field relations geochemistry and origin of the upper cretaceous volcaniclastic kannaviou formation in western cyprus evidence of a southerly neotethyan volcanic arc

sedimentological characteristics of small rivers with loessic headwaters in the chaco south america some sedimentological characteristics of uvial environments located in the northeastern region of the chaco pampa plain were analysed in order to determine the possible in uence of the loessic headwaters of local basins concentrations of suspended sediments as well as grain size of the river beds were compared unexpectedly it was found that the suspended load has an inverse relationship with the hydrometric levels with the exception of highly saline streams conductivity values between 4300 and 11 000 l sc m 1 the mean concentration of suspended sediments was 63 1 and 206 3 mg l 1 in ood and low water periods respectively the grain size of bed sediments was relatively homogeneous along the whole hydrological cycle sandy silty bottoms predominate in channels followed by silty sandy and clayey silty bottom types sediment transport mainly occurs in accelerating ow suspension overcoming the critical erosion velocity during ood periods some parameters exceeded by 70 the values recorded during the low water phase 2000 elsevier science ltd and inqua all rights reserved

origin and emplacement of mariana forearc seamounts large seamounts occur on the outer half of the mariana forearc they represent a new class of seamounts consisting of horsts and diapirs of metamorphosed forearc material the degree of metamorphism in this material depends on the amount of water available and the pressure temperature regime of the forearc wedge the major source for the water involved in the metamorphism is most likely the descending slab theoretical models for thermal regimes in convergent margins suggest that the lower grade metamorphic facies will be restricted to the outermost part of a forearc zeolite and chlorite facies rocks predominate in dredge hauls from horsts on the outer 50 km of the mariana forearc thermal models indicate that higher grade greenschist facies should occur farther from the trench seamounts that were probably formed in response to diapiric emplacement of serpentinite predominate from 50 to 120 km from the trench uplift of the horsts and emplacement of the serpentinite diapirs were probably facilitated by vertical tectonic movement in response to subduction of plate seamounts and by fracturing of the mariana forearc

a geomorphological approach to the management of rivers contaminated by metal mining as the result of current and historical metal mining river channels and floodplains in many parts of the world have become contaminated by metal rich waste in concentrations that may pose a hazard to human livelihoods and sustainable development environmental and human health impacts commonly arise because of the prolonged residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals this paper considers how an understanding of the processes of sediment associated metal dispersion in rivers and the space and timescales over which they operate can be used in a practical way to help river basin managers more effectively control and remediate catchments affected by current and historical metal mining a geomorphological approach to the management of rivers contaminated by metals is outlined and four emerging research themes are highlighted and critically reviewed these are 1 response and recovery of river systems following the failures of major tailings dams 2 effects of flooding on river contamination and the sustainable use of floodplains 3 new developments in isotopic fingerprinting remote sensing and numerical modelling for identifying the sources of contaminant metals and for mapping the spatial distribution of contaminants in river channels and floodplains and 4 current approaches to the remediation of river basins affected by mining appraised in light of the european union s water framework directive 2000 60 ec future opportunities for geomorphologically based assessments of mining affected catchments are also identified

friction of mineralogically controlled serpentinites and implications for fault weakness serpentines are common minerals in several major tectonic faults in a variety of geodynamic settings and have variable frictional strength and complex deformation processes here we present friction experiments carried out on a suite of serpentine samples that include veins of antigorite lizardite and fibrous serpentine chrysotile and polygonal serpentine together with massive samples of retrograde lizardite and chrysotile rich and prograde antigorite rich serpentinites these samples were characterized from the hand specimen down to the nanoscale to precisely constrain their mineralogical composition and are interpreted to represent typical fault rocks and host rocks in serpentine bearing shear zones respectively experiments were performed at effective normal stress from 5 to 120 mpa at temperatures of 25 c and 170 c and water saturated i e under the faulting conditions of the brittle upper lithosphere friction of antigorite samples either massive or vein is relatively high 0 53 retrograde massive serpentinites constituted primarily of lizardite and fibrous serpentines are frictionally weak 0 30 end members lizardite and fibrous serpentines are even weaker 0 15 0 19 and this weakness is unchanged at high temperature we document deformation of lizardite and fibrous serpentines occurring predominantly via mode ii cracking crystal fiber folding and frictional sliding which account for the observed mechanical weakness when combined with frictional reactivation analysis our data provide mechanical evidence for fault weakness inferred from earthquake dip distributions at oceanic outer rises and low angle normal faults beneath rifted continental margins and at slow ultraslow spreading mid ocean ridges

multiple tectonic rotations and transform tectonism in an intraoceanic suture zone sw cyprus abstract new palaeomagnetic data from the late cretaceous neotethyan troodos ophiolite and related units in sw cyprus provide compelling evidence that transform tectonism is recorded outside the main outcrop of the fossil southern troodos transform fault zone sttfz high level intrusive and extrusive sequences were sampled along the sw margin of the troodos massif and in ophiolitic slivers preserved along arcuate fault lineaments further to the south and west these units show cross cutting relationships with corresponding differences in remanent magnetisation directions characteristic of syn magmatic rotation in an active transform setting net tectonic rotation analyses allow decomposition of the total rotation at these sites into early and late components early transform related rotations are consistently clockwise in agreement with all other studies of rotations associated with the sttfz further to the east late rotations and the net rotations derived at localities where cross cutting relationships were not present are regarded as composite in origin the composite rotation axes closely relate to the orientation of observed regional structures in these circumstances additional constraints are used to attempt geologically viable interpretations the overall distribution of transform related rotations steeply and shallowly plunging rotation axes and spreading axis related rotations sub horizontal rotation axes is comparable with that along the sttfz and adjacent parts of the troodos massif this is most readily explained by simple along strike extension of the primary spreading axis and transform fabrics into sw cyprus with minor late disruption by high angle dextral shear zones and neotectonic graben systems

sinistral strike slip and transpressional tectonics in an ancient oceanic setting the mamonia complex southwest cyprus structural contacts between the triassic to cretaceous mamonia complex and the upper cretaceous troodos complex have been examined in southwest cyprus the contacts are invariably near vertical in the south of the region and moderate to high angle in the north field evidence suggests that these two contrasting oceanic basement types were juxtaposed by strike slip tectonics during the late cretaceous a sinistral strike slip fault zone was active in the southern area whilst in the northern area a central block was uplifted at a restraining bend this model can explain the presence of interleaved tectonic slivers of both mamonia and troodos basement and earlier formed metamorphic rocks it also explains the presence of diapirs of sepentinized harzburgite and dunite along the fault contacts which originated as deep oceanic fractures finally it provides a satisfactory explanation for the origin and distribution of submarine debris flows only found in the northern area derived from erosion of a transpressional push up structure constraints on the timing of strike slip faulting suggest that this episode of tectonism in southwest cyprus is coeval with the 90 anti clockwise rotation of parts of cyprus indicated by palaeomagnetic data a model is proposed which reconciles anti clockwise rotation of the troodos complex with sinistral strike slip displacement along its contact with the mamonia complex this model differs significantly from several recently published models which invoke dextral strike slip along the same contacts associated with anti clockwise rotation of the troodos microplate

model for the origin of the troodos massif cyprus and other mideast ophiolites any comprehensive model for the origin of the troodos complex and other mideast ophiolite complexes must explain the geochemical evidence for subduction zone involvement the thin inferred oceanic crust the extensional environment indicated by sheeted dikes the existence of fault zones perpendicular to the inferred spreading axes and the discontinuous nature of ophiolite exposures around the arabian block the andaman sea region of the indian ocean may provide an actualistic model for the origin of these ophiolites there spreading takes place in short segments above a subduction zone in the region of active spreading the andaman sea model substantially accounts for the known geologic and geophysical data from the circum arabian ophiolite belt and it leads to some predictions about the structural and geophysical relationships to be expected in this important belt the model also predicts that andaman sea spreading center magmas may be similar in composition to those found in the mideast ophiolites

the uplift of the troodos massif cyprus we constrain the fault pattern and the kinematics of faulting that facilitated the uplift of the troodos massif in cyprus in the eastern mediterranean the fault pattern consists of e w striking re

the mamonia complex sw cyprus revisited remnant of late triassic intra oceanic volcanism along the tethyan southwestern passive margin upper triassic volcanic and sedimentary rocks of the mamonia complex in southwestern cyprus are exposed in erosional windows through the post cretaceous cover where the mamonia complex is tectonically imbricated with the troodos and akamas ophiolitic suites most of these upper triassic volcanic rocks have been considered to represent remnants of triassic oceanic crust and its associated seamounts new nd and pb isotopic data show that the whole mamonia volcanic suite exhibits features of oceanic island basalts oib four rock types have been distinguished on the basis of the petrology and chemistry of the rocks volcanism began with the eruption of depleted olivine tholeiites type 1 and oceanic island tholeiites type 2 associated with deep basin siliceous and or calcareous sediments the tholeiites were followed by highly phyric alkali basalts type 3 interbedded with pelagic halobia bearing limestones or white reefal limestones strongly lree enriched trachytes type 4 were emplaced during the final stage of volcanic activity nd and pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts the trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions this is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes the correlations observed between incompatible elements nb th and varepsilon nd and pb isotopic initial ratios suggest that the mamonia suite was derived from the mixing of a depleted mantle dmm and an enriched component of high 238u 204pb himu type models using both nd and pb isotopic initial ratios suggest that the depleted tholeiites type 1 derived from a dmm source contaminated by an enriched mantle type 2 component em2 and that the oceanic tholeiites type 2 alkali basalts type 3 and trachytes type 4 were derived from the mixing of the enriched mantle source of the depleted tholeiites with a himu component none of the mamonia volcanic rocks show evidence of crustal contamination the upper triassic within plate volcanism likely erupted in a small southerly neotethyan basin located north of the eratosthenes seamount and likely floored by oceanic crust

variability in sediment delivery and storage along river courses in bega catchment nsw australia implications for geomorphic river recovery in many catchments in southeastern australia alluvial stores have been the dominant source of sediments mobilised in the period since european settlement in bega catchment on the south coast of new south wales nsw this has been reflected by dramatic changes to river morphology extensive volumes of material have been released and efficiently flushed to the lowland plain with a sediment delivery ratio of almost 70 however only 16 of these alluvial sediments have been flushed through to the estuary as antecedent controls on valley width have resulted in the lowland plain acting as a large sediment sink the changing nature of sediment source transfer and accumulation zones has varied markedly from subcatchment to subcatchment the volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area rather the pattern of river types dictates the spatial variability in storage and transfer over 67 of sediment released has been sourced from just 25 of the catchment from subcatchments characterised by large valley fills cut and fill river style that previously stored extensive volumes of material at the base of the escarpment these parts of bega catchment were especially sensitive to disturbance sediment exhaustion from these parts of the catchment and from river courses elsewhere has major implications for the geomorphic recovery potential of rivers constraining what can be realistically achieved in terms of river rehabilitation

structural organization of process zones in upland watersheds of central nevada and its influence on basin connectivity dynamics and wet meadow complexes abstract the drainage network within upland watersheds in central nevada can be subdivided into distinct zones each dominated by a unique set of processes on the basis of valley form the geological materials that comprise the valley floor and the presence or absence of surficial channels on hillslopes the type and structure frequency length and spatial arrangement of these process zones is related to the lithology and weathering characteristics of the underlying bedrock process zones dominated by sediment accumulation storage and groundwater recharge are associated with less resistant rocks that weather into abundant but relatively small particles sediment transport and runoff dominated zones are associated with resistant sparsely fractured rocks that produce limited but larger clasts the type and structure of process zones along axial valleys depend on the characteristics of the process zones on the hillslopes numerous sediment storage dominated reaches leads to a relatively high number of unincised fans located at the mouth of tributaries along the axial valleys and to frequent and lengthy unincised valley segments both of which disconnect large sections of the drainage basin from channelized flows in contrast a relatively high density of transport dominated process zones leads downstream to the incision of side valley fans and axial valley deposits as well as a high degree of basin connectivity defined by the integration of surficial channels connectivity also is related to the lithology of the underlying bedrock with higher degrees of connectivity being associated with volcanic rocks that presumably yield high rates of runoff lower levels of connectivity are associated most frequently with extensively fractured locally permeable sedimentary and metamorphic rock assemblages thus basins underlain by volcanic rocks appear to be more sensitive to incision and produce more dynamic channels in terms of the rate of channel valley modification than those underlain by other lithologies considerable attention has been devoted in recent years to the management of wet meadow ecosystems that serve as important riparian habitats within upland basins of central nevada the data presented here show that within basins characterized by a high degree of connectivity areas of wet meadow are minimal where they do exist in these basins they tend to be severely degraded by incision or gully erosion and will be difficult to manage given the dynamic nature of the axial channel processes wet meadows within basins that exhibit a low degree of connectivity and high sediment storage to transport ratios on hillslopes will likely be more responsive to management activities because of the reduced threats of channel incision and presumably a larger supply of groundwater flow to the meadows created by an extensive network of recharge sites importantly human activities that lead to an increase in basin connectivity can negatively impact downstream meadows through a decrease in groundwater recharge and an increase in stream dynamics in spite of the fact that these activities may be physically separated from the wet meadow areas

biostratigraphy of the supra ophiolite sediments of the troodos massif cyprus the cretaceous perapedhi kannaviou moni and kathikas formations the troodos massif of cyprus exposes a classic and much studied ophiolite sequence representing oceanic crust of late cretaceous age k ar dating of the sheeted dykes and of the overlying pillow lavas gives a range of 83 3 ma earliest campanian and 75 5 ma late campanian respectively for the formation of the upper levels of the ophiolite an autochthonous sequence of late cretaceous to recent age sediments is exposed resting on the ophiolite the oldest part of which reflects sedimentation in an apparently deep marine oceanic setting little biostratigraphical information is available to constrain the chronostratigraphy of these sediments in relation to the complex geological history of the island including the uplift and unroofing of the ophiolite despite their richness in microfauna and flora this paper provides an integrated biostratigraphical study based on radiolaria planktonic foraminifera and calcareous nannofossils of the oldest part of the supra ophiolite succession of the cretaceous perapedhi kannaviou moni and kathikas formations for the first time well defined micropalaeontological evidence establishes the relative ages of these formations the umbers of the perapedhi formation are no younger than campanian in age while the volcaniclastic sediments of the kannaviou formation were also deposited during campanian times the matrix of the moni formation contains a microfauna consistent with the hypothesis that it is derived from the kannaviou in contrast the kathikas formation is composed of sediment derived mainly from the allochthonous mamonia complex but autochthonous pelagic interbed horizons demonstrate that it was deposited probably within a very short time interval during the late maastrichtian key index species are figured including the first published micrographs of cretaceous planktonic foraminifera from cyprus

possible submarine tsunami deposits on the outer shelf of sendai bay japan resulting from the 2011 earthquake and tsunami off the pacific coast of tohoku abstract although it is accepted that large tsunami waves impact the sea floor the response of surface sediments to tsunami is not yet fully understood tsunami by the 2011 off the pacific coast of tohoku earthquake caused considerable damage to northeast japan surface sediments on the outer shelf of sendai bay also show evidence of strong ground motion and agitation by the subsequent tsunami sediments in the hemipelagic mud below the erosional surface contain vein like structures providing evidence of strong ground motions induced by the earthquake two turbidite sequences are present above the erosional surface in which 134 cs and 137 cs only occur in the upper turbidite unconsolidated mud on the inner mid sendai shelf was agitated and resuspended by the high frictional velocities associated with the tsunami waves the high concentration of suspended sediment in the water column above the shelf is likely to have generated turbidity currents and have made the lower turbidite after the release of 134 cs by the accident at the fukushima no 1 nuclear power plant the second turbidity current generated and created the upper turbidite

mechanical development of vein structures due to the passage of earthquake waves through poorly consolidated sediments abstract vein structures are typically the earliest expression of brittle deformation within sediments these mud filled veins which characteristically occur regularly spaced within bed parallel arrays form in sediments that possess a strong interlocking particle framework downslope creep has been proposed to explain the origins of vein structures however a recent suggestion that they are generated by the passage of earthquake shear waves through sediments explains aspects of their morphology and their dominant occurrence at active convergent margins their coexistence with less disruptive ghost veins in peru margin sediments and their almost normal attitude to bedding however suggests that vein structures were formed by processes more complex than downslope creep or seismically induced shearing alone experimental earthquake simulation was undertaken by laterally shaking a box containing crushed diatomite fractures were induced almost normal to the horizontal shaking direction and to a lesser extent as antithetic riedel shears both of which closely resembled vein structures the fracturing process during shaking may be viewed as a progressive fragmentation of the diatomite in which new fractures form half way between pre existing ones thus fracture spacings are progressively halved shear zones oriented at a low angle to the shaking direction were also generated combining with the high angle fractures to form structures very similar to those observed in peru margin sediments when shaken fines added to the diatomite segregated into planar zones that resembled ghost veins half way between fractures the alternating pattern of fractures and fines indicated that a standing pressure wave had been created within the box during shaking the fractures were created by alternating compression and extension at the antinodes while the fines concentrated in zones of minimum grain movement around the nodal planes this suggests that vein structures are initiated by the combined action of shear and pressure waves within a sediment the strain waves may be seismic in origin or may also form in downslope movement system

a gis based method for evaluating sediment storage and transport in large mining affected river systems currently the evaluation of sediment storage and transport for large river systems with variable flow has proven to be a challenge that often requires complex numerical models to be applied and sometimes costly direct data acquisition to be made the present study proposes a low cost widely available gis based method through which an initial assessment can be made on areas of sediment storage transport and deposition as well as possible environmental risks that the accumulation of contaminated material may pose to riverine communities along the rivers channel the method mainly relies on satellite imagery and elevation data to devise a quick model of the channel the model has been successfully applied to study the bolivian sector of the well known mining contaminated rio pilcomayo the analysis shows that the portion of the channel from villamontes to d orbigny accounts for more than half of the total c 314 km2 sedimentation area of the pilcomayo in bolivia and that the most environmentally problematic area is centreed around puente sucre where agriculture is practiced on the contaminated floodplain combined with supplementary bathymetric data on the depth of the river in various points around the channel the method could offer further insight into the sediment fluxes and transport capacity of the pilcomayo in various sectors and could thus be successfully used to assess other large mining contaminated river channels around the world

petrology and origin of primitive lavas from the troodos ophiolite cyprus parental magmas to the troodos ophiolite are characterised by low tio2 and al2o3 and high sio2 extremely fresh and chemically primitive high mgo rocks are found within the upper pillow lavas and along the arakapas fault belt of cyprus and contain forsteritic olivine enstatite and groundmass clinopyroxene set in glass or plagioclase with accessory magnesiochromite and sometimes hornblende they are quartz normative and may have originally contained up to 3 wt h2o geochemically there are three distinct groups of primitive lavas based on tio2 and zr contents but also reflected by cao na2o and ree abundances these groups cannot be related by crystal fractionation and are considered to have been generated by incremental melting of a variably depleted source region the parental magma to the least depleted group group i was that of the major portion of the troodos plutonic complex and is similar to those postulated for other low ti ophiolites chemically it has close affinities with komatiitic basalts the most depleted lavas group iii all have u shaped ree profiles and variable 143nd 144nd ratios interpreted in terms of metasomatism of the source region by an incompatible element enriched component which was probably derived from a subducted slab these lavas represent an intermediate step in the development of boninite series rocks

timing of subduction zone metamorphism during the formation and emplacement of troodos and baer bassit ophiolites insights from 40ar 39ar geochronology the troodos ophiolite in cyprus and baer bassit ophiolite in syria together form part of the tethyan ophiolite belt they were generated in a supra subduction zone setting in late cretaceous times as with many of the ophiolite occurrences in this belt the sequences are closely associated with tectonic coloured melange zones which contain among a variety of lithologies metre to kilometre size blocks of metamorphic rocks precise 40 ar 39 ar laser step heating experiments performed on four amphibolites from sw cyprus and six from nw syria yield plateau ages ranging from 75 7 0 3 ma to 88 9 0 8 ma in cyprus and 71 7 0 5 to 88 4 0 4 ma in syria the older limits of these time spans are coeval with the age of the formation of the associated ophiolites unlike other metamorphic sole rocks which seem to form in relatively short time spans these metamorphic rocks found in cyprus and syria are interpreted to have formed in late cretaceous times by accretion below the overriding troodos and baer bassit crust for a period of 15 18 ma the metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll back and the rotation of the overriding plate until the cessation of subduction in maastrichtian times in cyprus the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed mamonia passive margin sequence intercalated with rocks of the troodos ophiolite during plate collision in the maastrichtian concomitantly in syria the baer bassit ophiolite and subcreted metamorphic complex were emplaced onto the arabian passive margin and fragmented into blocks and knockers forming the baer bassit melange

modeling long term contamination in river systems from historical metal mining heavy metal contamination of sediments within river systems is a major environmental problem around the world deposited as a by product of metal mining contaminated sediments are persistent and widespread frequently affecting large areas of floodplains which makes precise assessments of contamination levels and patterns difficult this paper describes findings from a new generic catchment sediment model called tracer which uses historical mining records to accurately predict present day and future levels and patterns of contamination this model provides detailed views of the extent of contami nation and demonstrates how contaminated sediments form into hot spots which in turn become secondary sources of pollution the exceptional longevity of the contamina tion is also revealed 70 of the deposited contaminants remain within the river system for 200 yr after mine closure simulations of the impact of future climate changes in northern england show that increased flood magnitudes are likely to decrease surface contamination through dilution by cleaner sediment from hillslopes unaffected by mining activity

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

major and trace metal mobility during weathering of mine tailings implications for floodplain soils abstract mine tailings discharged to river systems have the potential to release significant quantities of major and trace metals to waters and soils when weathered to provide data on the mechanisms and magnitudes of short and long term tailings weathering and its influence on floodplain environments three calendar year long column leaching experiments that incorporated tailings from potosi bolivia and soil from unaffected downstream floodplains were carried out these experiments were designed to model 20 cycles of wet and dry season conditions two duplicate columns modeled sub aerial tailings weathering alone a third modeled the effects of long term floodplain tailings contamination and a fourth modeled that of a tailings dam spill on a previously contaminated floodplain as far as was practical local climatic conditions were modeled chemical analysis of the leachate and column solids optical mineralogy xrd sem epma bcr and water soluble chemical extractions and speciation modeling were carried out to determine the processes responsible for the leaching of al ca cu k na mg mn sn sr and ti over the 20 cycles the ph declined to a floor of ca 2 in all columns calcium cu mg mn and na showed significant cumulative losses of up to 100 60 30 95 and 40 respectively compared to those of al k sr sn and ti which were up to 3 1 5 5 1 and 0 05 respectively the high losses are attributed to the dissolution of relatively soluble minerals such as biotite and oxidation of chalcopyrite and cu sulfosalts while low losses are attributed to the presence of sparingly soluble minerals such as svanbergite cassiterite and rutile these results strongly suggest that the release of tailings to floodplains should be limited or prohibited and that all tailings should be removed from floodplains following dam spills

vein structures like ripple marks are formed by short wavelength shear waves vein structure a distinctive structure in deep sea hemipelagic clayey and siliceous mudstones at convergent plate boundaries consists of closely spaced mud filled veins forming an array usually parallel to the bedding plane this structure has been regarded as a seismite that formed during earthquake shaking by resonance of fractures our detailed field observations and shaking model experiments verified that both basic first stage and advanced developed stage vein structures can be explained by a systematic theory essentially a vein structure forms in an array of fractures as a result of shearing not by push waves but by shear waves of very short wavelength by a mechanism very similar to that which forms ripple marks we found the height of a vein array h to be systematically related to vein spacing s such that h 5s suggesting that the shear strength of the sediment is proportional to the thickness of the standing wave part of a sediment layer shear or oscillatory flow occurs in the top part of a sediment layer under which standing waves with wavelengths on the order of millimeters to centimeters lead to vein structure formation vein structure can develop not only in response to earthquake shaking but also by propagation of shear waves along a large fault or by other kinds of shears associated with density or debris flows landsliding or faulting

collapse of the pilcomayo river the pilcomayo river flows south eastwards from the bolivian andes across the chaco plains setting the border between argentina and paraguay it flows down along 1000km in principle to finally join the paraguay river it spills over the plains during the rainy season from january to march the sediment load of the pilcomayo is one of the largest in the world 140milliontons per year which is mostly wash load from the upland andes the mean concentration of suspended sediment is 15g l the maximum recorded concentration is as high as 60g l the river has built a large fan covering a surface of 210 000km2 with many abandoned channels today it is a river prone to avulsion raising border disputes between the two lowland countries argentina and paraguay moreover the very special feature of pilcomayo river is that it does not actually flow into the paraguay river very far upstream of the mouth in the paraguay the channel blocks itself with sediment and wood debris forcing water and sediment to spread across the plains moreover the point of blockage has moved hundreds of kilometers upstream throughout the 20th century many environmental issues arise because of this collapse channel discontinuity not the least of them is the migration of fish the future of the river concerns bolivia and the two lowland countries 2012 elsevier b v

effects of serpentinization on the lithospheric strength and the style of normal faulting at slow spreading ridges rock deformation experiments indicate that serpentinization can strongly influence the strength and tectonics of the oceanic lithosphere strength versus depth profiles calculated for conditions appropriate for slow spreading ridges indicate that the presence of serpentinite can reduce the integrated strength of the lithosphere by up to 30 results from flexural fault models indicate that if serpentinization is isolated to fault zones strain localization should be enhanced providing an explanation for the variations in the style of normal faulting along slow spreading ridge segments at segment centers where serpentinites are scarce deformation is accommodated on closely spaced faults with small throws at the segment ends where serpentinites are most abundant faults are widely spaced and have large throws q 1997 elsevier science b v

episodic seafloor mud brecciation due to great subduction zone earthquakes the nankai trough off southwest japan has an 1300 yr historical record of great earthquakes including the most recent the a d 1944 tonankai m 8 2 earthquake evaluation of the activity of an individual submarine fault is difficult when only onland observations are available submarine core records can pinpoint individual fault activity here we present integrated ocean drilling program iodp nankai trough seismogenic zone experiment data from the shallow portion iodp expedition 316 drilled and cored several holes in the shallow portion of the offshore tonankai earthquake area including sites in the hanging wall of a margin dominating splay fault that has previously been interpreted to have ruptured coseismically during megathrust earthquakes x ray computed tomography scanning revealed that the uppermost core at one site contains repeated occurrences of mud breccia radioisotope dating of the uppermost mud breccia indicates a deposition time consistent with the 1944 tonankai earthquake suggesting that the mud breccia layers result from episodic brecciation caused by seismic shaking mud brecciation provides a potential new tool to reconstruct ancient earthquake history in subduction zones

provenance and magmatic tectonic setting of campanian aged volcaniclastic sandstones of the kannaviou formation in western cyprus evidence for a south neotethyan continental margin volcanic arc abstract regionally developed late cretaceous subduction related magmatism in the eastern mediterranean records progressive closure of the southern neotethys in western cyprus the late cretaceous c 90 ma troodos ophiolite is depositionally overlain by volcaniclastic sandstones up to 750 m thick that are dominated by redeposited pyroclastic fallout interbedded with both non calcareous and calcareous radiolarian bearing mudstones the sands were mainly deposited by channelised mass flow processes and to a lesser extent by turbidity currents in a deep water forearc basin the succession was folded and locally thrust deformed related to latest cretaceous emplacement of adjacent mesozoic continental margin and oceanic units mamonia complex sims u pb analysis of euhedral to subhedral magmatic zircon crystals yielded a weighted mean 206pb 238u age of 80 1 1 1 ma campanian sandstone petrography including compositional framework q12f21l67 suggests sediment supply from a volcanic arc subordinate continentally derived detritus suggests a continental margin arc setting for the mafic to felsic fallout ash sims analysis of little altered volcanic glass indicates high th nb and th la ratios that suggest the involvement of continental crust and or subducted terrigenous sediments in magma genesis whole rock chondrite normalised ree patterns have comparable trends to modern and ancient forearc basin volcaniclastic sands and sandstones e g northwest pacific region trace element chemistry although scattered towards the continental island arc fields on some geochemical diagrams e g th sc zr mainly suggests an oceanic island arc source for the kannaviou formation sandstones with variable enrichments in v cr ni sc depletion in nb ta and relatively low trace element ratios e g la co th co la sc th sc an explanation for this apparent discrepancy is that the volcaniclastic sandstones were derived from a relatively primitive arc constructed on previously depleted rifted thinned neotethyan continental crust the inferred continental margin arc developed during early stage northward subduction of the southern neotethys beneath a tauride microcontinent to the north large volumes of volcanic ash were derived from continental margin arc volcanism probably in the vicinity of the kyrenia range in northern cyprus

from ocean depths to mountain tops uplift of the troodos ophiolite cyprus constrained by low temperature thermochronology and geomorphic analysis the timing and mode of uplift of the troodos ophiolite are constrained by low temperature thermochronology combined with geomorphic analysis zircon u th he and apatite fission track cooling ages in the troodos plutonic sequence are all cretaceous 83 106 ma and within error of published zircon u pb crystallization ages this indicates early cooling of the oceanic crust and termination of spreading axis magmatism at 90 ma apatite u th he ages decrease with reconstructed crustal depths from 40 ma near the top of the sheeted dike complex to 4 ma within the mantle sequence a prominent inflection point in the age versus depth curve defines the bottom of the exhumed helium partial retention zone and records the onset of rapid exhumation of the main troodos massif at 6 2 ma inverse thermal modeling supports this conclusion indicating that the timing of uplift is earlier than previously estimated the boundaries of the mantle sequence exposed in the core of the troodos structure closely overlap the boundaries of a concentric zone delineated by high local relief and higher channel steepness indices indicating differential exhumation and uplift of this area relative to its surroundings this zone also overlaps with a prominent negative bouguer gravity anomaly the timing and pattern of the troodos ophiolite uplift suggest that it is driven by serpentinite diapirism possibly triggered by miocene reactivation of subduction along the cyprean arc the worldwide ubiquity of suprasubduction zone ophiolites may thus reflect the importance of extensive serpentinization at the overthrusting mantle wedge in obduction processes

palaeomagnetic evidence for clockwise rotations related to dextral shear along the southern troodos transform fault cyprus abstract the southern troodos arakapas fault represents a late cretaceous oceanic fracture zone which was locally disrupted during late cretaceous eocene palaeorotation of the troodos microplate opinions are divided as to the sense of displacement along the transform fault and the exact timing of initiation of palaeorotation palaeomagnetic studies of turonian zeolite facies lavas and sediments exposed within the transform domain have revealed considerable variations in the declination of remanent magnetisation between sites along the arakapas fault belt the western margin of the limassol forest complex and the eastern flank of the troodos ophiolite at seven sites clockwise rotation of fault blocks has occurred about steeply inclined axes one fault block at the western end of the arakapas fault belt has experienced a net anticlockwise rotation while at six other sites only simple tilting about sub horizontal axes is indicated the overall clockwise sense of block rotation and initial dyke strikes calculated at three sites are consistent with right lateral slip along the transform cross cutting relationships revealed by the analysis of one site demonstrate that these rotations took place during crustal genesis and are not a product of post spreading disruption of the fracture zone sites located further south in the eastern limassol forest complex show no relative rotation with respect to the main troodos ophiolite to the north and have experienced only simple tilting however if our results are considered in conjunction with existing palaeomagnetic data from the area it appears that the entire area lay within a complicated zone of localised and predominantly clockwise block rotations produced by dextral slip along the transform some areas were rotated by over 100 about steeply inclined axes whereas others experienced only simple tilting the whole area was later subjected to a bulk 90 anticlockwise rotation along with the troodos microplate data obtained from the umbers and radiolarites perapedhi fm exposed on the eastern flank of the limassol forest block indicate that at least 30 and possibly up to 45 of this 90 rotation took place over a maximum of 15 ma

tectonics of the akamas and mamonia ophiolites western cyprus magnetic petrofabrics and paleomagnetism abstract the akamas ophiolite is shown to be a distal off axis extension of the main outcrop of cretaceous ophiolite in the troodos complex of cyprus mantle sequence harzburgites of both ophiolites share similarly oriented mantle flow fabrics and the same tertiary magnetizations acquired during exhumation however compared with the troodos mantle sequence rocks the akamas ferromagnetic mineralogy is more oxidized and remanences with lower blocking temperatures were acquired chemically paleopoles calculated from published vectors and our own new data define an apparent polar wander path apwp for the troodos microplate the apwp shows that between 88 and 50 ma the troodos microplate was equatorial and the vertical axis for its 60 anticlockwise rotation was located within the microplate subsequently the microplate drifted northward to 34 n with minor anticlockwise rotation at a reduced rate that requires microplate rotation about a vertical axis located to the west of cyprus in the last 50 ma the allochthonous triassic mamonia terrane docked with the cretaceous troodos terrane in sw cyprus within it disrupted tectonized ophiolite has been regarded as part of a triassic ocean floor or as sheared fragments of cretaceous troodos ophiolite incorporated into the mamonia terrane when it docked with the troodos terrane whatever their provenance their paleomagnetic signals postdate their penetrative deformation and metamorphism and their paleopoles may still be used to track their post strain motion our calculations of paleopoles from published vectors for the mamonia terrane smear along an extension of the apwp for the troodos microplate that is moreover concentric with the troodos microplate this suggests that the paleopole dispersion of the triassic mamonia rocks and their post magnetization disruption occurred during their accretion onto the anticlockwise spinning troodos microplate

mediaeval lead pollution in the river ouse at york england the city of york in northern england has a long history of being flooded by the river ouse excavations of a 9 m sedimentary profile were carried out by the york archaeological trust on the site of a pumping station associated with a flood prevention scheme at north street on the south west bank of the river ouse this profile records evidence of human activity and episodic river sedimentation over a period from the 2nd to the 14th century ad anthropogenic materials in the profile include waterfront timber and wattle structures and dumps of organic domestic debris and industrial waste evidence of historic floods is preserved in interleaved alluvial deposits this study reports on the degree of lead pb contamination at the site from roman to mediaeval times and the sources of both alluvial and manufactured lead deposited in the profile archaeological sedimentological geochemical and mineralogical evidence suggest that yorkshire dales mining activity during the 9th 13th centuries ad may have both directly and indirectly caused lead contamination of the alluvial deposits at north street

the environmental and geomorphological impacts of historical gold mining in the ohinemuri and waihou river catchments coromandel new zealand abstract between 1875 and 1955 approximately 250 000 mg yr 1 of mercury arsenic and cyanide contaminated mine tailings were discharged directly into the ohinemuri river and its tributaries in the coromandel region north island new zealand a devastating flood on 14 january 1907 deposited large amounts of mine waste across the floodplain of the ohinemuri and waihou rivers in the vicinity of the township of paeroa the 1907 mine waste flood deposit was located as a dirty yellow silt in cores and floodplain profiles with a thickness ranging from 0 15 0 50 m geochemical analysis of the mine waste shows elevated concentrations of pb 200 570 mg kg 1 and as 30 80 mg kg 1 compared to early holocene background concentrations pb 1 as 1 bulk sediment samples recovered from the river channel and overbank deposits also show elevated concentrations of pb 110 mg kg 1 zn 140 320 mg kg 1 ag 3 mg kg 1 and hg 0 4 mg kg 1 using the mine waste deposit as a chronological marker shows that sedimentation rates increased from 0 2 mm yr 1 in the early holocene to 5 5 26 8 mm yr 1 following the 1907 flood downstream trends in the thickness of the flood deposit show that local scale geomorphic factors are a significant influence on the deposition of mine waste in such events storage of mine waste is greatest in the upstream reaches of the floodplain the volume of mine waste estimated to be stored in the ohinemuri floodplain is 1 13 m m 3 an order of magnitude larger than recent well publicised tailings dam failures such as the 1996 south america porco 2000 romanian baia mare and baia borsa accidents and constituted and was recognised at the time a significant geomorphological and environmental event the mine waste material remains in the floodplain today representing a sizable legacy store of contaminant metals and metalloids that pose a long term risk to the ohinemuri and waihou ecosystems

the emplacement of peridotites and associated oceanic rocks from the lizard complex southwest england upper mantle peridotites and associated oceanic rocks from the lizard complex south west england preserve evidence for a multistage geological history steeply dipping pre emplacement fabrics record high temperature 900 1100 c shearing and exhumation of the mantle peridotites apparently formed during localized ne sw rifting in a pull apart basin setting c 400 390 ma associated oceanic rocks landewednack amphibolites preserve a pre emplacement prograde brown amphibole bearing metamorphic assemblage and steeply dipping fabric thought to have formed as the newly formed oceanic crust was juxtaposed with newly exhumed hot mantle peridotite during ne sw rifting in both the peridotites and landewednack amphibolites steep pre emplacement structures are cross cut by low angle mylonitic fabrics thought to have formed during the initial phases of emplacement of mantle over crustal rocks in a partially intra oceanic setting c 390 375 ma the fabrics in peridotites and amphibolites exhibit retrograde mineral assemblages c 500 800 c with the amphibolites preserving two superimposed assemblages green amphibole titanite and colourless magnesio hornblende respectively that are thought to record progressive down temperature deforma tion during thrusting emplacement related structures in both the basal peridotites and amphibolites consistently dip at low to moderate angles nw with down dip lineations and kinematic indicators showing consistent top to the nw senses of shear syn emplacement magmatism is recorded by intrusions of foliated kennack gneiss anastomosing serpentine filled faults mark many existing low angle contacts between the peridotites and landewednack amphibolites and appear to represent the final lowest temperature 250 c stages of emplacement c 370 ma this study shows that dynamothermal aureoles in ophiolites may preserve evidence for tectonothermal events that pre date thrust emplacement

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

re computing palaeopoles for the effects of tectonic finite strain abstract the pre messinian limestone cover 58 8 ma to the troodos ophiolite 88 ma of southern cyprus is penetratively strained as shown by ubiquitous magnetic fabrics and in many sites stylolitic cleavage these define a gently n dipping foliation and an n plunging extension south vergent folding and thrusting is well known in very localized whereas the bulk of the strained limestone cover dips gently south disturbed by faulting the magnetic fabrics and stylolitic cleavage define the axes of finite strain in all sites studied and the calcite matrix was suitably ductile to permit the original palaeomagnetic directions to be de strained assuming continuum behaviour the optimum de straining 30 40 shortening in a flattening strain is compatible with the stylolitic cleavage development restores bedding to the near horizontal and restores the characteristic remanent magnetization vectors chrms to concentrated symmetrical fisherian distributions the strain corrected chrms yield more reasonable palaeopole locations for the lefkara and pakhna limestone and more uniform micro plate rotation rates corrected palaeopoles reveal a relatively uniform anticlockwise rotation of the troodos plate since the creation of the late cretaceous 88 ma ocean lithosphere it did not accelerate during the deposition of the limestone cover as required by palaeopoles calculated from data not corrected for finite strain but turned at 1 5 ma 1 since 58 ma

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

the internal deformation of the peridotite nappe of new caledonia a structural study of serpentine bearing faults and shear zones in the koniambo massif we present a structural analysis of serpentine bearing faults and shear zones in the koniambo massif one of the klippes of the peridotite nappe of new caledonia three structural levels are recognized the upper level is characterized by a dense network of fractures antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics as a result the upper level keeps the record of at least two deformation events the first associated with the growth of antigorite wnw ese extension the second with the growth of polygonal serpentine nw se compression the lower level coincides with the serpentine sole of the nappe which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites the sole records pervasive tangential shear with top to sw kinematics and represents a decollement at the base of the nappe the intermediate level is characterized by the presence of several meters thick conjugate shear zones accommodating ne sw shortening like the sole these shear zones involve polygonal serpentine and magnesite as the main syn kinematic mineral phases the shear zones likely root into the basal decollement either along its roof or occasionally around its base compared to top to sw shearing along the sole the two deformation events recorded in the upper level are older

incongruent weathering of cd and zn from mine tailings a column leaching study the weathering of discharged mine tailings can contaminate groundwaters rivers and floodplains with potentially toxic cd and zn depending on tailings mineralogy storage dispersal and climatic conditions the mechanisms of long term tailings weathering and its influence on waste piles and floodplain environments were assessed by a column leaching experiment that incorporated tailings and soil from potosi bolivia and modelled 20 cycles of wet and dry season conditions over three calendar years chemical analysis of the leachate and column solids optical mineralogy xrd sem epma bcr and water soluble chemical extractions and speciation modelling were carried out to determine the processes responsible for the leaching of cd fe s and zn over this period approximately 50 to 95 of the original cd and 50 to 60 of the zn were leached from the columns large amounts of leached cd and zn at the beginning of the experiment are attributed to the dissolution of soluble sulphate minerals present in the original tailings and formed after the first wetting of the columns the zn cd mass ratios of the tailings and soil initially 429 and 400 respectively vary considerably over the course of the experiment low values between 220 and 300 in the early cycles are attributed to preferential weathering of cd rich wurtzite zn fe s and sequestration of zn in preference to cd in secondary fe phases forming in the columns in the middle cycles dissolution of secondary fe oh 3 under low ph 3 conditions and of ferroan cd poor sphalerite zn fe s releases zn and raises the zn cd ratio to 550 600 in the tailings only columns and up to 1500 in the mixed tailings soil columns the very high ratios in the latter are also ascribed to the formation of low molecular weight organic ligands that have high affinity for zn over cd in the later column cycles zn cd ratios return to near initial values due to the weathering of fe poor sphalerite and secondary fe phases and the declining preference of zn over cd in the soil organic acids under the strongly acidic conditions prevailing in the columns the formation and dissolution of secondary soluble sulphate minerals also play a role in cd and zn cycling especially at the beginning of the experiment

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

soft sediment deformation structures in the mio pliocene misaki formation within alternating deep sea clays and volcanic ashes miura peninsula japan abstract the mio pliocene misaki formation of the miura group miura peninsula japan shows an extremely wide variety of soft sediment deformation structures the most common deformation structures are load casts and associated flame structures dish and pillar structures synsedimentary faults multilobated convolutions chaotic deformation structures sedimentary veins and dykes and large scale slides and slump scars the formation which accumulated in a deep sea environment 2000 3000 m is well exposed in and around jogashima it consists of relative thin commonly dm scale alternations of deep marine fine grained sediments and volcanic ejecta that are as a rule coarse grained since the formation represents fore arc deposits of the izu bonin and the honsu arc collision zone it might be expected that tectonic activity also played a role as a trigger of the soft sediment deformation structures that abound in these sediments this is indicated indeed by the abundance of soft sediment deformations over large lateral distances that occur in numerous beds that are sandwiched between undeformed beds on the basis of their characteristics and the geological context these layers can be explained satisfactorily only by assuming deformation triggered by seismicity which must be related to the izu bonin and honsu arc collision the layers thus form deep marine seismites

chemical remobilization of contaminant metals within floodplain sediments in an incising river system implications for dating and chemostratigraphy metals such as pb zn cd and cu from historical mining activity have been used as stratigraphic markers for dating and provenancing vertically accreted fine grained floodplain overbank deposits this study presents evidence for chemical remobilization of these metals within overbank sediments in the tyne basin uk the evidence includes breakdown of metal bearing minerals sulphides carbonates iron and manganese oxyhydroxides shifts of chemical fractions within zones of relatively low ph towards more soluble and reactive phases and accumulation of secondary iron and manganese oxyhydroxides at levels related to fluctuating water table levels or to the breakdown of organic matter all of this suggests that fine centimetre scale chemostratigraphy using metal concentrations and ratios is unlikely to provide reliable data in river systems that have experienced or are experiencing major changes in water table levels or pedogenesis coarse tens of centimetre to metre scale chemostratigraphy when applied with caution may still provide a means of delineating contaminated units

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

reply to comment on tectonics of the akamas and mamonia ophiolites western cyprus magnetic petrofabrics and paleomagnetism by g j borradaile and k lucas

the ayia varvara formation of sw cyprus a product of complex collisional tectonics abstract the ayia varvara formation is a wedge of amphibole schists and intercalated metasediments within the intensely deformed pre upper maastrichtian volcanosedimentary mamonia complex all contacts are steep faults against upper triassic transitional to alkaline lavas with reefoidal limestones subalkaline depleted troodos type lavas and serpentinised harzburgite ophiolite related metamorphics are believed to have been formed by dynamothermal processes beneath young oceanic crust during emplacement characteristically such rocks might be expected to show a decrease of metamorphic grade away from the contact mineral analyses from the ayia varvara metamorphics however show no systematic variations that would indicate a metamorphic gradient hornblende remains generally calcic and of tschermakitic hornblende composition with an almost complete substitution of mg and fe2 suggesting disequilibrium plagioclase is essentially albitic and remains so for a distance of some 800 m from the harzburgite contact trace element analyses of the amphibolites and surrounding extrusives define four lava types types 1 3 are transitional to alkaline intraplate lavas believed to be remnants of intraoceanic islands and atolls type 4 lavas are extremely depleted in the hfs elements and are very similar to the arakapas transform fault lavas the amphibolites have in part a trace element geochemistry that is close to mid ocean ridge basalts morb a type that has not previously been recorded from cyprus the small area around ayia varvara records a long and complicated tectonic history that provides an insight into the evolution and emplacement of the troodos ophiolite the mamonia complex is interpreted as a passive margin sequence with intra oceanic islands that was accreted onto a late cretaceous north dipping subduction zone suprasubduction spreading produced the troodos ophiolite and associated fracture zones spreading and subduction ceased in the late maastrichtian when the newly formed troodos crust underwent a 90 anticlockwise rotation which juxtaposed mamonia and troodos arakapas fracture zone rocks along arcuate steep strike slip faults at least some of the ayia varvara metamorphic rocks most likely represent triassic oceanic crust and sediments metamorphosed during subduction by the overriding young troodos crust

a cellular model of holocene upland river basin and alluvial fan evolution coulthard t j macklin m g kirkby m j 2002 a cellular model of holocene upland river basin and alluvial fan evolution earth surface processes and landforms 27 3 269 288

sedimentological consequences of arc arc collision an example from mio pliocene miura group japan abstract this paper presents brief sedimentological inventory of the misaki and the overlying hasse formation constituting the miura group based on observations made at jogashima island miura peninsula and infers the nature of the stratigraphic transition from tectonic viewpoint the lower part of the misaki formation is made of very coarse to coarse grained scoriaceous normally graded sandstones fine grained sandstones siltstones and mudstones and indicates a deep sea submarine canyon depositional setting there is no evidence of storm reworking shallow marine processes in the lower parts of the misaki formation at least in the jogashima island as suggested by stow et al 1998 however the upper part of the misaki succession formed in a shallow marine depositional setting the overlying hasse formation characterized by brownish coloured very coarse to coarse grained large scale trough cross stratified very poorly sorted sandstones very poorly sorted polymictic and matrix dominated mass flow conglomerates with siltstone fine grained sandstone clasts derived from the underlying misaki formation and occasional reverse grading in significant contrast to the underlying misaki formation the hasse formation lacks very fine grained sandstone siltstone mudstone facies unlike the tholeiitic basalt composition of the lapilli and pebbles of the misaki sandstone beds the scoriaceous lapilli and pumiceous beds of the hasse formation are of calc alkaline composition the hasse sedimentation probably took place in much shallower paleogeography compared to the underlying misaki formation most probably in an alluvial fan braided fluvial setting the misaki hasse stratigraphic contact is very sharp and erosional and represents a subaerial unconformity i e depositional sequence boundary our sedimentological data from the jogashima island clearly indicate progressive shallowing of the depositional setting during the terminal phase of the misaki sedimentation and much abrupt shallowing across the misaki hasse transition possibly as a consequence of ongoing collision between the izu bonin and honshu arcs

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

evidence for upper cretaceous transform fault metamorphism in west cyprus abstract metamorphic rocks of low pressure medium temperature facies occur in west cyprus as blocks and slivers with mafic and ultramafic screens in high angle serpentinite filled fault zones a satisfactory explanation for the origin of the metamorphic rocks has previously remained a subject of controversy the evidence presented here based on a study of their bulk chemistry mineralogy and 40 ar 39 ar geochronology indicates they were produced by greenschist to amphibolite facies dynamothermal metamorphism of alkalic and tholeiitic mafic rocks and associated sediments at between 83 and 90 m y their field relations show similarities with present day oceanic fracture zones suggesting that metamorphism occurred within strike slip faults some of which were probably extensions of the arakapas transform we propose that hot crust generated at an oceanic spreading centre provided the heat for metamorphism when juxtaposed against older cooler rocks during ridge ridge transform movements in addition shear heating may have been facilitated by the strike slip faulting and contributed to the total heat available these interpretations are compatible with many aspects of the broader regional geology of cyprus provide new constraints on the early evolution of the troodos complex and form the basis of a model for transform fault metamorphism

kinematics of the alpine arc and the motion history of adria the alps have been interpreted traditionally in terms of north or northwest directed convergence between africa and europe1 with adria the continental underpinnings of the adriatic sea and northern italy acting as a promontory of the african continent2 this has been supported by recent analyses of africa europe relative plate motions3 5 which indicate dominantly north south directed convergence during the tertiary phase of intracontinental shortening we show here however that kinematic indicators from alpine tectonites are difficult to reconcile with this motion history figs 1 and 2 and are explained best by roughly west northwest directed adria europe motion since about 70 million years ago combined with an arc normal pattern of motion driven by local body forces this implies that adria has moved independently of both africa and europe since at least the late cretaceous

eocene paleoseismic record of the green river formation fossil basin wyoming u s a implications of synsedimentary deformation structures in lacustrine carbonate mudstones abstract laterally extensive intervals containing sedimentary deformation features are identified in outcrops of lacustrine deposits of the eocene 52 51 ma green river formation in fossil basin southwestern wyoming fossil basin is the smallest of the paleo lakes in the green river system and is located in the sevier fold and thrust belt which was tectonically active during deposition deformation structures include convolute lamination load structures hybrid brittle ductile features sedimentary dikes microfaults fluid escape features such as cusps and pipes oil shale breccias and mass transport deposits in most cases these structures are hosted by finely laminated variably organic rich carbonate mudstones that accumulated in a low energy profundal lacustrine environment deformed intervals range from a few centimeters to 5 m in thickness and are bound above and below by undeformed strata of the same facies which demonstrates the early post depositional timing of deformation the distribution of these features indicates a primary control exerted by sediment rheology resulting from variation in grain size clay and organic content and degree of lithification which in turn were governed by the depositional environment and early diagenesis based on their morphological attributes lateral extent and recurrence at different stratigraphic levels along with their sedimentary environment and the tectonic setting of the basin the deformation structures are interpreted to be seismites i e the result of stresses induced by syndepositional earthquakes and other potential trigger agents are rejected moreover stratigraphic relationships indicate that these small scale deformation features as well as the mass transport deposits formed on a virtually flat lake floor ruling out instability caused by the gravitational regime syndepositional deformation in fossil basin points to tectonic activity along the nearby absaroka and or hogsback thrusts and related fault systems seismites point to possible tectonic forcing as a mechanism for changes in bathymetry and sedimentation in the green river formation and consequently demonstrate their potential for elucidating the tectonic history of other lacustrine and marine basins

new evidence and interpretation of facies provenance and geochemistry of late triassic early cretaceous tethyan deep water passive margin related sedimentary rocks ayios photios group sw cyprus in the context of eastern mediterranean geodynamics abstract the late triassic early cretaceous deep sea sedimentary succession exposed in western cyprus is used here to help understand the wider context of continental break up and seafloor spreading in the easternmost mediterranean region the restored sequence begins with late triassic base of slope sandstone turbidites and mudrocks and fines upwards into mudrocks distal calciturbidites and metalliferous sediments after a hiatus late jurassic early cretaceous non calcareous mudstones and radiolarites accumulated beneath the carbonate compensation depth together with redeposited shallow water derived carbonates including calcirudites the succession culminates in late jurassic early cretaceous very thickly bedded and highly mature quartzarenites that accumulated by mass flow processes the fine grained siliciclastic sediments are terrigenous in origin as indicated by whole rock trace element and ree analysis fe mn and trace metal enrichment in the late triassic represents hydrothermal input related to submarine volcanism that was probably triggered by the nearby onset of seafloor spreading the late triassic sandstones were derived from a low to intermediate grade metamorphic source terrane the late jurassic early cretaceous sandstones reflect extreme physical and chemical maturity in the source area followed by transport and mass flow to a deep water base of slope setting regional facies variation and locally available palaeocurrent data suggest sediment supply originally from a continental block no more than tens of km to the west or north similar successions are exposed in w turkey represented by the antalya complex in the light of alternatives the sedimentary succession is restored as the base of slope apron of a rifted microcontinental block adjacent to the northern margin of the s neotethys the overall succession indicates unstable passive margin development after regional latest triassic early jurassic continental break up with implications for plate reconstructions and hydrocarbon exploration

kinematic analysis of serpentinite structures and the manifestation of transpression in southwestern puerto rico abstract faults and shear zones recorded in the monte del estado and rio guanajibo serpentinite masses in southwestern puerto rico show previously unrecognized southwestward tectonic transport the orientations of planar and linear structures and the sense of slip along faults and shear zones determined by offset rock layers drag folds in foliations and steps in slickensided surfaces and or s c fabrics from 1846 shear planes studied at more than 300 stations reveal two predominant groups of faults 1 northwesterly striking thrust faults and easterly striking left lateral faults and 2 northwesterly striking right lateral faults and easterly striking thrust faults shortening and extension p and t axes calculated for geographic domains within the serpentinite reveal early north trending shortening followed by southwestward directed movement during which older structures were re activated the sw directed shortening is attributed to transpression that accompanied late eocene left lateral shearing of the serpentinite a third younger group comprising fewer faults consists of northwesterly striking left lateral faults and north directed thrusts that also may be related to the latest transpressional deformation within puerto rico deformational events in puerto rico correlate to tectonic events along the caribbean north american plate boundary

tectonic reconstruction of cyprus reveals late miocene continental collision of africa and anatolia abstract the extended northern continental margin of africa is currently colliding with and under thrusting northward below cyprus the age of onset of this collision is poorly constrained but is critical if we are to quantify continental subduction and evaluate its role during spectacular recent uplift of southern turkey from 7 ma to the present here we reevaluate the evolution of northern cyprus and document the modern structure of the kyrenia fold thrust belt in a balanced cross section for the first time to determine the timing and amount of shortening the belt deformed an upper cretaceous to miocene stratigraphy which was deposited onto a metamorphic basement the fold thrust belt was previously proposed to have formed during two stages in eocene and late miocene time based on stratigraphic and limited structural evidence we revaluate evidence for an eocene phase of thrusting in kyrenia and find that 1 repetitions of eocene and older rocks are explained by miocene thrusting and newly documented olistoliths were misinterpreted as pre miocene thrust slices 2 uplift in eocene time was not isolated to kyrenia but also affected northern arabia and results from regional dynamic topography or forebulge formation based on kinematic constraints from a plate reconstruction we interpret that metamorphic rocks in kyrenia were metamorphosed by cretaceous burial below the troodos ophiolite and were subsequently exhumed by upper plate extension during latest cretaceous obduction onto the african margin the latest cretaceous miocene plate boundary between africa and the taurides was located to the north of kyrenia the kyrenia fold thrust belt accommodated a minimum of 17 5 km of shortening as a result of 9 6 ma thrusting as a result of initial africa taurides collision the northern edge of african continental crust arrived below the taurides where it has been seismologically imaged in late pleistocene time and may have caused or contributed to recently recognised major tauride uplift since 0 5 ma

abyssal peridotite mylonites implications for grain size sensitive flow and strain localization in the oceanic lithosphere abstract microstructures preserved in abyssal peridotites dredged from the oceans record several different physical regimes of deformation fabrics associated with deformation processes at slow spreading mid ocean ridges form two major classes of abyssal peridotites based on detailed microstructural observations the most abundant class are medium to coarse grained tectonites with microstructures that reflect deformation processes during mantle upwelling and emplacement to the base of the lithosphere these tectonites give geothermometric temperatures of 755 c or higher interpreted to represent lower temperature limits for diffusive exchange in coarse grained abyssal peridotites during cooling this conclusion is consistent with flow laws for olivine at these temperatures the second class of abyssal peridotites previously largely undescribed for the mid ocean ridge environment include fine grained mylonites associated with faulting and shear zones that develop during extension and cooling of the oceanic lithosphere when the brittle plastic transition extends into mantle rocks these mylonites give temperatures of 600 c which we suggest represent a lower temperature limit for plastic deformation reduced grain size in mylonites allows for diffusive exchange to continue to these low temperatures relict augen in the mylonitic samples preserve equilibration temperatures similar to those exhibited by the coarse grained tectonites based on flow laws for olivine we suggest that deformation in some fine grained mylonites occurred by diffusion creep down to 600 c rheological data for olivine indicate that dislocation creep is not likely to occur at this temperature we conclude that a reduction in grain size by cataclasis or dynamic recrystallization resulted in a transition in deformation mechanisms from dislocation to diffusion creep during uplift and or cooling the observation of these fine grained mylonites indicates that shear zones that extend into the upper mantle will be weaker than expected if deformation was accommodated by brittle processes or dislocation creep weak faults may promote the development of long lived detachments in the upper mantle this inference supports mid ocean ridge tectonic models that suggest that ultramafic rocks exposed at the inside corners of ridge axis discontinuities are exhumed along long lived detachment faults

uranium lead isotopic ages of plagiogranites from the troodos ophiolite cyprus and their tectonic significance zircon populations from two plagiogranites in the plutonic section of the troodos ophiolite yield u pb dates between 90 3 0 7 and 92 4 0 7 ma zircons from one of the two samples yield u pb dates of 90 3 0 7 and 92 1 0 7 ma this difference is greater than our analytical error and the zircons are therefore considered to be slightly discordant two fractions from another sample are internally and externally concordant and have an average date of 91 6 1 4 ma this date is adopted as the age of plagiogranite crystallization the plutonic section of the troodos ophiolite is complex in that several generations of intrusion can be identified the plagiogranites occur at the top of the intrusive section and represent fractionated residua of magma chambers related to the lower pillow lavas they are possibly slightly older than small ultramafic layered complexes that represent the final intrusive episode within the troodos ophiolite there is good agreement between our results and the ages of radiolaria which occur in umbers intercalated with the upper pillow lavas of troodos blome and irwin 1985 this shows that the 75 to 85 ma k ar dates on the lavas and sheeted dikes desmet et al 1978 delaloye and desmet 1979 delaloye et al 1980 staudigel et al 1986 represent age resetting unrelated to ophiolite formation the troodos u pb zircon ages are slightly lower than u pb zircon ages from the samail ophiolite in oman which vary between 93 5 and 97 9 ma and average 95 ma tilton et al 1981 the small difference in age between the troodos and the samail ophiolites and the geochemical similarities of basalts from both complexes to island arc volcanic rocks imply that a 3000 km axis of rift related island arcs formed between 91 and 98 ma emplacement of the ophiolites followed during the early maastrichtian

petrology and texture of the ultramafic rocks of the xigaze ophiolite tibet constraints for mantle structure beneath slow spreading ridges abstract the xigaze ophiolite southern tibet exhibits an unusual ophiolite sequence characterized by 1 1 the limited thickness less than 3 km of its crustal unit which is mostly composed of dolerite intrusives the gabbros being very scarce 2 2 the scarcity of harzburgites and dunites the ultramafic rocks consisting mostly of cr diopside bearing harzburgites and iherzolites although there are some textural and chemical variations from the basal iherzolites to the upper harzburgite and dunites no sharp discontinuity exists between the peridotite series of the xigaze ophiolite which all belong to the same peridotite suite the peridotites have been equilibrated at relatively low temperatures and pressures 1155 c 0 5 0 6 gpa for the cr diopside bearing harzburgites and 1255 c 1 0 1 1 gpa for the stratigraphically 2 km deeper iherzolites indicative of a low thermal gradient at the xigaze paleo ridge accordingly the peridotites have locally been deformed under low stress 0 2 gpa conditions and at decreasing temperatures from up to 1000 c to 900 800 c as evidenced by the activation of the 010 100 ok1 100 and 001 100 olivine glide systems the equilibrium temperatures and pressures estimated for the peridotites the inferred shape of the melting zone beneath the xigaze paleo ridge the low temperature low stress conditions inferred for the deformation of the peridotites and the pattern of the mantle structure determined on the basis of structural and microstructural data are in good agreement with a slow spreading ridge origin for the xigaze ophiolite

palaeomagnetic insights into the evolution of neotethyan oceanic crust in the eastern mediterranean abstract a synopsis of palaeomagnetic data from three late cretaceous eastern mediter ranean tethyan ophiolites troodos hatay and baer bassit and their sedimentary coversequences is presented these data provide valuable insights into the role of regional andlocal scale tectonic rotations in the geodynamic evolution of neotethyan oceanic crust thegeologically earliest phases of tectonic rotation are documented in the troodos ophiolite where rotations around both subvertical and subhorizontal axes are readily related to thedevelopment of the spreading fabrics and structures during crustal genesis subsequent c 74 anticlockwise intra oceanic rotation of a troodos microplate has been quantified throughanalysis of the in situ sedimentary cover of the troodos ophiolite results indicate that bulkanticlockwise rotation began soon after the cessation of spreading and ended by the end ofthe eocene with c 50 60 of microplate rotation being over by the maastrichtian the timeat which ophiolite thrust sheets were emplaced onto the arabian continental margin to theeast of troodos recent results from the emplaced structurally dismembered baer bassitophiolite indicate extreme anticlockwise rotations of ophiolitic thrust sheets varying on akilometre scale new data from the post emplacement sedimentary cover confirm that onlya small component of these rotations is due to post emplacement tectonism baer bassitrepresents the leading edge of the emplaced ophiolitic sheet new data from the morecoherent section preserved in the hatay ophiolite to the north demonstrate significantanticlockwise rotation this is equivalent to the rotation of the most northerly part of thebaer bassit units to the south and is of the same sense and magnitude as the pre maastrichtian phase of microplate rotation documented in the troodos this suggests acommon intra oceanic origin for the majority of the troodos and hatay rotations and asignificant component of the more variable rotations observed in baer bassit overall therefore the data support a model involving 1 intra oceanic rotation of a coherent regionof crust within the southern neotethyan basin this rotated unit is more areally extensivethan has previously been inferred from consideration of data from the troodos ophiolitealone 2 emplacement of part of the rotated unit onto the arabian platform 3 subsequentlocalized post emplacement modification related to the development of the current plateconfiguration

shear zones in the upper mantle evidence from alpine and ophiolite type peridotite massifs there is abundant field and microstructural evidence for localization of deformation in alpineand ophiolite type mantle massifs on the basis of field relationships and microstructures we recognize two types of tectonite shear zones mediumto coarseand fine grained as well as two types of mylonitic shear zones anhydrous and hydrous peridotite mylonites in tectonite shear zones softening processes responsible for localization are probably melt related weakening in the medium to coarse tectonites and a change in limiting slip system in the fine grained tectonites in peridotite mylonites the most likely cause for softening and localization is a change in dominant deformation mechanism from dislocation to grain size sensitive creep microstructural and petrological study of mylonite rocks reveals that reactions either continuous net transfer reactions anhydrous and hydrous or melt rock reactions play a key role in the formation of fine grained material that promotes grain size sensitive creep these reactions occur over a broad range of pressure temperature conditions encompassing a large part of the lithospheric upper mantle we conclude that mantle shear zones are widespread and that they reduce the bulk strength of the lithosphere significantly attempts to understand the dynamics of tectonic processes depend critically on quantitative knowledge concerning the mechanical properties of the lithosphere and the relative strength of the crust and upper mantle e g brun 2002 for many years it has been accepted that the upper part of the mantle lithosphere is strong compared to the crust e g kirby 1983 kuznir park 1986 the notion of a strong uppermost mantle is based on extrapolation of laboratory flow laws kohlstedt et al 1995 and the depth distribution of seismicity in the lithosphere chen rc molnar 1983 the inferred high strength of the shallow mantle implicitly refers to homogeneous flow however at large strains deformation of the mantle lithosphere may become localized within weak shear zones fig 1 so the application of low strain flow laws may seriously overestimate the strength of the mantle rutter brodie 1988 handy 1989 vissers et 01 1995 in a recent study on the seismicity and elastic thickness of continental lithosphere magi et al 2000 have suggested that the crust is in fact the strongest layer thus it is emerging that the strength of lithospheric upper mantle may vary considerably over the last decade we have studied a number of peridotite massifs both of orogenic alpine type and ophiolitic origin in order to establish under which conditions and to what extent deformation in mantle rocks is localized in this contribution we present an overview of shear localization features in these peridotite massifs from our data as well as published data from other workers it emerges that under lithospheric conditions localization of deformation in mantle rocks is a common phenomenon fig 1 table i in addition shear localization seems to occur over a wide range of pressure temperature conditions producing a number of distinct shear zone types the range of shear zone types is comparable to types of deformation structures found in crustal rocks e g carreras et al 1980 microstructural work has highlighted the importance of mineral reactions as a softening mechanism in the development of mantle mylonite shear zones handy 1989 drury et al from alsop g i holdsworth r e mccaffrey k j w hand m eds 2004 flow processes in faults and shear zones geological society london special publications 224 11 24 0305 8719 15 00 o the geological society of london 2004 12 a h dijkstra eta l

kinematics of late cretaceous subduction initiation in the neo tethys ocean reconstructed from ophiolites of turkey cyprus and syria formation of new subduction zones represents one of the cornerstones of plate tectonics yet both the kinematics and geodynamics governing this process remain enigmatic a major subduction initiation event occurred in the late cretaceous within the neo tethys ocean between gondwana and eurasia suprasubduction zone ophiolites i e emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers were generated during this subduction event and are today distributed in the eastern mediterranean region along three e w trending ophiolitic belts several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra neo tethyan subduction zone here we present new paleospreading directions from six upper cretaceous ophiolites of turkey cyprus and syria calculated by using new and published paleomagnetic data from sheeted dyke complexes our results show that nne ssw subduction zones were formed within the neo tethys during the late cretaceous which we propose were part of a major step shaped subduction system composed of nne ssw and wnw ese segments we infer that this subduction system developed within old triassic lithosphere along fracture zones and perpendicular weakness zones since the neo tethyan spreading ridge formed during gondwana fragmentation would have already been subducted at the pontides subduction zone by the late cretaceous our new results provide an alternative kinematic model of cretaceous neo tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old and cold lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges

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

extensional tectonics in the honshu fore arc japan integrated results of dsdp legs 57 87 and reprocessed multichannel seismic reflection profiles

the role of geomorphic processes in the transport and fate of mercury in the carson river basin west central nevada the historic processing of precious metal ores mined from the comstock lode of west central nevada resulted in the release of substantial but unquantified amounts of mercury contaminated mill tailings to the carson river basin geomorphic and stratigraphic studies indicate that the introduction of these waste materials led to a period of valley floor aggradation that was accompanied by lateral channel instability the combined result of these geomorphic responses was the storage of large volumes of mercury enriched sediment within a complexly structured alluvial sequence located along the carson river valley much of the contaminated sediment is associated with filled paleochannels produced by the cutoff and abandonment of meander loops and their subsequent infilling with contaminated particles geochemically these deposits are characterized by variations in mercury levels that exceed three orders of magnitude continued lateral instability coupled with an episode of channel bed incision followed the decline of comstock mining and has reexposed contaminated debris within the banks of the river erosion of bank sediments reintroduces mercury enriched particles to the modern channel bed it is suggested on the basis of geochemical and sedimentological data that during the bank erosion process much of the mercury associated with fine 63 valley fill deposits are carried downstream without being incorporated to any appreciable extent within the channel bed sediments in contrast mercury associated with larger and denser particles particularly mercury gold silver amalgam grains are accumulated in the channel bed sediments as the river traverses polluted reaches of the carson river valley concentration patterns developed along the modern channel indicate that the valley fill is the primary source of mercury to the river today thus these data imply that efforts to reduce the influx of mercury to the aquatic environment should examine methods for reducing bank erosion rates

using 3d kinematic models in subduction channels the case of the chanaral tectonic melange coastal cordillera northern chile abstract the chanaral tectonic melange northern chile is a local unit within the late paleozoic accretionary complex formed at the southwestern margin of gondwana the structural characteristics of the studied melange were mostly developed during a first deformation phase d1 and include a block in matrix fabric lineations l1 and foliations s1 tight to intrafoliar folds s c and s c c composite planar fabrics and a conspicuous spatial separation of domains with predominantly linear and linear planar fabrics folding during a second stage d2 modified the orientation of the previous fabrics and structures the eastern boundary of the chanaral melange is n s to nnw sse oriented moderately dipping to the east its western boundary is not exposed the plane showing the maximum structural asymmetry the vorticity normal section is ene wsw directed and sub vertical kinematic criteria consistently reveal top to the wsw displacement a kinematic model of triclinic transpression with inclined extrusion has been applied to evaluate the d1 structural features of the chanaral melange the pitch of the simple shear direction on the deformation plane ranged from 60 n to 90 the pitch of the estimated extrusion direction was of 30 40 s the coaxial component was clearly constrictional logarithmic k value of 2 to 5 the vorticity number has not been constrained by the model but its spatial variation can explain the domainal distribution of the fabrics in the melange the simulated particle paths show the predominance of material displacement parallel to the margin with low to moderate down dip displacements which is in accordance with the low pressure metamorphic assemblages found in the melange the convergence direction between the blocks separated by the melange unit was n50 60 e kinematic blocking of the chanaral melange probably related to the accretion of an oceanic volcanic domain allowed the d2 folding of the previous structures a process that at least initially proceeded without a change in the convergence direction

geomorphology and late quaternary of the chaco south america the chaco is a large tropical plain located in the interior of south america consisting of parts of argentina paraguay and bolivia it is 840 000 km2 in area and is characterized by forests savannas and extensive swamps which give it a marked climatic and biogeographic identity it encompasses five huge alluvial fans built by the major rivers which cross the region salado bermejo pilcomayo parapeti and grande the fans are composed of several sedimentary units deposited during different times of the late quaternary under diverse climates two fluvial terraces appear at the apex of each fan the older one is probably late pleistocene in age the second was formed in postglacial times humid climates such as the present one favoured the generation of soils and stable fluvial belts drier climates led to widespread sedimentation along small ephemeral channels and large spill outs during two intervals on in the late quaternary glacial maximum and the late holocene dry climates occurred in the region leading to the formation of dune fields and loess mantles

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

on the sense of slip of the southern troodos transform fault zone cyprus it is generally accepted that the 5 10 km wide zone of wrench faulting preserved in the arakapas valley and limassol forest areas of cyprus along the southern margin of the troodos ophiolite is part of a fossil oceanic transform fault system however despite detailed study of this the southern troodos transform fault zone and neighboring part of the main troodos massif no consensus has been reached as to its sense of motion some have postulated sinistral slip some dextral whereas others have suggested that it slipped both ways and reversed its sense of motion by ridge jumping to resolve this issue and better determine the spreading history of the troodos ophiolite we present new field observations from the transform tectonized area and reexamine existing evidence for the sense of slip of the transform although we find evidence for both sinistral and dextral shear along the fault zone while in an oceanic environment the overwhelming indications are for dextral slip genuine sinistral slip indicators are restricted to a few mylonitic shear zones of limited extent which can be related to local geometrical complexities associated with intrusion of gabbroic plutons into the transform zone there is no need to invoke wholesale reversals of slip along the transform fault nor therefore the radical reorganizations of the troodos spreading system that have previously been proposed

kinematic history of a reactivated oceanic suture the mamonia complex suture zone sw cyprus the mamonia complex suture zone in sw cyprus marks an arcuate tectonic suture between an upper cretaceous oceanic microplate of supra subduction zone origin troodos complex and a deformed triassic passive margin sequence mamonia complex mapping of the serpentinite filled fault zones that define the suture zone combined with microstructural studies of its constituent fault rocks has revealed evidence of three main tectonic events of upper cretaceous age 1 high temperature c 600 c transform related dextral strike slip and localized metamorphism of mamonia complex units c 90 83 ma 2 retrograde hydration c 83 73 ma 3 regional contractional reactivation at low temperatures which ceased by the latest maastrichtian c 65 ma the present day structural geometries are interpreted as the result of maastrichtian contractional reactivation of a pre existing steep and irregular structural architecture that formed during transtension the resultant orientation of finite strain axes and thrust displacements display a radial distribution documenting near fault normal contraction along the whole length of the arcuate suture zone this pattern of displacements suggests a model whereby the troodos microplate impinged on the mamonia complex during westerly to southwesterly directed plate motion contractionally reactivating the mechanically weak suture zone

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading