the complex tectonic evolution of the craton adjacent northern margin of the palaeoproterozoic ketilidian orogen southeastern greenland evidence from the geochemistry of mafic to intermediate and granitic intrusions abstract the archaean thrym complex exposed in southeastern greenland is part of the north atlantic craton its southernmost part is in a transitional zone containing archaean orthogneiss to the north and palaeoproterozoic paragneiss and granitic rocks to the south that are part of the ketilidian orogen this 50 km wide transitional zone includes ca 2830 ma orthogneiss that is similar in age to orthogneiss in the central and northern parts of the complex and ca 2740 ma orthogneiss that is synchronous with the ca 2790 2700 ma skjoldungen orogeny a significant difference between this zone and the complex to the north is the presence of greenschist facies sedimentary rocks unconformably overlying orthogneiss and intruded by ca 1820 1800 ma granitic and mafic to intermediate intrusions these intrusions are within the ca 1854 1799 ma age range of the julianehab igneous complex with suites both older and younger than ca 1830 ma that are not restricted to specific zones within the ketilidian orogen the geochemistry of the palaeoproterozoic mafic to intermediate rocks in the transitional zone shows contamination by orthogneiss from the thrym complex and emplacement within an oceanic continental transition in a within plate setting unrelated to subduction in contrast the palaeoproterozoic granites were sourced entirely from archaean orthogneiss of the thrym complex making them technically i type granites that have inherited their petrogenetic signature from the orthogneiss as a result the palaeoproterozoic granites and intermediate to mafic igneous rocks have similar chondrite normalised patterns to the orthogneiss in the archaean complex this demonstrates that discrimination diagrams cannot be assumed to be unequivocal for the rocks studied unless the geochemistry of the source rocks is also known

14c dating of buried soils in the volcanic chaine des puys france apparent ages of the paleosoils buried under ash deposits or lava flows cannot be used without a correct understanding of the soil type buried by the volcanic event

coupling and decoupling of crust and mantle in convergent orogens implications for strain partitioning in the crust topographic relief strain partitioning and crust mantle coupling within convergent orogens may be systematically related to the distribution of strength as a function of depth within continental crust this result is obtained by solving analytically for basally driven three dimensional flow within an idealized crust with a laterally invariant depth dependent newtonian viscosity two end member flow states are shown to occur in the first crustal flow is directly coupled to the underlying mantle and is controlled by stresses transmitted vertically through the crust in the second upper crustal to midcrustal flow is decoupled from the underlying mantle and is controlled by stresses transmitted horizontally through the crust this model is applied to deformation of continental crust above plate like mantle that undergoes oblique convergence across a narrow suture if no significant low viscosity zone develops within the crust crustal deformation is coupled to motion of the underlying mantle and a triangular mountain range develops surface shortening occurs at the foot of the mountains normal to the trend of the range while strike slip and extension are partitioned along the axis of the orogen if a low viscosity zone is initially absent but develops during crustal thickening a steep sided flat topped plateau forms crustal deformation is coupled to mantle motions on the plateau flanks but may be strongly decoupled beneath the plateau surface shortening normal to the plateau occurs at the foot of the plateau while surface extension normal to the plateau occurs at the plateau edge if a low viscosity zone is present in the lower crust prior to convergence a wide orogen with low topographic relief develops crustal deformation is decoupled from the mantle except at the edges of the deforming region and surface shortening is partitioned uniformly across the belt this study shows that horizontal and vertical partitioning of strain occur even in the absence of lateral strength variations and that shortening and extension may exist simultaneously in different parts of an orogen similar morphology and strain partitioning can be observed in many real orogenic belts including the eastern alps the tibetan plateau and the lachlan tasman fold belt

soil chronosequence and geomorphology in a semi arid valley in the andes of southern peru abstract soil development particularly in relation to relative age of geomorphic surfaces was studied in a high altitude valley on the semi arid western side of the andes in southern peru seven major fluvial surfaces in the colca valley were recognized including floodplains stream terraces and fans associated with the rio colca and its tributaries soils were also briefly examined on pleistocene andesite flows within the valley and on high volcanic plateaus surrounding the valley field and laboratory work indicate that most soils on stable surfaces above the floodplain are mollisols and that there is a consistent pattern of increasing subsurface horizon development on successively higher and older fluvial surfaces from 3300 to 3800 m elevation a developmental sequence of argillic horizons duripans and carbonate accumulation is present on these fluvial surfaces soils on the oldest fluvial surfaces exhibit strongly developed argillic horizons underlain by calcic horizons and strongly cemented duripans that contain illuvial carbonate and clay substantial development of these horizons also occurs on colluvial surfaces with slopes up to at least 65 relative depths of subsurface horizons on steeper colluvial surfaces differ from those on gently sloping fluvial surfaces in that argillic horizons and duripans are amalgamated this study indicates that significant chemical weathering and strong subsurface pedogenesis occur in high altitude mountainous environments within the tropics in contrast to findings at high altitudes in other climatic zones

shallow water eruption fed mafic pyroclastic deposits along a paleoproterozoic coastline kangerluluk volcano sedimentary sequence southeast greenland abstract the 200 300 m thick volcano sedimentary sequence at kangerluluk is part of the psammite zone one of four major zones which constitute the 1 8 ga ketilidian orogen in south greenland three lithofacies are emphasized in the study 1 the conglomerate sandstone 2 the volcanic and 3 the pyroclastic lithofacies the 2 40 m thick conglomerate sandstone lithofacies represents a subaerial to subaqueous fan delta deposit matrix and clast supported conglomerates are interpreted as debris flow and longitudinal gravel bar deposits erosive based conglomerate channel fills attest to stream incision trough crossbedded sandstone interpreted as lunate megaripples planar bedded sandstone indicative of upper flow regime bar top sands and small scale trough crossbeds reflecting ripples follow up section form collectively with the conglomerate 0 40 2 50 m thick fining upward sequences the sandstone dominated unit up section from the conglomerates and composed of planar and low angle crossbeds minor ripples and graded beds as well as mudstone is indicative of a lower shoreface deposit below normal wave base the clastic sedimentary rocks are suggestive of a fan delta setting the 100 200 m thick volcanic lithofacies composed of pillowed and pillow brecciated lava flows is consistent with shallow water deposition interstratification of lava flows with both conglomerate sandstone and pyroclastic lithofacies intrusion of dykes into volcaniclastic rocks and peperite formation accentuate contemporaneity between volcanism and sedimentation and is a common feature of island arcs the 1 50 m thick pyroclastic lithofacies with sharp depositional contacts to the overlying volcanic and underlying conglomerate sandstone lithofacies was emplaced in a subaqueous setting the lithofacies is divided into a planar to crossbedded tuff lapilli tuff and a bedded lapilli tuff breccia whereby both deposits are inferred to result from shallow water surtseyan type eruptions the 5 15 m thick bedded lapilli tuff breccia with abundant bomb sag structures and graded beds is considered a result of subaqueous eruptions strong enough to form an insulating steam cupola characterized by ballistically emplaced bombs that rapidly collapsed allowing for transport via mass flow processes the deposits are considered proximal to the vent the 2 50 cm thick planar to crossbedded tuff lapilli tuff featuring abundant euhedral and broken crystals of feldspar 2cm and minor pyroxene 1 cm are massive graded crossbedded and stratified the planar but laterally discontinuous beds characterized by abundant low angle scours are interpreted as low to high concentration sediment gravity flows produced directly from subaqueous tephra jets that collapsed due to massive water ingestion local breccia size pyroclasts disrupting beds are interpreted as bomb sags the mafic eruption fed surtseyan type deposits postulated to be a subaqueous counterpart of cold subaerial base surges originate from subaqueous tuff cones formed along a rugged volcanic dominated shoreline featuring high energy fan deltas

estimating the basin scale ocean circulation from satellite altimetry part i straightforward spherical harmonic expansion abstract direct estimation of the absolute dynamic topography from satellite altimetry has been confined to the largest scales basically the basin scale owing to the fact that the signal to noise ratio i more unfavorable everywhere else but even for the largest scales the results are contaminated by the orbit error and geoid uncertainties recently a more accurate earth gravity model gem t1 became available thus giving us the opportunity to examine the whole question of direct estimation under a more critical limelight it is found that our knowledge of the earth s gravity field has indeed improved a great deal however it is not yet possible to claim definitively that our knowledge of the ocean circulation has improved through direct estimation yet the improvement in the gravity model has come to the point that it is no longer possible to attribute the discrepancy at basin scales between altimetric and hydrographic results as mostly due to geoid uncertainties a substantial part of the differen

finite strain analysis of the zhangbaling metamorphic belt se china crustal thinning in transpression abstract finite strain analysis of pebbles in the metatillite and phyllite shows that the deformation of the metatillite phyllite zone is flattening to plane strain dominated results of spo analysis of the rigid plagioclase porphyroclasts in three perpendicular planes indicate monoclinic strain symmetry of the zhangbaling schist and oblate geometry of the clast forward strain modeling of rigid clasts is performed based on the shape fabric of the clast population integrated results of finite strain modeling and finite strain analysis indicate that this midcrustal section experienced at least 18 36 thinning in the oblique convergence between north and south china blocks

a refined gravity model from lageos gem l2 a refined gravity field model goddard earth model gem l2 has been derived using the lageos orbital data yielding better baseline measurements for the analysis of tectonic plate motion this field also contributes to an improved understanding of long wavelength features such as the sea slope across broad ocean basins through its significant improvement of the long wavelength geoid through degree and order 4 the geoid for these terms has an accuracy estimated at 8 cm in gem l2 gem l2 as in all recent goddard earth models relies heavily on the precise near earth satellite laser ranging data in this case provided by nasa s crustal dynamics program two and a half years of lageos laser data acquired from over 20 well distributed stations were combined with the existing data from the best satellite derived model gem 9 to develop the new lageos model testing shows that the lageos gravity field error at long wavelengths is less than half that for gem 9 independent tests using well determined longitude accelerations of 24 hour satellites have verified the improved accuracy of the new model a comparison of global laser base stations from independent data sets of alternating 15 day data segments over the 2 1 2 years of lageos show total inter station positioning to 1 8 cm when using this new field the same comparison using the 1979 versus the 1980 lageos data yields 5 2 cm this difference in agreement reflects the change in data distribution and other systematic errors along with the tectonic motion which has occurred between these chronologically distinguishable data sets five day average polar motion values with a precision of 10 cm and change in length of day values accurate to better than 5 msec have been derived in the solution the adjustment of these parameters are necessary to achieve the accurate stations and geopotential results in gem l2

circulation from a joint gravity field solution determination of the general ocean with the development of satellite altimetry it is possible to infer the geostrophic velocity of the surface ocean currents if the geoid and the position of the satellite are known accurately errors in current geoid models and orbit computations both due primarily to errors in the earth s gravity field model have limited the use of altimeter data for this purpose the objective of this investigation is to demonstrate that altimeter data can be used in a joint solution to simultaneously estimate the quasi stationary sea surface topography and the model for the gravity field satellite tracking data from twelve satellites were used along with seasat altimeter data for the solution the estimated model of compares well at long wavelengths with the hydrographic model of covariance analysis indicates that the geoid is separable from up to degree 9 at which point geoid error is comparable to the signal of

accuracy assessment of the large scale dynamic ocean topography from topex poseidon altimetry the quality of topex poseidon determinations of the global scale dynamic ocean topography have been assessed by determining mean topography solutions for successive 10 day repeat cycles and by examining the temporal changes in the sea surface topography to identify known features the assessment is based on the analysis of topex altimeter data for cycles 1 through 36 important errors in the tide model used to correct the altimeter data have been identified the errors were reduced significantly by use of a new tide model derived with the topex poseidon measurements maps of the global 1 year mean topography produced using four of the most accurate models of the marine geoid show that the largest error in the dynamic ocean topography is now the uncertainty in the geoid temporal variations in the spatially smoothed maps of the annual sea surface topography show expected features such as the known annual hemispherical sea surface rise and fall and the seasonal variability due to monsoon influence in the indian ocean changes in the sequence of 10 day topography maps show the development and propagation of an equatorial kelvin wave in the pacific beginning in december 1992 with a propagation velocity of approximately 3 m s the observations are consistent with observed changes in the equatorial trade winds and with tide gauge and other in situ observations of the strengthening of the 1992 el nino comparison of topex determined sea surface height at points near oceanic tide gauges shows agreement at the 4 cm rms level over the tropical pacific the results show that the topex altimeter data set can be used to map the ocean surface with a temporal resolution of 10 days and an accuracy which is consistent with traditional in situ methods for the determination of sea level variations

geomorphology and late holocene climatic change in northeastern spain abstract during the late holocene accumulation and downcutting stages affected the slopes and infilled valleys in the semiarid areas in ne spain the presence of archaeological remains charcoal and ashes within slope deposits and valley fills makes it possible to carry out accurate datings in the case of infilled valleys the different accumulations may be diachronous at a regional level these diachronisms among different infilled valleys may be caused by both human activity and complex responses of the system on the slopes one can distinguish between two accumulation periods separated by an incision period the older accumulation stage has a widespread distribution and developed from the bronze age to the iberian roman epoch the following accumulation period was formed in the post medieval period and is spatially more restricted because of the widespread synchronism shown by these accumulations a climatic cause is put forward as the possible triggering factor for the accumulation incision stages in the slopes the datings obtained indicate that the first accumulation corresponds to the iron age cold epoch 900 300 years b c and the second to the little ice age between both accumulation periods a downcutting stage took place approximately from 300 b c to 1450 a d this downcutting interval can be related to the warm stages of the subatlantic period during which there was a relatively lower percentage of vegetation cover finally the last incision period which is still taking place has affected previous accumulations

determination of the ocean circulation using geosat altimetry a spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth s geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using geosat altimeter data and tracking data from 14 different satellites the sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data currently errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower corresponding to a minimum wavelength of 4 000 km error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0 2 indicating good separation of the geoid and the sea surface topography at wavelengths of 4 000 km or longer estimates of the scale factor for the significant wave height h sub 1 3 which is used to compute the electromagnetic bias correction and the bias for the geosat altimeter are obtained the estimate of the h sub 1 3 correction is 3 6 plus minus 1 5 and the height bias estimate is zero

gravity model improvement for seasat analysis of the data from the seasat altimeter a 10 cm precision instrument requires accurate knowledge of the radial position of the spacecraft for oceanographic applications such as the study of tides and ocean circulation as well as for geodetic applications initial orbit determinations using the best available geodetic and force models gave radial errors approaching 5 m the dominant source of this radial error was the gravity field model improvements in the gravity modeling were made by successively incorporating the seasat laser and unified s band ground tracking data the geos 3 altimeter data and finally the seasat altimeter data with the most recent model a set of spherical harmonic coefficients complete to degree and order 36 seasat ephemerides have been computed for an orbital arc length of 12 days with an rms radial accuracy of about 70 cm

conditions for flow in the continental crust 1 earthquake focal depth distributions and effective elastic thickness variations on the continents suggest that in old cold regions such as shields the lower continental crust can be stronger than the upper mantle and imply that the upper mantle can flow even when the lower crust does not however in other places substantial flow in the lower crust does occur particularly near extensional metamorphic core complexes we suggest that the lower crust only flows when its viscosity is significantly reduced either by heating from igneous intrusions or by the addition of water in both cases the important characteristics of the flow are a consequence of the limited time over which the viscosity reduction occurs the timescale is controlled either by conductive cooling of intrusions or by the separation of melt from its matrix which removes the water

structural evolution of the makkovik province labrador canada tectonic processes during 200 myr at a paleoproterozoic active margin in the makkovik province the structures and plutonic rocks of the reworked southern edge of the archean nain craton parautochthon and an adjacent juvenile domain form a spatially concentrated record of 200 ma at a paleoproterozoic active margin d1 thin and thick skinned structures formed during terrane collision before ca 1896 ma were nearly erased by d2 transpressive structures present across the entire parautochthon that had been thermally softened by emplacement of arc plutons at ca 1895 1870 ma d3 transpressive inversion of a back arc rift and d4 strike slip shearing formed structures at the oceanward margin of the parautochthon and were responses to events in the active arc that was now widely separated from the parautochthon by accreted terranes the tectonic isolation of the parautochthon ended by the time of d5 ca 1740 1710 ma and d6 with the reappearance there of granite and low grade shear zones structural and plutonic style varied at each stage primarily controlled by the crustal level attained

anatomy and orogenic history of a paleoproterozoic accretionary belt the makkovik province labrador canada the makkovik province is a segment of a paleoproterozoic accretionary belt the makkovik ketilidian orogen that developed on the southern margin of laurentia at 1 9 1 7 ga in contrast to coeval laurentian orogenic belts that mainly resulted from collision of archean plates makkovikian ketilidian orogenesis was dominated by active margin processes including continental margin arc plutonism and juvenile terrane accretion both of which were accompanied by regional transpression in the makkovik province earliest deformation and amphibolite facies metamorphism of paleoproterozoic rift drift assemblages post hill and moran lake groups and the archean foreland nain province occurred at 1 9 ga in response to accretion of a paleoproterozoic island arc following this collision cratonward dipping subduction was established resulting in the formation of the 1895 1870 ma island harbour bay plutonic suite a calc alkaline magmatic arc built on reworked archean crust crust formation continued between ca 1

metallogeny of south greenland a review of geological evolution mineral occurrences and geochemical exploration data abstract south greenland has been the site of historic mining of cryolite copper graphite and gold hosts mineral deposits with gold uranium zinc niobium tantalum zirconium hafnium ree iron titanium vanadium fluorite and graphite and has additional potential for lithium beryllium phosphorus gallium and thorium data from stream sediment geochemical surveys document that south greenland is enriched in a range of these elements relative to the rest of greenland and to estimates of the upper crust composition distribution patterns for individual elements within south greenland exhibit enriched regions that are spatially related to lithological units crustal structure and known mineralisation the northern domain of south greenland includes the southernmost part of the orthogneiss dominated north atlantic craton orogenic gold mineralisation is hosted by quartz veins and hydrothermally altered rocks associated with shear zones intersecting the mesoarchaean tartoq group of mafic metavolcanic rocks geochemical exploration indicates that additional potential for gold mineralisation exists within palaeoproterozoic supracrustal rocks overlying the archaean basement rocks formed during the palaeoproterozoic ketilidian orogeny occupy a major part of south greenland and has been divided into two domains the central domain is underlain by the julianehab igneous complex forming a 100 km wide ene wsw zone centrally across south greenland intrusive and extrusive mostly felsic magmatic rocks were emplaced in two main stages 1850 1830 and 1800 1780 ma in a continental arc setting positive anomalies in aeromagnetic data indicate that mafic plutons are common in the late igneous complex intra arc mafic metavolcanic rocks contain syngenetic stratabound copper sulphide and epigenetic shear zone hosted copper silver gold mineralisation at kobberminebugt and kangerluluk whereas metasedimentary and metapyroclastic rocks contain stratabound uraninite mineralisation orthomagmatic iron titanium vanadium mineralisation is hosted by a gabbro a potential for porphyry type mineralisation related to the late intrusive stages of the julianehab igneous complex is suggested by showings with copper molybdenum and gold together with stream sediment anomalies for these elements vein type uranium mineralisation occurs in fault zones in the julianehab igneous complex related to mesoproterozoic rifting the southern domain contains an assemblage of palaeoproterozoic metasedimentary and metavolcanic rocks that underwent moderate to strong deformation peak ht lp metamorphism and partial melting with subsequent retrograde exhumation at 1790 1765 ma the supracrustal rocks contain syngenetic au as sb u and zn mineralisation in volcanic or graphite and sulphide rich sedimentary environments graphite was mined historically at two sites many stream sediment gold anomalies are located in a ne trending belt along the boundary between the early julianehab complex and the supracrustal rocks to the south they reflect a number of auriferous quartz vein occurrences including the nalunaq gold deposit hosted in a system of shear zones and probably generated as orogenic gold during ketilidian accretion the 1755 1730 ma a type ilua plutonic suite is the latest magmatic event in the ketilidian orogen the 1300 1140 ma gardar period involved continental rifting sedimentation and alkaline magmatism numerous dykes and 10 ring shaped intrusion complexes were formed across south greenland an orthomagmatic iron titanium vanadium deposit is hosted by troctolitic gabbro residual magmas and fluids resulting from extreme magmatic differentiation possibly combined with assimilation of older crust created mineral deposits including cryolite that was mined at ivigtut large low grade deposits of uranium rare earth elements zinc at kvanefjeld and tantalum niobium rare earth element zirconium at kringlerne in the ilimaussaq complex as well as tantalum niobium rare earth elements at motzfeldt so in the igaliko complex the south greenland crustal evolution records effects of mantle processes such as lithospheric extension subduction and underplating which resulted in recurrent magma emplacement in tectonically active environments as such the geology of south greenland reflects events and circumstances that are favourable to the generation and preservation of hydrothermal ore forming fluid systems during the ketilidian orogeny as well as to the development of extreme rock compositions within the gardar alkaline igneous province

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

properties and formation of black soils on the island of poel ne germany abstract recent soil mapping on the island of poel situated in the southern baltic sea shows an abundance of black soils developed in stratified parent material whereby the upper layers are of periglacial origin covering calcareous till the black soils have been formed in the upper layer overlying luvisols developed in decalcified till with different degrees of stagnic influence the luvisols are not the result of a degradation of the black soil as no humic clay coatings were detected in their bt horizons with a simplified ap ah eb ah 2 e 2bt g b c horizon sequence these soils differ from the better known degraded phaeozems on fehmarn and the uckermark region the properties of three pedons are presented and their pedogenesis is discussed ams 14c ages from soil organic carbon of the ah horizons from the black soils suggest that the development of the luvisols stopped within the first half of the subatlantic period

soil evolution over the quaternary period in a semiarid climate segre river terraces northeast spain abstract a macro and micromorphologic study was done on the soils from a stepped sequence of seven dated fluvial terraces in the lower segre river valley lleida northeast spain under a present day semiarid mediterranean climate the soils have evolved from the holocene through the early pleistocene providing an excellent morphostratigraphic framework for evaluating time dependent factors influencing soil formation in a dry and calcareous environment throughout the chronosequence some properties are regularly age related specially carbonatation in subsurface horizons the carbonates occur mainly as micrite and although microsparite and sparite also appear in the oldest soils they are replaced by fine grained calcite by dissolution reprecipitation processes micritization process which is active at present some pedological paleofeatures as the presence of sparite and recarbonated argillans in oldest terrace can be interpreted as the reflex of climatic changes during the quaternary in spite of this climate variability the soils display progressive and systematic patterns of carbonate accumulation on the lowest terraces the soils do not yet have secondary carbonates but in the beginning late pleistocene calcic horizons with carbonate pendents are developed these pendents increase its thickness with age although pendent growth rates decreases from late pleistocene to middle pleistocene in the middle of the late pleistocene calcic horizons evolved to petrocalcic horizons which increase its thickness in the middle and specially in early pleistocene the presence of calcic and petrocalcic horizons is the primary basis for soil classification this criterion is applicable not only to the soils of the lower segre river basin but also to many soils throughout the semiarid mediterranean region

absolute measurement by satellite altimetry of dynamic topography of the pacific ocean satellites are the only foreseeable possibility for obtaining observations of the ocean circulation on the basin and global scales required to understand it such observations are essential for an understanding of the role of the ocean in various important problems for example climate the 3 month seasat mission1 has demonstrated2 3 that altimetry is capable of providing global observations of oceanic variability we show here that the data from this short sub optimum mission are also adequate for a determination of the absolute sea surface topography of the ocean on large scales a much more difficult4 and even more valuable measurement an absolute determination of the subtropical gyre of the north pacific ocean has been obtained we believe this to be the first direct measurement showing the existence of such a feature that does not depend on conventional hydrography and a series of assumptions

rapid phytolith extraction for analysis of phytolith concentrations and assemblages during an excavation an application at tell es safi gath israel abstract a rapid phytolith extraction procedure is described that allows phytolith concentrations and morphotype assemblages to be analyzed within hours this procedure enables the results of these analyses to be used during an archaeological excavation in order to better understand how plants were used the new procedure was tested using a standard phytolith extract and two experimental phytolith sediment blends and found to be both accurate and precise the reliability of partial slide counting was evaluated and found to be as accurate and precise as existing phytolith quantification methods the new extraction and counting procedures were applied to an archaeological site tell es safi gath israel the results demonstrate how information on phytolith concentrations in sediments that are available from one day to the next can be used during an excavation to more effectively document the local features of interest and obtain better information

new reflections on the structure and evolution of the makkovikian ketilidian orogen in labrador and southern greenland marine seismic reflection profiles across the early proterozoic makkovikian ketilidian orogen in the labrador sea region suggest that it is a doubly vergent asymmetric orogenic belt comparable in width to younger collisional orogens a southeast dipping reflector package is correlated with on land shear zones that mark the southeastern limit of exposed reworked archean crust and is also associated with a cryptic isotopic boundary in granites which documents a transition from ancient to juvenile basement this boundary is interpreted as a suture along which juvenile proterozoic crust has been juxtaposed over thrust over the archean craton a major synorogenic to postorogenic plutonic terrane to the southeast has a poorly reflective upper crust but shows strong subhorizontal reflectivity in the lower crust and moho regions the southeastern part of the profile correlates with metasedimentary terranes of the ketilidian belt in greenland and contains low angle northwest dipping reflector packages suggestive of large scale crustal imbrication by thrusting at least two broad zones of reflectivity at mantle depths up to 16 s are also recognized one dips northwest below the archean craton but the most widespread mantle reflectivity is southeast dipping in opposition to the dominant fabric in the overlying crust these contrasting crustal and subcrustal reflectivity patterns define a geometric focus beneath the orogenic belt and may provide information about subduction polarity during its development the doubly vergent reflectivity pattern resembles images from possibly correlative precambrian orogenic belts such as the penokean and svecofennian and also younger small collisional orogens such as the appalachian and pyrenean belts it also broadly resembles some results of geodynamic crustal deformation models based on detachment and underthrusting of mantle lithosphere following collision and the squeezing of weak zones between rigid bounding blocks a speculative multistage model for the belt incorporates initial northward subduction beneath the craton shifting to later southward subduction followed by oblique accretion of a composite arc terrane and juvenile continental block the accreted hotter juvenile proterozoic crust behaved differently than the stable cool archean crust and experienced subhorizontal shearing in lower crustal and moho regions associated with southeast directed imbrication of the middle and upper crust by thrusting however the present reflectivity pattern of the orogen may also include elements related to post collisional extensional collapse

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

mid crustal partitioning and attachment during oblique convergence in an arc system palaeoproterozoic ketilidian orogen southern greenland abstract the ketilidian orogen in se greenland contains a continental magmatic arc julianehab batholith and forearc which formed in the overriding plate of a palaeoproterozoic oblique subduction boundary between c 1854 and 1795 ma during uplift and deformation of the forearc between c 1795 and 1780 ma its sedimentary sequences were invaded by arc type magmas and metamorphosed at ht lp upper amphibolite facies conditions which led to widespread anatexis and generation of abundant s type granites transpression during early deformation d 1 was partitioned into arc parallel sinistral strike slip in the magmatic arc rocks of the batholith and arc normal contraction in the sedimentary and volcaniclastic sequences of the proximal forearc psammite zone subsequently d 1 fabrics in the psammite zone were overprinted and transposed in an intense flat lying d 2 ductile shear zone with arc parallel stretching lineations and top ne kinematic indicators the kinematic significance of the d 2 shear zone is that it accommodated vertical differences in strain and displacement and permitted deformation to be partitioned differently at different levels in the crust as such it is an attachment or coupling zone that provided kinematic linkage between deformation at different crustal levels during ne transport of a forearc sliver overprinting of the upper crustal domain of d 1 strike slip partitioned transpression in the forearc during d 2 is attributed to migration of the attachment zone to a higher crustal level this migration was a consequence of an enhanced geothermal gradient in the proximal part of the forearc due to the emplacement of batholith related plutonic suites during d 2

radiocarbon age of holocene paleosols of the east european forest steppe zone abstract comparison of the radiocarbon ages of soils buried under previously dated burial mounds with those of surface background soils in surrounding areas indicates the rate of humus renewal and aids the dating of paleosols buried soils and relic horizons in surface soils together with evidence for the development of soils of watersheds in the holocene the soils of depressions indicate reactivation of erosion processes in the last 3 8 centuries agricultural erosion there is also evidence of erosion during the periods of 7 8 ka and 4 5 ka bp which was associated with abrupt climatic and environmental changes

dynamic sea surface topography gravity and improved orbit accuracies from the direct evaluation of seasat altimeter data a gravitational model incorporating seasat altimetry surface gravimetry and satellite tracking data has been determined in terms of global spherical harmonics complete to degree and order 50 this model pgs 3337 uses altimeter data as a dynamic observation of the satellite s height above the sea surface a solution for the ocean s dynamic topography is recovered simultaneously with the orbit parameters gravity and ocean tidal terms the recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 2 000 km and is very similar to the mean upper ocean dynamic height derived from historical ship observations the pgs 3337 geoid has an uncertainty of 60 cm rms globally but only 25 cm rms over the ocean because of the altimeter measurements seasat orbits determined in this solution have an estimated accuracy for the radial position of 20 cm rms the difference between the altimeter observed sea height and the geoid plus dynamic topography model is 30 cm rms contained in these residuals are the sea height variability as well as errors from the geoid orbits tidal models and altimeter range measurements this performance level is 2 to 3 times better than that achieved with previous goddard gravitational models

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

taphonomy of phytoliths and macroplants in different soils from olduvai gorge tanzania and the application to plio pleistocene palaeoanthropological samples the abundance and types of phytoliths in the fossil record are taphonomically biased and do not correspond with the macroplant record to better understand the bias and improve the interpretation of samples from olduvai gorge tanzania we analysed the phytoliths from three sample sets modern grasses sedges palm and dicots in the area modern soils in the area and the fossil soils from the eastern palaeolake margin in lowermost bed ii fourier transform infrared spectrometry analyses were performed in parallel to compare the mineral composition of both modern soils and fossil soils we found that the abundance of phytoliths is greatly reduced in soil samples compared with modern plant material but the morphotypes can be reliably interpreted dicotyledonous wood bark phytoliths appear to be over represented in the soil types grass phytoliths and sedges to a lesser degree are preserved in the soils but in lower abundances resulting in these groups being under represented the macroplant fossils are fragments of grass and sedge aerial culms and dicotyledonous stems that are preserved in fluvial and lacustrine deposits it is suggested that phytoliths represent the continuous flora whereas macroplant fossils represent the more robust tissues of selected plants preserved under more catastrophic conditions a post depositional model is proposed and the palaeovegetation is reinterpreted as being richer and more complex than indicated by other fossil data

buried a horizons in old bench terraces in les garrigues catalonia abstract a large part of les garrigues western catalonia is occupied by stone terraces locally known as bancals that were built up in the 18th century some soil surveys of the area noted the presence of buried thick a horizons with a well developed crumb structure and darker colour than the present day a horizons the objective of this study was to determine the conditions of the soil cover both at the time of the formation of these buried soils and at the onset of terracing the climate is semi arid and the landscape is defined by platforms and flat bottomed valleys four profiles were described from both slope and valley floor terraces and sampled for analyses a buried ahb horizon appears at various depths between 40 and 180 cm with thicknesses ranging from 35 to 160 cm probably due to earthworks since this depends on the position of the profile within the terrace many of these buried soils would correspond to phaeozems they are identified by an ahb having low values and chromas usually 4 or less a structure due to faunal activity 100 of the structural forms related to fauna either in the form of empty or infilled channels vermic qualifier and an organic matter content that is 1 7 3 3 which is higher but not significantly different than the som content of the present day topsoils p olsen is 1 6 ppm the present soils are non saline and highly calcareous 40 they show some calcium carbonate redistribution in the form of pseudomycelia and biogenic calcite charcoal is present in some of these buried horizons together with small ceramic fragments these buried horizons have several common micromorphological features a spongy highly porous structure due to high faunal activity frequent silt cappings charcoal fragments and biogenic carbonates queras in some cases the biogenic calcite has undergone dissolution and reprecipitated as micrite pollen assemblages of the buried horizons reveal a large forest cover mainly of oaks and pines which is also corroborated by the occurrence of quercus phytoliths but the presence of pollen of some deciduous crops such as cereals vitis vinifera and olea europaea at the top of the sequences points to a upper holocene origin of these soils the results from the charcoal study support the presence of perennial quercus and pines as well as shrubs in the period when the terraces were built the available information about present day similar soils indicates that the formation of these horizons took place under a moister milder climate in the past compared with the present one in the study area

biogenic silica storage in soils the role of plants in soil development has become of crucial interest in quantifying global weathering processes on the volcanic reunion island indian ocean a 15 cm thick phytolith rich horizon biogenic opal a developed at the expense of trachytic ashes between 3820 85 and 335 90 yr b p then 97 138 t km 2 yr of sio 2 were biogeochemically recycled from the weathering of parent rocks through a past forest of bamboos nastus borbonicus this rate is in the same range as the present chemical weathering rates of silica in the area considered to be among the highest in the world these results demonstrate that the storage of biogenic silica in soils may be significant and may retard the output of silica to rivers and ocean

topex poseidon the 2 cm solution the unprecedented accuracy of topex poseidon t p altimeter data warrants a new evaluation of the methods typically used to form time series of sea level change whereas explicit removal of orbit error has always been required as a first step in altimeter data processing the t p analysis presented here is based simply on unadjusted monthly averages this approach has the advantage of retaining the large scale ocean signal which would be distorted by orbit adjustment using 16 months of data we have evaluated the t p monthly means on spatial scales ranging from mesoscale to global in the tropical pacific comparisons with 17 island tide gauge records and dynamic height derived from 36 thermistor moorings show that the altimeter data have an accuracy of approximately 2 cm when averaged over spatial scales of a few hundred kilometers on basin scales in the northern hemisphere similar agreement is found between the t p data and the dynamic height climatology of levitus 1982 these new altimeter observations are thus providing the first reliable view of global sea level changes on seasonal to interannual timescales

attachment formation during partitioning of oblique convergence in the ketilidian orogen south greenland subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts a mid crustal attachment zone is exposed in the palaeoproterozoic ketilidian orogen south greenland which formed as a result of north directed oblique convergence at a cordilleran type margin rifting c 2 1 ga and compressional deformation and magmatism 1850 ma on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 ma now separated into three episodes or peaks of activity the first episode was focused on the back arc region and was followed by the main arc construction phase during which transpression was partitioned into strike slip and contraction components despite the longevity of this active margin system individual tectonic events took place rapidly e g development of fore arc d1 d3 and accompanying high temperature low pressure metamorphism took place over c 12 ma we explain the fore arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks this migration may be attributed to an increase in the geothermal gradient accompanied by or followed by exhumation of the mid crust the partially molten hence weak attachment zone solidified and strengthened during cooling before emplacement of the post orogenic rapakivi suite during the third distinct phase of mild sinistral transpression

prehistoric alteration of soil in the lower rhine basin northwest germany archaeological 14c and geochemical evidence in early holocene chernozems were assumed to have covered the entire loess landscape of the lower rhine basin today mirrored by the distribution of luvic phaeozems these luvic phaeozems have characteristic dark brown bht horizons accumulating clay and humus inherited and translocated from their precursors chernozem black humic a horizons we examined luvic phaeozems along a 33 km long and 2 0 2 5 m deep gas pipeline trench in the lower rhine basin west of cologne along this transect we discovered clusters of hundreds of regularly shaped pits these pits were always connected to the bht horizons of adjacent luvic phaeozems the luvic phaeozem horizons and the pits were investigated by combining methods from geo archaeology geographical distribution within the landscape shape of the pits soil texture geochemistry content of carbon nitrogen and black carbon palaeobotany species determination of charcoals and ams 14 c measurements we found that the luvic phaeozems occurred not only in the loess covered landscape but also in the sandy holocene floodplain and their distribution could not be limited to certain slope positions or parent material carbon and nitrogen concentrations in the luvic phaeozem horizons and pits were larger than in the surrounding luvisols whereas the c n ratios were small 10 material found in the luvic phaeozem pits was clearly different from material found in prehistoric settlements the pits investigated here never contained artifacts and carbon and nitrogen concentrations and c n ratios were smaller we found charcoal particles and black carbon contributed up to 46 of the total organic carbon the ams 14 c ages of charcoals and black carbon indicated that fire occurred from mesolithic 9500 5500 bc to the medieval ages 500 1500 ad and mainly in the late end neolithic period 4400 2200 bc we conclude that i the luvic phaeozem pits and horizons are man made formed during several archaeological epochs between mesolithic and middle ages ii these pits must have been formed outside the actual prehistoric settlements offsite and may serve as a novel archaeological feature iii the purpose of these pits at present is not clear and iv human activity has altered and ultimately formed the investigated soils of the lower rhine basin in prehistoric time

interaction of metamorphism deformation and exhumation in large convergent orogens coupled thermal mechanical models are used to investigate interactions between metamorphism deformation and exhumation in large convergent orogens and the implications of coupling and feedback between these processes for observed structural and metamorphic styles the models involve subduction of suborogenic mantle lithosphere large amounts of convergence 450 km at 1 cm yr 1 and a slope dependent erosion rate the model crust is layered with respect to thermal and rheological properties the upper crust 0 20 km follows a wet quartzite flow law with heat production of 2 0 w m 3 and the lower crust 20 35 km follows a modified dry diabase flow law with heat production of 0 75 w m 3 after 45 myr the model orogens develop crustal thicknesses of the order of 60 km with lower crustal temperatures in excess of 700 c in some models an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 pa s at 700 c in the upper crust and 900 c in the lower crust in these models a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where t 600 c the channel flow zone is characterised by a reversal in velocity direction on the pro side of the system and is driven by a depth dependent pressure gradient that is facilitated by the development of a temperature dependent low viscosity horizon in the mid crust different exhumation styles produce contrasting effects on models with channel flow zones post convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust related exhumation on the flanks velocities in the pro side channel flow zone are enhanced but the channel itself is not exhumed in contrast exhumation resulting from erosion that is focused on the pro side flank of the plateau leads to ductile extrusion of the channel flow zone the exhumed channel displays apparent normal sense offset at its upper boundary reverse sense offset at its lower boundary and an inverted metamorphic sequence across the zone the different styles of exhumation produce contrasting peak grade profiles across the model surfaces however p t t paths in both cases are loops where pmax precedes tmax typical of regional metamorphism individual paths are not diagnostic of either the thickening or the exhumation mechanism possible natural examples of the channel flow zones produced in these models include the main central thrust zone of the himalayas and the muskoka domain of the western grenville orogen

dating initial maori environmental impact in new zealand abstract over the last decade there has been an intense debate as to whether new zealand prehistory is long 1500 yr short

on the mechanism of tectonic transport in zones of oblique subduction abstract many cases of oblique subduction are known throughout the world today and many more must have existed in the past in at least one modern case sumatra the over riding plate has responded to oblique subduction by forming a strike slip fault that traverses the magmatic arc and displaces its leading edge in the direction of the transverse component of oblique convergence conditions favoring this sort of tectonic response are shown to be 1 1 a high angle of oblique convergence 2 2 a low angle of subduction and 3 3 relative thermal softening of the magmatic arc this mechanism may have been responsible in part for northward transport of western cordilleran magmatic arc and subduction zone rocks in the late cretaceous and earliest tertiary it also may help to explain evidence of southward transport and left lateral shear in northern mexico and the caribbean region in pre jurassic time

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

the calculation of the dynamic sea surface topography and the associated flow field from altimetry data a characteristic function method the quasi stationary sea surface topography qsst and associated oceanic circulation is determined by means of a characteristic function technique the method was originally implemented in an ideal simplified case the present application involves a 4 83 4 8grid in spherical coordinates approximating the boundaries of the main ocean basins the data field is provided by the first year of altimetric data from the topex poseidon mission the method requires the numerical determination of the eigenfunctions spanning the streamfunction field and the associated characteristic functions from the balance equation the former yields the flow field and the latter the surface height distribution or qsst these functions are determined by the geometry and topography of the ocean basins and satisfy the linear steady state dynamical equations they are defined within the basins only and avoid the problems encountered when using functions defined over the entire sphere the velocity field can be computed over the entire ocean area including the equatorial regions the coefficients of the height functions have been determined by fitting the surface height field provided by topex altimetry seasonal variations have been computed by subtracting a 32 cycle solution from each of the four 8 cycle seasonal solutions

emplacement of rapakivi granite and syenite by floor depression and roof uplift in the palaeoproterozoic ketilidian orogen south greenland in the palaeoproterozoic ketilidian orogen of south greenland tabular intrusions of the rapakivi granite suite exposed at graah fjelde lindenow fjord and qernertoq and a mesoproterozoic syenite of the gardar province exposed at paatusoq were emplaced by a combination of roof uplift and floor depression the strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere space for the emplacement of the rapakivi plutons was not created during regional extension on low angle ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening the rapakivi granites post date peak metamorphism in the orogen by 35 46 ma and their contacts cross cut and clearly post date intense flat lying d1 d2 fabrics that formed by partitioning of deformation into arc normal and arc parallel components during oblique convergence

biomorphic analysis as a part of soil morphological investigations abstract biomorphic analysis is the microscopic investigation of plant tissue detritus phytoliths pollen and other remains of biota for the reconstruction of ancient pedogenic conditions and the evolution of soils each biomorph is associated with certain types of landscape and provides information on conditions of soil development and on landscape evolution every stage of soil development forms its own biomorph profile and profiles of different stages can be distinguished they indicate the main vegetation changes during the holocene human impacts such as grazing tillage and tree felling also exert a considerable influence on the qualitative and quantitative distribution of biomorphs through the profile as examples samples were studied from soil profiles representing different climatic subzones of the russian plain the results show that biomorphic analyses can provide information that is otherwise unobtainable and can elucidate some controversial questions of soil genesis and cultural changes