reduction in northward incursions of the south asian monsoon since 1400 ad inferred from a mt everest ice core 1 a highly resolved mt everest ice core reveals a decrease in marine and increase in continental air masses related to relatively high summer surface pressure over mongolia and reduction in northward incursions of the summer south asian monsoon since 1400 ad previously published proxy records from lower sites south of the himalayas indicate strengthening of the monsoon since this time these regional differences are consistent with a south north seesaw in convective activity in the asian monsoon region and reflect a southward shift in the mean summer position of the monsoon trough since 1400 ad the change in monsoonal circulation at 1400 ad is synchronous with a reduction in solar irradiance and the onset of the lia this demonstrates a hemispheric scale circulation reorganization at this time and the potential for future large shifts in monsoonal circulation

are we studying deformed rocks in the right sections best practices in the kinematic analysis of 3d deformation zones abstract a standard procedure in kinematic analyses of deformed rocks is studying samples only on the foliation perpendicular lineation parallel section based on the assumption that the rotational component of deformation is restricted to that plane the theoretical background for this procedure is that deformation is plane strain which is often useful but fails to account for all relevant features observed in many natural cases more general 3d kinematic models reproduce several of these features and help to better understand 3d deformation likely predominant in nature so they are a more appropriate starting point for deformation zone analysis theoretical and natural 3d deformation examples suggest that the section with highest degree of asymmetry the vorticity normal section vns and the corresponding vorticity vector are independent from the finite strain fabric and thus may present varied orientations with respect to the tectonic foliation and lineation the vns orientation depends on the kinematics resulting from boundary conditions whereas the strain fabric orientation also depends on accumulated strain the orientation of the vns is itself an essential element of shear zone kinematics hence it cannot be pre assumed but must be determined independently

deformation temperatures vorticity of flow and strain symmetry in the loch eriboll mylonites nw scotland implications for the kinematic and structural evolution of the northernmost moine thrust zone

the rigid grain net rgn an alternative method for estimating mean kinematic vorticity number wm the use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number wm is important for quantifying the relative contributions of pure and simple shear in penetratively deformed rocks the most common methods broadly grouped into those that use tailed and tailless porphyroclasts have been applied to many different tectonic settings however attempts have not been made to unify the various methods here we propose the rigid grain net rgn as an alternative graphical method for estimating wm the rgn contains hyperbolas that are the mathematical equivalents to the hyperbolic net used for the porphyroclast hyperbolic distribution phd method we use the rgn to unify the most commonly used wm plots by comparing the distribution of theoretical and natural tailless porphyroclasts within a flowing matrix test samples from the south tibetan detachment tibet yield indistinguishable results when the rgn is compared with existing methods because of its ease of use ability for comparing natural data sets to theoretical curves potential to standardize future investigations and ability to limit ambiguity in estimating wm the rgn makes an important new contribution that advances the current methods for quantifying flow in shear zones 2006 elsevier ltd all rights reserved

tree ring δ 18 o a tool to crack the paleo hydroclimatic code in subtropical china abstract tree ring plays an important role in deciphering the paleoclimatic signals although tree ring width trw has obvious advantages in studying the hydroclimatic history in the middle high latitudes it has certain limitation in hydroclimatic signal extraction in the tropical to subtropical areas which greatly limits our fully understanding about the hydroclimatic history in these areas in this work tree ring 18o 18otree records from five independent tree ring cores were measured and a composite 18otree record 1939 2014 was developed in guilin subtropical southwest china no juvenile effect existed in this 18otree record and no relationship was found between 18otree and trw correlation analysis with the climatic parameters demonstrated that the 18otree record significantly p

seasonal incursion of indian monsoon humidity and precipitation into the southeastern qinghai tibetan plateau inferred from tree ring δo18 values with intra seasonal resolution abstract incursion of the indian monsoon flow onto the qinghai tibetan plateau is an important regional moisture delivery mechanism but the causes of intra seasonal and longer term variations are poorly understood we observed a clear intra seasonal cycle in the oxygen isotope composition 18o of smith fir abies forrestii var georgei growing at two different altitudes high elevation site 29 39 n 94 42 e 4200 m a s l low elevation site 29 39 n 94 43 e 3800 m a s l on a se facing slope in the sygera mountains southeastern qinghai tibetan plateau mechanistic modeling suggests that 18o of precipitation which in turn depends on relative humidity and precipitation amount is important in controlling the intra seasonal tree ring isotopic cycle and we speculate that the same controls also operate on interannual and longer time scales if so multi century 18o records with intra seasonal resolution may enable us to infer long term variations in the incursion of the indian monsoon onto the qinghai tibetan plateau

columbia river flood basalts from a centralized crustal magmatic system the columbia river basalt group in the northwestern united states derived from flood basalt eruptions that occurred 16 million years ago exhibits variability in geography and trace element geochemistry that has led to a number of proposed magma origins however the geochemical variability can be explained by a relatively simple model in which magma is derived from a mantle plume that assimilated continental crust in a centralized magma system the columbia river basalt group in the northwestern united states1 comprising about 230 000 cubic kilometres of rock exhibits unusual patterns in lava distribution geochemistry and its apparent relationship to regional tectonics consequently there is little consensus on the origin of its magmas2 3 4 5 6 7 8 9 10 11 12 here we examine the isotopic ratios of sr nd pb and os and trace element abundances in columbia river basalts the results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the north american craton and the accreted terranes of idaho and oregon other related basalts are the product of mixing between the mantle plume and different types of regional upper mantle magma was then transported over a wide region by an extensive network of dykes a process that has been identified in other flood basalt provinces as well13 interactions of the plume with surrounding upper mantle and of mantle derived magmas with regional crust provide a relatively simple6 7 9 14 15 model to explain the more unusual features of the main phase columbia river basalts

effect of finite strain on clast based vorticity gauges abstract clast based vorticity gauges utilize orientations of grains assumed to have behaved as isolated rigid particles suspended in a flowing viscous matrix a fundamental assumption behind use of the method is that sufficient strain has accumulated for high aspect ratio grains to rotate into positions approaching their stable sink orientation and that clasts below a critical aspect ratio may be observed in any orientation relative to the flow plane we constructed a numerical model to explore the effect of variable finite strain on development of the orientation distribution of a large population of rigid clasts embedded in a viscous medium for end member pure and simple shear and for several distinct general shear flows our model predicts the technique will tend to produce vorticity overestimates for lower vorticity flows for a wide range of finite strain the model also indicates that clast populations in moderate to high vortical flows tend to develop shape preferred orientations that closely resemble those expected for flows of lower vorticity we conclude that clast based methods are not effective for extracting detailed kinematic information from a mylonite deformed in a flow with arbitrary boundary conditions in fact it appears that most general shear flows continued long enough to develop moderate high finite strains will tend to produce a clast orientation distribution that will yield a visual estimate of the critical aspect ratio that suggests approximately equal contributions of pure and simple shear components

strain memory of 2d and 3d rigid inclusion populations in viscous flows what is clast spo telling us abstract we model the development of shape preferred orientation spo of a large population of two and three dimensional 2d and 3d rigid clasts suspended in a linear viscous matrix deformed by superposed steady and continuously non steady plane strain flows to investigate the sensitivity of clasts to changing boundary conditions during a single or superposed deformation events resultant clast spos are compared to one developed by an identical initial population that experienced a steady flow history of constant kinematic vorticity and reached an identical finite strain state allowing examination of spo sensitivity to deformation path rotation paths of individual triaxial inclusions are complex even for steady plane strain flow histories it has been suggested that the 3d nature of the system renders predictions based on 2d models inadequate for applied clast based kinematic vorticity gauges we demonstrate that for a large population of clasts simplification to a 2d model does provide a good approximation to the spo predicted by full 3d analysis for steady and non steady plane strain deformation paths predictions of shape fabric development from 2d models are not only qualitatively similar to the more complex 3d analysis but they display the same limitations of techniques based on clast spo commonly used as a quantitative kinematic vorticity gauge our model results from steady superposed and non steady flow histories with a significant pure shearing component at a wide range of finite strain resemble predictions for an identical initial population that experienced a single steady simple shearing deformation we conclude that individual 2d and 3d clasts respond instantaneously to changes in boundary conditions however in aggregate the spo of a population of rigid inclusions does not reflect the late stage kinematics of deformation nor is it an indicator of the unique mean kinematic vorticity experienced by a deformed rock volume

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

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

seasonal temperature and precipitation recorded in the intra annual oxygen isotope pattern of meteoric water and tree ring cellulose abstract modern and ancient wood is a valuable terrestrial record of carbon ultimately derived from the atmosphere and oxygen inherited from local meteoric water many modern and fossil wood specimens display rings sufficiently thick for intra annual sampling and analytical techniques are rapidly improving to allow for precise carbon and oxygen isotope measurements on very small samples yielding unprecedented resolution of seasonal isotope records however the interpretation of these records across diverse environments has been problematic because a unifying model for the quantitative interpretation of seasonal climate parameters from oxygen isotopes in wood is lacking towards such a model we compiled a dataset of intra ring oxygen isotope measurements on modern wood cellulose 18ocell from 33 globally distributed sites five of these sites represent original data produced for this study while the data for the other 28 sites were taken from the literature we defined the intra annual change in oxygen isotope value of wood cellulose 18ocell as the difference between the maximum and minimum 18ocell values determined within the ring then using the monthly resolved dataset of the oxygen isotope composition of meteoric water 18omw provided by the global network of isotopes in precipitation database we quantified the empirical relationship between the intra annual change in meteoric water 18omw and 18ocell we then used monthly resolved datasets of temperature and precipitation to develop a global relationship between 18omw and maximum minimum monthly temperatures and winter summer precipitation amounts by combining these relationships we produced a single equation that explains much of the variability in the intra ring 18ocell signal through only changes in seasonal temperature and precipitation amount r2 0 82 we show how our recent model that quantifies seasonal precipitation from intra ring carbon isotope profiles can be incorporated into the oxygen model above in order to separately quantify both seasonal temperature and seasonal precipitation determination of seasonal climate variation using high resolution isotopes in tree ring records makes possible a new understanding of the seasonal fluctuations that control the environmental conditions to which organisms are subject both during recent history and in the geologic past

variations in the kinematics of deformation along the zagros inclined transpression zone iran implications for defining a curved inclined transpression zone abstract the combination of inclined collision and plate boundary shape can control the nature of deformation and the sense of shear along a transpression zone the present study investigated the effects of a boundary zone with curvilinear shape along a transpression zone on the kinematics of deformation the kinematics of the zagros transpression zone varies with the orientation of the zone boundary detailed structural and microstructural studies showed sinistral sense of shear on the southeastern part of the zagros inclined transpression zone fars arc but dextral sense of shear on the northwestern part of the zone it is inferred that the both senses of shear were developed coevally under a bulk general shear regional scale deformation along a curved inclined transpression miming the shape of the fras arc of the zagros and the reentrant of the bandar abbas syntaxis the zagros transpression zone formed by inclined continental collision between the afro arabian continent and iranian microcontinent

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

precipitation stable isotope records from the northern hengduan mountains in china capture signals of the winter india burma trough and the indian summer monsoon abstract this project reports results of the first precipitation stable isotope 18 o and d time series produced for qamdo in the northern hengduan mountains in the southeastern tibetan plateau the data showed that the fluctuations of precipitation stable isotopes at qamdo during the different seasons revealed various moisture sources the westerlies and local recycling moisture dominated at the study area before the pre monsoon and after the post monsoon seasons which resulted in similar trends of both precipitation stable isotopes and temperature the marine moisture was transported to the northern hengduan mountains by the winter india burma trough combined with convection consequently stable isotopes in subsequent precipitation were occasionally observed to decrease suddenly however 18 o and d values of precipitation at qamdo were lower during the monsoon period and the duration of those low values was longer because of the effects of the indian summer monsoon and the strengthening convection our findings indicate that the effects of seasonal precipitation differences caused by various climate systems including the winter india burma trough and indian summer monsoon need to be considered when attempting to interpret tree ring and ice core records for the hengduan mountains

mechanical evolution of transpression zones affected by fault interactions insights from 3d elasto plastic finite element models abstract the mechanical evolution of transpression zones affected by fault interactions is investigated by a 3d elasto plastic mechanical model solved with the finite element method ductile transpression between non rigid walls implies an upward and lateral extrusion the model results demonstrate that a transpression zone evolves in a 3d strain field along non coaxial strain paths distributed plastic strain slip transfer and maximum plastic strain occur within the transpression zone outside the transpression zone fault slip is reduced because deformation is accommodated by distributed plastic shear with progressive deformation the 3 axis the minimum compressive stress rotates within the transpression zone to form an oblique angle to the regional transport direction 9 10 the magnitude of displacement increases faster within the transpression zone than outside it rotation of the displacement vectors of oblique convergence with time suggests that transpression zone evolves toward an overall non plane strain deformation the slip decreases along fault segments and with increasing depth this can be attributed to the accommodation of bulk shortening over adjacent fault segments the model result shows an almost symmetrical domal uplift due to off fault deformation generating a doubly plunging fold and a positive flower structure outside the overlap zone expanding asymmetric basins subside to negative flower structures on both sides of the transpression zone and are called transpressional basins deflection at fault segments causes the fault dip fall to less than 90 86 89 near the surface 1 5 km this results in a pure shear dominated triclinic and discontinuous heterogeneous flow of the transpression zone

rheology of a coaxial shear zone in the virginia blue ridge wet quartzite dislocation creep at 250 280 c abstract cambrian quartzite along the western margin of the blue ridge near front royal virginia records significant penetrative strain under subgreenschist facies conditions strain analyses of the quartzite indicate general flattening and octahedral shear strain values up to 1 25 x z up to 5 7 1 samples with x z as low as 1 5 1 have crystallographic preferred orientations that record a dominance of basal slip and patterns consistent with coaxial flattening in most samples quartz has undergone minor amounts of dynamic recrystallization with mean grain sizes 4 5 m locally the quartzite is brittlely deformed and subgrains and recrystallized bulges are present along fractures and extinction bands fluid inclusion planes and fluid inclusions along deformation lamellae are abundant and quartz ftir analyses yield average h 106si values of 1100 3300 indicating fluid flow and high intragranular water content during deformation higher strain samples generally record lower water contents which may indicate that fluids migrated to grain boundaries during deformation dissolution microstructures are rare in high strain samples and we interpret most strain to have been accommodated by dislocation creep thermal modeling of zircon low temperature thermochronology data coupled with quartz c axis opening angle thermometry suggest deformation temperatures were likely 250 280 c these deformation temperatures are lower than what is typically considered the brittle plastic transition in quartz we attribute localization of this high strain zone and dislocation creep at these temperatures to hydrolytic weakening and a relatively low strain rate estimated to be 10 15 s 1

kinematic finite strain and vorticity analysis of the sisters shear zone stewart island new zealand abstract the sisters shear zone ssz on stewart island new zealand is a greenschist facies extensional shear zone active prior to and possibly during the development of the pacific antarctica spreading ridge at 76 ma we report quantitative kinematic and rotation data as well as apatite fission track aft ages from the ssz early kinematic indicators associated with the nne trending stretching lineation formed under upper greenschist facies metamorphism and show alternating top to the nnw and top to the sse senses of shear during progressive exhumation lowermost greenschist facies and brittle ductile kinematic indicators depict a more uniform top to the sse sense of shear in the topmost ssz just below the detachment plane deformed metagranites in the ssz allow the reconstruction of deformation and flow parameters the mean kinematic vorticity number w m ranges from 0 10 to 0 89 smaller numbers prevail in the deeper parts of the shear zone with a higher degree of simple shear deformation in the upper parts of the shear zone deeper and upper parts relate to present geometry high finite strain intensity correlates with low w m and high w m numbers near the detachment correlate with relatively weak strain intensity finite strain shows oblate geometries overall our data indicate vertical and possibly temporal variations in deformation of the ssz most aft ages cluster around 85 75 ma we interpret the aft ages to reflect the final stages of continental break up just before and possibly during the initiation of sea floor spreading between new zealand and antarctica

sampling strategy and climatic implications of tree ring stable isotopes on the southeast tibetan plateau we explore the potential of tree ring cellulose d18o and d13c records for reconstructing climate variability in the southeast tibetan plateau our sampling strategy was designed to investigate intra and inter tree variability and the effects of the age of tree on d18o variation we show that intra tree d13c and d18o variability is negligible and inter tree coherence is sufficient to build robust tree ring d18o or d13c chronologies based on only four trees there is no evidence of an age effect regarding d18o in contrast with tree ring width in our warm and moist sampling site young tree d13c is not clearly correlated with monthly mean meteorological data tree ring d18o appears significantly anti correlated with summer precipitation amount regional cloud cover and relative humidity simulations conducted with the orchidee land surface model confirm the observed contribution of relative humidity to tree cellulose d18o and explain the weak correlation of d13c with climate by the non linear integration linked with photosynthesis altogether the tree ring cellulose d18o is shown to be a promising proxy to reconstruct regional summer moisture variability prior to the instrumental period 2010 elsevier b v

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

toward forward modeling for paleoclimatic proxy signal calibration a case study with oxygen isotopic composition of tropical woods a forward model of the oxygen isotopic composition 18o of wood cellulose is parameterized for time series prediction in tropical environments and driven with meteorological data observed at la selva biological research station costa rica for 1985 2001 monthly resolution model results correlate modestly r 0 34 p 0 05 with observed isotopic data with higher correlation r 0 45 p 0 01 over the earliest 10 years of comparison and nonsignificant correlation over the most recent 6 years of record analysis of model output for la selva suggests that isotopic variations are strongly controlled by rainfall amount the model simulates an analogous but stronger than observed negative isotopic anomaly associated with positive july september rainfall anomalies during el nino southern oscillation enso warm phase event years simulated tree isotope data for the global tropics suggest that a network of well replicated data series from selected locations may resolve the large scale precipitation anomaly pattern associated with enso

kinematics and vorticity of flow associated with post collisional oblique transpression in the variscan inner zone of northern sardinia italy abstract quartz c axis fabrics vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the variscan inner zone in sardinia italy in order to constrain the kinematics of exhumation of medium and high grade metamorphic rocks during d2 post collisional deformation we investigated two shear belts with opposing shear senses these shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes our data suggest that the sinistral shear belt initiated during the early stage of d2 deformation in a simple shear dominated regime whereas the dextral shear belt initiated later in a pure shear dominated regime we document a general non coaxial flow regime with contemporaneous pure and simple shear components geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub horizontal and orthogonal to the trend of the axial zone changes in the kinematics vorticity of flow and strain geometry that occurred during d2 deformation may be related to post collisional orogen parallel displacement caught up in the variscan orogeny

temperature signals in tree ring oxygen isotope series from the northern slope of the himalaya abstract oxygen isotope ratios 18 o are the most commonly used parameters recorded in paleoclimate archives since they link different natural archives via the water cycle tree ring 18 o 18 otr has been widely used for hydroclimate reconstructions in the himalaya however few of them record temperature signals which are dominant in himalaya ice core 18 o we hypothesize that the precipitation amount effect due to the south asian summer monsoon sasm may overprint temperature signals in 18 otr series the purpose of this study is to investigate whether temperature signals could be found in the 18 otr in locations where the influence of sasm is weak we developed a 105 yr 18 otr chronology from the northern slope of the western himalaya which greatly blocks the sasm our 18 otr clearly shows stronger correlations with temperature dominant winter and weak summer than summer precipitation signals it also agrees well with summer soil moisture 18 o simulated by the global isotope model lmdz4 r 0 72 1979 2010 in lmdz4 low winter temperature was found to increase winter snowfall and subsequent snow melt and thus to increase the contribution of winter snowfall to soil moisture in summer at the expense of summer precipitation since winter snowfall is more depleted than summer precipitation this leads to lower summer soil moisture 18 o the temperature signals found in our 18 otr series are consistent with those found in the dasuopu ice core 18 o this implies that 18 otr series from the southwest tibetan plateau tp with a weak monsoon hold great potential to capture temperature signals climate interpretations of 18 o proxies in the himalaya largely depend on the influence of seasonal water from the dominant atmosphere circulation systems of the westerlies or monsoon the 18 o proxies from the monsoon affected region have a higher potential for the reconstruction of boreal summer hydroclimate whereas 18 o proxies from westerly affected sites have a higher potential for temperature reconstructions

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

high elevation shrub ring δ18o on the northern slope of the central himalayas records summer may july temperatures abstract the potential of shrub ring oxygen isotopes sro as a paleoclimatic proxy is not well demonstrated in this study we explored the climate signals embedded in an sro chronology from saga on the northern slope of the central himalayas by correlation analysis with climate variables and comparison with tree ring and or ice core 18o records the saga sro had significant and positive correlations with may july temperatures in both local r 0 43 and moisture source areas r 0 49 during the period 1955 2015 ce while no significant correlations were found with hydroclimatic variables it is also in good agreement with two tree ring 18o series from the southern slope of the central himalayas the source of moisture to the site the temperature signals are further verified by an ice core 18o record from the tanggula mountains on the central tibetan plateau however it shows little similarity with the nearest himalayan ice core 18o record from dasuopu demonstrating temperature signals of different seasons this study suggests that sro could be used as an acceptable climate proxy like tree ring and ice core 18o to broaden the spatial extent of the paleoclimatic records network however we should be cautious when combining different proxies with climate signals of different seasons in paleoclimate studies

deformation temperatures vorticity of flow and strain in the moine thrust zone and moine nappe reassessing the tectonic evolution of the scandian foreland hinterland transition zone abstract examination of deformation temperature 3 d strain and flow vorticity wm in mylonites from the assynt loch more region of the moine thrust zone mtz allows quantitative kinematic and thermal characterization of shearing at the base of the scandian 435 425 ma orogenic wedge quartz microstructures and c axis fabric opening angles from mylonites in the immediate hangingwall and footwall to the moine thrust suggest that deformation temperatures are highest in the eastern part of the assynt region including mylonites close to alkaline intrusive complexes and decrease along strike both to the north stack of glencoul loch more and to the south knockan quartz c and a axis fabrics together with limited 3 d strain data indicate that deformation in both the footwall and hangingwall mylonites dominantly involved plane strain to general flattening although domains of more constrictional flow are identified adjacent to thrust transport parallel lineaments in the overlying moine nappe rigid grain analyses indicate a remarkably constant flow vorticity for tens of kilometers along orogenic strike 40 60 pure shear in both the hangingwall and footwall mylonites integration with previously reported strain and vorticity estimates from the assynt region indicates a 50 75 sub vertical shortening perpendicular to gently dipping foliation that must have been accommodated by either volume loss or extrusion of material toward the synorogenic topographic surface extrusion implies a causal link between upper and lower crustal processes with significant implications for the kinematic and geometric evolution of the scandian wedge

tibetan plateau summer monsoon northward extent revealed by measurements of water stable isotopes a program of individual precipitation events and river water sampling and of water isotopic measurements d 18o was carried out during summer 1996 along a northeast southwest transect of the tibetan plateau the spatial distribution of both 18o and deuterium excess d d 8 18o of the precipitation reveals three distinct regions simulations with a simple isotopic model and seasonal isotopic variations measured at two extreme south and north locations support our interpretation in terms of different summer moisture origins 1 south of the himalayan mountains the moisture provided by the indian monsoon has been recycled over the indian peninsula 2 between the himalayas and the tanggula mountains the oceanic moisture is directly transported from the bay of bengal along the brahmaptra river valley 3 north of the tanggula mountains the moisture is not provided by the monsoon anymore but by continental water recycling

spatial and temporal variability in the stable isotope systematics of modern precipitation in china implications for paleoclimate reconstructions the stable isotopic composition of materials such as glacial ice tree rings lake sediments and speleothems from low to mid latitudes contains information about past changes in temperature t and precipitation amount p however the transfer functions which link 18op to changes in t or p d 18op dt and d 18op dp can exhibit significant temporal and spatial variability in these regions in areas affected by the southeast asian monsoon past variations in 18o and d of precipitation have been attributed to variations in monsoon intensity storm tracks and or variations in temperature proper interpretation of past 18op variations here requires an understanding of these complicated stable isotope systematics since temperature and precipitation are positively correlated in china and have opposite effects on 18op it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions here we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord the strength of these transfer functions in china is investigated using multiple regression analysis of data from 10 sites within the global network for isotopes in precipitation gnip 18op is modeled as a function of both temperature and precipitation the magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence 18op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature and therefore exhibit more negative values in the summer in contrast 18op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between 18op and temperature the sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation comparison with simple linear models 18op as a function of t or p and a geographic model 18op as a function of latitude and altitude shows that the multiple regression model is more successful at reproducing 18op values at sites that are strongly influenced by the summer monsoon the fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally since the southeast asian monsoon intensity is known to exhibit large variations on a number of timescales annual to glacial interglacial and the magnitude and sign of the transfer functions is related to monsoon intensity we suggest that as monsoon intensity changes the magnitude and possibly even the sign of the transfer functions may vary therefore quantitative paleoclimate reconstructions based on 18op variations may not be valid