investigation of the sand sea with the tallest dunes on earth china s badain jaran sand sea abstract china s badain jaran sand sea features the tallest dunes on earth and a unique mega dune lake landscape it had been explored little until the 1990s though early scientific explorations surrounding the sand sea had begun by the early 20th century heated debates now focus on the desert environment and particularly how the mega dunes and desert lakes develop and evolve this paper reviews the status of these debates and summarizes the supporting evidences the environmental research mainly concerns formation and evolution of the sand sea and its relationship with climate change the proposed formation time ranges from the early pleistocene to the holocene opinions vary about climate change on different time scales the reconstructed climate change history is shorter than the sand sea s history with the longest record extending to the late pleistocene the mega dune research focuses on sediments dune morphology and formation processes it remains unclear whether the mega dunes result primarily from wind action control by the underlying topography or groundwater maintenance the sources of lake water are also debated but there are four main hypotheses atmospheric precipitation groundwater from nearby areas precipitation and snowmelt in remote areas such as the qilian mountains and the qinghai tibetan plateau or paleowater that formed during past periods of wet climate we believe that the sand sea deserves further study in terms of its dune geomorphology evolution and hydrology and their responses to climate change meteorological and hydrological observations and monitoring in the sand sea are particularly necessary

hydrothermal alteration as a trigger mechanism for earthquake swarms the vogtland nw bohemia region as a case study summary earthquake swarms occur mostly in regions with co2 enriched pore fluids it is generally accepted that both geodynamic stress accumulation and critical pore fluid pressures act as a triggering mechanism for most seismic events the new thesis presented here is that hydrothermal alteration processes in fault zones help facilitate the shear failure propagation due to mechanical weakening and dissolution of the wall rock in addition to the normal shear stress and fluid overpressure the basic idea that stress corrosion cracking results from chemical weakening and comminution has been discussed for many years however it has not yet been applied to explain the earthquake swarm phenomenon studies of extensive alteration as well as the latest investigations of co2 sequestration give evidence that these high dissolution rates of wall rock in contact with an acid fluid phase exist in seismogenic fault zones several indications support the assumption that in the vogtland nw bohemia region the weakening of stressed fault zones by hydrothermal alteration could take place at seismogenic depths and could generate earthquake swarms investigations of quartz samples from the fracture zones by means of cathodoluminescence as well as spatiotemporal analysis of seismicity and numerical modelling of alteration induced earthquake swarms support this hypothesis

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

geomorphology of the megadunes in the badain jaran desert the badain jaran desert features the highest megadunes on earth and a unique megadune lake alternation landscape based on field survey and interpretation of aerial photographs this paper examines the general characteristics of the badain jaran megadunes their morphometry and formation as well as the formation of megadune lake alternation landscape it is suggested that the megadunes in the badain jaran desert were developed in a low wind energy environment the compound transverse megadunes the dominant megadune type have a similar wind regime to barchanoid dunes and the compound star megadunes which occur near the mountains have a similar wind regime to star dunes similar to the barchanoid dunes the height base area and spacing of the compound transverse megadunes show reasonably good inter correlation the base area of the megadunes and the area of the leeward interdune lake basins are also inter correlated the alignment and spacing of the badain jaran megadunes implies that wind is the most important factor in their development the morphology underneath the megadunes does not determine the general pattern of the megadunes as previously suggested repetitions of dune fixation and reactivation in the development process played an important role in increasing the megadunes height hence their size the interdune lakes in the megadune area were mainly formed by talus springs and are only partly fed by atmospheric precipitation

evolution of megadunes and lakes in the badain jaran desert inner mongolia china during the last 31 000 years abstract the badain jaran desert located in western inner mongolia china is characterized by an arid climate and by occurrence of large dunes and permanent lakes within the dune field the main objective of this paper is to describe landscape evolution and climatic change in this desert since the late pleistocene special attention is given to the dune and lake deposits as well as to the water chemistry of the lakes on the megadunes of the desert several calcareous cementation layers and cemented plant roots were observed indicating a relatively moister climate during the last 31 000 years the present hypersaline lakes were filled with fresh or brackish water between 9 and 4 ka bp on the basis of dune morphology and stratigraphy and lacustrine deposits it is concluded that the enrichment of ions in the lakes and decline of their water surface result from aridification since the middle holocene the existence of more humid periods implies that the intensity of westerlies and asian monsoons has changed periodically in this desert since the late pleistocene

preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the bushveld layered intrusion abstract the preferred orientation of plagioclase and pyroxene in gabbronorites from the bushveld layered igneous intrusion south africa was investigated using electron backscatter diffraction in two localities 200 km apart belfast and rustenburg strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane defined by 010 planes of plagioclase and 100 planes of pyroxene the pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure primary magmatic oxides are also influenced by the preferred orientation of plagioclase generating an oblate magnetic susceptibility fabric parallel to the foliation plane plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p waves traveling 4 8 faster in the vertical than in the horizontal direction

fluid induced seismicity guided by a continental fault injection experiment of 2004 2005 at the german deep drilling site ktb 1 recent hydraulic experiments at the ktb site have shown that seismicity induced by long term fluid injection directly into a continental crustal fault remains guided by this fault the seismicity is triggered by pressure perturbations as low as 0 01 1 bars at the hypocenters a combination of sequential one year fluid extraction 2002 2003 and one year fluid injection 2004 2005 experiments has shown that only positive pore pressure perturbation i e injections was able to induce the seismicity moreover the onset of seismicity roughly coincides with the time of compensation of the extracted fluid volume by the following injection this confirms that the pressure diffusion is a dominant mechanism of seismicity triggering by fluid injections the probed fault shows a significant anisotropy and non linearity of its hydraulic behaviour its hydraulic diffusivity is up to one order of magnitude larger than that of surrounding rocks

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

induced microearthquake patterns in hydrocarbon and geothermal reservoirs six case studies the injection or production of fluids can induce microseismic events in hydrocarbon and geothermal reservoirs by deploying sensors downhole data sets have been collected that consist of a few hundred to well over 10 000 induced events we find that most induced events cluster into well defined geometrical patterns in many cases we must apply high precision relative location techniques to observe these patterns at three sedimentary sites thin horizontal strands of activity are commonly found within the location patterns we believe this reflects fracture containment between stratigraphic layers of differing mechanical properties or states of stress at a massive carbonate and two crystalline sites combinations of linear and planar features indicate networks of intersecting fractures and allow us to infer positions of aseismic fractures through their influence on the location patterns in addition the fine scale seismicity patterns often evolve systematically with time at sedimentary sites migration of seismicity toward the injection point has been observed and may result from slip induced stress along fractures that initially have little resolved shear in such cases triggering events may be critical to generate high levels of seismic activity at one crystalline site the early occurrence of linear features that traverse planes of activity indicate permeable zones and possible flow paths within fractures we hope the continued development of microseismic techniques and refinement of conceptual models will further increase our understanding of fluid behavior and lead to improved resource management in fractured reservoirs

the 3d quantitative lattice and shape preferred orientation of a mylonitised metagranite from monte rosa western alps combining neutron diffraction texture analysis and synchrotron x ray microtomography abstract two complementary 3d techniques neutron diffraction and synchrotron x ray microtomography sxr ct were used to compare the shape and lattice preferred orientations of a mylonitised metagranite from the monte rosa unit western alps italy the goal of using these techniques was to obtain two different orientation distribution functions although the two functions describe relatively independent characteristics of the rock fabric nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures thereby highlighting 3d features that cannot be obtained with either technique if used independently we describe an approach that can be potentially useful in various disciplines e g structural geology rock mechanics tectonics and geophysics when a complete data set of preferred orientations and size distribution is needed micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic spo and lpo whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and lpo these observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz feldspar layers this mechanical decoupling occurred during the alpine subduction collision when the monte rosa unit was part of the insubric line system and accommodated large vertical strain

deformation mechanisms and phase distribution in mafic high temperature mylonites from the jotun nappe southern norway abstract shear zones and mylonites in anorthositic to gabbroic rocks from the jotun nappe in southern norway have been studied as an example of high temperature deformation in polyphase rocks the deformation has taken place at approximately 700 c and maximum confining pressures of 900 mpa the constituent phases amphibole pyroxene and plagioclase have recrystallized synkinematically reducing the grain size of the rock to about 20 to 70 m two different microstructures develop depending on the recrystallization mechanism dynamic recrystallization of plagioclase hornblende and pyroxenes produces monophase layers which extend from porphyroclasts heterogeneous nucleation of phases due to chemical disequilibrium produces phase mixtures of hornblende and plagioclase or clinopyroxene and plagioclase these phase mixtures extend from hornblende or clinopyroxene porphyroclasts the product of the deformation and simultaneous recrystallization is a well laminated microstructure of some monophase hornblende pyroxene and plagioclase layers which alternate with abundant layers of phase mixtures different deformation mechanisms operate in the different types of microstructures dislocation substructures dynamic recrystallization microstructures and a crystallographic preferred orientation measured by ji and mainprice 1988 on samples of the same shear zone indicate crystal plastic deformation in monophase plagioclase layers dynamic recrystallization in monophase hornblende layers indicates also crystal plastic deformation the phase distribution of plagioclase and hornblende grain shapes and lower dislocation densities in the phase mixtures suggest that the deformation mechanism is not crystal plasticity but rather a granular flow grain boundary sliding probably accommodated by diffusional mass transfer in the plagioclase hornblende mixtures the phases show an anticlustered non random distribution grain boundary sliding may contribute to phase mixing but cannot be the main reason for the anticlustering of phases and the complete phase mixing directly at the boundaries of the porphyroclasts the reason for the anticlustered distribution is not clear but could be explained by preferential heterogeneous nucleation of hornblende at plagioclase grain boundaries

natural deformation and recrystallization of some intermediate plagioclase feldspars abstract intermediate an25 an48 plagioclase feldspars from the nordre stromfjord shear zone central west greenland have undergone extensive ductile deformation by intracrystalline slip and by twinning the plagioclases were deformed under low granulite facies conditions optical substructures include undulatory extinction deformation bands subgrains and deformational twins mainly on the albite law dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation migration of a high angle boundary as a secondary mechanism in some cases recrystallization is accompanied by a small decrease in the an content which is thought to indicate prograde metamorphic conditions the plagioclases exhibit a good crystallographic preferred orientation which is compatible with 010 001 being the principal slip system quartz has in the same rocks undergone more plastic deformation and more extensive recovery than plagioclase this is at least in part due to the fact that most dislocations in plagioclase are dissociated

albite crystallographic preferred orientation and grain misorientation distribution in a low grade mylonite implications for granular flow abstract crystallographic orientation data from pure albite domains in a low grade sheared metagabbro from the combin zone of the western italian alps were measured by electron backscatter diffraction crystallographic preferred orientations cpos in four high strain domains are non random and have a triclinic symmetry the clusters of 100 010 and 001 show an angular relationship that corresponds to that of the albite crystal lattice however the orientations of axis clusters to the kinematic axes vary from domain to domain cpos from a low strain domain also show clustered axes with triclinic symmetry but with more intense clustering than those in the high strain domains grain misorientation distributions are presented both for the low strain domain and one of the high strain domains in the high strain domain the distribution of misorientation angles between neighbouring grains displays a peak at about 70 the equivalent distribution in the low strain domain has a peak at 30 for both domains the misorientation axis distributions between neighbouring and non neighbouring grains are random except for some of axes with 160 180 misorientation that exhibit a slight concentration around 010 the diversity of cpos among the domains suggests that these cpos could not be produced by dislocation creep they are likely to have been inherited from plagioclase parents as a result of host control on the nucleation of the new albite grains these cpos do not contain any direct information about the deformation kinematics we interpret that deformation of these domains occurred by granular flow crystallographic axis dispersion due to grain boundary sliding gbs caused weakening of cpos modification of misorientation angle distributions and randomisation of misorientation axis distributions the fact that a cpo can survive gbs even after a high strain indicates that cpo is not always a sensitive indicator of deformation mechanisms misorientation distribution may provide a complementary and possibly a more sensitive indicator of deformation mechanisms

an experimental steady state foliation the history of the intensity and orientation of a grain shape foliation was investigated in octachloropropane deformed in simple shear at 80 of its absolute melting temperature and a shear strain rate of 4 10 5s 1 foliation orientation developed from the beginning of the deformation remains steady throughout the deformation foliation intensity becomes steady after a bulk shear strain of about 0 9 has been accumulated the steadiness of foliation orientation and intensity is achieved by some balance between foliation strengthening and foliation weakening processes the main foliation strengthening process is intragranular plastic deformation foliation weakening processes include dynamic recrystallization by migration of straight or or slightly wavy grain boundaries grain dissection rotational recrystallization grain amalgamation relative rigidity of hard grains and grain boundary sliding a small but definite angle although not constant is observed between the foliation and the long axis of the bulk total strain ellipse the average aspect ratio of grains is lower than that of the bulk total strain ellipse by a factor of about 0 4 at total shear strain of 1 3 the average grain size also stabilizes becoming steady from a shear strain of 0 5 onwards a steady grain shape foliation may be a possible paleostress or a paleostrain rate indicator but cannot be a paleostrain indicator

deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric miiller w h schmid s m and briegel u 1981 deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric in g s lister h j behr k weber and h zwart editors the effect of deformation on rocks tectonophysics 78 527 543 three anhydrite rocks of different grain size were experimentally deformed in the 20 to 45o c temperature range the strength of the finegrained varieties becomes strongly temperature and strain rate dependent above 3oo c and a flow law of the form 6 a exp h rt sinh o a with an activation energy h of 27 36 kcal mole and a very low value for the exponent n of 1 5 2 was found the course grained rock remains relatively insensitive to strain rate and temperature even at 45o c microstructural and x ray texture analyses suggest that intracrystalline glide and twinning are the major deformation mechanisms the transition from strong work hardening observed at high stresses into steady state flow at low stresses was found to correlate with the onset of dynamic recrystallization by grain boundary migration

seismic clustering in the sea of marmara implications for monitoring earthquake processes abstract quantifying regional earthquake cluster style is essential for providing a context for studies of seismicity patterns and earthquake interactions here we identify clusters of seismicity in the sea of marmara region of the north anatolian fault nw turkey using a recently derived high resolution seismicity catalog and the nearest neighbor earthquake cluster approach the detected earthquake clusters are utilized for 1 determining spatial distribution of mainshock and aftershock rates and estimating the proximity to failure on different fault segments 2 identifying fault sections having earthquake repeaters and 3 finding areas with enhanced foreshock activity about 6 70 and 24 of the events are identified as foreshocks mainshocks and aftershocks respectively with the largest concentration of aftershocks and foreshocks located along the western high and the cinarcik fault respectively the method successfully identifies regions where previous studies reported earthquake repeaters as indicator for fault creep and suggests additional repeater areas in the gulf of gemlik the largest proportion of mainshocks with associated foreshocks and aftershocks are along the western high and cinarcik fault segments potentially indicating that these segments are closer to failure and have increased susceptibility to seismic triggering continuing studies can contribute to monitoring possible preparation phase of a large m 7 earthquake in the marmara region near the istanbul metropolitan region

crystallographic preferred orientations of plagioclase via grain boundary sliding in a lower crustal anorthositic ultramylonite to clarify the rheological properties and deformational mechanisms that operate within lower crustal shear zones we analyzed deformation microstructures and fabrics in plagioclase grains from high strain regions of intrafolial drag folds of an anorthositic ultramylonite from langoya vesteralen northern norway these grains have developed weak crystallographic preferred orientations cpos other than deformation twinning they do not show any indications of intracrystalline plasticity or dynamic recrystallization in some domains of the drag fold plagioclase cpos are more distinct but the majority of inferred slip systems are not consistent with the main slip systems in plagioclase these suggest that neither dislocation creep nor dislocation accommodated grain boundary sliding gbs produced the plagioclase cpos but rather grain rotation via gbs along specific grain boundaries parallel or subparallel to crystallographic planes of 010 100 or 110 which led to an alignment of the easy slip grain boundaries in the flow direction that produced the observed cpo patterns the anisotropy of dissolution and growth rates may have been responsible for the development of the specific grain boundaries

preferred orientation and elastic anisotropy of illite rich shale shales display significant seismic anisotropy that is attributed in part to preferred orientation of constituent minerals this orientation pattern has been difficult to quantify because of the poor crystallinity and small grain size of clay minerals a new method is introduced that uses high energy synchrotron x rays to obtain diffraction images in transmission geometry and applies it to an illite rich shale the images are analyzed with the crystallographic rietveld method to obtain quantitative information about phase proportions crystal structure grain size and preferred orientationtexture that is the focus of the study textures for illite are extremely strong with a maximum of 10 multiples of a random distribution for 001 pole figures from the three dimensional orientation distribution of crystallites and single crystal elastic properties the intrinsic anisotropic elastic constants of the illite aggregate excluding contribution from aligned micropores can be calculated by appropriate medium averaging the illitic shale displays roughly transverse isotropy with c11 close to c22 and more than twice as strong as c33 this method will lend itself to investigate complex polymineralic shales and quantify the contribution of preferred orientation to macroscopic anisotropy

evidence of a large triggered event in the nepal himalaya following the gorkha earthquake implications toward enhanced seismic hazard a dc double couple constrained multiple point source moment tensor inversion is performed on the band passed 0 008 0 10 hz displacement data of the 25 april mw 7 8 2015 nepal mainshock from 17 broadband stations in india our results reveal that the 25 april event strike 324 dip 14 rake 88 ruptured the north dipping main himalayan thrust mht at 16 km depth we modeled the coulomb failure stress changes cfs produced by the slip on the fault plane of the 25 april nepal mainshock a strong correlation with occurrences of aftershocks and regions of increased positive cfs is obtained below the aftershock zone of the 2015 nepal mainshock we notice that predicted cfs at 16 km depth show a positive coulomb stress of 0 06 mpa at the location of the 12 may 2015 event these small modeled stress changes can lead to trigger events if the crust is already near to failure but these small stresses can also advance the occurrence of future earthquakes the main finding of our cfs modeling implies that the 25 april event increased the coulomb stress changes by 0 06 mpa at 16 km depth below the site of the 12 may event and thus this event can be termed as triggered we propose that the seismic hazard in the himalaya is not only caused by the mainshock slip on the mht rather the occurrence of large triggered event on the mht can also enhance our understanding of the seismic hazard in the nepal himalaya

the origin and distribution of soluble salts in the sand seas of northern china article i nfo article history basedonsamples takenfrom four large sandseasof northernchina thispaper first provides basicdataabout the concentrations and chemistries of soluble salts in deserts of northern china and then discusses the origins and parameters triggeringgeographicalvariations the total concentration ofsoluble saltsinthe aeolian sandsof four large sand seas in northern china ranges between 0 14 and 1 32 with the ph of the soluble salts solution mixing ratio of sand and water 1 5 changing between 8 4 and 9 6 confirming alkaline soil conditions in these regions sodiumchloride andbicarbonateare the dominantsaltsoccurringassoluble saltsinthe aeolian deposits of these sand seas the geographical changes of soluble salts concentration display a clear correlation with regionalclimaticparameters i e precipitationandtemperature thedominationofsedimentationofsolublesalts in the aeolian sands deposited via atmospheric processes is discussed which are heavily associated with dry deposition the mean percentages of na and cl derived from dry depositions are estimated to be n90 in both badain jaran and taklamakan deserts

plagioclase microfabrics in a ductile shear zone from the jotun nappe norway abstract gabbroic and anorthositic rocks from the jotun nappe are transected by small ductile shear zones in which a high grade paragenesis and a new foliation are formed most plagioclase grains show evidence of plastic deformation and have recrystallized by subgrain rotation and bulge processes to fine grained mylonite during these processes a plagioclase grain shape fabric was destroyed and with increasing strain a pre existing plagioclase crystal fabric was successively modified enhanced and finally obliterated this could be evidence of superplastic flow inverse pole figure analysis of the typical plagioclase crystal fabric in the shear zone indicates that 021 a could be an operative slip system and planes close to 132 could be possible slip planes

investigation of the strength contrast at the moho a case study from the oman ophiolite we investigate the viscosity contrast between the crust and mantle by analysis of deformed gabbronorite dikes in the mantle section of the oman ophiolite our study provides a rare opportunity to directly constrain the rheological contrast between a plagioclase rich lithology typical of the lower crust and an olivine dominated harzburgite we constrain deformation conditions using field relationships geothermometry grain size piezometry and electron backscatter diffraction the viscosity of gabbronorite was at least two orders of magnitude lower than the viscosity of the harzburgite consistent with the rheological contrast between plagioclase and olivine calculated via experimental flow laws these flow laws predict that a significant viscosity contrast exists at the crust mantle boundary where the crustal lithology is dominated by plagioclase or where deformation localizes within plagioclase rich layers

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

high temperature plastic deformation of quartz plagioclase multilayers by layer normal compression it is a common practice in rheological modeling to take the extrapolated compressive flow strengths of quartzite and plagioclase rock as the bulk flow strengths of the upper and lower continental crusts respectively such a practice implies that the bulk flow strength of polyphase rocks is identical to that of the pure weak phase to test this assumption we performed deformation experiments on synthetic layered and particulate quartz anorthite 50 50 composites and aggregates of the end members in a paterson gas medium apparatus at a confining pressure of 300 mpa a constant strain rate of 10 5 s 1 and temperatures from 1273 to 1473 k under these conditions anorthite deforms by recrystallization accommodated dislocation creep while quartz is semibrittle electron backscatter diffraction measurements show a strong lattice preferred orientation lpo of anorthite developed in deformed specimens and the lpo pattern is interpreted as a result of dislocation slip on the 010 100 system our experimental results show that the bulk flow strength of layered composites increases with decreasing thickness of the layers thinlayered composites are significantly stronger than pure anorthite aggregates and a homogeneous quartz anorthite mixture i e particulate composites with the same modal composition but weaker than pure quartz aggregates our experimental results together with the theoretical overview presented previously in the materials science literature demonstrate that 1 compressive flow strength of a polyphase rock cannot be represented by that of the weak phase and 2 thin layered rocks compressed normal to the layering are rheologically stronger than homogeneous isotropic mixtures under the same deformation conditions thus weak phase based rheology will lead to an underestimation of the bulk flow strength of the continental crust in which polyphase rocks dominate

quartz grain size reduction in a granitoid rock and the transition from dislocation to diffusion creep abstract in the gran paradiso metagranodiorite western alps small scale lower amphibolite facies shear zones record the transition from a mylonite composed of polycrystalline mineral aggregates to a homogeneous ultramylonite with a grain scale phase mixture polycrystalline quartz aggregates in the mylonite deform by dislocation creep developing a crystallographic preferred orientation cpo and a monoclinic surface orientation distribution function odf the polymineralic matrix of the mylonite and the ultramylonite deform by diffusion creep in the ultramylonite the quartz cpo is randomized and the surface odf becomes orthorhombic the transition from mylonite to ultramylonite is accompanied by a grain size decrease and a disintegration of quartz aggregates concomitant with the precipitation of k feldspar biotite between quartz grains in quartz reduction from the dynamically recrystallized grain size in the aggregates 110 m to the size of the dispersed grains in the ultramylonite 25 m occurs through the following processes k feldspar precipitates at opening sites along grain boundaries strain incompatibility pinning the grain size in quartz aggregates coalescence of k feldspar leads to enhanced grain boundary sliding and disintegration of the quartz aggregates solution precipitation reduces the size of the dispersed grains to less than subgrain size 45 m

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

grain size sensitive deformation of upper greenschist to lower amphibolite facies metacherts from a low p high t metamorphic belt abstract to identify the dominant deformation mechanism in continental middle crust at an arc trench system we used an sem ebsd system to measure the lattice preferred orientations of quartz grains in fine grained metachert from the low grade chlorite and chlorite biotite zones part of the low p high t ryoke metamorphic belt sw japan quartz c axis fabrics show no distinct patterns related to dislocation creep although the strain magnitudes estimated based on deformed radiolarian fossils are high enough that a distinct fabric might be expected to have formed during deformation fabric intensities are very low indicating a random distribution of quartz c axes quartz grains are equant in shape and polygonal and free of intracrystalline plasticity these observations suggest that the dominant deformation mechanism in the metacherts was grain size sensitive flow diffusion creep accompanied by grain boundary sliding rather than dislocation creep possibly reflecting the relatively low strain rate or low flow stress compared with that in high strain zones the development of grain size sensitive flow in metamorphic tectonites at mid crustal conditions would result in a significant decrease of the rocks strength of the continental middle crust

soil and water components of banded vegetation patterns abstract banded landscapes are comprised of alternating bands of vegetation and bare ground aligned along the contours in arid and semi arid regions 50 750 mm rainfall on very gentle and uniform slopes 0 2 2 vegetated bands can be perpendicular to the direction of the dominant wind or more frequently of the slope under given climatic conditions slope gradient is the controlling factor of the type of pattern spotted broadly or typically banded for a given slope gradient mean annual rainfall determines the contrast between the vegetated and bare phase as well as the band length and the interband width band width ratio a typical transect through such two phase mosaic includes a dynamic succession of surface crusts which generates a run off run on system this favours the capture of limited water resources and thus a biomass production greater for banded patterns than spotted patterns or uniformly scattered vegetation moreover vegetated bands act as natural bench structures that greatly limit soil erosion as suggested by modelling banded vegetation patterns can equally be derived from nearly bare areas or from dense vegetation patterns because banded vegetation patterns have often been considered as a form of degradation of previous continuous vegetation cover many attempts have been made by foresters to restore this initial cover by reforestation of the bare interbands however the numerous failures of reforestation of the bare interbands illustrate the key role of these mosaic components in the maintenance of the tiger bush ecosystem banded vegetation patterns are more resilient to climate change than to human disturbances the loss of landscape patchiness due to the clearing of the bands either for fuelwood or for ephemeral cropping induces a rapid decline in soil fertility and water infiltration potential long term monitoring shows that the interband width band width ratio adapts to rainfall variations that are intrinsic of semi arid zones moreover climatic changes might also induce a change in the type of patterning suggesting that banded vegetation patterns are highly self sustainable the ecological differences between the pioneer and the decaying edges of the vegetated bands the temporal spatial succession of soil crusts as well as other indices such as the spatial distribution of soil organic matter and termite nests suggest the upslope migration of the bands nevertheless field evidence of such a shift remains scarce profound lessons can be learnt from the study of banded landscapes in terms of ecosystems functions when designing water harvesting systems or restoring degraded arid and semi arid land banded vegetation patterns should be imitated to optimize biomass production and limit land degradation

preferred crystallographic orientation development during the plastic and superplastic flow of calcite rocks abstract grain size sensitive flow of fine grained rocks such as are often found in mylonitic shear zones is commonly inferred to be accomplished by grain boundary sliding so that no preferred crystallographic orientation is expected to develop pre existing fabrics are supposed to weaken and grain shapes to remain equant however many fine grained mylonites commonly exhibit marked preferred crystallographic orientation whilst displaying a stable but weak grain shape fabric we have examined preferred crystallographic orientation and shape fabric development during the flow of synthetic ultrafine grained 700 c the strong crystal plastic fabric develops more slowly but is not eliminated through the broad transition into true superplastic flow this is interpreted to reflect an important role of intracrystalline plasticity in the accommodation of grain boundary sliding from experiments designed to investigate the extent of survival or modification of an initial twinning fabric through recrystallization and subsequent hot working it was shown that although the microstructure could be totally annealed the early formed fabric survived even subsequent high temperature crystal plastic or superplastic flow this may explain the frequent occurrence of strong low temperature fabrics in calcite ultramylonites

strain softening and microstructural evolution of anorthite aggregates and quartz anorthite layered composites deformed in torsion torsion experiments of anorthite an aggregates and layered composites with equal volume fractions of quartz qtz and an were performed in a gas medium apparatus at a confining pressure of 400 mpa temperatures from 1373 to 1473 k and twist rates from 1 0 x 10 4 to 3 0 x 10 4 rad s dense specimens were fabricated from an glass and qtz crystalline powder using hot isostatic pressing hip techniques both an aggregates and qtz an layered composites show a continuous strain weakening from a peak stress at gamma 0 2 0 3 to gamma 3 2 and steady state flow has not reached under the experimental conditions the weakening is even more pronounced in the layered composites than the monolithic aggregates suggesting channeling or localization of flow into the weak material between strong layers the sheared an specimens developed pervasively c s c structures which are similar to those observed in natural ductile shear zones tem and electron backscattering diffraction ebsd fabric analyses suggest that grain boundary migration recrystallization accommodated dislocation creep with 010 100 as the dominant slip system was operating in the an the strain softening may be due to the development of crystallographic preferred orientation cpo the operation of dynamic recrystallization and the formation of extremely fine grained recrystallized material in the narrow c shear bands c 2004 elsevier b v all rights reserved

ultra high temperature and subsolidus shear zones examples from the poe mountain anorthosite wyoming abstract ultra high temperature shear zones formed with interstitial melts present during the emplacement of the poe mountain anorthosite wyoming the shear zones are characterized by coarse grained plagioclase with flat extinction and rare deformation microstructures dissected grain microstructures suggest that plagioclase underwent recrystallization by fast grain boundary migration orthopyroxene crystallized from interstitial melts as strain free foliation parallel tablet grains plagioclase has a magmatic petrofabric characterized by poles to 010 normal to the shear foliation and 100 parallel to the foliation and movement direction poles to 001 have a broad distribution with a point maximum roughly parallel to the foliation and normal to the movement direction orthopyroxene petrofabrics result from oriented growth parallel to the shear foliation 100 defines a point maximum perpendicular to the shear foliation and 010 and 001 have great circle distributions approximately parallel to the shear foliation microstructures of the ultra high temperature shear zones contrast with those of granulite grade shear zones cutting across the intrusion the granulite grade shear zones initiated as fractures which evolved into shear zones by dynamic recrystallization deformed primary plagioclase and orthopyroxene recrystallized by grain boundary rotation into smaller polygonal grains

the interplay and effects of deformation and crystallized melt on the rheology of the lower continental crust fiordland new zealand abstract microstructural electron backscatter diffraction ebsd and misorientation analyses of a migmatitic granulite facies orthogneiss from the exhumed lower crust of a cretaceous continental arc in fiordland new zealand show how deformation was accommodated during and after episodes of melt infiltration and high grade metamorphism microstructures in garnet omphacite plagioclase and k feldspar suggest that an early stage of deformation was achieved by dislocation creep of omphacite and plagioclase with subsequent deformation becoming partitioned into plagioclase continued deformation after melt infiltration resulted in strain localization in the leucosome of the migmatite where a change of plagioclase deformation mechanism promoted the onset of grain boundary sliding most likely accommodated by diffusion creep in fine recrystallized plagioclase grains our results suggest three distinctive transitions in the rheology of the lower crust of this continental arc where initial weakening was primarily achieved by deformation of both omphacite and plagioclase subsequent strain localization in plagioclase of the leucosome indicates that the zones of former melt are weaker than the restite and that changes in deformation mechanisms within plagioclase and an evolution of its strength primarily control the rheology of the lower crust during and after episodes of melting and magma addition

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

dislocation generation slip systems and dynamic recrystallization in experimentally deformed plagioclase single crystals abstract three samples of gem quality plagioclase crystals of an60 were experimentally deformed at 900 c 1 gpa confining pressure and strain rates of 7 5 8 7 10 7 s 1 the starting material is effectively dislocation free so that all observed defects were introduced during the experiments two samples were shortened normal to one of the principal slip planes 010 corresponding to a hard orientation and one sample was deformed with a schmid factor of 0 45 for the principal slip system 001 010 corresponding to a soft orientation several slip systems were activated in the soft sample dislocations of the 001 010 and 110 001 system are about equally abundant whereas 110 111 and 101 in 131 to 242 are less common in the soft sample plastic deformation is pervasive and deformation bands are abundant in the hard samples the plastic deformation is concentrated in rims along the sample boundaries deformation bands and shear fractures are common twinning occurs in close association with fracturing and the processes are clearly interrelated glissile dislocations of all observed slip systems are associated with fractures and deformation bands indicating that deformation bands and fractures are important sites of dislocation generation grain boundaries of tiny defect free grains in healed fracture zones have migrated subsequent to fracturing these grains represent former fragments of the fracture process and may act as nuclei for new grains during dynamic recrystallization nucleation via small fragments can explain a non host controlled orientation of recrystallized grains in plagioclase and possibly in other silicate materials which have been plastically deformed near the semi brittle to plastic transition

seismic reflectivity of a finely layered granulite facies ductile shear zone in the southern grenville province quebec abstract lithoprobe reflection profile 54 across the granulite facies morin shear zone msz in the grenville tectonic province quebec canada reveals a west dipping zone of strong reflections the origin of these reflections has been investigated by detailed field mapping laboratory measurements of p wave velocities and densities of representative rock samples from the main lithological units and forward synthetic modeling petrofabric and microstructural analyses were performed in order to interpret the measured seismic properties synthetic seismograms generated from the velocity and density data demonstrate that reflections originate from lithologic thin layers and thin layer clusters likely resulted from intensive tectonic transposition and metamorphic differentiation lattice preferred orientation lpo induced anisotropy of granulite facies mylonites except for those containing abundant sillimanite biotite or amphibole is very low and hence unlikely to be the primary cause for reflections confining pressure does not significantly affect the reflectivity of the shear zone because the reflection coefficients are not sensitive to pressure up to at least 600 mpa since composite reflections of thin layer clusters can cause high reflectivity the strong reflectivity from some deep crustal sections with low refraction velocities may be interpreted to be due to the presence of thin layer mafic clusters within dominantly felsic rocks

deformation mechanism maps for feldspar rocks abstract deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates the maps display constant temperature contours in stress grain size space for strain rates ranging from 10 16 to 10 12 s 1 two fields of dominance of grain boundary diffusion controlled creep and dislocation creep are separated by a strongly grain size sensitive transition zone for wet rocks diffusion controlled creep dominates below a grain size of about 0 1 1 mm depending on temperature stress strain rate and feldspar composition plagioclase aggregates containing up to 0 3 wt water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks the strength of water bearing feldspar rocks is moderately dependent on composition and water fugacity for a grain size range of about 10 50 m commonly observed in natural ultramylonites the deformation maps predict that diffusion controlled creep is dominant at greenschist to granulite facies conditions low viscosity estimates of 10 18 10 19 pa s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures 900 c or at lower temperatures diffusion creep of fine grained rocks possibly localized in abundant high strain shear zones for similar thermodynamic conditions and grain size lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks

plagioclase preferred orientation by tof neutron diffraction and sem ebsd abstract the lattice preferred orientation lpo of an anorthosite composed of andesine sampled from a highly deformed anorthositic mylonite grenville province quebec was measured by tof neutron diffraction and sem ebsd the quantitative texture analysis of neutron data was accomplished by using the rietveld texture analysis with the wimv algorithm implemented in the program package materials analysis using diffraction maud the texture calculations of the ebsd data were performed by using the program beartex analyses from neutron and electron diffraction data gave similar results if ebsd data are smoothed to account for grain statistics the principal pole figures show 010 roughly parallel to the rock foliation 001 poles exhibiting a low angle 25 to the pole to foliation and 100 poles close to the y direction perpendicular to the lineation and foliation pole the 100 crystallographic direction shows a maximum in the lineation direction 010 directions concentrate near the foliation pole the geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on 010 with 100 as slip direction elastic properties calculated by averaging document weak anisotropy that has implications for the seismic structure of the lower crust

ab initio calculations of elastic constants of plagioclase feldspars 2014 by walter de gruyter berlin boston plagioclase feldspars comprise a large portion of the earth s crust and are very anisotropic making accurate knowledge of their elastic properties important for understanding the crust s anisotropic seismic signature however except for albite existing elastic constants for plagioclase feldspars are derived from measurements that cannot resolve the triclinic symmetry we calculate elastic constants for plagioclase end members albite naalsi3o8 and anorthite caal2si2o8 and intermediate andesine labradorite nacaal3si5o16 using density functional theory to compare with and improve existing elastic constants and to study trends in elasticity with changing composition we obtain elastic constants similar to measured elastic constants and find that anisotropy decreases with anorthite content

a method to allow temporal variation of velocity in travel time tomography using microearthquakes induced during hydraulic fracturing abstract hydraulic injections produce fluid filled fractures that reduce the seismic velocity of the rock compared to intact rock the travel times of microearthquakes induced by the injections may be used to discern changes in the rock velocities as well as locating the microearthquakes determining the volumes of rock where the velocities have changed provides indirect evidence for the location of the injected fluid and the character of the changes produced in the fractured rock available data are generally insufficient to resolve both the spatial and temporal changes within the rock to extract information about temporal changes and to obtain an improved image of the velocity structure we chose a parameterization scheme in which the velocities of each block are allowed to change from the background velocity only after a threshold number of microearthquakes have occurred in the block regularizing by constraining the velocity of all the altered blocks to be similar helps stabilize the inversion the regularization can be relaxed somewhat to allow the velocity of an altered block to be different from other altered blocks if the travel time data are compelling the parameterization scheme is justified since observations show that the volume of the seismically stimulated rock increases linearly with the volume of the injected fluid we applied the method to data collected in a region of precambrian crystalline rock that was injected with 21 600 m 3 of water we use travel times from a total of 3886 microearthquakes that were induced by the injection the mean rms travel time residual decreases about 7 the velocity structure contains a low velocity zone located near the injection region other distinct low velocity zones are identified the pattern of microearthquake locations found using our method appears to contain more structure than the pattern found in locations determined using a homogeneous velocity structure two clear low velocity regions found near the point where water was injected into the rock are separated by a region whose velocity did not change the region of unaltered velocity had a large number of microearthquakes

experimental and texture derived p wave anisotropy of principal rocks from the transalp traverse an aid for the interpretation of seismic field data a representative suite of deformed metamorphic rocks from the transalp reflection seismic traverse in the eastern alps was studied in the laboratory with respect to elastic properties and whole rock texture compressional wave p wave velocities and their anisotropies were measured at various experimental conditions dry wet confining pressure and compared to the texture related component of anisotropy here texture refers to crystallographic preferred orientations cpos which were determined by neutron texture goniometry in gneisses and schists p wave anisotropies are mainly controlled by the microcrack fabric in marbles and amphibolites cpo contributes very significantly to anisotropy at 200 mpa confining pressure the degree of anisotropy is between 5 and 15 depending on rock composition and or cpo intensity special emphasis was also put on discussing possible effects of fluids on seismic velocity and anisotropy distributions of water filled microcracks and pores are distinctly anisotropic with maximum contribution to bulk rock velocity mostly parallel to the foliation pole decreasing p wave velocity and increasing anisotropy of immersed samples may be explained by crack induced changes of the elastic moduli of bulk rock the main conclusion regarding interpretation of transalp data is that strong reflections in the deep alpine crust are probably due to marble gneiss and metabasite gneiss contacts although p wave anisotropy and boundaries between zones of dry or wet series may contribute to reflectivity to some extent

transformation weakening diffusion creep in eclogites as a result of interaction of mineral reactions and deformation abstract the deformation of eclogites and the driving forces for their fabric development are an important topic potentially allowing to determine deformation rates and stresses in subduction zones where the greatest number of large earthquakes occurs here fabric studies of grain size and shape texture and chemical composition from two locations of variscan and alpine eclogites are presented all samples show a well developed crystallographic preferred orientation cpo of omphacite with a strong maximum of 001 in the lineation direction and a weaker maximum of poles to 010 normal to foliation garnet shows no systematic cpo anisotropic chemical zoning developed in omphacite and garnet during growth together with elongated grain shapes and can be related to a prograde in terms of pressure change p t path the individual chemically zoned and elongated grains orientated in the stretching direction are single crystals without major internal misorientations chemical microstructural and cpo data indicate that the deformation microstructure and texture were produced by preferential crystal growth of garnet and omphacite grains in the extension direction dislocation creep can be excluded as a possible fabric formation process by the systematic and oriented chemical zonation of single crystals and absence of dynamic recrystallization microstructures the dominant deformation is inferred to be diffusion creep where dissolution of material took place in reacting mafic phases plagioclase pyroxene and precipitation took place in the form of new eclogite facies minerals omphacite garnet zoisite this type of diffusion creep deformation represents a transformation process involving both deformation and metamorphic reactions it is emphasized that the weakening is directly connected to the transformation and therefore transient the weakening facilitates diffusion creep deformation of otherwise strong minerals pyroxene garnet zoisite at far lower stresses than dislocation creep the results imply low stresses during the deformation of eclogite blocks in subduction zones these results can be applied to other rock types too

fabric development in a middle devonian intraoceanic subduction regime the careon ophiolite northwest spain abstract a middle devonian suprasubduction zone ophiolite the careon unit northwest spain displays amphibolite facies ductile deformation fabrics related to the onset of the rheic ocean closure two different fabrics an early high t foliation and a subsequent lower t foliation each of which characterized by distinct deformation mechanisms have been identified in two distinct crustal scale shear zones of the same ophiolitic thrust sheet combined quantitative texture analysis by electron backscattered diffraction and time of flight neutron diffraction were carried out on the shear zones and correlated with micro and macrostructural data the results indicate that the regional lineation and shear zone kinematics east west top to the east represent fabrics developed essentially during the intraoceanic subduction of the rheic ocean and their orientation may be considered a reference vector for convergence models in this part of the variscan belt

sense of shear in high temperature movement zones from the fabric asymmetry of plagioclase feldspars abstract a new method for determining the sense of shear in plagioclase bearing tectonites from the 010 orientation of plagioclase feldspar is presented the method is based on the asymmetry of the 010 plane with respect to the structural frame foliation and lineation and the dominant activity of the 010 slip plane in the high temperature plasticity of plagioclase feldspar using examples from the zabargad gneisses red sea the method is applied to plagioclases of an25 an45 and compared with other methods of shear sense determination quartz c axis fabrics and microstructural criteria

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

the influence of dolomite on the plastic flow of calcite rheological microstructural and chemical evolution during large strain torsion experiments abstract aggregates composed of calcite and dolomite have been deformed and annealed at high temperature 700 800 c and high pressure 300 mpa to investigate the mutual effects of deformation and chemical reaction strain partitioning fabric development and phase segregation in a polyphase rock samples deformed in torsion displayed an almost newtonian creep with stress exponent of 1 7 0 3 specimens were deformed up to a maximum shear strain of 10 and developed a clear texture documented by electron back scatter diffraction measurements in both calcite and dolomite both the texture and the foliation created during the large strain experiments display a monoclinic symmetry closely reproducing that of naturally deformed carbonate marbles with the preferred orientation of the c axes inclined against the sense of shear detailed microstructural investigation shows that grains are internally strain free and that grain boundaries are preferentially aligned in straight segments implying that deformation occurred through a combination of grain boundary sliding and diffusion processes accommodated by dislocation activity chemical investigations performed on both statically annealed and torsion samples indicate that deformation may have an important influence on the phase equilibrium of a reacting system calcite grains deformed with excess of dolomite with respect to the equilibrium were able to incorporate higher amounts of mg within the calcite lattice than the static samples as documented by electron probe microanalysis moreover the above analysis documented that reaction rate was faster in torsion than in static experiments at the same conditions of pressure and temperature

the brittle to viscous transition in polycrystalline quartz an experimental study shear experiments on quartz gouge were performed at elevated confining pressures predominantly 1 5 gpa and temperatures 500 c 1000 c at shear strain rates of 3 5 10 6 s 1 to 2 10 3 s 1 to study the brittle to viscous transition an unsystematic temperature dependence of strength at low temperatures changes towards a clear temperature weakening dependence above 650 c the transition from a pressure strengthening to a pressure weakening relationship takes place continuously between 650 c and 800 c strain rate stepping experiments reveal power law breakdown at low temperatures 650 c between 800 c and 1000 c a stress exponent of n 1 9 0 6 and an activation energy of q 170 72 kj mol indicate a combination of diffusion and dislocation creep the goetze criterion is confirmed as the upper stress limit for viscous deformation mechanisms localised deformation in the form of semibrittle shear bands with riedel geometry at low temperatures changes to homogeneous deformation with a pervasive foliation accompanied by a continuous texture evolution between 700 c and 1000 c fracturing dominates at low temperatures accompanied by increasing amounts of dissolution and precipitation in fine grained zones with increasing temperature above 650 c dislocation and diffusion creep are the dominating deformation processes with dislocation creep being favoured in larger grains while dissolution precipitation is active in the fine grained fraction

texture and elastic anisotropy of a mylonitic anorthosite from the morin shear zone quebec canada a sample of anorthosite from the granulite facies morin shear zone quebec canada was investigated for crystal preferred orientation and elastic anisotropy time of flight neutron diffraction data obtained with the hippo diffractometer at lansce were analyzed with the rietveld method to obtain orientation distribution functions of the principal phases plagioclase clinopyroxene and orthopyroxene texture and microstructures are compatible with the plastic deformation of the aggregate under high t conditions all mineral phases depict a significant preferred orientation that could be related to the general top to the north shearing history of the morin shear zone texture patterns suggest that 010 001 in plagioclase and 110 001 in clinopyroxene are likely dominant slip systems using preferred orientation data p and s waves velocities and elastic anisotropy were calculated and compared with previous studies to explore elastic properties of rocks with different pyroxene plagioclase mixtures p wave velocity s wave splitting and anisotropy increase with clinopyroxene content seismic anisotropy is linked to the texture symmetry which can lead to large deviations between actual anisotropy and that measured along cartesian xyz sample directions lineation foliation reference frame this is significant for the prediction and interpretation of seismic data particularly for monoclinic or triclinic texture symmetries

phase boundary mobility in naturally deformed high grade quartzofeldspathic rocks evidence for diffusional creep abstract grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern grenville province ontario canada suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep in these rocks quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions in the naturally deformed rocks however phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation i e in directions of inferred finite extension which implies that phase boundary motion and cusp formation occurred during deformation optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep however the morphology of quartz feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone we propose that phase boundary motion resulted from a diffusion assisted process involving dissolution at foliation parallel quartz feldspar phase boundaries mass transfer over length scales of the order of feldspar domain size 200 m or greater and precipitation at quartz feldspar phase boundary cusps this study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks it also has important implications for the natural rheological behavior of the mid and lower continental crust

the deformation of plagioclase investigated using electron backscatter diffraction crystallographic preferred orientation data abstract extensive plagioclase grain orientation datasets have been collected using the rapid and accurate electron backscatter diffraction sem technique the crystallographic preferred orientation cpo of a porphyroclastic rich plagioclase layer and an equigranular plagioclase layer in an amphibolite facies shear zone from harris scotland were investigated in order to study their cpos and deformation mechanisms the layers have random cpos together with other microstructures and misorientation distributions these suggest dynamic recrystallisation followed by dominant grain boundary diffusion creep this is surprising given the coarse 100 250 m recrystallised grain size of the layers plagioclase within tectonites of these grain sizes in the amphibolite facies are generally inferred to deform by dislocation creep from microstructures and observed strong cpos deformation mechanism maps show that this style of deformation is possible at very slow strain rates

preferred lattice orientations of plagioclase from amphibolite and greenschist facies rocks near the insubric line western alps abstract preferred lattice orientations of plagioclase measured by the universal stage from deformed amphibolite and greenschist facies rocks near the insubric line western alps reflect the type and orientation of the strain system either 001 or 010 are oriented parallel or subparallel to the schistosity and form more or less complete girdles around the stretching direction by the preferred orientation patterns dominant 010 001 slip is indicated and additionally slip on 001 parallel to the a direction possibly at somewhat higher temperatures and or at a higher an content of the plagioclase it is suggested that obliquities of the symmetry planes of the orientation patterns against the principle axes of strain are related to the sense of shearing

plagioclase fabric development in a high grade shear zone jotunheimen norway abstract shear zones of precambrian age transform meta anorthositic rocks to mylonites of high metamorphic grade in jotunheimen norway a plagioclase microfabric study is presented for one of these shear zones the shear zone is heterogeneously and asymmetrically developed regarding the degree of recrystallization and this is inferred as reflecting strain variations pre shear zone plagioclase is preserved in the deformed rocks as porphyroclasts which display large variations in grain elongation in the plane of mylonitic foliation with aspect ratios long dimension average short dimension as large as 25 1 the preferred orientation of lattice and optical directions in the plagioclase porphyroclasts indicates that they are preferentially oriented with the pole to 010 at a moderate angle to the foliation pole in such a way that they are unfavorably oriented for mechanical twinning on the albite and pericline laws in a flattening strain across the plane of the mylonitic foliation this is taken to indicate that the porphyroclasts represent those pre shear zone plagioclase grains which were oriented in order to accommodate such a flattening strain by mechanical twinning while grains otherwise oriented accommodated the strain by kinking with an axis of external rotation at 100 and glide which accumulated lattice strain and eventually led to recrystallization the plagioclase porphyroclasts with large aspect ratios are preferentially oriented with 100 at a large angle to the inferred translation direction of simple shear strain they are the products of preferential recrystallization of zones of large lattice strain in grains which were strongly kinked due to their special orientation this implies that grain elongation is not applicable as a measure of strain the microstructures indicate that the recrystallization was dynamic the produced neoblasts display a preferred orientation which is weak although with a preference for 010 to have a low angle to the foliation plane which mimics the preferred orientation of the porphyroclasts there is a slight indication that the orientation of neoblasts is controlled by the plagioclase host such that 100 of the neoblasts prefer intermediate rather than large angles against 100 of the porphyroclast these features and microstructural observations indicate that rotation recrystallization is a basic recrystallization mechanism under high grade metamorphic conditions

conceptual model of recharge to southeastern badain jaran desert groundwater and lakes from environmental tracers sources of groundwater recharge to the badain jaran desert in china have been investigated using geochemical and isotopic techniques stable isotope compositions 18o and 2h of shallow groundwater and surface water from oasis lakes evolve from a starting composition considerably depleted compared to local unsaturated zone moisture confirming inferences from chloride mass balance that direct infiltration of precipitation is not a volumetrically important source of recharge to the shallow aquifer in the study area shallow phreatic and deeper confined groundwater bodies appear unconnected based on chemical composition and radiocarbon activities hydrogeologic evidence points toward a bordering mountain range yabulai as a likely recharge zone which is consistent with tracer results a mean residence time in the range of 1 2 ka for the desert s southeastern margin is inferred from radiocarbon these results reveal that some replenishment to the desert aquifer is occurring but at a rate much lower than previously suggested which is relevant for water resources planning in this ecologically sensitive area

determination of stress directions from plagioclase fabrics in high grade deformed rocks alem paraiba shear zone ribeira fold belt southeastern brazil abstract a new method to determine stress directions using the preferential orientation of plagioclase mechanical twins has been applied to high temperature mylonitic rocks from the alem paraiba shear zone ribeira fold belt southeastern brazil we have measured the lattice preferred orientation of plagioclase grains and calculated the orientation of the stress axes possible for the observed twin orientations the maximum compressive stress direction 1 determined for all studied samples is a function of the mechanical twin orientations of a number of distinct plagioclase populations the 1 direction is generally subperpendicular to the 010 plane the statistical treatment for most of the plagioclase grains examined for each sample shows that 1 is almost perpendicular to the foliation plane suggesting a significant coaxial component in the deformation process of these rocks

hydrological cycle and water balance estimates for the megadune lake region of the badain jaran desert china the hydrology and water balance of megadunes and lakes have been investigated in the badain jaran desert of china field observations and analyses of sand layer water content field capacity secondary salt content and grain size reveal 3 types of important natural phenomenon a vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone b seepage wet sand deposits and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone c zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes the seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes alternating layers of coarse and fine sand create the conditions for the formation of preferential flows the preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water our results indicate that a positive water balance promotes recharge of the megadunes which depends on the high permeability of the megadune material the shallow depth of the surface sand layer affected by evaporation the occurrence of rainfall events exceeding 15 mm and the sparse vegetation cover water balance estimates indicate that the annual water storage of the megadunes is about 7 5 mm accounting for only 8 of annual precipitation however the shallow groundwater per unit area under the megadunes receives only 3 6 of annual precipitation but it is still able to maintain a dynamic balance of the lake water from a water budget perspective the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water thereby enabling the long term persistence of the lakes overall our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts

complete texture analysis of a deformed amphibolite comparison between neutron diffraction and u stage data abstract this paper describes a new technique of analysing complex neutron diffraction patterns allowing the quantitative texture analysis of each rock forming mineral up to trielinic lattice symmetry in polymineralic rocks the method is demonstrated using hornblende and plagioclase fabrics in alzenau amphibolite from the spessart mountains mid german crystalline rise hornblende and plagioclase exhibit a pronounced shape preferred orientation with respect to the macroscopic fabric elements for control purposes crystallographic preferred orientations were also determined independently by individual grain measurements using a u stage from the neutron texture analyses we obtain only superposed pole figures hornblende and hornblende hornblende and plagioclase and plagioclase with plagioclase of low indexed lattice planes therefore the critical crystallographic directions were recalculated by the orientation distribution function odf which is given by texture components the optical and neutron derived pole figures are in a good agreement all pole figures display strong preferred orientation although the plagioclase texture is less pronounced the hornblende texture consists of a 001 maximum parallel to the stretching lineation with 010 showing a tendency to develop a girdle around the lineation 100 axes are distributed with a clearly split maximum representing the monoclinic angle between 100 and 001 the plagioclase texture is a rare one with 001 subparallel within the foliation and 100 oriented subparallel to the lineation 010 of plagioclase is concentrated normal to lineation within the foliation the technique outlined here is potentially the most useful one for texture analysis of polyphase rocks independent of crystal symmetry

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

plagioclase preferred orientation and induced seismic anisotropy in mafic igneous rocks fractional crystallization and crystal segregation controlled by settling or floating of minerals during the cooling of magma can lead to layered structures in mafic and ultramafic intrusions in continental and oceanic settings in the lower crust thus the seismic properties and fabrics of layered intrusions must be calibrated to gain insight into the origin of seismic reflections and anisotropy in the deep crust to this end we have measured p and s wave velocities and anisotropy in 17 plagioclase rich mafic igneous rocks such as anorthosite and gabbro at hydrostatic pressures up to 650 mpa anorthosites and gabbroic anorthosites containing 80 vol plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns vp z vp y 1 and vp z vp x 1 for anorthosites while 0 8 vp y than the gabbros laminated anorthosites with vp x vp y vp z display a strong crystal preferred orientation cpo of plagioclase whose 010 planes and 100 and 001 directions parallel to the foliation for the gabbros and amphibolites characterized by vp x vp y vp z and vp x vp y vp z respectively pyroxene and amphibole play a dominant role over plagioclase in the formation of seismic anisotropy the poisson s ratio calculated using the average p and s wave velocities from the three principal propagation polarization directions x y and z of a highly anisotropic anorthosite cannot represent the value of a true isotropic equivalent the cpo induced anisotropy enhances and decreases the foliation normal incidence reflectivity at gabbro peridotite and anorthosite peridotite interfaces respectively

on the measurement of plagioclase lattice preferred orientations abstract there are two major difficulties in measuring plagioclase lattice preferred orientations lpos by u stage the first which is caused by dependence of the lpo determination on anorthite content cannot be overcome using the u stage method at present the second difficulty which is caused by the dependence on orientation of thin sections can be overcome by measuring all twinned grains in any two orthogonal sections compared with previous methods published in the literature the present method using two rather than three orthogonal sections is more statistically meaningful and time saving in practice this method was used for measuring lpos of plagioclase an 50 from a typical anorthosite mylonite deformed under the granulite facies conditions in the morin ductile shear zone within the canadian grenville tectonic province

plagioclase and quartz preferred orientations in a low grade schist the roles of primary growth and plastic deformation albite in a lower greenschist facies haast schist from new zealand has a maximum of poles to 001 parallel to the elongation direction 010 forms a girdle about grain length plastic deformation with slip dominantly on 010 001 is rejected as the orienting mechanism because 1 the relationship of crystal axes to grain length would require multiple slip systems incompatible with the lack of rotation of albite twin planes 2 euhedral terminations and other textural features indicate primary crystallization 3 albites in quartzose layers are less elongate than those in sheet silicate rich layers the albite fabric is ascribed to growth anisotropy and competition in response to stress driven solution and growth during formation of metamorphic segregation layering this explanation is compatible with the common observation that plagioclase is brittle at low metamorphic grades associated weak quartz c axis fabrics are ascribed to plastic deformation and this deformation enhanced a dimensional preferred orientation already established by primary growth

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

estimates of stress and strain rate in mylonites based on the boundary between the fields of grain size sensitive and insensitive creep 1 microstructural analyses of mylonites next to the median tectonic line mtl sw japan reveal a transition in the dominant deformation mechanism of quartz from grain size insensitive dislocation creep to grain size sensitive grain boundary sliding gbs the transition occurred under greenschist facies conditions 300 400 c during grain size reduction by dynamic recrystallization the stereologically corrected grain size for the transition is approximately 4 3 m at the boundary between the fields of dislocation creep and gbs as calculated from creep constitutive relations the differential stress and strain rate for this corrected grain size are estimated to be 280 mpa and 1 2 10 11 s 1 for 300 c and 110 mpa and 1 0 10 10 s 1 for 400 c the strain rates estimated for the mylonites next to the mtl are much higher than those estimated for the surrounding metamorphic rocks 10 14 s 1 and the displacement rates calculated based on the thickness of high strain mylonites and their strain rates are comparable with the average slip rates of the most active intraplate faults in japan these inferences suggest that the high strain mylonite zones next to the mtl are the exhumed downward extension of a seismogenic fault in the ductile region the zones were highly localized 10 m and experienced very high strain rates 10 11 to 10 10 s 1

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

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

microstructural evidence for the transition from dislocation creep to dislocation accommodated grain boundary sliding in naturally deformed plagioclase abstract we use quantitative microstructural analysis including misorientation analysis based on electron backscatter diffraction ebsd data to investigate deformation mechanisms of naturally deformed plagioclase in an amphibolite gabbro mylonite the sample is from lower oceanic crust exposed near the southwest indian ridge and it has a high ratio of recrystallized matrix grains to porphyroclasts microstructures preserved in porphyroclasts suggest that early deformation was achieved principally by dislocation creep with subgrain rotation recrystallization recrystallized grain average diameter 8 m microstructures indicate that subsequent grain boundary sliding gbs was active in the continued deformation of the recrystallized matrix the recrystallized matrix shows four grain junctions randomized misorientation axes and a shift towards higher angles for neighbor pair misorientations all indicative of gbs the matrix grains also exhibit a shape preferred orientation a weak lattice preferred orientation consistent with slip on multiple slip systems and intragrain microstructures indicative of dislocation movement the combination of these microstructures suggest deformation by dislocation accommodated gbs disgbs strain localization within the recrystallized matrix was promoted by a transition from grain size insensitive dislocation creep to grain size sensitive gbs and sustained by the maintenance of a small grain size during superplasticity

feldspar fabrics in a greenschist facies albite rich mylonite from electron backscatter diffraction abstract the current database of plagioclase cpos in naturally deformed rocks is small and is not supported by cpos from experimentally deformed rocks or by numerical modelling so that the current understanding of plagioclase cpos is limited electron backscatter diffraction ebsd has the potential of measuring the full crystallographic orientation of small domains of any crystalline material including plagioclase we generate and test a file of the relative electron diffraction intensities for lattice planes in the albite structure this enables rapid and accurate individual orientation measurements of albite using ebsd ebsd is used to collect 360 data points from 7 areas across a 2 cm by 1 mm pure albite band in a greenschist facies albite mylonite from a gabbro protolith the cpos are unlike any published the a b and c axes of albite are not symmetrically distributed with respect to the kinematic axes of deformation and do not possess an internal monoclinic or orthorhombic symmetry there is some microstructural evidence for the operation of dislocation creep although this interpretation conflicts with the generally held view that crystal plastic deformation does not occur in plagioclase below about 500 c an alternative mechanism is one of granular flow accommodated by solution transfer however this mechanism would be expected to give a random cpo for either mechanism we need to explain the triclinic nature of the cpo it is possible that the cpo represents the modification by deformation of a pre existing cpo probably defined by a small number of original plagioclase grains

the influence of three dimensional grain size distributions on the rheology of polyphase rocks abstract in this study the relation between the deformational behaviour of two phase rocks and the grain size distributions of the constituent phases is investigated samples of hot isostatically pressed 50 50 volume percent mixtures of calcite and anhydrite were experimentally deformed in a triaxial apparatus at a temperature of 500 c a confining pressure of 300 mpa and a strain rate of 2 10 5 s 1 for calcite and anhydrite these are the deformational conditions for dislocation and diffusion creep respectively and for a grain size of 8 m these are the conditions of the equiviscous point it was found that samples from different batches of the synthetic material while having an identical average two dimensional grain size displayed significantly different rheological behaviour the ensuing full analysis revealed that the volumetric three dimensional grain size distributions of the different phases and the different batches varied significantly since the anhydrite is in the transition between the dislocation and the grain size sensitive diffusion creep regime the deformational behaviour of the bulk depends critically on the grain size distribution of the anhydrite phase the usefulness of the concept of an average grain size is discussed

statistics of fracture strength and fluid induced microseismicity 1 in this paper we develop an approach for estimating the strength of rocks by analyzing fluid induced microseismicity the strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to activate preexisting fractures i e to trigger earthquakes we assume that during hydraulic injection experiments in boreholes microseismicity is mainly triggered by a diffusive process of pore pressure perturbation an analytical solution can be applied to find time dependent pore pressure perturbations in rocks caused by fluid injections characteristics of the spatiotemporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes moreover we present a method for reconstruction of the full spectrum of rock strength that is we show how to estimate the probability density function of the critical pressure we verify the approach using numerical data and apply it to real data of injection induced microseismicity from two hot dry rock tests in crystalline rocks and one hydraulic fracturing experiment in a sedimentary rock the results show that such an analysis of microseismicity is able to provide us with a completely new feature of natural fractured rocks in situ namely the statistics of their strength we find that very low critical pressures in the range 0 001 1 mpa characterize the strength of preexisting cracks for all data sets analyzed the range of critical pressures is broadly distributed within 3 to 4 orders of magnitude however the probability density functions of critical pressure change very quickly from the zero level to significant values and from significant values to the zero level at the lower and upper limits of their nonvanishing value ranges respectively the lower bound of critical pressure is possibly defined by the magnitude of tidal induced stresses permanently occurring and relaxing in the earth

crystallographic preferred orientation in albite samples deformed experimentally by dislocation and solution precipitation creep abstract the crystallographic preferred orientations of a series of experimentally deformed fine grained albite aggregates were measured by synchrotron source x ray diffraction most samples were deformed and extensively recrystallized by low temperature recrystallization accommodated dislocation creep in axial compression as well as simple shear these samples developed weak but distinct crystallographic preferred orientations consistent with intracrystalline slip on 001 the sheared samples have a marked asymmetry of the maxima with respect to the shear zone boundaries one sample was axially compressed by solution precipitation creep it developed a somewhat different but equally strong preferred orientation perhaps reflecting crystallographic anisotropy in rates of dissolution and growth

recrystallization and fabric development in plagioclase the microstructures and fabrics of naturally deformed intermediate composition plagioclase feldspars from the amphibolite granulitic gneisses from the lower crust have been studied special interest in the effects of dynamic recrystallization and deformation fabrics has been taken the plagioclase feldspars an40 50 have undergone extensive ductile deformation by intracrystalline slip and twinning they show strong crystallographic preferred orientation which was produced by dominant 010 001 slip dynamic recrystallization is indicated by fine grained new grains neoblasts interspersed with deformed relicts porphyroclasts the neoblasts have formed preferentially along grain boundaries kink band boundaries kbbs intracrystalline shear zones and around solid inclusions such as garnet and pyroxene optical microstructural evidence suggests that dynamic recrystallization occurred primarily by grain boundary migration with subsidiary subgrain rotation which appears to have occurred only at low st

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

amphibole fabric formation during diffusion creep and the rheology of shear zones we conducted experiments to examine the effect of amphibole forming hydration reactions on mineral fabric development and the strength of mafic rocks both hydrostatic and general shear deformation experiments were conducted on powdered basalt with added water at lower continental crust conditions 800 c 1 gpa amphibole that formed under hydrostatic conditions exhibits a random lattice preferred orientation lpo in contrast amphibole formed during deformation exhibits both a strong shape preferred orientation spo and lpo with a 001 maximum aligned subparallel to the shear direction plagioclase in both hydrostatic and deformed samples shows a very weak to random lpo at low effective strain rates 10 5 s 1 to 10 6 s 1 the stress exponent is 1 1 5 consistent with deformation accommodated by diffusion creep the correlation of the spo and lpo coupled with the rheological evidence for diffusion creep indicates that the amphibole fabric results from oriented grain growth and rigid grain rotation during deformation the experimentally produced fabrics are strikingly similar to those observed in amphibolite grade natural shear zones supporting interpretations that such rocks deform by diffusion creep in addition the rheology of the fine grained experimental amphibolite is comparable to that predicted using flow laws for wet anorthite thus both our experiments and field analyses indicate that wet plagioclase rheology provides a good constraint on the strength of hydrated lower crust

crystallographic preferred orientation produced by diffusional creep of harzburgite effects of chemical interactions among phases during plastic flow 1 experimental deformation experiments have been conducted on fine grained two phase aggregates of olivine and orthopyroxene to investigate the role of grain and phase boundary sliding on rheology and fabric development a suite of large strain 1 general shear experiments conducted at t 1200 c and p 1 6 gpa on aggregates ranging from 65 to 0 vol orthopyroxene to characterize the evolution of fabric were complemented by small strain axial compression experiments at t 1200 c and p 0 3 gpa to better constrain the rheology microstructural and rheological data suggest that deformation of these two phase aggregates in the diffusion creep regime occurs via interface reaction controlled diffusion creep that is accompanied by extensive migration of olivine orthopyroxene phase boundaries the resulting rheologies suggest that olivine orthopyroxene composites are weaker than the olivine end member at the conditions tested physically this behavior arises because long range i e grain scale diffusion of si4 is unnecessary in these pseudobinary two phase aggregates we further demonstrate that interface controlled diffusion creep leads to strong crystallographic preferred orientations cpo of the component minerals which develops in the near absence of dislocation activity the cpo formed in these anhydrous low stress experiments has the olivine a axis aligned perpendicular to the flow direction type b fabric argued by some to be the unique result of deformation under conditions of high differential stress and high water fugacity phase boundary dynamics thus are argued as a significant factor in the accumulation of strain in polyphase aggregates

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment