survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

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

holocene floodplain soils along the rio mamore northern bolivia and their implications for understanding inundation and depositional patterns in seasonal wetland settings abstract the llanos de moxos lm in the bolivian amazon basin host one of the largest seasonally inundated savannah landscapes on earth very little is known of this area with regard to sedimentary dynamics soil formation or their relationship to longer term climatic and hydrological variability in this setting here we present a detailed study of three floodplain depositional sequences building up the inundation savannah along the mamore river in the central lm pleistocene sands and silts unit 1 are overlain by thick overbank deposits of mostly holocene age unit 2 on both sides of the mamore river and underline the importance of extensive flooding processes for the late quaternary sedimentary and geomorphic evolution of the lm the fine grained distal overbank sediments show signs of strong modification by hydromorphic processes and reflect spatial and temporal variations in flood inundation patterns in addition widespread dark gray to blackish soil and paleosol horizons are intercalated with the overbank sediments but lack evidence for significant weathering these horizons are likely the result of cumulative incorporation of organic material under conditions of particularly low sedimentation rates therefore their formation should be linked to processes such as channel migration longer term meanderbelt evolution avulsive drainage reorganization changes in sediment supply or climatically induced variations in flooding type frequency or magnitude the common occurrence of these floodplain soils in the early to mid holocene may thus reflect the combined effects of hydrological geomorphic and sedimentary changes during a drier mid holocene

thermochronology of the high pressure metamorphic rocks of crete greece implications for the speed of tectonic processes new fission track thermochronologic data from the high pressure p low temperature t rocks of crete greece combined with pressure temperature and stratigraphic constraints reveal that their subduction began between 36 and 29 ma metamorphism took place in western crete at peak conditions of 10 2 kbar and 400 50 c between 24 and 19 ma and rapid exhumation to 10 km and 300 c at a minimum rate of 4 km m y was completed before 19 ma constraints from the thermal history of the plate above the inferred extensional detachment reveal that tectonic unroofing contributed 85 to 90 of the overall exhumation of the high p low t rocks of crete we propose that the hellenic subduction zone has acted as a retreating plate boundary since at least the early oligocene and collision and extension during this time were driven by roll back associated with slab pull rather than by gravitational collapse as a consequence of crustal thickening the speed of subduction and exhumation of the high p low t rocks of crete within 10 m y has important implications for other orogenic belts showing that rocks can be subducted metamorphosed at high pressure and exhumed despite slow overall plate convergence within the uncertainties of many paleontologic and isotopic age data

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

the composition and formation of grainy void cutans in some soils with textural contrast in southeastern australia fine grained void cutans and grain cappings were observed in the a and upper b horizons of two podzolic soils at a site near canberra optically these features are dark coloured and grainy textured in transmitted plane polarized light and generally isotropic in crossed polarized light they consist of fine particles 5 m diameter of quartz clay minerals and traces of feldspars and iron and titanium oxides electron microprobe analyses indicate high si al ratios which largely result from the high quartz content of the cutans transmission electron microscopy indicated the presence of some poorly structured and only weakly crystalline to possibly amorphous mineral phases consisting of iron titanium and traces of silicon and aluminium as partial particle coatings and in voids mixed layer clays in the cutans also appeared to have been attacked by weathering on their margins the presence of euhedral quartz grains suggests that there may have been some authigenic quartz formation within the cutans illuvial clays in the lower b and c horizons consist of clear reddish orange ferri argillans it is probable that the reddish orange ferri argillans developed prior to the grainy cutans the latter consisting partly of translocated aeolian deposits post depositional weathering of both the grainy cutans and the ferri argillans has occurred in the a and upper b horizons ferrolysis promoted by periodic waterlogging above the textural contrast may be an important weathering process in the a horizons

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

early acheulean technology at es2 lepolosi ancient mhs bayasi in peninj lake natron tanzania abstract the aim of this paper is to undertake the technological description of es2 lepolosi one of the acheulean sites located on the sambu escarpment in the lake natron basin tanzania and dated to 1 5 1 4 ma through the combination of three different lithic collections glynn isaac s 1961 81 dominguez rodrigo s 1999 2002 and the sample retrieved during our own excavations carried out between 2007 and 2011 we provide here a comprehensive description of the technological characteristics seen in this classic african early acheulean site sedimentological archaeostratigraphic and soil micromorphological information acquired during the course of the 2008 2011 fieldwork is used as a contextual framework for assessing the environmental and post depositional history of the site

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

a flow law for dislocation creep of quartz aggregates determined with the molten salt cell we have used the molten salt cell to conduct an experimental study on the rheology of a natural quartzite containing 0 15 wt water co axial deformation experiments were conducted at constant piston displacement rates approximating constant strain rates at low strain the strengths of our natural quartzite measured in the molten salt cell are approximately half those measured at the same conditions in solid media because unlike solid confining media molten salt does not contribute to the strength of the sample it reduces the friction on the moving piston and it allows clear identification of the hit point we have limited the experimental conditions to those required for dislocation creep and have used only steady state flow stresses measured during climb accommodated dislocation creep to calculate the flow law parameters two flow laws were determined one for samples containing minor amounts of melt 1 2 and one for melt free samples in both cases the power law stress exponent n is 4 0 0 9 which is greater than that previously reported in flow laws for dislocation creep of quartz aggregates determined in solid media the activation energy q is 137 34 kj mol 1 for samples with melt and 223 56 kj mol 1 for those without within the range of previously determined values for quartz aggregates containing 0 1 wt water the pre exponential term a is 1 1 10 4 2 mpa ns 1 for samples without melt and 1 8 10 8 2 mpa ns 1 for those with melt the lower strengths measured in the molten salt cell indicate that previous piezometer relations for quartz experimentally determined in solid media are not correct extrapolation of the flow law for melt free aggregates to natural strain rates predicts higher strengths than most previous quartz flow laws however accurate extrapolation requires determining the dependence of flow stress on fh2o and or ah

tectono sedimentary evolution of lower to middle miocene half graben basins related to an extensional detachment fault western crete greece crustal extension in the overriding plate at the aegean subduction zone related to the rollback of the subducting african slab in the miocene resulted in a detachment fault separating high pressure low temperature hp lt metamorphic lower from non metamorphic upper tectonic units on crete in western crete detachment faulting at deeper crustal levels was accompanied by structural disintegration of the hangingwall leading to the formation of half graben type sedimentary basins filled by alluvial fan and fan delta deposits the coarse grained clastic sediments in these half grabens are exclusively derived from the non metamorphic units atop the detachment fault being in direct tectonic contact with hp lt metamorphic rocks of the lower tectonic units today the basins must have formed in the period between c 20 and 15 ma prior to the exposure of the hp lt metamorphic rocks at the surface and juxtaposed with the latter during ongoing deformation

constraints on the late thermotectonic evolution of the western alps evidence for episodic rapid uplift forty two new apatite and zircon fission track ages are presented for samples from the western alps in southern switzerland northern italy and southeastern france measured ages plotted against assumed closure temperatures yield cooling patterns for the final cooling uplift and exhumation of the western alps similar fission track zircon ages in the penninic gran paradiso massif dent blanche nappe sesia lanzo zone and ivrea zone indicate cooling of all four units to 225 c by 33 ma differences in apatite ages reveal differential cooling of the four blocks between 33 ma and the present in the sesia lanzo zone similarity of apatite ages regardless of elevation together with near volcanic confined fission track length patterns suggest rapid cooling and uplift at 25 ma compared with slow cooling of other western alps units around 12 ma uplift is thus not continuous but episodic often over a short time interval beyond the resolution of other methods such episodes of uplift as revealed here in the sesia lanzo zone may be the rule rather than the exception

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

timing of the amorgos detachment system and implications for detachment faulting in the southern aegean sea greece we present apatite and zircon fission track aft and zft ages from the amorgos detachment system in the aegean sea greece the amorgos detachment system consists of a basal and an upper detachment the lower amorgos detachment occupies the same tectonic position as the regionally important large magnitude cretan detachment and therefore can provide improved constraints on the evolution of the latter aft ages from the footwalls of both detachments show that detachment related cooling occurred in the early miocene coeval with an important phase of cooling in the footwall of the cretan detachment on crete we interpret the footwall aft ages to indicate an early miocene age of movement on the amorgos detachments essentially simultaneously with slip on the cretan detachment zft ages from rocks above the lower amorgos detachment are not reset indicating that metamorphic temperatures during the tertiary hellenic orogeny did not exceed c 300 c significantly we discuss a model in which top to the north movement on the cretan amorgos detachment commenced in the early miocene soon after the inception of the cretan amorgos detachment top to the south movement on the south cyclades shear zone deformed the latter and brought the amorgos detachment into a higher crustal position

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

a micromorphological record of contemporary and relict pedogenic processes in soils of the indo gangetic plains implications for mineral weathering provenance and climatic changes

confined fission track length measurement of zircon assessment of factors affecting the paleotemperature estimate abstract we carried out a series of laboratory annealing experiments in order to understand the factors affecting observed confined track lengths in thermally annealed zircon the variation of confined fission track lengths according to both experimental and analytical conditions was determined on zircons from nisatai dacite it was found that etching temperature track etching criteria measurement criteria of horizontal confined tracks hct s and the orientation of hct s significantly control the observed track lengths if samples are highly annealed i e 600 c for 1 hr annealing the first three factors may be related to the presence of gap zones in an annealed track whilst the fourth is caused by anisotropic annealing and etching characteristics for reliable thermal history reconstruction therefore it should be the minimum requirement to document explicitly the experimental and analytical conditions of these factors in zircon fission track analysis

evolution of the lower gangetic plain landforms and soils in west bengal india abstract three major landforms uplands old fluvial deltaic plains and young fluvial plains are identified from the lower gangetic plains of west bengal india on the basis of remote sensing and field studies morphologic quantitative and thermoluminescence studies of soils of the study area have been conducted two types of uplands are recognised upland in the west overlain by red soils autochthonous and allochthonous types and upland in the north barind tract characterised by three topographic levels aspects of the autochthonous upland red soils lower to middle pleistocene age show the ferrugination ferrisol phase of development soils of the old fluvial deltaic plains 6 3 ka and lower level of the barind tract have argillic horizons and exhibit the fersiallitisation phase of development development of ferrugination and fersiallitisation phases was favored due to the pre weathered nature of the parent material soils of the old fluvial deltaic plains barind tract lower level and young fluvial plains show effects of hydromorphism due to waterlogging in the form of segregations of fe mn oxides gleying and chloritisation probably due to ferrolysis in the upper horizons of some of these soils neotectonics seems to have affected development of landforms and soils significantly due to reactivation of some basement faults in the western region some tectonic blocks subsided causing transgression during the early pleistocene and at ca 7 ka subsequent uplift of these blocks caused regressions and development of soils on the exposed landscapes episodic uplift of the barind tract in the northern region may have given rise to three topographic levels some faults confine the courses of the damodar ganga and bhagirathi rivers

new information on the thermal history of the southwestern lower saxony basin northern germany based on fission track analysis the southwestern part of the lower saxony basin lsb is characterized by gravity and magnetic anomalies and by an extremely high thermal maturity of organic matter this was for many years attributed to a late cretaceous intrusion but actually deep burial is being debated the complex thermal history of the area has been studied by fission track analysis zircon data provide evidence for widespread hydro thermal activity during the permian and upper jurassic lower cretaceous apatite ages indicate a major cooling event in the mid cretaceous 89 72 ma reflecting the time of inversion of the lsb during the cretaceous the cooling of the basin centre was rapid compared to the basin margins apatite fission track ages from borehole samples which are recently within the upper part of the apaz indicate a young heating of the sedimentary sequences until present

timing of low temperature metamorphism and cooling of the paleozoic and mesozoic formations of the bukkium innermost western carpathians hungary k ar ages of illite muscovite and fission track ages of zircon and apatite were determined from various lithotypes of the bukkium which forms the innermost segment of the western carpathians the stratigraphic ages of these dinaric type formations cover a wide range from the late ordovician up to the late jurassic the grade of the orogenic dynamo thermal metamorphism varies from the late diagenetic zone through the anchizone up to the epizone chlorite maximally biotite isograd of the greenschist facies the k ar system of the illite muscovite in the 2 m grain size fraction approached equilibrium only in epizonal and high temperature anchizonal conditions the orogenic metamorphism culminated between the eo hellenic 160 120 ma phase connected to the beginning of the subduction in the dinarides and the austrian 100 95 ma phase characterized by compressional crustal thickening no isotope geochronological evidence was found for proving any hercynian recrystallization the stability field of fission tracks in zircon was approached using the thermal histories of the different tectonic units a temperature less than 250 c and effective heating time of 20 30 ma had only negligible effects on the tracks whereas total annealing was reached between 250 and 300 c apatite fission track ages from the paleozoic and mesozoic formations show that the uplift of the bukk mountains occurred only in the tertiary not earlier than ca 40 ma ago thermal modeling based on apatite fission track length spectra and preserved paleogene sediment thickness data proved that the late neogene burial of the recently exhumed plateau of the bukk mountains exceeded 1 km

low effective viscosity during high pressure metamorphism due to dissolution precipitation creep the record of hp lt metamorphic carbonates and siliciclastic rocks from crete the micro structural record of high pressure low temperature hp lt metamorphic rocks t 400 50 c p 10 2 kbar of the phyllite quartzite unit in western crete greece is interpreted in terms of deformation mechanisms and flow stress phyllites were deformed at low stress by dissolution precipitation creep governed by strongly enhanced dissolution along quartz mica 001 phase boundaries quartzites and quartz veins were deformed by dislocation creep at higher flow stress the contrasting effective viscosities caused stress concentration in the quartzites and quartz veins also microstructures from aragonite marbles indicate that dissolution precipitation creep was the dominant deformation mechanism and that dislocation creep has not been activated in these rocks pervasive ductile deformation was restricted to hp lt metamorphic conditions and the microstructural record of deformation at maximum depth has been preserved with all subsequent deformation localized and confined to the brittle field constraints on the timing of deformation allow an estimation of strain rates experimentally determined flow laws for dislocation creep are used to pose upper bounds on flow stress and bulk viscosities of rocks deformed by dissolution precipitation creep for the phyllites a conservative estimate is about 1019 pa s or below in contrast to 1020 pa s derived for the quartzites this compares well to the viscosity contrast of 1 2 orders of magnitude reflected by the mesoscopic structures since phyllites and carbonate rocks form large portions of the subducted sedimentary pile the low flow stress during rapid deformation of these rocks at hp lt metamorphic conditions and the lack of deformation along the burial and exhumation path imply very low strength of the plate boundary shear zones and negligible shear heating

miocene south directed low angle normal fault evolution on kea island west cycladic detachment system greece 1 new structural petrologic and thermochronologic data from kea west cyclades define a crustal scale ductile shear zone and ductile brittle low angle normal fault lanf system both the greenschist facies shear zone forming the footwall and the overlying lanf zone formed during constrictional strains with a consistent top to sw s shear sense with increasing finite strains toward higher structural levels but decreasing temperatures from footwall to hanging wall the tectonostratigraphy comprises a 450 m thick footwall of shallowly dipping schists and calcite marbles representing the intermediate unit of the attic cycladic crystalline acc above the footwall is a 60 m thick highly strained lanf zone consisting of phyllonites cataclastic schists ultramylonitic calcite marbles proto mylonitic calcite marbles and cohesive cataclasites that arch over the whole island these fault rocks exhibit multistage lanfs evolving from ductile to brittle conditions an up to 50 m thick brecciated limestone and dolostone sequence forms the unmetamorphosed hanging wall which is most probably part of the upper unit of the acc multiequilibrium p t estimates on chlorite white mica pairs in the footwall yield 7 5 5 kbar 360 c 450 c for inclusions in albite and epidote 5 5 3 kbar 400 c 350 c for the main foliation and 3 2 kbar 350 c 280 c in localized shear bands c and c foliations the 40ar 39ar white mica footwall cooling ages demonstrate that greenschist facies retrogression occurred between 21 and 17 ma localized late decimeter thick shear zones were active and dynamically recrystallized before 15 to 13 ma the lanf on kea together with similar structures in south attica and the west cyclades define the west cycladic detachment system characterized by ductile to brittle top sw s shear sense

post collisional tectonics in the northern cottian alps italian western alps field mapping and structural analysis have allowed us to characterise the fault geometry and the post metamorphic tectonics of an area located in the northern cottian alps inner western alps two main faulting stages were distinguished here the first oligocene early miocene is related to the development of an e w striking left normal shear zone this shear zone is interpreted as an antithetical of two regional n s right lateral structures the col del lis trana deformation zone ltz and the colle delle finestre deformation zone cfz the second faulting stage post early miocene is related mainly to the development of n s normal faults coeval with the extensional reactivation of the ltz and the cfz we discuss this kinematic evolution in the framework of the geodynamic evolution of the western alps

experimental evidence for the pressure dependence of fission track annealing in apatite abstract fission track analysis has seen a major expansion in application to general geological problems reflecting its advances in understanding the temperature dependence of track annealing and track length distributions however considerable uncertainties still persist in particular concerning the stability of fission tracks subjected to the interaction of environmental physical parameters e g pressure temperature stress and in extrapolation of laboratory data to geological time scales in this work we studied the fading behavior of spontaneous fission tracks in basic apatite hexagonal ca5 po4 3 oh f cl when exposed simultaneously to laboratory pressures temperatures and stress over varying time spans the experiments showed that track fading is a complex recovery mechanism which is extremely sensitive to the coupling of these three parameters in particular a strong decrease in the fission track fading rate was observed as a function of increasing pressure and a nearly temperature independent dramatic increase in fission track recovery was observed as a function of stress consequently 1 the stability field of fission tracks in apatite increases towards temperatures higher than 110 c depending on the absolute pressure 2 closure ages in apatite are underestimated 100 for an ideal geothermobarometric gradient 3 related exhumation and erosion rates are overestimated above the closure temperature and underestimated below the closure temperature and 4 since the widely applied statistical description of thermally induced fading kinetics does not account for the influences of either pressure or stress and is based on fission track annealing data produced at ambient pressure the accuracy in extrapolating fission track data to geological time scales and in their application to dynamical systems must be cast into doubt

genesis morphology and mineralogy of planosols developed from different parent materials in southern brazil abstract the genesis of planosols is a complex process since it can involve multiple cycles of soil formation deposition of allochthonous materials and also past climate changes furthermore this subject is still poorly studied in the humid tropics thus hindering a proper appraisal of the potentials and limitations of planosols the objective of this research was to study pedogenetic processes and properties of planosols formed from different parent materials in southern brazil four soils were sampled p1 hypereutric luvic albic planosol developed on lagoon plain sediments p2 orthoeutric luvic albic planosol on holocene alluvial deposits p3 hypereutric luvic albic planosol on granite and p4 orthoeutric luvic albic planosol on gneiss all planosols presented sandy horizons a and e with low ph

nongeometrically converted shear waves in marine streamer data under certain circumstances marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging these shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom they are called nongeometrical because the evanescent part in the water does not satisfy snell s law for real angles but only for complex angles the propagating shear waves then undergo reflection and refraction in the subsurface and arrive at the receivers via an evanescent compressional wave the required circumstances are that sources and receivers are near the water bottom irrespective of the total water depth and that the shear wave velocity of the water bottom is smaller than the p wave velocity in the water most often the normal situation this claim has been tested during a seismic experiment in the river danube south of budapest hungary to show that the shear related arrivals are body rather than surface waves a borehole was drilled and used for multicomponent recordings the streamer data indeed show evidence of shear waves propagating as body waves and the borehole data confirm that these arrivals are refracted shear waves to illustrate the effect finite difference modeling has been performed and it confirmed the presence of such shear waves the streamer data were subsequently processed to obtain a shear wave refraction section this was obtained by removing the scholte wave arrival separating the wavefield into different refracted arrivals stacking and depth converting each refracted arrival before adding the different depth sections together the obtained section can be compared directly with the standard p wave reflection section the comparison shows that this approach can deliver refracted shear wave sections from streamer data in an efficient manner because neither the source nor receivers need to be situated on the water bottom

density changes of fluid inclusions in high pressure low temperature metamorphic rocks from crete a thermobarometric approach based on the creep strength of the host minerals abstract the densities of fluid inclusions in quartz from high pressure low temperature metamorphic rocks are generally inconsistent with the p t conditions derived from solid phase equilibria therefore some process of change must regularly have occurred during exhumation however evidence of decrepitation is frequently lacking consideration of the rates of change of p and t in metamorphic rocks shows that very low strain rates are sufficient for volume adaptation dislocation creep appears to be a feasible deformation mechanism allowing for continuous ballooning driven by a small differential pressure during decompression down to temperatures of about 300 c in quartz decrepitation requires a higher differential pressure in natural rocks it is therefore restricted to relatively low temperatures this concept was tested on inclusions in the phyllite quartzite unit of crete in these rocks cooling to below ca 300 c at confining pressures of 3 to 4 kbar is indicated corresponding to depths of 10 to 13 km it is anticipated that in metamorphic rocks the isochores of all fluid inclusions in quartz that have been formed at higher temperatures and remain unaffected by decrepitation should intersect close to the 300 c isotherm thereby defining a point on the p t paths rarely accessible by other methods extension of this concept to other minerals with known mechanical properties is straightforward and can under favourable circumstances be used to fix several points on p t paths

postnappe stacking extension and exhumation of high pressure low temperature rocks in the island of crete greece the island of crete consists largely of nappes of contrasting lithologies and metamorphism that were stacked southward during an oligocene early miocene n s compression with the lower nappes undergoing a high pressure low temperature hp lt metamorphism this was followed by a n s miocene crustal extension that caused thinning of the nappes and uplift of the hp lt metamorphic rocks ductile conditions took place in the lower nappes associated with a retrograde greenschist metamorphism while semiductile to brittle conditions took place in the upper nappes a major normal detachment fault separates the lower and the upper nappes the quartz texture analyses and the symmetry of structures indicate bulk coaxial deformation while the results of strain analysis suggest both constrictional and flattening strains a younger ne sw compression affected both the thinned nappe pile and the late miocene pliocene sedimentary basins finally a pliocene ne sw extension led to further uplift and exhumation of the hp lt metamorphic rocks this cyclic tectonometamorphic process of alternate compression and extension took place during the migration of the hellenic orogenic belt toward the most external units including successive tectonic events

an ustult aquult tropept catena in sierra leone west africa i characteristics genesis and classification abstract morphological physical chemical and clay mineralogical characteristics of a catena of 13 different soils of the upland and river terraces of central sierra leone are described a hypothesis about the chronology of the main processes of soil and landscape development is offered the processes include the formation of various geomorphic surfaces weathering formation of plinthite formation of ironstone gravel ferrolysis clay illuviation and the formation of a gravel free layer by termites in the u s d a soil taxonomy the soils are classified as kandiustults kandiustox paleustults plinthaquults paleaquults and dystropepts in the fao unesco legend they are identified as plinthic acrisols albic plinthosols and dystric ferralic and umbric cambisols suggestions are made to modify the definitions of some of these units

miocene high pressure metamorphism in the cyclades and crete aegean sea greece evidence for large magnitude displacement on the cretan detachment the cyclades in the backarc region of the present hellenic subduction zone are known for widespread late cretaceous to eocene high pressure metamorphism in the cycladic blueschist unit we report 40 ar 39 ar and rb sr phengite ages of 24 21 ma for high pressure metamorphism 8 10 kbar 350 400 c in the lowest tectonic unit in the cyclades the basal unit which structurally underlies the cycladic blueschist unit the basal unit is correlated with the tripolitza unit of the external hellenides in the forearc region of the hellenic subduction zone the tripolitza unit is unmetamorphosed on crete where it is separated from the underlying high pressure 8 10 kbar 300 400 c plattenkalk and phyllite quartzite units by the extensional cretan detachment the age for high pressure metamorphism in the latter units is similar to our age for the basal unit in the cyclades because pressure temperature conditions in the plattenkalk and phyllite quartzite units on crete and the basal unit in the cyclades are also similar they must have been in close proximity in the early miocene hellenic subduction zone a palinspastic reconstruction suggests a subsequent displacement of 100 km on the cretan detachment this is one of the greatest displacement magnitudes ever reported from detachment faults because of this large offset the cretan detachment was an efficient agent for exhuming high pressure rocks

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

studying converted waves in shallow marine environment for many years waves converted from compressional to shear mode have been successfully applied in hydrocarbon exploration to image and characterize the subsurface since shear waves propagate with a velocity that is dependent on the shear modulus and are thus directly related to the shear strength of the sediment they are very useful for geotechnical purposes generally p wave reflection amplitudes contain s wave information but riedel et al 2001 showed that these reflections are not very sensitive to this an alternative approach is to obtain s wave information directly from converted waves however it is not clear whether these waves can be applied for geotechnical aims the main focus will be on understanding the dependence of mode conversion on the seismic properties in this study we investigate the possibility of acquiring converted waves in marine unconsolidated sediments from our numerical experiments we found that the conversion is maximal at two angles where the smallest angle appears to be more favorable in the environment of interest furthermore we show how and where converted waves can be observed on a seismogram and the optimum field configuration to acquire them

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

mid to late holocene fluvial activity behind pre columbian social complexity in the southwestern amazon basin the scale spatial variability and implications of pre columbian human induced changes in the amazon basin are controversial while some scholars believe that large settlements and complex societie

experimental approach of lessivage quantification and mechanisms abstract lessivage also called argilluviation consists of a substantial vertical transfer of particles less than 2 m from a superficial departure horizon to a deeper horizon this process is common in many soil types and responsible for the development of a textural differentiation in soil profiles in the subsurface however the mechanisms of lessivage are still poorly understood and to our knowledge lessivage has rarely been quantified we propose here two original experiments of in vitro pedogenesis on soil columns to analyse the mechanisms acting in eluviation and illuviation the two phases of lessivage and to quantify these two phases in terms of particle export and fixation we paid special attention to the experimental conditions so that the conditions were favourable for lessivage and as close as possible to field conditions the eluviation experiment showed that the release of particles was not the determining process for lessivage we also showed that the smectite selectivity of eluviation was not continuous over time both physical and chemical processes were identified as acting on both eluviation and illuviation concerning illuviation experiments showed that from 25 to 90 of the eluviated particles were retained in the deeper horizon although large to our knowledge this range represents the first quantification of illuviation

the hellenic subduction system high pressure metamorphism exhumation normal faulting and large scale extension the cenozoic history of the retreating hellenic subduction system in the eastern mediterranean involves subduction accretion arc magmatism exhumation normal faulting and large scale continental extension from 60 mya until the recent ages for high pressure metamorphism in the central aegean sea region range from 53 ma in the north the cyclades islands to 25 20 ma in the south crete younging of high pressure metamorphism reflects the southward retreat of the hellenic subduction zone the shape of pressure temperature time paths of high pressure rocks is remarkably similar across all tectonic units suggesting a steady state thermal profile of the subduction system and persistence of deformation and exhumation styles the high pressure metamorphic events were caused by the underthrusting of fragments of continental crust that were superimposed on slab retreat most of the exhumation of high pressure units occurred in extrusion wedges during ongoing lithospheric convergence at 23 19 mya large s

fission track dating of the western border of the bohemian massif thermochronology and tectonic implications since 1985 apatite fission track analysis was applied to more than 70 samples from surface outcrops and shallow boreholes at the western margin of the bohemian massif apatite ages were determined by the grain population method additional information from the frequency distributions of fully confined spontaneous tracks was used for modelling of t t paths in the low temperature range 120 c seven zircon samples were dated by the external detector method zircon ages between 283 and 215 ma indicate unroofing during the permian molasse stage and the triassic tectonic quiescence and slow subsidence prevailed from the jurassic until the middle cretaceous in the basement area south of weiden a mesozoic partial annealing zone for apatite fission tracks is now exposed at the surface farther north the basement was affected by stronger cretaceous and palaeogene erosion which yielded cooling ages between 110 and 49 ma this second period of post variscan denudation was correlated to reverse faulting along the franconian line

rapid exhumation of high pressure metamorphic rocks in kythera peloponnese greece revealed by apatite u th he thermochronology abstractapatite u th he and apatite fission track cooling ages from high pressure hp metamorphic rocks in the south aegean forearc along the kythera strait kythera and southeastern peloponnese suggest rapid exhumation during middle to late miocene times hp rocks from the kythera strait exhibit two perpendicular extensional structures samples with arc normal or arc parallel extensional fabrics yielded apatite u th he cooling ages of 8 10 ma the more precise u th he ages are consistent with previously reported apatite and zircon fission track ages obtained from the same rock units the less precise but still accurate fission track data provided a reference for u th he dating on relatively young uranium poor apatites the combined data therefore precisely and accurately constrain the exhumation history of hp rocks and indicate that localized arc parallel extension in the kythera strait was active for an 5 m yr interval during the regional arc expansion

uplift related retrogression history of aragonite marbles in western crete greece in the low grade high pressure 400 c 10 kbar metamorphic phyllite quartzite unit of western crete widespread occurrences of aragonite marbles have been discovered recently a sedimentary precursor is proved by relic structures bedding fossils partial or complete transformation of aragonite into calcite is ubiquitous compositional and microstructural features reflect the metamorphic history 1 the high pressure stage is documented by aragonite that is chemically characterized by incorporation of variable amounts of sr and the lack of mg the most sr rich aragonite has about 9 wt sro xsrarag 0 09 a compositional zoning observed in some aragonite crystals may be due to the prograde divariant calcite aragonite transformation in the system caco3 srco3 because the parent rocks probably were sr poor calcite limestones one can speculate that strontium has been supplied from an external source under high pressure conditions 2 during uplift calcite replacing aragonite did not equilibrate with unreplaced aragonite disequilibrium is indicated by highly variable compositions of calcite crystals that show topotactic relations to the host aragonite the calcite compositions range from that of the host aragonite sr rich and mg free to mg bearing and sr poor 3 calcite that recrystallized during retrogression is generally sr poor mean value ofxsr 0 005 mg bearing xmg 0 010 and chemically homogeneous because practically no sr remains in the calcite an interaction with a fluid phase is indicated in fine grained calcite marbles rich in solid organic matter microstructural features indicative of former aragonite may be present 4 the last stage of retrogression is documented by the appearance of radiating aragonite in veins and nodules this aragonite which shows neither deformation nor retrogression was probably formed metastably in a near surface environment

microorganism induced weathering of clay minerals in a hydromorphic soil abstract in order to improve the understanding of factors influencing weathering in hydromorphic soils the clay mineral and chemical compositions iron hydr oxides organic compounds and sr and nd isotopic compositions of hydromorphic soils on the banks of the liangzi lake hubei province south china were investigated the b horizon in the lower profile exhibits a distinct net like pattern with abundant short white veins within the red brown matrix their various 87sr 86sr and 143nd 144nd isotopic compositions showed only small variations of 0 7270 0 7235 and 0 51200 0 51204 respectively consistent with the composition of yangtze river sediments indicating that the soils were all derived from alluvium from the catchment the white veins contained notably more sio2 al2o3 tio2 and mobile elements relative to the red brown matrix while they both showed similar values for the chemical index of alteration of 86 7 and 87 1 respectively and displayed similar degrees of weathering the clay minerals in a ae and e horizons of the soil profile were illite kaolinite and mixed layer illite smectite these same three clay minerals comprised the white net like veins in the soil b horizon whereas only illite and kaolinite were observed in the red brown matrix iron hydr oxides in a ae and e horizons of the soil profile were hematite and goethite whereas in the red brown matrix of the b horizon they were hematite goethite and ferrihydrite different organic compounds were observed for the white vein and the red brown matrix in the soil b horizon an 18 2 fatty acid biomarker for fungi in the net like vein but not in the red brown matrix compared with the red brown matrix the white net like vein also clearly contained more mono unsaturated fatty acids which are sometimes associated with bacteria that have the capacity to reduce fe iii thus migration of iron and the formation of the net like veins involved the participation of biota during the hydromorphic pedogenesis process as ferrihydrite is usually formed with the assistance of biota redoximorphic processes will chemically affect phyllosilicates by changing their charge and fe iii in illite may serve as electron acceptor for fe iii reducing microorganisms this leads to an increase in negative charge in the illite structure which could be neutralized by electrostatic displacement of interlayer cations and adsorption of protons thereby promoting transformation of illite to mixed layer illite smectite and dissolution of the pre existing illite mineral our results suggest that microorganisms brought about iron leaching and dominated the alteration of clay minerals by redox processes and different mineral volumes formed in the net like b horizon of the hydromorphic soil were attributed to the microorganism induced weathering process

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

extension and exhumation of the hp lt rocks in the hellenic forearc ridge localized intensive ductile and ductile brittle extension of along the arc orientation is prominent in phyllite quartzite unit pqu rocks in kythera and the adjacent southeastern peloponnese but declines in prominence to the north and to the south along the cretan peloponnese ridge using zircon and apatite fission track dating we find that this structural characteristic is correlated with the youngest zircon fission track cooling ages of 14 to 9 ma and with the highest pressure temperature condition recorded in the metamorphic rocks below the structural detachment the cooling ages of the high pressure phyllite quartzite unit pqu rocks along the hellenic forearc ridge show that exhumation migrated from both crete and from the peloponnese to the area with the youngest ages in kythera and the southeastern peloponnese starting in the early miocene and continuing to the present trench rollback and slab retreat expanded the hellenic arc and this bending of the arc from an initial more rectilinear geometry increased areas of oblique convergence and we suggest this localized the subsequent arc parallel extension and local enhanced exhumation of hp rocks the zircon fit exhumation ages from the arc parallel stretching episode restrict the ductile part of this episode in exposed rocks to between about 14 and 9 ma apatite ft ages suggest brittle along arc extension continued to about 7 ma this episode is proposed to be the result of a temporary higher rate of rollback and slab retreat younger normal faults including those which define the margins of the present hellenic arc show return to arc normal extension

middle miocene graben development in crete and its possible relation to large scale detachment faults in the southern aegean the linkage between the development of south facing cretan graben and large scale detachment faulting in the southern aegean is unknown widespread serravallian deposits in the ierapetra graben of crete supply constraints to middle miocene graben development in the southern aegean the ierapetra graben and by inference the cretan graben in general were hitherto believed to have formed as a result of sinistral transpression during n s shortening we argue that the formation of the cretan graben is due to n s extension the south dipping n s extending kritsa normal fault served as the master fault controlling graben development in the ierapetra graben the kritsa normal fault is either an antithetic fault related to the top n cretan detachment or a synthetic fault associated with the top s ios detachment the overall geometry and timing relationships lead us to favour a connection with the ios detachment which in turn implies a large scale displacement on the ios detachment

reconstruction of the differentiated long term exhumation history of fuerteventura canary islands spain through fission track and u th sm he data miocene intrusives and lower cretaceous siliciclastic sedimentary rocks from the basal complex in western fuerteventura were analyzed with low temperature thermochronometric methods such as fission track and u th sm he dating in order to reveal the evolution of the island s exhumation history the obtained thermochronometric data yields a very slow rate of cooling in the order of 1 5 3 c myr from 50 to 20 ma for the early cretaceous siliciclastic rocks these sedimentary units have never been heated significantly above 240 c after deposition and still record the submarine onset of the island s formation in the eocene intrusive bodies associated with the early miocene magmatic activity of the central volcanic complex of the island show rapid initial cooling rates of 50 70 c myr from 20 to 14 ma contemporaneous with the intrusions the cooling rate of the cretaceous sedimentary units increased to 25 35 c myr and it is inferred that this increase is associated with enhanced uplift and erosion of the central volcanic complex after 14 ma rates slowed down to 3 6 c myr palaeosols overlying the sedimentary units are themselves covered by pliocene basalt flows and reveal that the sedimentary rocks reached the surface before 5 ma the thermochronometric data obtained in this study for central fuerteventura is difficult to reconcile with the cooling history derived from previously obtained fission track and k ar data from the north western part of the island this inconsistency is likely to indicate that the exhumation history of fuerteventura is more complex and regionally subdivided than previously believed

converted waves in a shallow marine environment experimental and modeling studies seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear wave velocity information but also for improved processing of deeper reflection data these waves generated at deep seas have been used successfully in hydrocarbon exploration however acquisition of good quality converted wave data in shallow marine environments remains challenging we have looked into this problem through field experiments and synthetic modeling a high resolution seismic survey was conducted in a shallow water canal using different types of seismic sources data were recorded with a four component water bottom cable observed events in the field data were validated through modeling studies compressional waves converted to shear waves at the water bot tom and at shallow reflectors were identified the shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments modeling results indicated the presence of a nongeometric shear wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water sediment interface as observed in air gun data this type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source thus these shear waves excited by the source water bottom coupled system kinematically behave as if they were generated by an s wave source placed at the water bottom in a shallow water environment the condition appears to be favorable for exciting such shear waves with nongeometric arrivals these waves can provide useful information of shear wave velocity in the sediments

avo investigations of shallow marine sediments amplitude variation with offset avo analysis is based on the zoeppritz equations which enable the computation of reflection and transmission coefficients as a function of offset or angle of incidence high frequency up to 700 hz avo studies presented here have been used to determine the physical properties of sediments in a shallow marine environment 20 m water depth the properties that can be constrained are p and s wave velocities bulk density and acoustic attenuation the use of higher frequencies requires special analysis including careful geometry and source and receiver directivity corrections in the past marine sediments have been modelled as elastic materials however viscoelastic models which include absorption are more realistic at angles of incidence greater than 40 degrees avo functions derived from viscoelastic models differ from those with purely elastic properties in the absence of a critical angle of incidence the influence of s wave velocity on the reflection coefficient is small especially for low s wave velocities encountered at the sea floor thus it is difficult to extract the s wave parameter from avo trends on the other hand p wave velocity and density show a considerably stronger effect attenuation described by the quality factor q influences the reflection coefficient but could not be determined uniquely from the avo functions in order to measure the reflection coefficient in a seismogram the amplitudes of the direct wave and the sea floor reflection in a common midpoint cmp gather are determined and corrected for spherical divergence as well as source and streamer directivity at cmp locations showing the different avo characteristics of a mud and a boulder clay the sediment physical properties are determined by using a sequential quadratic programming sqp inversion technique the inverted sediment physical properties for the mud are p wave velocity alpha 1450 25 m s s wave velocity beta 90 35 m s density rho 1220 45 kg m 3 quality factor for p wave qp 15 200 quality factor for s wave qs 10 30 the inverted sediment physical properties for the boulder clay are alpha 1620 45 m s beta 360 200 m s rho 1380 85 kg m 3 qp 790 660 qs 25 10

preparation and deformation of synthetic aggregates of quartz synthetic quartz aggregates of low porosity have been fabricated from natural quartz powder impure silica gel and high purity silicic acid by hydrothermal isostatic pressing at 300 mpa the resulting specimens have water contents comparable to those of natural quartzites and have been used for deformation tests the flow stress at 1200 1300 k was found to vary in an inverse relationship to the water pressure estimated under the assumption that the measured water content homogeneously filled the measured porosity it is questionable that the natural quartz origin specimens were fully equilibrated in respect to the activity of the water but equilibration has probably been achieved in the amorphous silica origin specimens which crystallized under the experimental conditions in the deformation of the latter materials the experimental activation energy at water pressures approaching the confining pressure was found to be about 150 kj mol 1 for both however the impure gel origin material gave a stress exponent of about 2 3 whereas the high purity silicic acid origin material gave a stress exponent of about 4 in spite of the grain sizes being about 90 m and 20 m respectively it is concluded that while the impure specimens have higher intragranular strengths there is also a significant contribution of grain boundary processes to the strain in them which is absent in the high purity specimens

variations in fault slip data and cooling history reveal corridor of heterogeneous backarc extension in the eastern aegean sea region abstract we report fault slip data across the boundary between the highly extended and largely submerged crust underlying the aegean sea from samos in the north to eastern crete in the south and the much less extended and emergent crust of western anatolia we identify three brittle deformation increments a late miocene mainly pliocene to recent crustal stretching increment an intermittent early to late miocene shortening increment concurrent with extension and magmatism and a miocene extensional event the youngest increment documents late miocene to recent nne extension over large areas but can locally also be oriented se amorgos and astipalea islands and ese eastern crete suggesting overall oblate strain geometry the intermittent miocene 24 5 ma fault slip records suggest overall prolate strain geometry where nne stretching is accompanied by e w shortening the older extension event is mainly nne directed but on samos island extension is e w probably reflecting local extension in a sinistral wrench corridor in the early mid miocene overall it seems that since the early miocene nne trending extension is the dominant regime in the eastern aegean with an intermittent component of short lived e w shortening the existence of a corridor of heterogeneous crustal deformation which is spatially associated with uncharacteristically old fission track ages and the apparent change in strain geometry in time challenge concepts that propose that the eastern aegean sea and western anatolia have been deformed as a continuous tectonic domain since the miocene we propose that the regional variation in extensional strain geometry resulted from a sinistral wrench component that was superimposed on the regional background nne extension by translation across a diffuse plate boundary we conclude that the eastern shoreline of the aegean sea is controlled by a miocene to recent sinistral wrench corridor that accommodated movement between different lithospheric domains

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

hydromorphic and clay related processes in soils from the llanos de moxos northern bolivia abstract the llanos de moxos is one of the largest wetlands in the world more than 100 000 km2 due to seasonal floods the soil parent materials are fine quaternary sediments brought by tributaries of the amazon river forests cover some areas although the dominant vegetation is a pastured savannah and backswamps at present the main land use is a very extensive rangeland and slash and burn agriculture in minor areas we have studied 15 profiles from several sample areas between trinidad and san ignacio field and laboratory studies have been carried out in order to elucidate the soil forming processes taking place and to gain basic knowledge for a sustainable land management coarser soils are located near the present river system or in former riverbank areas often under forest textures here are loam or silty loam silty clay loam being dominant finer soils may have up to 85 clay and are usually under savannah cover illite is the dominant clay mineral in all soils followed by smectite and kaolinite vermiculite is absent quartz is present in a very significant amount in the clay fraction of all studied soils goethite and lepidocrocite are present in all soils lepidocrocite being a good indicator of poor drainage conditions soils are mainly acid but there are soils with calcium carbonate accumulation in the subsoil or even saline soils salitrales soils are flooded for a significant period 3 6 months and bypass flow is very active hydromorphic processes are always present and morphologies include hard and soft iron manganese concretions with diffuse boundaries within peds impregnative fe coatings and fe depletion hypocoatings along pore walls the micromorphological study shows different degrees of hydromorphism some of them associated to the present pore system and some with a palaeo character often disturbed by active slickensides microsparite nodules are also present in some low lying soils the soils present several morphological features related to the mobility of the fine fraction that can be related to drainage conditions as recent clay coatings clay and silt infillings and coatings and clay depleted hypocoatings the most clayey soils show striated b fabrics and frequent slickensides and some others point to ferrolysis as iron depleted hypocoatings and low crystallinity clay coatings along pores although this is not supported by mineralogical data a moderate cation supply probably prevents strong acidification

mechanical re equilibration of fluid inclusions in san carlos olivine by power law creep fluid inclusions in san carlos olivine stretch via plastic mechanisms when heat treated at 1400 c and 0 1 mpa in controlled f o 2 atmospheres for several days measurable changes in both inclusion dimensions and fluid densities occur densities decrease from 1 0 to 0 7 g cc stretching is fastest along 100 and slower along 001 and 010 the dislocation microstructure around the inclusions suggests that creep mechanisms operate uncertainties in the experimental determinations of stretching rates result from optical resolution limits errors inherent in measuring homogenization temperatures uncertainties in the fluid equation of state and changes in fluid chemistry during the heat treatment inclusion stretching by dislocation creep can be treated using a model developed for hot isostatic pressing in this model we assume spherical symmetry of plastic flow that the material yields by steady state power law creep and that the parameters for the constitutive law and fluid equation of state are known stretching rates are predicted to depend on the difference between the fluid pressure and the external pressure the temperature the constitutive law governing power law creep and geometry predicted stretching rates show fair but not exact agreement with experimentally measured rates the amount of stretching predicted by the model is in rough agreement with estimates based on dislocation microstructures around natural inclusions if xenolith ascent rates are of the order of 1 cm s or faster

thermomechanical evolution of a ductile duplex the thermomechanical evolution of a midcrustal ductile duplex in central australia has been reconstructed through space and time using 40ar 39ar thermochronology flow stress estimates cross sectional restoration of dislocation creep microstructures and microstructural and structural analysis a critical aspect of this analysis is the identification of populations of white micas in quartzite mylonites that have neocrystallized below their closure temperature and which record the time when ductile deformation ceased in dating these micas the mylonitic microstructures have effectively been dated the time temperature history of the duplex has been constrained through multidomain thermal modeling of k feldspar 40ar 39ar data the modeling demonstrates that a temperature gradient existed across the duplex during its formation the concept of microstructural continuity during ductile deformation has great potential for elucidating the kinematic evolution of ductile duplexes mapping of the deformation mechanisms and recrystallized grain sizes of quartzites deformed under greenschist facies conditions has been used to evaluate tectonic offsets that occurred after microstructural freezing this analysis shows that the duplex formed as a forward propagating thrust system accommodating 60 km of convergence between the upper and lower plates of the megathrust with a significant fraction of the displacement occurring after microstructural freezing finally using the data as input to published flow laws for quartz aggregates provides a strain rate history for the duplex although uncertainties are clearly large the timing of highest estimated strain rates during duplex evolution does indeed correlate with the highest rates of convergence between the upper and lower plates of the megathrust system according to regional cooling history studies and with coeval sedimentation in adjoining molasse basins

formation processes and stratigraphic integrity of the middle to upper palaeolithic sequence at cova gran de santa linya southeastern prepyrenees of lleida iberian peninsula sediments from cova gran de santa linya southeastern prepyrenees of lleida iberia are investigated by geoarchaeological means micromorphological textural quartz grain morphoscopy and geochemical analyses are coupled with stratigraphic and sedimentary macroscopic data to provide new insights into the formation processes and the integrity of the occupation layers and embedded sterile deposit documented at the middle to upper palaeolithic boundary direct indicators of the anthropogenic and natural dynamics involved in the deposition and alteration of the sediments investigated are provided results reveal the presence of in situ combustion structures as a major sedimentary indicator of human activity and occupation surfaces at the site the overall good preservation of the combustion residues indicates that occupation layers have been preserved in their original context of deposition traits of surface exposure in parallel to progressive lessening of evidence related to human activity at the top of the middle palaeolithic sequence suggest discontinuity in the occupation of the site and a possible abandonment of the rock shelter at the end of this period formation processes of the sterile deposit documented between the mousterian and the early upper palaeolithic levels involved the accumulation of debris from local sediments and soils as well as from the structure of the rock shelter soil forming dynamics related to palaeoenvironmental moisture fluctuations have also been recorded throughout the sequence investigated and indicate periods of surface stability during the formation of the sterile deposit environmental dynamics active during the formation of the sterile partially disturbed the top of the mousterian layer however our data indicate that such dynamics did not substantially affect the overall integrity of the archaeological record our results highlight the crucial contribution of geoarchaeology and microstratigraphy to the characterisation and assessment of the anthropogenic and natural dynamics involved in the accumulation and taphonomy of middle to upper palaeolithic sequences

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

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

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

new zircon fission track analysis constraints on tectonic mineralization epochs in the ganzi litang gold belt eastern qinghai tibet plateau abstract the ganzi litang gold belt as a part of the sanjiang tethys orogen is located between the yidun block and songpan ganzi block terrane in the eastern qinghai tibetan plateau and experienced oceanic slab subduction continent arc collision and intracontinental convergence since the indosinian orogeny a series of gold ore deposits have been found within the region this paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track ft thermochronology a total of 15 zircon ft analysis results were obtained that can be divided into four age groups 217 213 ma 190 160 ma 155 93 ma and 72 67 ma representing four distinct episodes of gold mineralization of which the middle two episodes predominate eruption of the auriferous volcanic rocks that comprise the belt started at 217 213 ma when the ganzi litang meso tethys ocean began to subduct the mineralization episode at 190 160 ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional convergence of the ganzi litang belt finally the episodes at 155 93 ma and 72 67 ma are respectively related to the closing times of the bangong nujiang and yarlung zangbu oceans corresponding to tectonic quiet episodes

the oxidation state of manganese in ferromanganese nodules and deep sea sediments from the central indian ocean abstract ferromanganese nodules from different sediment facies including siliceous ooze pelagic clay sediments from transition zone of siliceous and pelagic clay and seamount crusts from the central indian ocean were analysed for chemical composition mineralogy and bulk oxidation state of mn by the iodometric method despite considerable variation in chemical composition mn fe ratio times from 1 35 to 7 42 and mineralogy the o mn ratio or mno x solid hydrous manganese oxide does not vary much from 1 73 to 1 81 suggesting most of the mn in the manganese nodules in mn iv the oxidised upper zone in the sediment cores decreases in thickness from 15 cm in the north 5 s to 11 cm in the southern part 14 s of the central indian ocean iodometric titration of deep sea sediments yields o mn ratios of 1 29 1 95 sediments from the manganese nodule field have maximum solid mn concentrations and lower o mn ratios in the core top 0 3 cm with minimum mn and o mn ratios at 11 cm depth and thus may reflect the mechanism controlling the supply of diagenetic mn to the nodules in contrast sediments from the non manganese nodule field have comparatively low solid phase mn concentrations in the core top 0 3 cm and almost uniform o mn ratios with depth indicating that mn is not preserved in the sediments but may be remobilised and deposited somewhere else

genesis of two planosols in the massif central france abstract two planosols developed on gravelly quaternary sediments of the river allier in the limagne rift valley massif central france were studied parent material contained in addition to a granitic component large amounts of volcanic particles morphological chemical mineralogical and physical properties of both profiles were investigated to indicate some of the changes which have taken place during pedogenesis both profiles were characterized by pronounced textural contrasts between sandy a and e horizons and clayey b horizons soil formation rather than a transient depositional environment is thought to be responsible for this marked textural change clear dissolution features of all mineral grains except quartz and increasing amounts of volcanic fragments with depth suggested weathering increasing ratios of mobile basic cations to tio 2 with increasing depth corroborated this observation the presence of non laminated isotropic and anisotropic limpid clay coatings were also evidence of in situ mineral weathering in both profiles kaolinite predominated as clay mineral and increased towards the surface micromorphological observations of microlaminated dusty and impure clay coatings in b horizons of both profiles were clear signs of clay illuviation bulk densities were high in lower e horizons and upper b horizons field observations and micromorphological data showed clear signs of periglacial features the combination of pedogenic and periglacial processes has apparently lead to a considerable compaction abundant cemented iron and manganese features predominantly occurring in e horizons suggested surface water gleying micromorphological observations of illuviation coatings in b horizons and of fine material in a and e horizons demonstrated grainy aspects suggesting ferrolysis

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