northland ophiolite new zealand and implications for plate tectonic evolution of the southwest pacific the northland ophiolite and coeval ocean floor sedimentary rock form the northland allochthon obducted from the northeast onto new zealand in the late oligocene the ophiolite was probably emplaced as a single sheet and separated into individual massifs during subse quent movement of the allochthon chemically the bulk of the igneous rocks are normal mid ocean ridge basalts but the ophiolite also includes a younger suite of hornblende modal within plate alkalic rocks believed to represent seamounts two alternative models one involving a subduction flip the other involving continuous westward subduction are proposed to account for the obduction of the upper part of the northland ophiolite the oceanic crust from which the ophiolite originated was formed simultaneously with tasman sea spreading on the western rim of a once much larger south fiji plate assemblage

a late cretaceous and cenozoic reconstruction of the southwest pacific region tectonics controlled by subduction and slab rollback processes abstract a cenozoic tectonic reconstruction is presented for the southwest pacific region located east of australia the reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for pacific australia and lord howe rise pacific relative plate motion the reconstruction is based on a conceptual tectonic model in which the large scale structures of the region are manifestations of slab rollback and backarc extension processes the current paradigm proclaims that the southwestern pacific plate boundary was a west dipping subduction boundary only since the middle eocene the new reconstruction provides kinematic evidence that this configuration was already established in the late cretaceous and early paleogene from 82 to 52 ma subduction was primarily accomplished by east and northeast directed rollback of the pacific slab accommodating opening of the new caledonia south loyalty coral sea and pocklington backarc basins and partly accommodating spreading in the tasman sea the total amount of east directed rollback of the pacific slab that took place from 82 ma to 52 ma is estimated to be at least 1200 km a large percentage of this rollback accommodated opening of the south loyalty basin a north south trending backarc basin it is estimated from kinematic and geological constraints that the east west width of the basin was at least 750 km the south loyalty and pocklington backarc basins were subducted in the eocene to earliest miocene along the newly formed new caledonia and pocklington subduction zones this culminated in southwestward and southward obduction of ophiolites in new caledonia northland and new guinea in the latest eocene to earliest miocene it is suggested that the formation of these new subduction zones was triggered by a change in pacific australia relative motion at 50 ma two additional phases of eastward rollback of the pacific slab followed one during opening of the south fiji basin and norfolk basin in the oligocene to early miocene up to 650 km of rollback and one during opening of the lau basin in the latest miocene to present up to 400 km of rollback two new subduction zones formed in the miocene the south dipping trobriand subduction zone along which the solomon sea backarc basin subducted and the north dipping new britain san cristobal new hebrides subduction zone along which the solomon sea backarc basin subducted in the west and the north loyalty south fiji backarc basin and remnants of the south loyalty santa cruz backarc basin subducted in the east clockwise rollback of the new hebrides section resulted in formation of the north fiji basin the reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere a change in plate kinematics or slab mantle interaction

groundwater recharge in arid areas induced by tropical cyclones lessons learned from gonu 2007 in sultanate of oman younger groundwater found in some omani aquifers is a result of recent recharge from cyclonic and storm events weyhenmeyer et al science 287 842 845 2000 young et al j appl geophys 57 43 61 2004 the analysis of the meteorological data in oman indicates an anomalous rainfall on a decadal interval whereas cyclones frequency is expected to increase due to global climatic changes the cyclone gonu has severely struck the eastern omani coasts in 2007 resulting in devastating floods huge volume of water 3 672 mm3 spread over the coastal plain calling for an assessment of potential groundwater recharge subsequent to this event the present study evaluates groundwater recharge with respect to gonu 2007 to assess the potential of recharge induced by such cyclones in the arid zones the hydrographs of several piezometers sited along the coastal plain in muscat province have been studied and variation in water table rise has been analyzed significant water table rise is indicated for areas with geological and structural settings favoring rapid infiltration of water yielding considerable groundwater mound whereas piezometers located in less favorable zones show minimum rise of water table however soon after the floods the aquifer hydrodynamics has readjusted to attain equilibrium and the groundwater mound dissipated the cumulative rise of the water table on an areal extent does not exceed a few centimeters indicating lesser volume of recharge comparatively recharge from frequent precipitation along favorable zones produces more significant recharge compared with cyclonic events where surface water residence time is shorter to allow for efficient infiltration

development of p t prograde and p retrograde t prograde isogradic surfaces during blueschist to eclogite regional deformation metamorphism in new caledonia as indicated by progressively developed porphyroblast microstructures the mid tertiary blueschists eclogites and eclogitic gneisses of northern new caledonia are the products of four phases of regional meta morphism and deformation d d4 omphacite lawsonite and mn rich garnet isogradic surfaces were developed during the second deformation d2 under prograde pressure and temperature conditions subsequent deformations d3 d folded these d isogradic surfaces however within the p retrograde t prograde metamor phic environment of the d phase omphacite altered to albite and chlorite as a result a late stage sub horizontal isogradic surface developed for omphacite out where this mineral is preserved as relics within syn d albite porphyroblasts other minerals that crystallized for the first time epidote or had rim additions almandine phengite during d also form nearly horizontal isogradic surfaces porphyroblastic garnet and albite contain inclusion trails which allow their microstructural development and crystallization of the matrix to be traced from d to d late syn d the temperature increased mark edly in association with an extensive exothermic decarbonation even though the rocks were in a state of pressure retrogression this caused considerable neocrystallization recrystallization and growth of matrix and porphyroblasts such that although s foliation crenulated by d and d is readily observable almost all signs of stored strain due to d and d have been removed and the deeper schists and eclogitic gneisses superficially appear to have undergone a drastic annealing recrystallization post dating deformation

generation and obduction of ophiolites constraints from the bay of islands complex western newfoundland constraints provided by the bay of islands ophiolite complex boic western newfoundland suggest that its generation as well as its obduction is related to collision of the dunnage zone island arc system with the irregular continental margin of eastern north america the constraints include the supra subduction zone setting of the boic its extensional environment of generation the synchronous occurrence of ophiolite generation with initiation of drowning and deformation of the north american continental margin and the restriction of the boic as well as other appalachian ophiolites and associated taconian allochthons to reentrants in the north american margin during the early phases of collision of the dunnage arc with the north american margin subduction of old oceanic lithosphere trapped in reentrants will continue and allow the development of two potential sites of ophiolite generation the first develops through trench rollback leading to ophiolite generation in the overriding arc plate outboard of the reentrant whereas the second develops in a transtensional environment with spreading centers offset by strike slip faults which propagate through the overriding plate away from the indenter promontory the configuration of the boic spreading ridge normal to the continental margin and the direction of initial obduction parallel to the margin favor generation of the ophiolite in an overall strike slip regime with complete subduction of the oceanic remnant extension in the overriding plate ceases and the buoyant newly formed oceanic lithosphere is obducted onto the continental margin diachronous collision of the arc with the irregular continental margin accounts for the range of ages for ophiolite generation and obduction observed within the dunnage zone and for termination of arc volcanism along the north american margin

overthrust emplacement of new caledonia ophiolite geophysical evidence geophysical studies support inferences from outcrop geology that during the late eocene an ophiolite sheet exposed on new caledonia was thrust southward over a rock complex consisting of sedimentary volcanic and metamorphic rocks that range in age from pre permian to eocene the outcropping ultramafic complex consists of a layered sequence approximately 3000 m thick including harzburgite dunite wehrlite serpentinite and gabbro the absence of pillow basalts and sheeted dikes on land suggests that during or after overthrusting these units were removed either by thrust faulting or by erosion seismic refraction profiles collected over the adjacent loyalty basin show that the lower crust and upper mantle are characterized by velocities of 4 7 5 8 6 8 and 8 1 8 4 km s suggesting the presence of a complete oceanic section that includes sediment basalt gabbro and peridotite the lower crust is probably 6 5 km thick beneath the loyalty basin a seismic reflection profile that extends across the loyalty basin is interpreted to show the oceanic crust rising toward new caledonia we suggest that the ophiolite on new caledonia is continuous with this rising oceanic crust studies of gravity anomalies observed both on land and offshore indicate the presence of a short wavelength high amplitude 180 mgal asymmetrical free air gravity anomaly along the northeastern coast of new caledonia a gravity anomaly profile calculated for a geological model characterized by a 10 km thick slab of oceanic crust and mantle material extending continuously from the ophiolite on new caledonia to the oceanic crust of the loyalty basin successfully matches the observed gravity data we interpret the extension of the high gravity anomaly over the whole length of the eastern lagoon as evidence for the lateral extension of the root zone of the ultramafic complex a tentative geodynamic reconstruction suggests that the proto loyalty basin crust formed a marginal basin along the eastern margin of gondwanaland prior to upper cretaceous time after the opening of the new caledonia basin during upper cretaceous to early paleocene time a subduction zone developed along the western margin of new caledonia while this zone was active the loyalty basin lithosphere overthrust new caledonia in a southeasterly direction and locally rotated clockwise this compressional tectonic event was terminated by upper eocene time

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

deformation mode switches in the penninic units of the urtier valley western alps evidence for a dynamic orogen abstract multiple deformation mode switches from shortening to extension have been detected in the penninic units of the urtier valley to the north of the gran paradiso massif an early shortening phase whose traces are poorly preserved led to the tectonic burial of rock units to high pressure conditions subsequent extensional shearing sz gr 1 led to the formation of mylonitic fabrics during this event the eclogitic piemonte unit was exhumed to greenschist facies conditions p 0 2 0 3 gpa in the footwall of the blueschist piemonte unit exotic slices of continental basement and mesozoic continental shelf carbonates are found along their contact implying the existence of older thrust stacks dissected by the younger extensional shear zones the extensional structures were later affected by upright folding fu indicating yet another deformation mode switch which led to re burial to p 0 6 0 8 gpa later multi stage deformation culminated in an episode of extensional shearing with top to the west kinematics sz gr 2 therefore at least two shortening extension cycles affected the piemonte units of the urtier valley existing geochronological data allow less than 20 myr for the complex deformation history discussed here shortening extension cycles can be inferred also from published studies from other sections of the western alps however while the first shortening extension cycle was widespread in the penninic units the lateral extent and relative timing of the second cycle in different areas are still unclear

shear zone model for the origin of metamorphic core complexes core complex tectonite results from simple shear rotational strain within regional ductile shear zones that have accommodated a tertiary crustal stretching the emplacement of younger and or upper level nontectonite rocks on older and or deeper level tectonites is the ordinary and predictable result of normal slip translation along shear zones that cut upward through the local geologic column progressive deformation produces a structural stratigraphy marked from bottom to top by normal country rock protolith mylonitic gneiss tectonite carapace microbrecciated tectonite microbreccia decollement and upper plate detachment rocks as young as mid miocene the reconstructions suggest that local regional crustal stretching locally exceeded 100

significant coherence for groundwater and rayleigh waves evidence in spectral response of groundwater level in taiwan using 2011 tohoku earthquake japan summary it was found that groundwater can be fluctuated by a variety of disturbances for instance seismic activity inducing the dilatation of earth can disturb groundwater level fluctuation as observed in groundwater wells in this research spectral analysis in the frequency domain was used to quantitatively evaluate coherence between groundwater head fluctuations and the ground motions recorded in taiwan from a distant earthquake the 2011 tohoku earthquake in northern honshu japan with magnitude of 9 the relationship between groundwater fluctuations and the decomposed ground motions of rayleigh waves are clearly identified by analyzing autospectral density cross spectral density and resultant coherence for the seismograms and groundwater head it was found that the rayleigh waves dominated the groundwater fluctuations at period of about 21 32 s for six pair of groundwater and seismograms of broadband distributed around taiwan fluctuations of groundwater are highly coherent with the radial and vertical components of ground motions our analysis also shows the time from event to station for rayleigh waves ranged from 780 to 900 s approximately wave parameter for seismic event to station of groundwater and seismograms were also identified as 3 0 3 5 km s and 64 110 km for wave velocity and wave length respectively the relationship of groundwater fluctuations and ground motions induced by seismic activity become feasible to assess using spectral analysis

plio quaternary thin skinned tectonics along the crustal front flexure of the southern central andes a record of the regional stress regime or of local tectonic driven gravitational processes we present here a record of plio pleistocene deformations above the flexural front of the southern central andes of argentina we combine a seismic profile with structural and geomorphological observations to show that thin skinned extension located on top of the crustal front flexure is coeval with thin skinned shortening at the toe of the topographic bulge the seismic line shows that a flat zone with no internal deformation separates the stretched and shortened domains such features are usually interpreted as the result of strike slip faulting along basement faults or tangential longitudinal strain folding in the soft sedimentary cover above crustal bending we propose an alternative linking extension at the apex of the crustal anticline to basal contraction by the downslope translation of a rigid thin nappe of sediments 30 30 km2 in area above evaporites at a depth of 700 900 m the size of such a process is unusually large onshore 630 810 km3 but mimics the gravity gliding observed in deltas and passive margins since this process disconnects zones with a shallow stress field from deeper crustal levels it could allow extension above a compressive deformation front and should not be interpreted merely as a record of the crustal stress regime large scale gravity gliding of the cover down the slope of a structural high could also explain some of the extension observed in mountain hinterlands

assessment of effect of recharge from a check dam as a method of managed aquifer recharge by hydrogeological investigations check dams are often used as a method of managed aquifer recharge mar and are generally preferred in non perennial rivers for intentional storage of the water the objective of this study is to evaluate the efficacy of a check dam constructed as a mar initiative across arani river north of chennai india by long term hydrogeological investigations electrical resistivity survey and drilling of borehole helped to understand the subsurface geology water level and water quality measurements were carried out periodically from july 2010 to may 2012 groundwater occurs in unconfined condition in the alluvial formations extending up to a depth of about 50 m below the ground surface water table is at a depth ranging from 3 to 12 m below the ground level the electrical conductivity and concentration of major ion were less in water stored in the dam and hence the recharge of this water has led to improvement in groundwater quality rainfall recharge of this study area was estimated to be about 17 of annual rainfall about 63 of water stored in the check dam resulted in groundwater recharge this has led to an increase in groundwater level from 1 to 3 5 m until a distance of about 2 km the cost of 1 m3 of water stored by the check dam will be rs 1 20 the comparison of groundwater level water level in the check dam and water quality assisted in demarcating the areas benefited by the storage of water in the check dam thus the electrical conductivity and major ion concentration of water which are inexpensive rapid and easy to measure were used as a tool for understanding the area that is benefited by the water stored in the check dam the study brought out the efficiency of check dam as a method of mar in improving the groundwater recharge and groundwater quality

emplacement of ophiolite in papua new guinea summary the major ophiolite complexes of papua new guinea lie on the northeastern margin of the australian craton and are flanked externally by palaeogene volcanic arcs the ophiolites are segments of oceanic lithosphere which occupied the forearc zone prior to arc continent collision in the case of the easternmost ophiolite the papuan ultramafic belt there is evidence that emplacement was preceded by development of a secondary rupture in the down going plate at some distance from the subduction zone and was followed by extension buoyant emergence and reversed movement of the ophiolite the westernmost ophiolite april ultramafics has more complex structure and probably developed as a series of thrust sheets in a subduction system the thrust sheets were subjected to renewed deformation and thrusting by continued convergence after arc continent collision

groundwater recharge dams in arid areas as tools for aquifer replenishment and mitigating seawater intrusion example of alkhod oman groundwater depletion and seawater intrusion constitute major challenges along coastal aquifers in arid areas this paper assesses the role of groundwater recharge dams constructed to replenish aquifers and fight seawater intrusion with reference to alkhod dam oman sited 7 km from the coast on a gravely unconfined aquifer water table rise in piezometers located downstream from the dam shows regular patterns correlating with magnitude of wadi flow whereas upstream piezometers show irregular patterns controlled release of water captured by the dam optimizes water percolation and enhances artificial recharge which was estimated in the wet years 1997 2003 and 2005 as 15 22 and 27 mm3 respectively using water table fluctuation method recharge contributed 40 60 of the total annual abstraction groundwater salinity increased in the 1980s and 1990s and the saline freshwater interface advanced inland but has receded partially after 1997 highest rainfall and completely after 2005 indicated by reduction in electrical conductivity and thickening of freshwater lens the recession is attributed to the dam s induced recharge and reduction of pumping in 2004 following the commissioning of barka desalination plant integrating artificial recharge with groundwater resources management is therefore an effective measure to replenish aquifers in arid areas and mitigate seawater intrusion along the coasts

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

large scale structure of the eclogite blueschist belt of new caledonia abstract this paper considers the large scale geometry of the northern part of the eclogite blueschist belt of new caledonia based largely on classical style structural analysis but in consideration of modern concepts regarding crustal extension exhumation of high pressure rocks and uplift shear zones played an important role in the evolution of the region early shear zones and high pressure metamorphism appear to be associated with overthrusting of an ultramafic sheet middle stage shear zones are associated with large scale continental extension during which the high pressure rocks were exhumed the extended crust was subsequently folded during renewed compression producing an orogen scale antiform throughout the high pressure belt that folds all previously formed structures late stage shear zones formed when the orogen was once again thrown into extension relatively youthful normal faults caused late block faulting uplifting a regional peneplain and producing the present geomorphology previously published interpretations of the structure and geometry of the belt have suggested that the high pressure rocks are found in the core of a regionally developed antiform interpreted as a metamorphic core complex our structural mapping shows that allochthonous slices of high pressure rocks are draped over a younger unrelated foliation antiform lower grade retrogressed equivalent rocks are found within the core of the antiform thus the metamorphic core complex model is rejected

numerical modeling the role of rubber dams on groundwater recharge and phreatic evaporation loss in riparian zones rubber dams have been widely built for their advantages in increase of flooding resources utilization in the north arid and semiarid plain regions of china rise in river water stage by the dams particularly during the drought periods increases lateral seepage of river water into groundwater and thus groundwater table and phreatic evaporation loss in the riparian zones in this study a riparian area of the baihe river in nanyang of henan province china was selected for investigation of influences of the river dams on the groundwater recharge and evaporation loss a hydraulic model hec ras was used for simulation of the river stage variations along the baihe river and a numerical groundwater model modflow was applied for simulation of groundwater dynamics and estimation of river flow seepage into aquifer and evaporation loss the results show that the dams increase river stages of 2 3 m during january 2000 december 2002 the increase in the captured groundwater recharge was 7 15 34 06 million m3 a and the increased phreatic evaporation loss occupies 10 of the increased recharge when four rubber dams were built

neoarchaean metamorphic evolution of the yilgarn craton a record of subduction accretion extension and lithospheric delamination abstract the greater part of the metamorphic record of the yilgarn craton formed during a protracted middle neoarchaean orogenic cycle spanning from about 2750 to 2620 ma at least six distinct metamorphic events are defined by parageneses in different tectono stratigraphic settings this review characterizes the middle neoarchaean metamorphic response of the entire craton using large databases rock descriptions from 60 000 sites in government databases and 1040 pt determinations from all sources are used to construct metamorphic map patterns for each of these metamorphic events p t paths and timing of each metamorphic event are characterized using petrology and the well constrained pt determinations from this study n 287 combined with metamorphic age determinations from all sources n 114 the spatial patterns and metamorphic conditions of each event provides critical constraints on tectonic settings and changes in tectonics over 130 million years the record of metamorphism in conjunction with stratigraphic kinematic and magmatic constraints shows that the neoarchaean craton evolved from an accretionary crustal growth phase ma and m1 to thermal reworking of the crust during massive influx of granitic intrusions m2 and lithospheric extension after the termination of subduction m3 these events were followed by lithospheric delamination resulting in a craton wide diffusion delayed thermal pulse that coincided with renewed contraction m4 m1 metamorphism at 2748 19 2727 8 and 2706 10 ma experienced high p moderate t hairpin clockwise p t paths during burial of magmatic arc margins during terrane accretion events m2 regional contact type metamorphism at 2671 6 ma tracked low p moderate t clockwise p t paths in back arc settings during voluminous felsic magmatism related to shallow subduction m3 metamorphism at 2656 5 ma experienced low p moderate t anticlockwise p t paths in post volcanic rift basins formed during lithospheric extension m4 metamorphic peaks at 2644 4 and 2629 7 ma experienced low p high t clockwise p t paths during regional scale thermal pulses resulting from lower crust and mantle lithosphere delamination at 2665 2668 ma

the response of water level in a well to a time series of atmospheric loading under confined conditions the water level in a well that penetrates a confined aquifer can fluctuate in response to changes in atmospheric pressure the response varies with the well casing and screen dimensions the transmissivity and compressibility of the aquifer and to a small extent its storativity recently this loading response problem has been solved in terms of a frequency response function that characterizes how attenuation and phase shifts in the response signal vary with frequency the counterpart of this solution in the time domain is an impulse response function this solution has the immediate appeal that it can be used directly to filter raw loading and water level records via serial convolution where the response at any time is a weighted aggregate of the previous loading signal the impulse response function derives from well known solutions to the slug test problem when based on the cooper bredehoeft papadopulos solution the response function is precise but computationally intensive based on the hvorslev solution the response function is computationally simple but applicable only to aquifers with small storativity simulations and a field example clearly illustrate the dominating influence of transmissivity in dampening and lagging the response of a confined aquifer to a loading signal and how both effects increase with higher frequency the results also illustrate the weak influence of storativity in modulating the response signal

shear zone origin of quartzite mylonite and mylonitic pegmatite in the coyote mountains metamorphic core complex arizona abstract mylonites derived largely from granite pegmatite and sedimentary quartzite occupy a 500 m thick gently n dipping zone along the northern flank of the coyote mountains west of tucson in southeastern arizona the quartzite mylonites are exceptionally well developed and occur as discrete layers and lenses 2 5 m thick within yet thicker boudinaged sill like lenses of mylonitic pegmatite mylonitization took place in the tertiary within a normal slip ductile shear zone the shear zones formed in response to regional extension of continental crust extension is along a north south line and n directed sense of shear is revealed by mica fish oblique foliations in dynamically recrystallized quartz aggregates and asymmetric quartz c axis fabrics the microstructures and c axis fabrics taken together disclose that ductile and brittle deformation was achieved by intense penetrative non coaxial laminar flow dominated by progressive simple shear

the importance of serpentinite mylonites for subduction and exhumation of oceanic crust abstract in the ultramafic erro tobbio unit voltri massif western alps a set of overprinting structures in serpentinite mylonites is related to alpine subduction to about 80 km depth and to subsequent exhumation antigorite mylonites are cut by en echelon olivine veins which in turn are dissected by multiple sets of shear bands containing olivine and titanian clinohumite the transition from olivine free to olivine bearing structures indicates recrystallization during prograde metamorphism all structures display the same top to the nw kinematics providing evidence for a continuous non coaxial deformation the serpentinite mylonites surround km scale bodies of pre alpine peridotite which show only minor alpine overprint this indicates that during subduction related deformation recrystallization and fluid flow were strongly localized within serpentinite mylonites olivine bearing discontinuous shear planes with top to the se sense of movement crosscut the prograde structures the inversion of shear sense suggests a change in position of the serpentinites relative to the downgoing slab i e from the subducted slab to the upper plate during accretion thus the shear sense inversion marks the change from burial to exhumation of the serpentinites the low density of antigorite serpentinites 2 75 g cm3 causes strong buoyancy thus providing a mechanism for the exhumation of deeply subducted rocks it is suggested that serpentinites may act as carriers for the uprise of eclogite bodies which have higher densities than the peridotitic upper mantle

constraints on long lived mesoproterozoic and palaeozoic deformational events and crustal architecture in the northern mount painter province australia abstract meta sedimentary and igneous rocks preserved in the hanging wall of the paralana fault northern mount painter province record a protracted ca 1600 myr multi staged metamorphic and poly deformational evolution related to mesoproterozoic and palaeozoic orogenic events the mount painter province was located near the margin of both the south australian craton and the north australian craton which allows comparisons of the tectonic evolution of these margins and provides context for the evolution of the eastern proterozoic australia for both the columbia and gondwana supercontinents within the mount painter province meta sedimentary rocks form part of a basin system developed adjacent to the margins of the gawler craton and curnamona province following the olarian wartakan orogenic system sedimentation was followed by ca 1590 1552 ma ductile deformation d 1 d 3 at mid to upper crustal levels preserving a rapid ca 6 myr burial and exhumation cycle initial deformation is characterised by the development of a layer parallel fabric s 1 s 1 is overprinted by recumbent north verging folds f 2 formed during mid to upper amphibolite facies peak metamorphism m 2 which are overprinted by tight upright shallow ne sw plunging folds f 3 d 3 folds developed contemporaneous with sinistral oblique shearing and the development of proto mylonitic to ultra mylonitic fabrics along the paralana fault zone the timing of d 3 deformation is constrained by the development of a penetrative steeply dipping foliation s 3 in the ca 1585 1569 ma shallowly emplaced mount neill granite and relatively undeformed granites dated at ca 1552 ma further constraint on the absolute timing of mesoproterozoic tectonism is provided through the dating of zircon growth from samples of the meta sedimentary radium creek metamorphics this dating reveals a 1555 16 ma metamorphic event interpreted to be the consequence of m 3 amphibolite facies regional metamorphism and accompanying metasomatism the transition between d 2 and d 3 is interpreted to reflect a shift from ca 1591 1585 ma n s shortening to ca 1585 1552 ma nw se shortening this episode of orogenesis is correlated with the ca 1585 1540 ma kararan orogeny in the northern gawler craton which distinctly postdates the ca 1600 1590 ma olarian orogeny as previously interpreted the mesoproterozoic structural architecture was reactivated during neoproterozoic extension d 4 and the ca 500 ma delamerian orogeny delamerian structures are formed in a predominantly brittle regime early thin skinned thrusting was followed by thick skinned deformation d 5 d 6 during which open f 5 folds developed above oblique lateral ramps and produced type 0 overprinting patterns with f 3 mesoproterozoic folds steeply plunging f 6 buckle folds with se trending axial traces are the last phase of deformation recorded both mesoproterozoic ductile deformation phases and the palaeozoic ductile brittle to brittle overprints were focussed along the paralana fault emphasising the repeated long lived evolution of this crustal scale fault system

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

the emplacement of the peridotite nappe of new caledonia and its bearing on the tectonics of obduction the peridotite nappe of new caledonia is one of the few ophiolites worldwide that escaped collisional orogeny after obduction here we describe the deformation associated with serpentinization in two klippes of the nappe in northwestern new caledonia the klippes are flat lying and involve s sw vergent reverse slip shear zones which are true compressional structures in origin further northeast the nappe is folded in association with the development of a steep schistosity in low grade metasediments this difference in structural style indicates that the peridotite nappe experienced compression at greater depths toward its root zone suggesting a push from the rear mechanism of emplacement this supports the view that the nappe has been emplaced through horizontal contraction sustained by plate convergence we establish a crustal scale cross section at the end of the obduction event before neogene extension this involves a large fold nappe of high pressure rocks bounded from below by a major thrust furthermore we show that obduction in new caledonia occurred through dextral oblique convergence oblique convergence probably resulted from the initial obliquity between the subduction trench and the continental ribbon that became incorporated in it this obliquity can solve the paradox of the peridotite nappe seemingly being emplaced at the same time the high pressure rocks were exhumed oblique convergence together with focused erosional denudation on the northeastern flank of the island led to exhumation of the metamorphic rocks in a steep fold nappe rising through the rear part of the orogen

core complex related extension of the aegean lithosphere initiated at the eocene oligocene transition 1 core complex related stretching of the aegean lithosphere was accommodated in part by the south cyclades shear zone scsz which outcrops on the islands of ios and thera aegean sea greece this paper reports new microstructurally focused 40ar 39ar geochronology that suggests the scsz initiated just before the time of the eocene oligocene transition at 35 ma therefore it is not only miocene extension that led to the tethyan metamorphic core complexes exposed in the cycladic archipelago it is shown here that pervasive top to the south directed ductile shear took place in the scsz for 5 ma during the early oligocene followed by initiation of overprinting north sense shear zones at the time of the oligocene miocene transition at 25 ma this means that modern core complex related extension in the aegean started much earlier than has been previously recognized and that stretching of the aegean lithosphere took place in a distinctly episodic fashion not in a manner that can be described as continuous or progressive the data also mean that the complementary shear sense geometry of the scsz and the north cyclades shear zone ncsz cannot be interpreted as crustal scale boudinage initiated during crustal extension in miocene time since the opposing sense shear zones operated at distinctly different times the paper illustrates the difficulties involved in systematically determining the age of deformation fabrics using 40ar 39ar geochronology and provides a case study that shows the value of carefully designed step heating experiments on microstructurally controlled samples in samples such as these from complex metamorphic tectonites laser fusion or step heating experiments with relatively few steps would have led to erroneous conclusions

40ar 39ar dating of white micas from the epidote to the omphacite zones northern new caledonia tectonic implications an 40ar 39ar study of white micas from high pressure metamorphic rocks of northern new caledonia yielded cooling ages of 37 1 ma for both epidote and omphacite zone samples whole rock samples from the lawsonite zone yielded ages in the range 44 51 ma with complicated age spectra probably reflecting both detrital and newly grown micas the areal extent of the mica samples over 300 km2 suggests that the epidote and omphacite zone rocks cooled through the muscovite closure temperature about 350 c as a coherent cooling unit simple thermal modeling suggests that these rocks could have closed at similar times if the unroofing rate were greater than 2 10 mm a 1 lawsonite zone rocks occur structurally within about 0 5 km of garnet omphacite rocks suggesting the possibility of major postmetamorphic tectonic displacement

tectonic mode switches and the nature of orogenesis abstract the birth and death of many mountain belts occurs in lithosphere that over rides major subduction zones here the tectonic mode shortening versus extension can abruptly switch even during continuous and otherwise smooth convergence if the hinge line of the foundering slab rapidly retreats i e rolls back the foundering slab creates a gravitational potential well into which the orogen collapses this motion coupled with stress guides can pull the orogen apart a slowing of roll back or of hinge retreat means that the subduction flexure may subsequently begin to be pushed back or be pushed over by the advancing orogen the consequence of such changes in relative motion is that orogenic belts are affected by abrupt tectonic mode switches the change from push to pull leads to a sudden change from horizontal extension to horizontal shortening potentially throughout the entire mass of the orogenic lithosphere that over rides the subducting slab the sequencing of these tectonic mode switches affects the thermal evolution of the orogen and thus fundamentally determines the nature of orogenesis this insight led to us to our quite different views as to how orogens work it is evident that orogens affected by abrupt push pull mode switches are characterized by high pressure metamorphism whereas orogens affected by abrupt pull push mode switches are characterized by high temperature metamorphism magmatism and anatexis

on the evolution of orogens pressure cycles and deformation mode switches abstract evidence of two burial exhumation cycles that took place during a single orogeny has been found in rocks belonging to the piemonte unit of the western alps an early high pressure event which resulted from tectonic burial down to pressures of 1 5 gpa was followed by exhumation to ca 0 20 0 35 gpa as a result of extensional deformation renewed shortening culminated in a second burial episode down to pressures of 0 65 0 80 gpa before the final exhumation took place existing geochronological data allow only ca 13 19 ma for the completion of both burial exhumation cycles therefore we suggest that the evolution of orogens is characterized by multiple short lived burial exhumation cycles related to orogen scale alternance between shortening and extensional deformation

recognizing episodic lithospheric thinning along a convergent plate margin the example of the early oligocene alps large scale tectonic mode switches from lithospheric shortening to lithospheric extension may play a fundamental role in the tectonometamorphic evolution of orogens located along convergent plate margins short lived episodes of lithospheric extension can be inferred from the concomitant occurrence of bimodal magmatism rapid exhumation of rock units activity of extensional shear zones steep geothermal gradients and possibly topographic collapse of the orogenic belt here we provide a synthesis of existing data from the european alps supporting the hypothesis on tectonic mode switches data are interpreted to suggest that at ca 38 34 ma a period of n s orogen perpendicular shortening led to the formation of medium to ultra high pressure mineral assemblages by lithosphere scale thrust imbrication a tectonic mode switch took place at ca 34 ma marked by the onset of e w extension during this extensional event internal units of the western and central alps were rapidly exhumed to mid crustal level in the footwall of regional scale extensional shear zones tectonic thinning was also accomplished through pervasive e w stretching of the nappe pile lithospheric stretching resulted in the onset of an anomalous thermal regime which was responsible for the overprint of the older medium to ultra high pressure mineral assemblages by barrovian type mineral assemblages and by migmatization at the same time attenuation of the isotherms led to partial melting of mantle lithosphere and to bimodal magmatism contemporaneous topographic collapse of the orogen is suggested by the deposition in the foreland of flysch units rich in minerals that were probably derived from erosion of the early oligocene calc alkaline volcanics erupted in the hinterland this short lived episode of lithospheric stretching took place in no more than 4 myr from ca 34 ma to ca 32 30 ma renewed lithospheric thickening which is observed in seismic tomography studies resulted in large scale folding of the extensional structures and the in rapid generation of topographic relief feeding abundant clastic sedimentation in the peripheral basins

peri collisional extension and the formation of oman type ophiolites in the banda arc and brooks range integration of data from field geochemistry and radiometric age invcstigations of the active banda arc australia collision zonc banda orogen and the jurassic brooks range ophiolite provide ncw constraints for the origin and emplacement of oman type ophiolites these ophiolites arc characterized by ultramafic residuals and mafic products that arc chemically modified by anous dcgrees of panial melting tile internal structure of thc igneous complcxcs documcnt acutc extcnsional strains a high tcmperaturc metamorphic solc with some contincntal margin protoliths arc locally prcserved at the structural base of the massifs agc relations between the ophiolites their metamorphic snle and collisional mountains in which they reside indicate important temporal and spatial associations somc of these relations arc inconsistent witll ophiolite gcnesis in intra oceanic settings formation of th savu and weber basins around the active banda orogen provide modern analogues of peri collision extensional processes these extensional domains are transitional bctween zoncs of active supra subduction zonc magmatism ophiolitc gcnesis and low angle overthrusting ophiolite emplacemcnt geochemical daw from the volc lilic basemcnt of the savu basin arc similar to transitional type ophiolite volcanic suites arl ar ages and stratigraphic and structural data from the basin indicate volcanism and forearc extcnsion coincide in time and space with initial collision bctween promontorics of the nw australian passive margin and the java trench suggesting a link betwecn the two proccsscs similar age and stratigraphic relations arc also documented in the 3rooks range and other oman type ophiolites peri collisional extension opens small ssz occan basins that may be obdueted during or shonly after thcy fonn by progressive convergencc at multi plate boundaries thcse processes provide a self perpetuating mechanism for ophiolite genesis and emplacement that accounts for both the similar and diversc aspccts of many uphiolitcs

high pressure metamorphism in the aegean eastern mediterranean underplating and exhumation from the late cretaceous until the miocene to recent above the retreating hellenic subduction zone 1 we report 40ar 39ar ages from various tectonic units in the aegean and westernmost turkey on the basis of published geochronologic data and our 40ar 39ar ages we propose that the aegean is made up of several high pressure units which were successively underplated from the late cretaceous until the miocene ages for high pressure metamorphism range from 80 83 ma in parts of the vardar izmir ankara suture zone in the north to 21 24 ma for the basal unit in the cyclades and the external high pressure belt on crete in the south published seismic data suggest that high pressure metamorphism is currently occurring underneath crete younging of high pressure metamorphism in a southerly direction mimics the southward retreat of the hellenic subduction zone we propose that distinct stages of high pressure metamorphism were controlled by the underthrusting of fragments of mainly thinned continental crust and that these punctuated events were superposed on progressive slab retreat by far most of the exhumation of the high pressure units occurred early during the orogenic history in a forearc position

nonlithostatic pressure during sediment subduction and the development and exhumation of high pressure metamorphic rocks a subduction shear zone can be modeled as a long narrow channel with the flow of subducted metasedimentary rocks in the channel driven by two sets of forces the downward shearing force exerted by the subducting slab and the gradient in the hydraulic potential which combines the effect of both pressure and buoyancy if the channel walls are effectively rigid very slight narrowing or broadening of the channel convergence angles 2 gpa in the channel at only 40 km depth the model is consistent with a horizontal balance of forces across the plates and with a reasonable value for the thickness of subducted sediment 650 m the practical limit for overpressures attainable in subduction zones is determined by the strength and permeability of the channel walls at 40 km depth the channel is effectively confined on both sides by cold lithospheric mantle which should be strong enough to support a significant tectonic overpressure episodic failure of the upper plate to produce great earthquakes at 30 40 km focal depth could vent overpressured fluid from the channel allowing a cyclical buildup and release of both rock and fluid pressure topography on the subducting plate e g seamounts and thinned continental crust may lead to an anvil like jamming of the channel and local high overpressures tectonic erosion by topography on the lower plate of slivers from overlying continental crust and the compression of these slivers between the topography and the narrowing channel walls could produce high overpressures in continental rocks a decrease in the convergence rate or cessation of subduction with a consequent general warming within the channel and associated viscosity decrease promotes exhumation by buoyant reverse flow the most rapid reverse flow occurs in the region of previously greatest overpressure since the exhumation distance is shorter than for a simple lithostatic pressure distribution and any increase in temperature is coupled with a strong increase in the rate of exhumation preservation of high pressure assemblages at the surface in fossil subduction zones is promoted for such a model

prograde sulfide metamorphism in blueschist and eclogite new caledonia in new caledonia blueschist and eclogite preserve as inclusions in porphyroblastic minerals a record of sulfide present during prograde subduction processes sulfide inclusions in prograde garnet and lawsonite became chemically isolated from the matrix whereas sulfide minerals in the matrix continued to equilibrate with matrix fluids or grew later during retrogression cu fe sulfide mineral inclusions have been found across metamorphic grade within silicate defined metamorphic mineral zones spanning a crustal profile of 30 km bulk area scans of sulfide inclusions provide compositions that represent mixtures of the solid sulfide that were included as the host silicate minerals grew in general single sulfide inclusion compositions and aggregate sulfide assemblages are distinct from those of matrix phases high cu contents in sulfide inclusions are interpreted to be a consequence of fe lost from sulfide to growing garnet rather than the result of intrinsically high cu in the bulk rock the distribution of sulfide inclusion compositions across metamorphic grade considered together with the available thermodynamic data suggests that covellite nukundamite bearing inclusions in lawsonite high in both cu and s disappear at higher grades as these sulfide minerals are no longer stable similarly clustering near the ratio fe cu 1 1 may cease with increasing grade owing to the replacement of chalcopyrite intermediate solid solution iss by the denser assemblage pyrite pyrrhotite bornite digenite

very low grade metamorphic evolution of pelitic rocks under high pressure low temperature conditions nw new caledonia sw pacific the p t gradient in a late eocene low t high p metamorphic belt in northern new caledonia increases from sw to ne metapelites in the pumpellyite prehnite and blueschist zones contain lawsonite mg carpholite fe stilpnomelane and fe glaucophane thermodynamic calculations indicate a progression of metamorphic conditions from less than 0 3gpa and 250 c in a kaolinitebearing rock in the sw up to 1 5gpa and 410 c in a lawsonite glaucophane bearing sample in the ne of the diahot terrane through a multi method investigation of phyllosilicates organic matter and fluid inclusions we demonstrate that the evolution of organic matter and illite crystallinity depends strongly on the evolution of the p t path with time in addition we show that the illite muscovite b cell dimension provides a robust estimate of maximum pressure reached in low temperature domains with polyphase metamorphic histories despite subsequent hightemperature low pressure events fluid inclusion study reveals an isothermal decompression in the diahot terrane

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

tectonic and metamorphic architecture of the hp belt of new caledonia abstract new caledonia includes a well exposed example of high pressure orogenic belt formed as a result of cenozoic plate tectonic reorganizations at the australia pacific plate boundary the metamorphic belt is relatively well accessible and has deserved extensive attention mainly for its metamorphic and petrological features the architecture of this belt however still lacks general consensus the aim of this paper is i to review the nature and origin of the main tectonic units of the belts and ii to revisit the available structural models describing its architecture and geodynamic evolution for that we integrate the available field petrological geochemical and geochronological data together with new results from large scale field survey and focused ar ar geochronological data all together these data allow proposing a new model for the tectonic and metamorphic architecture of the belt also comprising a newly established tectonostratigraphic unit this architecture resembles that characterizing alpine type metamorphic belts formed in non pacific settings and clearly differs from cordilleran type belts found in eastern pacific regions moreover the collected data also allow refining our understanding of the oceanic and transitional oceanic lithosphere involved in the eocene subduction and plausible analogies with hyper extended margins known in present day ocean continent transition zones

deepwater fold and thrust belt along new caledonia s western margin relation to post obduction vertical motions classically deepwater fold and thrust belts are classified in two main types depending if they result from near or far field stresses and the understanding of their driving and triggering mechanism is poorly known we present a geophysical dataset off the western margin of new caledonia sw pacific that reveals deformed structures of a deepwater fold and thrust belt that we interpret as a near field gravity driven system which is not located at a rifted passive margin the main factor triggering deformation is inferred to be oversteepening of the margin slope by post obduction isostatic rebound onshore erosion of abnormally dense obducted material combined with sediment loading in the adjacent basin has induced vertical motions that have caused oversteepening of the margin detailed morpho bathymetric seismic stratigraphic and structural analysis reveals that the fold and thrust belt extends 200 km along the margin and 50 km into the new caledonia trough deformation is rooted at depths greater than 5 km beneath the seafloor affects an area of 3500 km2 and involves a sediment volume of approximately 13 000 km3 this deformed belt is organized into an imbricate fan system of faults and one out of sequence thrust fault affects the seabed the thrust faults are deeply rooted in the basin along a low angle floor thrust and connected to new caledonia island along a major detachment this study not only provides a better knowledge of the new caledonia margin but also provides new insight into the mechanisms that trigger deepwater fold and thrust belts

what brought them up exhumation of the dabie shan ultrahigh pressure rocks metamorphic coesite and diamond in the dabie shan eastern china testify to subduction of continental crust to 100 km depth exhumation of these ultrahigh pressure rocks through the crust encompassed two stages 1 south dipping foliation southeast plunging stretching lineation lineation parallel isoclinal folds and boudins indicate extreme subhorizontal shortening and subvertical extension during top to northwest shearing at 200 180 ma syntectonic recrystallization occurred at eclogite and amphibolite facies temperatures and at pressures below coesite stability 2 northwest southeast subhorizontal extension from 133 to 122 ma was concentrated within an asymmetric structural dome in a magmatic complex that forms the northern half of the dabie shan pluton cores at deep structural levels have weak hypersolidus fabrics and pluton carapaces are mylonitic gneisses formed at upper amphibolite facies conditions deformation is concentrated in greenschist facies mylonites and ultramylonites along the xiaotian mozitang detachment fault at the northern topographic limit of the dabie shan our preferred exhumation model involves two stages triassic indentation vertical extrusion and erosion followed by cretaceous plate margin transtension

continental subduction and a mechanism for exhumation of high pressure metamorphic rocks new modelling and field data from oman abstract the physical model presented reveals two principal regimes of continental subduction a highly compressional hc regime and a low compressional lc regime characterised by high and low pressure between the overriding and subducting plates respectively the pressure is inversely proportional to the pull force which depends on the difference between average density of the subducting lithosphere and density of the mantle the subducting continental crust reaches a maximum depth which is proportional to the strength of the crust inversely proportional to the interplate pressure and is ca 200 km on average the crust then fails forming a major crustal thrust the location of failure depends on the regime of subduction on the interplate pressure in the hc regime failure occurs near the front of the subduction collision zone whereas the crust fails at greater depth under the base of the overriding plate in the lc regime the failure is followed by buoyancy driven uplift of the subducted crustal slice while the lithospheric mantle keeps subducting the uplift causes a normal sense displacement formation of a normal fault along the upper surface of the crustal slice for the lc regime failure of the crust near the base of the overriding plate a rapid spontaneous crustal uplift intrusion into the interplate zone brings the deeply subducted crust to shallow depths under the pressure of this crust the frontal part of the overriding plate undergoes local extension and then fails forming a tectonic window the rising material the high pressure rocks is exhumed within this window in the hc regime uplift of the subducted crust after its failure in front of the overriding plate is possible only with erosion of the relief which provides an unloading effect allowing the subducted crustal slice to rise up the exhumation depth is generally smaller in this regime but the volume of the exhumed material is larger the hc subduction regime has been shown earlier to match the himalayan situation the lc regime fits the situation in the oman mountains considered in this paper

natural and artificial recharge investigation in the zeroud basin central tunisia impact of sidi saad dam storage hydrochemical and isotopic data of waters from the zeroud aquifer have been used to potentially provide a means for locating occurrences and to trace movements of a variety of natural and anthropogenic recharge waters in the zeroud basin central tunisia geochemical data have been measured during the dam water release from may to september 2005 with a sampling time step of 15 days an implication of dam water has been demonstrated that is noticeable up along the main flow path to a distance of 10 km far from the injection site environmental isotopes 2h 18o and 3h of water molecule were studied to investigate the effect of dam water on the hydrological system and an isotope balance was established to compute the contribution of water storage component in groundwater based on isotopic mass balance we assess that an average of 13 of total groundwater in the upper aquifer came from dam water storage three distinctive recharge waters in the aquifer can be determined water from local rainfall pre dam zeroud river that infiltrated into the boundaries of the draa affane mountain was easily distinguished from the water influenced by anthropogenic recharge located in the zeroud right rivulet distinguishable isotopic signatures of native wadi zeroud recharge due to recent lineal recharge through the riverbed were also identified

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

assessment of sharp interface approach for saltwater intrusion prediction in an unconfined coastal aquifer exposed to pumping water over exploitation becomes a common problem in coastal aquifers as it disarranges the dynamic equilibrium of saltwater and freshwater and causes saltwater intrusion swi mathematical simulations become a necessary tool nowadays to predict swi under future pumping scenarios this study aims to assess the validity of sharp interface approach for an unconfined coastal aquifer subjected to pumping by comparison with sand tank observation and dispersive approach results the comparison was in terms of 1 transient movement of saltwater toward the well screen and 2 prediction of well salinity in times the sharp interface approach produced acceptable results although it over predicted the toe position of saltwater wedge salinity of extracted water was less predicted by sharp interface modeling the sharp interface approach was then applied for a synthetic field scale unconfined aquifer in steady condition with different pumping rates and well placements to explore the sensitivity of the modeling the results were compared with salinity contours of dispersive modeling the sharp interface approach produced better result for higher pumping rates where the saltwater was reached to the well screen additionally the results of fully penetrating wells compare to partially penetrating one and also closer location of well to shoreline matched better with the dispersive modeling outputs in real cases where the saltwater may wend a long distance toward the well screen the sharp interface modeling weakly matched with the dispersive modeling specially in terms of well salinities that is attributed to wider mixing zone

storage in confined aquifer spectral analysis of groundwater responses to seismic rayleigh waves summary it is frequently found that the fluctuations observed in aquifer well systems demonstrate high coherence to nearby boundary disturbances or more specific in response to the vertical motion of seismic rayleigh waves this study derives the spectral relationship between groundwater head and vertical displacement disturbed by rayleigh waves in the time frequency domain essentially the groundwater storage property e g storage coefficient or specific storage representing the amount of water released from storage when the head changes from water expansion and aquifer compression occur they can be determined using the spectral representation of the factors associated to groundwater head and rayleigh waves for this study the sumatra andaman islands earthquake with magnitude 9 at ut 2004 12 26 00 58 53 45 is used as the seismic source while a groundwater monitoring well and a seismological station located on the east of taiwan acted as the receivers the time series data associated with the observed groundwater head and vertical displacement of rayleigh waves are used to evaluate spectral response analyzing the autospectral density cross spectral density and coherence between them the resultant spectral estimates can be used to determine the storage coefficient and specific storage of the case site to be on the order of 10 3 and 10 4 m 1 respectively in addition the matrix bulk modulus also demonstrated a linear trend with porosity by taking the value of standard water modulus it suggests that the storage of an aquifer can be robustly estimated using spectral representations and responses from head changes in groundwater and vertical displacement of rayleigh waves

cyanide from gold mining and its effect on groundwater in arid areas yanqul mine of oman the use of cyanide cn which is characterized by volatility toxicity and high odor in gold mining is scarcely addressed in the literature and remain controversial environmentalists oppose cn usage as it potentially poses serious environmental threats whereas economic and mining geologists are in favor of its usage for its extracting capacity and economic feasibility the present study investigates the possible dispersion of cn into groundwater resources caused by a gold mine ca 15 years old located in the arid area of yanqul north oman the gold is hosted in gossan deposits associated with ophiolitic rocks and sulfide deposits sodium cyanide is mixed with 0 5 m3 of water and then added to a tonne of crushed ore rock to extract 6 g of gold mineral the final residues are dumped in engineered lined and uncovered tailing dams subsequent to rainfall water draining the mine plateau flows along the wadies and percolates into the shallow quaternary alluvium aquifer hence groundwater samples were collected from 16 piezometers adjacent to and around the mine the samples were analyzed for cn using the revised phenolphthalin method and they all show cn concentration below the detection limit 5 ppb the samples were also analyzed for heavy metals to investigate the potential of cn complexation most of heavy metals indicated very trace concentration the absence of cn in groundwater is attributed to volatilization of cn converted to hcn lined dam structure high evapotranspiration rate and deeper water table this finding is consistent with the historical cn analysis in the groundwater and solid wastes it can be pointed out that within few years of operation well engineered tailing dams can provide safe structure preventing cn groundwater pollution in arid areas potential threats to the air and soil are not addressed in this article

application of spectral analysis to determine hydraulic diffusivity of a sandy aquifer pingtung county taiwan the study demonstrates spectral relationships in the time frequency domain for one dimensional groundwater flow in aquifers bounded by fluctuating boundaries by nature the solutions of spectral equations are non linear complex functions to determine hydraulic diffusivity in the governing equations it is required that the data are collected from the spectra of water levels at the fluctuating boundaries and observation wells hydraulic diffusivity thus can be obtained by an iterative inverse approach this paper presents an application in pingtung county of taiwan to determine the hydraulic diffusivity of a sandy aquifer under confined conditions spectral density function of water level obtained from tidal boundaries and observation wells are used to approximate hydraulic diffusivity which yields an averaged value of 1 26 10 6 m 2 h copyright 2004 john wiley sons ltd