debris jets in continental phreatomagmatic volcanoes a field study of their subterranean deposits in the coombs hills vent complex antarctica abstract the ferrar large igneous province of antarctica contains significant mafic volcaniclastic deposits some of which are interpreted to fill large vent complexes such a complex was re examined at coombs hills to map individual steep sided cross cutting bodies in detail and we found several contrasting types two of which are interpreted to have filled subterranean passageways forcefully opened from below into existing non consolidated debris these transient conduits were opened because of the propagation of debris jets upward moving streams of volcaniclastic debris steam magmatic gases liquid water droplets following explosive magma aquifer interaction some debris jets probably remained wholly subterranean whereas others made it to the surface but the studied outcrops do not allow us to differentiate between these cases the pipes filled with country rock rich lapilli tuff or tuff breccia are interpreted to have formed following phreatomagmatic explosions occurring near the walls or floor of the vent complex causing fragmentation of both magma and abundant country rock material in contrast some of the cross cutting zones filled with basalt rich tuff breccia or lapilli tuff could have been generated following explosions taking place within pre existing basalt bearing debris well away from the complex walls or floor we infer that once focused jets were formed they did not incorporate significant amounts of existing debris while travelling through them instead incorporation of fragments from the granular host took place near explosion sites other basalt rich tuff breccia zones accompanied by domains of in situ peperite and coherent basalt pods are inferred to have originated by less violent processes

the origin of jadeitite forming subduction zone fluids cl guided sims oxygen isotope and trace element evidence jadeitite a rare high p t rock is associated spatially with blueschist and or eclogite terranes scanning electron microscope sem and cathodoluminescence cl petrography of jadeitite samples from several major occurrences in burma myanmar guatemala japan kazakhstan and the u s a show that grains were deposited from s uids jadeite grain compositions indicate these s uid compositions changed with time cl imagery guided the acquisition of oxygen isotope and trace element analyses with the ion microprobe jadeite grains in each rock grew in cycles that began with red and or blue luminescent and ended with green luminescent zones the cl images were used to order the data into crystallization sequences these data and electron microprobe major element analyses document the association of green cl with increases in ca mg and cr 1 toward grain exteriors 2 in ne grained matrix around porphyroblasts 3 in shear zones that cut grains 4 in former open spaces now lled with jadeite or 5 in veins abundances of many trace elements are greater in green cl jadeitite compared with the red or blue cl zones some of these elements in particular li rb sr ti hf zr y and ree are unlikely to have been derived from serpentinite although crystal chemical effects may explain some of the trace element systematics e g preferential incorporation of ree into ca richer jadeite some kinetic control is suggested by sector zoned rhythmically zoned grains the oxygen isotope data suggest that jadeitite depositing s uids either had multiple sources or evolved in composition along their s ow paths or both

processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

reservoir potential of late cretaceous terrestrial to shallow marine sandstones taranaki basin new zealand abstract late cretaceous coals and coaly source rocks are the main source of hydrocarbons in the taranaki basin yet to date there have not been any hydrocarbon discoveries within cretaceous strata and sandstone distribution and reservoir quality for this interval have been poorly understood the late cretaceous sediments were deposited in several sub basins across taranaki with their distribution largely determined by sediment supply subsidence and sea level change in this study we describe potential reservoir facies in well penetrations of cretaceous strata in taranaki as well as from outcrop in northwest nelson on the southern edge of the basin study of cretaceous outcrop has shown that facies distribution is a major control on reservoir quality shoreface intertidal and estuarine depositional facies contain both excellent well sorted sandstone reservoir facies as well as low net to gross reservoir poor facies these contrast with deposits from generally less well sorted and more heterolithic coastal plain environments much of the facies distribution is attributed to relative sea level fluctuations which occurred throughout deposition late cretaceous sandstones display a range of mean grain sizes and compositions with the latter related to geographic location and sediment source burial depths are highly variable across the basin ranging from 6 km and this has had a profound effect on reservoir quality the main petrographic controls on reservoir quality are sandstone composition volume of clay minerals degree of mechanical compaction related to maximum burial depth and proximity to a source of acidic pore fluids for the generation of secondary porosity results from this study suggest that cretaceous strata are a viable reservoir play over much of the western part of the taranaki basin and into parts of the south eastern basin palaeogeographic maps and textural compositional data can be used to high grade regions for further exploration

global trends of pco2 across the cretaceous paleogene boundary supported by the first southern hemisphere stomatal proxy based pco2 reconstruction reliable reconstructions of atmospheric carbon dioxide concentrations pco2 are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo pco2 levels such reconstructions are needed 1 at a high temporal resolution for constraining the pre and post extinction atmospheres and 2 at a sufficient spatial resolution to constrain potential inter hemispheric differences here we estimate pco2 based on fossil lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest cretaceous to the mid paleocene including a new cretaceous paleogene boundary k pg locality in new zealand we use two independent methods of stomatal density based pco2 reconstructions a transfer function calibrated using herbarium material and the stomatal ratio method producing three calibration sets our results based on the mean values of each of the three calibration methods indicate pco2 ranging between ca 460 and 650 ppm during the latest cretaceous falling precipitously to average values between ca 360 and 430 ppm across the k pg boundary and further to ca 305 320 ppm in the mid paleocene a spike of extremely high pco2 at the k pg could not be confirmed but our results are nonetheless consistent with previously published pco2 records from the northern hemisphere and show that stomatal density worldwide was responding to significant changes in pco2 across the k pg

the age and emplacement of obducted oceanic crust in the urals from smnd and rbsr systematics the urals contain a 2000 km belt of mafic ultramafic bodies the sm nd and rb sr systematics of two of these bodies the kempersai massif in the south ural mountains and the voykar syninsky ophiolite complex in the polar ural mountains have been examined these data confirm the hypothesis that these bodies represent fragments of pre collision oceanic crust and establish constraints on the nature and timing of events in the uralian orogeny two kempersai gabbros define sm nd internal isochrons of 397 20 my and 396 33 my with e nd t 8 7 0 6 and 8 4 1 3 respectively whole rock samples of pillow basalt diabase gabbros troctolite and a metasediment give sm nd values which lie on this isochron indicating that these rocks are genetically related and have an igneous crystallization age of 397 my whole rock samples of voykar syninsky diabase gabbros and clinopyroxenite give sm nd values which lie on or within 1 e unit of this isochron indicating an age and e nd t virtually identical to those of kempersai e nd t for the kempersai and voykar syninsky mafic samples range from 7 3 to 9 0 with an average value of 8 4 this indicates that the urals ophiolites are derived from an ancient depleted mantle source and are most plausibly pieces of the oceanic crust and lithosphere the fact that a metasediment has the same e nd 397 my as the other samples indicates derivation from an oceanic source with negligible continental input e nd t for the massifs is 1 5 e units lower than the average for modern morbs this may be due to the differential evolution of the morb source over the past 397 my and in conjunction with data for other ophiolites and mesozoic morb suggests that over the past 750 my the source for morb has evolved at a rate less than or equal to its rate of evolution averaged over the age of the earth initial 87 sr 86 sr ratios are highly variable ranging from e sr t 25 2 for a gabbro to 70 3 for a highly serpentinized harzburgite this reflects the effects of seawater alteration which is particularly strong on ultrabasic rocks we conclude that the long belt of mafic ultramafic rocks in the urals which includes the kempersai and voykar syninsky massifs represents segments of siluro devonian oceanic crust our igneous age for kempersai in conjunction with other age constraints suggest that these segments of oceanic crust formed at least 80 my before the collision that produced the urals

a red corundum bearing vein in the rai iz ultramafic rocks polar urals russia the product of fluid activity in a subduction zone abstract the veins in the mantle wedge peridotite can record the activity of slab derived melt fluid which is the reflection of the material circulation between crust and mantle a red corundum bearing vein is present in the rai iz ultramafic rocks in the polar urals russia the ultramafic rocks are harzburgite and dunite and the red corundum bearing rocks consist of phlogopite paragonite oligoclase red corundum and chromian spinel red corundum occurs as prophyroblasts or fine grains that contain 92 98 wt al2o3 and 2 7 wt cr2o3 chromian spinel has cr values 100cr cr al atomic ratio of 46 78 oligoclase is characterized by an values of 20 30 phlogopite is ba rich bao 0 8 2 7 wt and paragonite is sr rich sro 0 8 2 3 wt zircons from the oligoclasite show oscillatory zoning and th u values of

latest cretaceous earliest paleogene vegetation and climate change at the high southern latitudes palynological evidence from seymour island antarctic peninsula abstract fluctuations in late cretaceous climate were already influencing biotic change prior to the environmental upheaval at the cretaceous paleogene k pg boundary but their general nature magnitude and timing remain controversial a high resolution dataset on terrestrially derived palynomorphs is presented from the high southern palaeolatitudes that unlocks details of small scale climate variability throughout this period of significant global change specifically this is a quantitative spore and pollen analysis of an expanded uppermost cretaceous to lowermost paleogene maastrichtian earliest danian shallow marine sedimentary succession from seymour island off the northeastern tip of the antarctic peninsula then as now located at 65 s using nearest living relatives the first detailed vegetation habitat and climate reconstruction is presented for the emergent volcanic arc at this time on the coastal lowlands a cool to warm temperate rainforest is envisaged growing in a riverine landscape with both wet river margin pond and relatively dry interfluve canopy gap habitats diverse podocarps and southern beech trees grew alongside angiosperm herbs and shrubs in mean annual temperatures of 10 15 c higher altitude araucarian forests gave way to open ericaceous heathland beyond the tree line in subalpine to alpine conditions with mean annual temperatures of a cold 5 8 c there is no exact modern botanical equivalent but the closest modern flora is that of the andes of southern chile and argentina maastrichtian climate is shown to have fluctuated from cool humid conditions through a rapid warming 2 million years prior to the k pg transition followed by cooling during the earliest danian a trend supported by previous work on this interval

latitudinal temperature gradient during the cretaceous upper campanian middle maastrichtian y18o record of continental vertebrates latitudinal variations in model biogenic apatite d18o values were calculated using fractionation equations of vertebrates and weighted rainfall y18o values along with mean annual air temperatures provided by iaea wmo meteorological stations the reference equation obtained was used to compute a continental temperature gradient for the late campanian middle maastrichtian interval by using published and new d18o values of phosphate from vertebrates samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83 4 n alaska to 32 3 s madagascar the temperature gradient was less steep 0 4 0 1 c latitude than the present day one 0 6 c latitude with temperatures that decreased from about 30 c near the equator to about 5 c at the poles above 30 of paleolatitude air temperatures were higher than at present the validity of these results is discussed by comparison with climatic criteria inferred from paleontological paleobotanical and sedimentological data the latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying mesozoic terrestrial climates

coniacian flora of the sudetes south western poland palaeoecological and palaeoclimatic interpretations abstract palaeoecology of the coniacian flora of the sudetes idzikow flora south western poland is reconstructed on the basis of fossil plant morphology palynology and taphonomy four plant communities are reconstructed salt marsh mangrove forest dominated by frenelopsis wetland coastal forest dominated by geinitzia pandanites monheimia riparian forest dominated by ettingshausenia debeya dryophyllum and mesophytic forest dominated by microphyllous angiosperms proxy palaeoclimatic data for the idzikow flora have been estimated using clamp technique the numerical variables are as follows mean annual temperature 17 2 c warm month mean temperature 25 2 c cold month mean temperature 8 7 c length of the growing season 9 4 months growing season precipitation 841 mm mean monthly growing season precipitation 135 mm precipitation during the three consecutive wettest months 484 mm precipitation during the three consecutive driest months 100 mm relative humidity 68 5 specific humidity 8 9 and enthalpy 32 57 the reconstructed vegetation was probably a warm temperate seasonal to tropical forest experiencing hot summers and a short relatively dry season

quantification of uncertainties in fossil leaf paleoaltimetry does leaf size matter 1 the utility of multivariate foliar physiognomy specifically the climate leaf analysis multivariate program clamp to yield reliable estimates of enthalpy and hence paleoelevation has been demonstrated by comparison with other proxies yet concerns have arisen regarding uncertainties arising from 1 apparent ambiguities in the scoring regime and 2 the way leaf size is scored regarding the first concern scoring ambiguities are examined by reporting on scoring tests with novice users and interlaboratory comparisons the uncertainties were found to be less than those arising from the statistical methodology underpinning clamp in respect to the second concern the effect of removing all size data both from modern test sites and fossil data was tested specifically the effect of removing leaf size data from the 15 ma namling data set from south central tibet was investigated removal of all size data from modern sites demonstrated that size data contributes little to estimates of mean annual temperature and enthalpy similarly the removal of leaf size information from the namling data set alone but with calibration unchanged and from both the namling site and calibration sites this time with recalibration still yield paleoelevation estimates that have been independently matched by oxygen isotope techniques moreover the removal of all leaf size information results in only small increases in uncertainty 52 m

the late cretaceous environment of the arctic a quantitative reassessment based on plant fossils abstract late cretaceous megafossil floras from the palaeo arctic of northeastern russia and northern alaska are reviewed in respect of their age composition structure and floral dynamics palaeofloral correlations and comparisons are made between the two regions nine angiosperm rich predominantly cenomanian to coniacian floras from the palaeo arctic are re evaluated using climate leaf analysis multivariate program clamp calibrated using a global gridded 0 5 0 5 climate data set derived from that used in climate modelling additional floras from lower palaeolatitudes were used to derive latitudinal temperature gradients seven from n america five from around 30 n palaeolatitude in europe and one from kazakhstan the arctic climatic determinations similar to previous estimates support the existence of a northern pacific ocean cold gyre and a warm arctic ocean at palaeolatitudes greater than 80 n floras are insufficiently diverse in woody dicot taxa to use clamp but using clamp derived latitudinal temperature gradients arctic ocean coastal environments at 70 ma and 82 n and which supported a diverse dinosaur magafauna are predicted to have experienced a mean annual temperature of 6 3 2 2 c a warm month mean of 14 5 3 1 c and a cold month mean no colder than 2 0 3 9 c all uncertainties are 2 the new estimates are in good agreement with a wide range of non palaeobotanical climate proxies and render as an outlier warmer temperature estimates for the arctic ocean derived from the tex 86 proxy modelling however shows that land to ocean temperature gradients could have been steep the clamp estimates also suggest high values for humidity and precipitation consistent with sedimentological indicators and coupled with warm temperatures support the existence of a persistent polar cloud cap that helped maintain high terrestrial air temperatures throughout prolonged periods up to 5 months of winter darkness

foliar physiognomic record of climatic conditions during dormancy climate leaf analysis multivariate program clamp and the cold month mean temperature abstract the extent to which the leaves of woody dicots encode in their physiognomy the climatic conditions that exist during dormancy was tested by sampling 20 sites along an approximately west east transect across european russia the crimean peninsula western siberia and central eastern siberia this transect encompassed the most extreme mean annual temperature range recorded in the modern world where vegetation exists climate leaf analysis multivariate program clamp revealed little change in calibration of the warm month mean temperature compared with the physg3ar data set derived from less extreme sites primarily in north america and japan but significant change with respect to the cold month mean temperature cmmt calibration although clamp underestimated the cmmt by up to 9 c in the coldest sites the addition of the transect sites improved clamp s performance at low temperatures this suggests that winter cold is encoded in foliar physiognomy even though the leaves are functional only duri

climate model predictions for the latest cretaceous an evaluation using climatically sensitive sediments as proxy indicators to date many general circulation model gcm experiments have failed to reproduce the warm high latitude temperatures suggested for the cretaceous by geological proxy climate indicators especially for the northern hemisphere and within continental interiors the vast majority of these proxies are biologically based and it is important to determine whether alternative sedimentologically based proxies indicate similar cold biases in models therefore we have performed an evaluation of the very latest generation of climate model predictions for terrestrial sites using climatically sensitive sediments as palaeoclimate indicators evidence from the geological record comprising coal peat evaporites bauxite and laterite deposits are portrayed on a series of palaeoclimate data maps these are then compared with the global distributions of potential deposits generated from model simulations of the maastrichtian using versions of the hadley centre climate model the maastrichtian was chosen because of the greater range and sophistication of gcms adapted for its climate simulation and sediment prediction than for other cretaceous stages this thus represents the first attempt at comparing such state of the art models to lithological climate indicators and quantifying their relative performances for peat coal there is generally good correspondence between maastrichtian model predictions for predicted potential deposits and the observed record for evaporites there is also very close agreement between predictions by the models and the geological record minor differences between the individual model versions resulting from their differing levels of atmospheric co2 and the different palaeogeographical representations of intracontinental seaways in the northern hemisphere for bauxites and laterites the models predict less than half of the documented deposits successfully portraying equatorial accumulations but omitting the majority of mid to high latitude deposits the main discrepancy is therefore identified as the failure of all models to predict bauxite and laterite deposits corresponding with recorded accumulations within the mid to high latitudes of europe and asia in many cases the effects of co2 have minimal impact on the skill of model prediction however for evaporite distributions the low co2 model is appreciably worse in general the best match across the geological data and models is achieved by the simulation with open northern hemisphere seaways overall these results confirm those inferred from biological proxies showing that climate models have a serious cold bias in high latitudes and continental interiors during the cretaceous and that the latest generation of climate models still produces results which are incompatible with the geological data levels of atmospheric co2 and uncertainties in palaeogeography cannot explain the discrepancy the cold bias is common to many climate models and suggests that a process or mechanism is poorly represented or omitted in the current generation of climate models or that we are failing to recognise a major boundary condition change in the cretaceous if the former this implies that we may be underestimating the extent of extreme future climate change at high latitudes and in continental interiors

the use of a resemblance function in the measurement of climatic parameters from the physiognomy of woody dicotyledons abstract wolfe compiled a data set clamp of the physiognomy of woody dicotyledon leaves with a view to using it to extract climatic information from fossil floras attempts made using these data to identify and describe the relationship between plant physiognomy and climate have all searched for a global relationship applicable throughout data space we investigate the possibility that the relation between climate and physiognomy is so non linear that only local relationships should be sought we use a resemblance function to select sites that are physiognomically similar to each unknown site these similar sites alone yield a climatic estimate for the unknown site data collected from new zealand and australia are then added to wolfe s data set in order to test this new method we show that the use of a resemblance function enables us to produce mean annual temperature estimates for all modern sites that lie within 2 6 c of meteorological data for 90 of the sites this method also allows the objective identification of outliers based on their distance in physiognomic space from their nearest neighbours when a method is used that searches for a global relationship between physiognomy and climate the misfit of estimated mean annual temperature for the combined southern hemisphere and clamp sites is almost twice as great 5 c as that to the clamp sites alone in contrast when the resemblance function is used the rms misfit of estimated mean annual temperature increases by only 0 2 c this result demonstrates the robustness of the new method

an early middle eocene antarctic summer monsoon evidence of fossil climates abstract a warmer and mostly ice free south polar region prevailed during the early middle eocene indicative of a low latitudinal temperature gradient climatic models mostly fail to reconstruct such a low gradient demonstrating our poor understanding of the mechanisms involved in heat transfer here we describe a new phenomenon that shaped the southern high latitude climate during the early middle eocene the antarctic summer monsoon our palaeoclimatic reconstruction is based on 25 morphotypes of fossil dicotyledonous leaves from the early middle eocene fossil leaf assemblage of fossil hill from king george island the antarctic peninsula we use a novel clamp climate leaf analysis multivariate program calibration which includes new climatic parameters that allow us to characterise better the seasonality in precipitation our reconstruction indicates a warm humid temperate climate with strong seasonality in temperature and precipitation seasonality in precipitation indicates a rainfall rate of 6 4 1 30 mm day during summer summer daily rate of precipitation sdr and a summer precipitation representing more than 60 3 8 28 of annual rainfall ratio of summer precipitation rsp which fulfils the definition of a summer monsoon in the modern world this implies a seasonal alternation of high and low pressure systems over antarctica during the early middle eocene such a climate regime would have impacted upon global atmospheric circulation and heat transfer this climatic regime presents a challenge for climatic models and their ability to reconstruct accurately palaeoclimates at high southern latitudes and thereby understand latitudinal heat transfer in a greenhouse earth regime

the distinct foliar physiognomy of the late cretaceous forests of new zealand probably deciduous abstract three features of leaf physiognomy craspedodromous venation compound teeth and a lobed leaf outline figure prominently in the late cretaceous vegetation of southern new zealand these make it distinctly different from typical extant predominantly evergreen forests and some deciduous vegetation the physiognomy of the late cretaceous vegetation at the assemblage level shows more similarity with predominantly deciduous forests of the northern hemisphere in terms of the proportions of these characters in the flora at the taxon level combinations of characters found in fossils are very similar to and in some cases restricted to widespread extant northern hemisphere deciduous taxa but also to rarer components of evergreen forests it may not be possible to categorically determine whether any one fossil was deciduous the distinctly different assemblage level foliar physiognomy implies a distinctly different lifestyle for the new zealand forests that bordered gondwana in the late cretaceous it is highly likely that this physiognomy reflects an important deciduous component this is unexpected as for at least part of this time new zealand was apparently below north of the polar circle with a temperate and everwet climate

zircon u pb dating of jadeitite from the syum keu ultramafic complex polar urals russia constraints for subduction initiation abstract high pressure low temperature metamorphic rocks record subduction of oceanic crust and sediments into the mantle but the timing of subduction initiation is commonly difficult to determine however the appearance of fluid activity in the mantle wedge above a subduction zone can be correlated with incipient subduction here we describe jadeitite veins up to 5 m wide which are hosted in serpentinites of the syum keu ultramafic complex polar urals russia the jadeitites consist of both jadeite 86 88 mol jd and omphacite 54 75 mol jd multi stage growth of the jadeite is indicated by variations in color and structure such as growth zoning and the distribution of fluid inclusions we consider that the jadeitite veins formed from na al si rich fluids under hp lt conditions during active subduction and that the source material was subducted ocean crust shrimp u pb dating of zircons from the jadeitite yielded a concordant weighted mean 206pb 238u age of 404 7 ma which we interpret as the age of peridotite serpentinization and jadeitite formation in the suprasubduction zone mantle this age indicates that subduction was initiated about 40 ma earlier than peak metamorphism 360 355 ma of eclogite in the polar urals

ion microprobe zircon u pb age and geochemistry of the myanmar jadeitite combined geochemistry and geochronology of the myanmar jadeitite were determined bulk rock trace element compositions display u shaped ree patterns with pronounced positive eu anomalies the total ree abundances are very low less than half chondritic and the high field strength elements and some large ion lithophile elements are moderately enriched these features indicate a metasomatic origin there are three groups of zircons with different interior characteristics cathodoluminescence mineral inclusions chemical compositions and sensitive high resolution ion microprobe u pb ages group i zircons with a mean age of 163 2 3 3 ma mostly have distinct oscillatory zoning highest u and th contents and na free mg rich mineral inclusions and thus indicate an igneous formation of oceanic crust or hydrothermal serpentinization and or rodingitization event in the middle jurassic group ii zircons with a mean age of 146 5 3 4 ma have bright luminescence without oscillatory zoning and include jadeite and jadeitic pyroxene inclusions suggesting that formation of the myanmar jadeitites as well as subduction of the eastern indian oceanic plate occurred in the late jurassic group iii zircons have an age of 122 2 4 8 ma which represents a later unknown thermal event discovery of the middle jurassic zircons provides geochronological constraint on the tectonic evolution of the eastern indo burman range

cenozoic paleogeography of the central mogollon rim southern colorado plateau region arizona revealed by tertiary gravel deposits oligocene to pleistocene lava flows and incised streams eocene to pleistocene paleogeography of the mogollon rim southern colorado plateau region in central arizona is interpreted by use of tertiary sedimentary deposits and mafic lavas that have been correlated on the bases of provenance of pebbles stratigraphic sequence geomorphic positions of deposits and flows published k ar ages tracing of lava flows to vents and lava textures and structures five categories of tertiary sedimentary deposits are 1 paleocene to oligocene fluvial and lacustrine deposits on the margin of the colorado plateau that were derived from local and distant southern sources 2 oligocene to miocene deposits in valleys at the base of the mogollon rim that were derived from local and distant southern sources 3 oligocene to pliocene locally derived gravel on pediments and in canyons along the rim 4 miocene locally derived lag gravel beneath sheet flows on the plateau and 5 miocene to pleistocene locally derived channel filling gravel on the plateau mafic lavas used are 1 upper oligocene to lower miocene basalt and minette in the transition zone 2 miocene pahoehoe sheet flows on the colorado plateau and draped over the mogollon rim 3 middle miocene to pleistocene cones and flows of basalt scattered across the region and 4 pliocene to pleistocene basalts of the mormon and san francisco volcanic fields basalt sheet flows in ten middle ca 12 ma and upper ca 6 ma miocene flow fields traced to 12 low profile vent structures cover nearly 30 of a 9000 km2 area of the central mogollon rim region and depict the paleogeography at the times of eruption principal conclusions are 1 the mogollon rim developed near its present position after precambrian rocks in central arizona had been unroofed during the paleocene to eocene epochs and before late oligocene to early miocene mafic volcanism 2 after erosional quiescence during the paleogene triassic strata were stripped off the southern colorado plateau in a miocene to pleistocene erosional sweep from the southwest to the northeast 3 incision of meanders on the mogollon slope occurred in the late pliocene to pleistocene epochs as a result of integration of the little colorado river with the colorado river in the grand canyon

the fekete hegy balaton highland hungary soft substrate and hard substrate maar volcanoes in an aligned volcanic complex implications for vent geometry subsurface stratigraphy and the palaeoenvironmental setting the fekete hegy volcanic complex is located in the centre of the bakony balaton highland volcanic field in the pannonian basin which formed from the late miocene to pliocene period the eruption of at least four very closely clustered maar volcanoes into two clearly distinct types of prevolcanic rocks allows the observation and comparison of hard substrate and soft substrate maars in one volcanic complex the analyses of bedding features determination of the proportion of accidental lithic clasts granulometry and age determination helped to identify and distinguish the two types of maar volcanoes ascending magma interacted with meteoric water in karst aquifers in mesozoic carbonates as well as in porous media aquifers in neogene unconsolidated wet siliciclastic sediments the divided basement setting is reflected by distinct bedding characteristics and morphological features of the individual volcanic edifices as well as a distinct composition of pyroclastic rocks country rocks in hard substrate maars have a steep angle of repose leading to the formation of steep sided cone shaped diatremes enlargement and filling of these diatreme is mainly a result of shattering material by fci related shock waves and wall rock collapse during downward penetration of the explosion locus country rocks in soft substrate maars have much shallower angles of repose leading to the formation of broad bowl shaped structures or irregular depressions enlargement and filling of these diatremes is mainly the result of substrate collapse for example due to liquefaction of unconsolidated material by fci related shock waves and its emplacement by gravity flows the fekete hegy is an important example illustrating that the substrate of a volcanic edifice has to be taken into account as an important interface which can have major control on phreatomagmatic eruptions and the resulting characteristics of the volcanic complex

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

artificial neural networks reveal a high resolution climatic signal in leaf physiognomy the relationship linking leaf physiognomy and climate has long been used in paleoclimatic reconstructions but current models lose precision when worldwide data sets are considered because of the broader range of physiognomies that occur under the wider range of climate types represented our aim is to improve the predictive power of leaf physiognomy to yield climate signals and here we explore the use of an algorithm based on the general regression neural network grnn which we refer to as climate leaf analysis with neural networks clann we then test our algorithm on climate leaf analysis multivariate program clamp data sets and digital leaf physiognomy dlp data sets and compare our results with those obtained from other computation methods we explore the contribution of different physiognomic characters and test fossil sites from north america the clann algorithm introduced here gives high predictive precision for all tested climatic parameters in both data sets for the clamp data set neural network analysis improves the predictive capability as measured by r 2 to 0 86 for mat on a worldwide basis compared to 0 71 using the vector based approach used in the standard analysis such a high resolution is attained due to the nonlinearity of the method but at the cost of being susceptible to 39 noise 39 in the calibration data tests show that the predictions are repeatable and robust to information loss and applicable to fossil leaf data the clann neural network algorithm used here confirms and better resolves the global leaf form climate relationship opening new approaches to paleoclimatic reconstruction and understanding the evolution of complex leaf function

quantitative palaeoclimate estimates from late cretaceous and paleocene leaf floras in the northwest of the south island new zealand three new plant macrofossil assemblages were collected from late cretaceous and paleocene fluvio lacustrine sediments of the pakawau and kapuni groups in the northwest of the south island new zealand palaeoenvironmental interpretations were made from each locality and palaeoclimate was deduced from the dicotyledonous angiosperm leaf component of each flora a latest cretaceous pakawau bush road locality flora yielded 58 different dicotyledonous leaf forms the two paleocene collections ian s tip and pillar point track included 23 and 28 dicotyledonous leaf forms respectively quantitative palaeoclimate estimates were obtained using both leaf margin analysis lma and the climate leaf analysis multivariate program clamp temperature estimates suggest that there was a slight cooling from the latest cretaceous into the early paleocene in the northwest nelson region of new zealand supporting similar southern hemisphere palaeoclimate findings from antarctic data consistency in temperature estimates using different methods including lma multivariate leaf morphological analysis clamp oxygen isotope data regional versus local studies and global palaeoclimate models suggests that the mean annual temperature for the pakawau region in the latest cretaceous was between 12 and 15 c lma produced temperature estimates between 6 5 and 8 c for the two paleocene assemblages whereas clamp produced estimates were slightly higher between 9 and 12 5 c 2002 elsevier science b v all rights reserved

blueschists and eclogites a possible plate tectonic mechanism for their emplacement from the upper mantle the most significant problem of blueschists and eclogite origin is explaining the mechanism by which they were transported from great depths to the surface three aspects of this problem are discussed 1 1 prograde and retrograde trajectories in blueschist and eclogite bearing belts and the preservation conditions for such minerals as aragonite lawsonite and coesite 2 2 the mechanism by which low density crustal rocks with coesite and diamond descend to a depth of 100 150 km and the high rate of return from these depths to the surface 3 3 the origin of a tectonic mixture of rocks from different depths in melange zones using estimations of p t conditions and constructed p t t trajectories four types of blueschist belt are proposed these include two of the ernst types the alpine and franciscan and two additional types the dora maira and sanbagawa types key examples of geologically and mineralogically well studied complexes in the soviet union are discussed the kokchetav massif maksutov complex syumkeu belt borus belt the various models for the origin of different types of high pressure metamorphic belts are considered 1 1 slow uplift or uplifting of the thickened crust after cessation of subduction 2 2 more rapid tectonic pushing out 3 3 the same as in case 2 but with an additional champagne cork effect 4 4 the most complicated process with repeated deformation and metamorphism

maar diatreme geometry and deposits subsurface blast experiments with variable explosion depth basaltic maar diatreme volcanoes which have craters cut into preeruption landscapes maars underlain by downward tapering bodies of fragmental material commonly cut by hypabyssal intrusions diatremes are produced by multiple subsurface phreatomagmatic explosions although many maar diatremes have been studied the link between explosion dynamics and the resulting deposit architecture is still poorly understood scaled experiments employed multiple buried explosions of known energies and depths within layered aggregates in order to assess the effects of explosion depth and the morphology and compaction of the host on the distribution of host materials in resulting ejecta the development of subcrater structures and deposits and the relationships between them experimental craters were 1 2 m wide analysis of high speed video shows that explosion jets had heights and shapes that were strongly influenced by scaled depth physical depth scaled against explosion energy and by the presence or absence of a crater jet properties in turn controlled the distribution of ejecta deposits outside the craters and we infer that this is also reflected in the diverse range of deposit types at natural maars ejecta were dominated by material that originated above the explosion site and the shallowest material was dispersed the farthest subcrater deposits illustrate progressive vertical mixing of host materials through successive explosions we conclude that the progressive appearance of deeper seated material stratigraphically upward in deposits of natural maars probably records the length and time scale for upward mixing through multiple explosions with ejection by shallow blasts rather than progressive deepening of explosion sites in response to draw down of aquifers

new quantitative palaeocolimate data for the late cretaceous arctic evidence for a warm polar ocean abstract physiognomic analysis of four taphofloras one from the coniacian of n alaska one from the coniacian of kamchatka one from the turonian of kamchatka and one from the turonian of novaya sibir island using the clamp technique of wolfe 1993 yielded quantitative data on the mean annual warm month mean and cold month mean temperatures the length of the growing season mean annual precipitation mean growing season precipitation mean monthly growing season precipitation and the precipitation during the three consecutive driest months these new results represent the first application of multivariate statistical analysis of foliar physiognomy to determine palaeoclimatic parameters clamp to arctic cretaceous floras and demonstrate its robustness even in the context of vegetation which has no living analogues these new estimates were comparable to those from previous quantitative or qualitative sedimentological or palaeobotanical data where they were available but offer greater measurable precision the results also suggest that an arctic ocean with a winter surface temperature of approximately 6 c maintained n alaska coastal temperatures above freezing locally reversing the equator to pole temperature gradient a phenomenon not seen in the northern proto pacific this anomalously warm arctic ocean could have been produced by marine poleward heat transport precipitation in alaska kamchatka and novaya sibir island was predicted to have been high e g 1760 mm yr in the coniacian of n alaska reflecting a very weak polar high pressure cell and substantially different precipitation patterns to present

primary fluids entrapped at blueschist to eclogite transition evidence from the tianshan meta subduction complex in northwestern china the tianshan is the first locality worldwide where primary fluids at blueschist to eclogite transition have been documented veins containing high pressure minerals in massive host eclogites transitional to blueschists or eclogite boudins surrounded by blueschists indicate that a free fluid phase was present at the time of eclogitization the high pressure veins are predominantly composed of omphacite fibers with minor quartz or calcite the transition from blueschist to eclogite facies parageneses occurs as dehydration halos around these veins clinozoisite paragonite glaucophane and omphacite inclusions preserved in garnet porphyroblasts in wall eclogites document the transformation of blueschist to eclogite c axis parallel non planar populations of fluid inclusions were trapped during the growth of omphacite in high pressure veins and dehydrated wall rocks low salinity h2o nacl solid bearing inclusions are preserved in omphacite fibers in veins and matrix omphacite of wall rocks none of the isochores of these low salinity aqueous fluid inclusions intersect peak eclogite facies metamorphic conditions suggesting that although the textural evidence constrains the entrapment of fluid inclusions to peak metamorphic conditions their densities must have been modified during exhumation the fluids are interpreted to have been derived from the host blueschist as a result of dehydration reactions such as 13 gln 5 czo 9 prp 26 jd 12 di 19 qtz 15 h2o and gln pg prp 3 jd 2 otz 2 h2o the similarity of vein and wall rock mineral compositions fluid inclusion characteristics and o isotope data also favor an internal source for the fluids the major element composition of veins indicate that si na and ca rich aqueous fluids were released during dehydration at a depth of 50 10 km within a paleozoic subduction zone

oxygen isotope and paleobotanical estimates of temperature and δ18o latitude gradients over north america during the early eocene empirical estimates of climate parameters such as mean annual temperature mat are essential to describe both ancient climate and to ground truth climate model simulations of past climates in terrestrial settings no single proxy record is able to provide detailed temporal yet geographically widespread information and it thus becomes essential that paleoclimatic information obtained from different proxies be comparable as an example of how to compare estimates and to illustrate what can be learned by doing so we measured oxygen isotope ratios of phosphate in the tooth enamel of fossil mammals and the body scales of freshwater fish in order to estimate the mean annual temperature mat in which they lived the samples were collected from paleogene rocks of the bighorn green river and powder river basins of wyoming earliest eocene samples provide mat estimates that are similar to mat estimates for the same times and areas obtained from leaf margin analysis furthermore isotopic data from the paleocene eocene thermal maximum petm which has not yet yielded fossil floras indicate a significantly higher mat of 26 c we also used temperature estimates obtained by both methods to investigate paleoelevation and to reconstruct geographic patterns of mat over north america for the early eocene larger laramide basins have higher temperatures and lower inferred elevations compared to associated volcanic highlands where cooler temperatures are consistent with substantial elevations in turn latitudinal gradients in temperature indicate that warming centered on polar regions played an important role during the eocene hothouse lastly we show that the reconstructed eocene relation between oxygen isotope ratios of precipitation and mat is significantly different from the modern relation between these two variables because the relation has changed over time the modern correlation should not be used to estimate paleo mat from measurements of oxygen isotope ratios in fossil material

rb sr record of fluid rock interaction in eclogites the marun keu complex polar urals russia abstract rb sr internal mineral isochrons in the eclogite facies marun keu metamorphic complex polar urals russia date periods of fluid rock interaction and record the metamorphic reaction history the marun keu complex consists of late proterozoic to early ordovician mostly igneous rocks that experienced a subduction related non pervasive eclogite facies metamorphism followed by a local decompression related amphibolite facies overprint during the uralian orogeny field observations show that metamorphic reactions as well as ductile deformation are controlled by local availability of a free fluid phase isotopic data reveals that availability of fluids similarly exerts control on isotope distribution from a relic gabbro which has never been infiltrated by free fluids a premetamorphic rb sr age of 467 39 ma was obtained rb sr isochron ages for 14 samples of eclogite and amphibolite facies assemblages sampled from within or close to metamorphic fluid veins range from 352 5 ma to 360 3 ma a sm nd isochron for a metagranite yields an age of 354 4 ma taken together the ages for both prograde and retrograde metamorphic assemblages overlap within analytical uncertainty and yield an average value of 355 5 1 4 ma indicating that the metamorphic evolution and incipient exhumation of the marun keu complex proceeded rapidly the results demonstrate that assemblages preserve their rb sr isotopic signatures as long as they remain devoid of free fluids and that only fluid rock interaction may cause sr isotope redistribution in addition the data suggest local fluid rock equilibrium low fluid rock ratios with overall fluid deficiency and limited fluid mobility at depth however some fluids must have been mobile on the km scale since they can be traced into the suprasubduction zone mantle wedge metasomatic veins in the rai iz ophiolite yield a rb sr mineral isochron age of 373 1 5 4 ma they are interpreted as evidence for suprasubduction zone metasomatism in an oceanic setting prior to subduction of the east european margin and associated formation of eclogites in the marun keu complex we propose that rb sr mineral isochron ages provide hygrochronological rather than thermochronological constraints they define the cooling history only in combination with zircon and apatite fission track data the straightforward interpretation of rb sr mineral ages as cooling ages is obsolete

quantitative reconstruction of the late miocene monsoon climates of southwest china a case study of the lincang flora from yunnan province the miocene lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern yunnan sw china and the evolution of monsoon intensity three quantitative methods were chosen for this reconstruction i e leaf margin analysis lma climate leaf analysis multivariate program clamp and the coexistence approach ca these methods however yield inconsistent results particularly for the precipitation as also shown in european and other east asian cenozoic floras the wide range of the reconstructed climatic parameters includes the mean annual temperature mat of 18 5 24 7 degrees c and the mean annual precipitation map of 1213 3711 mm compared with the modem lincang climate mat 17 3 degrees c map 1178 7 mm the miocene climate is slightly warmer wetter and has a higher temperature seasonality a detailed comparison on the palaeoclimatic variables with the coeval late miocene xiaolongtan flora from the eastern part of yunnan allows us to investigate the development and interactions of both south asian and east asian monsoons during the late miocene in southwest china now under strong influence of these monsoon systems our results suggest that the monsoon climate has already been established in southwest yunnan during the late miocene furthermore our results support that both southeast asian and east asian monsoons co occurred in yunnan during the late miocene c 2010 elsevier b v all rights reserved

the relationship between leaf physiognomy and climate based on a large modern dataset implications for palaeoclimate reconstructions in china abstract in this paper correlation between modern leaf physiognomy and climate in china are examined to optimize the use of leaf characters as a palaeoclimate proxy a large dataset was compiled recording the distribution of leaf physiognomic characters among 3166 native dicot trees species across 732 calibration grids on a county level grids span a range of ecological environments tropical rainforests to alpine shrubs across humid areas thirteen climatic parameters were included for each grid and 22 leaf physiognomic characters were scored for each tree species the correlation between leaf physiognomic characters and climatic parameters were calculated based on single linear regressions slr and multiple linear regressions mlr results indicate clear spatial distribution patterns linked to latitude exist for all leaf characters with temperature coldest month mean temperature cmmt and precipitation growing season precipitation gsp being the main climate controls moreover because leaf characters are more closely correlated with precipitation during the three wettest consecutive months p3wet rather than with precipitation during the three driest consecutive months p3dry seasonal variations in rainfall associated with the asian monsoon might especially influence leaf physiognomic characters closer correlations between leaf physiognomy and climate are seen using mlr compared with slr therefore mean annual temperature mat and mean annual precipitation map based on mlr equations provide the most promising basis for palaeoclimate reconstructions in china

refining clamp investigations towards improving the climate leaf analysis multivariate program clamp climate leaf analysis multivariate program has been used for the past 17 years to estimate palaeoclimatic conditions the reliability and applicability of this method based on leaf physiognomic characters of fossil woody dicots has been widely discussed over the same period the present study focuses on some technical aspects of clamp mainly on its robustness in the context of the theoretical unimodal requirements of canonical correspondence analysis and introduces correction coefficients for these aspects of the statistical approach as a new way of interpreting and improving on clamp estimates this tool was tested on datasets derived from 17 european fossil floras ranging in age from the late oligocene to the pliocene additionally an objective statistical method for the selection of the best suited modern vegetation dataset from 144 site physg3br or 173 physg3ar extant biotopes is proposed

deriving temperature estimates from southern hemisphere leaves abstract the percentage of woody dicots with entire margined leaves in a flora is known to be positively correlated with mean annual temperature leaf margin analysis lma but this relationship is not globally uniform in particular the floras of australia and new zealand have been regarded as displaying a different physiognomic relationship to climate than floras seen in the northern hemisphere this difference is more marked in new zealand where the lma relationship appears entirely absent here we amass data for both northern and southern hemispheres using standard protocols and show that regional variations in the leaf margin mean annual temperature relationship are real but become less significant when other characters are included even new zealand falls into line and most of the mean annual temperature signal in new zealand floras is encoded in non margin features we introduce a new clamp climate leaf analysis multivariate program calibration dataset for the southern hemisphere comprising leaf physiognomic data from argentina bolivia south africa australia new zealand and other pacific islands that offers comparable precision for climate prediction to similar datasets derived from the northern hemisphere

petrotectonic evolution of the high to ultrahigh pressure maksyutov complex karayanova area south ural mountains structural and oxygen isotope constraints the maksyutov complex consists of three fault bounded lithologic units a quartzofeldspathic gneiss containing mafic eclogite boudins unit a1 a metasedimentary blueschist facies yumaguzinskaya unit and a meta ophiolitic melange unit a2 the geologic history of the high to ultrahigh pressure hp uhp assembly of the maksyutov complex is complicated by several stages of prolonged retrograde metamorphism and deformation the sakmara river exposes all three units near the former village of karayanova a structuralrpetrologic cross section through the area yields new quantitative data for the complex and regionally for the south urals analysis of the karayanova area has identified the major structures regional folding within the complex is parallel to the dominant foliation trending northeast southwest stereonet data show that during exhumation this large scale folding was refolded about axes trending southeast unit a1 and the yumaguzinskaya are tectonically and petrologically distinct units juxtaposed by west vergent thrusting and recrystallization within the same subduction zone a shear zone developed later between unit a2 and the unit a1q yumaguzinskaya tectonic package accompanying exhumation field relations and petrofabric demonstrate that blueschist facies recrystalliza tion overprinted an earlier eclogite facies metamorphism thermobarometric measurements yield p t values of 594 6378c 1 5 1 7 gpa for eclogite but these conditions may reflect annealing during the early stage exhumation at 375 ma cuboid graphite aggregates testify to precursor conditions for unit a1 within the diamond stability field if such textures are correctly interpreted measured 18 or 16 o partitioning between pairs of coexisting phases yield three main recrystallization temperature ranges 1 678 838c attending unit a1 eclogite facies metamorphism 2 453 178c during transitional blueschistrgreenschist facies metamorphism for the amalgamated unit a1q yumaguzinskayaq unit a2 assembly and 3 250 688c reflecting late stage hydrothermal alteration and exhumation oxygen isotope data for units a1 and a2 indicate that garnet blue amphibole and pyroxene crystallized in isotopic equilibrium validating previous thermobarometric calculations for a unit a1 retrograde metamorphic event variations in d 18 o values for phengites suggest the possibility of late metamorphic fluid infiltration retrograde recrystallization at high pressure in the presence of fluids and a calculated

quantification of large uncertainties in fossil leaf paleoaltimetry 1 estimates of paleoelevation potentially constrain geodynamic models of continental deformation and inform interpretations of landscape and climate evolution one widely used paleobotanical approach reconstructs paleoelevation from the difference in estimated atmospheric enthalpy between a known sea level and a targeted coeval elevated fossil floral site enthalpy is estimated using climate leaf analysis multivariate program clamp on 31 leaf size and shape variables that have been calibrated in living forests errors related to clamp are significantly greater than often reported and there are many sources of large potential error related to this method that are either difficult to quantify or unquantifiable and are thus not documented here we quantify one significant bias toward underestimation of leaf area in the clamp data set 50 that affects all clamp climate estimates including enthalpy crucially errors in paleoelevation when the leaf size bias is included are in the range of 2 km or more at least 2 times the previous estimates and exceeding the plausible paleoelevations of many fossil sites previously published paleoelevations derived from this technique are unlikely to be accurate either in magnitude or in estimated error

dikes sills and stress regime evolution during emplacement of the jagged rocks complex hopi buttes volcanic field navajo nation usa abstract the dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of the simplest volcanic plumbing systems their geometry is controlled by interaction of magma driven cracks with country rock and reveals regional structural and stress patterns at the time of their emplacement the shallow stress field however may change during the time an intrusion complex is emplaced in response to addition or removal of magma and country rock during associated surface eruptions the jagged rocks complex in the miocene hopi buttes volcanic field navajo nation arizona is exposed 300 350 m below the pre eruptive surface it comprises a group of generally nw se striking dikes punctuated in places by buds a saucer like intrusion larger pyroclastic massifs and a diatreme we made measurements of 13 dikes divided into 172 segments with thicknesses from 8 to 122 cm mean 43 cm and lengths of 60 to 780 m several sills and inclined sheets in places are thicker than dikes having mean thicknesses of 48 cm and 73 cm respectively dikes typically show straight parallel and en echelon patterns while sills and inclined sheets are curved the northwestern dikes differ from the rest in containing large mafic crystals and are inferred to have been emplaced after the others we find that the strike of the overall complex dikes and other sheets elongate massifs and aligned sub cylindrical bodies reflects a crystalline basement control that is evident throughout hopi buttes over the period of the complex s emplacement local stress patterns were not stable we infer that excavation of deep maar craters and perhaps the construction of a scoria cone at the surface modified the local stress patterns to favor emplacement of sills and en echelon dikes later in the complex s evolution in contrast to simple straight dikes as the complex first formed

subsurface structure of a maar diatreme and associated tuff ring from a high resolution geophysical survey rattlesnake crater arizona abstract geophysical survey techniques including gravity magnetics and ground penetrating radar were utilized to study the diatreme and tuff ring at rattlesnake crater a maar in the san francisco volcanic field of northern arizona significant magnetic anomalies 1600 nt and a positive gravity anomaly 1 4 mgal are associated with the maar joint modeling of magnetic and gravity data indicate that the diatreme that underlies rattlesnake crater has volume of 0 8 1 km 3 and extends to at least 800 m depth the modeled diatreme comprises at least two zones of variable density and magnetization including a low density highly magnetized unit near the center of the diatreme interpreted to be a pyroclastic unit emplaced at sufficiently high temperature and containing sufficient juvenile fraction to acquire thermal remanent magnetization magnetic anomalies and ground penetrating radar gpr imaging demonstrate that the bedded pyroclastic deposits of the tuff ring also carry high magnetization likely produced by energetic emplacement of hot pyroclastic density currents gpr profiles on the tuff ring reveal long 100 m wavelength undulations in bedding planes elsewhere comparable bedforms have been interpreted as base surge deposits inflated by air entrainment from eruption column collapse interpretation of these geophysical data suggests that rattlesnake crater produced highly energetic phreatomagmatic activity that gave way to less explosive activity as the eruption progressed the positive gravity anomaly associated with the maar crater is interpreted to be caused by coherent bodies within the diatreme and possibly lava ponding on the crater floor these dense magnetized bodies have excess mass of 2 4 10 10 kg and occupy approximately 5 of the diatreme by volume magnetic anomalies on the crater floor are elongate nw se suggesting that the eruption may have been triggered by the interaction of ascending magma with water in fractures of this orientation gpr imaging of the tuff ring also suggests that substantial land slip may have occurred on the western rim perhaps causing part of the tuff ring to collapse into the crater strong radar reflections indicative of well developed weathering horizons are present as well the techniques employed at rattlesnake crater demonstrate the value of combining multiple geophysical techniques in areas where exposures are limited and invasive exploration is not an option

dynamic tensile strength of terrestrial rocks and application to impact cratering dynamic tensile strengths and fracture strengths of 3 terrestrial rocks san marcos gabbro coconino sandstone and sesia eclogite were determined by carrying out flat plate pmma and aluminum impact experiments on disc shaped samples in the 5 to 60 m sec range tensile stresses of 125 to 300 mpa and 245 to 580 mpa were induced for gabbro and eclogite respectively with duration time of 1 s for sandstone porosity 25 tensile stresses normal to bedding of 13 to 55 mpa were induced with duration times of 2 4 and 1 4 s tensile crack failure was detected by the onset of shock induced damage p and s wave velocity reduction the dynamic tensile strength of gabbro determined from p and s wave velocity deficits agrees closely with the value of previously determined values by post impact microscopic examination 150 mpa tensile strength of coconino sandstone is 20 mpa for a 14 s duration time and 17 mpa for a 2 4 s duration time for sesia eclogite the dynamic tensile strength is 240 mpa the fracture strength for gabbro is 250 mpa 500 mpa for eclogite and 40 mpa for sandstone relative crack induced reduction of s wave velocities is less than that of post impact p wave velocity reductions for both gabbro and eclogite indicating that the cracks were predominantly spall cracks impacts upon planetary surfaces induce tensile failure within shock processed rocks beneath the resulting craters the depth of cracking beneath impact craters can be determined both by seismic refraction methods for rocks of varying water saturation and for dry conditions e g the moon from gravity anomalies in principle depth of cracking is related to the equations of state of projectile and target projectile dimension and impact velocity we constructed a crack depth model applicable to meteor crater for the observed 850 m depth of cracking our preferred strength scaling model yields an impact velocity of 33 km s and impactor radius of 9 m for an iron projectile

palaeoclimate analysis of late cretaceous angiosperm leaf floras james ross island antarctica the fossilized remains of cretaceous angiosperm leaves are preserved within sandstones and siltstones of the coniacian hidden lake formation gustav group and the santonian early campanian santa marta formation marambio group in the james ross basin antarctic peninsula region the leaves represent the remains of vegetation that grew at approximately 65 s on an emergent volcanic arc now represented by the antarctic peninsula and were subsequently transported and buried in marine sediments in the adjacent back arc basin some of the angiosperm leaf morphotypes show similarities to leaves of living families such as sterculiaceae lauraceae winteraceae cunoniaceae and myrtaceae palaeoclimate analysis based on physiognomic aspects of the leaves such as leaf margin analysis indicates that the mean annual temperatures for the hidden lake and santa marta formations were 13 21 c mean 17 c and 15 23 c mean 19 c respectively the fossil plants are indicative of warm climates without extended periods of winter temperatures below freezing and with adequate moisture for growth this period of cretaceous warmth in antarctica corresponds with the cretaceous thermal maximum an interval of peak global warmth from the turonian to the early campanian

serpentinites of the zermatt saas ophiolite complex and their texture evolution the zermatt saas serpentinite complex is an integral member of the penninic ophiolites of the central alps and represents the mantle part of the oceanic lithosphere of the tethys metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean floor hydration subduction related high pressure overprint meso alpine greenschist facies metamorphism and late stage hydrothermal alteration the early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures the primary serpentine minerals were completely replaced by antigorite the stable assemblage in subduction related mylonitic serpentinites is antigorite olivine magnetite diopside the mid tertiary greenschist facies overprint is characterized by minor antigorite recrystallization textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high pressure metamorphism of up to 2 5 gpa and 650 c the zermatt saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth

modelling equable climates of the late cretaceous can new boundary conditions resolve data model discrepancies late cretaceous maastrichtian climate and vegetation is modelled using the hadcm3l fully coupled atmosphere ocean model and the triffid dynamic vegetation model we investigate data model inconsistencies in the high latitudes and continental interiors by exploring the sensitivity of modelled terrestrial climate to vegetation treatment changing atmospheric pco2 levels and the representation of arctic seaway connections we expand on previous work by using millennial scale gcm runs with dynamic vegetation to allow for improved representations of ocean heat transport and terrestrial boundary conditions incorporating realistic vegetation drives high latitude warming particularly during summer through reductions in surface albedo and induced atmosphere ocean feedbacks resulting regional warming can exceed 10 c as pco2 rises some regions cool as deciduous to evergreen change increases albedo incorporating enhanced arctic connectivity reconfigured ocean heat transport drives widespread terrestrial warming of 3 c and 5 c regionally applying sensitivities in combination significant palaeobotanical data model inconsistencies in the northern high latitudes and continental interiors remain further work is required to resolve climate and vegetation model deficiencies and improve the interpretation and geographic distribution of quantitative climate sensitive geological proxies

immense vent complex marks flood basalt eruption in a wet failed rift coombs hills antarctica large lava effusions can have impressive explosive antecedents although our picture of flood basalt is overwhelmingly effusive phreatomagmatic eruptions have preceded quiet effusion of some flood basalts and reflect the same influence of vent architecture and hydrology on eruptive style as seen for small volume eruptions the scale of phreatomagmatic deposits associated with flood basalts can be huge at coombs hills a vast but otherwise typical phreatomagmatic vent complex is exposed over more than 25 km 2 and its features are interpreted to reflect processes of tephra jet eruptions with diatreme development similar vent complexes are probably the source of laharic deposits reported elsewhere in the transantarctic mountains and in the karoo province of south africa