folded continental and oceanic nappes on the southern side of monte rosa western alps italy anatomy of a double collision suture 1 previous work suggested a double collision suture including ophiolites from two oceanic basins valais and piemont liguria on the southern side of monte rosa penninic alps northern italy this area was studied using field mapping microstructural analysis and neutron texture goniometry after its formation and eclogite facies metamorphism of continental and oceanic units the suture was deformed by four successive folding and shearing events under greenschist facies conditions all of them taking place between 40 and 28 ma after fold retrodeformation the following tectonostratigraphy results from base to top monte rosa gneiss european margin balma serpentinite eclogite unit cretaceous crust of valais ocean stolemberg gneiss iberia brianconnais continent zermatt saas and tsate ophiolites jurassic crust of piemont ligurian ocean sesia nappe continental fragment off the adria margin the preservation of this lithological sequence suggests that deep seated deformation during multiple continent collision produces heterogeneous strain and extreme thinning of nappes but their original stacking order can still be reconstructed using kinematic analysis and overprinting criteria this is due to the ductile nature of the collisional deformation which retains the continuity of tectonic contacts

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

nappe geometry in the western swiss alps abstract detailed geological mapping during the last 20 years in the western swiss alps has shown clearly that most of the lower basement nappes are fold nappes possessing normal and inverted limbs moreover their cores are made of strongly deformed gneisses indicating that important ductile strain took place during the formation of the fold nappes it is therefore probably wrong to imagine deep basement nappes as rigid slices as often actually claimed especially when interpreting seismic profiles true brittle type thrust nappes involving basement rocks only occur in the internal and upper parts of the belt cover nappes on the contrary are in most parts of the alpine belt thrust sheets following more or less the rules of thin skinned tectonics many basement fold nappes lost part of their sedimentary cover during or just before their formation by decollement along ductile horizons the result is that many cover thrust nappes in the external part of the alps are directly related to their original basement fold nappes

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

metamorphic evolution of the sesia lanzo zone western alps time constraints from multi system geochronology the sesia lanzo zone is a polymetamorphic unit containing hercynian granulite relics overprinted by eclogite and greenschist facies metamorphism and deformation during the alpine orogeny different parts of the unit record different stages on the p t deformation evolution allowing multi system isotopic studies to unravel the precise timing of the metamorphic history new rb sr white mica and u pb sphene data constrain the age of eclogite facies metamorphism and deformation to 60 70 ma this substantially alters the common view of early to mid cretaceous eclogite facies metamorphism in this unit the new results are more consistent with the established geotectonic framework for the alpine orogeny since they do not require a prolonged period of depressed geothermal gradient at a time when the region was in extension it is also more concordant with recent studies of other units that demonstrate post cretaceous high pressure metamorphism step heated 40ar 39ar analysis of phengites yields good plateaux giving ages older than the corresponding rb sr age such anomalously high ages indicate the presence of radiogenic argon rich fluids in the grain boundary network under the fluid pressure conditions acting during this high pressure metamorphic event the u pb sphene ages are variable in polymetamorphic rocks and show inheritance of older pb or sphene crystals into the high pressure event two monometamorphic assemblages yield concordant ages at 66 1 ma reflecting crystallisation of the eclogite facies assemblage the gneiss minuti complex gmc lies structurally below the eclogitic micaschists and its pervasive greenschist facies fabric yields tightly clustered rb sr white mica ages at 38 39 ma this greenschist event did not affect the majority of the emc the 40ar 39ar ages of micas formed at this time were very disturbed whereas micas surviving from an earlier higher pressure assemblage had their 40ar 39ar system reset the greenschist event did not strongly affect u pb systematics in hercynian age sphenes suggesting that the gmc did not uniformly suffer an eclogite facies metamorphism during the alpine cycle but was juxtaposed against the emc later in the orogeny this model still requires that the locus of deformation and metamorphism and possibly fluid flux moved outboard with time leaving the sesia lanzo basement as a shear bounded unreactive block within the orogenic wedge

compression versus extension in the exhumation of the dora maira coesite bearing unit western alps italy abstract several recent papers suggest that uplift and exhumation of high pressure low temperature hp lt metamorphic rocks are due to crustal extension coeval with and or post dating the contraction responsible for the metamorphism a detailed survey of the coesite bearing unit of the southern dora maira massif offers an opportunity to discuss the relative importance of extension and compression in the exhumation tectonics of ultra high pressure uhp rocks this uhp unit consists of pre alpine basement rocks which equilibrated at a depth of 100 km probably 120 100 ma ago it is overlain by two units with a similar lithology and eoalpine metamorphic age and high p t gradients which equilibrated at 60 and 50 km respectively this eoalpine basement complex is intercalated between blueschist facies units the whole pile was affected by a mesoalpine greenschist facies mylonitic deformation during which the early contacts were reactivated as low angle shallow dipping shear zones extension is documented only during the mesoalpine collisional period and is referred to the gravity collapse of a thickened orogenic wedge with an exhumation rate of about 1 mm yr the most important part of the exhumation of the uhp rocks occurred earlier at a higher rate close to 4 mm yr a forced return flow or extrusion tectonics of imbricate slices in an on going subduction setting seems appropriate to account for this early stage the fact that the omission of intermediate pressure rocks between juxtaposed units is an unreliable criterion for demonstrating extension is discussed

late stage deformation in a collisional orogen western alps nappe refolding back thrusting or normal faulting nappe refolding back thrusting and normal faulting frequently cause severe late stage overprinting of the architecture of an orogen a combined investigation of nappe stack polarity kinematics of shearing and metamorphic gradients in the western alps develops criteria for distinguishing between these three modes of late stage deformation this distinction is a prerequisite for any retro deformation necessary for understanding the main tectonic and metamorphic evolution of collisional orogens in the case of the western alps overprint was by mega scale nappe refolding in the oligocene this implies exhumation of the hp rocks prior to postnappe folding i e during nappe stacking and by foreland directed ascent within a subduction channel

tertiary age and paleostructural inferences of the eclogitic imprint in the austroalpine outliers and zermatt saas ophiolite western alps the austroalpine sesia lanzo inlier and upper austroalpine dent blanche mt mary and pillonet outliers occur on top of the western alpine orogenic wedge and as a whole override the structurally composite ophiolitic piemonte zone instead the mt emilius glacier rafray etirol levaz and other lower austroalpine eclogitic outliers are inserted within the piemonte zone between its upper combin and lower zermatt saas tectonic elements or within the latter rb sr dating on phengitic micas show that the eclogitic imprint in the lower austroalpine outliers conventionally regarded as late cretaceous by comparison with the sesia lanzo inlier is of eocene age 49 40 ma like the underlying zermatt saas ophiolite 45 42 ma between the aosta valley and gran paradiso massif 40ar 39ar plateau ages on the same mica concentrates of the ophiolitic zermatt saas nappe 46 43 ma are consistent with rb sr dating whereas that on the austroalpine glacier rafray klippe 92 ma is influenced by argon excess the lower austroalpine outliers underwent the subduction metamorphism concurrently with the zermatt saas nappe 20 25 ma later than the eclogitic sesia lanzo inlier and blueschist pillonet klippe the temporal gap and present intra ophiolitic position mean that the lower austroalpine outliers were probably derived from an intraoceanic extensional allochthon mt emilius domain stranded inside the piemonte ligurian ocean far from the dent blanche sesia domain and adriatic margin

contrasting plate tectonic styles of the qinling dabie sulu and franciscan metamorphic belts the dabie mountains are part of the 2000 km long qinling dabie sulu suture zone juxtaposing the sino korean and yangtze cratons an eastern extension apparently crosses korea and lies along the japan sea side of honshu as the imjingang and sangun terranes respectively a northeastern segment may be present in sikhote alin russian far east this orogenic belt records late paleozoic ocean floor consumption and the triassic collision of two precambrian continental massifs in east central china coesite and microdiamond inclusions in strong refractory minerals of eclogite facies ultrahigh pressure uhp metamorphic rocks in the dabie sulu area attest to profound subduction of a leading salient of the old cold yangtze craton now recovered through tectonic exhumation and erosion northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high pressure hp and uhp metamorphism documented in the western alps in both regions subduction of narrow prongs of continental material uhp metamorphism and return toward midcrustal levels of relatively lower density buoyant microcontinental blocks resulted from delamination of these rocks from the descending higher density oceanic crust capped lithospheric plate such salients of continental crust represent an integral structural part of the downgoing slab remain intact and may be dragged to great depths before disengaging and rising differentially as coherent blocks uhp parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 c and 28 35 kbar or more in contrast pacific type hp metamorphic belts as represented by the franciscan complex of western california recrystallized under physical conditions up to 200 500 c 10 3 kbar in this setting voluminous quartzo feldspathic and graywacke debris was carried downward on oceanic crust capped lithosphere choking the subduction zone with incompetent material sited between both plates and strongly adhering to neither this buoyant largely sedimentary complex decoupled at 25 30 km depth and ascended toward the surface in both alpine type intracontinental collision and pacific type underflow light sialic material displaced dense mantle thus the return to midcrustal levels was propelled dominantly by body forces

fold controlled quartz textures in the pennine mischabel backfold near zermatt switzerland abstract quartz fabric analyses along the basal thrust of the dent blanche nappe and in the footfall pennine units indicate south directed thrusting for the last stage of austro alpine pennine nappe emplacement quartz fabrics in particular those from the pennine mischabel backfold imply complex spatial and temporal texture developments with crystallographic preferred orientations cpo that are commonly in disagreement with mesoscopic grain shape lineations in consequence kinematic directions inferred by quartz textures do not necessarily coincide with those predicted by mesoscopic structural elements such as grain shape lineations in our particular case orientation of grain shape lineations is rather complex in the study area while principal axes inferred from the quartz textures remain geographically constant and exhibit a simple geometric relationship to the mischabel backfold it is suggested that the grain shape lineations correspond to the total accommodated finite strain whereas the quartz fabrics reflect late increments of deformation quartz cpos in the hinge of the mischabel fold are similar to those along the thrust revealing asymmetric single girdles to c axes point maxima subgrain rotation is the predominant recrystallization mechanism suggesting steady state conditions in fabric development during progressive rotational deformation in contrast asymmetric cross girdles dominate the upper limb and uneven small circle c axes distributions characterize the lower limb although recrystallization in both limbs is characterized by grain boundary migration this clear separation of quartz textures and recrystallization deformation mechanism conflicts with the common view on heterogeneous deformation patterns in folds where the major component of rotational shear is expected in the fold limbs our study suggests that fabric development in the limbs of the recumbent mischabel fold was reset during progressive deformation shortly prior to the transition from an active buckling to passive fold amplification while the hinge suffered continuous bulk deformation provided by the back thrusting of the dent blanche nappe

horizontal contraction or horizontal extension heterogeneous late eocene and early oligocene general shearing during blueschist and greenschist facies metamorphism at the pennine austroalpine boundary zone in the western alps mylonitic structures related to two orogenic events are described from the upper and lower contacts of the combin zone and the immediately overlying upper austroalpine dent blanche nappe mont mary klippe and the directly underlying lower austroalpine etirol levaz slice the first event late eocene in age commenced during blueschist facies p t conditions but pre dated the peak of subsequent greenschist facies overprint the second event early oligocene in age took place during retrograde greenschist facies conditions most sense of shear indicators associated with the retrograde mylonites indicate top se shearing but subordinate top nw displacing shear sense indicators have also been mapped mylonitic top se shearing appears to be restricted to the combin zone and its upper and lower contacts within the dent blanche nappe and mont mary klippe and at the base of the etirol levaz slice structures were observed which developed during blueschist greenschist facies conditions and are in conjunction with the p t t history of these rocks inferred to be older associated kinematic data indicate a top nw shear sense comparable blueschist greenschist facies shear sense indicators have not been observed in the combin zone nonetheless the foliation in the combin zone shows a progressive evolution from blueschist facies to greenschist facies to retrograde greenschist facies conditions this indicates that the combin zone and the immediately over and underlying austroalpine units shared a common tectono metamorphic evolution since the late eocene finite strain data reveal oblate strain fabrics which are thought to result from a true flattening strain geometry flow path modelling reveals a general non coaxial deformation regime and corroborates significant departures from a simple shear deformation in the study area mylonitic top se shearing in the combin zone is attributed to early oligocene backfolding and backthrusting of the mischabel phase temperature time curves suggest slight reheating in the monte rosa nappe underneath and cooling in the dent blanche nappe above the combin zone hence confirming a thrust interpretation for this event the top nw displacing structures are thought to result from late eocene emplacement of the dent blanche nappe and the combin zone onto the middle pennine barrhorn series along the combin fault as related structures initiated during mildly blueschist facies conditions in the dent blanche nappe and the underlying combin zone and both were emplaced together onto the greenschist facial barrhorn series it is concluded that the structures developed as the nappes moved upward relative to the earth s surface thus the combin fault is regarded as a thrust the geometry of this structure indicates that the combin fault is an out of sequence thrust that locally cut down section hence top nw out of sequence thrusting caused local thinning of the metamorphic structural section in association with horizontal shortening out of sequence thrusts cutting down section and back thrusts offer the possibility of explaining the pronounced break in the grade of metamorphism across the combin fault i e the contact between the eclogite facial zermatt saas zone and the overlying lower grade combin zone by contractional deformation

early 21st century glacier thickness changes in the central tien shan abstract although studies based on satellite gravimetry 2003 2010 and laser altimetry 2003 2009 measurements have achieved region wide glacier mass change for the tien shan the dynamic process of glacier yet to be closely monitored and understood so that its impact can be assessed accurately in this study we investigated region wide glacier thickness change in the central tien shan cts during 2000 2012 by differencing the shuttle radar topographic mission srtm digital elevation model dem with a newly constructed dem from 27 tandem x images for a total glacier area of 7239 8 527 2 km 2 an average glacier thickness change rate of 0 24 0 22 m a was derived this result agrees well with the result based on satellite laser altimetry measurements reported earlier 0 31 0 41 m a with temporal synchronization a fine spatial resolution and wide coverage our measurements are able to reveal abundant glacier change features and dependencies in the cts firstly the lower mountains have seen a more severe glacier decline and the glaciers facing the prevailing wind westerlies have experienced a greater decline because of the stronger evaporation furthermore those glaciers lying along the extremely high meridian mountain range have obviously gained mass in their upper reaches because the air current from the west is blocked and lifted by the meridian mountain range secondly for the entire glacier body the theoretical hyperbolic dependence between debris thickness and ice decline was very difficult to establish some huge glaciers covered by heavy debris have still experienced a severe decline however even though the heavy debris did not prevent the ablation its attenuating effects were considerable thirdly for the glaciers that surged before 2000 the mass gain in the restoring zones has not been enough to cover the mass loss in ablation zones some large glaciers surged again during 2000 2012 however with much lower magnitudes than in previous surges in general the surge glaciers have experienced a greater decline than the non surge glaciers fourthly due to the ice front calving and subglacial thermal erosion glaciers connected to proglacial lakes have receded and thinned much more rapidly than the land terminated glaciers overall the glaciers in the cts are more stable than those in other parts of the tien shan however the glacier state there is still alarming a moderate average thinning rate was derived because the drastic thinning in the ablation zones was balanced by the slight thinning in the broad accumulation zones

tectonic implications of lawsonite formation in the sesia zone western alps lawsonite of early alpine age formed in different tectonic sub units of the sesia zone western italian alps in the southern part of the eclogitic micaschists subunit em lawsonite grew with quartz jadeite during the early alpine retrograde path which just post dates the eclogite thermal peak the early retrograde path of the southern em occurred at decreasing temperature and at p t conditions comparable to those of the metamorphic peak in some blueschist facies thrust sheets which separate the em from the southern alps such a post eclogitic cooling path may have been induced by conductive cooling linked to migration of the underthrust surfaces and to stacking with colder nappes like the other sesia subunits or the piemonte metaophiolites stacking and thermal interaction between the different units probably occurred at depth during the early stages of exhumation which followed subduction underthrusting of early mid cretaceous age during the paleogene continental collision between the european and african plates determined further underthrusts of more westerly units these units underwent a high pressure very low temperature recrystallization meso alpine event characterized by the growth of lawsonite at the peak metamorphic conditions consequently propagation of the underthrust surfaces may represent an effective mechanism to prevent the rise of the isotherms and to favor post peak cooling paths in some units of the western alps this effect is more obvious in the structurally upper units which were first brought to deep crustal levels in the early alpine imbricated subduction zone

neogene lateral extension during convergence in the central alps evidence from interrelated faulting and backfolding around the simplonpass switzerland abstract the simplon fault zone occurs at the western end of the lepontine metamorphic dome in the central alps and represents a major low angle 25 dip normal fault associated with wsw ene directed lateral extension movement began in the early miocene and continued until at least 3 ma accumulating a total vertical throw of around 10 km corresponding to 24 km displacement parallel to the fault this displacement is partitioned between a broad zone of ductile mylonites in the footwall and a more discrete cataclastic detachment fault the simplon line in the central region simplon village to zwischbergen some 3 km of the total vertical displacement is accommodated by the discrete cataclastic zone due to the higher exposed structural level the importance of the cataclastic component increases towards the northwest in the northern steep belt around the simplonpass retrograde greenschist facies mylonite formation and younger cataclastic faulting associated with lateral extension occurred contemporaneously with sse vergent large scale backfolding representing nnw sse shortening and crustal thickening the combined effect was an overall shortening across the orogen accommodated by an extension parallel to the orogen allowing lateral escape of continental material normal faulting and the resultant lateral escape was not just superficial it extended to depths of at least 15 km and probably to depths exceeding 25 km the overall geometry and kinematics of the simplon fault zone and in particular the interplay between folding and faulting is very similar to that described from the metamorphic core complexes and detachment faults of the cordillera of the southwestern usa within the central alps extension was associated with rapid exhumation of the lepontine metamorphic dome as evidenced by very rapid cooling rates determined from mineral ages in the footwall similar to the cenozoic tectonics of the himalayas and tibet orogen parallel extension in the mountain belt may have been promoted by an overall reduction in the horizontal compressive stress in this direction more limited extension of the same age and orientation is known from a large area of the european foreland greater extension in the mountain belt compared with the foreland was accommodated by major strike slip transfer fault systems and was linked to coeval overthrusting of the lowlands towards the southwest in the external southwestern alps of haute provence france coeval folding and orogen parallel extension such as at the simplonpass were developed in a dextral transpressive regime due to oblique wnw ese convergence across the alps during the neogene

sequence and style of major post nappe structures simplon pennine alps abstract in the upper pennine nappe complex of the simplon pennine alps switzerland and italy at least three phases of major post nappe folding in places associated with thrusting can be distinguished these are superimposed on an earlier formed partly chaotic complex of tectonic units including the bernhard and monte rosa continental flakes and the zermatt saas and antrona ophiolite complexes the earliest post nappe folds were essentially isoclinal throughout the whole region and were accompanied by a strong schistosity which is the main foliation in most areas later two successive phases of back folding led to the present overall structure both phases typically show rapid variations in style from open folds lacking axial planar schistosity to very tight structures with complete foliation transposition this has been demonstrated by systematically mapping the major axial traces over the whole region successively removing the major structures in reverse order shows that the ophiolite complexes were originally part of a continuous unit marking an important suture between the bernhard and monte rosa nappes

misalignment of quartz c axis fabrics and lineations due to oblique final strain increments in the ruby mountains core complex nevada abstract to interpret c axis stereonet patterns of deformed quartz the patterns must be viewed in the xz strain plane which is usually assumed to contain the elongation lineation this study describes several c axis patterns from a region of complex amphibolite facies deformation in the northern ruby mountains where the late xz plane is oblique to most of the lineations without the lineation as a guide the proper orientation for interpretation of each pattern is determined by rotating the c axis data around the normal to the foliation until the c axes within the foliation plane lie at the center of the stereonet this new view is inferred to be the xz plane for the final increments of strain the rotation produces an internal symmetry in the patterns in addition the rotated views across the area show a more consistent geographic orientation than the lineations this geographic orientation is aligned with strain in a mylonitic shear zone which represents the latest macroscopic evidence for plastic strain along the edge of the study area the complete reorientation of the quartz textures during the final strain increments implies that they record very little of the finite strain history quartz is the only mineral recrystallized during the late strain thereby providing insight into the geometry of strain increments that cannot be determined from other minerals

kinematics of an arcuate fold thrust belt the southern eastern carpathians romania abstract flysch and molasse nappes of the eastern carpathians strike mainly n s and were folded and imbricated since the late early cretaceous boundaries of stratigraphic and structural units and calculated fold trend axes from the southern part of the eastern carpathians indicate a curvature of the orogen by 80 kinematic data from fault slip analysis of all nappe systems exposed in the arc document an overall nw se contraction nappes of the external moldavides nappe complex underwent deformation since the late cretaceous peaking in the miocene and exhibit fanning subhorizontal contraction axes from e w in the n striking part of the eastern carpathians through wnw ese and nw se in the northern part of the arc to nnw sse in its southwestern part geometric relations between faults and folds indicate that this fan pattern reflects an extended interval and was contemporaneous to nappe stacking and subsequent continental collision statistical analysis reveals correlation between orientation of the fanning kinematic axes and the structural trend where fanning of subhorizontal contraction axes is systematically smaller than change of strike of fold thrust structures orogen parallel extension in the tarcau nappe of the moldavides nappe complex is estimated to be 20 this low value of orogen parallel extension indicates a primary arc in contrast to bending of a previously straight fold thrust belt low orogen parallel extension and the observed pattern of structural and kinematic axes can be simulated in sand wedge indentation models where the indenter moves oblique to its margins in these models thrust traces and fold axes are curved around the arc but are parallel to the margins of the indenter away from the corner area the movement directions of the thrust faults in the models are deflected from normal to fault strike towards the movement direction of the indenter leading to fanning contraction directions similar to those observed in the eastern carpathian arc thus the main controlling factors on arc formation were the plate margin geometry i e the shape of the upper plate and the movement direction of the upper plate relative to the orientation of its margins the influence of the geometry of the continental margin in the lower plate was mainly by imposing constraints on the movement direction of the upper plate

a 40ar 39ar laser probe study of micas from the sesia zone italian alps implications for metamorphic and deformation histories two samples from the eclogite micaschist complex emc and the seconda zona diorito kinzigitica iidk of the sesia zone have been studied using a high spatial resolution laser probe 40ar 39ar technique with the aim of investigating the complexities of argon behaviour in metamorphic rocks and comparing their thermal histories data from a single large phengite grain from the emc show a range of ages from mid jurassic to upper cretaceous these apparent age variations are spatially related to both location within the grain and to intragrain microstructure modelling of the data shows that the profile formed by the diffusion of an excess argon component into the grain parallel to the mica cleavage profile asymmetry is explained by temporal variations in microstructural development enabling excess argon to enter the grain at different times in different places the temperatures of the initiation of deformation and the possible time scales for the deformation can be calculated as a function of cooling rate all estimates suggest deformation at greenschist facies in accord with the observed retrograde mineral assemblage absolute temperature estimates for deformation vary by less than 22 c for different cooling rates of 10 and 30 c ma 1 but vary by 80 c with different estimates of diffusion parameters the duration of deformation was for at least 2 ma at 10 c ma 1 or 0 7 ma at 30 c ma 1 biotites from the iidk sample record a permian to upper cretaceous age range that correlates with grain size the smallest grain sizes yielding the youngest ages this relationship is best explained by a partial resetting of biotites during an alpine thermal event initiated not more than 70 ma ago modelling of these data suggest that the sample never exceeded 300 c during the alpine the profoundly different thermal histories of the two units the emc recrystallized at 550 c whilst the iidk remained below 300 c suggests that they may not have been juxtaposed until much later than the eclogite facies metamorphism

quartz textures from the simplon fault zone southwest switzerland and north italy quartz textures measured from monomineralic veins within the simplon fault zone show very similar patterns over a strike length of some 30 km the c axes form asymmetric kinked single girdles with variably developed vestiges of crossed girdle limbs the kinking of the girdle may be controlled by the two c axis orientations where double rhomb a slip is possible a strong a maximum lies between 20 and 30 to the lineation in the xz plane which seems too large to be the angle to the bulk shear plane straight single girdle patterns may be possible for strict simple shear in natural fault zones where deformation is in general heterogeneous on all scales kinked single girdles and type i crossed girdle textures are much more common perhaps because such textures provide more freedom to accommodate a general two dimensional strain

the julich neutron diffractometer and data processing in rock texture investigations abstract the texture diffractometer sv7 b which is operated at the forschungszentrum julich as a user and service instrument has been improved with respect to the efficiency of the position sensitive detector system and to the variety of wavelengths available instrumental aspects of data collection and different methods of data processing for pole figure evaluation are discussed recent examples of texture investigations on geological materials are presented for quartz hematite hematite quartz orthopyroxen quartz and anorthosite rocks

fabric domains in quartz mylonites localized three dimensional analysis of microstructure and texture fabric domains of a quartz vein deformed under greenschist facies conditions arc analysed with domainal x ray texture goniometry optical microscopy computer integrated polarization microscopy cip and shape analysis in two mutually perpendicular sections the analysed domains consist of large non recrystallized deformed clast fragments prolate non recrystallized ribbon grains and prolate recrystallized domains in terms of texture monomaximal and polymaximal domains have been distinguished pronounced partitioning of deformation is observed between these domains this strain partitioning asks for caution when making kinematic inferences for fault zones based on a study of domainal fabrics domains persist as fabric elements up to high strains this emphasizes the often neglected role of a non random initial fabric neighbouring domains with alternating c axis orientations and grain boundary preferred orientations indicating opposing senses of shear occur in both sections the bulk texture is controlled by clast and ribbon domains rather than being strictly deformation induced we infer that prolate elongation of clasts and ribbons is achieved mainly by combined prism and basal slip recrystallized domains are characterized by different textures they are deformed by intracrystalline slip combined with grain boundary migration and sliding inclined preferred grain boundary orientations are continuously maintained by grain boundary migration copyright 0 1996 elsevier science ltd

structural evolution of the contact between two penninic nappes zermatt saas zone and combin zone western alps and implications for the exhumation mechanism and palaeogeography the boundary zone between two penninic nappes the eclogite facies to ultrahigh pressure zermatt saas zone in the footwall and the blueschist facies combin zone in the hanging wall has been interpreted previously as a major normal fault reflecting synorogenic crustal extension quartz textures of mylonites from this fault were measured using neutron diffraction together with structural field observations the data allow a refined reconstruction of the kinematic evolution of the pennine nappes the main results are 1 the contact is not a normal fault but a major thrust towards northwest which was only later overprinted by southeast directed normal faulting 2 exhumation of the footwall rocks did not occur during crustal extension but during crustal shortening 3 the sesia dent blanche nappe system originated from a continental fragment cervinia in the alpine tethys ocean and the combin zone ophiolites from the ocean basin southeast of cervinia 4 out of sequence thrusting played a major role in the tectonic evolution of the penninic nappes