c with maximum pressures between 8 and 9 kbar this p t discontinuity implies a tectonic contact but otherwise the two sections of the drill core do not show evidence for a separate metamorphic history and probably lay on a common crustal paleogeotherm at peak conditions homogenization of mg fe and mn in garnet at or near peak conditions points to a significant time interval between burial and subsequent decompression accordingly the prograde metamorphic episode must be significantly older than the 380 370 ma decompression and cooling period possibly mid ordovician following nearisothermal decompression with partial breakdown of garnet and growth of sillimanite a second previously unrecognized pressure peak was reached at 5 7 6 7 kbar and temperatures of around 590 c a late low pressure imprint is documented by the local presence of andalusite the lack of a continuous metamorphic p t gradient in the drilled crustal section either requires strong postmetamorphic tilting of isograds and or small scale intraformational stacking of crustal slices of similar metamorphic grade

kinematics and dynamics of the namche barwa syntaxis eastern himalaya constraints from deformation fabrics and geochronology abstract field observations deformation and fabric analyses and precise age data acquired by zircon shrimp la icp ms u pb and 40 ar 39 ar dating methods have yielded new constraints on the kinematics and dynamics of the namche barwa syntaxis nbs which is the eastern corner of the himalaya a two stage model has been established to explain the formation and evolution of the nbs the northward indentation of the indian plate beneath the lhasa terrane began at 55 40 ma and crustal materials at this corner were subducted to depths 70 km where they experienced hp uhp metamorphism since 40 ma large scale right lateral strike slip along the sagaing fault has accommodated the rapid northward movement of the eastern indian plate corner with respect to the indochina block this caused significant and progressive bending of the indus yarlung suture zone iysz such that it became the dongjiu milin left lateral strike slip shear zone dmsz in the west and the aniqiao motuo right lateral strike slip shear zone amsz in the east both zones underwent strong mylonitization meanwhile the hp uhp metamorphic rocks were rapidly exhumed first into the deep crust at 22 18 ma and then to the shallow crust to form an antiformal dome at 6 2 ma our model provides new insight into the processes of post collisional crustal thickening related to the formation of the himalayan orogenic belt

secondary lineation in a high t quartzite galicia spain an explanation for an abnormal fabric using refractory inclusions in quartz grains as a marker for the x finite direction xf of the strain undergone by the quartzites it is shown in our case that the shape preferred orientation of the quartz grains xq is perpendicular to xf within the foliation plane and is a secondary lineation according to that reinterpreted frame the lattice preferred orientation patterns become normal resulting from the dominant activity of the m a slip systems in a non coaxial shear regime and not from c slip development of xq is attributed to grain growth during a post tectonic thermal event with a faster rate of boundary migration parallel to c and without substantial change in the lattice fabric tem data give support to the latter interpretation but do not demonstrate the absence of c slip this example suggests that a close examination of the significance of the grain shape lineations is necessary in case of high temperature deformations operation of c as a dominant slip direction identified in experimental deformation of high water content synthetic quartz crystals is still to be established in natural quartz tectonites

geology of the western flank of the coast mountains between cape fanshaw and taku inlet southeastern alaska the western flank of the coast mountains batholith between cape fanshaw and taku inlet is underlain primarily by jura cretaceous strata of the gravina belt pre permian permian and triassic strata of the taku terrane and mid proterozoic to upper paleozoic rocks of continental margin affinity the continental margin rocks include mid proterozoic to lower paleozoic quartzite and marble of the tracy arm assemblage mid paleozoic metavolcanic and subordinate metasedimentary rocks of the endicott arm assemblage and upper paleozoic quartz rich metaturbidites and metaconglomerate of the port houghton assemblage we suggest that these three assemblages are correlative with components of the yukon tanana terrane which underlies a large region of yukon and eastern alaska rocks of the gravina belt taku terrane and yukon tanana terrane are juxtaposed along west vergent thrust faults of mid cretaceous age and are internally deformed and disrupted along latest cretaceous to early eocene dip slip and possibly strike slip shear zones these rocks and structures together with mid cretaceous to eocene plutons of the coast mountains batholith separate rocks of the alexander wrangellia terrane to the west from rocks of the stikine terrane to the east mid cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the alexander wrangellia terrane from central alaska to northwestern washington the continental margin rocks in the northern coast mountains may be part of the in situ north american margin that has been overthrust by the stikine and adjacent terranes alternatively these rocks may have 1 rifted from and then returned to the north american margin 2 moved 800 km along left lateral or right lateral faults from elsewhere along the north american margin or 3 originated near a continent other than north america

stress dependent morphological features on fracture surfaces of quartz and glass abstract stress dependent morphological features have been found on tensile fracture surfaces of natural brazilian quartz and synthetic quartz specimens which were flexed in air at room temperature these features are similar to stress dependent morphological features found on fracture surfaces of pyrex soda lime and lead glass when deformed in similar experiments for glass the relevant morphological feature is the fracture mirror a planar region surrounding the initial flaw stress dependent index features chosen for measurement in quartz depend upon the crystallographic orientation on the fracture surface their development is related to the crack system energy but in contrast to glass the features are not directly related to crack branching the experimental results follow an equation of the form a f r 1 2 where f is the fracture stress r is the size of a particular morphological feature e g the mirror radius in the case of glass and a is a constant from the magnitudes of a and the fracture toughness determined in these experiments we conclude that the natural brazilian quartz used in this study has significantly higher resistance to fracture than synthetic quartz

granitoid emplacement during a thrusting event structural analysis microstructure and quartz c axis patterns an example from hercynian plutons in the french massif central in the french massif central the rouergue albigeois area consists of three tectonic units stacked during the hercynian orogeny the structural analysis of the units and particularly the quartz c axis textural and structural observations in the syntectonic pinet type plutons allow us to determine the deformation history a first thrusting event d1 is responsible for a southwestward emplacement of the high grade levezou nappe above the lower gneiss unit itself overlying the para autochthonous micaschists in late devonian early carboniferous this stack of nappes experienced a second event d2 characterized by a top to the nw emplacement under medium pressure medium temperature conditions of the para autochtonous unit upon the lower gneiss unit during d2 the pinet type plutons were deformed by a shearing consistent with the kinematics recorded in the country rocks in contrast to previous works which considered the pinet type plutons emplacement to be coeval with the d2 event we argue that the emplacement of the plutons occurred during the top to the sw d1 nappe stacking this work emphasizes the importance of the quartz c axis and microstructure analysis for the identification of the early structural history in polyphase deformed terranes

changes in hydrological conditions in the central qing zang tibetan plateau inferred from lake bottom sediments abstract grain particle and chemical analyses of core samples obtained from siling co a lake on the central tibetan plateau and a sedimentation model for the lake with 14 c dating show fluctuations in the hydrological environment of the area during the past 15 000 yr the area of the lake was small and the water level low in the late part of the last glacial period thereafter the lake became larger and the water level high because of meltwater and rainfall this hydrological environment continued until 4000 yr b p at about which time the level of the lake fell sharply and the lake area shrank after a short period of low level and aridity the water level increased markedly but did not reach the previous high level after the large water inflow for a short period the climate became again arid at about 3500 yr b p the change in this interval is closely related to global change statistical analyses of the datasets of the grain particle components of bottom sediments preserved in an aquatic condition over the past 13 000 yr show that most datasets for grain size and chemical parameters had a common period of 2000 2200 yr during this interval

evolution of quartz microstructure and c axis crystallographic preferred orientation within ductilely deformed granitoids arolla unit western alps abstract we have studied quartz microstructures and the c axis crystallographic preferred orientations cpos in four granitoid samples representative of increasing ductile shear deformation from a weakly deformed granitoid stage 1 to a mylonitic granitoid stage 4 the quartz c axis cpo measured in the mylonitic granitoid has been compared with the one observed in a fully recrystallized quartz mylonite from the same area all the samples belong to the austroalpine arolla unit western alps and were deformed at greenschist facies conditions the quartz c axis cpo was analyzed using a u stage and the optical orientation imaging technique the magmatic plagioclase forming more than 50 of the volume of the granitoid is extensively replaced by a mica rich aggregate even in weakly deformed samples of stage 1 these aggregates flow to form an interconnected weak matrix with increasing deformation wrapping relatively less strained quartz grains that undergo dominantly coaxial strain recrystallization of quartz ranges from less than 1 in the weakly deformed granitoid to up to 85 in the mylonitic granitoid with average grain strain of 41 and 64 respectively with increasing strain and recrystallization quartz grains in the granitoids show a sequence of transient microstructures and cpos crystal plastic deformation is initially accomplished by dislocation glide with limited recovery and at 50 grain strain it results in a cpo consistent with dominantly basal a slip at 60 grain strain recrystallization is preferentially localized along shear bands which appear to develop along former intragranular cracks and the recrystallized grains develop a strong c axis cpo with maxima orthogonal to the shear band boundaries and independent of the host grain orientation within the granitoid mylonite at an average quartz grain strain of 64 recrystallization is extensive and the c axis cpo of new grains displays maxima overlapping the host c axis orientation and therefore unrelated to the bulk sense of shear the host controlled cpo is inferred to reflect pervasive recrystallization by progressive subgrain rotation the switch from shear band control to host control on c axis cpo occurred between 40 and 70 of recrystallization in the quartz mylonite the quartz c axis cpo develops an asymmetric single girdle consistent with the bulk sense of shear and the synkinematic greenschist facies conditions this study indicates that the cpo evolution of quartz may significantly differ in cases of polymineralic vs monomineralic rocks under the same deformation conditions if quartz in the polymineralic rock behaves as a strong phase

microfracturing and regional stress field a study of the preferred orientations of fluid inclusion planes in a granite from the massif central france abstract a study of the deformation of a granitic massif indicates a relationship between palaeostress fields and the geometry of microfractures as defined by fluid inclusion trails that is healed microfractures a statistical study of the distribution of the trails leads to the following conclusions trails exhibit several distinct preferred orientations on the scale of a grain which may be observed in many samples the orientations of the trails are similar to those of micro and mesoscale fractures in the granite and the dominant trail direction is parallel to the main direction of regional shortening thus fluid inclusion trails are mode i cracks which can be used as excellent markers of palaeostress fields

an illustration of the advantages of a complete texture analysis described by the orientation distribution function odf using quartz pole figure data abstract the preferred orientation of eight crystal directions of quartz was measured with an x ray texture goniometer for selected quartz bearing tectonites with a clear pattern of c axis preferred orientation the advantages of data analysis by means of calculations of the orientation distribution function and other forms of data presentation derived from the odf are demonstrated

sedimentological and carbonate data evidence for lake level variations during the past 3700years from a southern indian lake abstract over the years several proxies have been developed to reconstruct rainfall variability however most rely on indirect approaches to provide qualitative paleorainfall estimate in an attempt to obtain a more direct measure of paleorainfall shankar et al 2006 explored the rock magnetic properties of lake sediments from thimmannanayakanakere tk in tropical southern india they proposed the use of magnetic susceptibility as a proxy for rainfall in the tropics warrier and shankar 2009 provided geochemical evidence in support of this proposition here sedimentological and carbonate data is provided as further evidence to bolster shankar et al s 2006 proposition high low values of lf indicate high low rainfall in the region of tk during the past 3700 years particle size variations suggest that the sand was high low during arid humid periods when the tk lake level was low high hence a negative correlation is documented between sand and lf along with other rock magnetic parameters hirm an indicator of magnetically hard minerals like haematite and goethite is suggestive of a relatively arid climate the high low hirm values in tk sediments indicate arid humid conditions for this reason sand is positively correlated with hirm by contrast fine silt and clay contents are low during low rainfall periods and vice versa thus both fine silt and clay contents are positively correlated with lf and other rock magnetic parameters but negatively correlated with hirm magnetic minerals reside principally in the fine silt fraction of tk sediments as evidenced from the positive correlation between fine silt content and magnetic susceptibility carbonate content too is indicative of paleorainfall conditions being high low during arid humid climatic conditions based on the lf sand and carbonate data we have inferred lake level variations in tk during the past 3700 years

formation and evolution of snowball quartz phenocrysts in the dongping porphyritic granite hebei province china insights from fluid inclusions cathodoluminescence trace elements and crystal size distribution study abstract quartz phenocrysts are common in many granites volcanic rocks metamorphic rocks and hydrothermal deposits the dongping porphyritic granite contains large amounts of rounded to sub rounded quartz phenocrysts minerals in this porphyritic granite show weak but distinct orientation dense clusters of fluid inclusions and albite crystals exist in the quartz showing snowball texture two types of snowball quartz are recognized 1 large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle and 2 small snowball quartz crystals containing small albite grains the granite is characterized by high sio2 7 15 73 44 wt k2o 4 70 5 10 wt and na2o 4 93 5 21 wt contents low cao 0 41 0 71 wt mgo 0 03 0 05 wt fe2o3 0 87 0 94 wt tio2 0 02 0 03 wt and ree 7 10 9 80 ppm contents the granite has similar mineral and chemical composition with the aplite in the area and they were derived from the residual melt of the shuiquangou magma that suffered assimilation fractional crystallization process fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260 380 c and salinities of 1 4 12 4 wt nacl equiv for liquid vapor type inclusions and 34 1 44 3 wt nacl equiv for brine ones the quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning the trace element contents in the quartz phenocrysts are extremely low ti 3 4 5 1 ppm al 13 118 ppm li

holocene vegetation history precipitation changes and indian summer monsoon evolution documented from sediments of xingyun lake south west china we present a pollen based precipitation reconstruction and multi proxy records from a 485 cm long sequence from a sediment core from xingyun lake yunnan plateau south west china which depicts the evolution of the indian summer monsoon ism during the last 8500 years pollen and other palaeoenvironmental records document several stages of vegetation history and climate change the warmest and wettest climate in the xingyun lake catchment occurred before 5500 cal a bp and subsequently the climate became gradually drier after 2000 cal a bp the regional environmental conditions became unstable and a wet medieval warm period is probably recorded our reconstruction of the ism is similar to that portrayed by holocene speleothem o 18 records from southern china but is distinctly different from the east asian summer monsoon easm evolution which features a mid holocene maximum our results support the hypothesis that the ism and easm evolved asynchronously during the holocene and imply that the chinese speleothem o 18 records from southern china may principally reflect changes in moisture source from the indian monsoon domain and thus record the history of the ism rather than the easm

time variations of erosional force and grain size in pleistocene lake sediments abstract theoretical investigations on models of the developmental processes of erosional features show that the time variations in erosional force have more sensitive influence on the time fluctuation of eroded material such as sediments in lakes than that of the quantity representing erosional features such as volume of mountains time sequences of grain size distributions from the pleistocene sediments in lake biwa central japan indicate dominant periodicities of about 40 000 and 20 000 yr very close to those predicted from the milankovitch theory the time variations of the grain size parameters which may be indicators of erosional forces are very similar to that of the caloric summer insolation in the northern hemisphere

sediment underthrusting within a continental magmatic arc coast mountains batholith british columbia nsf ear 0309885 ear 1338583 idaho state university romanian national science funding agency uefiscdi grant pn iii p4 id pce 2016 0127

crystallographic orientation of microcracks in quartz and inferred deformation processes a study on gneisses from the german continental deep drilling project ktb abstract this study was carried out on four gneiss samples from the german continental deep drilling project ktb taken at depths between 556 and 8633 m the crystallographic orientation of microcracks in quartz was determined by a combination of the electron channelling pattern method ecp and u stage microscopy the distinct preferred crystallographic orientations of various crack generations point to different processes of crack initiation and propagation which partly seem to be depth dependent for older healed cracks a crystalplastic initiation due to dislocation pile up and related lattice distortion is indicated by cracking normal to prominent slip directions which are a at lower or c at comparatively higher temperatures in contrast younger open cracks preferentially formed on crystallographic planes with low surface energy rhombs and prisms which is interpreted in terms of pure elastic crack mechanisms because of the thermoelastic anisotropy of quartz internal stresses resulting from thermal contraction during cooling may be the main driving force for the initiation or further propagation of cracks parallel to the c axis crack propagation preferentially affects grains with crystal lattices and operating crack mechanisms being in a direction appropriate to the applied external tectonic stresses this selective cracking explains why cracks also show constant orientations with respect to geographic directions up to regional dimensions

crystallographic control and texture inheritance during mylonitization of coarse grained quartz veins abstract quartz veins within rieserferner pluton underwent deformation during post magmatic cooling at temperature around 450 c different crystallographic orientations of cm sized quartz vein crystals conditioned the evolution of microstructures and crystallographic preferred orientations cpo during vein parallel simple shear up to high shear strains 10 for glide in ribbons with c axis sub parallel to the shear zone vorticity y axis ribbons with c axis orthogonal to y xz type ribbons were stronger and hardened more quickly they show lower aspect ratios and fine grain size 10 20 m recrystallization along sets of microshear zones szs exploiting crystallographic planes distortion of xz type ribbons and recrystallization preferentially exploited the slip systems with misorientation axis close to y new grains of szs initiated by subgrain rotation recrystallization sgr and thereupon achieved high angle misorientations by a concurrent process of heterogeneous rigid grain rotation around y associated with the confined shear within the sz dauphine twinning occurred pervasively but did not play a dominant role on sz nucleation recrystallization became widespread at 2 and pervasive at 10 ultramylonitic quartz veins are fine grained 10 m similar to new grains of sz and show a cpo banding resulting in a bulk c axis cpo with a y maximum as part of a single girdle about orthogonal to the foliation and orientations at the pole figure periphery at moderate to high angle to the foliation this bulk cpo derives from steady state sgr associated with preferential activity in the different cpo bands of slip systems generating subgrain boundaries with misorientation axes close to y the cpo of individual recrystallized bands is largely inherited from the original crystallographic orientation of the ribbons and therefore vein crystals from which they derived high strain and pervasive recrystallization were not enough to reset the initial crystallographic heterogeneity and this cpo memory is explained by the dominance of sgr this contrast with experimental observation of a rapid erasure of a pristine cpo by cannibalism from grains with the most favourably oriented slip system under dominant grain boundary migration recrystallization

magnetic fabric and microstructures of late paleozoic granitoids from the north patagonian massif evidence of a collision between patagonia and gondwana abstract widespread late paleozoic magmatism in northern patagonia is a target to test hypotheses on the long standing question over the origin of patagonia in recent years a dispute over whether it is an accreted crustal block that collided with gondwana in paleozoic times or an autochthonous part of south america has taken place as part of a multidisciplinary study an integrated microstructural and magnetic fabric study was carried out on the late carboniferous yaminue complex and the early permian navarrete plutonic complex both exposed in the northeastern corner of the north patagonian massif 40 5 s 67 0 w other investigated units are the late carboniferous tardugno granodiorite the newly defined cabeza de vaca granite and the late permian san martin pluton over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility ams measurements a systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units microstructures in the yaminue complex are indicative of a transition from magmatic to solid state deformation microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex the cabeza de vaca granite intrusive in yaminue complex is the most evolved unit and records less intense high temperature solid state deformation which suggests that the stress field that controlled the emplacement of the yaminue complex outlasted it according to petrologic and structural considerations the navarrete plutonic complex has been subdivided into three facies i e robaina guanacos and aranda respectively microstructures of the navarrete plutonic complex are mostly magmatic to submagmatic versus the solid state fabric that characterizes the robaina facies at the contact with the yaminue complex combined analyses of ams and microstructural data lead us to suggest that the yaminue complex cabeza de vaca granite and possibly tardugno granodiorite were intruded during a major compressional event associated with top to the ssw thrusting this event is most likely related to a frontal collision of the north patagonian massif and the southwestern gondwana margin at around 300 ma the navarrete plutonic complex and san martin pluton were emplaced after that tectonic event which must have ended by 281 ma previous magmatic geochronological and paleomagnetic data that suggest close connection of the north patagonian massif with the south american gondwana blocks during the paleozoic can be reconciled with a late paleozoic collision by a model of a para autochthonous north patagonian massif that rifted away from gondwana after the ordovician and collided again in the late carboniferous early permian

deformation of continental crust along a transform boundary coast mountains british columbia new structural paleomagnetic and apatite u th he results from the continental margin inboard of the queen charlotte fault 54 n delineate patterns of brittle faulting linked to transform development since 50 ma in the core of the orogen 250 km from the transform north striking dip slip brittle faults and vertical axis rotation of large crustal domains occurred after 50 ma and before intrusion of mafic dikes at 20 ma by 20 ma dextral faulting was active in the core of the orogen but extension had migrated toward the transform continuing there until 9 ma local tilting in the core of the orogen is associated with glacially driven post 4 ma exhumation integration with previous results shows that post 50 ma dextral and normal faulting affected a region 250 km inboard of the transform and 300 km along strike initially widespread the zone of active extension narrowed and migrated toward the transform 25 ma after initiation of the transform while dextral faulting continued throughout the region differential amounts of post 50 ma extension created oroclines at the southern and northern boundaries of the deformed region this region approximately corresponds to continental crust that was highly extended just prior to transform initiation variation in neogene crustal tilts weakens interpretations relying on uniform tilting to explain anomalous paleomagnetic inclinations of mid cretaceous plutons similarities to the gulf of california suggest that development of a transform in continental crust is aided by previous crustal extension and that initially widespread extension narrows and moves toward the transform as the margin develops

dynamic recrystallization near the brittle plastic transition in naturally and experimentally deformed quartz aggregates the electron backscattering diffraction technique ebsd was used to analyze bulging recrystallization microstructures from naturally and experimentally deformed quartz aggregates both of which are characterized by porphyroclasts with finely serrated grain boundaries and grain boundary bulges set in a matrix of very fine recrystallized grains for the tonale mylonites we investigated a temperature range of 300 380 c 0 25 gpa confining pressure a flow stress range of 0 1 0 2 gpa and a strain rate of 10 13 s 1 were estimated experimental samples of black hills quartzite were analyzed which had been deformed in axial compression at 700 c 1 2 1 5 gpa confining pressure a flow stress of 0 3 0 4 gpa a strain rate of 10 6 s 1 and to 44 to 73 axial shortening using orientation imaging we investigated the dynamic recrystallization microstructures and discuss which processes may contribute to their development our results suggest that several deformation processes are important for the dismantling of the porphyroclasts and the formation of recrystallized grains grain boundary bulges are not only formed by local grain boundary migration but they also display a lattice misorientation indicative of subgrain rotation dynamic recrystallization affects especially the rims of host porphyroclasts with a hard orientation i e with an orientation unsuitable for easy basal slip in addition dauphine twins within porphyroclasts are preferred sites for recrystallization we interpret large misorientation angles in the experimental samples which increase with increasing strain as formed by the activity of fluid assisted grain boundary sliding

evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using ebsd and fabric analyser techniques quartz crystallographic preferred orientations cpo from three distinct orthogneisses using both the electron back scatter diffraction ebsd and fabric analyser fa techniques reveal a clear trend from basal and rhomb slip for high p t conditions 670 20 degrees c 9 kbar rhomb and basal slip for medium p t 590 15 degrees c 6 kbar and a dominance of prism slip for lower p t conditions 570 degrees c 4 5 kbar the textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences locally quartz cpus are different within one thin section and in comparison to bulk orientation measurements both ebsd and the fabric analyser techniques are ideal to determine such textural heterogeneities while the ebsd is a powerful technique to determine the full cpo measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the fa is an accurate tool to determine cpus of c axis orientations in uniaxial materials in a cpo focussed study the fa is a cheap alternative to ebsd as the analysis of whole thin section can be accomplished in a very short time with minimal sample preparation with the fa it is possible to evaluate the cpus of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity

two stage exhumation of midcrustal arc rocks coast mountains british columbia 1 new geologic data from the central gneiss complex along douglas channel help delineate the burial and exhumation of the late cretaceous to eocene coast mountains magmatic arc arc plutonism was on going between 90 and 60 ma replaced by formation of dikes to 52 ma supracrustal rocks were buried to midcrustal levels by 90 ma and garnet and kyanite grew from 90 through 70 ma subsequent exhumation was nearly isothermal and took place in two stages the first occurred from 70 to 59 ma as the arc contracted obliquely and sillimanite replaced kyanite exhumation was slow 0 5 mm yr probably accomplished by erosion aided by coaxial crustal thinning exhumation rates about doubled in the second stage of exhumation after 59 ma and before 52 ma penetrative deformation ended prior to intrusion of the quottoon pluton at 59 ma and 6 5 kbar production of cordierite rims on garnet at 4 5 kbar and 700 c signaled the end of near isothermal decompression prior to 52 ma rapid cooling 100 c 106 years of the central gneiss complex followed cordierite growth temperatures dropped to 250 by 48 ma the increase in exhumation rate and the subsequent rapid cooling are attributed to excision of 6 km of crust on a detachment system on the northeastern side of the central gneiss complex comparison to other parts of the coast mountains arc the sierra nevada and fiordland new zealand shows that the amount and tempo of exhumation vary greatly within and between arcs suggesting that the processes accommodating exhumation vary significantly

the effect of dauphine twinning on plastic strain in quartz we present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies t 300 400 c granitoid protomylonite from the arolla unit of the nw alps mechanical dauphine twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane z almost orthogonal to the compression direction z twin orientation twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb r nearly parallel to the compression direction r twin orientation in contrast we report the lack of twinning in two porphyroclasts already oriented with one of the r planes orthogonal to the compression direction one twinned porphyroclast has been investigated with more detail it shows the localization of much of the plastic strain into discrete r twins as a consequence of the higher amount of elastic strain energy stored by r twins in comparison to z twins the presence of dauphine twins induced a switch in the dominant active slip systems during plastic deformation from basal regions without twinning to and pervasively twinned regions dynamic recrystallization is localized along an r twin and occurred dominantly by progressive subgrain rotation with a local component of bulging recrystallization part of the recrystallized grains underwent rigid body rotation approximately about the bulk vorticity axis which accounts for the development of large misorientation angles the recrystallized grain size piezometer for quartz yields differential stress of 100 mpa the comparison of this palaeostress estimate with literature data suggests that mechanical dauphine twinning could have a potential use as palaeopiezometer in quartz bearing rocks

periodic variations in late pleistocene speleothem abundance in britain abstract temporal change in the growth of speleothems in the united kingdom during the past 150 000 years is shown to be related to the insolation variation by the milankovitch theory the speleothem data compiled by gordon et al 1989 quarternary research 31 14 26 have two milanokovitch frequencies the ca 40 000 yr period related to change in the earth s obliquity and the ca 20 000 yr period related to the precession of the equinoxes the abundance of speleothem growth was in general large during the last interglaciation and small during the last glaciation in both periods however speleothem abundance was greater during periods of strong insolation and less during weak insolation

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

modelling and simulation of holocene marine terrace development in boso peninsula central japan abstract in the southern part of boso peninsula central japan we can observe a series of well developed holocene marine terraces we modeled the development of these marine terraces by considering sea level fluctuation and steady land uplift the evolution of coastal landform is generally described as follows altitude change erosion deposition sea level rise land uplift in this study the erosion rate is supposed to be proportional to the dissipation rate of wave energy and the deposition rate of eroded materials to decay exponentially as they are transported seaward the rate of sea level rise is given by the time derivative of a sea level curve obtained from the sediment core records of oxygen isotope ratios steady plate subduction generally brings about steady crustal uplift subsidence independently of earthquake occurrence and so the land uplift rate is regarded as time independent on a long term average our simulation results show that a pair of sea cliff and abrasion platform is efficiently formed about a stationary point of the sea level curve the holocene sea level curve has four peaks and three troughs and so basically seven terraces are formed one by one during the past 10 000 yr however when the land uplift rate is low most of the terraces formed at older times sink in the sea when the land uplift rate is high the overlap and or reverse of older and younger terraces occur frequently and so the correspondence between the age and present altitude of terraces is not necessarily one to one taking the land uplift rate to be 3 4 mm yr we can reproduce a series of well developed holocene marine terraces in boso peninsula independently of coseismic uplifts from these simulation results we may conclude that the holocene marine terraces in boso peninsula were developed as a result of the composite process of sea level fluctuation and steady coastal uplift

the scotia quaal metamorphic belt a distinct assemblage with pre early late cretaceous deformational and metamorphic history coast plutonic complex british columbia the scotia quaal metamorphic belt extends from hawkesbury island to work channel between the early late cretaceous ecstall and the paleogene quottoon plutons the belt consists of a proterozoic paleozoic metasedimentary and metavolcanic sequence the middle devonian big falls orthogneiss early jurassic orthogneiss and jurassic or cretaceous mafic and ultramafic intrusive rocks the assemblage may be correlative with nisling terrane lithologies and may have shared a common history at least from early jurassic time on with rocks of stikine terrane strong planar and linear fabrics abundant folds and scarcity of kinematic indicators characterize the belt s deformational style development of a strong foliation followed by three episodes of folding occurred between emplacement of the middle devonian big falls orthogneiss and early late cretaceous ecstall intrusion paleogene fabrics occur in the quottoon pluton and in the easternmost 1 5 km of the scotia quaal belt if a major paleogene shear zone is po

oxygen self diffusion in quartz under hydrothermal conditions oxygen self diffusion dox has been monitored in single crystal quartz in the temperature range 515 850 c under hydrothermal conditions in the beta field between 700 and 850 c the data are represented by two linear arrhenius relations for transport parallel and perpendicular to c values for do m2 s 1 are 2 09 10 11 parallel to c and 3 16 10 10 perpendicular to 101 0 values for h kj mol 1 are 138 54 parallel to c and 203 72 perpendicular to 101 0 at 700 c in the total pressure range 11 5 100 mpa dox is independent of water f h2o and oxygen f o2 fugacities between the ni nio and fe3o4 fe2o3 buffers the results are consistent with diffusion via a simple charged vacancy mechanism under an extrinsic point defect regime further experiments are required to confirm the nature of the mobile oxygen defect a key aspect of the results is the observation that at the low water fugacities of the present experiments a hydrogen containing defect appears to play no role in the oxygen transport mechanism this is in contrast to other published sets of data and leads directly to the requirement for detailed interlaboratory comparisons

microcracks in ultrabasic rocks under uniaxial compressive stress the initiation and propagation of microcracks under stress are highly dependent upon the mineralogical and textural characteristics of the various lithotypes detailed observation and quantification of microcracks before and after uniaxial compression test were conducted a fresh olivine rich harzburgite and a serpentinized dunite were analyzed collected from the pindos and vourinos ophiolites northern greece respectively in order to compare their microcrack patterns quantitative analysis indicated that during uniaxial compression the intragranular microcracks which are the dominating crack type are gradually transformed or organized into transgranular cracks some of the newly formed transgranular cracks may also be a result of the growth of existing grain boundary cracks the new intragranular microcracks in the olivine rich harzburgite are oriented predominantly parallel to the compressive stress direction while those in the serpentinized dunite show a scattered orientation presumably due to the mesh texture of this rock type the new transgranular cracks of both peridotites tend to be subparallel to the compressive stress direction however many of them show a random orientation due to the fact that they have been formed as a result of the propagation of grain boundary cracks the occurrence of the soft serpentine along fracture surfaces of olivine when it is in assemblage with orthopyroxene tends to absorb the applied stress hampering the development of microcracks in olivine on the other hand in serpentinized peridotites the microcracks are enhanced in olivine because it is surrounded by large amounts of the much softer and flexible serpentine microcracks are usually formed along the cleavage planes of orthopyroxene porphyroclasts indicating that such crystallographic preferred orientations act as planes of weakness controlling the direction of the crack paths cr spinel grains likely comprise locations of initiation of microcracks due to their very hard nature and different mechanical behaviour relative to the surrounding silicate phases knowledge of the mineralogical and textural characteristics may assist in the prediction of potential development of failure surfaces of an ultrabasic rock in service

fabric development during shear deformation in the main central thrust zone nw himalaya india abstract quartz microfabrics and associated microstructures have been studied on a crustal shear zone the main central thrust mct of the himalaya sampling has been done along six traverses across the mct zone in the kumaun and garhwal sectors of the indian himalaya the mct is a moderately north dipping shear zone formed as a result of the southward emplacement of a part of the deeply rooted crust that now constitutes the central crystalline zone of the higher himalaya over the less metamorphosed sedimentary belt of the lesser himalaya on the basis of quartz c and a axis fabric patterns supported by the relevant microstructures within the mct zone two major kinematic domains have been distinguished a noncoaxial deformation domain is indicated by the intensely deformed rocks in the vicinity of the mct plane this domain includes ductilely deformed and fine grained mylonitic rocks which contain a strong stretching lineation and are composed of low grade mineral assemblages muscovite chlorite and quartz these rocks are characterized by highly asymmetric structures microstructures and quartz c and a axis fabrics that indicate a top to the south sense that is compatible with south directed thrusting for the mct zone an apparently coaxial deformation domain on the other hand is indicated by the rocks occurring in a rather narrow belt fringing and structurally above the noncoaxial deformation domain the rocks are highly feldspathic and coarse grained gneisses and do not possess any common lineation trend and the effects of simple shear deformation are weak the quartz c axis fabrics are symmetrical with respect to foliation and lineation moreover these rocks contain conjugate and mutually interfering shear bands feldspar quartz porphyroclasts with long axes parallel to the macrosopic foliation and the related structures microstructures suggesting deformation under an approximate coaxial strain path on moving towards the mct the quartz c and a axis fabrics become progressively stronger the c axis fabric gradually changes from random to orthorhombic and then to monoclinic in addition the coaxial strain path gradually changes to the noncoaxial strain path all this progressive evolution of quartz fabrics suggests more activation of the basal rhomb and a slip systems at all structural levels across the mct

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

high temperature crustal scale shear zone at the western margin of the eastern ghats granulite belt india implications for rapid exhumation abstract a mylonitic shear zone occurs along the western margin of the eastern ghats granulite belt india in the northern sector it separates metapelitic and mafic granulites from the granite gneisses of the bastar craton while in the southern sector it separates charnockitic gneisses and mafic granulites from the granite gneisses of the bastar craton this boundary shear zone is characterized by a mylonitic foliation and a stretching lineation microstructures characterize high grade conditions and quartz c axis patterns show strong point maxima close to the long axes of the strain ellipsoids indicating dominant prism c slip in quartz commonly interpreted in terms of ductile deformation at high temperatures quartz c axis patterns in the recrystallized and unrecrystallized domains also imply grain boundary migration as the principal mechanism of dynamic recrystallization at high temperature conditions a rapid exhumation during shearing in this marginal part of the convergent eastern ghats orogen is indicated by decompression reaction textures and retrograde hydration reactions presumably due to hydrous fluid ingress in the shear zone rocks