crustal scale mass transfer geotherm and topography at convergent plate boundaries end member cases for the fate of the crust at convergent lithospheric plate boundaries accommodated by subduction are considered combining i plate kinematics slab retreat vs slab advance and ii mechanical coupling decoupling within the subducting slab slab advance is accommodated by thickening of the overriding lithospheric mantle whereas slab retreat is associated with thinning crust mantle mechanical coupling results in continental subduction whereas decoupling leads to continental accretion the thermal and topographic evolutions of the associated orogenic belts are functions of the crust mantle thickness ratio resulting from the combined effects of crust mantle coupling decoupling and slab advance retreat crustal accretion associated with slab advance results in crustal thickening and contributes to an increase in radioactive heat production and buoyancy which is impeded by concomitant thickening of the conductive and dense lithospheric mantle in contrast crustal accretion combined with slab retreat results in thickening simultaneous with thinning of the lithospheric mantle this peculiar situation is the most favourable for generating a high temperature and buoyant orogenic belt

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

deformation history of the high pressure lycian nappes and implications for tectonic evolution of sw turkey 1 in southwestern turkey the lycian nappe complex which overlies the autochthonous menderes massif and bey dag platform consists from base to top of metasediments a melange unit and an ophiolitic sequence fresh fe mg carpholite occurrence in the metasediments attests to a high pressure low temperature metamorphic event we report the distribution of fe mg carpholite and its breakdown products e g pyrophyllite and chloritoid on the bodrum peninsula south of the menderes crystalline massif the distribution of fe mg carpholite and its relics shows that the low grade high pressure metamorphism affected a widespread area in the lower units of the lycian nappes analysis of the ductile deformation in hp lt metasediments indicates shear senses top to the northeast to top to the east most of this deformation is contemporaneous with the retrogression of high pressure low temperature parageneses and is therefore coeval with exhumation from a depth of about 30 km at the top of the menderes massif cover series close to the contact with the lycian nappes similar eastward displacements are observed and trajectories of the stretching lineations are continuous from the lycian nappes to the menderes massif across the contact these observed movements are incompatible with the southward transport of the lycian nappes over the menderes massif we discuss the regional tectonic implications and conclude that the lycian nappes and the southernmost part of the menderes massif were exhumed in two stages 1 eocene top to the ne shear syn orogenic extension 2 miocene deformation contemporaneous with the aegean extension

the evolution of the southern menderes massif in sw turkey as revealed by zircon dating this geochronological study concentrates on the evolution of the southern part of the menderes massif a metamorphic core complex in w turkey by dating single zircons with the pb pb evaporation and the u pb methods we have analysed zircons from granitic augen gneisses of the core as well as from quartzites of the metasedimentary envelope zircons from the granitic core gneisses are euhedral with typical igneous morphologies the single zircon ages of these gneisses indicate a time span for magmatic activity from 520 to 570 ma with a major event at about 550 ma some gneisses contain older zircons of c 660 ma which are interpreted as inherited grains zircons from the quartzites are detrital as indicated by their rounded shapes and pitted surfaces their ages vary from 526 to 2094 ma these data partially coincide with the ages of the gneisses but also indicate an older source region for the sediments neither a tertiary origin nor metamorphic overgrowth is documented in the pb ages of the zircons the results suggest that the southern part of the menderes massif developed during a major magmatic episode in latest proterozoic times thus suggesting a relation with other pan african regions in n africa

on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

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

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

first occurrence of fe mg carpholite documenting a high pressure metamorphism in metasediments of the lycian nappes sw turkey in the basal thrust sheets of the lycian nappes fresh fe mg carpholite documents low grade high pressure hp metamorphism here we describe the first occurrences of this hp indicator mineral in turkey its regional distribution and geodynamic consequences carpholite and its breakdown products such as chloritiod and pyrophyllite occur in the lycian nappes s s relics of fe mg carpholite were also found in klippen of lycian nappe material located on top of the menderes crystalline massif the distribution of the fe mg carpholite and its relics traces an extensive area of hp metamorphism in the sediments of a passive continental margin

exhumation paths of high pressure low temperature metamorphic rocks from the lycian nappes and the menderes massif sw turkey a multi equilibrium approach the menderes massif and the overlying lycian nappes occupy an extensive area of sw turkey where high pressure low temperature metamorphic rocks occur precise retrograde p t paths reflecting the tectonic mechanisms responsible for the exhumation of these highpressure low temperature rocks can be constrained with multiequilibrium p testimatesrelyingonlocalequilibria whereasasimple isothermal decompression is documented for the exhumation of highpressure parageneses from the southern menderes massif various p t paths are observed in the overlying karaova formation of the lycian nappes in the uppermost levels of this unit far from the contact with the menderes massif all p t estimates depict cooling decompression paths these high pressure cooling paths are asso

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

strain analysis and vorticity of flow in the northern sardinian variscan belt recognition of a partitioned oblique deformation event abstract a field example of strain partitioning has been analysed along the nurra asinara transect of the nw sardinian variscan chain italy the section in the nurra asinara area is in a continuous sequence of tectono metamorphic complexes made of low to high grade metamorphic rocks affected by a polyphase tectonic history the principal fabric of the area is controlled by a d2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains the d2 stretching lineation and shear sense show a clear change from south to north the principal meso and micro structures vorticity gauges and a quantitative kinematic analysis of local strain suggest that the d2 kinematic history could be envisaged as an oblique heterogeneous deformation similar to the transpressive systems described in ancient and modern settings elsewhere using a simple kinematic model we also propose that both a transpressive system followed by thrusting or a partitioned transpressive system could be responsible for the fabric distribution and strain accumulation described in the study transect

earthquake clustering in shallow subduction zones kamchatka and mexico this paper studies regularities in earthquake clustering at shallow depths 0 60 km in two pacific subduction zones the mexican and the kamchatkan these zones were formed by subduction under the north american plate of old and fast pacific plate kamchatkan region and young and slow rivera and cocos plates mexican region we use events of magnitude 5 5 and greater 95 events for 1964 1993 from the kamchatkan region and 52 events for 1974 1993 from the mexican region we have two active kamchatkan and cocos and one passive rivera subduction zones for the passive rivera zone where subduction may be considered aseismic after the great jalisco event of 1932 magnitude ms 8 2 and its aftershock activity during 1932 1934 we can study only seismic events along the western border of the plate related to oceanic rises and the rivera fracture zone here we have a well developed clustering of earthquakes 47 of all 17 studied events occurred in clusters mainly of swarm type for the two active subduction zones the kamchatkan and the cocos we can formulate the following results 1 most of the studied events of the cocos subduction zone 74 occurred in clusters and within the kamchatkan subduction zone 45 of the events recorded were in clusters 2 the clustering events occurred mainly at a depth interval from 0 to 40 km 98 of all clustering events in kamchatka and 61 for the cocos subduction zone at the same time the single events were distributed mainly in a depth interval from 30 to 60 km 73 of all single events in kamchatka and 100 for the cocos subduction zone 3 comparison of the spatial distribution for the different types of clustering in kamchatka and the cocos zone shows the absence of a band of swarms along the slope of the middle american trench whereas such a band is obvious in the kamchatkan region 4 the study of temporal distribution for single events and mainshock aftershock sequences within the region of large earthquakes shows that there was a change from a long term sequence of single events to events with aftershocks 1 4 years before a large earthquake this regularity was observed before both large magnitude greater than seven earthquakes in kamchatka and before the magnitude 8 1 michoacan earthquake in mexico

the death valley turtlebacks reinterpreted as miocene pliocene folds of a major detachment surface determining the origin of extension parallel folds in metamorphic core complexes is fundamental to understanding the development of detachment faults an excellent example of such a feature occurs in the death valley region of california where a major undulatory detachment fault is exposed along the well known turtleback antiformal surfaces of the black mountains in the hanging wall of this detachment fault are deformed strata of the copper canyon formation new age constraints indicate that the copper canyon formation was deposited from 6 to 3 ma the formation was folded during deposition into a se plunging syncline with an axial surface coplanar with that of a synform in the underlying detachment this relation suggests the turtlebacks are a folded detachment surface formed during large scale extension in an overall constrictional strain field the present more planar black mountains frontal fault system may be the result of out stepping of a normal fault system away from an older detachment fa

microstructures of deformed grains in the augen gneisses of southern menderes massif western turkey and their tectonic significance a detailed fabric and microstructural analysis of the granitic mylonites was carried out on the southern side of bes parmak mountain north of selimiye milas the mylonitic augen gneisses have a blastomylonitic texture characterized by large retort shape porphyroclasts or augen of feldspars around which a more ductile medium to fine grained matrix of muscovite biotite quartz and feldspar is deflected feldspars behave in both plastic and brittle fashion because size reduction occurs through grain boundary migration and or subgrain rotation and also through fracturing typical core and mantle structure characterized by a large feldspar core surrounded by a mantle of fine recrystallized grains is very characteristic the majority of plagioclase twins obey the albite twin law however the association with pericline law twinning suggests that many of the twins are mechanical evidence of strain such as deformation twins bent or curved twins undulatory extinction deformation bands and kink bands occur characteristically in plagioclase myrmekite is ubiquitous at k feldspar grain boundaries most notably on the long sides of inequant grains parallel to the s foliation direction which invariably face the maximum finite shortening direction deformation of quartz in mylonitic augen gneisses commonly results in the development of core and mantle structure and type 4 quartz ribbons of elongated preferably oriented newly recrystallized quartz aggregates suggesting a primary dynamic recrystallization undulatory extinction deformation bands and lamellae are the strain related features associated with quartz porphyroclasts micas especially biotite undergo internal deformation by bend gliding and kinking most of the micas are completely attenuated and aligned such that their 001 planes are subparallel or parallel to the margins of quartz ribbons and define the foliation in the rock these microstructures of feldspars quartz and mica in the mylonitic augen gneisses in this part of the southern menderes massif are broadly consistent with fabric development under upper greenschist to lower amphibolite facies conditions rather than almandine amphibolite facies as was previously believed this supports the previous contention of the authors that the protoliths of augen gneisses are younger granitoids and do not represent an exposed precambrian pan african basement in the menderes massif

simultaneous pure and simple shear the unifying deformation matrix abstract any simultaneous combination of finite simple shear and finite pure shear is a linear transformation which can be expressed as a single transformation matrix for two dimensions the matrix is upper triangular with an off diagonal term called the effective shear strain is a simple function of the pure and simple shear components for three dimensions a simultaneous combination of thrusting in the x direction thrusting in the y direction and a wrench in the x direction in addition to 3 orthogonal components of coaxial strain can also be represented by a 3 3 upper triangular matrix here three off diagonal terms xy x y and y z occur xy is a simple function of the horizontal coaxial strain values and thrusting in the x direction yz depends on the coaxial strain components in the y and z directions and the thrusting in the y direction while xz is related to all six strain components the matrix also allows for volume change either homogeneously or preferentially in a single direction a method of decomposing the deformation matrix into a series of incremental deformation matrices where each incremental deformation records the same kinematic vorticity number as the finite deformation is shown the orientation and magnitude of the finite strain ellipsoid ellipse is easily and accurately found at any increment during the deformation

strain and fabric analyses based on porphyroclast interaction abstract two dimensional computer models of the interaction of elliptical clasts in a variety of kinematic conditions are used to study how clast imbrication and shape fabric development relate to strain and strain history the models provide templates for a known clast density and clast ellipticity that correlate clast imbrication angle of collision and clast shape fabric to strain and kinematics of deformed rocks modeling also shows that the mode of clast interaction plays a significant role in the accumulation of imbricated clasts and the development of shape fabric upon collision between clasts the trains formed can remain fixed or rotate if they rotate imbricated clasts can become independent when they are no longer forced together by the flow based upon the mode of clast and train rotation using the march rotation of passive lines and the jeffery rotation of rigid particles as end members three models are defined in an attempt to simulate the conditions of clast interaction under varying conditions the march fixed train march rotating train and jeffery rotating train models simulate solid state intermediate and magmatic conditions respectively modeling shows that the two march models produce similar results but the jeffery model of train rotation always produces a lower proportion of imbricated clasts and a much weaker shape fabric application of the modeling to the study of a syntectonic granite in the sierra nevada suggests that deformation was dominated by simple shear some k feldspar imbrication and fabric development took place initially in the magmatic stage and culminated in the solid state to produce a large proportion of imbricated k feldspar porphyroclasts which define a strong shape fabric this type of analysis provides a rationale to determine syn vs post emplacement deformation in the granite

volcanic earthquakes of kamchatka classification nature of source and spatio temporal distribution abstract volcanic earthquakes on kamchatka can be divided into two large groups earthquakes with depths of 0 40 km generated by stresses which arise during magma migration in the earth s crust under volcanos the first group and the earthquakes directly connected with the eruptions volcanic tremor explosive earthquakes etc the second group this paper presents a review of some energetic spectral and spatio temporal characteristics of the kamchatkan volcanic earthquakes of the first group and their relationship with volcanic phenomena seismicity related to volcanic activity has the following specific features a local and predominantly swarm like pattern of earthquake origination iteration of earthquake swarms in the same seismically active zones many shallow and relatively small events a small magnitude limit up to 5 5 6 the existence of longer period variations of volcanic earthquake foci as compared to the tectonic one and a comparatively high value of the slope of the earthquake recurrence plot at the same time similarity in behaviour of some parameters of the seismic regime during the preparation and development of eruptions and prior to large earthquakes as well as the destruction of samples are noted

geology of the bozdag area central menderes massif sw turkey pan african basement and alpine deformation the menderes massif consists of a precambrian core series that preserves evidence for a polymetamorphic history and a paleozoic mesozoic cover series that experienced only the alpine tectonometamorphic evolution structural petrographic and geochronologic investigations in the central menderes massif demonstrate that a part of the metamorphic and structural evolution of the precambrian basement is older than the undeformed 551 1 4 ma old birgi metagranite and b inferred alpine fabrics overprinting the cover series largely have the same attitudes as the old structures in the much older core series the inferred alpine fabrics include both contractional and extensional structures contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the core and cover series and generated an inverted metamorphic sequence by north directed thrusting during alpine extension most of the south dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

prism c slip in the quartzites of the oakhurst mylonite belt california abstract quartz c axis fabrics from 21 amphibolite facies quartzites of the oakhurst mylonite belt california suggest that prism c prism a and basal a slip systems were activated during deformation qualitative two dimensional kinematic models consistent with meso and microscopic shear criteria are constructed based on a regime of combined pure and simple shear in this kinematic framework most of the observed c axis fabric patterns of the oakhurst mylonite belt can be explained if prism c slip was dominant during the early increments of deformation until a transition to dominant basal a slip occurred an apparent relationship between grain size and type of crystallographic fabric is interpreted as resulting from some quartz syntectonic vein quartz having recorded only the latest increments of deformation comparison with the metamorphic evolution of fault zones of similar tectonic origin in california suggests that prism c slip was enhanced by the circulation of hot fluids which hydrolytically weakened quartz and allowed prism c slip to occur at relatively low temperature

southern menderes massif an incipient metamorphic core complex in western anatolia turkey in the southern sector of the menderes massif north of selimiye milas augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed palaeozoic envelope the granitic rocks exhibit a moderately dipping mylonitic foliation and nne ssw trending mineral elongation lineation the progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked from bottom to top by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite the kinematic indicators exhibit a top to the south down dip sense of shear these structures are attributed to exhumation of the granitic rocks of the massif along a major south dipping normal sense shear zone that accommodated crustal extension during late oligocene collapse of the orogen in western turkey thus the southern menderes massif may be interpreted as the exhumed footwall of a major extensional shear zone and possibly as an incipient core complex

granitoid rocks of the southern menderes massif southwestern turkey field evidence for tertiary magmatism in an extensional shear zone recent field campaign in the southern menderes massif in southwestern turkey revealed that the so called core of the massif comprises two distinct types of granitoid rocks an orthogneiss traditionally known as augen gneisses and leucocratic metagranite where the latter is intrusive into the former and the structurally overlying cover schists these differ from one another in intensity of deformation degree of metamorphism and kinematics the orthogneiss display penetrative top to the n nne fabrics formed under upper amphibolite facies conditions during the eocene main menderes metamorphism mmm whereas foliation and stretching lineation exists in the leucocratic metagranites but are not strongly developed the leucocratic metagranites show evidence of syn to post emplacement deformation in a series of weakly developed top to the s ssw fabrics formed under lower greenschist facies conditions leucocratic metagranite bodies occur all along the augen gneiss schist contact in the southern menderes massif they are emplaced as sheet like bodies into country rocks previously deformed and metamorphosed during a top to the n nne alpine orogeny along a ductile extensional shear zone located between orthogneisses and metasediments which was possibly active during emplacement the data presently available indicate that emplacement and associated ductile extensional deformation occurred during late oligocene early miocene time these results confirm previous contentions that there are tertiary granites in this part of the menderes massif

changes in earthquake source properties across a shallow subduction zone kamchatka peninsula this paper studies the source properties of earthquakes originating within the shallow subduction zone near kamchatka peninsula we use the regional catalog of 1962 1993 kamchatkan earthquakes completed by the institute of volcanology russia our previous investigations zobin 1990 1996a and this study allow us to show a gradual change in source properties of earthquakes from trench to coast it was demonstrated that the swarm sequences change to the mainshock aftershock sequences from trench to coast the source area of aftershock sequences is generally smaller than the swarm areas for the same magnitude m s of the mainshock or clue event of the swarm study of the m s k s relation where k s is the energy class for kamchatka earthquakes reveals that the events radiate relatively higher frequencies from trench to coast

fold fault relationships in low angle detachment systems a close kinematic and timing relationship between low angle extensional faulting and upright to moderately inclined folding with fold axes parallel to the extension direction is established for two well exposed neogene detachment systems in the simplon region of the alps and in the death valley region of california fold amplitude is largest in the oldest mylonitic foliation of the footwall these folds are transected by younger mylonitic foliation s and cataclastic detachment faults which are themselves folded about similar axes in general the amplitude decreases and the wavelength increases for progressively younger fold structures consistent with a history of progressive folding during faulting the interplay between folding and faulting in the footwall reflects a component of shortening perpendicular to fold axial surfaces during extension parallel to fold axes this strain pattern can develop in regions with a transcurrent component or during lateral extrusion and does not necessarily require overall crustal thinning

three dimensional model of the late cenozoic history of the death valley region southeastern california the accumulation of a large database on the timing and kinematics of late cenozoic deformation in the death valley region of southeastern california indicates a complex three dimensional history on the basis of paleogeographic reconstructions we suggest the system was initiated as a localized pull apart between two conjugate strike slip faults the garlock and furnace creek faults and evolved into a system characterized by distributed transtension related to the eastern california shear zone our reconstructions differ from previous models in the incorporation of significant vertical axis rotations of a number of crustal blocks to explain paleomagnetic data from the region the model may resolve 1 a long standing problem of the eastern termination of the garlock fault which is explained here as a complex system of splays that initially terminated in the pull apart between the furnace creek and garlock systems and 2 the complex architecture of the black mountains which is explained here in terms of initial extreme attenuation between the garlock and furnace creek systems with overprinting by a fold and normal fault system that operated simultaneously as a result of distributed transtension this model suggests much of the displacement field is taken up in rotations and translations and the actual crustal thinning in our model is relatively small 50 66 of original thickness

extensional v contractional origin for the southern menderes shear zone sw turkey tectonic and metamorphic implications the southern menderes massif in southwest turkey consists mainly of orthogneisses and overlying palaeozoic middle paleocene schists and marbles the contact between the two distinct rock types is almost everywhere structural herein named the southern menderes shear zone a s facing high angle ductile shear zone that separates metamorphic rocks of differing grade although there is a consensus that the shear zone was associated with top to the s ssw shearing and is of tertiary age its origin and nature have been highly debated over the last decade some claim the contact is a thrust fault while others have argued for an extensional shear zone integration of field and microstructural data the identification of different fabrics associated kinematics and overprinting relationships with fission track thermochronology and the p t paths of the rocks above and below the shear zone supports the conclusion that the southern menderes shear zone is an extensional shear zone and not a thrust the data are consistent with a model that the exhumation and cooling of the southern menderes massif occurred after a period of extensional deformation pervasive top to the n nne high temperature medium pressure ductile shear structures d 2 deformation overprint an early hp event d 1 deformation the subsequent top to the s ssw greenschist shear band foliation d 3 deformation developed mostly around the orthogniess schist contact and forms the most characteristic features of the massif the top to the n nne structures are attributed to the main alpine constructional deformation that developed during back thrusting of the lycian nappes during the latest palaeogene collision between the sakarya continent and the anatolide tauride platform across the neotethyan ocean the top to the s ssw structures are interpreted to be the result of the exhumation of the massif during the activity of the southern menderes shear zone the presence of these two distinct fabrics with differing kinematics suggests that the southern menderes shear zone operated as a top to the n nne thrust fault during early alpine contractional deformation but was later reactivated with an opposite sense of movement top to the s ssw during subsequent oligocene miocene extensional collapse

the menderes massif of western turkey and the cycladic massif in the aegean do they really correlate based on lithostratigraphic comparisons the menderes massif has been correlated with the cycladic massif thereby implying that the eastern mediterranean consists of a narrow pre alpine basement belt which is laterally continuous over a long distance and which experienced a similar alpine orogenic history our work indicates that the architecture the age of basement and the pre alpine and alpine tectonometamorphic history of both massifs differ fundamentally from each other the menderes massif consists of remnants of the cycladic massif which overly an exotic unit the menderes nappes both massifs do not represent lateral continuations which has implications for palaeogeographic reconstructions

multistage exhumation of the menderes massif western anatolia turkey structural analyses along selected transects across the menderes massif and incorporation of existing data have resulted in a synthetic cross section across southwestern turkey the tectonic interpretation has been combined with 40ar 39ar laser probe experiments on two syn kinematic white mica populations which respectively predate and overprint documented early miocene deformational fabrics our results indicate that the regional extension had initiated by eocene oligocene times a 36 2 ma 40ar 39ar age derived from white mica which formed during a regionally observed northward directed tectonic transport suggests that the extension was contemporaneous with the tectonic emplacement of mid crustal continental basement alternatively the age may relate to the regional cooling of the basement sequence and thus postdates the tectonic emplacement in the latter scenario the analysis fails to solve the present ambiguity on the pan african or alpine affinity of the northward directed transport further exhumation of basement rocks is characterized by a dominant displacement along the north dipping gediz detachment at the northern margin of the massif which developed under ductile conditions in the early miocene by partial exploitation of older zones of weakness which originated from an earlier phase of basement emplacement youngest semi ductile activity along the gediz detachment has been recorded as having a 7 1 ma 40ar 39ar age derived from syn kinematic white mica in the top of the detachment following the initiation of the ductile gediz detachment an antithetic semibrittle and south dipping buyuk menderes detachment had developed in the center of the massif which together with the gediz detachment accommodated further doming of the central part of the menderes massif and controlled the architecture of the surrounding supradetachment basins

menderes massif western turkey structural metamorphic and magmatic evolution a synthesis the menderes massif covers large areas in western turkey the better understanding of its tectono metamorphic history would provide insight for the alpine evolution of western turkey and the entire eastern mediterranean region this paper summarizes the available literature on the metamorphic rocks of western turkey and that of the menderes massif with special reference and emphasis to the papers presented in the special issue

fabric stability in oblique convergence and divergence forward modeling of transpression transtension assuming homogeneous strain and a direct relationship between finite strain axes and foliation lineation in tectonites investigates fields of stability of foliation and lineation orientations in oblique convergence and divergence vertical foliation horizontal lineation vf hl develop for angles of convergence divergence between 0 and 20 with increasing finite strain this narrow window of stability is further reduced lineation switches to vertical in transpression and foliation switches to horizontal in transtension if a shear zone contains vf hl it either developed as a zone very close to pure wrenching or recorded low finite strain the stability of vf hl at high strain and higher angles of convergence is enhanced by lateral extrusion of material along transpression zones vf hl may be stabilized in magmatic bodies that progressively intrude transtension zones if the wrench component of deformation partitions within them alternatively if these bodies are dike like cool fast and do not record large deformation they take up the extension component of transtension through anisotropic volume addition leaving a larger component of wrench deformation in the country rocks this effect stabilizes vf hl effectively at low strain but only marginally so at high strain

permian diamictites in northeastern asia their significance concerning the bipolarity of the late paleozoic ice age despite a lack of detailed sedimentologic analyses diamictites in the middle permian atkan formation were previously interpreted as glaciomarine and glacially influenced marine deposits this interpretation allowed this unit to play a prominent role in paleoclimatic and biogeographical reconstructions associated with presumed bipolar glaciation during the late paleozoic ice age lpia in this sense the lpia is considered to be a close analog to bipolar glaciation and climate change during the cenozoic here results are presented that challenge the glacigenic interpretation for these strata and negate interpretations of the bipolar nature of the lpia the 400 to 1500 m thick atkan formation was deposited in back arc basins associated with activity of the okhotsk taigonos volcanic arc along the leading edge of pangea as it drifted across the north polar circle the occurrence of tuffs volcanic clasts and glass shards indicate derivation from a nearby arc cooling and solidification of some clasts during sedimentation is suggested by the occurrence of clasts with embayments and protrusions that extend into the surrounding matrix clasts with columnar like jointing and alteration of the matrix surrounding some clasts ca tims dating of tuff zircons indicate a late capitanian age which is consistent with fossils within the strata bedded diamictites deposited as debrites dominate these diamictites which occur as tens of m thick downlapping packages that thicken then thin upward were deposited as prograding and abandoning sediment gravity flow fans chaotic and folded strata formed as slumps graded sandstones and conglomerates were deposited as turbidites and mudstones were deposited as mudflows low density turbidites and hemipelagic deposits striated clasts and outsized clasts piercing bedding were not observed in the study area strata above and below the atkan formation contain abundant graded beds and deep water trace fossils indicating deposition as turbidites the combination of debrites turbidites slumps volcanic grains clasts glass and tuffs and an absence of glacigenic indicators suggest that atkan strata were deposited in deep water basins associated with the development of the volcanic arc rather than due to glacial activity these findings are significant as they require reconsideration of current views of lpia glaciation and suggest that ice sheets were limited to gondwana

tectonic controls on metamorphism partial melting and intrusion timing and duration of regional metamorphism and magmatism in the nigde massif turkey protracted heating and melting of orogenic middle crust followed by emplacement of a syn extensional pluton during decompression and cooling are demonstrated for a metamorphic core complex in central turkey new geochronologic data for the nigde massif of the central anatolian crystalline complex document an interval of melting crystallization and pb loss at elevated ambient temperature 85 92 ma determined by u pb shrimp within a single sample of peraluminous granite crustal melting was syn to post peak metamorphism 725 c dated at 91 0 2 0 ma by shrimp analysis of zircon rims in sillimanite schist that is part of the country rock to the pluton metamorphic monazite in sillimanite schist yields a younger age of 84 7 0 7 ma for matrix grains and inclusions in garnet hornblende 40ar 39ar ages from amphibolites interlayered with the sillimanite schists coincide with the timing of emplacement of magma into metamorphic country rock that had experienced cooling and decompression to 12 km and 550 c the similarity of 40ar 39ar ages for biotite in the pluton 79 ma and hornblende 79 81 ma biotite 74 76 ma and muscovite 78 83 ma in the metamorphic country rock document rapid cooling 100 c my following intrusion the coincidence of the youngest u pb magmatic zircon ages and the oldest 40ar 39ar ages combined with structural evidence for normal sense shearing and tectonic unroofing in the late cretaceous suggests that intrusion was driven by extension we propose that crustal melting occurred in the middle crust during prograde metamorphism and or initial decompression and that ascent and emplacement of magma as a pluton were only triggered once extension occurred and removed upper crustal rocks

earthquake swarms in the kamchatka commander region summary a swarm sequence is an earthquake sequence where no single event is dominant in size in this paper we define a swarm as an earthquake sequence where the energy difference between the largest shocks of the sequence is kf 0 5 kf is an energy class of earthquake and represents an estimate of the energy of earthquakes in log units of joules for the frequency range 0 5 2 0 hz the relation between kf and magnitude mlh is kf 0 85 mlh 8 3 magnitude mlh 1 3 ms 1 3 for the kamchatkan earthquakes we analysed swarm sequences if they contained five or more events of the energy class kf 8 5 mlh 1 0 occurring three days either side of the largest event or when more than one event happened with the same magnitude as the largest the first of these termed a clue event and were located not further than 50 km from this clue event these criteria allowed us to select 32 swarms with clue events of kf 11 5 mlh 4 0 in the period 1962 1989 in the kamchatka commander region the majority of swarms 86 per cent were located within structures subject to horizontal tension mainly on the slopes of the aleutian and kurile kamchatka trenches and in zones of modern volcanism at the same time the appearance of earthquake swarms did not depend on the fault nature of the clue event in that swarm we studied the relationships between the swarm characteristics swarm area duration and number of events and the clue event parameters energy class magnitude and stress drop the regression equations were computed for parameters with significant correlation at 95 per cent confidence level all three swarm characteristics depend on the energy class of the clue event magnitudes mlh are correlated with swarm area and duration the clue event stress drop gives a negative correlation with the number of events in a swarm

a pulsed extension model for the neogene recent e w trending alasehir graben and the ne sw trending selendi and gordes basins western turkey abstract we have developed a significant body of new field based evidence relating to the history of crustal extension in western turkey we establish that two of the ne sw trending basins in this region the gordes and selendi basins whose sedimentary successions begin in the early miocene are unlikely to relate to late stage alpine compressional orogeny or to e w extension of tibetan type grabens as previously suggested we argue instead that these basins are the result of earlier late oligocene low angle normal faulting that created approximately n s scoop shaped depressions in which clastic to lacustine and later tuffaceous sediments accumulated during early mid miocene time separated by elongate structural highs these basins were later cut by e w trending plio quaternary normal faults that post date accumulation of the neogene deposits in addition we interpret the alasehir gediz graben in terms of two phases of extension an early phase lasting from the early miocene to the late miocene and a young plio quaternary phase that is still active taking into account our inferred earlier phase of regional extension we thus propose a new three phase pulsed extension model for western turkey we relate the first two phases to roll back of the south aegean subduction zone and the third phase to the westward tectonic escape of anatolia

suspension freezing of bottom sediment and biota in the northwest passage and implications for arctic ocean sedimentation ice observations and sediment collected in a summer transit through the northwest passage provide insights on suspension freezing the most important sediment entrainment mechanism for the arctic ocean no evidence was seen for entrainment by bottom adfreezing bluff slumping river flooding dragging ice keels or significant eolian transport from land to sea lack of eolian sediment loading in the northwest passage together with that already reported for northern alaska eliminates wind as an important source for fine sediment in the pack of the beaufort gyre and related parts of the transpolar drift muddy sediment with pebbles and cobbles algae with holdfasts ostracodes with appendages and well preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice these materials indicate that suspension freezing reaching to a water depth of 25 30 m during the previous fall was responsible for entrainment this mechanism requires rapid ice formation in open shallo

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

folding in regions of extension summary many extension zones have been subjected to folding and shortening in a direction perpendicular to the stretching such deformation can be accounted for by the extension of a thin superficial elastic layer overlying a substrate that has small elastic moduli or that deforms in a viscous regime laboratory experiments are used to document the wavelength and amplitude of the folds for a range of geometrical configurations folding is observed even for very small amounts of extension less than 1 per cent with characteristics that are consistent with finite amplitude scaling laws because of the intrinsically 3 d nature of the deformation field the size of the region affected by folding and the direction of the fold axes depend on the orientation of the extension with respect to the rigid blocks that bound the deforming region for regions of extension where the elastic thickness is about 10 km as in the basin and range province for example it is predicted that folding occurs with wavelengths in a 20 40 km range such that it induces little deformation in the lower crust and maintains a flat moho discontinuity these predictions are consistent with the observations the characteristics of faulting that is associated with such deformation are discussed

pan african high pressure metamorphism in the precambrian basement of the menderes massif western anatolia turkey the menderes massif is made up of pan african basement and a paleozoic to early tertiary cover sequence imbricated by late alpine deformation the precambrian basement comprises primarily medium to high grade schists paragneisses migmatites orthogneisses metagranites charnockites and metagabbros high pressure relics in the pan african basement are divided into two groups eclogites and eclogitic metagabbros the mineral assemblage in the eclogites is omphacite jd 44 garnet clinozoisite rutile the eclogites occur as pods and boudinaged layers in the basement schists and paragneisses inclusions found in the cores of the garnets indicate a medium pressure protolith the eclogitic metagabbros are closely related to precambrian gabbroic stocks the igneous texture and relic magmatic phases are preserved in these high pressure rocks which are characterized by the mineral assemblage omphacite jd 25 garnet rutile kyanite the p t conditions of the pan african high pressure metamorphism in the eclogites are estimated to be 644 c with a minimum pressure of approximately 15 kbar the eclogites are partly to completely retrograded to garnet amphibolites by a barrovian type overprint which developed under isothermal decompression conditions for this post eclogitic event the p t estimates are 7 kbar and 623 c the eclogite relics provide strong support for a correlation of the menderes massif with the bitlis massif in terms of common pan african high pressure evolution

monazite ages and the evolution of the menderes massif western turkey the menderes massif experienced polyphase deformation but distinguishing pan african events from alpine tectono metamorphic evolution and discriminating eocene oligocene shortening from recent extension remain controversial to address this monazite in garnet bearing rocks from the massif s gordes central and cine sections were dated in thin section in situ using the th pb ion microprobe method cambro ordovician monazite inclusions in cine and central menderes massif garnets are 450 m y older than matrix grains monazites in reaction with allanite from the kuzey detachment which bounds the northern edge of the central menderes massif are 17 5 ma and 4 5 1 0 ma the pliocene result shows that dating of monazite can record the time of extension the kuzey detachment might have exhumed rocks a lateral distance of 53 km at a rapid rate of 12 mm year assuming the present 20 ramp dip pliocene monazite crystallization at 450 c and a geothermal gradient of 25 c km assuming an angle of 60 the rate decreases to 5 mm year with the detachment surface at 21 km depth in the pliocene two gordes massif monazites show a similar allanite monazite reaction relationship and are 29 6 1 1 ma and 27 9 1 0 ma suggesting that the cenozoic extension in the gordes massif and possibly the entire menderes massif might have begun in the late oligocene

stable positions of rigid objects in non coaxial flow a study in vorticity analysis abstract distortions of a homogeneous fabric which occur around rigid objects in rocks deformed by non coaxial ductile flow are useful to determine the sense of shear but also contain information on other aspects of the flow rigid objects in a non coaxial flow fall into two categories those which are permanently rotating and those which can reach stable positions at high finite strain the orientation of such immobilized objects with respect to eigenvectors of instantaneous flow is a function of the vorticity number of the flow the ratio of instantaneous stretches and the axial ratio of the object in naturally deformed rocks immobilized rigid objects may be recognized from the geometry of the surrounding fabric tails of recrystallized material around porphyroclasts in a mylonite rotate towards parallellism with the extensional eigenvector of the flow and the shape of tails reflects the rotational behaviour of the porphyroclast the axial ratio of immobilized porphyroclasts and their orientation with respect to the tails can theoretically be used to determine the vorticity number of the flow and deviations from isochoric plane strain in practice such an analysis is as yet difficult but a tentative example is given of the way in which the vorticity number can be calculated from a population of feldspar porphyroclasts in a quartzite mylonite from the french pyrenees

a key extensional metamorphic complex reviewed and restored the menderes massif of western turkey article i nfo this paper provides a review of the structure and metamorphism of the menderes massif in western turkey and subsequently a map view restoration of its neogene unroofing history exhumation of this massif among the largest continental extensional provinces in the world is generally considered to have occurred along extensional detachments with a ne sw stretching direction restoration of the early miocene history however shows that these extensional detachments can only explain part of the exhumation history of the menderes massif and that ne sw stretching can only be held accountable for half or less of the

tectonic significance of deformation patterns in granitoid rocks of the menderes nappes anatolide belt southwest turkey deformation fabrics in proterozoic cambrian granitic rocks of the cine nappe and mid triassic granites of the bozdag nappe constrain aspects of the tectonometamorphic evolution of the menderes nappes of southwest turkey based on intrusive contacts and structural criteria the proterozoic cambrian granitic rocks of the cine nappe are subdivided into older orthogneisses and younger metagranites the deformation history of the granitic rocks documents two major deformation events an early pre alpine deformation event dpa during amphibolite facies metamorphism affected only the orthogneisses and produced predominantly top to ne shear sense indicators associated with a ne trending stretching lineation the younger metagranites are deformed both by isolated shear zones and by a major shear zone along the southern boundary of the cine submassif we refer to this alpine deformation event as da3 da3 shear zones are associated with a n trending stretching lineation which formed during greenschist facies metamorphism kinematic indicators associated with this stretching lineation reveal a top to south sense of shear the greenschist facies shear zones cut the amphibolite facies structures in the orthogneisses 207pb 206pb dating of magmatic zircons from a metagranite which crosscuts orthogneiss containing amphibolite facies top to ne shear sense indicators shows that dpa occurred before 547 2 1 0 ma such an age is corroborated by the observation that mid triassic granites of the cine and bozdag nappes lack dpa structures the younger top to south fabrics formed most likely as a result of top to south alpine nappe stacking during the collision of the sakarya continent with anatolia in the eocene

apparent stress of earthquakes within the shallow subduction zone near kamchatka peninsula apparent stresses of 105 moderate sized magnitude mb from 4 5 to 6 0 shallow earthquakes from the subduction zone near kamchatka peninsula nw pacific were analyzed our results allowed us to formulate the following properties of the earthquake apparent stress for the seismic moment range 1015 to 1018 n m and the focal depth range from 0 to 60 km 1 apparent stresses depend on the fault nature of earthquakes they are greater for thrusts and smaller for normal faults a difference of a factor of 3 2 average apparent stresses were greater in the coastal zone near kamchatka where subducting oceanic and overriding continental plates interact 2 5 mpa and just under the trench axis 2 9 mpa but lower in near trench zones on the western slope of the trench 0 4 mpa this difference is a factor of 6

intrusion age of pan african augen gneisses in the southern menderes massif and the age of cooling after alpine ductile extensional deformation

evidence from the gediz graben for episodic two stage extension in western turkey western turkey falls within a wide belt of nne ssw directed active continental extension generally similar to the basin and range province of the usa it comprises a zone of wnw ese trending major grabens detailed study of the gediz graben reveals two contrasting infills that represent two distinct extensional stages separated by a short phase of compression the older infill consists of an 800 m thick folded and exhumed continental sedimentary sequence with intercalated calc alkaline volcanics it accumulated in a basin formed in the northern hanging wall of a detachment fault during miocene early pliocene times the younger infill rests on the older infill with angular unconformity and consists of about 170 m of undeformed terraced continental sediments and basaltic lavas it accumulated during plio quaternary times in an asymmetric graben bounded by step like normal faults this later extension was probably triggered by the commencement of sea floor spreading along the red sea in early pliocene times and has persisted to the present almost all the grabens in western turkey are best explained by this episodic two stage graben model with an intervening phase of short term compression which differs from the progressive evolution inferred for the basin and range province of the usa

timing of cenozoic extensional tectonics in west turkey the timing of the transition from compressional to extensional tectonics in the late cenozoic evolution of west turkey has been constrained by k ar geochronology from acidic volcanic rocks and tourmaline leucogranite dykes in the central and east margin respectively of the gordes basin dacites and rhyolites in the centre of the gordes neogene sedimentary basin cut both the basement ophiolites of the izmir ankara suture zone and the neogene sediments on the basin s eastern margin the leucogranites cut metamorphic basement along a major ne sw trending normal fault that controls the regional structure of the basin pebbles of these leucogranites occur in adjacent neogene turfites and conglomerates k ar dates on biotites from the central volcanic rocks vary from 18 4 0 8 ma to 16 3 0 5 ma early miocene whilst muscovite from a leucogranite on the eastern margin of the basin provides ages of 24 2 0 8 ma and 21 1 1 1 ma latest oligocene to early miocene geochronological data and field relationships demonstrate that the earlier compressional regime had been replaced by extensional tectonics by latest oligocene early miocene

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

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

lawsonite vorticity and subduction kinematics the exceptional preservation of lawsonite in eclogite and blueschist in a subduction complex sivrihisar turkey allows evaluation of high pressure h p deformation and exhumation using vorticity analysis of a h p index mineral the sivrihisar h p rocks were deformed during h p metamorphism and initial decompression by oblique normal and or dextral shearing beneath serpentinized peridotite we evaluated kinematic vorticity w m pure shear 0 w m simple shear 1 using the shape fabric of lawsonite crystals in blueschist layers and meter scale eclogite pods pods record dominant simple shear w m 0 8 in their eclogitic core and at pod margins partially transformed to blueschist map scale blueschist layers record a large component of pure shear w m 0 4 0 6 consistent with oblique extrusion at depth in the subduction zone and local simple shear w m 0 8 at the fault contact with serpentinite a combination of oblique unroofing from beneath a weak serpentinized hanging wall and pure shear extrusion in the subduction channel accounts for rapid exhumation along a low geothermal gradient and the rare preservation of lawsonite eclogite during exhumation to the earth9s surface

tectonic denudation of a late cretaceous tertiary collisional belt regionally symmetric cooling patterns and their relation to extensional faults in the anatolide belt of western turkey t hermochronological data reveal that the late cretaceous tertiary nappe pile of the anatolide belt of western turkey displays a two stage cooling history three crustal segments differing in structure and cooling history have been identified the central menderes metamorphic core complex represents an inner axial segment of the anatolide belt and exposes the lowest structural levels of the nappe pile whereas the two outer submassifs the g ordes submassif to the north and the ci ne submassif to the south represent higher levels of the nappe pile a regionally significant phase of cooling in the late oligocene and early miocene affected the outer two submassifs and the upper structural levels of the central menderes metamorphic core complex in the northern part of the g ordes submassif cooling was related to top to the nne movement on the simav detachment as the apatite fission track ages show a northward younging trend in the direction of movement on this detachment in the ci ne submassif relatively rapid cooling in late oligocene and early miocene times may have been related to top to the s extensional reactivation of the basal thrust of the overlying lycian nappes the second phase of cooling in the anatolide belt is related to pliocene to recent extension resulting in the formation of the central menderes metamorphic core complex in the inner part of the anatolide belt core complex development caused the formation of supra detachment graben which document the ongoing separation of the central menderes metamorphic core complex from the outer submassifs

gneiss domes and orogeny many gneiss domes record positive feedback between decompression and partial melting of orogenic middle crust exhumed orogens are riddled with gneiss domes cored by migmatites that underwent dehydration melting during decompression the decreasing buoyancy associated with increasing melt fraction drives further decompression at near isothermal conditions as the partially molten crust rises diapirically this combination of processes may explain the generation and retention of large volumes of crustally derived melt recorded in many deep seated migmatite terranes and inferred for active orogens in exhumed orogens the signature of the rapid ascent of partially molten crust is a gneiss dome cored by migmatite granite the large volume of material involved in the vertical transfer of partially molten crust indicates that the formation of gneiss domes is an efficient mechanism for heat advection during orogenesis

seismicity and source parameters of earthquakes in the region of the large tolbachik fissure eruption this study discusses the focal mechanisms of 61 earthquakes and dynamic parameters of 97 earthquakes mi 2 0 and focal depths 0 20 km occurring in the region of the large tolbachik fissure eruption in 1975 1978 variations of these parameters during the different eruptive stages are examined three stages can be distinguished 1 june 27 july 2 1975 from the beginning of the seismic preparation to the large earthquakes of july 2nd withm 5 0 2 july 2nd july 6th 1975 before the onset of eruption 3 from july 6th 1975 to the end of 1976 during the eruption

supra pan african unconformity between core and cover series of the menderes massif turkey and its geological implications abstract well preserved primary contact relationships between a late proterozoic metasedimentary and the metagranitic core and palaeozoic cover series of the menderes massif have been recognized in the eastern part of the cine submassif on a regional scale metaconglomerates occur as laterally discontinuous channel fill bodies close the base of the metaquartzarenite directly above the basement the pebbles in the metaconglomerates consist mainly of different types of tourmaline rich leucocratic granitoids tourmalinite and schist in a sandy matrix petrographic features geochemical compositions and zircon radiometric ages 549 6 3 7 552 3 3 1 ma of the diagnostic clasts of the metaconglomerates e g leucocratic granitoids and tourmalinites show excellent agreement with their in situ equivalents 549 0 5 4 ma occurring in the pan african basement as stocks and veins the correlation between clasts in the metaconglomerates and granitoids of the basement suggests that the primary contact between the basement and cover series is a regional unconformity supra pan african unconformity representing deep erosion of the pan african basement followed by the deposition of the cover series hence the usage of core cover terminology in the menderes massif is valid consequently these new data preclude the views that the granitic precursors of the leucocratic orthogneisses are tertiary intrusions

gneiss domes metamorphic core complexes and wrench zones thermal and structural evolution of the nigde massif central anatolia 1 the nigde massif a migmatite cored structural dome in south central turkey was metamorphosed deformed intruded and exhumed in an oblique tectonic regime involving a switch from transpression prograde metamorphism to transtension exhumation an 80 ma history of transpression and transtension is recorded in metamorphic rocks of the massif and the last 50 ma are recorded in both basement and overlying basin deposits nigde metamorphic rocks record a high temperature top to north syntranspression ductile fabric that was overprinted by lower grade top to south syntranstension ductile shear zones the 40ar 39ar data for hornblende muscovite and biotite document rapid late cretaceous cooling with the oldest ar hornblende ages 88 79 ma overlapping u pb ages in monazite and zircon 92 78 ma muscovite ar ages are dominantly 81 79 ma suggesting a short time between crystallization of high temperature metamorphic rocks and their cooling biotite ar ages are 79 74 ma with the exception of disturbed samples from the eastern margin of the massif and from eocene granitic stocks in the dome core the eastern margin adjacent to the sinistral central anatolian fault zone records another cycle of burial and exhumation that overprinted earlier fabrics and disturbed isotopic systems these two cycles of burial exhumation took place repeatedly along the same zone this may be characteristic of highly oblique tectonic regimes in the nigde massif burial and exhumation became more localized and of lower amplitude over time suggesting stabilization of the crust

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

late orogenic crustal extension in the northern menderes massif western turkey evidence for metamorphic core complex formation the simav metamorphic core complex of the northern menderes massif western turkey consists of a plutonic tertiary and metamorphic precambrian core footwall separated from an allochthonous cover sequence hanging wall by a low angle ductile to brittle extensional fault zone i e detachment fault the core rocks below the detachment fault are converted into mylonites with a thickness of a few hundred metres two main deformation events have affected the core rocks the first deformational event d1 was developed within the precambrian metamorphic rocks the second event d2 associated with the tertiary crustal extension includes two distinct stages stage one is the formation of a variably developed ductile mylonitic deformation d2d in metamorphic and granitic core rocks under greenschist facies conditions the majority of the mylonites in the study area have foliations that strike nnw to nne and dip sw to se stretched quartz and feldspar grains define the mineral lineation trending sw ne direction and plunging gently to sw the kinematic indicators indicate a top to ne sense of shear stage two formation of brittle deformation d2b that affected all core and cover rocks d2b involves the development of cataclasites and high angle normal faults an overall top towards the north sense of shear for the ductile mylonitic fabrics in the core rocks is consistent with the n s regional extension in western turkey

aftershocks of shallow earthquakes near kamchatka peninsula summary we considered aftershock sequences of earthquakes with magnitude m 4 0 7 8 recorded near the kamchatka peninsula coast at depths of 0 59 km in 1962 1987 the events of magnitude m 1 0 that occurred in the 3 days following the main shock and located not further than 50km from the main shock epicentre were recognized as aftershocks two types of aftershock sequences were distinguished quakes with one to four aftershocks and quakes having more numerous aftershocks aftershock sequences of the first type comprise the majority of the considered events more than 80 per cent they are distributed within the overall seismic zone aftershock sequences of the second type tend to cluster in space this type of aftershock sequence zoning can be a useful supplement to standard seismic zoning the space distribution of the second type of aftershock was used to estimate the dimensions of the source of the main shock a correlational dependence of source length and area upon energy magnitude and seismic moment was obtained comparison of these estimates of source dimensions with those obtained from p wave spectra corner frequencies shows good agreement it has been shown that there exists a linear dependence between energy of the main shock and energetic difference between the main shock and the largest aftershock

metamorphic history of the southern menderes massif western turkey metamorphic mineral compositions and textures are integrated with microstructures to test tectonic models for the construction and exhumation of a mid crustal terrane in western turkey the southern menderes massif part of the alpine orogen is composed of a tilted sequence of metasedimentary rocks that structurally overlies orthogneiss garnet biotite equilibria for schists collected along north south traverses consistently indicate temperatures of 430 c for the southernmost structurally highest garnet bearing rocks 500 c for structurally intermediate rocks and 550 c for the structurally deepest rocks near the contact with the orthogneiss there are no detectable discontinuities in metamorphic grade from north to south within the schist unit or between the schist and overlying lower grade and underlying higher grade rocks pressure estimates are less certain geobarometric results for the schists yield p 8 kbar but mineral assemblages and structural data are consistent with lower pressures 6 kbar metamorphic textures and garnet zoning in the menderes schists indicate metamorphism during a single thermal event accompanying development of the main penetrative foliation top to north fabrics formed during folding thrusting and were synkinematic with garnet growth top to south chloritic shear bands truncate the earlier foliation and overprint peak metamorphic assemblages and textures we propose that these metamorphic features and structures indicate synmetamorphic shortening followed by extension during alpine orogenesis

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

tectonics of mid tertiary extension along a transect through west central arizona large magnitude miocene extension in west central arizona occurred primarily along three imbricate northeast dipping normal faults the structurally highest of these faults the gently dipping buckskin rawhide detachment fault accommodated approximately 66 km of crustal extension whereas the two structurally lower faults accommodated a total of about 20 km extension due to this large magnitude extension an area at the earth s surface that was 10 to 20 km wide is now over a 100 km wide and crystalline rocks with mid tertiary mylonitic fabrics uncovered by detachment faulting are exposed over roughly 2000 km in the harcuvar metamorphic core complex most of the upper plate of the buckskin rawhide detachment fault was largely undeformed by internal extension only the thin tapered end of the upper plate was highly extended during extension the lower plate must have flexed to conform to the listric underside of the upper plate and to have flattened to its present subhorizontal form as it was uncovered grooves on the underside of the upper plate were apparently imposed on the pliable lower plate as it was denuded forming extension parallel folds in the lower plate low flexural strength characterized the lower plate during denudation and a highly mobile low viscosity deeper crust must have effectively decoupled the upper crust from the mantle lithosphere

thermochronologic evaluation of postcollision extension in the anatolide orogen western turkey 1 to better understand the driving mechanisms behind the transition from collision to extension in a convergent orogen data from multiple low temperature thermochronometers were obtained from the simav detachment fault sdf the earliest developed major extensional structure recognized in the western anatolide orogen of western turkey twenty two zircon fission track ft 26 apatite ft 12 apatite u th he ages and 26 apatite ft track length analyses are presented the data establish that the sdf was a major extensional fault active between 25 and 19 ma the coincidence in timing of magmatism with cessation of sdf activity implies the detachment became locked owing to doming induced by magma emplacement zircon ft ages away from the influence of miocene magmatism record rapid footwall cooling between 25 and 21 ma at a slip rate of up to 15 km myr and demonstrate that active ductile deformation along the sdf migrated northward with time apatite ft ages from the footwall of the sdf are spatially invariant over 100 km and consistently 2 3 myr younger than the zircon fission track ages from the same samples these data are consistent with a regional but relatively rapid erosion linked cooling phase that removed 2 3 km of overburden following cessation of sdf activity but before deposition of sedimentary rocks on the detachment surface at 16 4 ma postcollision extension of the anatolide orogen with development of the sdf can be best explained as the result of postcollision magmatism and thermal weakening of the crust inducing the extensional reactivation of an earlier major out of sequence thrust

the 2013 earthquake swarm in helike greece seismic activity at the root of old normal faults the corinth rift in central greece has been studied extensively during the past decades as it is one of the most seismically active regions in europe it is characterized by normal faulting and extension rates between 6 and 15 mm yr 1 in an approximately n10e direction on 2013 may 21 an earthquake swarm was initiated with a series of small events 4 km southeast of aigion city in the next days the seismic activity became more intense with outbursts of several stronger events of magnitude between 3 3 and 3 7 the seismicity migrated towards the east during june followed by a sudden activation of the western part of the swarm on july 15th more than 1500 events have been detected and manually analysed during the period between 2013 may 21 and august 31 using over 15 local stations in epicentral distances up to 30 km and a local velocity model determined by an error minimization method waveform similarity based analysis was performed revealing several distinct multiplets within the earthquake swarm high resolution relocation was applied using the double difference algorithm hypodd incorporating both catalogue and cross correlation differential traveltime data which managed to separate the initial seismic cloud into several smaller densely concentrated spatial clusters of strongly correlated events focal mechanism solutions for over 170 events were determined using p wave first motion polarities while regional waveform modelling was applied for the calculation of moment tensors for the 18 largest events of the sequence selected events belonging to common spatial groups were considered for the calculation of composite mechanisms to characterize different parts of the swarm the solutions are mainly in agreement with the regional nne ssw extension representing typical normal faulting on 30 50 north dipping planes while a few exhibit slip in an nne ssw direction on a roughly subhorizontal plane moment magnitudes were calculated by spectral analysis of s waves yielding b values between 1 1 and 1 2 in their frequency magnitude distribution the seismic moment release history indicates swarm like activity during the first phase which could have acted as a preparatory stage for the second phase after 12 july that presented a more typical main shock aftershock behaviour the spatiotemporal analysis reveals that the swarm has occurred in a volume that is likely related with the extension at depth of the nne dipping pirgaki normal fault outcropping 8 km to the south the slow velocity of eastward migration of the epicentres during june implies triggering by fluids the situation appears different in the second phase of the sequence which was probably triggered by a build up of stress during the first one the relatively deep hypocentres of the 2013 swarm compared to the shallower seismic layer within the rift and their coincidence with the steeply dipping pirgaki fault favour an immature rift detachment model previous results from instrumental data indicate that approximately the same region had been activated during july august 1991 the availability of the dense permanent seismological network data thus allowed for a detailed analysis of this crisis a better understanding of its mechanical context and of the earlier events

patterns of surface downwearing on shore platforms in eastern canada downwearing rates were measured on shore platforms at about 200 transverse micro erosion meter tmem stations over periods ranging from 2 to 6 years there were seven study areas in eastern canada the platforms were surveyed and a schmidt rock test hammer was used to measure rock hardness more than 1200 rock samples from three of the study areas were also subjected each day over a 3 year period to two tidal cycles of immersion and exposure which simulated the central intertidal zone a further 840 samples were subjected to longer periods of exposure and immersion over a 1 year period which represented different elevations within the upper and lower intertidal zone respectively these experiments suggested that tidally generated weathering and debris removal is an effective erosional mechanism particularly at the elevation of the lowest high tides in the field mean rates of downwearing for each study area ranged from 0 24 mm yr 1 to more than 1 5 mm yr 1 rates tended to increase with elevation in the field with maxima in the upper intertidal zone this trend in the field cannot be attributed entirely to the tidally induced weathering processes that were simulated in the laboratory and must reflect in part the effect of waves frost ice and other mechanisms it is concluded that there are no strong spatial downwearing patterns on shore platforms and that downwearing rates in the intertidal zone are the result of a number of erosional mechanisms with different elevation efficacy characteristics furthermore even if only one or two mechanisms were dominant in an area any resulting relationship between downwearing rates and elevation would be obscured or eliminated by the effect of variations in the chemical and physical characteristics of the rocks copyright 2010 john wiley sons ltd

bivergent extension in orogenic belts the menderes massif southwestern turkey the central menderes massif is characterized by an overall dome shaped foliation pattern and a north northeast trending stretching lineation the asymmetry of shear bands and quartz c axis fabrics on either side of the structural dome demonstrate a top to thenorth northeastshearsenseinthenorthernpartandatoptothesouth southwestshear sense in the southern part of the submassif i e a bivergent downdip movement this suggests a symmetric collapse of the alpine menderes orogenic belt along two extensional shearzones conjugateshearbandsandsymmetricquartzc axisfabricsintheeast trendingtransitionzonedemonstrateacoaxialdeformationbetweenthetwoextensiondomains bivergent extension in the menderes massif is in contrast to asymmetric extension in the aegeansea here thestill activehellenicsubductionzoneevolvedfromanadvancingplate boundary associated with crustal thickening into a retreating plate boundary in oligocene miocene time southward rollback of the subducting plate during continuous northward subduction allowed asymmetric top to the north northeast extension in the back arc region during the exhumation of the cycladic core complexes in western turkey the arrival of the thick continental crust of the menderes massif halted subduction and probably caused the symmetric collapse of the massif because the high potential energy of the thickened crust was no longer supported by subduction

viscous collision in channel explains double domes in metamorphic core complexes in hot orogens gneiss domes are a response to upper crustal stretching and lower crustal flow two dimensional thermal mechanical modeling shows that localization of extension in the upper crust triggers in the deep crust oppositely verging horizontal flows that converge beneath the extended region upon viscous collision both flowing regions rotate upward to form two upright domes of foliation double domes separated by a steep median high strain zone in such systems horizontal shortening in the infrastructure develops in an overall extensional setting dome material follows a complex depth dependent strain history from shearing in the deep crustal channel to contraction upon viscous collision in the median high strain zone to extension upon advection into the shallow crust this depth dependent strain history is likely a general feature of dome evolution and is arguably well preserved in double domes such as the montagne noire france and naxos greece gneiss domes

evidence against the core cover interpretation of the southern sector of the menderes massif west turkey the menderes massif in western anatolia has been described as a lithological succession comprising a basal precambrian gneissic core of sedimentary origin overlain in sequence by palaeozoic schist and mesozoic cenozoic marble forming the envelope the boundary between core and schist envelope was interpreted as a major unconformity the supra pan african unconformity by contrast our field observations and geochemical data show that around the southern side of besparmak mountain north of selimiye milas the protoliths of highly deformed mylonitized augen gneisses are granitoid rocks intrusive into the adjacent palaeozoic metasedimentary schists the field relationships indicate the age of intrusion to be younger than late permian and there is no evidence for the existence of either an exposed precambrian basement or the supra pan african unconformity in this sector of the menderes massif