misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

contribution of cross barrier moisture transport to precipitation in the upper indus river basin abstractthe upper indus river basin is characterised by bi seasonal heavy precipitation falling on the foothills of major mountain ranges hindu kush karakorm himalayas numerical studies have c

deformation microstructures reveal a complex mantle history for polycrystalline diamond 1 detailed quantitative electron backscatter diffraction ebsd analysis of polycrystalline diamond rocks diamondites provides insights into their formation and significance the fine grain size of diamondites is usually attributed to rapid crystallization however ebsd reveals significant intragrain bending distinct low angle boundaries and straight to highly irregular high angle grain boundaries highly deformed grains may be in contact with others showing little or no deformation these features are typical for crystal plastic deformation in which differential stress generates dislocations according to the dominant slip systems in diamond dislocations accumulate to form subgrain boundaries with grain size reduction by rotation of subgrains nucleation and growth of new grains and migration of grain boundaries such features are seen in other polygranular materials such as deformed metals and quartzite deformed at high temperatures during this process interaction with fluids produced interstitial garnets with compositions different from those of the primary inclusions oscillatory cl zoning in diamonds developed through diffusion along subgrain boundaries rather than being a primary growth feature diamondites are thus not simply products of primary crystallization but may be strongly deformed recrystallized and modified integrated ebsd cl and in situ chemical and isotopic analysis provide the spatial control and new insights into mantle processes

characteristics of rain induced landslides in the indian himalaya a case study of the mandakini catchment during the 2013 flood abstract landslides triggered by monsoon rainfall are a recurring hazard that lead to loss of life and cause enormous property and infrastructure damage in the indian himalaya this study is focused on understanding the role of extreme rainfall and physical factors in causing landslides in the indian himalaya particularly in the mandakini catchment where an enormous landslide and flood disaster occurred in june 2013 following a two day extreme rainfall event results indicate that sub daily extreme rainfall depths causing landslides vary with elevation across the catchment antecedent rainfall six days prior to the extreme rainfall event was found to have substantial depths that could have primed the area for landslides except for aspect of slopes the causative factors including land use land cover lithology elevation slope river network distance to roads and total extreme rainfall as a triggering factor were found to be statistically significant in causing landslides in the catchment the final product of the study is a new landslide susceptibility map that better delineates the landslide prone regions in the disaster prone mandakini catchment after the june 2013 extreme rainfall event the map was prepared using logistic regression that shows medium and high susceptibility zones at upper sections of the catchment as well as along the mandakini river and its tributaries where major sacred shrines tourist spots and human establishments are located

earthquake cutoff depth as a possible geothermometer applications to central japan abstract geothermal models of the earth s crust are constructed for eight individual structural units of honshu island japan for each unit thermal models responding to possible property variations are calculated in addition to conductive heat transfer the considered geothermal models account also for the thermal effects of fluid circulation within the crust and tectonic motions across the faults on the basis of these geothermal models theological models of the crust are derived those thermal models are considered as most reliable where there is reasonable correspondence between rheological stratification of the crust and the variations of crustal seismicity it is demonstrated that earthquake cutoff depth serving as a kind of geothermometer can be used as additional information to decrease the uncertainties involved in the geothermal models

the modulation of the subtropical and extratropical atmosphere in the pacific basin in response to the madden julian oscillation abstract the 40 yr ecmwf re analysis era 40 data are combined with a number of novel climatologies to conduct a comprehensive examination of the response of the subtropical and extratropical atmosphere over the pacific basin to an evolving madden julian oscillation mjo event the adopted approach constitutes a symbiosis of a climatological analysis during the northern hemisphere winter from 1979 to 2002 and a case study analysis of a distinct mjo event that occurred in january february 1993 the former is designed to obtain the general characteristics observed during a composite mjo life cycle while the latter is used to provide insight into the instantaneous mechanisms responsible for the observed composite evolution a primary component of the study involves the diagnosis of anomalous wave breaking activity in response to mjo forcing in the form of tropical convection and or upper level divergence wave breaking events are separated by their characteristic life cycles lc1 anticyclonic and lc2 c

the petrological significance of misorientations between grains misorientation analysis quantifies microstructural features in tectonites metamorphic and igneous rocks and allows hypotheses on their formation to be tested the misorientation between two lattices can be expressed by a rotation axis and rotation angle for lattices with symmetry it is conventional to take the minimum angle that enables one lattice to be rotated into the other for a group of lattice measurements two types of misorientation distribution can be calculated selecting random pairs of grains gives the random pair misorientation distribution selecting neighbouring pairs gives the neighbour pair misorientation distribution the forms of both distributions are visualised using histograms or cumulative frequency diagrams they are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry in many rocks the random pair misorientation distribution and neighbour pair misorientation distribution are statistically significantly different quantified using the kolmogorov smirnov test differences between the random pair misorientation distribution and neighbour pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure interactions include 1 reduction in surface energy by lattice alignment we show this may have occurred in garnet clusters in schist and olivine in a cumulate it is well known in metals and may be a common geological process 2 nucleation where those nuclei have influenced the orientation of adjacent nuclei 3 mechanical rotations of facetted grains in compacting crystal mushes so that faces become parallel 4 growth twinning inheritance includes 1 subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes 2 mechanical and transformation related twinning 3 domainal microstructures e g where grains have formed from a few large original grains may give rise to spurious correlations when the orientation data cover more than one domain with this proviso misorientation analysis can be used to investigate many important microstructural processes

temperature dependent grain boundary migration in deformed then annealed material observations from experimentally deformed synthetic rocksalt abstract grain boundary migration between strained substructured grains and newly appearing strain free grains has been observed during static in situ annealing of pre deformed rocksalt in the sem with increasing temperature t the migration velocity increases and the character of grain boundary migration changes as temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates in addition the frequency of migrating boundaries that form traces of a 100 boundary plane of at least one of the crystals involved increases and moving grain boundaries between new and old grains change from highly irregular to smooth straight boundaries at the same time there is a decrease in the influence of the substructure of pre existing strained grains on the grain boundary movement resultant microstructures reflect these changes at 325 350 c the deformed then annealed microstructure is characterized by very irregular grain boundaries a high abundance of 5 50 m scale remnants of old substructured grains within new grains giving a poikilitic microstructure at 350 400 c grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old strained grains are located at former grain boundaries at 400 c grain boundaries between new and old strained grains are straight to smoothly curved the grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations additionally at low annealing temperature impurity solute drag and driving force variations are influential while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks thereby making it is possible to relate microstructural characteristics to the pre annealing and post deformational annealing history

carbonado physical and chemical properties a critical evaluation of proposed origins and a revised genetic model abstract carbonado diamond is the most controversial of all diamond types and is found only in brazil and the central african republic bangui neither an affinity to earth s mantle nor an origin in the crust can be unequivocally established carbonado diamond is at least 3 8 ga old an age about 0 5 ga older than the oldest diamonds yet reported in kimberlites and lamproites on earth derived from neo to mid proterozoic meta conglomerates the primary magmatic host rock has not been identified discovered in 1841 the material is polycrystalline robust and coke like and is best described as a strongly bonded micro diamond ceramic it is characteristically porous which precludes an origin at high pressures and high temperatures in earth s deep interior yet it is also typically patinated with a glass like surface that resembles melting with exotic inclusions of highly reduced metals carbides and nitrides the origin of carbonado diamond is made even more challenging but the challenge is important because a new diamondiferous host rock may be involved and the development of a new physical process for generating diamond is possibly assured the combination of micro crystals and random crystal orientation leads to extreme mechanical toughness and a predicable super hardness the physical and chemical properties of carbonado are described with a view to the development of a mimetic strategy to synthesize carbonado and to duplicate its extreme toughness and super hardness textural variations are described with an emphasis on melt like surface features not previously discussed in the literature but having a very clear bearing on the history and genesis of carbonado selected physical properties are presented and the proposed origins diverse in character and imaginatively novel are critically reviewed from our present knowledge of the dynamic earth all indications are that carbonado is unlikely to be of terrestrial origin a revised model for the origin of carbonado is developed based on 1 new observations which show that white dwarf stars can have diamond cores 2 c rich exoplanets may have diamond bearing mantles and 3 new shock wave experiments on methane suggest that diamond may be present in large gaseous planets such as saturn uranus and neptune where diamond in the core is solid and in jupiter where liquid diamond may be present it is proposed that carbonado diamond was delivered to earth from extra solar sources during the episode of late heavy bombardment 4 1 3 8 ga if the currently held view that r process heavy elements were added as a late veneer to earth through the collision of white dwarfs in kilonova explosions then why not carbonado diamond during this epic event

seismicity in the northeast area of izu peninsula japan comparing with three dimensional velocity structure and temperature distribution of geothermal water abstract seismicity in the northeast area of izu peninsula was compared with the three dimensional p wave velocity structure and the temperature distribution of geothermal water at 400 m below sea level it is found that regional seismicity in the eastern margin of hakone volcano is concentrated within a zone of both high velocity and low temperature surrounded by a low velocity zone at depths of 10 15 km low seismic activity however seems to be associated with a low velocity and high temperature zone at depths of 5 10 km a simple model for brittle ductile transition was applied in order to examine the relationship between seismicity and the seismogenic layer in the region theoretical calculations suggest that the depth of brittle ductile transition becomes gradually shallower with increasing surface temperature and or heat flow accordingly the seismogenic layer becomes gradually thinner from sagami bay to the land area of the northeast izu peninsula this simple model can well explain the seismicity pattern in the study area

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

modeling of anisotropic grain growth in minerals the role of surface energy anisotropy during grain growth is investigated using both physical experiments on octachloropropane and numerical experiments using the elle microstructural modelling system in particular the effects of anisotropy on growth rates grain shapes and lattice preferred orientations are analysed anisotropic growth in thin polycrystalline sheets of octachloropropane is found to systematically remove certain c axis orientations from the sample without obviously modifying the grain shapes by comparison with equivalent numerical experiments we can explain these observations with a simple boundary layer model that treats each side of each grain boundary as an independent system the observed growth exponent in the physical experiment of 0 35 is significantly below the theoretical level of 1 and although the numerical experiments have growth rates as low as 0 68 apparently some other factor which suppresses the growth rate in the octachloropropane was also active the anisotropy of surface energies also leads to an increase in the grain size distribution and when it occurs in rocks with a strong pre existing crystallographic preferred orientation may even lead to the development of a shape preferred orientation which is completely unrelated to the shape of the finite strain ellipsoid corresponding author e mail address bons mail uni mainz de accepted for publication in the hans ramberg volume bulletin of the american geological society bons et al anisotropic grain growth 17 januar 2000 page 2

pseudotachylyte and the development of ultramylonite bands in the saint barthelemy massif french pyrenees abstract in mylonitic gneisses of the saint barthelemy massif in the french pyrenees evidence was found that ultramylonite bands developed by ductile deformation of pseudotachylyte in the gneiss a mylonitic shape fabric was produced by a continuous structural event during retrogression from amphibolite to upper greenschist facies decrease in temperature caused gradual hardening in the gneiss which led to the development of pseudotachylyte bands by intermittent seismic slip these acted as weak zones in which ductile deformation was concentrated a microstructure typical of ultramylonite was produced in these deformed pseudotachylyte bands

a seasonal climatology of rossby wave breaking in the 320 2000 k layer abstract differential advection in rossby waves can lead to potential vorticity pv p contours on isentropic surfaces folding over in latitude py 0 in a process called rossby wave breaking rwb exploring the properties of rwb may shed light on underlying dynamics and enable quantification of irreversible transport a seasonal climatology of py and rwb statistics is presented for the 320 850 k layer using ncep reanalysis data during 1979 2005 and for the 320 2000 k layer using the met office ukmo data during 1991 2003 a primary goal is to depict the spatial extent and seasonality of rwb maxima this analysis shows seven distinct rwb regimes poleward and equatorward of the subtropical westerly jets poleward and equatorward of the stratospheric polar night jets flanking the equator in the stratosphere and mesosphere equatorward of subtropical monsoon anticyclones and the summertime polar stratosphere a striking pv gradient maximum exists at the equator throughout the layer 360 2000 k flanke

thermal regime rheology and seismicity in central japan abstract in the present study geothermal models of the crust for a number of individual structural units of honshu island japan are constructed the depth distribution of crustal seismicity is used as a tool to assess the reliability of the calculated thermal models it is demonstrated that where reliable information is available on cutoffs in seismicity at certain depths the temperature at those depths can be estimated from theological considerations to the accuracy of not worse than from geothermal modelling such temperatures can then be used as reference values in checking the validity of a geothermal model for a region this approach may be especially useful in constructing geothermal models for tectonically disturbed areas with non steady state thermal conditions

radiation induced diamond crystallization origin of carbonados and its implications on meteorite nano diamonds abstract ten carbonados from central africa were studied for u th pb systematics to extract u th and pb from the samples we developed a cold combustion technique wherein diamond was burnt in liquid oxygen the technique gave low blanks 25 50 pg for pb 3 pg for u and 5 pg for th after very thorough acid treatments of the carbonados with hot hno3 hf and hcl over one week most of u th and pb were removed from the samples lead in the acid leached diamonds was highly radiogenic 206pb 204pb up to 470 however the amounts of u and th in the acid leached diamonds are too low to account for the radiogenic pb even if we assume 4 5 ga for the age of the diamonds therefore we conclude that the radiogenic pb was implanted into the diamonds from surroundings by means of recoil energy of radioactive decays of u and th from the radiogenic lead isotopic composition we estimate a minimum age of 2 6 ga and a maximum age of 3 8 ga for the formation of the carbonados the above findings of the implantation of recoiled radiogenic pb into carbonados is consistent with the process of radiation induced crystallization which was proposed for carbonado by kaminsky 1987 we show from some theoretical considerations that when highly energetic particles such as those emitted from radioactive decay of u and th interact with carbonaceous materials they give rise to cascades of atomic disturbance over regions of about a few nanometer and the disturbed atoms are likely to recrystallize to form micro diamonds because of increasing surface energy due to small size the radiation induced diamond formation mechanism may be relevant to the origin of nano diamonds in primitive meteorites

multiscale aspects of the storm producing the june 2013 flooding in uttarakhand india abstractconditions producing disastrous flooding in uttarakhand india in june 2013 differed from conditions that produced other notorious floods in the himalayan region in recent years during the week preceding the uttarakhand flood deep convection moistened the mountainsides making them vulnerable to flooding however the precipitation producing the flood was not associated with a deep convective event rather an eastward propagating upper level trough in the westerlies extended abnormally far southward with the jet reaching the himalayas the south end of the trough merged with a monsoon low moving westward across india the merged system produced persistent moist low level flow oriented normal to the himalayas that advected large amounts of water vapor into the uttarakhand region the flow was moist neutral when it passed over the himalayan barrier and orographic lifting produced heavy continuous rain over the region for 2 3 days the precipitation was largely stratiform in nature although emb

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

the effect of different second phase particle regimes on grain growth in two phase aggregates insights from in situ rock analogue experiments the aim of the study was to investigate the effect of rigid second phases on grain growth of a matrix phase for this purpose variable mixtures of norcamphor as the matrix phase with glass beads 0 08 0 51 volume fraction as second phase were used to perform see through rock analogue experiments under static conditions at constant temperatures 50 c irrespective of the second phase content grain size evolution of all mixtures can be subdivided into a stage of continuous grain growth a transient stage and a stage of a finally stabilized grain size on the grain scale the second phases affect the migrating grain boundaries either by pinning by single particles by multiple particles or even by particle clusters summed up over the entire aggregate these pinning regimes affect the average bulk grain size of the matrix grains such that the changes in matrix grain size directly correlate with the amount of second phases their dispersion and their degree of clustering in this way the matrix grain size decreases with increasing second phase content which can be expressed as a zener relationship originating from the modification of an ordinary grain growth law a new mathematical expression is defined which allows the calculation of changes in the matrix grain size as a function of different second phase volume fractions and particle sizes such models will be helpful in the future to predict microstructural changes in polymineralic rocks at depth

monsoon extratropical circulation interactions in himalayan extreme rainfall extreme precipitation and flood episodes in the himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture laden tropical monsoon circulation while previous studies have documented precipitation characteristics in the himalayan region during severe storm cases a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted in this study a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the western himalayas weh during the period 1979 2013 our results provide evidence for a common large scale circulation pattern connecting the extratropics and the south asian monsoon region which is favorable for extreme precipitation occurrences in the weh region this background upper level large scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough a blocking high over western eurasia and an intensifying tibetan anticyclone it is further seen from our analysis that the key elements of monsoon midlatitude interactions responsible for extreme precipitation events over the weh region are 1 midlatitude rossby wave breaking 2 west northwest propagation of monsoon low pressure system from the bay of bengal across the indian subcontinent 3 eddy shedding of the tibetan anticyclone 4 ageostrophic motions and transverse circulation across the himalayas and 5 strong moist convection over the himalayan foothills furthermore high resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the weh region

mechanisms of crustal deformation thirty sixthwilliam smith lecture the energy source for crustal deformation is isotopic heating and secular cooling of the mantle in a true solid heat would be lost to the surface by conduction however solid state creep processes allow the earth s solid mantle to exhibit a fluid behaviour thus thermal convection can convert heating into directed motion variations in temperature lead to variations in densitythrough thermal expansion and contraction although the resultant body forces are vertical horizontal variations in temperature lead to horizontal body forces at an ocean ridge the variations in the thickness of the lithosphere lead to the elevation of the ridge the result is a substantial horizontal ridge push force this force along with the trench pull force on the descending lithosphere is the primary force driving plate tectonics lithospheric thinning must occur beneath continental rifts and plateau uplifts i suggest that lithospheric thinning is caused by the diapiric penetration of hot asthenospheric rock to the crust mantle boundary this penetration may also cause lithospheric stoping and plateau uplifts lithospheric thinning leads to large tensional stresses above the zone of thinning these forces are generally much larger than the compressional forces generated by crustal thinning the forces generated by lithospheric thinning are quite large and may be responsible for the propagation of continental rifts in island arcs and andean type orogenic belts both lithospheric thinning and crustal thickening result in large tensional forces probably the most complex zone of crustal deformation is the continental collision variations in types of continental collisions are discussed

stress and flow beneath island arcs summary the flow pattern stress distribution topography and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the aleutian arc the results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench in models with simple distributions of rheological parameters the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab models with the resistance to flow thus reduced had outer rises deep trenches horizontal tension seaward of the trench horizontal compression under the trench and downdip tension in the slab free air gravity anomalies which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow were not fit excellently by any of the models in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc an alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench this is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism

post deformational annealing at the subgrain scale temperature dependent behaviour revealed by in situ heating experiments on deformed single crystal halite the dynamics of substructures which encompass all structures present at the subgrain scale were investigated by static in situ annealing experiments deformed single crystal halite was annealed

impacts of indo pacific sea surface temperature anomalies on the summer monsoon circulation and heavy precipitation over northwest india pakistan region during 2010 abstractquite a few studies have documented the evolution of monsoon synoptic systems and midlatitude atmospheric blocking associated with the recent heavy precipitation and floods over northwest pakistan during 2010 this period also witnessed a very unusual indo pacific sea surface temperature sst evolution with a strong la nina event in the pacific substantial indian ocean warming and a negative indian ocean dipole event together with significant enhancement of precipitation over both the equatorial western pacific ocean and the eastern indian ocean here the authors perform a suite of high resolution atmospheric general circulation model experiments to investigate the influence of indo pacific sst anomalies on the south asian monsoon circulation and heavy precipitation over pakistan and adjoining northwest india during 2010 the realistic simulation of these rainfall anomalies using observed ssts motivated the authors to explore the specific influence of indian ocean and pacific sst anomalies thr

some garnet microstructures an illustration of the potential of orientation maps and misorientation analysis in microstructural studies the microstructures of two contrasting garnet grains are mapped using automated electron backscatter diffraction in both cases there is a very strong crystallographic preferred orientation with measurements clustered round a single dominant orientation each garnet grain is divided into domains with similar orientations limited by boundaries with misorientations of 2 or more in both samples most of misorientation angles measured across orientation domain boundaries are significantly lower than those measured between random pairs of orientation domains one sample is a deformed garnet that shows considerable distortion within the domains lines of orientation measurements within domains and across domain boundaries show small circle dispersions around rational crystallographic axes the domain boundaries are likely to be subgrain boundaries formed by dislocation creep and recovery the second sample is a porphyroblast in which the domains have no internal distortion and the orientation domain boundaries have random misorientation axes these boundaries probably formed by coalescence of originally separate garnets we suggest that misorientations across these boundaries were reduced by physical relative rotations driven by boundary energy the data illustrate the potential of orientation maps and misorientation analysis in microstructural studies of any crystalline material

a multiscale analysis of the extreme weather events over western russia and northern pakistan during july 2010 abstractthis manuscript presents a detailed multiscale analysis using observations model analyses and ensemble forecasts of the extreme heat wave over russia and historic floods over pakistan during late july 2010 with an emphasis on the floods over northern pakistan the results show that recirculation of air and dynamically driven subsidence occurring with the intensification of the blocking anticyclone in late july 2010 were key factors for producing the exceptionally warm temperatures over western russia downstream energy dispersion from the blocking region led to trough deepening northwest of pakistan and ridge building over the tibetan plateau thereby providing the linkage between the russian heat wave and pakistan flood events on the large scale in agreement with previous studies the extratropical downstream energy dispersion and enhanced convective outflow on the large scale associated with the active phase of the madden julian oscillation facilitated the formation of an intense upper level

intragranular dynamic recrystallization in naturally deformed calcite marble diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization abstract intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains intragranular recrystallized grains within large twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study lattice distortions low angle boundaries and some high angle boundaries 15 in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb accommodated dislocation creep involving subgrain rotation recrystallization changes in the ratio of host and twin domain as the deformation zone is entered show that twin boundary migration also occurred recrystallized grains have similar sizes 10 60 m to subgrains suggesting that they formed by subgrain rotation however within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15 and misorientation axes are randomly oriented moreover recrystallized grain orientations average around the porphyroclast orientation we suggest that the recrystallized grains once formed are able to deform partly by diffusion accommodated grain boundary sliding which is consistent with predictions made from lab flow laws

the effect of pre tectonic reaction and annealing extent on behaviour during subsequent deformation insights from paired shear zones in the lower crust of fiordland new zealand granulite facies pargasite orthogneiss is partially to completely reacted to garnet granulite either side of narrow 20 mm felsic dykes in fiordland new zealand forming 10 80 mm wide garnet reaction zones the metamorphic reaction changed the abundance of minerals and their shape and grain size distribution the extent of reaction and annealing temperature related coarsening and nucleation is greatest close to the dykes whereas further away the reaction is incomplete as a consequence grain size and the abundance of garnet decreases away from the felsic dykes over a few centimetres the aspect ratios of clusters of s1 pyroxene and pargasite in the orthogneiss which are variably reacted to post s1 garnet decrease from high in the host to near equidimensional close to the dyke post reaction deformation localized in the fine grained partially reacted areas this produced a pattern of paired shear zones located at the outer parts of the garnet reaction zone our study shows that grain size sensitive deformation occurs where the grain size is sufficiently reduced by metamorphic reaction the weakening of the rock due to the change in grain size distribution outweighs the addition of nominally stronger garnet to the assemblage

a three dimensional numerical study of an oklahoma squall line containing right flank supercells abstract a nonhydrostatic numerical mesoscale model has been applied to the study of an oklahoma squall line with initial conditions taken from the oklahoma kansas preliminary regional experiment for storm central pre storm data for 7 may 1985 the model reproduced features typical of organized propagating convection occurring during spring and summer in this region namely a squall line mesoscale convective system containing strong right flank convection resembling many documented cases the alignment and motion of the system change during its development and are determined by the ambient wind at three levels the steering level of the mature cells the level of free convection and the surface layer three persistent right flank cells had a characteristic rightward propagation relative to the mean wind shear vector their propagation occurred through successive mergers of cells that had formed at a downdraft outflow convergence front and were similar to the flanking line often seen to the south of str

the role of upper level dynamics and surface processes for the pakistan flood of july 2010 in july and august 2010 floods of unprecedented impact afflicted pakistan the floods resulted from a series of intense multi day precipitation events in july and early august at the same time a series of blocking anticyclones dominated the upper level flow over western russia and breaking waves i e equatorward extrusions of stratospheric high potential vorticity pv air formed along the downstream flank of the blocks previous studies suggested that these extratropical upper level breaking waves were crucial for instigating the precipitation events in pakistan here a detailed analysis is provided of the extratropical forcing of the precipitation piecewise pv inversion is used to quantify the extratropical upper level forcing associated with the wave breaking and trajectories are calculated to study the pathways and source regions of the moisture that precipitated over pakistan limited area model simulations are carried out to complement the lagrangian analysis the precipitation events over pakistan resulted from a combination of favourable boundary conditions with strong extratropical and monsoonal forcing factors above normal sea surface temperatures in the indian ocean led to an elevated lower tropospheric moisture content surface monsoonal depressions ensured the transport of moist air from the ocean towards northeastern pakistan along this pathway the air parcel humidity increased substantially 60 90 of precipitated moisture via evapotranspiration from the land surface extratropical breaking waves influenced the surface wind field substantially by enhancing the wind component directed towards the mountains which reinforced the precipitation

the numerical simulation of an unbalanced jetlet and its role in the palm sunday 1994 tornado outbreak in alabama and georgia abstract meso beta scale numerical model simulations and observational data are synthesized in an effort to develop a multistage paradigm for use in forecasting tornadic convection in the southeastern united states the case study to be utilized as an example of the multistage sequence of events is the palm sunday 1994 outbreak which culminates with the development of an unbalanced mesoscale jet streak or jetlet that focuses a given region for significant values of low level vertical wind shear low level confluence and vertical vorticity midtropospheric cooling and storm relative helicity the five stage paradigm includes 1 the existence of a jet exit region accompanying a deep balanced thermally indirect circulation south of the outbreak and a return branch ageostrophic low level southerly jet both typically accompanying the subtropical jet stream and the leading edge of hot continental air 2 the existence of a jet entrance region accompanying a deep balanced thermally direct circulation north of

the extratropical transitions of hurricanes felix and iris in 1995 abstract the extratropical transitions of hurricanes felix and iris in 1995 are examined and compared both systems affected northwest europe but only iris developed significantly as an extratropical system in both cases the hurricane interacts with a preexisting extratropical system over the western atlantic the remnants of the exhurricanes can be identified and tracked across the atlantic as separate low level potential vorticity pv anomalies the nature of the baroclinic wave involved in the extratropical transition is described from a pv perspective and shown to differ significantly between the two cases the role of vertical shear in modifying the hurricane structure during the early phase of the transition is investigated iris moved into a region of strong shear the high pv tower of iris developed a marked downshear tilt felix moved into a vertically sheared environment also but the shear was weaker than for iris and the pv tower of felix did not tilt much iris maintained its warm core struc

quantification of mineral behavior in four dimensions grain boundary and substructure dynamics in salt here we present the first four dimensional time and three dimensional space resolved experiment on a strongly deformed geological material results show that even complicated microstructures with large continuous and discontinuous changes in crystallographic orientation can be resolved quantitatively the details that can be resolved are unprecedented and therefore the presented technique promises to become influential in a wide range of geoscientific investigations grain and subgrain scale processes are fundamental to mineral deformation and associated earth dynamics and time resolved observation of these processes is vital for establishing an in depth understanding of the latter however until recently in situ experiments were restricted to observations of two dimensional surfaces we compared experimental results from two dynamic in situ annealing experiments on a single halite crystal a 2d experiment conducted inside the scanning electron microscope and a 3d x ray diffraction experiment this allowed us to evaluate the possible effects of the free surface on grain and subgrain processes the extent to which surface effects cause experimental artifacts in 2d studies has long been questioned our study shows that although the nature of recovery processes are the same the area swept by subgrain boundaries is up to 5 times larger in the volume than observed on the surface we suggest this discrepancy is due to enhanced drag force on subgrain boundaries by thermal surface grooving our results show that while it is problematic to derive absolute mobilities from 2d experiments derived relative mobilities between boundaries with different misorientation angles can be used

the initiation of strain localisation in plagioclase rich rocks insights from detailed microstructural analyses abstract in order to shed light on the cause for onset of strain localisation in plagioclase rich rocks we have performed detailed microstructural analyses on a sheared anorthosite leucogabbro using optical microscopy electron backscatter diffraction ebsd and chemical analyses the analysed sample is from an archaean unit sw greenland deformed at lower to mid crustal conditions t 675 700 c and moderate pressure the initial deformation occurred dominantly by dislocation creep and the grain size was reduced primarily by subgrain rotation recrystallisation recrystallised plagioclase grains average size 80 m are dominantly found in i clusters ii lenses and iii continuous bands subparallel to shear zone boundaries recrystallised grains in clusters and lenses display inherited crystallographic orientations their bulk crystallographic preferred orientation cpo is random however crystallographic characteristics show that parent and daughter grains have the same misorientation axes and possibly the same active slip systems recrystallised grains in continuous bands show a cpo with a single dominant active slip system 001 aligned with the structural xyz framework for these parent and daughter grains misorientation axes are random and the dominant slip system is different grain rotations of recrystallised grains are traceable back to the orientation of the adjacent porphyroclast we infer that the cause for strain localisation is recrystallisation and development of a cpo in continuous recrystallised bands microstructures in combination with misorientation and slip system analyses indicate a possible change from dislocation creep in clusters and lenses to dislocation accommodated grain boundary sliding disgbs in continuous bands this inferred shift in dominant deformation mechanism would lower the strength of the shear zone

microstructural evolution during initial stages of static recovery and recrystallization new insights from in situ heating experiments combined with electron backscatter diffraction analysis we present in situ observations performed using electron backscatter diffraction of static recovery and recrystallization processes occurring in a plastically deformed geological material namely rocksalt static heating experiments carried out in a scanning electron microscope at temperatures of up to 450 c allowed direct detailed observations of grain boundary migration between substructured grains in deformed polycrystalline samples contrary to expectations crystallographic orientation maps reveal that behind slowly migrating grain boundaries new subgrain boundaries form while pre existing subgrain boundaries are sometimes inherited moreover the crystallographic character especially the preferred orientation of misorientation axes of the new substructures reflects the character of the previous deformation history these results imply that substructural features such as subgrain misorientation distributions may be relatively robust indicators of deformation mechanisms and conditions even in tectonites that have undergone late static recrystallization in addition our observations suggest that the process of static grain boundary migration does not necessarily reset earlier deformation microstructures as commonly assumed the kinematic observations of boundary migrations are inconsistent with simple models in which migration is achieved by single atoms jumping across the boundary

inelastic models of lithospheric stress i theory and application to outer rise plate deformation summary outer rise stress distributions determined in the manner that mechanical engineers evaluate inelastic stress distributions within conventional materials are contrasted with those predicted using simple elastic plate models that are frequently encountered in studies of outer rise seismicity this comparison indicates that the latter are inherently inappropriate for studies of intraplate earthquakes which are a direct manifestation of lithospheric inelasticity we demonstrate that the common practice of truncating elastically superimposed stress profiles so that they are not permitted to exceed laboratory based estimates of lithospheric yield strength will result in an accurate characterization of lithospheric stress only under relatively restrictive circumstances in contrast to elastic plate models which predict that lithospheric stress distributions depend exclusively upon the current load inelastic plate models predict that stress distributions are also significantly influenced by the plate loading history and in many cases this influence is the dominant factor in determining the style of potential seismicity e g thrust versus normal faulting numerous intuitive interpretations of outer rise earthquakes have been founded upon the implicit assumption that a unique relationship exists between a specified combination of plate curvature and in plane force and the resulting lithospheric stress distribution we demonstrate that the profound influence of deformation history often invalidates such interpretations finally we examine the reliability of yield envelope representations of lithospheric strength that are constructed on the basis of empirically determined frictional sliding relationships and silicate plastic flow laws although representations of this nature underestimate the strength of some major interplate faults such as the san andreas they appear to represent a reliable characterization of the strength of intraplate oceanic lithosphere

dynamics of breaks in the indian summer monsoon abstract in this paper the authors present results of diagnostic analysis of observations and complementary experiments with a simple numerical model that enable them to synthesize the morphology and dynamics of breaks in the indian summer monsoon ism almost one week ahead of the onset of a break spell over india a monotonically decreasing trend in convective activity is found to occur over the bay of bengal in response to a steady eastward spreading of dry convectively stable anomalies from the equatorial indian ocean a major intensification of the convectively stable anomalies over the bay of bengal is seen about 2 3 days prior to commencement of a monsoon break both observations and modeling experiments reveal that rapid northwest propagating rossby waves are triggered in response to such a large strengthening of the convectively stable anomalies it is shown that an abrupt movement of anomalous rossby waves from the bay of bengal into northwest and central india marks the initiation of a break

the influence of phase and grain size distribution on the dynamics of strain localization in polymineralic rocks abstract deformation microstructures of a quartzo feldspathic pegmatite deformed at mid crustal levels allow the study of the dynamics of strain localization in polymineralic rocks strain localization results from i difference in grain sizes between phases both original and obtained during fluid present reactions and ii initial compositional banding due to original difference in grain size stress concentrates in the initially finer grained phases resulting in their intense grain size reduction via subgrain rotation recrystallization sgr when the grain size is sufficiently reduced through either deformation or interphase coupled dissolution precipitation replacement of the coarse grained feldspar aggregates start to deform by dominantly diffusion accommodated grain boundary sliding gbs phase mixing inhibits grain growth and sustains a grain size allowing gbs consequently discontinuous microscale shear zones form locally within initially coarse grained areas at the same time difference in strain rate between feldspar rich and quartz rich domains needs to be accommodated at domain boundaries this results in the formation of continuous mesoscale shear zones deformed by gbs once these are formed deformation in the coarse grained parts is arrested and strain is mainly accommodated in the mesoscale shear zones resulting in superplastic behaviour consistent with diffusion creep

what happens to deformed rocks after deformation a refined model for recovery based on numerical simulations deformation in large parts of the middle crust results in strained rocks consisting of grains with variable dislocation densities and microstructures which are characterized by gradual distortion

scale interaction during an extreme rain event over southeast india the major rains and floods over south east india during october through december of 2015 are addressed in the context of atmospheric scale interactions in the frequency domain some of the salient observational features of this period include i the major el nino of 2015 ii the stretch of lower tropospheric easterlies from the region of the warm sea surface temperature anomalies westwards to the east coast of india iii presence of shear flow instability in the presence of convection along a long stretch of the easterly wind belt from the eastern pacific ocean to the eastern bay of bengal iv large conversions of horizontal shear vorticity to curvature vorticity along this stretch of easterly trades where these rain producing storms were forming v an active iso time scale oscillation in the wind field that alternated between cyclonic and anticyclonic phases over south east india during this period of heavy rains vi active quasi biweekly oscillation that provides alternating onshore and offshore winds during this same period the iso and the quasi biweekly components contribute to the enhancement of the moisture supply from the bay of bengal during the extreme rain events the synoptic scale receives its energy largely from organized convection within these disturbances on horizontal scales of the order of 2500 km other aspects such as the role of the sea surface temperatures of the bay of bengal and the role of gill s antisymmetric heat source of the el nino are also examined in this study

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

evidence for dominant grain boundary sliding deformation in greenschist and amphibolite grade polymineralic ultramylonites from the redbank deformed zone central australia abstract microstructural and textural investigations by scanning sem and transmission electron microscopy tem techniques have been performed on samples taken across two quartzo feldspathic mylonite zones from the redbank deformed zone central australia one has been deformed at greenschist facies gs the second at amphibolite facies am conditions with increasing strain the rock type changes from protomylonite to mylonite to ultramylonite the protomylonites and mylonites consist of alternating quartz and polymineralic quartz feldspar bands at the highest strains a homogeneous fine grained polymineralic ultramylonite occurs shear zone geometry and microscale structures indicate that these ultramylonites experienced higher strains and were weaker than the encapsulating protomylonites and mylonites tem and sem studies of the ultramylonites reveal a rectangular to square grain shape a continuous alignment of grain and interphase boundaries across several grain diameters a grain size gs 0 5 m am 5 11 m less than the equilibrium subgrain size and open and void containing grain and interphase boundaries analysis of local textures by electron back scatter diffraction ebsd in the sem showed a very weak crystallographic preferred orientation cpo for the quartz the grain misorientation relationships are not consistent with dislocation creep being the dominant deformation mechanism all structures are of the type expected if grain boundary sliding processes had contributed significantly to the deformation consequently the deformation of such quartzo feldspathic rocks and by implication the rheology of the redbank deformed zone must have been controlled by the mechanical properties of these fine grained polymineralic ultramylonites deforming by grain boundary sliding processes this is in contrast to the pure quartz bands which deformed by dislocation creep mechanisms and were less important in the rheology of the redbank deformed zone

rheological implications of the strong seismic reflector in the kakkonda geothermal field japan abstract we re processed the seismic reflection survey data of the kakkonda geothermal field the pre stack migration delineates a strong and continuous reflector between 1800 and 2800 m depth below which formations are not reflective earthquake data exhibit seismicity in the upper crust the lower boundary of seismogenic layer is interpreted as the brittle ductile transition the thermal structure is thought to be the major factor controlling its depth we compared the strong reflector with the thermal and rheological structure from drillholes the depth of the reflector corresponds to the top of the highly very highly fractured zone observed from formation microscanner imagery fmi logging in the miocene formations the density of fracture in the kakkonda granite is very low suggesting that granite corresponds to the nonreflective zone the temperature depth profile of well wd 1a shows that the temperature at the highly very highly fractured zone is about 350 c this corresponds to a hydrothermal convection zone filled with two phase geothermal fluid the cut off depth of seismicity that indicates the brittle ductile transition lies at the isotherm of 300 350 c near the reflector we conclude that the strong seismic reflector is a strong contrast in acoustic impedance at the top of the fractured layer the fractured layer could be a decoupling plane caused by different tectonic behaviors between the upper brittle and the lower ductile layers or a dehydration front by thermal diffusion the similarity between the strong reflector and k horizon the strong reflector found in southern tuscany italy suggests that the p wave reflector at the top of highly fractured zone at the brittle ductile transition be common in areas with magmatic activity

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

dynamical response of the south asian monsoon trough to latent heating from stratiform and convective precipitation simulation experiments using a simplified atmospheric gcm and supplementary diagnostic analyses of observations are performed to understand how the south asian monsoon trough mt responds dynamically to latent heating from mesoscale convective systems mcss observations reveal that the mt during active monsoons is characterized by a deep cyclonic vorticity extending from the surface to 350 hpa and organized mcss covering over 3500 4000 km along the indo gangetic plains the mcss during active monsoons are composed of a relatively higher abundance of stratiform type precipitation mostly nimbostratus as compared to the convective type the results suggest that a stratiform type heating profile is very effective in promotingupward development of continental scale cyclonic circulation well above the midtroposphere over the mt region the vertical development involves a dynamical uplift of the layer of cyclonic circulation and is induced by midlevel 600 500 hpa convergence and vorticity stretching above 500 hpa by varying the population of stratiform and convective rain types in the simulation the horizontal scale of midlevel vorticity response is shown to increase significantly with stratiform population in contrast the midlevel response is more localized when the mcs is dominated by deep convective clouds for large stratiform populations the midlevel responseis found to extend far westward up to the northernflanks of the africanitcz indicativeof rossby wave dispersion of pv anomalies that are generated near the level of maximum heating gradient from the present findings one can conclude that the vertical deepening of mt during active monsoons is not merely a localized phenomenon instead it represents a large scale dynamical response to organized mcss that exert pivotal influence on the upward development of cyclonic circulation well above the midtroposphere

on the anomalous precipitation enhancement over the himalayan foothills during monsoon breaks an intriguing feature associated with breaks in the indian summer monsoon is the occurrence of intense flood producing precipitation confined to central eastern parts of the himalayan ceh foothills and north eastern parts of india past studies have documented various large scale circulation aspects associated with monsoon breaks however the dynamical mechanisms responsible for anomalous precipitation enhancement over ceh foothills remain unclear this problem is investigated using diagnostic analyses of observed and reanalysis products and high resolution model simulations the present findings show that the anomalous precipitation enhancement over the ceh foothills during monsoon breaks emerges as a consequence of interactions between southward intruding mid latitude westerly troughs and the south asian monsoon circulation in its weak phase these interactions facilitate intensification of mid tropospheric cyclonic vorticity and strong ascending motion over the ceh foothills so as to promote deep convection and concentrated rainfall activity over the region during monsoon breaks mesoscale orographic effects additionally tend to amplify the vertical motions and precipitation over the ceh foothills as evidenced from the high resolution model simulations it is further noted from the model simulations that the coupling between precipitation and circulation during monsoon breaks can produce nearly a threefold increase of total precipitation over the ceh foothills and neighborhood as opposed to active monsoon conditions

the mesoscale forcing of a midlatitude upper tropospheric jet streak by a simulated convective system part i mass circulation and ageostrophic processes abstract the mutual forcing of a midlatitude upper tropospheric jet streak by organized mesoscale adiabatic and diabatic processes within a simulated convective system scs is investigated using isentropic diagnostics results from a three dimensional numerical simulation of an scs are examined to study the isallobaric flow field modes of dominant ageostrophic motion and stability changes in relation to the mutual interdependence of adiabatic processes and latent heat release isentropic analysis affords an explicit isolation of a component of isallobaric flow associated with diabatic processes within the scs prior to convective development within the simulation atmospheric destabilization occurs through adiabatic ageostrophic mass adjustment and low level convergence in association with the preexisting synoptic scale upper tropospheric jet streak the scs develops in a baroclinic zone and quickly initiates a vigorous mass circulation by the mature stage a pronounced vertical couplet of low level

rheology of two phase systems a microphysical and observational approach abstract ductile shear zones commonly contain distinctive bands of high strain rock characterized by intimately mixed fine grained two phase or polyphase material these ultramylonite bands are weaker than the surrounding material and may play a critical role in strain localization how such zones develop how the phases become evenly dispersed the bulk rheology and the controls on grain size are all unclear the following generic scenario may resolve some of these questions 1 dislocation creep and dynamic recrystallization cause grain size reduction commonly the recrystallized grain sizes of the two phases differ 2 grain size reduction causes a switch to grain boundary diffusion creep which requires grain boundary sliding diffusion allows one phase to fill spaces that open between grains of the other this will happen most rapidly in the finer grained phase the grain size of the resulting mixture is therefore controlled by that of the finer grained phase this leads to mixing and dispersion of the two phases producing a fine grained evenly dispersed two phase aggregate 3 the bulk rheology will be controlled by grain boundary diffusion creep of the two phases with the grain size controlled by the finer grained phase bulk flow laws can be developed for quartz feldspar and olivine orthopyroxene ultramylonites based on these concepts using appropriate mixing laws

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

the normal grain growth behaviour of nominally pure calcitic aggregates the normal grain growth behaviour of four different but all nominally pure calcite powders 99 analytic grade calcite 99 7 chalk 99 97 crushed iceland spar 99 95 chelometric grade calcite has been investigated as a function of temperature 550 600 650 700 c and confining pressure 100 190 mpa under both dry and hydrostatic pfluid ptotal conditions the initial particle size of both the analytic grade and chelometric grade calcite was about 5 m and that of the chalk was about 3 m while the experiments on the iceland spar were conducted on powders of three different initial particle sizes 3 4 7 5 38 5 m on each material at each pressure temperature condition 6 to 15 experiments equally spaced in log time from 15 minutes to 50 days were conducted under dry conditions all four materials recrystallized to aggregates which contained less than 2 porosity and which had a grain size of between 4 and 20 m depending on the initial particle size subsequently the aggregates coarsened by normal grain growth with the kinetics of the growth process being controlled by the rate at which the grain boundaries could drag the residual pores with them as they migrated under nominally identical conditions both the mechanism and rates of pore drag differed greatly for the different materials implying that this process is highly sensitive to trace solute impurity concentrations this sensitivity renders the task of providing a systematic account of dry calcite grain growth kinetics highly problematic under hydrostatic conditions all the powders followed the same normal grain growth kinetics in which the growth process was rate controlled by diffusion through the pore fluid on the grain boundaries an activation enthalpy of 162 6 kj mol 1 and an activation volume of 34 35 cm3 mol 1 was obtained for this process

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

on the direction of rossby wave breaking in blocking the direction of rossby wave breaking at the onset of large scale atmospheric blocking events is shown to relate closely to its position relative to the location of the climatological storm tracks using era interim reanalysis data from october 1989 to march 2009 and a dynamically based blocking index rossby wave breaking is shown to occur preferentially cyclonically to the north and anticyclonically to the south of the average storm tracks location therefore the results support existing theory on the relation between rossby wave breaking direction and barotropic shear of the background wind the further away from the storm tracks the breaking occurs the stronger this preference in breaking direction regional differences can also be explained for the european region on average 70 of the detected blocking took place after anticyclonic rossby wave breaking event that occurred on average 6 south of the climatological storm tracks position over western pacific wave breaking prior to blocking occurs predominantly cyclonically and on average 6 north of the storm tracks differences in blocking duration and intensity are found to be within estimated error margins at most longitudes except for the atlantic europe sector where the blocking events following anticyclonic blocking are also the strongest

effect of surface orientation on dissolution rates and topography of caf2 this paper reports how during dissolution differences in surface chemistry affect the evolution of topography of caf2 pellets with a microstructure similar to uo2 spent nuclear fuel 3d confocal pr

depth and evolution of a silicic magma chamber melting experiments on a low k rhyolite from usu volcano japan we estimated the depth of the magma chamber system beneath usu volcano one of the most active volcanoes injapan by melting experiments on the eruptive product of the ad 1663 plinian eruption us b pumice this pumice is a low k rhyolite with a k2o content of only 1wt the experiments were conducted using internally heated pressure vessels at 98 392mpa and 700 9008c under nickel nickel oxide nno buffered and water saturated conditions the pre eruptive conditions of the 1663 eruption were estimated to be 780 208c and around 200 250mpa the phase equilibria mineral compositions plagioclase orthopyroxene and fe ti oxides melt composition and melt fraction are all in agreement with this conclusion this pressure corresponds to a depth of 8 10 km assuming a lithostatic condition with an appropriate crustal density structure the magma was at near water saturated conditions deviation between the estimated pressure and the true total pressure was estimated to be less than 50mpa the us b magma was under very uniform conditions with a temperature variation of less than c 208c deduced from the narrow range of the phase equilibrium conditions crystallizing orthopyroxene without quartz and the homogeneous composition of plagioclase c an 41 45 we also estimated the pre eruptive conditions of post 1663 eruptions where it has been proposed that two magmas high p and low p members mixed prior to each eruption the pressure of the deep magma was also around 200 250mpa whereas that of the shallow magma was estimated to be 100 150mpa 4 6 km depth according to the pressure dependence of the plagioclase composition obtained in our experiments thus there appear to be two magma chambers beneath usu volcano our estimate is consistent with geophysical observations made during the 2000 eruption including identification of an inflation and deflation source at a depth of 10 km a low frequency 12 s tremor source at a depth of 5 6 km and an earthquake swarm at a depth of less than 4 km the depth of the rhyolitic magma chamber 8 10 km is deeper than the level of neutral buoyancy for the magma and is comparable with that of mafic magma that existed beneath the rhyolitic magma this suggests that the depth of the 8 10 km deep magma chamber was controlled by the emplacement of the mafic magma and that the rhyolitic magma was produced at that depth when compared with other silicic magma systems the usu magma system has similar characteristics including a similar pre eruptive pressure of around 200mpa and a pressure decrease with time suggesting upward magma movement towards a neutral buoyancy level the low potassium content of the usu magma prohibited crystallization of biotite k feldspar or hornblende which are common phases in magmas with intermediate to high potassium contents the absence of hydrous minerals at near liquidus conditions may cause a rapid increase in water content

planetary wave breaking and nonlinear reflection seasonal cycle and interannual variability abstract forty six years of daily averaged ncep ncar reanalysis data are used to identify the occurrence of planetary wave breaking pwb in the subtropical upper troposphere as large amplitude waves propagate into the subtropics where the zonal flow is weak they may break pwb is diagnosed by observing the large scale meridional overturning of potential vorticity pv contours on isentropic surfaces near the subtropical tropopause pwb occurs most often during summer and almost exclusively over the subtropical ocean basins in the northern hemisphere the seasonal evolution of the zonal flow and the associated latitudinal pv gradient regulates the location and frequency of pwb significant interannual variability in pwb is associated with well known modes of climate variability one of the most interesting dynamical consequences of pwb is the possibility of nonlinear reflection poleward out of the wave breaking region modeling studies have found nonlinear reflection following pwb observations show

eddy shedding from the upper tropospheric asian monsoon anticyclone abstract the authors investigate the transient behavior of the asian monsoon anticyclone in the summertime upper troposphere for the four northern summers 1987 90 the evolution of potential vorticity near the tropopause shows the development of westward migrating anticyclones breaking off from the main anticyclone a few times each summer these disturbances are relatively shallow being confined to the upper troposphere

is northern honshu a microplate abstract seismic slip vectors along the japan trench the eastern margin of the japan sea and the sagami trough are compared with global relative plate motions rm2 minster and jordan 1978 to test a new hypothesis that northern honshu japan is part of the north american plate this hypothesis also claims that the eastern margin of the japan sea is a nascent convergent plate boundary kobayashi 1983 nakamura 1983 seismic slip vectors along the japan trench are more parallel to the direction of the pacific north american relative motion than that of the pacific eurasian relative motion however the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence seismic slip vectors and rates of shortening along the eastern margin of the japan sea for the past 400 years are also consistent with the relative motion between the north american and eurasian plates calculated there seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south kanto beneath which the philippine sea plate is subducting indicate two major directions one is the relative motion between the north american and philippine sea plates and the other that between the eurasian and philippine sea plates one possible interpretation of this is that the eastern margin of the japan sea may be in an embryonic stage of plate convergence and the jump of the north american eurasian plate boundary from sakhalin central hokkaido to the eastern margin of the japan sea has not yet been accomplished in this case northern honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates behaving as part of either the eurasian or north american plate another possibility is that the seismic slip vectors and crustal deformations in south kanto do not correctly represent the relative motion between plates but represent the stresses due to non rigid behaviors of part of northern honshu

rossby wave breaking and transport between the tropics and extratropics above the subtropical jet abstractrossby wave breaking is an important mechanism for the two way exchange of air between the tropical upper troposphere and lower stratosphere and the extratropical lower stratosphere the authors present a 30 yr climatology 1981 2010 of anticyclonically and cyclonically sheared wave breaking events along the boundary of the tropics in the 350 500 k potential temperature range from ecmwf interim re analysis era interim lagrangian transport analyses show net equatorward transport from wave breaking near 380 k and poleward transport at altitudes below and above the 370 390 k layer the finding of poleward transport at lower levels is in disagreement with previous studies and is shown to largely depend on the choice of tropical boundary in addition three distinct modes of transport for anticyclonic wave breaking events are found near the tropical tropopause 380 k poleward equatorward and symmetric transport associated with cyclonic wave breaking events however is predominantly poleward

seismotectonics of the hida region central honshu japan abstract seismotectonic features of the northern hida region central honshu japan have been investigated in some detail mainly on the basis of the last 6 years of observations of seismicity and focal mechanism of a large number of earthquakes with reference to the geological and tectonic setting and evidence of a large earthquake in the past it was found that high seismicity is concentrated with a remarkably clear lineation but with a relatively low activity in the central section along the atotsugawa fault extending for about 70 km this is one of major quaternary faults in this region the high seismicity with spatially nonuniform distribution may be related to postseismic stress concentration after the 1858 hida earthquake m 7 0 and to heterogeneous fault strength seismicity is also high with belt like extension beneath the hida mountain range which is the highest mountain system in the japan islands the depth distribution of seismicity is clearly bounded at 15 km below the atotsugawa fault and 8 km beneath the hida mountains the local variations can be interpreted as being due to the difference in the brittle ductile transition depth which suggests higher temperature beneath the mountains involving active volcanoes the focal mechanism solutions indicate that the maximum compressive stress is oriented in an ese wnw direction which is more consistent with the direction of motion of the pacific plate relative to the eurasian plate rather than the suggested relative motion between the north america and eurasian plates the magnitude of the shear stress working in this region is estimated to be less than 700 bar

development of garnet porphyroblasts by multiple nucleation coalescence and boundary misorientation driven rotations two types of garnet porphyroblast occur in the schneeberg complex of the italian alps type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz decussate mica and small garnet grains and a margin containing large garnet grains orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains individual garnet grains without subdomains are small 50 m faceted and idioblastic and have simple zoning profiles with ca rich cores and ca poor rims subdomains of larger garnet grains are similar in size to the individual small garnet grains type 2 porphyroblasts comprise only ellipsoidal garnet with small subdomains in the centre and larger subdomains at the margin each subdomain has its own ca high ca dropping towards subdomain boundaries garnet grains with or without subdomains all have the same ca poor composition at rims in contact with other minerals the compositional zonation patterns are best explained by simultaneous multiple nucleation followed by growth and amalgamation of individual garnet grains the range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre the difference between type 1 and type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast electron backscatter diffraction shows that small individual garnet grains are randomly oriented large marginal garnet grains and subdomain bearing garnet grains have a strong preferred orientation clustering around a single garnet orientation misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations the only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other this process was driven by the reduction of subdomain boundary energy associated with misorientation loss rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals quartz and mica around the garnet an analytical model in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz suggests that at the conditions of metamorphism the rotation required to give a strong preferred orientation can occur on a similar time scale to that of porphyroblast growth

changing monsoon and midlatitude circulation interactions over the western himalayas and possible links to occurrences of extreme precipitation historical rainfall records reveal that the frequency and intensity of extreme precipitation events during the summer monsoon june september season have significantly risen over the western himalayas wh and adjoining upper indus basin since 1950s using multiple datasets the present study investigates the possible coincidences between an increasing trend of precipitation extremes over wh and changes in background flow climatology the present findings suggest that the combined effects of a weakened southwest monsoon circulation increased activity of transient upper air westerly troughs over the wh region enhanced moisture supply by southerly winds from the arabian sea into the indus basin have likely provided favorable conditions for an increased frequency of certain types of extreme precipitation events over the wh region in recent decades

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

carbonado revisited insights from neutron diffraction high resolution orientation mapping and numerical simulations abstract one of the most controversial diamond types is carbonado as its origin and geological history are still under debate here we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation quantitative crystallographic orientation analyses performed on transmission electron microscope tem sections reveal that the 2 10 m grains exhibit locally significant internal deformation such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation characterized by a high number of nucleation sites and no crystallographic preferred orientation crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries even at low bulk strains inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post deformation annealing occurring to variable degrees in the carbonado samples differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement respectively during annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry grain scale numerical modelling shows that anisotropic grain growth where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a zigzag pattern in addition in diamond anisotropic grain growth results in triple junctions that rarely show 120 angles our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation crystal plastic deformation to low strains and variable degrees of post deformation annealing such a history is commonly observed in earth s crustal or mantle rocks hence for carbonados it is not necessary to invoke an extraordinary and or extraterrestrial origin and history the combination of methods utilized here promises to help advance our understanding of diamond and diamond aggregates in the future

pure shear and simple shear calcite textures comparison of experimental theoretical and natural data abstract the pattern of lattice preferred orientation texture in deformed rocks is an expression of the strain path and the acting deformation mechanisms a first indication about the strain path is given by the symmetry of pole figures coaxial deformation produces orthorhombic pole figures while non coaxial deformation yields monoclinic or triclinic pole figures more quantitative information about the strain history can be obtained by comparing natural textures with experimental ones and with theoretical models for this comparison a representation in the sensitive three dimensional orientation distribution space is extremely important and efforts are made to explain this concept we have been investigating differences between pure shear and simple shear deformation incarbonate rocks and have found considerable agreement between textures produced in plane strain experiments and predictions based on the taylor model we were able to simulate the observed changes with strain history coaxial vs non coaxial and the profound texture transition which occurs with increasing temperature two natural calcite textures were then selected which we interpreted by comparing them with the experimental and theoretical results a marble from the santa rosa mylonite zone in southern california displays orthorhombic pole figures with patterns consistent with low temperature deformation in pure shear a limestone from the tanque verde detachment fault in arizona has a monoclinic fabric from which we can interpret that 60 of the deformation occurred by simple shear

the variation of heat generation density and seismic velocity with rock type in the continental lithosphere abstract the petrophysical properties radioactive heat generation compressional wave velocity and density are related to rock type in crystalline rocks the cation fraction in the rock forming minerals is applied to determine the relationships quantitatively heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks therefore the relation between heat generation and rock type has been split into a relation for phanerozoic rocks and another for precambrian rocks which exhibit significantly lower heat generation only 1 3 of that of phanerozoic rocks the interrelations between the petrophysical properties are applied to fennoscandia precambrian terrane and southern bavaria northern alpine foreland phanerozoic rocks to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle

statistical analysis for thermal data in the japanese islands abstract we calculated statistical average of thermal data to speculate regional thermal structure of the forearc area of the japanese islands the three thermal statistical averages show a difference of a high thermal regime in the western part of forearc inner zone and a low in the kanto forearc outer zone the kanto zone marks 18 k km 1 for mean geothermal gradient 44 mw m 2 for mean heat flow while the western inner zone shows 27 k km 1 for mean geothermal gradient 63 mw m 2 for mean heat flow the geothermal gradients of the nobi plain and the osaka plain in the western inner zone are 29 and 36 k km 1 respectively while the value of the kanto plain in the kanto zone is 21 k km 1 taking account of the effect of accumulation of sediments we see the difference in the thermal regime between the plains and conclude that the difference is significant heat flux in the crust depends on the volume of granite rich in radioactive elements there are few granitic rocks in the kanto zone while granitic rocks are dominant in the western inner zone the heat flow of 20 mw m 2 is attributed to the granitic rocks of about 8 km in thickness there are two oceanic plate subductions of the pacific plate and the philippine sea plate under the kanto zone while only the philippine sea plate has been subducting under the western inner zone the model simulation based on thermal and subduction model shows a heat flow ranging 50 60 mw m 2 in the southwest japan forarc area and a low value of about 20 mw m 2 in the northeast japan forearc area the heat flux from the cooling oceanic lithosphere depends on the age of plate the shikoku basin a part of the philippine sea plate off the western inner zone is 15 30 ma while the pacific plate off the kanto zone is 122 132 ma theoretically heat flux values of 15 and 50 ma oceanic plates range 60 120 mw m 2 and those of 122 132 ma could be about 10 mw m 2 if the heat flux contribution from the philippine sea plate under the kanto zone is smaller than the plate under the western inner zone there could be a thermal regime difference in order of several tens of mw m 2 conclusively the cause of the difference of heat flux could be the uneven granitic rocks distribution and or the difference of heat flux between the two subducting plate

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

thermal effects of thrust faulting abstract calculations based on simple models of overthrust sheets in crystalline basement rocks show that significant thermal effects may result from their movements if rates are sufficiently high e g plate tectonic rates the thrust sheets sufficiently thick 5 10 and 15 km are modelled here the distances moved sufficiently large and for reasonable values of the coefficient of friction along the thrust plane overthrusting can cause metamorphic mineral zonations and heat flow anomalies observable in the field regions where large scale overthrusting has occurred should be characterized by a decrease with depth of grade of metamorphic mineral assemblages and anomalously low heat flow the theoretical effects are presented as a series of maximum temperature vs depth and heat flow vs time plots

three dimensional p wave velocity structure beneath central japan low velocity bodies in the wedge portion of the upper mantle above high velocity subducting plates abstract the three dimensional 3 d p wave velocity structure beneath central japan has been investigated in detail by an inversion method 7490 p wave arrival times from 120 shallow and intermediate depth earthquakes that have occurred in this region are used to estimate velocity anomalies in 3 d subdivided blocks and hypocentral perturbations simultaneously the results reveal complex 3 d structures with low velocity zones in the wedge portion of the upper mantle above the high velocity philippine sea and pacific plates subducting beneath this region prominent low velocity bodies exist just beneath active volcanoes particularly in the hida mountain range low velocity bodies are spatially correlated with the low q zones estimated from seismic intensity data one low velocity body coincides with an anisotropic body detected from the study of shear wave splitting dome shaped low velocity masses seem to represent partially melted mantle diapirs no clear evidence on velocity contrast has been identified across the fossa magna which is a tectonic boundary between northeast and southwest japan

problems in the extrapolation of laboratory rheological data abstract the many types of variables and deformation regimes that need to be taken into account in extrapolating rheological behaviour from the laboratory to the earth are reviewed the problems of extrapolation are then illustrated with two particular cases in the case of divine rich rocks recent experimental work indicates that within present uncertainties of extrapolation the flow in the upper mantle could be either grain size dependent and near newtonian or grain size independent and distinctly non newtonian both types of behaviour would be influenced by the present of trace amounts of water in the case of quartz rich rocks the uncertainties are even greater and it is still premature to attempt any extrapolation to geological conditions except as an upper bound the fugacity and the scale of dispersion of the water are probably two important variables but the quantitative laws governing their influence are not yet clear

dynamic recrystallization of quartz under greenschist conditions abstract the sem electron channelling technique has been used to investigate the dynamic recrystallization of three quartz grains representative of optical textures observed in quartzite deformed under greenschist facies conditions the degree of recrystallization has been determined at 10 20 50 and 100 respectively we demonstrate that dynamic recrystallization is a sequential process involving subgrain grain rotation and grainboundary migration it initiates via subgrain polygonization on a single crystal slip system and continues via subgrain and neoblast rotation on several slip systems in the early stages of recrystallization

a potential vorticity based study of the role of diabatic heating and friction in a numerically simulated baroclinic cyclone abstract a particularly intense case of western atlantic baroclinic cyclogenesis was investigated in this study specifically the roles of latent heat of condensation and surface friction were examined from the potential vorticity or pv thinking perspective the methodology used for this study involves three key components 1 a full physics mesoscale model which provides a continuous and dynamically consistent dataset and provides full user control over physical processes 2 a partitioned pv integration which temporally integrates the accumulation of pv due to various physical processes in the model s eulerian framework and 3 the piecewise inversion method of davis and emanuel which calculates the balanced wind and mass field associated with particular pv anomalies potential vorticity features obtained through the partitioned integration technique were inverted to yield their direct contributions to the total circulation in addition sensitivity studies were carried out to determine the overal

the carbonado diamond conundrum abstract the reviewer presents the results of a literature search on the enigmatic occurrences of carbonado a form but not the only form of polycrystalline diamond which is mined for industrial diamonds the principal occurrences are in brazil the central african republic car and siberia yakutia in the latter the name yakutite has been coined but though there are differences between these polycrystalline diamonds and the brazil car minerals they would seem to be little more significant than differences within the gondwana occurrences and yakutite should probably be regarded as another name for carbonado most occurrences are in placers and the minerals have probably been recycled more than once by sedimentary processes the ultimate source being unknown polycrystalline diamond has been described from the udachnaya pipe yakutia and though it is strictly framesite defined as an eruptive pipe variety of carbonado it differs little from other carbonados the fact that all occurrences known are in areas with kimberlites and gem diamond developments present suggests that carbonado does stem from terrestrial eruptive processes though not necessarily kimberlite pipes nevertheless this can be only a provisional personal conclusion there is much contradictory evidence in the literature the evidence of subjection to radiogenic agencies in car carbonados seems to be unexplained but it may be a secondary effect and not present in all carbonados this is a conundrum which still calls for much more research

ion microprobe pb pb dating of carbonado polycrystalline diamond abstract we report in situ ion microprobe pb pb dating of quartz rutile and clay mineral inclusions and matrix part of polycrystalline diamonds carbonado derived from a proterozoic conglomerate in diamond bearing deposit of minas gerais in brazil together with u pb ages of zircons also extracted from the deposit thirty four spots on seven quartz grains located in the cavity of the gm01 carbonado yield 207pb 206pb isochron age of 3247 800 ma 2 mswd 0 75 and six spots on three rutile inclusions give the age of 3916 1300 ma 2 mswd 0 092 seven spots on three clay mineral inclusions of the do3 carbonado show common lead compositions while four spots on matrix define 207pb 206pb isochron age of 3811 1800 ma 2 mswd 0 012 seventy six spots on seventy zircon grains derived from the same conglomerate show three major u pb concordant ages of 2151 17 ma 2692 20 ma and 2931 22 ma with two concordant zircon outliers of 1726 58 ma and 3599 12 ma the youngest age is consistent with the formation age of 1750 1700 ma in the proterozoic conglomerate estimated by other workers the 3 6 ga zircon is the oldest record in the south american platform it may be detrital in origin and reflect the remnant of an archean craton the pb pb age of quartz and rutile inclusions in gm01 carbonado and that of do3 carbonado matrix are 3315 720 ma and 3811 1800 ma the matrix age is consistent with pb pb age of 2 6 3 8 ga of central african carbonados in the literature suggesting a close genetic relationship between brazilian and african carbonados

measurements and full field predictions of deformation heterogeneities in ice we have made creep experiments on columnar grained ice and characterised the microstructure and intragranular misorientations over a range of length scales a fft full field model was used to predict the deformation behaviour using the experimentally characterised microstructure as the starting material this is the first time this combination of techniques has been used to study the deformation of ice the microstructure was characterised at the cm scale using an optical technique the automatic ice texture analyser aita and at the micron scale using electron backscattered diffraction ebsd the crystallographic texture and intragranular misorientations were fully characterised by ebsd 3 angles the deformed microstructure frequently showed straight subgrain boundaries often originating at triple points these were identified as kink bands and for the first time we have measured the precise misorientation of the kink bands and deduced the nature of the dislocations responsible for them these dislocations have a basal edge nature and align in contiguous prismatic planes enabling deformation along the c axis in addition non uniform grain boundaries and regions of recrystallization were seen we present coupling between fine scale characterization of intragranular misorientations from experiments and prediction of internal stresses that cause it the model predicts the morphology of the observed local misorientations within the grains however it over predicts the misorientation values this is because the annealing and recrystallization mechanisms are not taken into account in the model ice is excellent as a model material for measuring predicting and understanding deformation behaviour for polycrystalline materials specifically for ice this knowledge is needed to improve models of ice sheet dynamics that are important for climatic signal interpretation

kyanite deformation in whiteschist of the ultrahigh pressure metamorphic kokchetav massif kazakhstan microstructures in minerals from ultrahigh pressure metamorphic uhpm terranes are keys to understanding the rheological properties and the exhumation mechanisms of rocks from subduction zones kyanite bearing whiteschist associated with eclogite lenses is part of uhpm unit ii located south west of lake zheltau in the kulet region of the kokchetav massif the equilibrium assemblage is kyanite garnet talc phengite coesite quartz previously reported peak pressure temperature p t conditions are 3 5 gpa at 750 c a strong foliation is defined by the talc and phengite with a corresponding weak shape preferred alignment of kyanite crystallographic orientation maps and analysis of kyanite blades were performed using electron backscatter diffraction methods the data are consistent with a 100 001 slip system for the formation of undulose extinction and kink bands in kyanite rotations measured across individual kink bands are 10 50 about and rotations along kyanite with undulose extinction are up to 50 about with variations between adjacent points typically 2 the undulose extinction is interpreted to have developed through crystal plastic deformation by dislocation creep kink bands mark the development of high angle grain boundaries by dislocation climb the deformation of kyanite occurred in the fault bounded terrane during the exhumation of the kokchetav massif