propagation velocity of a natural hydraulic fracture in a poroelastic medium the propagation rate of a natural hydraulic fracture is limited by the rate that fluid flows from the saturated rock into the void space created by fracture growth unlike induced hydraulic fractures natural hydraulic fractures can not be modeled by specifying rates of fracture growth or fluid flow into the fracture as boundary conditions numerical solutions of the governing equations for natural hydraulic fracture growth in a poroelastic medium indicate that growth rates are primarily controlled by the hydraulic conductivity the storage sp and the initial flaw length 2 o computationally more efficient models which partially and completely decouple material stresses from fluid pressures give similar results results for several rock types indicate that although the rate of fracture propagation is limited by fluid flow fracture growth still accelerates results are generalized in dimensionless plots of fracture length versus time for various values of the dimensionless parameter 1 gsp where g is the shear modulus and is the drained poisson s ratio

source parameter inversion of a reservoir induced seismic sequence lake kariba africa 1963 september summary the depth and seismic source parameters of the three largest reservoir induced earthquakes associated with the impoundment of lake kariba africa were determined using a moment tensor formalism of the generalized inverse technique the events characterized by mb 5 5 consisted of the foreshock and main event 0640 and 0901 gmt 1963 september 23 and the principal aftershock 0703 gmt 1963 september 25 from the analysis of analogue rift valley source crustal models a three layer over a half space model were selected for the analysis of the lake kariba events the epicentral proximity and the comparable source parameters of the three large events suggest a common source fault with an approximate strike of s 9 w 4 dip of 62 10 and rake of 266 4 the body wave modelling indicates that the lake kariba events occurred at depths of less than 10 km the inferred source parameters complemented by the structural maps derived from the photo interpretation of landsat imagery of the region indicate a normal fault that uniquely transects the reservoir s deep sanyati basin in a north south heading the active fault seems to correlate with the location of the umi river s submerged river channel the confirmation of shallow depths and the determination of source parameters establishes a basis for addressing the actual triggering mechanisms of these earthquakes

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

a ductile extensional shear zone at the contact area between hp lt metamorphic units in the talea ori central crete greece deformation during early stages of exhumation from peak metamorphic conditions we report on an extensional ductile shear zone in central crete at the contact area between the high pressure low temperature hp lt metamorphic phyllite quartzite unit sensu stricto pq s str and the talea ori group plattenkalk unit mapping and microscopic analysis along the 20 km long contact reveal extensional shear bands shear band cleavages c type and associated quartz veins in both units occurring over a width of up to a kilometer the shear offset along the shear bands is systematically perpendicular to the contact with the hanging block pq s str being downfaulted abundant discordant quartz veins are associated to shear band boundaries asymmetric boudinage and foliation boudinage forming m wide vein networks these mesoscopic deformation structures together with related microstructures such as strain shadows growth rims of albite porphyroblasts and stylolites indicate dissolution precipitation creep as main deformation mechanism accompanied by vein formation temperatures during deformation are indicated to be close to peak metamorphic temperatures 300 350 c by the growth rims of albite porphyroblasts and micas present in the shear band cleavages which are consistent with quartz vein microstructures showing subgrains and sutured high angle grain boundaries peak metamorphic temperatures inferred by the degree of graphitization of carbonaceous material are similar in the hanging wall and the footwall of the shear zone which is consistent with fast and nearly adiabatic exhumation our study demonstrates the importance of ductile shear zones with high strain rate dissolution precipitation creep and vein formation in hp lt metamorphic rocks for the early exhumation history

the transition from single layer to foliation boudinage a dynamic modelling approach abstract foliation boudinage is a deflection of foliation in the vicinity of a central discontinuity in foliated rocks mostly filled with vein material it shows evidence for brittle deformation and void opening during ductile flow we used a two dimensional visco elastic spring model based on a discrete element approach to study the dynamic development of foliation boudinage and the behaviour of anisotropic visco elastic material deformed under pure shear conditions the anisotropies are set by defining rheological heterogeneities in the models with 1 a single layer in a weaker matrix 2 multi layers with different elastic properties and 3 random distributed micas rows of horizontally aligned elements with the same elastic properties the models show the nucleation and propagation of fractures during ductile deformation and flow perturbation and localization in the vicinity of fractures voids localize along extension fractures at intersections of conjugate shear fractures and in small pull apart structures along shear fractures which look identical to boudin necks in isolated stiff layers results show that strain localization is strong in models with lower elastic constants and anisotropy whereas it is distributed in the models with higher elastic constants and anisotropy in which asymmetric and complex geometries develop the models successfully show the development of and transitions between a single layer multi layer and foliation boudinage that are common structures in high strain zones

quartz veins record earthquake related brittle failure and short term ductile flow in the deep crust abstract discordant quartz veins in a retrograded eclogite amphibolite western gneiss region norway formed at temperatures of about 500 to 550 c the parental fractures crosscut the foliation and show branching indicating rapid crack propagation at high differential stress the shape of the quartz veins indicates intense inhomogeneous ductile deformation of the host rock during opening and sealing controlled by the presence of the cohesionless fluid filled fractures the vein quartz microfabrics indicate crystallization in an open cavity implying a stage of very high permeability and fluid flow the event of brittle failure at 500 to 550 c followed by an episode of inhomogeneous ductile deformation is attributed to stress changes related to the earthquake cycle i e coseismic loading and postseismic creep the record suggests seismic activity at the nearby low angle normal fault at 15 to 25 km depth and provides insight into transient crustal properties and processes near active faults at great depth

new evidence for coesite in eclogite and gneisses defining an ultrahigh pressure province in the western gneiss region of norway widespread evidence of ultrahigh pressure metamorphism is reported from the nordfjord and stadtlandet area of the western gneiss region in norway outlining a distinct ultrahigh pressure province coesite has been found as inclusions in garnet omphacite or kyanite in eclogite from 5 new localities and quartz pseudomorphs after coesite occur in eclogite minerals at an additional 12 localities quartz pseudomorphs after coesite within garnet and clinozoisite are reported for the first time from associated gneisses which is evidence for in situ ultrahigh pressure metamorphism at least at a local scale the boundary to an ultrahigh pressure province is defined by a metamorphic break from lower pressure 2 8 gpa within a 10 km wide mixed zone in the nordfjord area this zone may mark the disrupted tectonic boundary to a small ultrahigh pressure unit and casts doubt on the assumption that the western gneiss region behaved as a coherent terrane during burial and exhumation

evolution of caledonian deformation fabrics under eclogite and amphibolite facies at vardalsneset western gneiss region norway the vardalsneset eclogite situated in the western gneiss region sw norway is a well preserved tectonite giving information about the deformation regimes active in the lower crust during crustal thickening and subsequent exhumation the eclogite constitutes layers and lenses variably retrograded to amphibolite and is composed of garnet and omphacite with varying amounts of barroisite actinolite clinozoisite kyanite quartz paragonite phengite and rutile the rocks record a five stage evolution connected to caledonian burial and subsequent exhumation 1 a prograde evolution through amphibolite facies t 490 63 c is inferred from garnet cores with amphibole inclusions and bell shaped mn profile 2 formation of l s tectonite eclogite t 680 20 c p 16 2 kbar related to the subduction of conti nental crust during the caledonian orogeny lack of asymmetrical fabrics and orientation of eclogite facies extensional veins indicate that the deformation regime during formation of the l s fabric was coaxial 3 formation of sub horizontal eclogite facies foliation in which the finite stretching direction had changed by approximately 90 disruption of eclogite lenses and layers between symmetric shear zones characterizes the dominantly coaxial deformation regime of stage 3 locally occurring mylonitic eclogites t 690 20 c p 15 1 5 kbar with top w kinematics may indicate however that non coaxial deformation was also active at eclogite facies conditions 4 development of a widespread regional amphibolite facies foliation t 564 44 c p 10 3 8 1 kbar quartz veins and development of conju gate shear zones indicate that coaxial vertical shortening and sub horizontal stretching were active during exhumation from eclogite to amphibolite facies conditions 5 amphibolite facies mylonites mainly formed under non coaxial top w movement are related to large scale movement on the extensional detachments active during the late orogenic extension of the caledonides the structural and metamorphic evolution of the vardalsneset eclogite and related areas support the exhumation model including an extensional detachment in the upper crust and overall coaxial deformation in the lower crust

microstructural evolution of syntaxial veins formed by advective flow veins are common in earth s crust and are formed by a wide range of processes which lead to crystal growth in dilation sites the first order processes in vein formation have been identified but it is much less clear how these can be diagnosed from field studies in order to better understand the microstructural evolution during vein growth we grew veins of analogue material alum kal so4 2 12h2o in a transmitted light cell from an advecting supersaturated fluid real time observation shows the effects of flow rate and supersaturation on the evolving microstructure 1 along vein trends in growth rate caused by decreasing supersaturation and 2 growth competition between clear crystals in the absence of nucleation and primary fluid inclusions although the overall trends in growth rate are in agreement with previous work the local effects at the scale of individual grains reported here are less well understood these new data form a basis for better interpretation of natural microstructures to explore the possible effects of experimentally observed processes during vein growth we simulate the growth kinetics of a quartz vein at various conditions of advective flow in earth s crust results show that in general the along vein changes in growth rate occur at length scales much larger than a typical outcrop

experimental study of syntaxial vein growth during lateral fluid flow in transmitted light first results abstract in situ observations of transmitted light experiments of syntaxial vein growth during lateral fluid flow in a simulated fracture show a decrease in growth rate towards the downstream end as a consequence the fracture is sealed at the inlet our observations show the rapid non linear growth competition of grains which is a result of anisotropic growth kinetics and the complex fluid flow around the individual crystals we compared our results with simulations based on a simplified numerical model which builds on existing simulation techniques of this system the model incorporates plug flow and a fluid flow velocity dependent crystal growth rate law based on literature data simulations are in reasonable agreement with experimental results a sensitivity analysis shows that a high fluid flow velocity and a low supersaturation increase the potential to seal a vein homogeneously in agreement with previous work additionally the effect of the initial crack shape is explored

cascadia subducting plate fluids channelled to fore arc mantle corner ets and silica deposition in this study we first summarize the constraints that on the cascadia subduction thrust there is a 70 km gap downdip between the megathrust seismogenic zone and the episodic tremor and slip ets that lies further landward there is not a continuous transition from unstable to conditionally stable sliding seismic rupture occurs mainly offshore for this hot subduction zone ets lies onshore we then suggest what does control the downdip position of ets we conclude that fluids from dehydration of the downgoing plate focused to rise above the fore arc mantle corner are responsible for ets there is a remarkable correspondence between the position of ets and this corner along the whole margin hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore arc mantle laboratory data show that such fore arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone at the fore arc mantle corner these fluids are released upward into the more permeable overlying fore arc crust an indication of this fluid flux comes from low poisson s ratios and vp vs found above the corner that may be explained by a concentration of quartz which has exceptionally low poisson s ratio the rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner

rheology of the plate interface dissolution precipitation creep in high pressure metamorphic rocks abstract subduction zone models invoke deformation to be concentrated along the plate interface in a region of particularly low temperature geophysical observations do not provide constraints on temperature stress and deformation patterns with desired resolution in contrast the record of high pressure metamorphic rocks exhumed from subduction zones provides details on p t history deformation mechanisms and stress state albeit not readily correlated with the former dynamic situation on larger scale here we review available information on dissolution precipitation creep dpc in high pressure metamorphic rocks which if representative for subduction zones in general can pose constraints on conditions rheology and flow patterns along the plate interface the key observations and conclusions are that 1 deformation is typically highly inhomogeneous and localized into shear zones 2 stresses are generally too low to drive crystal plastic deformation 3 microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism 4 an aqueous fluid at quasi lithostatic pressure is available throughout allowing for tensile fracturing and crack healing or sealing 5 low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity and 6 contribution of shear heating to the thermal budget of subduction zones should be moderate the dominant deformation mechanism dpc is reviewed in some detail including experimental and theoretical approaches various examples of dpc in high pressure metamorphic rocks are illustrated emphasizing the role of interphase boundaries as sites of dissolution rheology governed by dpc is proposed to control interplate coupling and development of a subduction channel with return flow being a likely candidate for rapid exhumation of high pressure metamorphic rocks

age of matuyama brunhes boundary constrained by u pb zircon dating of a widespread tephra abstractthe youngest geomagnetic polarity reversal the matuyama brunhes boundary mbb provides an important datum plane for sediments ice cores and lavas its frequently cited age of 780 ka is based on orbital tuning of marine sedimentary records and is supported by 40 ar 39 ar dating of hawaiian lavas using recent age calibrations challenging this age how ever are reports of younger astrochronological ages based on oxygen isotope stratigraphy of high sedimentation rate marine records and cosmogenic nuclides in marine sediments and an antarctic ice core here we present a u pb zircon age of 772 7 7 2 ka from a marine deposited tephra just below the mbb in a forearc basin in japan u pb dating has a distinct advantage over 40 ar 39 ar dating in that it is relatively free from assumptions regarding stan dardization and decay constants this u pb zircon age coupled with a newly obtained oxygen isotope chronology yields an mbb age of 770 2 7 3 ka our mbb age is consistent with those based on the latest orbitally tuned marine sediment records and on an antarctic ice core we provide the first direct comparison between orbital tuning u pb dating and magnetostratig raphy for the mbb fulfilling a key requirement in calibrating the geological time scale introduction

vein quartz microfabrics indicating progressive evolution of fractures into cavities during postseismic creep in the middle crust discordant quartz veins in metamorphic rocks formed at temperatures similar to 300 c in an extensional tectonic regime the vein shape is characterized by an aperture to length ratio exceeding the maximum value feasible for purely elastic deformation by orders of magnitude non elastic ductile deformation of the host rock must have controlled widening of the arrested cracks fracture parallel shortening is low due to the low accumulated strain the microstructural record of this stage of deformation cannot be isolated in the polyphase host rock information is exclusively obtained from the microfabrics of the vein sealing quartz there the density of geometrically necessary dislocations derived from orientation maps created by electron backscatter diffractometry ebsd decreases markedly from the vein wall to the centre the gradient is attributed to progressive cavity formation and buckling of the vein walls during sealing early grown crystals at the vein margins record a prolonged deformation history compared to lately grown grains in the centre of the vein the gradient and the lack of significant crystal plastic deformation of the crystals in the vein centre show that deformation of the completed vein is insignificant compared to deformation during progressive opening and sealing in view of the precursory brittle deformation and the intense crystal plastic deformation at the vein margins the monogenetic veins are interpreted to record a single mid crustal stress transient related to the earthquake cycle fracturing is proposed to be a consequence of coseismic loading while progressive opening and sealing record the deformation during postseismic stress relaxation by creep

stable isotope geochemistry and formation mechanisms of quartz veins extreme paleoaltitudes of the central alps in the neogene quartzveins ranging in size from less than 50 cm length and 5 cm width to greater than 10 m in length and 5 m in width are found throughout the central swiss alps in some cases the veins are completely filled with milky quartz while in others sometimes spectacular void filling quartz crystals are found the style of vein filling and size is controlled by host rock composition and deformation history temperatures of vein formation estimated using stable isotope thermometry and mineral equilibria cover a range of 450 c down to 150 c vein formation started at 18 to 20 ma and continued for over 10 my the oxygen isotope values of quartz veins range from 10 to 20 permil and in almost all cases are equal to those of the hosting lithology the strongly rock buffered veins imply a low fluid rock ratio and minimal fluid flow in order to explain massive nearly monomineralic quartz formation without exceptionally large fluid fluxes a mechanism of differential pressure and silica diffusion combined with pressure solution is proposed for early vein formation fluid inclusions and hydrous minerals in late formed veins have extremely low d values consistent with meteoric water infiltration the change from rock buffered static fluid to infiltration from above can be explained in terms of changes in the large scale deformation style occurring between 20 and 15 ma the rapid cooling of the central alps identified in previous studies may be explained in part by infiltration of cold meteoric waters along fracture systems down to depths of 10 km or more an average water flux of 0 15 cm3 cm 2yr 1 entering the rock and reemerging heated by 40 c is sufficient to cool rock at 10 km depth by 100 c in 5 million years the very negative d values of

elevated stresses and creep rates beneath the brittle ductile transition caused by seismic faulting in the upper crust 1 large faults in the brittle upper continental crust are envisaged to terminate near the brittle ductile transition zone at a depth that is a complex function of material properties temperature stress and strain rate here we investigate the effect of coseismic displacement along a fault in the upper crust on the adjacent middle and lower crust using a two dimensional numerical model of faulting within an elastic frictional viscous rheology results demonstrate that a major displacement event can cause a dramatic increase in differential stress and creep strain rates in the crust near and below the lower termination of the fault a transient deflection of the brittle ductile transition zone and a zone of elevated strain rates down to the base of the crust the perturbation decays over timescales consistent with postseismic relaxation the stresses and strain rates predicted in such models are in accord with those inferred from microstructural damage analysis of exhumed metamorphic rocks indicating short term deformation at decaying stress and strain rates

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

textural record of the seismic cycle strain rate variation in an ancient subduction thrust active faults slip at different rates over the course of the seismic cycle earthquake slip c 1 m s 1 interseismic creep c 10 100 mm year 1 and intermediate rate transients e g afterslip and slow slip events studies of exhumed faults are sometimes able to identify seismic slip surfaces by the presence of frictional melts and slow creep by textures diagnostic of rate limited plastic processes the pasagshak point thrust preserves three distinct fault rock textures which are mutually cross cutting and can be correlated to different strain rates ultrafine grained black fault rocks including pseudotachylyte were formed during seismic slip on layers up to 30 cm thick well organized s c cataclasites 7 31 m thick were formed by slow creep with pressure solution as a dominant rate limiting mechanism these must have formed at strain rates consistent with long term plate boundary motion but solution creep healing acted to reduce porosity of the cataclasites and eventually restricted fluid connectivity such that creep by this mechanism could not continue disorganized non foliated rounded clast cataclasites were formed at shear rates faster than solution creep and are interpreted as representing shear at intermediate strain rates these could have formed during afterslip or delocalization of slip associated with an earthquake rupture

two dimensional numerical modeling of fracturing and shear band development in glacier fronts in this contribution we present a two dimensional numerical model of a deforming glacier front the model is based on a hybrid lattice spring network approach where particles in the model can deform in a volume conservative visco elastic manner but at the same time they can be compressed elastically and fracture by discrete failure we restrict ourselves to a simple setting where the glacier sits on a frictionless slope that dips with 5 10 the ice block is fixed on one side and has a free surface on the other the glacier varies in viscosity and can flow at the base whereas it is brittle at the top results show that the head of the glacier is unstable failure happens as a combination of extension fractures crevasses at the top surface of the glacier and shear fractures that are dipping toward the glacier head once the shear fractures intersect with the free side wall of the glacier a triangular ice block is carving from the glacier head during successive flow of the glacier the failure is stepping backwards into the glacier and large shear planes develop that connect the sliding ice at the base with crevasses at the top variations of overall viscosity of the glacier indicate that higher viscosities and thus a more brittle glacier lead to larger spacing of shear surfaces and thus to larger ice blocks that are carving from the head of the glacier in addition the geometry of the deformation structures within the glacier does not vary significantly with the height of the ice indicating that larger glaciers carve larger blocks a higher tilt of the ground surface however leads to tighter spacing of shear surfaces and a more pronounced crevasse development this indicates that glacier heads that lie on steeper slopes will carve smaller blocks than glacier heads that lie on shallower slopes failure and carving of ice from the model glaciers is a combination of early developing closely spaced extension fractures crevasses and later developing wider spaced and more localized shear fractures or shear zones

how vein sealing boosts fracture widening rates the buckling enhanced aperture growth mechanism for syn tectonic veins abstract the paper introduces the mechanism of buckling enhanced aperture growth for syn tectonic veins that formed in simple shear dominated kinematic frameworks in the middle or lower crust apart from the well understood concepts of fracture widening driven by effective tensile stresses buckling enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn tectonic veins driven by fracture parallel compressive creep strain in the host rocks thus the mechanism proposed here follows similar principles as tectonic folding although important differences exist inspired by the structural record of low aspect ratio veins exposed in hp lt metamorphic rocks cropping out on south evia island greece generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates the models indicate 1 that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers 2 an increase in the thickness of the cement layers cause acceleration of aperture growth 3 that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips and 4 that fracture aperture growth is possible against fully compressive fracture normal stresses the buckling enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture bound permeability and for the mechanical state of the middle and lower crust in seismically active regions

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

static recrystallization of vein quartz pebbles in a high pressure low temperature metamorphic conglomerate abstract microfabrics of quartz pebbles in hp lt c 1 gpa c 350 c metamorphic conglomerates are investigated the conglomerate was deformed by dissolution precipitation creep while the interior of the pebbles remained undeformed the different pebbles display a wide variety of quartz microstructures imported from the source rocks one type of pebble is derived from quartz veins it shows old grains with numerous fluid inclusions subgrains and undulatory extinction which are partly replaced by new grains devoid of inclusions and substructure free dislocation densities are on the order of 1012 m 2 in both grains we conclude that 1 the quartz vein underwent inhomogeneous crystal plastic deformation in the source rock 2 recrystallization took place by strain induced grain boundary migration starting from small crystalline volumes poor in defects 3 recrystallization was purely static and commenced during re burial of the conglomerate which 4 was simultaneously deformed by dissolution precipitation creep at low differential stress insufficient for crystal plastic deformation of quartz 5 fluid inclusions within old grains were eliminated and their fluid content was drained along the migrating high angle grain boundaries and 6 strain induced grain boundary migration ceased once the driving force became too low by static recovery concurrent to recrystallization within the deformed old grains