ionospheric symmetry caused by geomagnetic declination over north america 1 we describe variations in total electron content tec in the north american sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination patterns were uncovered by applying an empirical orthogonal function eof decomposition procedure to a 12 year ground based american longitude sector gps tec data set the first eof mode describes overall average tec while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second eof mode or the second most significant component we find a high degree of correlation between spatial variations in the second eof mode and vertical drifts driven by thermospheric zonal winds along with well organized temporal variation results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time season and solar cycle this study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range

eof analysis and modeling of gps tec climatology over north america an empirical ionospheric model of the total electron content tec over north america 20 60 n 40 140 w is constructed using the gps tec data collected by massachusetts institute of technology mit haystack observatory during the years 2001 2012 this model is based on an analysis of quiet time monthly averages using the empirical orthogonal function eof decomposition technique allowing for separation of spatial and temporal variations the importance of different types of spatial temporal variations to the overall tec variability can be well represented by the characteristics of eof basis functions and associated principal components coefficients with various modes the mode one eof decomposition constitutes 97 5 of the total variance and therefore represents the essential feature of north america spatial and diurnal variation of the tec the mode two eof as reported in an earlier study reveals a large and significant symmetric longitudinal variation of the ionosphere organized with respect to magnetic declination the mode three eof decomposition shows midlatitude latitudinal structure that varies with season in a manner very similar to the so called winter anomaly because of the quick convergence of eof decomposition modes the first four eof modes are utilized for constructing a tec empirical model for each of the eof modes the temporal variations are expressed analytically in terms of local time season and solar activity and the spatial variations by cubic spline functions an analysis of accuracy and quality indicates that this regional empirical tec model can reflect the majority of the quiet time monthly means and represent characteristic temporal spatial variations in the north america

trace element zoning in garnet as a monitor of crustal melting x ray composition maps of sc y p and cr in garnet have been measured using the electron microprobe zoning is discontinuous and is correlated with fluid absent crustal melting reactions the magnitude of the discontinuity is a function of the amount of muscovite that melts and the partition coefficients of solids versus melt trace element zoning is apparently not modified by diffusive processes so the zoning can be used to monitor the extent of melting and to examine kinetics of melting and the participation of accessory phases in crustal anatexis

the geomagnetic storm time response of gps total electron content in the north american sector over the last two decades maps of gps total electron content tec have improved our understanding of the large perturbations in ionospheric electron density which occur during geomagnetic storms however previous regional and global studies of ionospheric storms have performed only a limited separation of storm time local time longitudinal and seasonal effects using 13 years of gps tec data we present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the north american sector where dense ground receiver coverage is available the rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer lasting negative phase across all latitudes and local times our results show clear seasonal variations in the storm time tec such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects we find no discernable difference between spring and fall equinox events with both being equivalent to the average storm time response across all seasons we also identify a prominent magnetic declination effect such that stronger dayside positive storm effects are observed in regions of negative declination i e eastern north america on the nightside asymmetries in the tec response are observed near the auroral oval and midlatitude trough which may be attributed to thermospheric zonal winds pushing plasma upward downward along field lines of opposite declination

prolonged acadian orogenesis revelations from foliation intersection axis fia controlled monazite dating of foliations in porphyroblasts and matrix numerous phases of garnet growth are revealed by detailed studies of foliation inflection intersection axes preserved in porphyroblasts fias in acadian metamorphic rocks in the chester dome region of vermont u s a a regionally consistent succession of four different fia tends in garnet porphyroblasts has been dated by analyzing monazite inclusions with an electron microprobe these monazite inclusions which lie within the various foliations that define the fias provide absolute ages for multiple periods of deformation and episodic phases of garnet growth the monazite inclusions reveal a progression in foliation ages from 431 2 to 349 3 million years within porphyroblasts and from 366 3 to 327 5 million years in pervasive matrix foliations three samples of schist reveal ages ranging through 75 to 70 million years from the cores of porphyroblasts through the medians to the rims and then into the matrix ages determined from monazite grains within garnet porphyroblasts link directly to periods of multiple deformation and episodic garnet growth defined by the fias the four fia sets began forming prior to 424 3 405 6 386 6 and 366 4 million years ago respectively thus multiple stages of garnet growth occurred throughout acadian deformation and metamorphism in vermont and orogenesis was far more prolonged than previously thought invariably garnet growth occurred early in the accompanying deformation event dating of monazite inclusions without careful separation of phases of garnet growth by fia studies will lead to a spread of ages that will confuse rather than elucidate the metamorphic and structural history analysis of monazite grains in the matrix alone will likely only present ages for the youngest events these ages can be amalgamated from grain to grain to yield apparently precise ages but such ages reveal nothing about the deformation and metamorphic processes operating during orogenesis or the overall continuity of the deformation and metamorphism that accompanies plate motion fia and microstructural studies of inclusion trail successions allow numerous phases of garnet growth to be distinguished and then dated using monazite that has dissolved and regrown many times as multiple successive foliations developed this in turn allows very long and involved metamorphic histories to be fully integrated with similarly complex structural histories

deformation volume and cleavage development in metasedimentary rocks from the ballarat slate belt psammites from the ballarat slate belt in se australia exhibit well developed differentiated or spaced cleavage defined by alternating phyllosilicate and quartz rich domains termed p and q domains respectively strain estimates derived from independent microstructural and chemical observations suggest that the p q fabrics developed in response to plane strain deformation dominated by solution transfer with the principal finite shortening in the p domains approximately twice that in the adjacent q domains significant finite extensions are indicated by ubiquitous quartz albite chlorite overgrowths in both p and q domains while pressure shadow development around syntectonic pyrite porphyroblasts suggest finite extension of at least 100 this estimate is comparable with the extension predicted for constant volume deformation and consequently there appears to have been no significant bulk material loss or gain on the hand specimen scale these observations are consistent with solute transfer scales as little as a few centimetres via diffusion in a stationary fluid and do not require although do not necessarily preclude large scale advective fluid transport through the slate belt during cleavage formation as suggested in previous studies

sigmoidal inclusion trails punctuated fabric development and interactions between metamorphism and deformation porphyroblast inclusion fabrics are consistent in style and geometry across three proterozoic metamorphic field gradients comprising two pluton related gradients in central arizona and one regional gradient in northern new mexico garnet crystals contain curved sigmoidal inclusion trails in low grade chlorite schists these trails can be correlated directly with matrix crenulations of an older schistosity s1 the garnet crystals preferentially grew in crenulation hinges but some late crenulations nucleated on existing garnet porphyroblasts at higher grade biotite staurolite and andalusite porphyroblasts occur in a homogeneous s2 foliation primarily defined by matrix biotite and ilmenite biotite porphyroblasts have straight to sigmoidal inclusion trails that also represent the weakly folded s1 schistosity staurolite and andalusite contain distinctive inclusion rich and inclusion poor domains that represent a relict s2 differentiated crenulation cleavage together the inclusion relationships document the progressive development of the s2 fabric through six stages garnet and biotite porphyroblasts contain stage 2 or 3 crenulations staurolite and andalusite generally contain stage 4 crenulations and the matrix typically contains a homogeneous stage 6 cleavage the similarity of inclusion relationships across spatially and temporally distinct metamorphic field gradients of widely differing scales suggests a fundamental link between metamorphism and deformation three end member relationships may be involved 1 tectonic linkages where similar p t time histories and similar bulk compositions combine to produce similar metamorphic and structural signatures 2 deformation controlled linkages where certain microstructures particularly crenulation hinges are favourable environments for the nucleation and or growth of porphyroblasts and 3 reaction controlled linkages where metamorphic reactions particularly dehydration reactions are associated with an increase in the rate of fabric development a general model is proposed in which 1 garnet and biotite porphyroblasts preferentially grow in stage 2 or 3 crenulation hinges and 2 chlorite consuming metamorphic reactions lead to pulses in the rate of fabric evolution the data suggest that fabric development and porphyroblast growth may have been quite rapid of the order of several hundreds of thousands of years in these rocks these microstructures and processes may be characteristic of low pressure first cycle metamorphic belts

p t d histories from quartz a case study of the application of the titaniq thermobarometer to progressive fabric development in metapelites 1 this study investigates the ability of quartz to record segments of the pressure temperature deformation p t d path in poly deformed metamorphic terranes and the associated application of the ti in quartz thermobarometer titaniq metapelites from the strafford dome eastern vermont were selected for this study because they record progressive fabric development during prograde metamorphism and have well constrained p t d histories from previous work results of this investigation are in agreement with previous studies and demonstrate that quartz in these samples records additional distinct intervals of the p t d path six preserved quartz equilibration events include 1 early prograde growth during burial 2 kyanite in quartz producing reactions 3 prenappe emplacement equilibration during isobaric heating 4 precipitation of quartz in quartz feldspar domains during crenulation cleavage development due to solution transfer 5 quartz producing chlorite out reactions during heating postnappe emplacement and 6 retrograde quartz overgrowths from an influx of siliceous fluids modeling quartz volume allows for the identification of quartz producing reactions in p t space the same may be done for ti phases to better constrain activities during reequilibration events an integration of cathodoluminescence imaging microstructural and petrographic investigation isochemical forward stability modeling and thermobarometry allows identification and interpretation of zoning patterns in quartz to unravel histories that would otherwise not be obtainable

analysis of tec data from the topex poseidon mission 1 topex poseidon mission has provided an extensive database of vertical tec over the ocean since august 1992 data from nearly 10 years of topex tec observations were analyzed to study the tec climatology first tec data were binned by season geomagnetic activity and solar activity to create longitudinally averaged tec maps in magnetic latitude and local time these maps show the annual and semiannual anomalies well known from climatological studies of nmf2 but lack the seasonal anomaly because of the longitudinally averaged binning the equatorial anomaly is the most prominent feature in the maps and they show strong tec variations with solar activity but relatively weak variations with geomagnetic activity in our three kp bins compared with the low solar activity conditions f10 7 120 the tec values for f10 7 120 are much larger and the equatorial anomaly lasts longer into the night up to midnight during geomagnetically active periods the tec maps generally show a noticeable increase at low latitudes for f10 7 120 but this effect is barely detectable for f10 7 120 finally three longitudinal bins indian pacific and atlantic were added in order to see how the tec morphology varies with longitude the tec measurements display strong longitudinal variations that closely follow the longitudinal variation of the magnetic declination in the southern pacific where the declination is positive and large the diurnal tec variations significantly differ from those in the other longitude sectors where the magnetic declination is negative in the southern hemisphere also at noon the phase of the longitudinal tec variation is typically opposite to that at midnight

east west differences in f region electron density at midlatitude evidence from the far east region the global configuration of the geomagnetic field shows that the maximum east west difference in geomagnetic declination of northern middle latitude lies in the us region similar to 32 degrees which produces the significant ionospheric east west coast difference in terms of total electron content first revealed by zhang et al 2011 for verification it is valuable to investigate this feature over the far east area which also shows significant geomagnetic declination east west gradient but smaller similar to 15 degrees than that of the us the current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density nmf2 electron density ne of different altitudes in the far east regions with a longitude separation of up to 40 60 degrees based on ground ionosonde and space based measurements although the east west difference r ew over the far east area displays a clear diurnal variation similar to the us feature that is negative r ew west ne east ne in the noon and positive at evening night the observational results reveal more differences including 1 the noontime negative r ew is most pronounced in april june while in the us during february march thus for the late spring and summer period negative r ew over the far east region is more significant than that of the us 2 the positive r ew at night is much less evident than in the us especially without winter enhancement 3 the magnitude of negative r ew tends to enhance toward solar maximum while in the us showing anticorrelation with the solar activity the altitude distribution of pronounced negative difference 300 400 km moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude the result in the paper is not simply a comparison corresponding to the us results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude citation zhao b m wang y wang z ren x yue j zhu w wan b ning j liu and b xiong 2013 east west differences in f region electron density at midlatitude evidence from the far east region j geophys res space physics 118 542 553 doi 10 1029 2012ja018235

structure and tectonics of the hudson valley fold thrust belt eastern new york state analysis of structural features displayed in silurian and devonian strata of the hudson valley region indicate that these rocks form the western edge of a now largely eroded west verging fold thrust belt the hudson valley fold thrust belt or hvb west of the hudson river remnants of this fold thrust belt define a miniature valley and ridge province faults of the hvb die out to the west as blind thrusts in the basal units of the catskill clastic wedge structural geometries displayed in the hvb vary rapidly along strike and are locally complicated by internal deformation of thrust sheets and by movement on out of the syncline faults it is proposed that exposed faults of the hvb west of the river arise from a basal detachment here called the rondout detachment that lies above the taconic unconformity the rondout detachment and the overlying thrust system have been bent into large amplitude folds ordovician units beneath the rondout detachment must have shortened during development of these folds area balancing of cross sectional models suggests that the shortening affecting ordovician units could be restricted to rock above a lower blind detachment the austin glen detachment positioned within ordovician strata at a depth of 400 m below ground surface the age of deformation and the tectonic setting of the hvb is enigmatic its spatial relation to the catskill clastic wedge and to acadian metamorphic terranes suggests that the belt represents foreland shortening developed during the acadian orogeny

large volume loss during cleavage formation hamburg sequence pennsylvania green reduction spots in red slate of the hamburg sequence exposed near shartlesville pennsylvania have axial ratios of 1 42 1 0 0 28 on the limbs of near isoclinal folds and 1 0 0 79 0 41 in fold hinge zones conodont cusps and denticles within the reduction spots have been brittlely pulled apart and give independent measures of extension in various directions comparison of conodont extensions with reduction spot shapes on limbs and hinges indicates that sedimentary compaction of 44 preceded the tectonic strain associated with cleavage formation this strain having identical maximum extensions but greater shortening in fold hinges as compared to limbs was characterized by 41 extension in x no change in y 50 to 59 shortening in z and 29 to 42 tectonic volume loss the general lack of directed overgrowths on grains reflects the large volume loss and contrasts with other slates where deformation was an almost constant volume process and extension in x compensated for shortening in z

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

potential minerals for determining u th pb chemical age using electron microprobe abstract after a decade of studies and development it is now accepted that reliable u th total pb isochron ages can be calculated for monazite using an electron microprobe at m scale either directly on thin sections or on separated grains mounted in polished section the potential for determining u th pb chemical ages from other u and th enriched phases has been investigated compared to chemical monazite dating results for which individual spot age precisions of 20 to 100 ma can be achieved from individual spot analyses using isochron plots for monazite the age homogeneity of a given population of data can be assessed and depending upon the number of analyses n 50 a precision of 5 to 10 ma can be obtained the u content in xenotime widely varies from less than 0 1 wt up to 3 wt but th rarely exceeds 1 wt as a consequence the amount of radiogenic pb produced during a given period remains significantly lower for xenotime than for monazite leading to a lower precision 20 ma on the mean ages xenotime however appears to remain as a closed system but common pb must be carefully checked furthermore the electron microprobe technique epma allows controlling any age discrepancy on xenotime grains as small as 10 20 m that cannot be dated by other isotopic methods such xenotime ages can be useful when studying the monazite xenotime equilibrium the electron microprobe is not the most reliable method for dating zircon since u and th concentrations are generally low and common pb is not negligible nevertheless the spatial resolution of epma coupled with isotope methods allows conclusive in situ studies about radiogenic pb mobility and metamictization thorite does not seem suitable for dating with either isotope methods or epma because of continuous radiogenic pb loss conversely the oxide phases thorianite and baddeleyite are robust minerals with closed systems they are rather rare and seem to incorporate negligible common pb making epma a method of choice for dating them for thorianite the precision on the mean age can be similar as that obtained for monazite or even better while the precision for baddeleyite cannot be significantly better than 20 to 50 ma due to the limited amount of u 0 1 and the lack of th

ionospheric local model and climatology from long term databases of multiple incoherent scatter radars empirical ionospheric local models have been developed from long term data sets of seven incoherent scatter radars spanning invariant latitudes from 25 to 75 in american european and asian longitudes at svalbard tromso sondrestrom millstone hill st santin arecibo and shigaraki these models as important complements to global models represent electron density ion and electron temperatures and ion drifts in the e and f regions giving a comprehensive quantitative description of ionospheric properties a case study of annual ionospheric variations in electron density and ion temperature is presented based on some of these models clear latitudinal longitudinal and altitude dependency of annual and semiannual components are found

magnetic declination and zonal wind effects on longitudinal differences of ionospheric electron density at midlatitudes 1 a prominent ionospheric longitudinal variation at midlatitudes in particular over the continental us was found recently this variation is characterized as a higher east side electron density in the evening and a higher west side electron density in the morning and with clear seasonal and solar activity dependencies a combined effect of geomagnetic declination and changing zonal winds was proposed to explain it this paper represents a comprehensive investigation of this effect by examining climatology for both electron density longitudinal differences and the nighttime zonal winds in the eastern us electron density is from incoherent scatter radar extra wide coverage experiments during 1978 2011 over millstone hill for which the spatial separation of the data can be up to 50 in longitude the thermospheric zonal wind is from the on site fabry perot interferometer measurements during 1989 2001 the observed zonal wind climatology is found to be perfectly consistent with the expectation based on the east west electron density differences in terms of local time seasonal and solar cycle dependencies the correlation between the zonal wind and the east west differential ratio is extremely high with an overall correlation coefficient of 0 93 the observed time delay of 3 hours in the response of electron density differences to zonal winds is a marked feature thus these results confirm positively the declination zonal wind mechanism and provide new insight into longitudinal variations at midlatitudes for other geographic sectors

local volume change vs overall volume constancy during crenulation cleavage development in low grade rocks abstract the role of volume change in crenulation cleavage development involving possible pressure solution of quartz and mica is investigated taking into account two end member crenulation cleavage evolutionary models involving 1 mica loss from microlithons and 2 immobile mica mathematical relationships derived for both models are used to generate data sets for comparison with measured mineralogical proportions for two samples of crenulation cleavage from the singhbhum district eastern india the development of crenulation cleavage is considered to be under overall volume constancy if the average volume loss from cleavage domains is counterbalanced by average volume gain in adjoining microlithons a test based on 2 statistics obtained from comparison of expected values from model calculations and observed proportions of mineral phases in microlithon and cleavage domains is proposed to accept or reject the null hypothesis of overall volume constancy during crenulation cleavage development an application of the test to the two examples of crenulation cleavage from india suggests that mica was relatively immobile local volume loss in cleavage domains was about 6 19 and there was an overall volume constancy on a decimetre scale during crenulation cleavage development

coupled deformation and metamorphism in the roof of a tabular midcrustal igneous complex the 370 377 ma mooselookmeguntic igneous complex was emplaced at 14 km depth into steeply dipping metaturbidites that were folded and metamorphosed ca 400 405 ma during the acadian orog eny gravity and drill hole data isograd geometry thermal modeling and struc tural measurements all indicate that the eastern aureole of the complex represents an areally extensive roof above the gently east dipping tabular shaped intrusion this roof preserves a classic example of low pressure high temperature metamorphism caused by the underlying intrusion ther mal modeling indicates that the roof is no more than 1000 m thick over an area exceed ing 100 km2 unlike other roofs described in the literature the mooselookmeguntic igneous complex roof preserves a thick 600 m emplacement related strain gradi ent with a deformational fabric that evolved through all stages of crenulation cleavage to become an intense nondifferentiated folia tion approximately parallel to the intrusive contact and perpendicular to the steeply dip ping regional acadian age foliation fabric evolution through all stages of crenulation cleavage requires the vertical growth of the tabular intrusion to have been largely accommodated by dissolution precipitation creep which is a linear viscous deformation mechanism that can occur at lower differ ential stress than for example dislocation creep as the crenulation cleavage evolves a stage is reached where further deformation requires a change in deformation mecha nism which may lead to hardening of the rock development of crenulation cleavage requires a mica rich foliation at an initially high angle to the emplacement related fl at tening plane and this confi guration may be the primary reason why the strain aureole in the mooselookmeguntic igneous complex roof is so well developed compared to other published examples of midcrustal roofs

numerical simulations of spiral shaped inclusion trails can 3d geometry distinguish between end member models of spiral formation numerical 3d simulations of the development of spiral inclusion trails in porphyroblasts were conducted in order to test the proposals that a 3d spiral geometry differs between the rotation and nonrotation end member models of spiral formation proposed in the literature and b 3d spiral geometry can be used as a criterion to distinguish between the two end member models in rocks four principal differences are identified between the two sets of simulations smoothness of spiral curvature spacing of foliation planes alignment of individual foliation planes either side of the sphere representing the porphyroblast and spiral asymmetry with respect to matrix shear sense of these differences only spiral asymmetry and possibly the alignment of individual foliation planes are diagnostic criteria for distinguishing between the end member models in the absence of a readily applied test to distinguish the end member models interpretation of spiral inclusion trails is problematic it is necessary to determine complementary evidence to distinguish porphyroblast rotation or nonrotation during spiral formation

finite strain heterogeneity and volume loss in slates of the taconic allochthon vermont u s a abstract slates of the taconic allochthon have ellipsoidal reduction spots which have been used to determine the finite state of strain at seven sites the strain is highly heterogeneous at all scales ranging from several centimeters to many kilometers variations in x y ratios is small but variations in y z ratios is large and this pattern is seen at all scales the heterogeneity can be used to determine a strain path which is nearly horizontal on a flinn diagram we propose that uniaxial flattening associated with late stage cleavage development was accommodated by volume loss and that the most highly strained sites have experienced an average 55 volume loss at a minimum explaining our results without volume loss requires a subhorizontal extension and creates strain compatibility problems consideration of the strain history of these rocks suggests that folding related strains have been modified by later cleavage related events the last of which was uniaxial flattening accommodated by volume loss the finite strains are reflective almost exclusively of the latest cleavage producing strains

specifying the equatorial ionosphere using cindi on c nofs cosmic and data interpolating empirical orthogonal functions 1 data interpolating empirical orthogonal functions dineofs are a data based method for determining a few orthogonal basis functions that optimally reproduce a given data set this technique is applied to meridional drift measurements performed by the coupled ion neutral dynamics investigation cindi onboard the communication navigation outage forecasting system c nofs as well as electron density profiles derived from gps radio occulations ro performed by the constellation observing system for meteorology ionosphere and climate cosmic the low densities of the equatorial ionosphere spanning 2009 2010 restricted quality drift measurements by cindi to altitudes near perigee limiting the local time coverage of measurements full local time descriptions may be obtained as perigee moves through all local times though this requires a minimum 67 day season to increase the data coverage of the ionosphere cindi data are supplemented with cosmic gps ro data dineofs are applied to median meridional drift measurements as well as cosmic measurements spanning 2009 2010 and are used to make a best estimate of the equatorial ionosphere at locations not observed the scattered distribution of cosmic profiles as well as the physical relationship between meridional ion drifts and the distribution of density with altitude improves the quality of the reconstructions compared to using cindi alone the dineof reconstructions demonstrate that the annual anomaly of reduced ionospheric densities in june compared to december measured by cosmic is coincident with a change in the meridional ion drifts at the geomagnetic equator measured by cindi

volume loss during cleavage formation in the meguma group nova scotia canada abstract diffusive mass transfer pressure solution is a widely recognized cleavage forming mechanism under low grade conditions the amount of accompanying volume change during cleavage development however is difficult to quantify and remains controversial the distance between sites of mineral dissolution and reprecipitation and transport mechanisms also are controversial the structural history of the cambrian ordovician meguma group nova scotia canada is well known and abundant strain markers provide an opportunity to assess geometrically volume changes accompanying cleavage development during diagenesis about 70 compaction in muds and 15 in silts and sands occurred the pelitic to psammitic meguma group was cleaved prior to being folded pressure solution was the dominant cleavage forming deformation mechanism under chlorite grade metamorphic conditions during the early devonian acadian orogeny measurement of tectonic strain in principal directions x y z shows that bedding parallel coaxial shortening z is 60 and there is no evidence of fold hinge parallel extension y estimation of tectonic vertical extension x in the cleavage plane is complicated by diagenetic compaction corrections to primary strain markers but is insufficient to compensate for the observed 60 shortening in z indicating 40 60 volume loss during cleavage formation because cleavage formed at least 50 ma after deposition and under approximately 6 km of silurian to early devonian strata porosity of the sediments upon onset of cleavage was likely less than 15 pore space reduction therefore cannot account for the apparent volume loss during cleavage formation cleavage related volume loss applies regionally and to a stratigraphic thickness of several thousand meters implying that a large amount of material was removed and transported large distances when combined with 50 shortening by folding a bulk tectonic shortening of 80 is estimated for the meguma group during the acadian orogeny

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

on volume change and mass transport during the development of crenulation cleavage abstract a comparison of the bulk chemistry between isolated zones of crenulation cleavage and the surrounding relatively homogeneous slates from three localities boscastle sw england moselle valley germany lac de roselend french alps demonstrates that marked bulk volume change is not a prerequisite for the development of crenulation cleavage x ray powder diffraction results also demonstrate that there is no significant mineralogical change between crenulated and uncrenulated zones for the samples studied mineralogical differentiation and mass transfer takes place on a local scale between the limb and hinge domains of individual crenulation folds and of larger scale folds in layering but can occur without significant overall volume change on the scale of crenulated zones containing many microlithon and cleavage domains relative volume changes between crenulated and uncrenulated regions do not exceed ca 5 at boscastle and the majority of samples from the moselle valley at one locality in the moselle valley however a volume loss of around 35 40 occurred from the crenulated zone produced almost entirely by loss of sio2 as quartz from the system isolated parallel sided bands of crenulation cleavage such as the examples from boscastle and the moselle valley are geometrically constrained to represent some combination of volume change and heterogeneous simple shear superimposed upon a background homogeneous strain in examples with minimal volume changes the heterogeneous strain component must be one of simple shear

behavior of the f2 peak ionosphere over the south pacific at dusk during quiet summer conditions from cosmic data 1 the six satellite constellation observing system for meteorology ionosphere and climate cosmic mission makes routine ionospheric measurements over the entire globe using occultation techniques these observations have been used in this study to develop global scale climate maps of nmf2 and hmf2 during the southern northern summer winter enhanced electron densities that appear to be associated with the southern equatorial appleton anomaly are displaced far southward at dusk and within about an hour form the weddell sea anomaly coincidentally the height of the f2 peak increases on the northern boundary of this anomaly this height increase is also displaced southward as the enhanced electron densities are displaced southward suggesting that the electron density increases are associated with the f2 peak rising as well as being an interesting phenomenon in its own right this behavior may shed new light on the formation of the weddell sea anomaly no unambiguous explanation for this behavior can be determined from the data presently available but an examination of some possibilities suggests that an evening downward flux of plasma from the plasmasphere may be at least partly responsible for the phenomenon

scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite grade phyllites se vermont detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south eastern vermont show that grain scale zoning is common and sympathetic zoning in adjacent minerals is nearly universal we interpret this to reflect a pressure solution mechanism for cleavage development where precipitation from a very small fluid reservoir fractionated that fluid multiple analyses along single muscovite biotite and chlorite grains 30 200 m in length show zoning patterns indicating tschermakitic substitutions in muscovite and both tschermakitic and di trioctahedral substitutions in biotite and chlorite using cross cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite grade chlorite grade overprinted by biotite grade and biotite grade zoning patterns are comparable in all three settings requiring a similar cleavage forming mechanism independent of metamorphic grade moreover the use of 40ar 39ar geochronology demonstrates this is true regardless of age furthermore samples with chlorite grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of al si mg and fe ions are greater than the temperature of the biotite isograd 400 c parallel and smoothly fanning tie lines produced by coexisting muscovite chlorite and muscovite biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization these results do not support theories suggesting cleavages form in fluid dominated systems if crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir then the compositions of individual grains defining these cleavages would be uniform on the contrary the fine scale chemical zoning observed probably reflects a grain scale process consistent with a pressure solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation thus the role of fluids was probably limited to one of catalysing pressure solution and fluids apparently did not drive cleavage development

gnss observations of ionospheric variations during the 21 august 2017 solar eclipse u s national science foundation grant nasa grant nasa lws funding support muri grant onr

the winter anomaly in the middle latitude f region during the solar minimum period observed by the constellation observing system for meteorology ionosphere and climate 1 the winter anomaly or seasonal anomaly at middle latitudes is a phenomenon during which the daytime plasma density at the f peak height nmf2 is greater in winter than in summer radio occultation measurements from the constellation observing system for meteorology ionosphere and climate cosmic satellites provide a new data source for study of the winter anomaly on a global scale in this study we investigate the altitude local time latitude longitude and hemispheric variations of the electron density in the middle latitude ionosphere by analyzing the cosmic data measured in 2007 during a magnetically quiet period kp 3 the seasonal mean behavior of the nmf2 obtained from cosmic data shows the occurrence of the winter anomaly feature during 0800 1600 lt in the northern hemisphere but not in the southern hemisphere the intensity of the winter anomaly is variable with longitude and a more intense winter anomaly is likely to occur at longitudes closer to the magnetic pole at northern middle latitudes a greater electron density in the winter than in the summer occurs in the narrow altitude range near the f peak height except for the winter anomaly feature at northern middle latitudes the electron density at middle latitudes is greater during the summer than during the winter in both hemispheres

zoning patterns in orthopyroxene and garnet in granulites implications for geothermometry compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the minto terrane of northern quebec the compositional maps provide clear evidence of late exchange of fe fe mg after ca in garnet and al in orthopyroxene had been quenched in the extent of late fe mg exchange was controlled by neighbouring minerals with negligible fe mg gradients against plagioclase and quartz and substantial gradients against exchangeable fe mg minerals cores of grains in contact with exchangeable fe mg neighbours are progressively more reset in fe fe mg as grain size decreases whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in fe fe mg than cores of the largest grains gradients of ca in garnet and of al in orthopyroxene in grains of uniform fe fe mg preserve a high temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular fe mg diffusion in garnet and orthopyroxene was rapid enough to homogenize fe fe mg the transition from efficient intergranular exchange at relatively high temperatures to local fe mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock possibly an internally generated dehydration melt phase implications for geothermometry of granulites include the following numerical values are particular to this study 1 core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in fe fe mg relative to the most refractory compositions by an amount equivalent to 120d c 2 fe mg exchange thermometry using even the most refractory fe fe mg compositions may not record peak granulite conditions possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock and 3 temperature sensitive net transfer equilibria involving al solubility in orthopyroxene yield temperatures up to 150d c higher than maximum fe mg exchange temperatures even in grains with flat fe fe mg compositional profiles making them a better means of estimating peak granulite temperatures than fe mg exchange thermometry

limited localized nonvolatile element flux and volume change in appalachian slates geometric evidence for major nonvolatile volume losses at several appalachian slate localities contradicts geochemical evidence for minimal compositional changes during low grade metamorphism of shales relative to adjoining microlithons spaced cleavage zones are depleted in si quartz na albite and for carbonate rich slates ca mn and mg calcite and dolomite zr ti al p and fe are enriched in cleavage zones the greatest enrichments are in zr proportional k gains and na and si losses suggest that cleavage fractionation combines stoichiometric reactions e g k albite chlorite muscovite sio 2 na with pressure solution of quartz and carbonate minerals cleavage and sorting pelite to psammite fractionation patterns are similar but can be distinguished by higher zr in al rich cleavage zones relative to zr in al rich pelitic rocks the compositional similarities of homogeneous shales and slates do not indicate large volume losses during slate metamorphism for paleozoic slates from localities where large volume losses have been hypothesized on geometric grounds martinsburg slate belt of pennsylvania and new jersey meguma group of nova scotia and taconic slate belt of vermont and new york slate compositions show no evidence of large nonvolatile volume losses relative to likely shale protoliths detailed sampling of slates folded at hand specimen to quarry scales indicate that substantial element and volume fluxes are limited to the submeter scale in small scale folds volume losses in tight inner arcs appear to be balanced by volume gains in adjoining areas the complications of metamorphic recrystallization and heterogeneous strain are probably responsible for erroneous interpretations of large nonvolatile volume losses in these appalachian slate localities

midlatitude summer nighttime anomaly of the ionospheric electron density observed by formosat 3 cosmic 1 this paper presents monthly variations of the midlatitude summer nighttime anomaly msna of the ionosphere for the first time by global observations of the formosat 3 cosmic f3 c mission the anomaly is characterized by the greater nighttime 1800 lt 0200 lt ionospheric electron density than during daytime 0800 1800 lt at middle latitudes during months around june and december solstices the anomaly shown during december solstice was known as the weddell sea anomaly wsa occurring around the antarctica and nearby the pacific ocean this paper demonstrates that the wsa like feature also exists in the northern hemisphere and is most prominent near the northeast asia europe africa and central pacific longitudes around june solstice in both hemispheres the anomalies with similar electron density characteristics and variations caused by the similar mechanism prompts us to name this phenomenon the msna the monthly f3 c observations indicate that the anomaly appears as the most prominent structure of the global ionosphere around midnight hours

finding multiscale connectivity in our geospace observational system network analysis of total electron content we present the first complex network theory based analysis of high latitude total electron content tec data including dependencies on interplanetary magnetic field imf clock angle and hemisphere we examine several network measures to quantify the spatio temporal correlation patterns in the tec data for winter and summer months in 2016 we find that significant structure exists in the correlation patterns distinguishing the dayside and nightside ionosphere and specific features in the high latitudes such as the polar cap and auroral oval including the cusp and ionospheric footpoints of magnetospheric boundary layers these features vary with the imf exhibiting a strong dependence on the north south direction and generally larger variations during the winter months in both hemispheres our exploratory results suggest that network analysis of tec data can be used to study characteristic ionospheric spatial scales at high latitudes thereby extending the utility of these data we explore meso and large scales 10s km and 100s km respectively as a function of winter summer season hemisphere and imf direction and conclude that the relative importance of different ionospheric scales is not a constant relationship together with an identification of important areas of future work our findings provide a foundation for the application of network analysis techniques to ionospheric tec our results suggest that network analysis can reveal new physical connections in the ionospheric system

zoning and recrystallization of phengitic micas implications for metamorphic equilibration white micas phengites in the metasediments of the scottish dalradian display a large range of compositions within single samples the variations in the composition of these phengites are strongly controlled by their structural age with early fabrics containing a paragonite poor celadonite rich phengite whereas in later fabrics the micas are generally paragonite rich and celadonite poor retrograde phengite growth identified using back scattered electron imaging occurs as celadonite rich rims on micas within all existing fabrics and appears to be preferentially developed along existing white mica plagioclase grain boundaries the presence of these chemically distinct phengite populations within single samples implies that chemical exchange between the individual micas was inefficient it is proposed that diffusion controlled exchange reactions in phengites have relatively high closure temperatures below which major element exchange is effectively impossible this closed system behaviour of micas questions the ease with which phengites may equilibrate with other phases during prograde greenschist and lower amphibolite facies metamorphism many of the chemical variations preserved in phengites from such metamorphic rocks may reflect deformation recrystallization controlled equilibria

electron microprobe age mapping of monazite high resolution x ray maps of th u pb and y in monazite can be used to construct age maps which reveal the continuous spatial distribution of ages in a single grain of monazite the age mapping algorithm and three examples are presented to illustrate the capabilities and applications of this mapping technique the insights it can provide into monazite geochronology in general and its limitations compared to electron microprobe emp quantitative dating and other in situ geochronologic techniques age maps offer critical information for unraveling metamorphic and tectonic histories and for interpreting results from other geochronologic techniques and they are a valuable aid for rigorously locating in situ analytical points age mapping also can be used to better understand the behavior of the u th pb system in monazite during metamorphism deformation and s uid circulation events age maps presented in this paper reveal unsuspected age heterogeneities on the micrometer scale like a now healed fracture not visible in back scattered electron bse images or young domains less than 5 m in width located inside an older core in both cases using age maps as a template for locating in situ analysis points will minimize the peril of age mixing and erroneous geological interpretations in addition to providing critical information for illustrating and interpreting the history of complex polygenetic monazite age mapping may ultimately lead to a better understanding of the processes involved with monazite growth and recrystallization and thus even more powerful applications of the monazite geochronometer the agemap program is available in a windows version and can be downloaded from the internet at the following address http www geo umass edu probe agemap

evidence for tectonic emplacement of ultramafic and associated rocks in the pre silurian eugeoclinal belt of western new england vestiges of an ancient accretionary wedge in northern vermont detailed 1 10 000 mapping of the hazens notch ottauquechee stowe and moretown formations in the 60 km 2 jay area has shown that metasedimentary rocks and serpentinites are highly faulted to produce a tectonic stratigraphy in which serpentinites and talc carbonate rocks occur as slivers along faults that separate contrasting lithic assemblages remnants of the ophiolite sequences of quebec in western massachusetts the ultramafic bearing section of the rowe schist and the western part of the moretown formation are largely equivalent to the rocks in northern vermont mapping at 1 24 000 scale and compilation work for the new bedrock map of massachusetts have shown that the rowe schist consists of numerous lenses of greenschist carbonaceous schist gray schist amphibolite and serpentinite although the geometric arrangement of the lenses and serpentinites is strikingly similar to that seen in the jay area higher grade taconian and acadian metamorphism has partially obscured the fault fabrics seen in vermont modified journal abstract

high resolution compositional mapping of matrix phases implications for mass transfer during crenulation cleavage development in the moretown formation western massachusetts abstract high resolution compositional maps provide a new tool for investigating mass transfer during cleavage formation the moretown formation of western massachusetts contains a well developed crenulation cleavage with alternating mica rich crenulation limbs and mica poor crenulation hinges compositional mapping shows two generations of plagioclase the second of which was synchronous with the crenulation cleavage a significant amount of the syn crenulation plagioclase 10 20 modally grew in hinge domains a small amount of syn crenulation plagioclase 1 and a large amount of phengitic muscovite grew in limb domains the maps also show that uncrenulated domains experienced mass transfer and reactivation of older cleavages and thus cannot be used as undeformed reference domains for comparison with crenulated regions compositional mapping facilitates a new degree of integration between petrologic and structural analysis knowledge of the structural context of compositional domains allows better selection of phases and compositions for interpreting metamorphic reactions and linking metamorphism to deformational stages knowledge of syntectonic reactions provides new insights into mass transfer and volume change during deformation in the moretown formation plagioclase and phengite producing reactions play a large role in controlling the nature and magnitude of mass transfer but microstructures control the location of reactants and products within the evolving fabric

tectonic synthesis of the taconian orogeny in western new england a tectonic synthesis based on stratigraphic and structural analysis of western new england is proposed for the ordovician taconian orogeny it emphasizes arc continental collision in which ocean floor continental margin and ensialic rift rocks were imbricated westward in a repeatedly deformed accretionary wedge continued compression displaced segments of the north american sialic crust to the west and deformed the earlier emplaced slices of the taconic allochthons which were derived from the continental margin critical arguments for this synthesis are 1 the west to east stratigraphic relations among the basal rift clastic rocks of the dalton pinnacle and hoosac formations of late precambrian to early cambrian age 2 the stratigraphic and sedimentological similarities between the rocks of the lower taconic sequence and rocks in the pinney hollow and underhill slices to the east and north of the green mountain massif 3 the environmental similarities between the cambrian and lower ordovician section of the giddings brook slice and the age equivalent section in the st albans synclinorium 4 the presence of carbonate platform rocks as slivers between each of the successively higher and younger premetamorphic slices groups 1 and 2 of the taconic allochthons 5 the presence of synmetamorphic fault related structures in the youngest and highest slices group 3 of the taconic allochthons 6 the recognition of extensive thrust zones in the pre silurian eugeoclinal sequence east of the middle proterozoic basement of the housatonic berkshire green mountain and lincoln massifs 7 the location of the taconic root zone within the pre silurian eugeoclinal sequence 8 the recognition of numerous faults in the serpentinite belt 9 the similarity between the rocks of the moretown formation and modern fore arc basin sequences 10 the recognition that the volcanic arc continental complexes of the ascot weedon and bronson hill have been displaced westward over the moretown and or hawley formations along such faults as the bristol and coburn hill thrusts 11 the allochthonous and internally imbricated nature of the north american basement in the berkshire massif 12 the proposition that the housatonic green mountain and lincoln massifs as well as the middle proterozoic cored domes of southeastern vermont are also thick sialic slices of north american basement 13 the recognition of medium high to high pressure metamorphic mineral assemblages in the pre silurian eugeoclinal rocks of vermont and 14 the recent synthesis of isotopic age data by sutter and others 1985 on the basis of an analysis of the foregoing arguments and relationships a chronological sequence of seven structural sections between albany new york and the bronson hill anticlinorium in central massachusetts is used to depict the evolution of the taconian orogeny retrodeformed distances are based on structural overlap and restoration of the taconic slices to their depositional setting along the ancient north american continental margin these easterly younging diverticulated slices formed as a result of horizontal compression rather than gravity sliding this palinspastic analysis implies the following 1 approximately 1 000 km of shortening has occurred during the emplacement of the taconic allochthons and the subsequent imbrication of north american basement as thick sialic slices approximately 330 km of this shortening is attributed to multiple cleavage generations 2 repeated movement along such major surfaces as the cameron9s line whitcomb summit belvidere mountain thrust zone has buried the taconic root zone we suggest that the northern extension of this root zone is exposed to the east of the lincoln massif in vermont where the underhill pinney hollow and hazens notch formations are exposed these formations here considered thrust slices disappear along the belvidere mountain whitcomb summit thrust zone as it is traced southward into western massachusetts and western connecticut 3 taconian metamorphic rocks particularly the older medium high pressure rocks in northern vermont have been transported westward on such reactivated surfaces as the belvidere mountain thrust 4 the anticlinorial form of the middle proterozoic basement in the green mountain and lincoln massifs may have resulted from fault bend folding on deep mantle involved thrusts that developed late in the taconian orogeny

ipy observations of ionospheric yearly variations from high to middle latitude incoherent scatter radars 1 upper atmospheric research during the 2007 international polar year features unprecedented yearlong observations by incoherent scatter radars this valuable data set collected under very low solar and magnetic activity conditions from a set of four radars spanning middle millstone hill auroral poker flat and higher latitudes sondrestrom and svalbard enables us to address a fundamental question of background climatology on ionospheric yearly variations the main focus of this paper is on the noon time baseline annual and semiannual variations with an emphasis on the less known height dependency for those geophysically important areas the radar measurements of ion drifts allow us to examine dynamic effects which have not been well addressed previously high latitude ionospheric climatology shows some interesting features in particular the two semiannual peaks of electron density ne the two peaks neither of which is near summer solstice are essentially of equinoctial symmetry at very high latitude sites where downward ion drifts are strong in summer thus causing ne reduction the symmetry vanishes at the midlatitude site clear phase progression is seen from the topside to the f2 peak at the midlatitude site comparisons of millstone hill data from this period and prior solar minima indicate decreases in the ion temperature throughout the f2 peak and the topside ionosphere these decreases do not seem to be associated with solar flux and magnetic activity effects

numerical modeling of crenulation cleavage development a polymineralic approach abstract the finite element method was used to investigate how the elastic interactions of quartz and muscovite minerals affect grain scale stress and strain distributions at different stages of crenulation cleavage development the polymineralic structure comprises individual grains that were each assigned their own 3d stiffness tensor and orientation gradients in mean stress and volumetric strain within quartz grains develop between the limbs and hinges of microfolds at the earliest stages of crenulation development with higher values in the microfold limbs these gradients decrease with development of the crenulation cleavage as the microfold limbs become phyllosilicate rich p domains and the hinges become quartz and feldspar rich qf domains crystallographic orientations of the quartz grains have a relatively minor effect on the mean stress and volumetric strain distributions our findings are broadly consistent with both pressure solution and strain driven dissolution models for crenulation cleavage development however because crenulation cleavage development typically involves metamorphic reactions we favor a model in which dissolution is driven by those reactions and mass transfer leading to development of the mineralogically segregated fabric is driven by pore fluid pressure gradients that follow gradients in volumetric strain local concentrations of stress and strain across mineral interfaces may identify sites of enhanced reaction

volume change accompanying cleavage development in graptolitic shales from gisborne victoria australia studies on shape changes in deformed oncograptus upsilon combined with strain analysis of pressure shadows around framboidal pyrite revealed that a small volume change of the order of 5 percent accompanied the cleavage development in the shales from gisborne victoria starting from the proximal end oncograptus upsilon exhibits progressive increase in the spacing between successive thecae along the stipes a new technique utilizing the distance between a specific number of thecae is used for computing the change in length along stipes of oncograptus upsilon the low volume change accompanying a more than 70 percent shortening deformation indicates that there is a less significant mass loss during cleavage development than has been inferred from some studies on volume change from thecal spacing in deformed graptolites

east west coast differences in total electron content over the continental us 1 total electron content tec measurements made by a network of dense gps receivers over the continental us are used to investigate ionospheric longitudinal differences we find that the evening tec is substantially higher on the us east coast than on the west and vice versa for the morning tec the longitudinal difference displays a clear diurnal variation through an analysis of morning evening variability in the east west tec difference minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental us we suggest that these new findings of longitudinal differences in ionospheric tec at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day this study indicates that longitudinal variations in tec measurements contain critical information on thermospheric zonal winds the proposed declination zonal wind mechanism may also provide a new insight into longitude ut changes at midlatitudes on a global scale as well as into some geospace disturbances

ionospheric climatology and variability from long term and multiple incoherent scatter radar observations climatology in eastern american sector 1 ionospheric climatology and variability studies are conducted using long term incoherent scatter radar isr observations from seven sites around the world these studies result in an empirical model system the isr ionospheric model isrim which represents local and regional ionospheric climatology and variability of the ionosphere this paper addresses some new climatological features revealed by the model for latitudes spanning 18 70 n over the eastern american sector the latitudinal change of the f2 layer electron density exhibits a clear depletion near millstone hill latitudes when solar activity is median or low accompanied by a te enhancement and electron density peaks at 10 both to the north and south of millstone hill possible explanations are discussed we also characterize several types of variation in plasma temperatures in this region including ion temperature elevation for quiet conditions in the auroral zone and electron temperature increases toward higher latitudes

the summer evening anomaly and conjugate effects 1 the constellation observing system for meteorology ionosphere and climate cosmic gps occultation data have been analyzed in this study to provide a better understanding of the weddell sea anomaly wsa and to place it in the wider context of a general phenomenon that occurs near dusk in summer which we are calling the summer evening anomaly to better capture its global nature the terminator and the magnetically conjugate points for the terminator in the other hemisphere have been plotted on top of global maps of cosmic nmf2 and hmf2 for 2 months either side of the december and june solstices for 2006 2008 these plots show that there are distinct enhancements of nmf2 and increases in hmf2 as soon as the conjugate footprint of the field line on the winter terminator is seen at middle latitudes in the summer hemisphere this effect is most pronounced where the wsa is formed but it also occurs across the south pacific ocean in the southern summer and across much of the north atlantic ocean siberia and kamchatka during the northern summer an hmf2 increase occurs between the two terminators even at locations where there is no increase in nmf2 a similar but reversed effect occurs in hmf2 near dawn this behavior appears to be most consistent with upward and poleward ion drifts in the evening but neutral wind and downward precipitation may make important contributions to this effect

first observations of the midlatitude evening anomaly using super dual auroral radar network superdarn radars 1 under geomagnetically quiet conditions the daytime midlatitude ionosphere is mainly influenced by solar radiation typically electron densities in the ionosphere peak around solar noon previous observations from the millstone hill incoherent scatter radar isr have evidenced the presence of evening electron densities higher than daytime densities during the summer the recent development of midlatitude super dual auroral radar network superdarn radars over north america and japan has revealed an evening enhancement in ground backscatter during the summer superdarn observations are compared to data from the millstone hill isr confirming a direct relation between the observed evening enhancements in electron densities and ground backscatter statistics over a year of data from the blackstone radar show that the enhancement occurs during sunset for a few hours from april to september the evening enhancement observed by both superdarn and the millstone hill isr is shown to be related to recent satellite observations reporting an enhancement in electron densities over a wide range of longitudes in the northern hemisphere midlatitude sector during summer time finally global results from the international reference ionosphere iri and the horizontal wind model hwm07 are presented in relation with previously published experimental results and proposed mechanisms of the evening enhancement namely thermospheric horizontal winds and geomagnetic field configuration it is shown that the iri captures the features of the evening enhancement as observed by superdarn radars and satellites

the influence of crenulation cleavage development on the bulk elastic and seismic properties of phyllosilicate rich rocks abstract the anisotropy of seismic wave propagation is strongly influenced by the mineralogy and microstructure of rocks phyllosilicates are elastically highly anisotropic and are therefore thought to be important contributors to seismic anisotropy in the continental crust crenulation cleavage is one of the most common microstructural fabrics found in multiply deformed phyllosilicate rich crustal rocks we calculated the bulk elastic properties and resulting wave velocities for rock samples that preserved three different stages of crenulation cleavage development an initial planar foliation a moderately developed crenulation cleavage and a well developed crenulation cleavage mineral orientation maps were obtained using electron backscatter diffraction and calculations were made using asymptotic expansion homogenization combined with the finite element method the difficulties involved with sample preparation and data acquisition of phyllosilicate rich rock samples are also discussed we compare our results to more conventional methods for calculating an aggregate stiffness matrix from a mineral orientation map namely voigt and reuss averages these averages do not account for grain scale interactions and therefore deviate from the results calculated using asymptotic expansion homogenization our results show that the rocks characterized by a planar foliation and a moderately developed crenulation cleavage are highly anisotropic with p wave anisotropies up to 30 9 and s wave anisotropies up to 34 2 whereas the rock characterized by a well developed crenulation cleavage is only mildly anisotropic with a p wave anisotropy of 15 5 and s wave anisotropy of 10 7 progressive development of the fabric also causes the orientations of p and s wave velocity maxima and s wave polarization directions to change markedly despite the high anisotropy imparted by a planar schistosity the variety of folds and fabrics typically found in phyllosilicate rich rocks within larger scale crustal volumes will tend to mute the anisotropy possibly to the point of appearing nearly isotropic

regional and local ionospheric models based on millstone hill incoherent scatter radar data 1 local and regional statistical models to describe millstone hill incoherent scatter radar observations of electron density electron temperature and ion temperature since 1976 are developed using a bin fit technique the local models generate ionospheric variations with local time day number and altitude from 150 1000 km the prior day s f107 and the ap index from the previous 3 hour period are keyed inputs to specify solar and geomagnetic activity the regional models have a latitude coverage of 32 55 geodetic and an altitude coverage of 200 600 km these climatology models are capable of reproducing primary ionospheric variation features seen in previous studies as well as several newly revealed features such as the semiannual variation of electron density they are accessible through the world wide web at the url http www openmadrigal org

porphyroblast rotation during crenulation cleavage development an example from the aureole of the mooselookmeguntic pluton maine usa in the low pressure high temperature metamorphic rocks of western maine usa staurolite porphyroblasts grew at c 400 ma very late during the regional orogenesis these porphyroblasts which preserve straight inclusion trails with small thin section scale variation in pitch were subsequently involved in the strain and metamorphic aureole of the c 370 ma mooselookmeguntic pluton the aureole shows a progressive fabric intensity gradient from effectively zero emplacement related deformation at the outer edge of the aureole 2900 m map distance from the pluton margin to the development of a pervasive emplacement related foliation adjacent to the pluton the development of this pervasive foliation spanned all stages of crenulation cleavage development which are preserved at different distances from the pluton the spread of inclusion trail pitches in the staurolite porphyroblasts as measured in two dimensional 2 d thin sections increases nonlinearly from 16 to 75 with increasing strain in the aureole these data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage the data spread is qualitatively modelled for both pure and simple shear and both solutions match the data reasonably well the spread of inclusion trail orientations 40 75 in the moderately to highly strained rocks is similar to the spread reported in several previous studies we consider it likely that the sample scale spread in these previous studies is also the result of porphyroblast rotation relative to one another however the average inclusion trail orientation for a single sample may in at least some instances reflect the original orientation of the overgrown foliation

from static alteration to mylonitization a nano to micrometric study of chloritization in granitoids with implications for equilibrium and percolation length scales strain accommodation in upper crustal rocks is often accompanied by fluid mediated crystallization of phyllosilicates which influence rock strength and shear zone formation the composition of these phyllosilicates is frequently used for pressure temperature time constraints of deformation events although it is often highly heterogeneous even in mylonites this study investigates the reactions producing a phyllosilicate chlorite in and below grenschist facies conditions and the variations in chlorite composition along a strain gradient in the variscan bielsa granitoid axial zone pyrenees compositional maps of chlorite including iron speciation are compared to nanostructures observed by transmission electron microscopy in increasingly strained samples and related to mechanisms of fluid percolation in the bielsa granitoid altered at the late variscan alpine age shear zones are found with high strain gradients the undeformed granitoid exhibits local equilibria pseudomorphic replacement and high compositional heterogeneities in chlorite this is attributed to variable reaction mechanisms at nanoscale and element supply little interconnected intra and inter grain nanoporosity and isolation of fluid evolving in local reservoirs in samples with discrete and mm sized fractures channelized fluid triggered the precipitation of homogeneous alpine chlorite in fractures preserving late variscan chlorite within the matrix in low grade mylonites where brittle ductile deformation is observed micro and nanocracks and defects allows the fluid percolating into the matrix at the scale of hundreds of m this results in a more pervasive but incomplete replacement of late variscan chlorite by alpine chlorite despite the high strain in studied granitoids deformed under greenschist facies conditions local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according reaction mechanisms and element mobility controlled by i matrix fracture porosity contrasts at nanoscale and ii the location and interconnection of nanoporosity between crystallites of phyllosilicates this preservation influences our ability to reconstruct the pre and syn kinematic metamorphic history of granitic rocks in low grade units of orogens

lack of porphyroblast rotation in the otago schists new zealand implications for crenulation cleavage development folding and deformation partitioning porphyroblasts of garnet and plagioclase in the otago schists have not rotated relative to geographic coordinates during non coaxial deformation that post dates their growth inclusion trails in most of the porphyroblasts are oriented near vertical and near horizontal and the strike of near vertical inclusion trails is consistent over 3000 km2 microstructural relationships indicate that the porphyroblasts grew in zones of progressive shortening strain and that the sense of shear affecting the geometry of porphyroblast inclusion trails on the long limbs of folds is the same as the bulk sense of displacement of fold closures this is contrary to the sense of shear inferred when porphyroblasts are interpreted as having rotated during folding several crenulation cleavage fold models have previously been developed to accommodate the apparent sense of rotation of porphyroblasts that grew during folding in the light of accumulating evidence that porphyroblasts do not generally rotate the applicability of these models to deformed rocks is questionable whether or not porphyroblasts rotate depends on how deformation is partitioned lack of rotation requires that progressive shearing strain rotational deformation be partitioned around rigid heterogeneities such as porphyroblasts which occupy zones of progressive shortening or no strain non rotational deformation therefore processes operating at the porphyroblast matrix boundary are important considerations five qualitative models are presented that accommodate stress and strain energy at the boundary without rotating the porphyroblast a a thin layer of fluid at the porphyroblast boundary 2 grain boundary sliding 3 a locked porphyroblast matrix boundary 4 dissolution at the porphyroblast matrix boundary and 5 an ellipsoidal porphyroblast shadow unit