retrograde net transfer reaction insurance for pressure temperature estimates retrograde net transfer reactions significantly affect compositions of metamorphic minerals yet are rarely considered when determining pressure temperature p t conditions two natural amphibolite facies metapelites from the central himalaya of nepal exhibit extremely common compositional patterns including increases in mn and fe fe mg at the rims of garnets which are the result of retrograde garnet dissolution and fe mg exchange with biotite however typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3 6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids these large errors result because dissolution of high fe garnet has strongly affected the fe mg ratio of matrix biotite x ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest t compositions or through a new data processing approach by permitting correction of mineral compositions to original high t values these approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies they ultimately yield p t estimates that are more petrologically reasonable and permit rapid screening of samples for those least affected by retrograde reactions reconsideration of thermobarometry in the central and eastern himalaya indicates that retrograde net transfer reactions are extremely common therefore previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated

short lived polyphase deformation during crustal thickening and exhumation of a collisional orogen ribeira belt brazil abstract the ribeira belt brazil is a neoproterozoic collisional related feature that was located in a south central position in west gondwana we present quantitative data on finite strain flow vorticity and deformation temperatures for the curitiba terrane a major segment of the southern ribeira belt six deformation phases d 1 d 6 related with crustal thickening and exhumation were recognized d 1 and d 2 related microstructures are preserved exclusively within porphyroblasts in part grown during stages of high pressure 9 12 kbar isobaric heating after crustal thickening d 3 phase was active from peak metamorphism attained in contrasting crustal levels 810 400 c to the early stage of exhumation 500 400 c as indicated by petrological microstructural and quartz c axis fabric evidence kinematic vorticity results indicate that the sl 3 mylonitic fabric resulted from a simple shear dominated deformation related with westward thrusting north verging overturned d 4 folds with e w trending subhorizontal axes derived from a pure shear dominated deformation regional d 5 open folds with subvertical axes and nne ssw trending traces were produced by indentation tectonics d 6 phase comprises retrograde orogen parallel transcurrent shear zones related with scape tectonics geochronological data indicate that d 3 d 6 phases occurred between 584 and 580 ma suggesting a fast exhumation rate of 8 mm year for the deepest rocks from the southern ribeira belt

a magma loading model for barrovian metamorphism in the southeast coast plutonic complex british columbia and washington barrovian metamorphism linked to crustal thickening in the southeast coast plutonic complex of british columbia and washington is proposed in this paper to be the product of magmatic loading relevant observations and arguments are the following 1 isotopic ages coupled with structural and fabric relations document that throughout the region barrovian metamorphism and plutonism are broadly coeval 2 baric patterns in country rock indicate steep sided crustal loads originating within the high grade parts of the orogen 3 patterns of subsidence and uplift are localized and diachronous precluding a single event regional thickening mechanism 4 country rock fabrics are dominated by steep orogen parallel foliations and shallow strike parallel lineations features not easily reconciled with tectonic thickening mechanisms 5 abroad zone of schists flanking the large 25 x 100 km scuzzy batholith in british columbia bears metamorphic isograds and foliations that track the border of the pluton across regional structural trends implicating pluton emplacement as the cause of metamorphism 6 the crustal loading event in the vicinity of the scuzzy pluton is bracketed by mineral and textural features as being coeval with emplacement of the pluton which occurred over a period of 7 m y 7 the regionally developed chiwaukum schist in washington has petrologic and structural features and a metamorphic age that suggest it was formed by and represents the floor of an eroded extension of the scuzzy pluton the proposed magma loading model invokes the diapir and ballooning concepts of previous workers in which rising plutons displace country rock downward this mechanism results in a type of convective crustal overturn and at least partially solves the space problem related to batholithic emplacement as a result of this process relatively broad tracts of country rock acquire barrovian mineralogy following plutonism magmatically thickened crust is eroded and isostatically up lifted to expose the plutonic roots and high grade country rock basement

kinematics of fault related folding derived from a sandbox experiment we analyze the kinematics of fault tip folding at the front of a fold and thrust wedge using a sandbox experiment the analog model consists of sand layers intercalated with low friction glass bead layers deposited in a glass sided experimental device and with a total thickness h 4 8 cm a computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation active deformation at the tip of the forward propagating basal decollement is monitored along the cross section with a high resolution ccd camera and the displacement field between pairs of images is measured from the optical flow technique in the early stage when cumulative shortening is less than about h 10 slip along the decollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium in this stage of detachment tip folding horizontal displacements decrease linearly with distance toward the foreland vertical displacements reflect a nearly symmetrical mode of folding with displacements varying linearly between relatively well defined axial surfaces when the cumulative slip on the decollement exceeds about h 10 deformation tends to localize on a few discrete shear bands at the front of the system until shortening exceeds h 8 and deformation gets fully localized on a single emergent frontal ramp the fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system as long as strain localization is not fully established the sand layers experience a combination of thickening and horizontal shortening which induces gradual limb rotation the observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds relate finite deformation to incremental folding and derive shortening rates from deformed geomorphic markers or growth strata

soil moisture fluctuations recorded in saharan dust deposits on lanzarote canary islands over the last 180 ka abstract aeolian sediments trapped in volcanically dammed valleys on lanzarote canary islands were investigated in order to reveal environmental changes over the last 180 ka clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo soil moisture during the last 180 ka these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest africa and inverse correlations with both sea surface temperatures in the northeast atlantic and the extent of mediterranean vegetation possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones a change in relative humidity due to fluctuating air temperatures and an occasional influence of the african summer monsoon although it is not yet possible to clearly differentiate among these factors it is clear that the first two factors must have been primarily dominant these results represent the first quasi continuous terrestrial data testifying to environmental changes in the northwest african coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region high latitude dynamics had a major influence in this area and were intermediated by north atlantic sea surface temperatures a possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag which is similar to the lag recorded from north atlantic sea surface temperatures

quaternary glaciers and climate on cerro chirripo costa rica abstract glacial lake sediments and glacial geomorphology in valle de las morrenas a glacial trough on the north face of cerro chirripo costa rica provide evidence on high altitude pleistocene conditions in central america the most recent glacier in the valley chirripo stage i receded very rapidly near the end of the younger dryas chronozone radiocarbon dates on basal organic sediments from lakes beneath upper middle and lower limits of that glacier fall close together and two sigma calibrated ages overlap for the period 9700 9600 cal yr b p earliest datable transition sediments from the central lake date to 12 360 11 230 cal yr b p larger older moraines and associated trimlines allowed reconstruction of three paleoglaciers chirripo stages ii iii and iv computer analysis of hypsometry using published tropical glacier vertical mass balance profiles yields elas of 3506 3523 3515 3537 and 3418 3509 m respectively chirripo ii ela estimate positions applied to chirripo i yield an ela of 3538 3546 m we infer minimal temperature depressions of 7 4 8 0 c for the chirripo i iv stages modeling the behavior of modern tropical glaciers yields basinwide net accumulation estimates of 440 620 550 830 and 960 1760 mm yr 1 for the chirripo ii iii and iv stages

marine boundary layers associated with ocean upwelling over the eastern equatorial pacific ocean this paper deals with structure and processes in the marine boundary layer along air mass trajectories over and in the vicinity of the cold water tongue of the eastern equatorial pacific ocean the study is based on three nasa p3 b aircraft missions from guayaquil ecuador part of the nasa pacific exploratory mission tropics experiment the observations were made during september 1996 which is part of the cold season when the lowest sea surface temperatures are expected the boundary layer and the overlying free troposphere showed several unique features not observed previously while the boundary layer was advected over the equatorial cold tongue toward the intertropical convergence zone the overlying free tropospheric air consisted of warm moist outflow from the south american continent where deep convection was taking place the specific humidity just above the inversion was typically i 2 g kg t higher than that in the boundary layer these conditions tend to suppress cloud top radiative cooling and entrainment at the boundary layer top over the coldest upwelling areas shallow thermal internal boundary layers were observed we discuss changes in cloudiness sensible and latent heat fluxes and the scale of turbulence in and above the thermal internal boundary layers and during the reestablishment of the convective boundary layer upon passing over a warmer sea surface ularly during the cold season when as will be shown the mbl displays some rather unique characteristics reflecting the influence of cold ocean upwelling and a warm moist continental outflow in the overlying free troposphere these observations provide a basis for un derstanding transport and mixing of trace species and the formation and dissipation of clouds in this area and season both of these topics have implications for cli mate research we focus on data from the nasa p3 b research air craft collected during flights from guayaquil ecuador the area covered is adjacent to and se of the area in vestigated using dropwinsondes in the first global at mospheric research program garp global experi

duration of activity on lobate scarp thrust faults on mercury lobate scarps landforms interpreted as the surface manifestation of thrust faults are widely distributed across mercury and preserve a record of its history of crustal deformation their formation is primarily attributed to the accommodation of horizontal shortening of mercury s lithosphere in response to cooling and contraction of the planet s interior analyses of images acquired by the mariner 10 and mercury surface space environment geochemistry and ranging messenger spacecraft during flybys of mercury showed that thrust faults were active at least as far back in time as near the end of emplacement of the largest expanses of smooth plains however the full temporal extent of thrust fault activity on mercury particularly the duration of this activity following smooth plains emplacement remained poorly constrained orbital images from the messenger spacecraft reveal previously unrecognized stratigraphic relations between lobate scarps and impact craters of differing ages and degradation states analysis of these stratigraphic relations indicates that contraction has been a widespread and long lived process on the surface of mercury thrust fault activity had initiated by a time near the end of the late heavy bombardment of the inner solar system and continued through much or all of mercury s subsequent history such deformation likely resulted from the continuing secular cooling of mercury s interior

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

approach and application of industry software to structural investigations in the subsurface of mercury s thrust fault related landforms abstract historical efforts to model structures underlying planetary tectonic landforms have prioritized characterizing the dips depths and orientations of faults vertical displacement of rock along faults has been assumed to produce observed positive topography model derived fault parameters and values for fault displacement and strain have been estimated and these estimates have then been used to describe strain accumulated within regions of a planet or within entire planetary lithospheres previous modeling efforts have used finite element methods to reproduce topography associated with structure related landforms with acceptable models being determined through statistical best fit testing the approach presented in this work describes how software originally designed for industrial applications can be used in combination with the interpretation of topography and imagery to inform our understanding of the subsurface complexity of structures including faults and folds through a case study of ten structures in a smooth plains unit on mercury a detailed approach is provided for three dimensional modeling of subsurface faults and folds working with qualitative and semi quantitative criteria for acceptable or successful models and using those models to determine the relative importance of faulting and folding on topographic development through these details this work seeks to break through the black box often associated with modeling with the potential to support genuinely reproducible research

tropical snowline depression at the last glacial maximum comparison with proxy records using a single cell tropical climate model 1 the substantial lowering of tropical snowlines at the last glacial maximum lgm circa 21 kya is examined using a modified version of the single cell tropical climate model of betts and ridgway 1989 these authors concluded that it was difficult to reconcile the large depression of snowlines at the lgm with the small reduction in mean tropical sea surface temperature sst of the climate long range investigation mapping and prediction climap reconstruction here climatic implications of the snowline depression are compared not with climap but with temperature proxies 18o and sr ca ratios in corals noble gas concentrations in aquifers alkenone and mg ca ratios in deep sea sediments and recent faunal reconstructions whose lgm values have been interpreted as implying lower surface temperatures in the tropics it proves difficult in the framework of this model to reconcile the coldest of the indicated paleotemperatures with the observed snowline depression which by itself is found to be consistent with an sst reduction of 3 k a cooling of this magnitude corresponds most closely to recent warm pool lgm sea surface temperature estimates based on mg ca paleothermometry discordance among the various proxy reconstructions may result at least in part from regional variations in surface temperature change at the lgm

trmm radar observations of shallow precipitation over the tropical oceans abstract observations from the precipitation radar aboard the tropical rainfall measuring mission satellite provide the first opportunity to map vertical structure properties of rain over the entire tropics and subtropics storm height histograms reveal a distinct bimodal distribution over the oceans with the lowest mode near 2 km and the upper mode at 5 km the low mode is the dominant feature over regions previously associated with precipitating marine stratocumulus stratus and trade wind cumulus in those regions a lognormal distribution fits the observed storm height distributions quite well and a strong correlation exists between conditional mean rainfall rate and storm height in addition the low mode appears within the major tropical convergence zones associated with significant precipitation and in those regions a mixed lognormal distribution is used to separate the storm height distribution into two parts shallow and deep in this exploratory analysis the correlation between rainfall intensi

a 4000 year record of fire and forest history from valle de bao cordillera central dominican republic we examined evidence of past vegetation climate and disturbance history in a sediment core from a bog on the windward slope of the cordillera central in the dominican republic the sediments revealed a continuous 4000 cal yr history of pine pinus occidentalis dominance and fire bog formation may have been linked with a regional shift toward wetter conditions seen at other highland sites around 4000 cal yr bp low pollen influx low organic content and poor pollen preservation suggested periodic drying of the bog surface between 3700 and 1200 cal yr bp and the loss of sediments to either deflation or erosion spikes in pollen of broadleaf trees and shrubs mainly before 2500 cal yr bp may indicate warmer or wetter intervals remobilized old charcoal along with peaks in poaceae cyathea and lophosoria indicate a possible large tropical storm event around 2900 cal yr bp transported clasts of peat and soil in the core signal other high precipitation events we found no clear evidence of prehistoric human activity d 2005 elsevier b v all rights reserved

the distribution and origin of smooth plains on mercury 1 orbital images from the messenger spacecraft show that 27 of mercury s surface is covered by smooth plains the majority 65 of which are interpreted to be volcanic in origin most smooth plains share the spectral characteristics of mercury s northern smooth plains suggesting they also share their magnesian alkali basalt like composition a smaller fraction of smooth plains interpreted to be volcanic in nature have a lower reflectance and shallower spectral slope suggesting more ultramafic compositions an inference that implies high temperatures and high degrees of partial melting in magma source regions persisted through most of the duration of smooth plains formation the knobby and hummocky plains surrounding the caloris basin known as odin type plains occupy an additional 2 of mercury s surface the morphology of these plains and their color and stratigraphic relationships suggest that they formed as caloris ejecta although such an origin is in conflict with a straightforward interpretation of crater size frequency distributions if some fraction is volcanic this added area would substantially increase the abundance of relatively young effusive deposits inferred to have more mafic compositions smooth plains are widespread on mercury but they are more heavily concentrated in the north and in the hemisphere surrounding caloris no simple relationship between plains distribution and crustal thickness or radioactive element distribution is observed a likely volcanic origin for some older terrain on mercury suggests that the uneven distribution of smooth plains may indicate differences in the emplacement age of large scale volcanic deposits rather than differences in crustal formational process

spatial variability of atmospheric boundary layer structure over the eastern equatorial pacific abstract variations in the atmospheric boundary layer structure over the eastern equatorial pacific are analyzed using 916 soundings collected during the first global atmospheric research program global experiment unstable boundary layer structures are observed much more frequently in soundings north of the ocean front located near 2 5 n in the eastern equatorial pacific than in soundings south of the front an objective criterion is applied to identify the presence of the transition layer a weak stable layer near cloud base in the soundings the transition is observed in about 45 of the soundings in both the unstable and the inversion categories a comparison of soundings over the cold tongue with those over the itcz indicates that differences in static stability between these regions are limited to the layer from the surface to about 850 mb which is the mean height of the inversions capping the cloud layer over the cold tongue the cold tongue soundings on average are found to be drier from the sur

large extensional structures developed during emplacement of a crystalline thrust sheet the mondonedo nappe nw spain the mondonedo nappe is a crystalline thrust sheet characterized by large recumbent folds regional intermediate pressure metamorphism synkinematic intrusion of granitoids during nappe emplacement and an extensional ductile shear zone developed within the nappe during thrusting a large tectonic window permits the study of the footwall unit revealing another extensional shear zone contemporaneous with thrusting and a low pressure metamorphic evolution in contrast to that of the hanging wall unit the two main extensional shear zones produced e w extension parallel to the direction of orogenic shortening and normal to the orogenic structural trend furthermore subordinate n s longitudinal extension was accommodated by normal faults in the footwall and some of these faults were used as lateral ramps in late stages of thrusting the role of the extensional shear zones and faults described is discussed in the context of an evolving orogenic wedge dominated by plate convergence but characterized by large scale rheological heterogeneities within it deep seated viscous flow triggered by heat accumulation seems to account for the horizontal stretching and probable tapering of the orogenic wedge which was induced by gravitational instabilities due to partial melting and underplating by buoyant continental crust

potential vorticity generation by west african squall lines abstractthe west african summer monsoon features multiple complex interactions between african easterly waves aews moist convection variable land surface properties dust aerosols and the diu

dynamical adjustment of the trade wind inversion layer abstract in schematic north south cross sections the trade inversion layer is often depicted as sloping upward as air flows toward the intertropical convergence zone this conceptual view is consistent with purely thermodynamic boundary layer models which predict a deeper boundary layer with increasing sea surface temperature and decreasing large scale subsidence the slopes implied by such thermodynamic models and incorporated into schematic diagrams are approximately 2000 m 1000 km in contrast observational studies of the inversion structure over the atlantic and pacific oceans reveal a less dramatic slope on the order of 300 m 1000 km to address this inconsistency the authors adopt a somewhat different view of the trade inversion layer in particular rather than regarding it as a purely thermodynamic structure it is regarded as a dynamical structure by formulating a generalization of the rossby adjustment problem the authors investigate the dynamical adjustments of a trade wind inversion laye

observation of quasi 2 day convective disturbances in the equatorial indian ocean during dynamo abstractthis study examines the westward propagating convective disturbances with quasi 2 day intervals of occurrence identified over gan island in the central indian ocean from mid to late octobe

diurnal cycle of the itcz in dynamo abstractduring the 2011 special observing period of the dynamics of the madden julian oscillation dynamo field experiment two sounding arrays were established over the central indian ocean one

p t fluid deformation regime of the ediacaran serra do cavalo magro orogenic gold deposit ribeira belt brazil abstract the serra do cavalo magro orogenic gold deposit is located in the southern ribeira belt brazil gold quartz veins are hosted in calymmian 1500 1450 ma metasedimentary and metabasic rocks and ediacaran 610 600 ma granitic rocks geochronological data available in previous literature and structural petrological relationships with host rocks and shear zones indicate that the gold mineralization was formed within 580 540 ma during the late stage evolution of the brasiliano pan african orogeny related with gondwana supercontinent assembly petrological modeling indicates peak metamorphic conditions from 560 c and 7 kbar chlorite biotite phyllite to 625 c and 6 8 kbar garnet biotite phyllite recorded in immediate host rocks gold mineralization occurs in quartz shear and extensional veins structurally controlled by ne trending second and third order sinistral transcurrent shear zones the nnw trending subvertical and subhorizontal extensional veins are oriented 55 85 in relation to the fault planes indicating the shear zones were severely misoriented to frictional reactivation deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates while feldspar aggregates from the granitic protolith underwent cataclastic flow or were replaced by sericite epidote producing phyllonites gold precipitated during stages of vein deformation within microfractures in shear and extensional veins with quartz previously subjected to bulging recrystallization metamorphic ore bearing fluids are recorded in distinct assemblages of low to moderate salinities 1 18 wt nacleq h2o nacl cacl2 and h2o co2 n2 nacl cacl2 fluid inclusions and co2 n2 inclusions microthermometric data indicate entrapment conditions of 250 350 c and 0 3 2 3 kbar recording hydrostatic to supralithostatic fluid pressures in post peak metamorphic stages sharp fluid pressure fluctuations 0 4 1 6 kbar resulted from earthquake rupture events and the fault valve behavior induced circulation of fluids from distinct sources with limited partial fluid mixing favoring the gold transportation and precipitation

west gondwana amalgamation based on detrital zircon ages from neoproterozoic ribeira and dom feliciano belts of south america and comparison with coeval sequences from sw africa

fault dislocation modeled structure of lobate scarps from lunar reconnaissance orbiter camera digital terrain models 1 before the launch of the lunar reconnaissance orbiter known characteristics of lobate scarps on the moon were limited to studies of only a few dozen scarps revealed in apollo era photographs within 20 of the equator the lunar reconnaissance orbiter camera now provides meter scale images of more than 100 lobate scarps as well as stereo derived topography of about a dozen scarps high resolution digital terrain models dtms provide unprecedented insight into scarp morphology and dimensions here we analyze images and dtms of the slipher racah x 1 mandel shtam 1 feoktistov simpelius 1 and oppenheimer f lobate scarps parameters in fault dislocation models are iteratively varied to provide best fits to dtm topographic profiles to test previous interpretations that the observed landforms are the result of shallow low angle thrust faults results suggest that these faults occur from the surface down to depths of hundreds of meters have dip angles of 35 40 and have typical maximum slips of tens of meters these lunar scarp models are comparable to modeled geometries of lobate scarps on mercury mars and asteroid 433 eros but are shallower and 10 steeper than geometries determined in studies with limited apollo era data frictional and rock mass strength criteria constrain the state of global differential stress between 3 5 and 18 6 mpa at the modeled maximum depths of faulting our results are consistent with thermal history models that predict relatively small compressional stresses that likely arise from cooling of a magma ocean

tectonic implications of juxtaposed high and low pressure metamorphic field gradient rocks in the turvo cajati formation curitiba terrane ribeira belt brazil abstract the turvo cajati formation tcf is an important unit forming the curitiba terrane a major segment of the southern ribeira belt se brazil it is composed of rocks of greenschist ltcf amphibolite mtcf and granulite htcf facies conditions previous studies in the htcf indicate that the unit underwent extensive partial melting under high pressure conditions 670 810 c and 9 5 12 kbar within the kyanite stability field in this paper a study of the metamorphic zoning within the ltcf and mtcf is undertaken using pseudosection modeling in the nckfmashto and mnnckfmashto model systems coupled with detrital zircon u pb geochronology four metamorphic zones are recognized for the ltcf and mtcf biotite garnet staurolite and sillimanite zones with predominance of sillimanite zone and pressures lower than 8 kbar as staurolite breaks down straight to sillimanite without formation of a kyanite zone pseudosections yielded metamorphic peak conditions of 530 560 c and 6 7 5 kbar garnet zone and 660 690 c and 6 7 5 kbar sillimanite zone the metamorphic field gradient is flat and of low to medium pressure below the typical barrovian type baric regime and different from the htcf available petrological and geochronological data suggest that the tcf comprises a paired low p and high p metamorphic belt associated with a major ediacaran suture zone in the southern ribeira belt probability density plots from detrital zircon u pb ages indicate late cryogenian ediacaran arc related and rhyacian sources for all tcf sub units this scenario suggests that the tcf is made up of a collisional juxtaposition of an accretionary wedge htcf and a back arc basin ltcf and mtcf on the border of a microplate which includes a rhyacian basement microcontinent the atuba complex it is inferred the high metamorphic gradient recorded in the ltcf and mtcf was related with asthenospheric upwelling in the back arc region which also produced extensive partial melting in the atuba complex basement

climatological description of seasonal variations in lower tropospheric temperature inversion layers over the indochina peninsula abstract in this study operational rawinsonde data are used to investigate climatological features of seasonal variations in static stability in order to understand the behavior of temperature inversion layers that is extremely stable layers in the lower troposphere over the indochina peninsula region at the southeastern edge of the asian continent static stability was evaluated from the vertical gradient in potential temperature z stable z 10 k km 1 and unstable z 1 k km 1 layers frequently appear over the indochina peninsula region during boreal winter temporal and vertical variations in stability during the boreal winter can be categorized into three characteristic types type i the mean height of stable layers increases from 2 to 5 km from the dry to the rainy season over inland areas of the indochina peninsula and southern china type ii similar to type i with the additional occurrence of stable layers at a height of 1 km mainly over coastal areas of the indochina pen

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

marine atmospheric boundary layer height over the eastern pacific data analysis and model evaluation the atmospheric boundary layer abl height h is a crucial parameter for the treatment of the abl in weather and climate models about 1000 soundings from 11 cruises between 1995 and 2001 over the eastern pacific have been analyzed to document the large meridional zonal seasonal and interannual variations of h in particular its latitudinal distribution in august has three minima near the equator in the intertropical convergence zone itcz and over the subtropical stratus stratocumulus region near the west coast of california and mexico the seasonal peak of h in the itcz zone between 5 68 and 11 28n occurs in the spring february or april while it occurs in august between the equator and 5 68n comparison of these data with the 10 yr monthly output of the community climate system model ccsm2 reveals that overall the model underestimates h particularly north of 208n in august and september directly applying the radiosonde data to the ccsm2 formulation for computing h shows that at the original vertical resolution with the lowest five layers below 2 1 km the ccsm2 formulation would significantly underestimate h in particular the correlation coefficient between the computed and observed h values is only 0 06 for cloudy cases if the model resolution were doubled below 2 1 km however the performance of the model formulation would be significantly improved with a correlation coefficient of 0 78 for cloudy cases

seasonal changes in a vertical thermal structure producing stable lower troposphere layers over the inland region of the indochina peninsula abstractthe authors performed a thermal budget analysis to understand the nature of seasonal changes in stable lower troposphere layers over the inland region of the indochina peninsula using atmospheric reanalysis data the analysis focuses on subseasonal stable layers stability increase in the generation of stable layers is classified into three dominant thermal factors vertical differences in horizontal potential temperature advection vertical potential temperature advection and their residual component q1 the largest contributor to the stability increase is defined as the dominant thermal factor climatological typical heights where stable layers most frequently appear are the 850 700 700 600 and 600 500 hpa levels in november january february march and april respectively according to a previous study from november to january most of the stable layers in the typical height are generated by vertical differences in horizontal potential temperature advection their generation dissipation

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

the atuba complex southern south american platform archean components and paleoproterozoic to neoproterozoic tectonothermal events abstract the atuba complex consists of an archean terrane containing rocks differentiated from the mantle and incorporated into the continental crust between 3 1 2 7 ga this terrane was later reworked several times the main metamorphism occurred in the paleoproterozoic at about 2 1 ga and can be related to the amalgamation of the paleoproterozoic supercontinent atlantica ages around 1 7 ga may be related to the break up of atlantica during the mesoproterozoic there was little activity in the atuba complex and also in the entire south american platform isolated u pb zircon ages of 1 4 ga and sm nd model ages of about 1 2 ga may be associated to the assembly of rodinia the evidence from the south american platform indicates that the rodinia rifting pulses started as early as the latest collisional events of the grenville cycle instead of at ca 0 7 ga as commonly believed finally in the neopropterozoic at 0 52 0 65 ga u pb rb sr sm nd and k ar dates there were high grade tectonothermal events associated with gondwana assembly

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press