western hellenic subduction and cephalonia transform local earthquakes and plate transport and strain abstract focal parameters of local earthquakes in the region of the ionian islands of western greece are constrained with a temporary dense array of three component seismographs operated jointly offshore and onshore seismic deformation is documented to be confined to the east of the n20 e striking steep continental slope west of cephalonia island the right lateral cephalonia transform fault ctf inferred from large earthquakes the pre apulian continental material appears to be only deforming east of the transform fault where it is in upper plate position to the hellenic subduction east of the transform fault the transmission velocity tomography from local earthquakes compared in depth section with a previous marine reflection profile provides evidence in support of a shallow landward dipping boundary around 12 km deep under the ionian islands along which they may override the lower plate on either side of this interface local earthquakes occur with different focal mechanisms in support with its interpretation as the interplate under cephalonia island reverse faulting deforms the upper plate along nw se structures which may also be affected by left lateral bookshelf faulting small earthquakes show normal faulting along the western coast of cephalonia and its extension 20 km ssw the trace of the ctf as inferred from the occurrence of the large strike slip earthquakes another group of normal fault earthquakes locates in the lower plate from under cephalonia to zante just outboard of a possible change of interplate dip suggested from reflection seismics landward under the islands these normal fault earthquakes appear to coincide in position with that of the load imposed by the upper plate transported over them rather than occurring in an outer rise outboard the plate boundary and trench as observed in other subductions and attributed to the control by the flexural bending of the lower plate under the pull of the sinking slab interpretation has to consider several peculiar features of plate interaction in western greece with respect to a steady state model for major subduction zones in particular a fast deformation of the upper plate in front of an orogenically overthickened crust and of the southwestward push of extruding anatolia its transport which is the cause of the migration of the plate boundary rather than the roll back of a slab which has been proposed to be detached possibly a flat and ramp shape of the interplate the geometrical complexity of the shear limit across the ctf between subduction and collision and the nearby variation of the nature of the foreland crust

crustal stress and seismic activity in the ionian archipelago as inferred by satellite and ground based observations kefallinia greece different observational techniques are compared in order to investigate possible correlations in seismic activity the study site is the island of kefallinia greece where measure ments available included 1 dinsar dgps and dem data 2 soil exhalation measured by monitoring radon rn well content and 3 acoustic emissions ae at high and low frequency point like records with high temporal resolution ae records provide 1 relative time variation of the applied stress intensity and 2 the state of fatigue of stressed rock volumes the ae source our results indicate that the large spatial scale poor time resolution may be considered quite sat isfactory whereas fractal analysis of the ae time series displayed some discrepancies when com pared to analogous investigations in the italian peninsula therefore some refinement is needed in order to reach more precise interpretations of the relevant information available with this kind of data however both sets of observations appear in agreement with each other although more exhaustive investigations would require a suitable array of point like ae and rn or other measuring sites as well as longer data series the latter are particulary helpful for detailed interpretations of the different occurrences within tectonically complex settings where crustal stress crises are marked by various types of geological phenomena

geochemical investigations of selected eastern united states watersheds affected by acid deposition the effects of acid deposition on surface waters in eastern united states watersheds having similar size physiography climate and land use are related to the composition of the underlying bedrock watersheds developed on greenstone calcareous shale sandstone granite and schist differ in their ability to neutralize acid deposition surface waters in watersheds developed on greenstone and calcareous shale are not discernably affected by acidification wastersheds developed on sand stone have little capacity to neutralize acid rain consequently stream acidity is similar to that of precipitation watersheds developed on granite and schist are intermediate in their capacity to neutralize acid deposition bedrock composition appears to be the major property controlling surface water chemistry in these systems hydrologic flow paths and the nature of surficial materials and vegetation also influence chemical responses to acid deposition in watersheds

kinematic links between subduction along the hellenic trench and extension in the gulf of corinth greece a multidisciplinary analysis abstract rapid northeast vergent subduction along the hellenic trench at 35 mm yr exists in concert with widespread extensional and strike slip faulting within the upper plate lithosphere of western greece integration of regional geomorphic geologic seismic gps remote sensing and field data demonstrates that young and active deformation in the area extending from the hellenic subduction boundary near kephalonia to the gulf of corinth consists of an interconnected network containing highly localized zones of deformation these bound a series of crustal fragments with relatively little internal deformation these deformation zones merge to form triple junction like features at the western end of the gulf of corinth and in the amvrakikos gulf at the western end of the corinth gulf most of its 14 2 mm yr of extension is relayed to the northwest along a prominent zone of left slip and extension through lake trichonis and the amphilochia fault zone 11 2 mm yr the remaining displacement across the western gulf of corinth is relayed into 7 2 mm yr of right slip on the southwest striking achaia fault zone which traverses the northwestern margin of the peloponnesus a second triple junction like feature occurs in the amvrakikos basin where the left slip amphilochia fault zone the right slip kephalonia transform fault 15 2 mm yr and the convergent thrust front of northern hellenides 4 2 mm yr are joined thus the extensional deformation in the gulf of corinth can be shown to be connected to convergence and subduction along the hellenic trench through a series of discrete deformation zones that are not dissimilar from those observed in the global plate tectonic system

hydrogeochemical cycling and chemical denudation in the fort river watershed central massachusetts an appraisal of mass balance studies the fort river watershed in central massachusetts receives precipitation with a composition similar to that in hubbard brook new hampshire yet the average stream water chemistry is substantially different showing higher ph and tds this is largely a function of bedrock and surficial geology and chemical differences among small streams within the fort river watershed are apparently controlled by the composition and thickness of the prevailing surficial cover the surficial deposits determine groundwater and surface water flow paths thereby affecting the resultant contact time with mineral matter and the chemistry of the runoff despite the rural setting over 95 of the annual sodium and chloride in the streams comes from road salt after correcting for this factor cation denudation rates are about equal to those at hubbard brook however silica removal is occurring at a rate more than 30 greater in the fort river when climatic conditions in hubbard brook and fort river are normalized weathering rates appear consistently higher in the fort river reflecting differences in weathering processes i e cation exchange and silicate breakdown and hydrogeology because of uncertainties in mechanisms of cation removal from watersheds the silica denudation rate may be a better index of weathering intensity

factors controlling the major ion chemistry of streams in the blue ridge and valley and ridge physiographic provinces of virginia and maryland the factors controlling the chemistry of 69 low order streams in the blue ridge and valley and ridge physiographic provinces of virginia and maryland were studied over a 13 month period principal component analysis was used to examine regional patterns in stream chemistry and to examine the degree to which the chemistry of low order streams is controlled by the bedrock upon which they flow streams clustered into regionally isolated groups strongly related to bedrock type with so2 4 and hco 3 the chemical variables of most importance sulphate concentrations appear to be strongly controlled by climate and hydrology and sorption in the soils within the watershed much of the atmospherically derived so2 4 accumulates in watersheds during the growing season and is later flushed out weathering reactions were found to be particularly important in the production of hco 3 accounting for 91 per cent on an annual basis and export of divalent cations from these watersheds accounting for 48 50 per cent on an annual basis about half of non anthropogenic na was derived from weathering of silicates whereas nearly all k was identified with leaching by so2 4 water chemistry was strongly related to the rock type in the watershed and the weatherability of the component minerals rock type is not a randomly distributed function instead it is controlled by geologic factors that result in clusters of similar rock types in a given region when planning large synoptic studies it is extremely important to consider that a sampling scheme based on random sampling of a non randomly distributed function may not provide the most accurate representation of the variables of interest instead a hierarchical sampling scheme may be indicated our results also suggest that although one sample in time may be sufficient to characterize the primary geochemical factors controlling stream chemistry throughout the year it may not be sufficient to detect subtle flow related alterations in chemistry

gondwana breakup and plate kinematics business as usual 1 a tectonic model of the weddell sea is built by composing a simple circuit with optimized rotations describing the growth of the south atlantic and sw indian oceans the model independently and accurately reproduces the consensus elements of the weddell sea s spreading record and continental margins and offers solutions to remaining controversies there at their present resolutions plate kinematic data from the south atlantic and sw indian oceans and weddell sea rule against the proposed but controversial independent movements of small plates during gondwana breakup that have been attributed to the presence or impact of a mantle plume hence although supercontinent breakup here was accompanied by extraordinary excess volcanism there is no indication from plate kinematics that the causes of that volcanism provided a unique driving mechanism for it

evidence for a two phase palmer land event from crosscutting structural relationships and emplacement timing of the lassiter coast intrusive suite antarctic peninsula implications for mid cretaceous southern ocean plate configuration 1 new analysis of the relationships between geological structural data and radiometric ages for the lassiter coast intrusive suite indicate that the collisional mid cretaceous palmer land event orogeny in the antarctic peninsula has had two kinematic phases forming an intersection orocline one of which can be related to cretaceous southern ocean plate motions both are compressional phases along the eastern palmer land shear zone phase 1 occurred at 107 ma with a principal paleostrain axis of 341 and is best expressed in southern palmer land although evident elsewhere on the antarctic peninsula phase 2 occurred at 103 ma with a principal paleostrain axis of 259 5 but is confined to between 68 s and 74 s a peak in lassiter coast intrusive suite magma emplacement rate was coeval with phase 1 whereas phase 2 may have coincided with a lull during phase 1 the allochthonous central and western domain terranes may have been transported to the gondwana margin represented by the para autochthonous eastern domain on board the phoenix plate or on board the south american plate the variable provenance indicators from the central and western terranes can be cited to support either or a combination of these scenarios the convergence direction evident from phase 2 structures cannot easily be reproduced in regional plate kinematic models this and the localized evidence for superposition of phase 2 structures on phase 1 structures suggests that phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered

cretaceous demise of the moa plate and strike slip motion at the gondwana margin radiolaria and paleomagnetic data from deep sea drilling project sites 595 and 596 indicate that early cretaceous seafloor was formed at moderate to high latitudes in the pacific this inference requires a cretaceous spreading ridge south of the pacific phoenix ridge and substantial dextral strike slip motion at the gondwana margin the previously unrecognized southern oceanic plate called here the moa plate was obliquely subducted beneath the gondwana margin and material accreted from it is now part of the eastern province of new zealand

late cenozoic deformation of the hellenide foreland western greece the late cenozoic structural evolution of western greece involved the shortening of mesozoic passive continental margin and cenozoic foreland basin sequences in a foreland propagating fold and thrust system and superimposed neotectonic deformation related to the development of an active island arc although the pre apulian zone has been regarded as the undeformed western foreland to the thrust belt three dimensional exposures in the ionian islands of kephalonia and zakinthos afford evidence of significant late neogene and quaternary shortening including thrusting on reactivated normal faults time relations and fault kinematics show that these structures are compatible with the westward migration of the locus of hellenide thrusting beyond its previously recognized limit and outer arc compression related to active subduction the presence of the pre apulian zone in the west contrasts with other aegean foreland areas where no such intermediate block lay between the thrust pile and old mesozoic oceanic crust consequently the pre apulian block took up continued hellenide shortening in the late miocene while oceanic crust was being overridden subducted in southern parts of the arc to the east the pre apulian zone subsequently overrode the ocean floored ionian sea during the late neogene the confusion in determining driving mechanisms for late cenozoic deformation in western greece and the apparent conflict between evidence for the age of initial subduction in different parts of the arc are explained by this model which is consistent with regional considerations including structuration in adjacent areas and important paleomagnetic rotations in the arc

iterative deconvolution of regional waveforms and a double event interpretation of the 2003 lefkada earthquake greece the moment tensor inversion for multiple point sources based on kikuchi and kanamori 1991 was extended to full waveform data at regional or local distances the new code proved to be efficient for retrieving major source contributions of the 2003 lefkada greece earthquake the source model was derived from five three component regional stations epicentral distances 140 km at periods 10 20 s two main events dominated the rupture process one at the lefkada island comprising three subevents of total moment 0 9 1018 n m and the other at the cephalonia island comprising one subevent of 0 5 1018 n m their spatial and temporal separation is 40 km and 14 s respectively they can be understood as two earthquakes the uncertainty estimate based on reduced data sets repeatedly excluding a station shows that the cephalonia subevent and the major lefkada subevent are very well resolved regarding their position time and focal mechanism the source model explains well the aftershock distribution characterized by two clusters at the lefkada and cephalonia islands respectively the focal mechanisms of the two main subevents are predominantly right lateral strike slip of south southwest north northeast orientation the cephalonia subevent occurred on a less steeply dipping fault with a small thrust component large deviations from pure double couple were found but interpreted as artifacts the new software developed in this article fortran code and matlab graphic user interface is freely available online material color graphics and 3d visualization of the 2003 lefkada earthquake sequence

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

cretaceous oblique extensional deformation and magma accumulation in the fosdick mountains migmatite cored gneiss dome west antarctica 1 the fosdick mountains west antarctica expose a 15 x 80 km migmatite cored gneiss dome consisting of migmatitic gneisses diatexite migmatite and subhorizontal leucogranite sheets the fosdick dome was emplaced and exhumed in the mid cretaceous due to oblique extension associated with the west antarctic rift system along the west antarctic new zealand segment of east gondwana the dome is bounded to the south by a dextral oblique detachment structure and to the north by an inferred dextral strike slip fault within the fosdick dome and in the detachment zone granite occupies leucosomes dikes sills and dilatant and shear structures the pattern of kilometer scale domains of migmatite and granite suggest that lithologic variations and heterogeneous deformation boudinage resulted in pressure gradients that enhanced melt flow and magma accumulation in the fosdick dome steep foliations are overprinted folded and transposed by subhorizontal fabrics the crosscutting relationship is interpreted as a transition from wrench deformation to oblique divergence steep structures in the dome host concordant subvertical leucosome and granite sheets yielding shrimp u pb zircon ages between ca 117 and 114 ma prevalent subhorizontal domains host large volumes of subhorizontal diatexite migmatite and granite sheets that yield u pb zircon ages between ca 109 and 102 ma these ages indicate a timescale for melt influx of approximately 15 ma and that the transition from wrench to oblique divergence may have occurred in as little as 5 ma granites with crystallization ages between ca 109 and 102 ma were also emplaced in the south fosdick detachment zone indicating that the detachment was active during oblique divergence shrimp u pb titanite ages between ca 102 and 97 ma for late to post tectonic diorite dikes are interpreted as emplacement ages and give a minimum age for gneissic foliation development during detachment faulting the fosdick mountains preserve a record of the middle to lower crustal response to a transition from wrench to oblique extensional deformation overprinting structural relationships show that a change in the angle of oblique extension can induce accumulation of subhorizontal magma sheets and lead to initiation of a detachment zone

mesozoic radiolarian faunas from the antarctic peninsula age tectonic and palaeoceanographic significance new assemblages of radiolaria including some of the few occurrences of high southern latitude jurassic and cretaceous radiolarian faunas show that several localities in the lemay group of alexander island range in age from latest jurassic earliest cretaceous to at least albian by demonstrating that sedimentation and deformation in the lemay group was diachronous younging oceanwards to the northwest these new age assessments support the model of the lemay group as an accretionary complex the polarity of subduction beneath alexander island was not affected by arc collisions from at least the lower jurassic to the oligocene and such a long period of continuous accretion appears to be unusual deposition of the lemay group spans the kimmeridgian to albian sedimentation in the fossil bluff group fore arc basin thus making the earlier concept of the lemay group as pre jurassic basement untenable allochthonous latest jurassic earliest cretaceous radiolarian assemblages with some supposed tethyan affinities are present in the lemay group in contrast an in situ latest jurassic assemblage from the nordenskjold formation of the back arc basin and a further jurassic assemblage from a probable trench slope basin have characteristics believed diagnostic of high latitudes the biogeographic affinities of radiolarians from cherts in the lemay group accretionary complex suggest that both these cherts and associated basalts are far travelled slices of the phoenix plate rocks from the probable trench slope basin formerly assigned to the younger fossil bluff group fore arc basin sequence now appear to be part of a new previously unrecognized formation

the cephalonia transform fault and its extension to western lefkada island greece the central area of the ionian islands is dominated by the existence of a major tectonic structure called the cephalonia transform fault ctf its main part cephalonia segment has been identified by previous work based on the spatial distribution of earthquake foci fault plane solutions of strong earthquakes active tectonics structural studies and geodetic measurements this part cephalonia segment which exhibits strike slip motion with a thrust component strikes in a northeast direction dips to the southeast and has a length of 90 km in the present paper information concerning new fault plane solutions orientation of isoseismals sea bottom topography and recent gps results are used to further check the properties of this southern part of the ctf and to explore its northeastward prolongation to lefkada island it is shown that the ctf is extended to the western coast of lefkada this northern branch lefkada segment of the ctf which is also characterized by strike slip motion with a thrust component strikes in a north northeast direction dips to the east southeast and has a length of 40 km these two segments of the ctf form a major kinematic boundary where the slip rate is 2 3 cm yr

aluminium solubility controls in acid waters the need for a reappraisal abstract stability diagrams have been frequently used to demonstrate aluminium solubility controls in acidic stream and soil waters this paper shows that it is possible by this method to generate apparent controls using random numbers in place of stream chemistry data thermodynamic arguments demonstrate that a wide variety of reactions can produce relationships similar to al oh 3 solubility controls it is proposed that stability diagrams alone should be used with great caution in identifying aluminium solubility controls taking care that their axes are independent thermodynamic solubility calculations should be used with due scepticism supplementary investigations should be used where possible to identify phases precipitating or dissolving

mass balance modeling of mineral weathering rates and co2 consumption in the forested metabasaltic hauver branch watershed catoctin mountain maryland usa mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested metabasaltic hauver branch watershed in north central maryland usa previous studies of hauver branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering including biomass more equations in the mass balance matrix were added using existing mineralogic information the stoichiometry of a deciduous biomass term was determined using multi year weekly to biweekly stream water chemistry for a nearby watershed which drains relatively unreactive quartzite bedrock at hauver branch calcite hosts 38 mol of the calcium ion ca2 contained in weathering minerals but its weathering provides 90 of the stream water ca2 this occurs in a landscape with a regolith residence time of more than several ka kiloannum previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream ca2 na ratios the relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone of the carbon dioxide co2 consumed by mineral weathering calcite is responsible for approximately 27 with the silicate weathering consumption rate far exceeding that of the global average the chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles and therefore climate on geological timescales based on carbon balance calculations atmospheric derived sulfuric acid is responsible for approximately 22 of the mineral weathering occurring in the watershed our results suggest that rising air temperatures driven by global warming and resulting in higher precipitation will cause the rate of chemical weathering in the hauver branch watershed to increase until a threshold temperature is reached beyond the threshold temperature increased recharge would produce a shallower groundwater table and reduced chemical weathering rates copyright 2013 john wiley sons ltd

geochemical mass balances and weathering rates in forested watersheds of the southern blue ridge ii effects of botanical uptake terms abstract geochemical mass balance methods are commonly used in small watershed studies to estimate rates of primary mineral weathering and soil formation and the contribution of these processes to cation budgets nutrient cycling and landscape susceptibility to acid deposition many researchers employ the balance sheet approach a system of simultaneous linear equations with constant coefficients which represent the steady state behavior of the modelled system most workers also assume that the steady state assumption for the entire system means that botanical factors can be ignored in other words that there is no net elemental transfer between biomass and inorganic compartments of the system however the widely invoked assumption that biomass is at steady state is mathematically a second explicit assumption not a built in mathematical consequence of the assumption of overall steady state the common assumption that the biomass is necessarily at steady state in a steady state system ignores the possibility of uptake of elements into the forest biomass to quantify the implications of the separate mathematical assumptions weathering rates for seven forested watersheds in the southern blue ridge mountains are calculated twice once allowing for net element exchange with biomass and once assuming no net exchange with biomass our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors underestimates of up to a factor of 4 in the calculated rates of mineral weathering and soil formation this problem is most pronounced for minerals which contain major nutrient elements and for rates calculated from mass balances of those nutrient elements

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

new constraints on the rapid crustal motion of the aegean region recent results inferred from gps measurements 1993 1998 across the west hellenic arc greece abstract in this paper we present the most recent observations of crustal motion across the entire west hellenic arc wha these are based on repeated gps measurements carried out in the period from 1993 to 1998 the results are presented in terms of trajectories and rates relative to eurasia within these five years southwestern greece has moved to the southwest by an average rate of 30 mm a increasing from 10 mm a at the island of lefkada in the center of the ionian islands to nearly 40 mm a along the southwest part of the peloponnesus and to 35 mm a on the islands of crete and gavdhos the data provide strong evidence that distributed shear strain starts at the kephalonia fault zone kfz were an anomalously high earthquake activity is also observed a striking interruption of the motion is seen at the island of strofades at the southwest leading edge of the wha where a south oriented displacement of 12 cm was detected coincident with the m 6 4 strofades earthquake of nov 18 1997

a window on west antarctic crustal boundaries the junction between the antarctic peninsula the filchner block and weddell sea oceanic lithosphere abstract a new airborne magnetic survey of the southeastern antarctic peninsula and adjacent weddell sea embayment wse region suggests a continuity of geological structure between the eastern antarctic peninsula and the attenuated continental crust of the filchner block this has implications for the reconstructed position of the ellsworth whitmore mountains block in gondwana which is currently uncertain palaeomagnetic data indicate that it has migrated from a palaeozoic position between south africa and coats land to its current position as a microplate embedded in central west antarctica the most obvious route for migration is between the antarctic peninsula and the weddell sea embayment evidence that geological structures are continuous across the boundary places constraints on the timing and pathway of migration magnetic textures suggest the presence of shallow features extending from the beaumont glacier zone bgz in the west for at least 200 km into the weddell sea embayment these data suggest that the eastern domain of the antarctic peninsula and the stretched continental crust of the filchner block share a common recent probably post early jurassic history however examination of deep anomalies indicates differences in the magnetic characteristics of the two blocks the boundary may mark either the edge of extended continental crust or a discontinuity between two once separated blocks this discontinuity or pre late jurassic antarctic peninsula terrane boundaries to the west may have allowed the passage of the ellsworth whitmore mountains block to its present location

role of strike slip faulting in the tectonic evolution of the antarctic peninsula the antarctic peninsula mesozoic magmatic arc has had a long history of dextral strike slip deformation the deformation was initially associated with the development of a wide accretionary complex by the migration of fore arc slivers and the formation and inversion of a thick fore arc basin succession it also formed an important component within major shear zones in the arc and may have controlled the formation of sedimentary basins in the back arc region although some transcurrent motion within the fore arc region was related to a component of oblique subduction the main movement occurred during the breakup of gondwanaland and the formation of a major transtensional rift system a new reconstruction for this part of gondwanaland is presented taking this transcurrent motion into consideration

computer assisted discrimination of morphological units on north central crete greece by applying multivariate statistics to local relief gradients traditional manual methods have been employed for decades to measure geomorphometric properties from topographic maps such measurement techniques tend to be tedious and time consuming and the designated landform elements cannot be easily overlaid on any digital map and imagery for further applied research this study deals with a new quantitative geomorphometric procedure based on the multivariate statistical analysis of local topographic gradients within a part of northcentral crete this method employs sets of computer algorithms that automatically extract and classify geomorphometric properties from digital elevation models dems this was done by evaluating the morphological setting around each pixel of the dem along the eight azimuth directions isodata unsupervised classification was implemented to generate 10 morphometric classes showing the spatial distribution of areas with a similar geomorphic scenario results revealed that this approach permitted a quick estimation of the spatial distribution of morphologically homogeneous terrain units it also demonstrated the ability of the delineated landform elements to be superimposed on any digital map and imagery for further investigation this became apparent during the examination of the relationship between the geomorphological units and the land cover land use types in the study area both relative association and the dominant land cover land use types in relation to geomorphological units are presented d 2003 elsevier b v all rights reserved

mapping small elevation changes over large areas differential radar interferometry a technique that uses synthetic aperture radar sar images to measure very small 1 cm or less surface motions with good resolution 10 m over large swaths 50 km is presented along with experimental results the method could be used for accurate measurements of many geophysical phenomena including swelling and buckling in fault zones residual displacements from seismic events and prevolcanic swelling the method is based on sar interferometry where two images are made of a scene by simultaneously flying two physically separated antennas then the phases of corresponding pixels are differenced and altitude formation is deduced from some simple computation and image rectification it is also possible to use one antenna flown twice over the same scene then if the second flight exactly duplicates the track of the first an interesting possibility occurs there would be no phase changes between the images at all unless there was a physical change in the scene such as ground swelling that would alter the distance from some resolution element to the antenna since the phase changes all occur at the short carrier wavelength the basic limitation on sensitivity is only the phase noise in the system when the two imaging passes are made from flight tracks that are separated which is the case with the seasat images used here it is no longer possible to distinguish surface changes from the parallax caused by topography however with some additional computation a third image made at some other baseline may be used to remove the topography and leave only the surface changes this method was applied using seasat data to an imaging site in imperial valley california where motion effects were observed that were ascribed to the expansion of water absorbing clays phase change images of this area are shown along with associated ground truth about the presence of water problems with the technique are explored along with a discussion of future experimental possibilities on upcoming sar missions like earth observing system eos earth resources satellite ers 1 sir c and the venus imaging radar magellan

plutonism oblique subduction and continental growth an example from the mesozoic of california major episodes of mesozoic plutonism in california correlate with periods of oblique subduction and trench parallel transport of western california along intrabatholithic faults major episodes of plutonism occurred in the late jurassic during left oblique convergence and in the mid cretaceous during right oblique convergence in contrast a conspicuous lull in plutonism but continuation of volcanism in the earliest cretaceous coincides with a time when the north america farallon convergence vector although large in magnitude was oriented perpendicular to the trench this correlation suggests that plutonism is facilitated by strike slip faulting within the batholithic belt one explanation which helps to solve the plutonic room problem is that plutons are passively emplaced at releasing bends in the strike slip faults and volume is conserved by thrusting at the trench if this correlation is generally applicable then it implies that mid crustal plutonism is limited beneath areas in which the convergence vector is subperpendicular to the trench continental growth in such areas may occur dominantly by volcanism

discrimination of geophysical phenomena in satellite radar interferograms various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar sar images the fringes generated by the topographic relief can be removed using a digital elevation model dem the remaining fringes map the change in satellite to ground range which occurred between the acquisition times of the two images by comparing different pairs of images spanning different intervals of time it is possible to discriminate between geophysical signal and interferometric artifact here we apply this pair wise logic to the area around the 1992 landers california earthquake using sar images acquired by the ers 1 satellite the range varies with time as a constant step impulsive or sloping function examples of each type include a dem error an aftershock two atmospheric perturbations and postseismic afterslip respectively their signatures are identified and separated using the pair wise logic

processes controlling acid attenuation in the unsaturated zone of a triassic sandstone aquifer u k in the absence of carbonate minerals abstract continuous core samples were taken through the unsaturated zone at three sites on the outcrop of permo triassic sandstone in the british west midlands sample sites were chosen for lack of recent direct anthropogenic disturbance and for differing vegetation heathland birch woodland and conifer forest interstitial water was extracted and analyzed for 32 major and trace elements solid phases were analyzed for exchangeable cations and mineralogy the rate of recharge calculated using a cl mass balance method was three times greater below heathland than below afforested sites owing to higher evapotranspiration rates in the woodlands carbonate minerals were absent from the unsaturated zone at each site soil solutions were acidic and soils at the woodland sites were more acidic ph 4 0 than those at the heathland site ph 4 5 acidic interstitial water solutions were found to up to 5 0 m depth in the unsaturated zone and are partially neutralized by two aluminosilicate mineral reactions in the unsaturated zone cation exchange and k feldspar dissolution the rate at which these acid neutralizing reactions act to neutralize acidity is revealed by the rate of depletion of base cations from the unsaturated zone in recharge solutions k dissolution ca 2 mg 2 cation exchange the total base cation depletion rate was greatest below heathland this can be attributed mainly to the greater rate of so 4 assimilation by the woodland biome

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

solute geochemical mass balances and mineral weathering rates in small watersheds ii biomass nutrient uptake more equations in more unknowns and land use land cover effects abstract paired watersheds are used to develop a deciduous nutrient uptake stoichiometry the watersheds are those of the house rock run and the brubaker run located in the pennsylvania appalachian piedmont usa these two watersheds are nearly identical with respect to bedrock regolith climate geomorphology morphometry baseflow hydrology and type and successional stage of forest vegetation they only differ by the percentage of deciduous forest cover with house rock run having 59 and brubaker run having 76 from differences in their stream chemistries the biomass nutrient uptake stoichiometry of k1 0mg1 0ca1 4 was determined this stoichiometry applies to an aggrading deciduous biomass and differs from those previously used which were derived from net primary production npp data the difference may reflect that macronutrients in plant tissue may also originate from atmospheric inputs and or decomposing biomass although this stoichiometry may not be applied to all deciduous forest covered watersheds it is likely an improvement over a stoichiometry determined from npp data mass balance calculations of mineral weathering rates often suffer from the number of unknowns exceeding the number of equations to add equations to the mass balance matrices two methods are introduced the first method employs zr normalized bulk chemical compositions of bedrock and soil to calculate a mass transfer coefficient for chemical weathering the second approach uses chemical formulae and modal abundances of primary minerals undergoing complete dissolution during weathering both methods allow for calculation of weathering rate constraints without biomass and cation exchange influences these constraints serve as additional equations in the mass balance matrix this study finds that the watershed with the higher percentage of recently abandoned agricultural fields previously used for growing row crops has the higher chemical weathering rate the higher chemical weathering rate reflects greater runoff resulting from reduced evapotranspiration

surface displacement of the 17 may 1993 eureka valley california earthquake observed by sar interferometry satellite synthetic aperture radar sar interferometry shows that the magnitude 6 1 eureka valley earthquake of 17 may 1993 produced an elongated subsidence basin oriented north northwest parallel to the trend defined by the aftershock distribution whereas the source mechanism of the earthquake implies a north northeast striking normal fault the 3 millimeter accuracy of the radar observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event these observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west dipping north northeast fault plane reactivating the largest escarpment in the saline range

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

reverse fault step at engel peaks antarctic peninsula abstract a steep reverse fault at engel peaks antarctic peninsula cuts granophyre and overlying volcanic rocks and incorporates a lower angle zone or fault step the reverse fault step differs from the more familiar thrust ramp in that it cuts down section in the footwall in the direction of tectonic transport accommodation of the fault zone to this step and its associated sidewall are discussed with reference to kinematic models for pull apart zones and for the movement of thrust sheets over non planar surfaces during movement on the main fault the step acted as a fault jog and pull apart zone preserving cataclasite breccia and other structures demonstrating a brittle to ductile deformation history ultra fine grained rock in the step zone is the result of dynamic recrystallization of ultracataclasite during episodes of brittle slip the fault step acted as a dilational fault jog between the main steep reverse fault segments rotation of mylonite into the reverse fault step and its sidewall involved flexural flow parallel to foliation movement of material through the step zone resulted in shear parallel to the base of the step enhancement of breccia layering mixing of lithologies and cleavage formation it also involved extension at a high angle to the main movement direction to accommodate the extra length of the fault zone late steep reverse fault zones propagating from the main fault folded the breccias in the step and crenulated the earlier cleavage the fault step was a zone of brittle dilation hydration diffusive mass transfer and mineralization

crustal growth of the antarctic peninsula by accretion magmatism and extension a subduction accretion model incorporating new geophysical data is presented to explain the geology of the antarctic peninsula from late palaeozoic to cenozoic time according to the model the peninsula consists of overlapping accretionary magmatic and extensional regimes that were diachronous across the peninsula and have built the crust to its present form the crust which contains a small proportion of sialic basement was mainly formed by accretionary and magmatic processes and modified to its present shape by extension the gondwanide orogeny for the antarctic peninsula is interpreted in terms of the accretionary processes

sedimentology and structure of the trench slope to forearc basin transition in the mesozoic of alexander island antarctica the mesozoic forearc of alexander island antarctica is one of the few places in the world where the original stratigraphic relationship between a forearc basin and an accretionary complex is exposed newlydiscovered sedimentary rocks exposed at the western edge of the forearc basin fill the kimmeridgian albian fossil bluff group record the events associated with the basin formation these strata are assigned to the newly defined selene nunatak formation bathonian and atoll nunataks formation bathonian tithonian within the fossil bluff group the selene nunatak formation contains variable thicknesses of conglomeratesand sandstones predominantly derived from the lemay group accretionary complex upon which it is unconformable the formation marks emergence and subsequent erosion of the inner forearc area it is conformably overlain by the1 km thick atoll nunataks formation characterized by thinly bedded mudstones and silty mudstones representing a marine transgression followed by trench slope deposition the atoll nunataks formation marks a phase of subsidence possibly in response to tectonic events in the accretionary prism that are known to have occurred at about the same time the atoll nunataks formation is conformably overlain by the himalia ridge formation a thick sequence of basin wide arc derived conglomerates this transition from fine to coarse grained deposition suggests that a well developed depositional trough and hence trench slope break had formed by that time the atoll nunataks formation therefore spans the formation of the forearc basin and marks the transition from trench slope to forearc basin deposition

the source of granitic gneisses and migmatites in the antarctic peninsula a combined u pb shrimp and laser ablation hf isotope study of complex zircons zircons gneisses and migmatites collected from the antarctic peninsula have different core rim hafnium isotope ratio relationships depending on whether evidence for zircon dissolution is present or absent two samples contain inherited zircon that is partially dissolved in these samples the 176hf 177hf rations of the inherited zircon and new magmatic zircon rims are on average indistinguishable and consistent with in situ melting in such cases the hafnium isotopic composition of the melt was probably strongly influenced by the dissolved zircon component at the source variation in 176hf 177hf within the magmatic zircon rims from grain to grain suggests that hf isotopes were only partially homogenized during melt migration alternatively zircon growth may have taken place within small volumes of partial melt other samples do not preserve textural evidence for zircon dissolution during melt generation in these samples the 176hf 177hf values of the inherited zircon and new magmatic zircon rims are different the zircon rims apparently suggest a source of less evolved hafnium than that contained within the inherited zircon whether this relates to a separate juvenile source or alternatively is derived from minerals other than zircon at the source cannot be resolved inherited zircon irrespective of age has been strongly influenced by the reworking of a juvenile late mesoproterozoic source suggesting that such crust underlies the antarctic peninsula our results therefore suggest that hf isotope analyses provide great potential for future studies investigating the source and processes involved in the generation of crustal melts

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet