short paper terrane rotations in the irish caledonides palaeozoic palaeomagnetic data from scotland and ireland have been compared on a terrane model and early caledonide clockwise rotation of a terrane through 65o 30 connemara massif and later anticlockwise rotation of up to 50 in the vicinity of clew bay have been deduced these are the firfirst estimates of terrane rotations in the european part of the caledonian appalachian orogen terrane analysis of orogenic belts is currently a major field of study to a large extent this has been stimulated by studies in the north american cordillera where large rotations and translations have been determined palaeomagnetically see beck et al 1986 and references therein terrane analysis may be applied to older orogenic belts such as the caledonides which have been particularly intensively studied previously published palaeomagnetic data from connemara morris tanner 1977 and nw galway morris et al 1973 had indicated local block rotations but furnished few constraints on either their age and magnitude or on the identities of the blocks this paper relates the currently available palaeomagnetic dataseto a terrane model of w ireland hutton dewey 1986 see fig 1 new data new palaeomagnetic data from the irish caledonides comprise the following connemara gabbro robertson 1988 the dalradian rocks of the connemara massif are unique in the british caledonides in lying to the south of a caledonian ophiolite and also south of a thick sequence of ordovician shales and volcanics of low metamorphic grade in clew bay and the south mayo trough respectively the structural

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

multicomponent magnetizations from the mississippian mauch chunk formation of the central appalachians and their tectonic implications previous paleomagnetic study of mississippian red beds of the mauch chunk formation from the central appalachians reported shallow inclination directions a positive fold test was obtained after thermal demagnetization typically to only 550 c the near equatorial position for north america indicated by these results has been used to support the idea of a circa 15 latitudinal tectonic offset of the acadia displaced terrain in the northern appalachians the present study of 153 samples from 29 sites occupied in the mauch chunk formation of eastern and southern pennsylvania reveals multicomponent magnetizations a characteristic component declination d 161 0 inclination i 27 8 alpha95 a95 7 9 with unblocking temperatures usually concentrated above 650 c and with dual polarity 10 sites normal 13 sites reversed is isolated in 23 sites and passes a fold test at the 99 confidence level it is interpreted as an early acquired hematitic detrital or chemical magnetization of pre alleghanian orogeny and pre kiaman reverse polarity interval age a southern hemisphere paleolatitude of 15 for the sampling area is indicated another component has generally lower unblocking temperatures which however can extend up to 650 c or more and therefore is also likely to be carried by hematite this secondary magnetization d 170 6 i 5 3 a95 5 0 isolated in 25 sites is of uniform reverse polarity and application of fold tests suggests that it is of synfolding origin a near equatorial paleolatitude 3 n at the time of acquisition is obtained consistent with permo carboniferous kiaman directions from north america incomplete removal of the secondary component can explain the previous results from the mauch chunk comparison of the present paleomagnetic results with those from similar age rocks in the canadian maritimes does not support a latitudinal offset of acadia with respect to interior north america in the early carboniferous in fact according to these and other paleomagnetic data thought to be representative of this age the atlantic bordering continents already were near to a pangea configuration the alleghanian and particularly the hercynian orogenies therefore may not be associated with the closure of a large latitudinal ocean later in the carboniferous and permian alleghanian deformation however may have resulted in the partial bending of the pennsylvanian salient on the basis of apparently systematic deviations in paleomagnetic declinations

methods for inferring regional surface mass anomalies from gravity recovery and climate experiment grace measurements of time variable gravity 1 the gravity recovery and climate experiment grace will deliver monthly averages of the spherical harmonic coefficients describing the earth s gravity field from which we expect to infer time variable changes in mass averaged over arbitrary regions having length scales of a few hundred kilometers and larger to accuracies of better than 1 cm of equivalent water thickness these data will be useful for examining changes in the distribution of water in the ocean in snow and ice on polar ice sheets and in continental water and snow storage we describe methods of extracting regional mass anomalies from grace gravity coefficients spatial averaging kernels were created to isolate the gravity signal of individual regions while simultaneously minimizing the effects of grace observational errors and contamination from surrounding glacial hydrological and oceanic gravity signals we then estimated the probable accuracy of averaging kernels for regions of arbitrary shape and size

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

paleomagnetism of the upper silurian and lower devonian carbonates of new york state evidence for secondary magnetizations residing in magnetite abstract paleomagnetic directions for the upper silurian and lower devonian carbonates of the helderberg escarpment new york state differ from expected late silurian and early devonian directions for cratonic north america the mean direction d 165 i 10 paleopole at 50 n 129 e is similar to late carboniferous and early permian results negative fold tests and a lack of reversals suggest that the magnetization is secondary however low coercivities low blocking temperatures the thermomagnetic curves tc near 570 c and the acquisition of isothermal remanent magnetizations all suggest that the remanence is carried by magnetite if a detrital origin of these magnetites is assumed the secondary nature of the remanence would argue for thermal resetting as a result of deep burial of the rocks however no evidence for such thermal resetting is seen in the alteration of conodonts more likely perhaps is a chemical or thermochemical origin of the remanence this would require the magnetites to be authigenic

multicomponent magnetization in the helmsdale granite north scotland geotectonic implication abstract a palaeomagnetic study of the helmsdale granite u pb 420 m y k ar 400 m y northeast scotland has revealed a multicomponent remanence dominated by two characteristic axes of magnetization the suggested oldest of these magnetizations the direction of which is nearly horizontal and directed n s is thought to have been acquired in upper silurian lower devonian times the existence of this shallow direction of magnetization discounts a recent hypothesis of a ca 2000 km sinistral offset along the great glen fault the second component of magnetization appears to be partly carried by haematite that apparently formed through disintegration of biotite and or plagioclase this secondary magnetization has a direction that can be associated with a permian early mesozoic age similar overprinted magnetizations are characteristic features also in the devonian sedimentary sequences north of helmsdale

paleomagnetism of lower devonian volcanics and devonian dykes from northcentral new brunswick canada abstract some 50 oriented samples 120 specimens have been collected on eight sites of volcanic rocks from the lower devonian dalhousie group of northern new brunswick and devonian andesitic to basic dykes from central new brunswick univectorial and occasional multivectorial components were extracted from the various samples results after af and thermal demagnetization compare relatively well in the volcanics and tuffs two components of magnetization have been isolated a d 33 i 58 95 7 3 k 236 for four sites and b d 66 i 53 for three sites the grouping of component a is improved after tilt correction but the fold test is not significantly positive at the 95 confidence level component a is interpreted as being primary while component b is unresolved and appears to be the resultant magnetization of a late paleozoic and a recent component the pole position obtained for tilt corrected component a is 268 e 1 s dp 6 5 dm 8 8 the paleolatitude calculated for component a is 39 s the paleopole of in situ component a is located close to those of the early middle devonian formations from quebec new brunswick and new england states while the paleopole of tilt corrected component a is similar to lower devonian poles of rock units from the canadian arctic archipelago if component a is primary as we believe it to be then the western half of the northern appalachians had already docked onto the north american craton by early devonian time alternatively if component a is secondary the same conclusion applies but the juxtaposition took place in middle devonian time

thelodont and other agnathan distributions as tests of lower palaeozoic continental reconstructions abstract syntheses of palaeomagnetic and palaeontological data indicate that the distribution of the siluro devonian agnathans particulary the thelodonts were strongly influenced by palaeolatitude and the availability of direct land connections the great spread of thelodonts in the lower devonian suggests that either this dependence on direct land connections became less important for the turinia fauna which seems unlikely or that the dispersal occurred as a result of temporary land bridge connections the cessation of such bridges at the end of the devonian causing an isolation of the fauna in australasia which later became extinct because of climatic changes caused by migration of the continental blocks into different latitudes or by direct competition such dispersal and extinction patterns appear to be a fore runner and directly analogous to the dispersion and partial extinction of the marsupial fauna in cretaceous tertiary times if such a model is valid then it also places constraints on the life habitats of the agnathans

substantial glacier mass loss in the tien shan over the past 50 years long term changes of the mountain glaciers in the tien shan central asia are not well constrained remote sensing data and glaciological models reveal a 27 decline of glacier mass from 1961 to 2012 linked to increased summer melting

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

evaluation of new grace time variable gravity data over the ocean 1 monthly grace gravity field models from the three science processing centers csr gfz and jpl are analyzed for the period from february 2003 to april 2005 over the ocean the data are used to estimate maps of the mass component of sea level at smoothing radii of 500 km and 750 km in addition to using new gravity field models a filter has been applied to estimate and remove systematic errors in the coefficients that cause erroneous patterns in the maps of equivalent water level the filter is described and its effects are discussed the grace maps have been evaluated using a residual analysis with maps of altimeter sea level from jason 1 corrected for steric variations using the world ocean atlas 2001 monthly climatology the mean uncertainty of grace maps determined from an average of data from all 3 processing centers is estimated to be less than 1 8 cm rms at 750 km smoothing and 2 4 cm at 500 km smoothing which is better than was found previously using the first generation grace gravity fields

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

geochemistry and thermodynamics of an earthquake a case study of pseudotachylites within mylonitic granitoid abstract pseudotachylites are melts produced by frictional heating during seismic slip understanding their origin and their influence on slip behavior is critical to understanding the physics of earthquakes to provide insight into this topic we conducted a case study in the proto mylonitic to mylonitic asbestos mountain granitoid in the eastern peninsular ranges batholith california which records both ductile mylonites and brittle deformation features pseudotachylites and ultracataclasites u pb chronology and zr thermometry of titanite porphyroblasts in the mylonites indicate that mylonitization of the plutons occurred at near solidus conditions 750 c over a 10 ma interval from 89 to 78 ma mylonitization resulted in recrystallization of quartz plagioclase and biotite with the biotite concentrated into biotite rich foliation planes subsequent brittle deformation is superimposed on the ductile fabrics micro xrf elemental mapping and in situ la icp ms analyses on these brittle deformation products show that the pseudotachylites are more mafic lower si but higher fe and k rich than the host mylonite while the ultracataclasites are intermediate between the host and the pseudotachylites inverse mass balance calculations show that both brittle deformation products are depleted in quartz but enriched in biotite with the pseudotachylites showing the most significant enrichment in biotite indicating preferential involvement of biotite during brittle deformation we suggest that biotite rich layers generated during ductile deformation may have been the preferred locus of subsequent brittle deformation presumably because such layers represent zones of weakness frictional heating associated with slip along such planes results in melting which causes a decrease in viscosity in turn leading to further strain localization during the short time span of an earthquake frictional melting appears to be a disequilibrium process in which the minerals are melted in order of their melting points from biotite 800 c to plagioclase 1400 c and finally to quartz 1700 c rather than by equilibrium melting which results in silicic eutectoid melts at lower temperatures 650 c thus with progressive slip melt composition should evolve from mafic to felsic eventually approaching the bulk composition of the host rock the mafic composition of the pseudotachylites thus indicates that they formed between the melting point of biotite and plagioclase 800 1400 c our chemical and modeling analyses on the pseudotachylites suggest that the chemical composition of pseudotachylites can potentially be used to constrain the thermodynamic conditions in the shear zone as well as earthquake source mechanics

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

non isotropic gaussian smoothing and leakage reduction for determining mass changes over land and ocean using grace data summary we present a new non isotropic gaussian filter for smoothing mass changes computed from gravity recovery and climate experiment grace l2 products and a new method to reduce land ocean signal leakage caused by gaussian smoothing the kernel of our non isotropic filter is the product of two gaussian functions with distinct latitudinal and longitudinal smoothing radii when expressed as number of kilometres at the earth s surface the longitudinal smoothing radius defined as a fixed longitude interval is longer at the equator and shorter at higher latitude this is principally in accordance with the resolution of the grace data and permits us to produce homogeneously smoothed results without excessive smoothing in latitudinal direction this filter is not applicable in polar regions where we choose to use the classical isotropic gaussian filter a smoothing radius choice scheme is proposed for the two filters to mesh seamlessly in our leakage reduction method the inputs are the mass change data after smoothing using a gaussian filter along coasts where mass change signal on land is far larger than that over ocean or signal over ocean is reduced to a very small magnitude by removing a model beforehand and adding the model back afterwards our method approximately recovers a smoothed mass change signal over both land and ocean sides as if a regional gaussian filter with the same smoothing radius were applied over land and ocean separately in which no signal leakages appear the side lobe problem does not appear in our approach our leakage reduction method could also be used to study mass changes within a region where signal is far larger than that in surrounding regions or where signal in surrounding regions could be reduced to very low magnitude by removing a model

oroclinal bending in the caledonides of western ireland new palaeomagnetic data from the caledonides of western ireland indicate that the silurian rocks of south mayo underwent oroclinal bending following folding in siluro devonian time bending was accommodated on faults cutting the silurian sequence and was driven by strike slip motion across the antrim galway line a recently recognized major curvilinear lineament we propose that the silurian rocks in the east of the region suffered up to 30 clockwise rotation increasing towards the west to approximately 70 this newly inferred differential rotation of the silurian rocks about a sub vertical axis implies that the underlying dalradian rocks of the connemara massif to the south must also have undergone clockwise rotation in late silurian early devonian time this is consistent with published palaeomagnetic data from the connemara gabbro and accounts for the swing in strike of the caledonian orogen in this part of western ireland from this we deduce that the swing in strike of the caledonian rocks elsewhere on the west coast of ireland might have a similar explanation

a middle late silurian paleomagnetic pole from limestone reefs of the wabash formation indiana u s a a middle late silurian paleomagnetic pole has been obtained from reefal limestones in north central indiana eleven of 25 collected sites yielded well clustered characteristic directions after stepwise alternating field demagnetization one additional site gave the same characteristic direction after great circle analysis these 12 site level directions were used to calculate the mean paleomagnetic pole reef flank beds dip steeply about 38 away from reef centers field and petrographic studies demonstrate that part of this dip is a primary depositional dip and that part is due to a tilt caused by early postdepositional differential compaction of underlying mudstone beds present attitudes of geopetal surfaces indicate that the postdepositional component of the observed bedding dip is about 12 a 12 tilt correction to paleomagnetic directions from oppositely dipping flank beds brings the mean directions into significantly better agreement indicating that the magnetization was acquired early the presence of both normal and reversed polarities also suggests early acquisition of the characteristic remanence the mean of the site paleomagnetic poles with sites from steeply inclined flank beds corrected for 12 of tilt is 16 8 n 124 9 e k 74 a95 5 1 in good agreement with the middle silurian rose hill pole for north america

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

palaeomagnetism of the foyers and strontian granites scotland abstract palaeomagnetic data from the newer granites of foyers and strontian show similar directions of magnetization with southerly declinations and horizontal to intermediate mostly downward dipping inclinations these palaeomagnetic directions which accord with previous data from the helmsdale granite are thought to be of siluro devonian age the present results are not sufficiently precise to justify discussion of possible lateral displacements along the great glen fault of the order of a few hundred kilometres but it is clear that the recent idea of a c 15 20 latitudinal offset along the fault in the carboniferous has to be disregarded

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

palaeomagnetism of late precambrian cambrian volcanics and intrusives from the armorican massif france samples of the keratophyre tuffs of treguier 640 12 myr of the upper brioverian series and the microgranite dykes of loguivy 548 24 myr have been collected from the north coast of brittany france the samples were progressively demagnetized with af and predominantly thermal methods blocking temperatures coercivities and acquisition of isothermal remanent magnetization irm indicate that the keratophyre remanence is variably carried in magnetite hematite or occasionally in both after removal of a soft viscous component two stable palaeomagnetic directions were found one in magnetite the other in hematite the characteristic magnetite direction tb 300 580 c is a pre folding primary thermoremanent magnetization trm which after structural correction has a mean declination inclination of 217 9 30 4 the younger hematite component has a mean in situ direction of 320 4 20 3 the microgranite natural remanent magnetization nrm intensity distribution is distinctly bimodal forming high and low 1 6 a m 1 intensity groups upon demagnetization a single stable remanence in magnetite was removed between 300 and 580 c or 20 and 100 mt two characteristic directions were found to be statistically related to the intensity groups at the 99 per cent confidence level low intensity samples have a mean direction of 201 9 2 3 and probably resulted from a late devonian early carboniferous local magnetization high intensity microgranites have a mean direction of 200 50 8 and this remanence is shown to be a primary trm palaeopoles obtained from the two keratophyre magnetizations magnetite 44 7 n 116 4 e hematite 39 5 n 233 6 e as well as the high intensity microgranite remanence 5 8 s 339 9 e show good agreement with similar age poles from the apparent polar wander path for the armorican massif comparison of these data to recent palaeomagnetic data from southern england and wales gives additional evidence to link that region with the armorica plate as proposed by van der voo and hagstrum et al

late ordovician to early silurian amalgamation of the dalradian and adjacent ordovician rocks in the british isles from detailed radiometric and pressure temperature estimates of the metamorphic history uplift and erosion of the dalradian rocks of the british isles we find that 15 25 km of erosion took place mainly in ordovician time none of this vast volume of material is apparently present in the ordovician sedimentary basins that now flank the dalradian block we conclude that the ordovician basins to the south of the dalradian block are exotic terranes and we document their emplacement into their present position during late ordovician to early silurian time i e taconic by using evidence mainly from western ireland

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

u pb zircon geochronology of plutonism in the northern peninsular ranges batholith southern california implications for the late cretaceous tectonic evolution of southern california

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

implications of early devonian poles from the canadian arctic archipelago for the north american apparent polar wander path lower devonian red beds from the upper member of the peel sound formation at prince of wales island canadian arctic yield two different paleopoles at 25n 099e and at 01n 091e the first one being

evaluation of glacier changes in high mountain asia based on 10 year grace rl05 models in this paper 10 years of time variable gravity data from the gravity recovery and climate experiment release 05 have been used to evaluate the glacier melting rate in high mountain asia hma using a new computing scheme i e the space domain inverse method we find that in hma area there are three different kinds of signal sources that should be treated together the two generally accepted sources glacier melting and india underground water depletion are estimated to change at the rate of 35 0 5 8 gt yr 0 09 mm yr sea level rising and 30 6 5 0 gt yr respectively the third source is the remarkable positive signal 30 gt yr in the inner tibetan plateau which is challenging to explain further we have found that there is a 5 year undulation in pamir and karakoram which can explain the controversies of the previous studies on the glacier melting rate here this 5 year signal can be explained by the influence of arctic oscillation and el nino southern oscillation

palaeozoic terrane accretion in the western irish caledonides the southern boundary of the early caledonides in the british isles the dalradian supergroup is represented by the major highland boundary fair head clew bay line in the west of ireland accretion along this laurasian margin occurred by sinistral strike slip during two phases the earliest was responsible for the docking of the connemara terrane a displaced part of the dalradian outboard of the south mayo trough in the llanvirnian llandeilian this event is recorded independently by radiometrically dated sinistral strike slip deformation in the ox mountains of western ireland following deposition of a silurian overlap sequence sinistral movements were renewed between the upper llandoverian and the siegennian this event is part of a major phase of sinistral strike slip throughout the british isles involving accretion of the cadomian terrane and the devonian accretion of the avalon terrane in the northern appalachians

early devonian marine isotopic signatures brachiopods from the upper gaspe limestones gaspe peninsula quebec canada abstract brachiopods from the upper gaspe limestones gaspe peninsula eastern canada document the isotopic geochemistry 18o 13c and 87sr 86sr of marine calcites for the siegenian and emsian stages early devonian nonluminescent brachiopods nlb from five species of a deep water benthic community show a narrow range of 13c values 1 3 to 1 7 average 1 5 and a much wider range of 18o values 2 7 to 4 6 average 3 7 that partially overlaps the field of luminescent brachiopods this is probably related to retention of fabric during diagenesis despite oxygen isotope exchange the heaviest 18o values for nonluminescent brachiopods 3 3 siegenian 2 7 emsian are interpreted as the signature of marine low mg calcite the 18o values for the gas e brachiopods suggest a negative 18o shift at the end of the early devonian the heaviest 18o values documented by previous workers for late early devonian emsian brachiopods cluster around 4 5 a figure that differs by 1 8 from the heaviest value for gaspe brachiopods this difference is most likely related to the growth of the gaspe brachiopods in deeper and cooler seawater as suggested by independent sedimentologic and biologic evidence rather than a 7 c warming of ocean surface temperatures or a rapid 7 ma shift in the 18o of seawater in a period of nonglaciation the 87sr 86 data for early devonian brachiopods fill the early devonian gap in the burke et al 1982 curve for devonian seawater the siegenian value is slightly more radiogenic than the younger emsian ones and support a continuous decrease in 87sr 86sr values from latest silurian to middle devonian time

paleomagnetic evidence for post devonian displacement of the avalon platform newfoundland the possibility that the avalon platform where the avalonian lithotectonic belt is best developed was involved in late paleozoic displacement was tested by paleomagnetic study of red sandstones of the upper devonian terrenceville formation of eastern newfoundland two magnetization directions were identified by thermal demagnetization analysis of 60 oriented samples from 10 sites a high blocking temperature thermally discrete a component of normal and reversed polarity and an intermediate blocking temperature thermally distributed b component of reversed polarity the b component d 185 9 i 3 3 a95 7 2 for n 8 sites is interpreted as a postfolding secondary magnetization and gives a paleomagnetic pole position latitude 43 6 n longitude 117 1 e near early to late permian paleopoles for north america the a component d 181 6 i 28 0 a95 10 1 for n 9 sites is interpreted as the characteristic magnetization possibly dating from near the time of deposition of the terrence ville formation the corresponding paleomagnetic pole position latitude 27 4 n longitude 123 5 e falls within a group of late devonian early carboniferous paleopoles obtained from the acadia displaced terrain encompassing the coastal areas of new england and the canadian maritimes which form another part of the avalonian belt these paleopoles are systematically offset by 15 to 20 in latitude from coeval pole positions obtained from cratonic north america thus the avalonian belt of the northern appalachians which is thought to represent a remnant of a precambrian and early paleozoic microcontinent on tectonostratigraphic considerations appears to correspond to a late paleozoic displaced terrain on the basis of paleomagnetic evidence

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

paleomagnetism of the north american precambrian a look at the data base more than half of the approximately 650 paleopoles reported from all precambrian cratons have been obtained from north america the observations have spurred a proliferation of apparent polar wander paths to support different hypotheses for the tectonic evolution of the continent many of the reasons for this development can be traced to the inadequacy of the data base with its average of only 1 6 poles 10 ma 1 as compared to 7 poles 10 1 ma for the last 300 ma even when it is assumed that a primary pole has been derived from each rock unit sampled the total number of primary poles excluding the 900 1200 ma interval yields an average of only 0 4 pole 10 ma 1 an inspection of the data base shows a non systematic sampling of a non continuous fragmented paleomagnetic record with gaps as large as tens and even hundreds of ma more importantly a search through the literature reveals that very few poles have an age known to better than 50 ma and for many poles the age bracket could be as large as a few hundreds of ma this is partly owing to the fact that radiometric and paleomagnetic sites rarely originate from the same localities it is shown that this limited data base with all its deficiencies and uncertainties cannot be used to support certain hypotheses or for the drawing of a meaningful apparent polar path for the whole of the precambrian it appears that because of the enormous time scale precambrian paleomagnetism should rather be directed towards the construction of segments of polar paths such as those in the 900 1200 ma interval comparison of well dated contemporaneous segments from different parts or structural provinces could be used most effectively to delineate relative movements if any and reconstruct the mosaic of the past continent for certain time intervals one of the recent developments of precambrian paleomagnetism has been to show that the apparent pole did not remain constrained to the equatorial region but made several excursions into high latitudes

diagenetic magnetite carries ancient yet secondary remanence in some paleozoic sedimentary carbonates many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite when such magnetizations are observed it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition however paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the helderberg and bonneterre carbonates united states indicate that the magnetite present in these rocks is most likely of diagenetic i e postdepositional origin

the palaeogeographic evolution of southern britain during early palaeozoic times a reconciliation of palaeomagnetic and biogeographic evidence abstract palaeomagnetic biogeographic and palaeoclimatic evidence together suggest that in the early ordovician southern britain lay off the west african margin of gondwana at around 60 s the combination of these disciplines reduces latitude uncertainties to around 5 to 10 degrees rifting of avalonia from gondwana was followed during most of the ordovician by northward drift as avalonia and baltica converged with subduction of tornquist sea crust both continents had similar moderate northward drift rates 3 6 cm yr so their convergence probably had a considerable longitudinal component silurian and early devonian data indicate that northward drift of avalonia and baltica continued after their collision and that southern britain reached a latitude of around 20 s by c 400 ma

paleomagnetism of the lower devonian traveler felsite and the acadian orogeny in the new england appalachians a suite of felsic extrusive rocks from the lower devonian traveler felsite north central maine 46 1 n lat 68 9 w long was collected for paleomagnetic study 28 samples from 5 sites in the lower pogy member 56 samples from 10 sites in the upper black cat member and 13 samples from 10 cobbles in the basal conglomerate of the overlying trout valley formation characteristic magnetizations based on af demagnetization analyses and supported by thermal studies give a formation mean direction after simple correction for bedding tilt of d 25 2 i 20 2 95 10 6 for 13 sites in the traveler felsite the occurrence of normal and reversed magnetozones under stratigraphic control and the antiparallel directions of the polarity units following the tilt correction indicate an acquisition of remanence near the time of formation of the rock units the mean direction corresponds to a south paleopole position of 29 s lat 262 e long p m 6 11 for the traveler felsite this pole position is in close agreement with poles from two other rock units of similar age from the same lithostratigraphic belt in the northern appalachians the mean of these three poles is distinct from late silurian and middle devonian poles from cratonic north america laurentia and from early devonian results from the acadia displaced terrane suggesting that this area constituted a separate tectonic unit during the early devonian we propose a tectonic model in which a traveler terrane is rotated 20 to 30 while converging with laurentia and undergoing deformation during the early to middle devonian acadian orogeny

evidence against large scale carboniferous strike slip faulting in the appalachian caledonian orogen kent and opdyke1 have argued that during the late devonian and early carboniferous the eastern part of the northern appalachians acadia was situated 1 500 km further south relative to cratonic north america than it is at present and that it moved to its present position sometime later in the carboniferous fig 1 van der voo and scotese2 proposed an even greater displacement of 2 000 km which they attribute to motion between cratonic north america and europe acadia being attached to europe fig 1 the argument is that palaeolatitudes p derived palaeomagnetically from upper devonian and lower carboniferous rocks of cratonic north america are 15 20 more northerly than those of acadia and europe the proposed shear zone passes through central newfoundland using palaeomagnetic results from eastern and western newfoundland we show here that no such motion occurred we also show that kiaman late carboniferous and permian overprinting is widespread in newfoundland and that these secondary magnetizations agree with two exceptions attributed to dextral rotation of the colorado pleateau with observations from late devonian and early carboniferous rocks of the north american craton confirming the proposal3 that magnetizations of the cratonic early carboniferous rocks are kiaman not early carboniferous in age our results also enable us to extend this proposal3 to late devonian rocks of the craton hence the palaeolatitudinal offset of fig 1 is almost certainly not tectonic but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages

deceleration in the earth s oblateness 1 for over three decades satellite laser ranging slr has recorded the global nature of the long wavelength mass change within the earth system analysis of the most recent time series of 30 day slr based estimates of earth s dynamical oblateness characterized by the gravitational degree 2 zonal spherical harmonic j2 indicates that the long term variation of j2 appears to be more quadratic than linear in nature the superposition of a quadratic and an 18 6 year variation leads to the unknown decadal variation reported by cheng and tapley 2004 although the primary trend is expected to be linear due to global isostatic adjustment there is an evident deceleration j 2 18 1 10 13 yr2 in the rate of the decrease in j2 during the last few decades likely due to changes in the rate of the global mass redistribution from melting of the glaciers and ice sheets as well as mass changes in the atmosphere and ocean

paleomagnetism of the lac st jean anorthosite and related rocks grenville province quebec alternating field and thermal demagnetization study of the lac st jean anorthosite and related rock units in the central portion of the exposed grenville province reveals two components of magnetization one of reversed and the other of normal polarity both components are thought to have been acquired during the last regional metamorphism which was sufficiently intense in this area mostly amphibolite grade to reset any earlier magnetization corresponding paleopoles at 193 w 8 s dm 7 3 dp 4 6 and 213 w 19 s dm 10 5 dp 8 5 lie along the 950 900 ma segment of the recently calibrated grenville track of the north american apparent polar wander path a track that has thus far been defined largely by results from rock units of the western grenville

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

evidence for silurian sinistral accretion of avalon composite terrane in canada the kingston dyke complex forms a regionally developed belt of sheeted bimodal dykes within the avalon composite terrane of southern new brunswick canada dyke orientation relative to the belt suggests their injection accompanied sinistral movement and the belt has previously been attributed to transform activity within the late precambrian magmatic arc regime typical of the avalon composite terrane in the northern appalachians however rhyolite dykes of the sheeted complex yield a u pb age of 435 5 1 5 ma that is interpreted to date their emplacement the complex therefore provides evidence of early silurian sinistral displacement in the northern appalachians such movement is suggested by palaeomagnetic data and may record the accretion of the avalon composite terrane to cratonic north america

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

superimposed recent permo carboniferous and ordovician palaeomagnetic remanence in the builth volcanic series wales the builth volcanic series of llanvirnian age in llanelwedd quarries mid wales carries three components of natural remanent magnetisation component p regarded as primary is a thermochemical remanence directed at d 181 7 i 54 5 95 4 4 relative to bedding component s is a secondary component with in situ d 178 7 i 6 7 95 5 4 and is believed to be a low temperature chemical remanence crm of permo carboniferous age component r is directed close to the present geomagnetic field and is believed to be a recent viscous remanence vrm the results are of interest for three reasons first they are an unusually good example of multi component nrm analysis the three components being so clearly discriminated by thermal demagnetisation because they have almost completely separate blocking temperature ranges second they provide evidence of a permo carboniferous event possibly a mild thermal or hydrothermal pulse promoting crm acquisition some 40 km north of the hercynian orogenic front third they illustrate very clearly the importance of detailed demagnetisation this work revises the pole position for these rocks by 10 and removes an obstacle to the palaeomagnetic recognition of the 1000 km wide iapetus ocean cutting britain in ordovician time

palaeomagnetic investigations in the hercynian mountain belt of central europe abstract the palaeomagnetism of sediments and volcanics of middle devonian to early carboniferous age has been studied in the hercynian realm of the vosges harz and franconian forest france and germany after appropriate cleaning characteristic directions of natural remanent magnetization nrm have been determined which are considered to be of pretectonic origin according to rock magnetic and structural geological evidence a mean palaeopole for the devonian rocks in the areas investigated was determined at 29 7 n and 9 0 e the site latitude derived from the devonian rocks agrees very well with that observed in great britain and britanny the significant difference in longitude between our devonian poles and the other european data may be due to an anticlockwise rotation of central europe with respect to the northern hercynian foreland the carboniferous rocks yield a mean palaeopole at 41 7 n and 340 4 e matching the carboniferous part of the european polar wander path a fold test within carboniferous greywackes from the harz mountains proves a pre folding origin of the nrm of these rocks however this stable magnetization direction indicates local or regional tectonic displacement our results do not support any major latitudinal motions of continental segments in central europe during the hercynian orogeny the palaeozoic palaeomagnetic data from the vosges franconian forest harz britanny and central massif can be used to interpret the hercynides in terms of a large scale shear belt

a revised palaeozoic apparent polar wander path for southern britain eastern avalonia summary a revised apparent polar wander path apwp is presented for palaeozoic southern britain the new path based on a structural reinterpretation of existing data combined with new data from wales differs significantly from previous estimates in the following ways 1 the 1 ocus of the ordovician path segment is extended by approximately 25 degrees of arc 2 revised time calibration of the apwp suggests more ordovician apw than previously calculated and 3 the new path implies middle ordovician separation across the british sector of iapetus to be greater than previous palaeomagnetic estimates based on apwp analyses c 3300 km northern britain c 133 southern britain c 45s

terrane amalgamation in the clew bay region west of ireland the caledonides of the west of ireland provide a well exposed and well mapped example of an oblique collision zone the east northeast trending deer park and achill beg fault system is a crustal scale ductile sinistral strike slip duplex of late ordovician age imbricating late precambrian granulite facies lower crustal rocks near eclogite facies supracrustal rocks up to amphibolite facies dalradian metasedimentary rocks and greenschist facies cambro ordovician rocks this fault system is correlated with a pre devonian component of the highland boundary fault system in southern scotland in the clew bay area the high pressure low temperature facies metamorphic rocks in tectonic contact with greenschist facies cambro ordovician rocks are together interpreted as an accretionary prism complex related to northwestward directed subduction both of these are allocthonous terrains with respect to the dalradian terrane to the north north west mayo to the south the cambro ordovician rocks docked with a probable dalradian block containing ultramafic intrusives deer park complex during the late ordovician the deer park complex and south mayo trough linked earlier during the arenig silurian and lower middle devonian redbed successions sit unconformably on the metamorphic rocks deposition and deformation of these cover rocks was controlled by oblique strike slip movements on the leek fault whose strike swings from west northwest to north northeast following earlier basement trends as it is traced eastwards from clew bay the leek fault system may be correlated with the leannan fault of northwest donegal a splay of the great glen fault system of central scotland east of clew bay this sinistral shear generated local dilation on the more northerly trending bend of the leek fault lower and middle old red sandstone redbeds were developed here the west northwest trend of the leek fault in clew bay acted as a compressional bend during these sinistral movements and transpressional southwest directed thrusting developed in silurian rocks post middle old red sandstone pre late tournaisian dextral displacement on the leek fault reversed this pattern with transtension in clew bay allowing intrusion of small carbonated peridotite bodies into silurian rocks and easterly directed thrusting of middle old red sandstone rocks east of the bay on the transpressional north south bend a tectonic model for the region is presented here this model involves a northwestward directed subduction system 150 to 750 km of arenig sinistral strike slip movement and eastwards insertion of the connemara block with formation of the ordovician south mayo trough as a pull apart basin subsequently a further 130 to 650 km eastward displacement of rocks took place south of the deer park fault in later ordovician times the magnitudes of these estimates are directly proportional to an assumed maximum wavelength of 1500 km for promontories on the original laurentian margin and using the current juxtaposition of terranes a minimum wavelength of 300 km is inferred

palaeomagnetic signature of slow post orogenic cooling of the north east highlands of scotland recorded in the newer gabbros of aberdeenshire summary consideration of previous work and new data show a systematic distribution of the directions of high coercivity and high blocking temperature magnetization in the newer gabbros of aberdeenshire the site mean directions show a non fisherian distribution with the corresponding pole positions distributed along a published early palaeozoic apparent polar wander path for great britain the mean of the distribution closely agrees with the mean direction previously reported and widely quoted there is a close correlation of the site mean directions with the position of the sampling sites with respect to the contours chrontours of the k ar coolingage sites where stable nrm has se declinations and shallow 20 inclinations have the oldest chrontour ages 468 myr the mean palaeomagnetic direction progressively shifts and the sites with the youngest chrontour ages 428 myr have sw declinations with moderately steeper 45 inclination the relative age of magnetization determined from the position of the corresponding pole on the apparent polar wander path is consistent with the relative chrontour age the gabbros have therefore recorded the shift of the north east highlands with respect to the palaeomagnetic pole during the slow cooling of the terrain the slow cooling is presumably related to uplift and erosion and the resulting downward migration of isothermal surfaces a previously published suggestion that all magnetizations with southerly declinations and moderately downward inclination are the resultant of normal and reversed magnetizations with shallow inclination is shown to be incorrect

non isotropic filtering of grace temporal gravity for geophysical signal enhancement summary monthly mass variations within the earth system produce temporal gravity changes which are observable by the nasa gfz gravity recovery and climate experiment grace twin satellite system mass load changes with spatial scales larger than 1000 km have been observed using conventional filters based on a gaussian smoother which applies a weight to grace spherical harmonic sh coefficients depending only on sh degree this practice is consistent with a degree dependent error model for grace monthly geopotential solutions the gaussian filters effectively dampen all power of ill determined higher degree components in the estimates however the spatial sampling provided by grace yields errors that vary with both sh degree and order the consequence is that maps of spatial loads shall not be smoothed with an isotropic degree only filter but shall be constructed using anisotropic smoothing thus also yielding better spatial resolution in latitude we have developed a non isotropic filter to optimize the smoothing of grace temporal gravity observations by considering the degree and order dependent quality of grace estimates the latter analysed from the correlation with the predicted signals of hydrologic and ocean models in order to retain grace coefficients in the filtering process that show reasonable correlation with the geophysical hydrology and ocean models we applied gaussian type smoothing but with averaging radius depending on the order of the geopotential coefficient estimates applied to 2 yr of grace data we showed that the resulting non isotropic filter yields enhanced grace signals with significantly higher resolution in latitude and the same resolution in longitude without reducing the accuracy as compared to the conventional gaussian smoother

slight mass gain of karakoram glaciers in the early twenty first century the mass balance of hindu kush karakoram himalaya glaciers has been debated partly because of a severe lack of observations from the region an analysis of the regional mass balance of karakoram glaciers by comparison of digital elevation models from 1999 to 2008 reveals a small glacier mass gain in the area

major southward thrusting of the dalradian rocks of connemara western ireland the connemara schists are of dalradian late precambrian cambrian age and since the work of kilburn et al 1 it has been apparentthat they occupy an anomalous geographical position south southeast of the strike continuation of the dalradian rocks of scotland and ireland and south of the inferred position of the highland boundary fault fig 1 also the connemara schists are unusual in having reached a higher metamorphic grade and having had a different metamorphic history from most other parts of the dalradian the model which we propose here for the connemara dalradian that of an allochthonous thrust sheet offers an explanation for these anomalies and highlights hitherto unsuspected similarities between the tectonic histories of the south east margins of the metamorphic caledonides in the british isles and scandinavia

palaeomagnetic studies of fold development and propagation in the pembrokeshire old red sandstone abstract the geometry of two folds in lower devonian old red sandstone in pembrokeshire deformed in the hercynian has been defined at intermediate stages during their evolution by this preliminary palaeomagnetic study this is possible because remagnetization appears to have occurred in discrete episodes during deformation and the shape can be reconstructed by restoring the fold limbs to an angle at which the remagnetization directions coincide the plunge of the folds is shown to vary considerably during evolution one fold having an early easterly plunge which changed to the present westerly plunge the other fold having an early plunge which was more steeply to the west than its present attitude clockwise rotation of the whole of southern pembrokeshire by 40 towards the end of or since the hercynian deformation is indicated by the palaeomagnetic data and a structural model for this is proposed

a new devonian palaeomagnetic pole for the russian platform and baltica and related apparent polar wander summary of published palaeomagnetic data from the russian platform and britain for mid palaeozoic times places an ocean between the two of the order of 2000 km latitudinal width this contradicts geological evidence which favours contiguity between the two continental units by devonian times we propose that this discrepancy can be attributed to the incorrect dating of palaeomagnetic remanence we strove to remedy this situation by conducting a new palaeomagnetic investigation of silurian and devonian sediments in west ukraine ussr latitude 48 7 n longitude 26 e that investigation uncovered a pervasive upper palaeozoic remagnetization corresponding to a palaeomagnetic pole at lat 45 8 s long 348 2 e dpldm 1 6 3 1 n 25 sites reversed polarity a second primary or near primary devonian remanence was identified with pole at lat 3 7 n long 325 5 e dpldm 5 2 8 7 n 25 samples mixed polarity the age determination for this devonian result is based on its dual polarity evidence for a detrital remanent mode and early host mineral phase haematite the new devonian result for the russian platform is conformable with the devonian parts of the british apparent polar wander paths and therefore eliminates the aforementioned discrepancy between palaeomagnetic and geological evidence for the timing of assembly of the old red continent

on the role of chemical weathering of continental arcs in long term climate regulation a case study of the peninsular ranges batholith california usa abstract the long term stability of atmospheric pco2 is dominantly determined by the balance between the rate of co2 input from magmatic metamorphic degassing and the efficiency of co2 uptake by silicate weathering via eventual precipitation as marine carbonate and by organic carbon burial silicate weathering is thought to represent a negative feedback to changes in atmospheric pco2 the late cretaceous early cenozoic was characterized by elevated atmospheric pco2 and greenhouse climate widely thought to be due to increased magmatic flux from mid ocean ridges flood basalts and continental arcs of interest here is the role of continental arcs in modulating long term atmospheric co2 contents and climate continental arc magmatism is accompanied by rapid uplift and erosion due to magmatic tectonic thickening of the crust thus the development of continental arcs might also enhance the global efficiency of silicate weathering in turn increasing the efficiency of carbon sequestration to assess the contribution of continental arcs to global carbon sinks we conducted a case study in the cretaceous peninsular ranges batholith prb and associated forearc basin in southern california usa representing one segment of a mesozoic circum pacific continental arc system arc magmatism occurred between 170 85 ma peaking at 100 ma erosion occurred during magmatism and continued well into the early eocene with forearc sediments representing the products of this protracted unroofing of the arc by calculating the depletion of ca in forearc sediments relative to their arc protoliths we estimate chemical weathering fluxes in equivalent co2 to be 106 mol km 2 yr 1 near the end of magmatism decreasing to 105 mol km 2 yr 1 by the early eocene integrated over the entire magmatic and post magmatic history of the batholith the total amount of co2 consumed through chemical weathering is comparable to that degassed however during magmatism the regional degassing flux exceeds the regional weathering flux even though the efficiency of weathering is increased due to magmatic and tectonic uplift after magmatism ends continued erosion from remnant topography causes the arc to transition into a net regional sink increasing the global efficiency of chemical weathering and amplifying cooling after magmatism ends understanding how atmospheric co2 and climate vary over long timescales requires an understanding of how magmatic orogenies enhance degassing but also increase the strength of the global silicate weathering feedback

optimized smoothing of gravity recovery and climate experiment grace time variable gravity observations 1 high degree and high order spherical harmonics of time variable gravity fields observed by the gravity recovery and climate experiment grace gravity mission are dominated by noise we develop two smoothing methods that suppress these high degree and high order errors with results superior to more commonly used gaussian smoothing these optimized smoothing methods considerably improve signal to noise levels of grace terrestrial water storage estimates relative to residual signal and noise over the oceans and show significantly better spatial resolution and lower leakage error on the basis of analysis using an advanced land surface model the equivalent spatial resolution from these optimized smoothing estimates is about 500 km compared to the roughly 800 1000 km gaussian smoothing that is required to suppress high degree noise in the grace fields

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

new paleomagnetic data from carboniferous volcanics and red beds from central new brunswick it has long been argued on the basis of paleomagnetic data derived from devonian carboniferous and permian lithological units from eastern north america that a sinistral megashear of carboniferous age parallels and lies within the faults delimiting the appalachian caledonian chains recent paleomagnetic studies in the northern appalachians have cast doubt on the models of a carboniferous offset the geologic evidence suggests that only a small amount of dextral and not sinistral strike slip has occurred on faults which are parallel with pre acadian paleogeographic realms the purpose of this paleomagnetic study is to test the validity of the proposed left lateral motion at one of the sites of its presumed passage in central new brunswick six sites 80 oriented specimens in carboniferous red beds and volcanics were collected on both sides of the fredericton fault and other parallel faults after af and thermal cleaning the mean direction of magnetization is 158 38 the fold test is indecisive the corresponding paleopole is 135 e 21 n and the paleolatitude 20 s the paleopole positions and paleolatitudes are not significantly different on either side of the fredericton fault and no left lateral motion was detected by paleomagnetic means as no such motion was detected in south central new brunswick and newfoundland it is possible but unlikely that it took place in northern new brunswick and in the western gaspe peninsula this contribution is useful in discussing possible motions of acadia

oroclinal bending in the caledonides of western ireland a mid palaeozoic feature controlled by a pre existing structural grain abstract the caledonides of the west of ireland mark a segment of the caledonian appalachian orogen where the structural grain swings from the ne sw trend that typifies the caledonides of northern britain to an e w orientation the origin of this arcuate structure has previously been proposed to be either primary reflecting the original geometry of promontories and embayments in the laurentian margin in this sector of the orogen or secondary as evidenced by palaeomagnetically determined clockwise rotations in silurian rocks in the region we report the results of a palaeomagnetic investigation of the early to middle ordovician mweelrea ignimbrites llanvirn from an accreted taconic arc the south mayo trough in that part of the western irish caledonides that has an e w trend after removal of a low temperature component of magnetisation l interpreted to represent a viscous component of the earth s present field a high temperature component of magnetisation h was isolated at fifteen sites in four ignimbrite flows h passes a palaeomagnetic fold test yielding a tilt corrected mean remanence direction d 132 6 i 29 1 95 17 9 which corresponds to a palaeopole at 36 4 e 9 9 s the pole is in reasonable agreement with established early to middle ordovician reference poles for laurentia and indicates that no significant rotation occurred between the e w south mayo trough and the laurentian margin after accretion and therefore that the curvature of this segment of the orogen is likely to be primary this contrasts with other results from silurian sequences to the south which record significant post silurian clockwise rotations examination of all reliable palaeomagnetic data from the region indicates that the clockwise rotations are restricted to the rocks south of the south mayo trough we propose that the rotations in the south are linked with the superposition of the pre existing structural grain on the younger rock units during late silurian and early devonian sinistral transpression

paleomagnetism of middle tertiary volcanic rocks from the western cascade series northern california the western cascade series wcs is a 3 5 km thick crudely homoclinal east dipping calcalkaline volcanic sequence of mid oligocene to early miocene age that crops out near the southern tip of the cascade range in northern california the mean direction of remanent magnetization in the wcs is d 4 9 i 57 6 n 53 k 14 4 95 5 3 when compared to a reference direction for the north american craton the wcs direction indicates that the southern cascade range has rotated 14 0 9 0 since the wcs accumulated a difference in mean direction between the lower and upper halves of the wcs suggests that much of this rotation occurred during the late oligocene six other paleomagnetic studies of rock units of an age roughly comparable to the wcs also are available from western oregon northwestern california and southwestern washington all show statistically significant clockwise rotation inclinations of all but one are concordant comparison of directions indicates that the pacific northwest did not rotate as a rigid body but neither did it behave as a collection of small independently rotating domains the amount of rotation found throughout the area increases to the west or northwest suggesting a driving force for rotation operating at the continental margin