a palynofacies study of past fluvio deltaic and shelf environments the oligocene miocene succession north sea basin a reference data set for similar cenozoic systems abstract correct interpretations of depositional environments are fundamental for evaluating the geological history of a sedimentary basin palynofacies analyses are a valuable supplement to sedimentological and seismic studies in order to develop a palynofacies reference dataset for fluvio deltaic and shelfal successions a study of the assemblages of sedimentary organic particles from seven different well defined depositional environments within the uppermost oligocene lower miocene succession onshore denmark eastern north sea basin has been performed the study deals with the following environments floodplain lagoon washover fan flat prodelta shoreface offshore transition and shelf the sedimentary organic particles were grouped into four major categories 1 structured wood particles 2 amorphous organic matter aom in the present study mainly consisting of partly degraded vitrinite 3 cuticle and membranes and 4 palynomorphs the palynomorphs were grouped into eight subcategories 1 microspores 2 non saccate pollen 3 bisaccate pollen 4 botryococcus 5 other freshwater algae 6 fungal hyphae and spores 7 acritarchs and 8 organic walled dinoflagellate cysts a combination of a univariate box plots and a multivariate principal component analysis pca of the palynofacies data clear revealed the quantitative characteristics and variations within each discrete environment as well as their principal similarities and differences in spite of some natural overlaps for example between the lagoon and offshore transition environments the data revealed distinct characteristics e g a strong dominance of wood particles in the shoreface environment a strong dominance of bisaccate pollen in the washover fan flat environment and a near absence of dinocysts in the floodplain environment an overall increase in relative abundances of dinocysts and a decrease in abundances of non saccate pollen in the proximal distal trend were also outlined this study outlines a palynofacies reference dataset that can be used as a tool for interpreting depositional environments in equivalent settings preferentially combined with other information such as seismic data well logs and or lithology

carbon concentrations and isotopic ratios of eclogites from the dabie and sulu terranes in china abstract both concentration and isotope composition of bulk carbon in apatite and host eclogites from the dabie sulu ultrahigh pressure uhp terranes in china have been determined along with their oxygen isotope composition the results show significant 13 c depletion in the apatite 13 c 27 7 to 20 8 with the carbon concentrations of 0 59 to 1 65 wt co 2 despite a large variation in 18 o 6 5 to 9 5 the bulk carbon in 21 of the 24 eclogites has low 13 c values of 26 1 to 17 9 with low carbon content of 500 to 1000 ppm whereas the other three samples show high 13 c values of 7 1 to 2 8 with high carbon contents of 2400 to 4300 ppm noncarbonate carbon was measured by treating the all eclogites with 5 n hcl solution yielding uniformly low 13 c values of 27 9 to 24 2 and carbon contents of 200 to 300 ppm carbonate carbon is thus calculated by mass balance to have also low 13 c values of 25 6 to 15 1 for the 21 samples but high 13 c values of 4 3 to 1 2 for the remaining three samples secondary carbonate was identified in the three eclogites that are also depleted in 13 c primarily but subjected to overprint of 13 c rich co 2 bearing fluid subsequent to the uhp metamorphism the isotopically light carbon in both eclogite and apatite is interpreted to represent the isotope composition of carbon in eclogite precursors before plate subduction and thus has an origin of organic carbon from the earth s surface the uniformly low 13 c values of apatite suggest that the co 2 of metamorphic fluid in equilibrium with the host eclogites would be derived from the oxidation of organic carbon rather than the decarbonation of underthrust carbonates during progressive metamorphism protoliths of the eclogites are inferred to be of igneous origin which underwent more extensive interaction with organic matter than with meteoric hydrothermal fluid on the subsurface of the continental crust the break off of the subducted plate containing the isotopically light carbon and subsequent interactions with the surrounding mantle could produce the mafic and or silicic magmas that are significantly depleted in 13 c relative to the primary mantle carbon this may provide evidence for a linkage of the 13 c depleted mantle carbon to a surficial source via plate subduction

analytical solutions to hillslope subsurface storm flow and saturation overland flow we present the analytical solutions to a hillslope based formulation of subsurface storm flow and saturation overland flow here a hillslope is defined as the area between two streamlines originating from two ends of a channel link or from the channel head and ending at the ridgelines the three dimensional soil mantle of a hillslope is reduced to a one dimensional profile along which the soil moisture and discharge are modeled continuity and a kinematic form of darcy s law lead to quasi linear wave equations solvable with the method of characteristics examples are given to illustrate the ability and limitations of the solutions in capturing the essential runoff behavior of different slope types

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

carbon concentrations and isotopic ratios in fluid inclusion bearing upper mantle xenoliths along the northwestern margin of north america abstract at least three and perhaps four carbon components have been identified by step heating extraction of upper mantle xenoliths from nunivak island and prindle volcano alaska fort selkirk and alligator lake yukon jacques lake and castle rock british columbia one component released mostly between 200 and 600 c comprises 30 95 of the total carbon extracted and has 13c values between 28 and 23 this carbon corresponds mostly to complex carbon compounds condensed on surface minerals and cracks and will be referred to as isotopically light carbon ilc co2 released between 600 and 800 c is derived from interstitial carbonates it has variable 13c and concentrations that generally do not exeed 24 ppm c the carbon extracted from 1000 to 1450 c is a mixture of co2 from fluid inclusions and the ilc fraction the amount of ilc released in this temperature interval never exceeds 10 ppm because part of this ilc may have been introduced from the host lava the 13c variations of this carbon extracted above 800 c is not only characteristic for the original carbon present in fluid inclusion poor xenoliths however xenoliths enriched in co2 fluid inclusions show c isotopic variations at the highest temperature steps that fall in a relatively narrow range between 10 and 4 depending upon the fluid inclusion abundance the concentration of high temperature c derived from fluid inclusions varies from 0 1 to 66 ppm anhydrous spinel lherzolites and harzburgites generally contain

patterns of incidence of oil reserves in niger delta basin data on oil reserves in the niger delta basin show a bimodal lognormal distribution with the break in slope reflecting variation in exploration maturity quality of prospect and distribution of giant oil fields several areas of anomalous reserves are defined by the selected threshold oil reserves density of 200 000 bbl km2 five major prolific centers with reserves contrast 3 are aligned in an arcuate belt prolific belt which is an image of the present coastline the prolific belt marks the transition zone between oceanic and continental crusts a zone of weakness characterized by increased tectonic activity during passage through the belt the niger delta system was predominantly constructive and consisted of at least five delta complexes which now define the prolific centers beyond the prolific belt predominance of destructive processes resulted in merging of the delta complexes in these areas the distribution of zones of major concentration of reserves developed in response to alternate channel switching and extension superimposed on growth fault activity the prolific belt and offshore zone coincide with a hot geothermal belt that frames a geothermal minimum at the delta center the coincidence together with the progressively younger sediments from north to south suggests that the maturity per unit depth is less in the offshore zone and central delta nose than in the prolific belt implied are deeper levels of hydrocarbon occurrence as well as a lesser amount of generated hydrocarbons offshore and on the central delta nose than in the prolific belt these factors and the relatively shallow depth of investigation probably account for the present absence of prolific centers south of the prolific belt

aspects of palyno organic facies analysis comprehensive evaluation of the source rocks and age of some subsurface lower cretaceous core materials in the north western desert egypt abstract the palyno organic facies aspects of the subsurface lower cretaceous core samples are extensively investigated in three wells in the northern part of the western desert of egypt these wells are burg el arab 1 and mamura 1 mersa matruh 1 bax 1 max 1 and mmx 1 respectively the study is based on the palynofacies and organic geochemical analyses the palynofacies examination includes a statistical analysis of the different classes of organic particles by cluster analysis and principal component analysis pca this analysis leads to identify 4 palynofacies types a b c1 and c2 which are dominated by various levels of terrestrial floral materials the paleoenvironmental settings that are attributed to these palynofacies types are the distal suboxic oxic proximal oxic transitional oxic and highly distal oxic the principal component analysis pca differentiates between these palynofacies types mathematically by the biplot of components 1 and 2 the component 1 corresponds to distance from the terrestrial floral sources the identification of quantity type quality and thermal maturity of organic matter is discussed depending on the palynofacies and organic geochemical analyses the thermal maturity is assessed digitally by measuring the rgb color channels in the spore images and their corresponding thermal alteration index tai incorporated with values of tmax these measures are integrated in burial history models with geothermal gradient and depositional history the study reveals that most of the core samples represent generally fair to good enriched sources of gas prone type iii kerogen and less mixed gas oil type ii iii kerogen additionally some occasional high levels of organic conversions are recorded the burial history models indicate that oil expulsion window initiated in the cretaceous the examinations indicate mature oil sources in the alam el bueib formation in mmx 1 well the organic geochemical parameters are correlated versus the component 1 and sum of all components of pca the correlation coefficients r2 pointed to good correlation between the oxygen index oi toc and s2 and lower correlation with hydrogen index hi

ultradeep metamorphic rocks the retrospective viewpoint ultradeep or ultra high pressure uhp metamorphic rocks formed from crustal protoliths within the stability field of coesite at pressures 2 5 3 0 gpa corresponding to depths 80 120 km occur locally though regionally distributed in at least five continental areas their recognition is solely based on characteristic minerals and mineral assemblages calibrated by experimental high pressure studies detailed petrographic and microprobe work especially on mineral inclusions in favorable cases allows the derivation of prograde pt paths during subduction and of retrograde ones during exhumation commonly the gneisses adjacent to the uhp rocks do not exhibit signs of ultradeep metamorphism apparently because the kinetics of their mineral reactions are sufficiently fast to allow complete reequilibration to shallower pt conditions during the retrograde path it is also possible however that uhp equilibria were not attained throughout the rock volumes subducted but only along zones of shearing and fluid introduction if it is true that not all uhp metamorphic rocks return to the crustal orogenic belts but some continue to be subducted to greater mantle depths the classical geochemical pattern of a one way mass transfer from mantle to crust throughout the earth s history is at stake the assumed gradual growth of continents may have had a counterpart of continent destruction during collision events most recent experimental studies at high pressures and relatively low temperatures show that at least three new hydrous mg a1 silicates exist that were not found in nature thus far but may be characteristic minerals in the cold portions of old subduction zones thus extending the water retentivity of subducting slabs to greater and hitherto unexpected depths

sm nd and rb sr dating of pyroxene garnetite from north dabie in east central china problem of isotope disequilibrium due to retrograde metamorphism abstract oxygen isotopes may serve as a guide to evaluate whether equilibria are preserved in the sm nd and or rb sr systems in eclogites that experience retrograde metamorphism this study demonstrates that sm nd rb sr and o isotopes for minerals from two portions of a clinopyroxene garnetite from north dabie in east central china record both equilibrium peak metamorphic conditions and disequilibrium conditions resulting from anhydrous retrograde metamorphism the minerals are homogeneous in terms of major elements and show no variation across the sample but clinopyroxene shows variable degrees of alteration pure primary mineral separates that are in o isotope equilibrium yield triassic sm nd isochron ages of 219 11 and 229 13 ma that match previously published zircon u pb ages for peak metamorphism thus the sm nd system in these minerals equilibrated during peak metamorphism and remained unaffected by retrograde metamorphism in contrast altered and impure clinopyroxenes that display oxygen isotope disequilibria fall off the sm nd isochron defined by the pure minerals implying that like oxygen the sm nd systems in these clinopyroxene were disturbed during retrogression no meaningful isochrons are found from the rb sr dating even in the pure primary minerals implying that these systems were disturbed during retrograde metamorphism and the diffusion rate of sr is faster than those of sm nd and o in mafic minerals our results suggest that the oxygen isotopes in metamorphic minerals can be used to evaluate the validity of sm nd mineral isochrons in dating peak metamorphic events in addition variations in the sm nd concentration and isotopic compositions of altered and impure clinopyroxenes from the two portions suggest heterogeneous effects on the minerals from external and internal fluids

eco geomorphic implications of hillslope aspect inferences from analysis of landscape morphology in central new mexico 1 we investigate the influence of hillslope aspect on landscape morphology in central new mexico where differences in soils vegetation and landforms are observed between mesic north facing and xeric south facing slopes slope area and curvature area relations derived from a digital elevation model dem are used to characterize the opposing hillslope morphologies in all geologies and elevation ranges studied topographic data reveal significantly steeper slopes in north facing aspects and shallower slopes in south facing aspects north facing slope curvatures are also greater than south facing curvatures using a conceptual slope area model we suggest that for a given drainage area steeper north facing slopes imply lower soil erodibility we argue that this interpretation consistent with recent views of ecosystem control on semiarid erosion rates shows the influence hillslope aspect on topography and its associated vegetation communities observed valley asymmetry in the region reinforces this concept and suggests a long term legacy of aspect modulated ecogeomorphic processes

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

human impact on land ocean sediment transfer by the world s rivers abstract land ocean transfer of sediment by rivers is a key pathway for material transfer on earth contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact the key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance including logging activity and mining although programmes for soil conservation and sediment control can result in reduced sediment loads the trapping of sediment by dams represents the dominant cause of reduced loads this influence is currently assuming increasing importance at the global scale any attempt to link these drivers to changes in the global land ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins which can cause damping and even removal of signals of increasing flux within the upstream basin and complicate the link between upstream and downstream response to human impact further work is required to provide a precise quantitative assessment of the human impact on global land ocean sediment fluxes and the net effect of increasing and decreasing fluxes particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes

classification and analysis of palynodebris from the palaeocene sediments of the forties field sedimentary organic matter behaves as sedimentary particles and this study attempts to interpret its occurrence in the palaeocene sands and mudstones of the forties field of the north sea new nomenclature and classification of this palynodebris are presented and are used to make quantitative counts of the palynodebris from nearly 600 samples of known sedimentary character the new categories are further refined by objective testing of the data by principal components analysis and cluster analysis it is argued that two types of sedimentary organic matter are of particular value because they are preferentially deposited in different environments palynowafers are most commonly deposited in the submarine fan lobes and channel complexes and amorphous matter occurs mostly in the lower energy basin plain sediments

carbon isotope anomaly in marbles associated with eclogites from the dabie mountains high 13c values up to 5 7 pdb were measured in marbles associated with ultrahigh pressure eclogites in the dabie mountains east china such a carbon isotope anomaly is interpreted to represent the carbon isotope composition of premetamorphic limestone i e the protolith of the marbles because there is no known process to enrich carbonate in 13c during regional metamorphism the high 13c also corresponds to high 18o of up to 22 9 smow suggesting that premetamorphic 13c values would be about 5 to 6 for their protolith limestones the carbon isotope anomaly in the protolith of the marbles implies a local change in the redox state of water during deposition of the limestones preservation of the unusually high positive 13c values in the marbles supports the previous conclusion that there was no significant isotopic exchange with the mantle during subduction of supracrustal rocks to mantle depths of greater than 100 km

stable isotope characteristics of eclogites from the ultra high pressure metamorphic terrain east central china abstract a stable isotope study was made for the ultra high pressure uhp metamorphic rocks in the dabie and sulu terrains east central china 18 o values of minerals in eclogites cover a wide range from 4 to 6 the o isotope fractionations between minerals i e omphacite phengite and or amphibole and garnet in eclogites are mostly not in isotopic equilibrium the large range of o isotope composition of garnet may approximate the 18 o variations of eclogites during uhp metamorphism and must have been largely inherited from their pre subduction basaltic precursors which might have interacted with meteoric waters under variable temperature conditions and water rock ratios before uhp metamorphism the o isotope disequilibrium between minerals and garnet in eclogites was caused by retrograde hydration reactions the fluids required for these hydration reactions must have low or even negative o isotope compositions it is postulated that such fluids were either originated from meteoric deep infiltration or were derived from low 18 o para gneisses

talc magnesite and ti clinohumite bearing ultrahigh pressure meta mafic and ultramafic complex in the dabie mountains china

evolutionary trends of the niger delta shoreline during the last 100 years responses to rainfall and river discharge article there is growing evidence that the world river deltas are influenced by climate change and anthropogenic activ ities in this study shoreline changesalong the niger delta coastofthegulf ofguinea northatlanticoceaninthe last ten decades were investigated the relationships between these changesand hydrometeorologic variables of rainfall and river discharge were considered topographic maps and satellite imagery in addition to rainfall and hydrological data from the lower niger river basin were used for the study the results show two distinct shoreline dynamics patterns phases first mobility with high net retreat between 1923 and 1987 interval and second mobility with low net progradation from 1987 to 2013 during the first phase shoreline retreat is mainly concentrated on the western and arcuate sections of the delta in the second phase all sections of the niger delta coast prograded seaward strong correlations between shoreline change and the river discharge r 2 0 95 shoreline change and rainfall variability r 2

oxygen isotope equilibrium between eclogite minerals and its constraints on mineral sm nd chronometer abstract sm nd and oxygen isotope analyses were carried out for mineral separates of ultrahigh pressure eclogites from the sulu terrane in eastern china the results show a direct correspondence in equilibrium or disequilibrium state between the oxygen and sm nd isotope systems of eclogite minerals the omphacite garnet pairs of oxygen isotope equilibrium at eclogite facies conditions yield meaningful triassic sm nd isochron ages whereas those of oxygen isotope disequilibrium give non triassic ages of geological meaninglessness this can be reasonably interpreted by the fact that the rates of oxygen diffusion in garnet and pyroxene are lower than or close to those of nd diffusion and thus attainment of isotopic equilibrium in the omphacite garnet o system suggests achievement of nd isotope equilibrium in the same mineral pairs the presence or absence of fluid in the eclogite protoliths is a major rate controlling factor for isotopic equilibration during high grade metamorphism it appears that the state of oxygen isotope equilibrium between cogenetic minerals can provide a critical test for the validity of the sm nd mineral chronometer in addition the exact timing of the ultrahigh pressure metamorphism in the dabie sulu terranes is constrained at early triassic rather than late triassic

the carbonate content in high temperature apatite an analytical method applied to apatite from the jacupiranga alkaline complex we present a method to measure carbonate content of apatite that uses infrared spectroscopy the method was calibrated against the amount of c02 released by reaction of apatite with phosphoric acid and may be used to study apatite with c02 content below i wt we have applied the method to apatite from carbonatite 0 3 0 4 wt c02 and metasomatic 0 6 1 0 wt c02 and alkaline silicate 0 3 wt c02 rocks from the jacupiranga alkaline complex the results show that higher concentration of carbonate was found in apatite related to metasomatic processes and in particular to metasomatism related to the intrusion of carbonatite from j acupiranga major and trace elements of the analyzed apatites do not show a simple substitution mechanism that would explain the presence of carbonate in the apatite structure in a series of exploratory laboratory experiments in which apatite was synthesized under high temperature and pressure no clear relationship was observed between the carbonate content of the synthetic apatite and the total c content in the coexisting fluid molecular c02 or carbonate ions in solution however even though these experiments were not conclusive they suggest that apatite coexisting with carbonate ions in solution has a c02 content above 0 3 wt whereas apatite coexisting with molecular c02 has a c02 content 0 3 wt these results indicate that the c02 content of apatite depends not only on total fluid c content but also on the c speciation in the fluid

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

fluid rock interactions during ultra high pressure metamorphism dabie shan china oxygen isotope analyses of garnet separates and whole rock samples of gneiss and marble hosted eclogites from the ultra high pressure uhp dabie shan terrain fall in the range 6 76 to 10 76 comparison of the isotopic compositions of the eclogites with those of their host rocks leads to the following conclusions 1 the basaltic protolith of the eclogites had isotopic compositions in the range 2 15 to 4 99 it is proposed that this is the result of contamination of the parent basaltic magma with hydrothermally altered18o depleted source materials 2 18o enriched eclogite compositions resulted from local scale 3 m interaction between this basaltic eclogite protolith and fluids produced by decarbonation of impure marble lithologies during uhp metamorphism 3 18o depleted eclogite and gneiss compositions resulted from regional scale meteoric hydrothermal alteration of the basalts and their host rocks prior to uhp metamorphism epidote separates and whole rocks from the cores and rims of mineralogically zoned eclogite boudins within amphibolite grade biotite gneisses show no distinct isotopic differences this suggests that the preferential recrystallisation of the gneisses and the associated amphibolite grade overprint of the rims of eclogite bodies could not have resulted from regional scale infiltration of significant volumes of fluid during the exhumation of the dabie shan terrain

composition and pre metamorphic geodynamic setting of the ultrahigh pressure metabasic rocks from dabie shan e china as part of the yangtze plate segments of the dabie shan terrane of central china underwent ultra high pressure metamorphism during triassic subduction we studied the geochemistry of the abundant eclogites to evaluate the nature of the protoliths and their geodynamic setting although some previous geochemical work exists the analyses and interpretation herein are based on a new subdivision of the ultra high pressure sequence into basement and cover units changpu and ganghe unit revealing new and important results in addition eclogites of the so called hp unit south of the uhp units were studied whereas the large ion lithophile elements indicate postmagmatic metasomatic changes of some samples the high field strength elements and the rare earth elements display original magmatic trends the geochemical characteristics of the eclogites of the ultra high pressure areas display a strong dependence on their structural and geographic position the eclogites of the basement and the changpu unit indicate melt intrusion and extrusion in a continental rift system i e during extensional tectonics in contrast the ganghe unit is characterized by a pronounced chemical homogeneity the composition of the eclogites indicates generation from a mantle source highly influenced by slab derived fluids those of the hp unit show similar characteristics magmatism of the ganghe and hp unit probably occurred in a continental arc setting a similar age for both units geographically and or tectonically separated is possible the geodynamic interpretation based on the geochemistry of the four units points to a neoproterozoic scenario in which the protoliths of the hp and the cover units could have been of similar age and deposited in one evolving geological system a rift related larger scale basin might have formed e g a continental back arc basin behind a magmatic arc after or simultaneous to sedimentation and magmatism in the magmatic arc alternatively magmatism occurred in independent geodynamic settings distinct in time and space the units were juxtaposed during exhumation after subduction to varying depths

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

carbon isotopes in xenoliths from the hualalai volcano hawaii and the generation of isotopic variability abstract the isotopic composition of carbon has been determined in a suite of xenoliths from lava of the 1800 1801 kaupulehu eruption of hualalai volcano hawaii several lithologies are represented in the suite including websterite dunite wehrlite pyroxenite and gabbro in addition there are composite xenoliths in which contacts between lithologies are preserved most of the xenoliths represent deformed cumulates the contact relations in the composite samples indicate that the lithologies originated from the same source region which based on pressures determined from fluid inclusions is estimated to be at a depth of 20 km or near the crust mantle boundary samples were heated in steps from 200 to 1475 c to obtain separation of the different carbonaceous phases and the isotopic composition of carbon released at each step was determined grossular glass was found to be a suitable flux to fuse refractory samples upon heating carbon exhibits the typical bimodal evolution behavior observed in other studies of xenoliths and basalts carbon extracted from all samples at temperatures below 900 c is characterized by a 13 c of about 25 vs pdb and is thought to be composed dominantly of graphitic and organic material which is known to be present on virtually all cracks the 13 c of the carbon fraction extracted at 1200 c and above from wehrlite and dunite is in the range 1 5 to 5 2 whereas that extracted from websterite ranges from 22 to 26 similarly in one composite sample the compositions of dunite and websterite were found to be 2 4 and 7 0 respectively the large difference can be associated with specific petrographic features unique to each lithology in wehrlite and dunite carbon exists mostly as co 2 rich inclusions in arrays representing partially annealed microcracks the websterite xenoliths contain megascopic zones of large irregularly shaped inclusions the zones traverse entire thinsections and are interpreted to represent fractures annealed at depth most of the carbon is believed to exist in the inclusion rich zones and to consist of carbonaceous material precipitated from fluid the observations and isotopic results demonstrate that isotopic variability can be generated by multistage fractionation processes such as degassing of co 2 from magma and precipitation of co 2 rich fluids to form graphitic compounds such processes operated over regions the scales of which were determined by style and intensity of deformation and by lithology

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

long term shoreline changes and the concentration of heavy minerals in beach sands of the nile delta egypt abstract analyses have been undertaken of shoreline positions established from beach profile surveys at 65 positions along the coastline of the nile delta spanning the years 1971 to 1990 the analyses identify long term linear trends as well as any cycles in the horizontal movement of shoreline positions the results reveal longshore patterns wherein erosion along a stretch of coast gives way to accretion in an adjacent stretch defining a subcell within the overall littoral system of the delta the rate of shoreline retreat has been greatest along the rosetta promontory 106 m yr and damietta promontory 10 4 m yr significant erosion has also occurred along the central bulge of the delta coast but at a lesser rate 6 5 m yr areas of accretion exist within the saddles or embayments between the promontories with the maximum shoreline advance averaging about 13 m yr the identified patterns of erosion versus accretion along the delta reflect the natural processes of wave induced longshore currents and sediment transport associated with this longshore sediment movement is a selective transport of different minerals according to their densities and grain sizes with the light minerals quartz and feldspar having the highest advection rates and the dense opaque minerals the lowest rates tending to remain behind as a lag within the erosion areas as a result of this longshore grain sorting paralleling the patterns of shoreline erosion versus accretion there are correlations between the rates of shoreline change and the heavy mineral contents and mean grain sizes of the beach sediments these large scale delta wide patterns are affected somewhat by local shoreline changes and mineral variations induced by the construction of jetties or shoreline protection structures

contrasting plate tectonic styles of the qinling dabie sulu and franciscan metamorphic belts the dabie mountains are part of the 2000 km long qinling dabie sulu suture zone juxtaposing the sino korean and yangtze cratons an eastern extension apparently crosses korea and lies along the japan sea side of honshu as the imjingang and sangun terranes respectively a northeastern segment may be present in sikhote alin russian far east this orogenic belt records late paleozoic ocean floor consumption and the triassic collision of two precambrian continental massifs in east central china coesite and microdiamond inclusions in strong refractory minerals of eclogite facies ultrahigh pressure uhp metamorphic rocks in the dabie sulu area attest to profound subduction of a leading salient of the old cold yangtze craton now recovered through tectonic exhumation and erosion northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high pressure hp and uhp metamorphism documented in the western alps in both regions subduction of narrow prongs of continental material uhp metamorphism and return toward midcrustal levels of relatively lower density buoyant microcontinental blocks resulted from delamination of these rocks from the descending higher density oceanic crust capped lithospheric plate such salients of continental crust represent an integral structural part of the downgoing slab remain intact and may be dragged to great depths before disengaging and rising differentially as coherent blocks uhp parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 c and 28 35 kbar or more in contrast pacific type hp metamorphic belts as represented by the franciscan complex of western california recrystallized under physical conditions up to 200 500 c 10 3 kbar in this setting voluminous quartzo feldspathic and graywacke debris was carried downward on oceanic crust capped lithosphere choking the subduction zone with incompetent material sited between both plates and strongly adhering to neither this buoyant largely sedimentary complex decoupled at 25 30 km depth and ascended toward the surface in both alpine type intracontinental collision and pacific type underflow light sialic material displaced dense mantle thus the return to midcrustal levels was propelled dominantly by body forces

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

analytical solution of the linearized hillslope storage boussinesq equation for exponential hillslope width functions 1 this technical note presents an analytical solution to the linearized hillslope storage boussinesq equation for subsurface flow along complex hillslopes with exponential width functions and discusses the application of analytical solutions to storage based subsurface flow equations in catchment studies

hillslope to valley transition morphology new opportunities from high resolution dtms abstract the search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology topographic attributes derived from digital terrain models dtms such as slope curvature and drainage area provide a basis for topographic analyses the slope area relationship has been used to distinguish diffusive hillslope from linear valley processes and to infer dominant sediment transport processes in addition curvature is also useful in distinguishing the dominant landform process recent topographic survey techniques such as lidar have permitted detailed topographic analysis by providing high quality dtms this study uses lidar derived dtms with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern italian alps where shallow landsliding and debris flows are dominant the analysis considered the scaling regimes of local slope versus drainage area the spatial distribution of curvature and field observations of channel head locations the results indicate that i hillslope to valley transitions in slope area diagrams become clearer as the dtm grid size decreases due to the better representation of hillslope morphology and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer dtms ii regarding the channel head distribution in the slope area diagrams the scaling regimes of local slope versus drainage area obtained with grid sizes of 1 3 and 5 m are more consistent with field data and iii the use of thresholds of standard deviation of curvature particularly at the finest grid size were proven as a useful and objective methodology for recognizing hollows and related channel heads

evidence for control of abyssal agglutinated foraminiferal community structure by substrate disturbance results from the hebble area abstract deep sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in june 1983 at the hebble high energy benthic boundary layer experiment site 40 27 n 62 20 w 4815 4825 m depth and hebble shallow site 40 53 n 63 44 w 4185 m depth on the nova scotian continental rise samples from the relatively tranquil hebble shallow site can be distinguished from the hebble site on the basis of their microfauna a q mode varimax factor analysis of species frequency data delineates three major faunal assemblages 1 1 a faunal assemblage from the hebble site dominated by ammobaculties sp cf a americanus this assemblage exhibits lowest species diversity suggesting a disturbed community and strongly associated with box cores containing fine grained laminated sediments 2 2 an assemblage associated with box cores from the hebble meadow dominated by saccammina tubulata psammosphaera sp cf p fusca a coarsely grained species of psammosphaera and reophax sp 1 3 3 a fauna occurring at the hebble shallow site dominated by hormosinella distans with reophax bacillaris and ammobaculites agglutinans unique to the assemblage this fauna displays a higher ratio of calcareous to agglutinated species significantly higher species diversity lower variability and a greater proportion of hormosinids and species utilizing finer grains than samples from the hebble site which is interpreted as reflecting environmental stability marked heterogeneity exists among agglutinated foraminiferal assemblages within box cores at the hebble meadow within box core faunal variability exceeds between box core variability suggesting that environmental factors influencing the distribution of species are patchy on a scale of approximately 40 cm

unusually low δ18o ultra high pressure metamorphic rocks from the sulu terrain eastern china eclogite and quartzite interlayers containing ultra high pressure uhp metamorphic mineral assemblages occur at qinglongshan in the sulu terrain eastern china these rocks exhibit some of the most negative oxygen isotope compositions that have ever been reported for metamorphic rocks the 18 value of minerals in eclogite ranges from 10 4 to 9 0 o and in quartzite ranges from 10 2 to 7 3 near isotopic equilibrium between minerals and rocks suggests that these rocks must have acquired such low oxygen isotope compositions before the uhp metamorphism through near surface meteoric water rock interactions the rocks were then subducted to a great depth during continent continent collision forming uhp minerals with concomitant local oxygen isotope redistribution it is significant that the rocks have retained such negative oxygen isotope compositions despite subduction into the upper mantle

fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe dabie shan china fluid inclusions in coesite bearing eclogites and jadeite quartzite at shuanghe in dabie shan east central china have preserved remnants of early prograde and or peak metamorphic fluids reset during post uhp ultrahigh pressure metamorphic uplift inclusions occur in several minerals e g omphacite epidote notably as isolated primary inclusions in quartz included in various host minerals two major fluid types have been identified non polar fluid species n2 or co2 and aqueous the latter is by far the most predominant aqueous fluids cover a wide range of salinity from halite bearing brines to low salinity fluids for non polar fluids few n2 inclusions occur in undeformed eclogite whereas a number of co2 rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences the primary character of n2 and high salinity aqueous inclusions indicates that they are remnants from uhp metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre metamorphic fluids this conclusion is supported by the preservation in some samples of microdomains containing synchronous inclusions of variable salinities which tend to relate to the chemical composition of the host crystal carbonic fluids may be derived from neighbouring rocks notably marble and carbonate bearing metasediments during post metamorphic uplift during post uhp exhumation a limited decrease of the fluid density has occurred with formation of new sets of fluid inclusions fluid movements however remained exceedingly limited at the scale of the enclosing crystal

transition of uhp eclogites to gneissic rocks of low amphibolite facies during exhumation evidence from the dabie terrane central china the shuanghe ultrahigh pressure uhp slab in the dabie mountains consists of layered coesite bearing eclogite jadeite quartzite marble and biotite gneiss and is fault bounded against hosting orthogneiss representative assemblages of eclogite are grt omp coe rt ky phn mgs it formed at p 27 kbar and 680 720 50 c during exhumation these uhp rocks experienced multistage retrograde metamorphism coesite was overprinted by quartz aggregates phengite by biotite muscovite and rutile by titanite garnet was successively replaced by a thin rim of amp amp pl and amp ep bt pl minor omphacite and kyanite were replaced by amp pl cpx or bt and by zo pl ms mrg bt respectively secondary calcite occurs as irregular pockets in some layers an outcrop near the uhp slab border is composed of 20 thin concordant layers of foliated eclogites amphibolite and gneissic rocks of variable bulk composition these layers exhibit mineral assemblages and textures transitional from less altered through extensively retrograded eclogite to gneissic rock of low amphibolite facies through hydration metasomatism and recrystallization retrograde metamorphism has caused oxygen and hydrogen isotope disequilibria between some of the minerals but the fluid for retrograde reactions was internally buffered in the stable isotope compositions retrograde metamorphism of variable extent may be attributed to selective infiltration of retrograde fluids of co2 rich and low salinity aqueous intensity of deformation and mineral resistance to alteration the fluid phase for retrogression may have occurred either as discontinuous flow along grain boundaries in completely retrograded eclogites and or as isolated pockets in extensive or less altered eclogite layers

low carbon isotope ratios in apatite an unreliable biomarker in igneous and metamorphic rocks abstract carbon isotope ratios of apatite have been used to interpret the source of carbon in magmas and metamorphic fluids using the assumption that carbon isotope fractionations between phases are small in igneous and metamorphic systems measured carbon isotope fractionations between co existing apatite and calcite from igneous metaigneous and metasedimentary rocks are large and variable 13c 2 3 to 20 8 reflecting variability in 13c ap sampled by combustion this result indicates that carbon isotopes in apatite sampled by common techniques combustion ion microprobe step heating do not have a straightforward interpretation these data suggest that the low 13c values in apatite that have previously been used as indicators of biological activity may be the result of the carbon isotope fractionation systematics of apatite rather than a reflection of incorporation of organic carbon this unusual fractionation behavior may require reconsideration of the significance of low 13c carbonaceous inclusions in apatite from 3 8 ga metamorphic rocks from akilia island greenland

a review of wave dominated clastic shoreline deposits abstract barrier islands beaches wave dominated deltas and chenier plains probably form more than one fifth of present coasts and constitute an even larger proportion of the subsiding lowland coasts likely to be preserved in the stratigraphic record the geometry vertical sequences and composition of their deposits are the result of 1 shoreline behaviour whether transgressive regressive or stable 2 physical processes particularly the relative intensities of waves and tides 3 climate 4 global tectonic setting and 5 topography of underlying deposits published interpretations indicate that equivalent deposits are abundant in the geological record sandstones are mostly quartzose cemented by carbonates and quartz and have sheet or linear geometries ancient deposits can provide evidence of palaeogeography and some are economically significant particularly as hydrocarbon reservoir rocks four end member sedimentation models are proposed for the interpretation of ancient deposits 1 transgressive sheet sands associated with deltas 2 non deltaic transgressive sheet sands 3 regressive sheet sands and 4 linear sand bodies probable depositional settings geometries characteristics of deposits and palaeocurrent patterns are discussed

excess argon in phengite from eclogite evidence from dating of eclogite minerals by smnd rbsr and 40ar39ar methods the existence of excess ar in phengites from coesite bearing ultrahigh pressure eclogites of the dabie mountains and su lu terrain china has been confirmed by dating of minerals using sm nd rb sr and 40ar39ar methods 40ar39ar ages of phengites for two samples studied are much older than the sm nd and rb sr mineral isochron ages sample ql 1 has rb sr age of 219 5 0 5 ma sm nd age of 226 3 4 5 ma and phengite 40ar39ar age of 877 5 15 9 ma the corresponding ages for sample zb 4 are 223 9 0 9 ma rb sr 228 4 6 0 ma sm nd and 943 3 12 4 ma 40ar39ar phengite an age of 225 ma based on the sm nd and rb sr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the north china and yangtse blocks and formation of these eclogites we call for greater caution in 40ar39ar dating of phengites from other occurrences of ultrahigh pressure environments

an ancient submarine canyon in the oligocene miocene of the western niger delta abstract an anomalous sequence of thick fossiliferous marine shale of late oligocene early miocene age here termed the opuama shale member occurs within the paralic agbada formation in the subsurface of the western niger delta the opuama shale fills a deep palaeochannel which was cut into eocene early oligocene paralic beds planktonic and benthic foraminifera suggest that deposition in the channel began in the late oligocene early miocene at outer shelf slope depths and that by the late early miocene the channel had filled to shallow neritic depths the channel which is believed to be of submarine origin is termed the opuama canyon the opuama canyon originated during the pronounced early middle oligocene drop in sea level and was cut by turbidity currents it was filled during the major late oligocene early miocene rise of sea level the location of the opuama canyon in the western re entrant of the niger delta supports burke s 1972 conclusion that the western and eastern where ancient submarine canyon fills are known re entrants of the delta are potential sites for ancient submarine canyons burke based his conclusion on the observation that the eastern and western re entrants of the modern delta are areas where opposing longshore drifts converge and generate turbidity currents which cut submarine canyons

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

anatomy of a barrier platform outer barrier lagoon southern delmarva peninsula virginia abstract a 7 9m thick prism of fine grained sediment occurs below the floor of barrier lagoons of the southern delmarva peninsula these fine grained sediments provide a platform for retreating barriers to migrate across initially the complete fine grained sedimentary column was believed to represent the infilling of the barrier lagoon during the holocene transgression marine microfauna confirm that deposition of mud occurred in a coastal estuarine environment however x ray radiographic and palynological analyses suggest shallow water deposition associated with a cool climate boreal forest much of the lagoonal mud behind the barriers is apparently pre holocene and primordial holocene lagoons were apparently very shallow hence along the southern delmarva peninsula landward migrating barrier islands retreated across topographic highs composed of silt and clay

global coastal segmentation and its river catchment contributors a new look at land ocean linkage here we present the coscats global database of 151 catchments in exorheic areas the catchments connect to oceans through coastal segments according to three sets of criteria natural limits continents oceans regional seas major capes and bays continental shelf topography sills basins island chains and geophysical dynamics climate ocean currents and tectonics the coscats segmentation scheme is designed to improve earth system analysis and to harmonize reporting of global riverine transfers from land to oceans each coscat is characterized by its coastal segment limits and length median 2 400 km by its catchment characteristics including area median 0 45 m km 2 width latitudinal range runoff average value and direction including its related physiographic units n 500 we apply the coscat segmentation to all 151 basins to estimate water discharge and total nitrogen impacts to oceans and find that the average runoff mm yr and n yields y n in kg km 2 yr 1 range over more than 3 orders of magnitude at this coarse resolution and that their average population density ranges over 2 orders of magnitude hyperactive regions defined as segments with 5 to 10 times the world average yield river transfers per unit area of land are differentially placed for water runoff and total contemporary nitrogen coscats have been designed to facilitate the budget reporting and the analysis of global scale heterogeneity for riverine fluxes and can be applied to other material such as suspended solids carbon species or other nutrients particularly for areas draining into regional seas

middle miocene palaeoenvironments of the niger delta abstract in order to recognize the palaeoenvironments of the deltaic sequence of the middle miocene oil bearing e2 0 reservoir in the kolo creek field investigations of sediment grain size textures structures trace fossils mineralogical composition diagenetic imprints palynodebris types palynomorphs and foraminifera have been carried out on materials from two boreholes using this multidisciplinary approach the following have been identified in the reservoir ten lithofacies two palynofacies associations a total of 103 palynomorph taxa and a low diversity assemblage of benthic foraminifera these criteria have provided information on the positions of the deposits relative to the palaeocoastline as well as the physical and ecological conditions within the delta the overall depositional conditions were found to be broadly similar to those in the present day niger delta although the climatic conditions were somewhat drier in the middle miocene as reflected in the abundance of the grass pollen graminidites seven or possibly eight deltaic sub environments of deposition have been recognized based on an interpretation of gamma ray and resistivity log profiles as well as sedimentological and microfossil data from cores of two boreholes in the field these depositional settings are the distributary channel fill tidal channel fill lagoon tidal flat lagoonal delta flood tidal delta in the lower delta plain the coastal barrier and the delta fringe and prodelta in the outer delta the two palynofacies associations a c and b d which emerged from average linkage cluster analysis of the palynodebris are environmentally significant

carbonaceous matter in peridotites and basalts studied by xps sali and leed abstract carbonaceous matter in peridotite xenoliths and basalt from the hualalai volcano in a basalt glass collected directly from an active lava lake on the east rift of kilauea in garnet and diopside megacrysts from the jagersfontein kimberlite and in gabbros from the stillwater and bushveld complexes has been studied by x ray photoelectron spectroscopy xps thermal desorption surface analysis by laser ionization sali and low energy electron diffraction leed the basalt and two of the four xenoliths from hualalai and both jagersfontein megacrysts yielded trace quantities 10 nanomoles of organic compounds on heating to 700 c organics were not detected in the rocks from the layered intrusions and neither carbonaceous matter nor organics were detected in the glass from the lava lake where detected organics appear to be associated with carbonaceous films on microcrack surfaces carbonaceous matter exists as films less than a few nm thick and particles up to 20 m across both of which contain elements expected to be present in significant quantities in magmatic vapors namely si alkalis halogens n and transition metals leed studies suggest that the carbonaceous films are amorphous the data suggest two possible mechanisms for the formation of the organics one is that they are a product of abiotic heterogeneous catalysis of volcanic gas on new chemically active mineral surfaces formed by fracturing during cooling alternatively organics may have been assimilated into the volcanic gases prior to eruption and then deposited on cracks formed during eruption and cooling in any case there is no evidence to suggest that the organics represent laboratory or field biogenic contamination

geochemical and u pb age constraints on the occurrence of polygenetic titanites in uhp metagranite in the dabie orogen abstract relict magmatic titanite was identified in the core of a few titanite grains with the overgrown rim of metamorphic titanite in uhp metagranite in the dabie orogen la icpms u pb dating gave neoproterozoic ages for the magmatic titanite but triassic ages for the metamorphic titanite the magmatic and metamorphic titanites are clearly distinct by differences in petrological and geochemical compositions the magmatic titanite occurs as residual cores that show bright bse the presence of allanite and quartz inclusions low contents of cao al2o3 and tio2 but high contents of fe2o3 and mgo in trace elements the magmatic titanite exhibits high ree and hfse contents distinctly negative eu anomalies with flat mree hree patterns and high th u ratios in contrast the metamorphic titanite occurs as rims and grains of homogeneously dark bse that contain inclusions of epidote quartz k feldspar rutile biotite and phengite and have relatively high contents of cao al2o3 and tio2 but low contents of fe2o3 and mgo and relatively low ree and hfse contents slightly negative eu anomalies with hree depletion relative to mree and low th u ratios the zr in titanite thermometry yields 727 to 877 c at 0 5 to 1 0 gpa for the magmatic titanite and 729 to 870 c at 1 5 to 2 0 gpa for the metamorphic titanite the neoproterozoic u pb chronometric system of magmatic titanite survived the triassic continental subduction zone hp uhp metamorphism this suggests a relatively high closure temperature of 800 c for the titanite u pb system the metamorphic titanite is principally a product of retrograde metamorphism during decompression exhumation at the transition from hp eclogite facies to amphibolite facies therefore titanite holds a great potential to geochronological and petrogenetic studies of continental subduction zone metamorphic rocks

analytical solutions to runoff on hillslopes with curvature numerical and laboratory verification predicting the behavior of overland flow with analytical solutions to the kinematic wave equation is appealing due to its relative ease of implementation such simple solutions however have largely been constrained to applications on simple planar hillslopes this study presents analytical solutions to the kinematic wave equation for hillslopes with modest topographic curvature that causes divergence or convergence of runoff flowpaths the solution averages flow depths along changing hillslope contours whose lengths vary according hillslope width function and results in a one dimensional approximation to the two dimensional flow field the solutions are tested against both two dimensional numerical solutions to the kinematic wave equation in parflow and against experiments that use rainfall simulation on machined hillslopes with defined curvature properties excellent agreement between numerical experimental and analytical solutions is found for hillslopes with mild to moderate curvature the solutions show that curvature drives large changes in maximum flow rate q peak and time of concentration t c predictions frequently used in engineering hydrologic design and analysis

oxygen self diffusion in calcite dependence on temperature and water fugacity oxygen self diffusion in natural calcite single crystals was studied hydrothermally at 400 800 c and 10 350 mpa confining pressure diffusion coefficients d were determined from18o concentration profiles measured with an ion microprobe at 100 mpa confining pressure the arrhenius parameters yield an activation energy q 173 6 kj mole and pre exponential factor d0 7 10 9 m2 s over the temperature range 400 800 c and there is no measurable anisotropy constant temperature experiments at 700 c indicate that there is a strong linear correlation slope 0 9 of d with water fugacity over the range 4 240 mpa consistent with the interpretation that in the presence of water the dominant oxygen bearing transport species in calcite is molecular water a sample containing 1180 ppm mn shows a marked increase in observed d values at temperatures below 600 c however when pre annealed at 700 c the d values obtained at 550 c are within a factor of four of the value obtained for the low 100 ppm mn sample the results of this study confirm that in contrast to carbon oxygen diffusion rates in calcite are greatly enhanced when water is present the difference in the effect of water on doxygen and dcarbon in calcite may provide valuable information for evaluating the role of fluids in the thermal histories of calcite bearing rocks

overland flow generation on hillslopes of complex topography analytical solutions the analytical solution of the overland flow equations developed by agnese et al 2001 hydrological processes15 3225 3238 for rectangular straight hillslopes was extended to convergent and divergent surfaces and to concave and convex profiles towards this aim the conical convergent and divergent surfaces are approximated by a trapezoidal shape and the overland flow is assumed to be always one dimensional a simple shape factor accounting for both planform geometry and profile shape was introduced for each planform geometry a brachistochrone profile was obtained by minimizing a functional containing a slope function of the profile minima shape factors are associated with brachistochrones interestingly brachistochrones associated with rectangular surfaces have a simple power law form for a fixed profile shape the rapidness of overland flow increases with the degree of divergence for a fixed planform geometry however the overland flow associated with convex profiles is more rapid than that associated with concave profiles an extended analytical solution is also proposed for the instantaneous response function copyright 2007 john wiley sons ltd

dam impacts on the changjiang yangtze river sediment discharge to the sea the past 55 years and after the three gorges dam 1 in 5 recent years 2000 2004 the changjiang yangtze river has discharged past datong 600 km from the river mouth an average of 250 million tons mt of sediment per year a decrease of more than 40 since the 1950s and 1960s whereas water discharge at datong has increased slightly water and sediment discharge data from the upper middle and lower reaches of the river suggest that the reduction of the changjiang sediment load has occurred in two phases between 1950 and 2002 following the closure of the danjiangkou reservoir on the hanjiang tributary in 1968 and following the installation of numerous dams and water soil conservation works in the jialingjijang catchment after 1985 as the three gorges dam tgd started operating in 2003 the changjiang entered a third phase of sediment reduction with annual sediment loads at datong less than 200 mt yr upon completion of the three gorges dam tgd in 2009 the sediment load at datong will decrease to 210 mt yr for the first 20 years then will recover to 230 mt yr during 2030 2060 and will reach 310 mt yr during 2060 2110 from the sediment budget and sediment erosion data for the changjiang subaqueous delta it can be assumed that the delta will be eroded extensively during the first five decades after tgd operation and then will approach a balance during the next five decades as sediment discharging from tgd again increases

petrology geochemistry and isotope data on a ultrahigh pressure jadeite quartzite from shuanghe dabie mountains east central china abstract in the dabie ultrahigh pressure terrane of east central china coesite bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite this rock assemblage is in turn enclosed within quartzofeldspathic gneisses metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history the primary peak metamorphic assemblage consists of jadeite garnet coesite rutile apatite minor coesite and coesite pseudomorphs occur as inclusions in jadeite and garnet three stages of retrograde assemblages are observed in the jadeite quartzites stage a is represented by the polymorphic transformation of coesite to quartz aggregates stage b is characterized by formation of coronas around jadeite porphyroblasts consisting of an inner layer of oligoclase amphibole and an outer layer of albite aegirine augite the last stage stage c involved total replacement of jadeite and most garnets by taramitic amphibole albite aegirine augite peak metamorphic p t conditions were 26 kbar at 660 c and are consistent with the estimates from the adjacent coesite bearing eclogites the jadeite quartzites display clockwise p t path that matches those of the adjacent eclogites major and trace element data suggest that the protolith of the jadeite quartzite could have been an albitized siltstone enriched in na and depleted in k and ca the highly negative present day end value 24 7 indicates a very old age for the protolith its late archean model age tdm of 2 58 ga is among the oldest so far identified for rocks from the dabie uhpm terrane concordant field relations and petrogenetic considerations suggest that all mafic politic carbonate and gneissic rocks have experienced in situ uhp metamorphism during triassic continental collision between the sino korean and yangtze cratons

an experimental calibration of the temperature dependence of oxygen isotope fractionation between apatite and calcite at high temperatures 350 800 c the fractionation of oxygen isotopes between apatite and calcite has been measured experimentally using the direct exchange technique in a piston cylinder apparatus at high temperature and pressure 350 800 c 1 1 gpa the fractional approach to equilibrium ranged from 20 to 80 and varies systematically with temperature and run duration isotopic xrd and sem analyses of the run products indicate that the exchange occurs dominantly by recrystallization in the early stages of the experiments the equilibrium fractionation over the temperature range of this study ranges from 5 5 to 2 but the data at 350 and 425 c have relatively large errors for t 500 c an error weighted least squares fit yields 1000 ln ap cc 0 68 1 60 0 26 106t 2 the magnitude of the temperature dependence is intermediate to that for felsic and mafic minerals to calcite mineral pairs involving apatite are potentially useful indicators of temperature cooling rates and equilibrium disequilibrium phenomena in igneous and metamorphic rocks

the afam clay member a lower miocene incised channel in the south eastern niger delta abstract this paper describes a lower miocene incised channel system and its lithic fill within the niger delta sedimentary succession stratigraphic cross sections which clearly show the base to be generally asymmetric and very sharp with erosive characteristics in places suggest a channel configuration for the base of the afam clay the geometry of the channel and its lithic fill supports this interpretation the channel was cut by fluvial processes into pre existing unconsolidated eocene miocene sediments of the benin and agbada formations during a period of low sea level the imo river proto channel is thought to have aided the channelling the channel was subsequently enlarged by marine processes associated with a middle miocene rise in sea level the lithic fill of the afam channel is dominated by clay beds with localized development of sand bodies in time and space analysis of the spatial distribution of the sand units and their sp shapes supports the hypothesis of sand input from the north east central and west central flanks of the channel these are interpreted to reflect sand contributions from tributaries that fed the main channel the faunal lithological and textural characteristics of the afam sediments suggest a predominance of marine conditions in the south paralic conditions in the central area and fluvial processes in the north in addition the southern flanks of the channel may constitute truncation stratigraphic traps for hydrocarbons and it is proposed that these flanks should be fully explored

coherent changes of southeastern equatorial and northern african rainfall during the last deglaciation during the last deglaciation wetter conditions developed abruptly 14 700 years ago in southeastern equatorial and northern africa and continued into the holocene explaining the abrupt onset and hemispheric coherence of this early african humid period is challenging due to opposing seasonal insolation patterns in this work we use a transient simulation with a climate model that provides a mechanistic understanding of deglacial tropical african precipitation changes our results show that meltwater induced reduction in the atlantic meridional overturning circulation amoc during the early deglaciation suppressed precipitation in both regions once the amoc reestablished wetter conditions developed north of the equator in response to high summer insolation and increasing greenhouse gas ghg concentrations whereas wetter conditions south of the equator were a response primarily to the ghg increase

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

petroleum play of the lower cretaceous alam el bueib formation in the el noor 1x well in the north western desert egypt a sequence stratigraphic framework abstract the north umbaraka concession in umbaraka basin in the northern the western desert of egypt has been the subject of continuous exploration efforts in the recent years despite many oil discoveries gave evidence of a working petroleum system however there is little economic production the petroleum plays of the alam el bueib formation are in the central focus of the exploration in this region because of their high economic reservoir potentiality in other areas of the western desert in the present study three powerful tools are used to delineate the sequence stratigraphic frame that considers the occurrences of the petroleum play chances of alam el bueib formation in el noor 1 well these tools are palynofacies electric log and organic geochemistry the palynofacies analysis revealed three biotopes that cover deposition in wave dominated to fluvial wave dominated deltas with energetic oxic and active reworking conditions these environmental settings are only suitable for deposition of organic lean hydrocarbon source however there are abundant organic materials that fluoresce under the uv v blue incident light especially in proximal delta front prodelta slope biotope a and these materials can generate oil as indicated also by pyrolysis gas chromatography in addition analysis of electric logs is used to assess reservoir capacities and effective porosities in the studied rocks eight sequences are identified based on these trends including e4 e3 e2 e1 d1 c1 c2 and b1 four petroleum plays are determined in the studied succession within the frame of the stratigraphic sequences e d c and b there are six reservoirs identified in the sandy bodies of the lowstand systems tracts and the carbonates of the transgressive and highstand systems tracts the critical moment of hydrocarbon generation occurred during the campanian 76 ma the entire succession of the alam el bueib formation is in the oil window and the source rocks in this formation initiated petroleum expulsion during the eocene time 32 myr

effects of smectite dehydration and illitisation on overpressures in sedimentary basins a coupled chemical and thermo hydro mechanical modelling approach abstract diagenetic smectite dehydration and smectite to illite transition in clay rich sediments can contribute to the generation of overpressure in sedimentary basins because of the release of water associated with these mineralogical reactions however the challenge of deciphering the contribution of smectite dehydration and illitisation to fluid pressure amongst other mechanisms generating overpressure requires the different mechanisms at play to be jointly considered here we developed a coupled chemical and thermo hydro mechanical code named surp to calculate the overpressure generation in a sedimentary pile because of sediment compaction during its burial temperature increase water flow and because of the release of water by clay dehydration and illitisation for this purpose a revised thermodynamic model describing smectite dehydration by a solid solution approach was considered together with the different thermo hydro mechanical processes occurring in sedimentary basins the surp code was applied to the case study of an overpressured passive margin in the niger delta composed of thick shale layers in a sedimentary pile in this geological scenario smectite dehydration was simulated and could explain 10 30 20 50 bar of the present day overpressure in the main reservoirs in addition to compaction disequilibrium

fluid inclusion and mineral isotopic compositions hco in eclogitic rocks as tracers of local fluid migration during high pressure metamorphism eclogite facies metagabbros from the monviso ophiolitic complex italian western alps provide a unique opportunity to trace fluid migration processes in a portion of the oceanic crust that has undergone subduction at a depth of 40 km we have determined the omphacites 18o and the abundance d and 13c of hydrous and carbonaceous compounds present in whole rocks which are believed to trace the residual phases of what was mobilized in the original rocks during subduction prograde dehydration reactions and eclogitization of hydrothermally altered oceanic metagabbros was accompanied by approximately 90 fluid loss the remaining fluid was trapped as primary water rich fluid inclusions in omphacite megacrysts that developed at the expense of the precursor magmatic pyroxene deformation of the eclogitic rocks resulted in continuous recycling of fluid between mylonites and omphacite veins without further fluid loss from the host ductile shear zone oxygen isotopes of omphacite omp and hydrogen isotopes of water in the fluid inclusions fi analyzed in low strain rocks mylonites and undeformed deformed veins show marked variations 18oomp and dfi values ranging from 3 0 to 5 3 and from 31 to 93 respectively detailed isotopic analysis of several individual vein wallrock pairs show that the scale of isotopic equilibration is of the order of one centimeter therefore the eclogitic minerals and fluids filling the veins are concluded to be locally derived our results argue against recent models which suggest large scale mass flushing of isotopically homogeneous fluids during subduction zone metamorphism on average the h2o contents and dfi value are within the upper mantle range the carbon has been inherited from the metamorphic transformation of the original carbon present in the oceanic crust and has a mean 13c value of 24 2 1 2 two carbonaceous components can be recognized condensed carbon which represents the major carbon species and carbonate daughter crystals present in fluid inclusions 18oomp values are significantly lower than those reported for mantle minerals and are similar to pyroxene and whole rock values from hydrothermally altered oceanic crust it is suggested that the isotopic imprint of the monviso eclogitic minerals and fluids represents the signature of mid ocean ridge hydrothermal alteration and subduction zone eclogitization processes the rocks studied could be the missing link between altered oceanic gabbros and eclogitic xenoliths in addition the range in 18oomp values recorded in the different microstructural domains covers most of the 18o values reported in type a b and c eclogitic xenoliths implying that caution must be exercised when using oxygen isotopes as an indicator of the origin of eclogitic xenoliths

isotope geochemistry of oxygen and carbon in phosphate and carbonate of phosphorite francolite oxygen isotope ratios in phosphate delta sup 18 o sub p were determined in 219 samples of phosphoritic rocks from all major phosphogenic provinces of the world ranging in age from lower proterozoic to recent in 58 samples oxygen was analyzed in the two oxygen lattice sites of francolite both in phosphate and in structural carbonate delta sup 18 o sub c delta sup 13 c was also analyzed in the latter and in coexisting calcite for 10 of them both delta sup 18 o sub p and delta sup 18 o sub c decrease sharply from the recent to the cretaceous and decrease with a gentler slope to the precambrian the nature of the time variation is elucidated by means of a delta sup 18 o sub p vs delta sup 18 o sub c plot which suggests that a the main cause of the time trends is the increase in temperature between recent and the cretaceous b the pre cretaceous trend is overprinted by both low temperature nonequilibrium exchange between sup 18 o depleted water and the rocks and higher temperature exchange between phosphate and carbonate c the observed trend cannot be explained by sup 18 o depleted cretaceous and paleozoic oceans the calcite coexisting with apatite in phosphatic rocks is similar in both delta sup 18 o and delta sup 13 c to the structural carbonatemore of the apatite even though phosphate may exchange its oxygen with environmental water to a greater extent than the authors originally claimed it is probably still a very good isotopic recorder of sedimentary environments less

hydrogen and oxygen isotope evidence for fluid rock interactions in the stages of pre and post uhp metamorphism in the dabie mountains abstract hydrogen and oxygen isotope studies were carried out on high and ultrahigh pressure metamorphic rocks in the eastern dabie mountains china the 18 o values of eclogites cover a wide range of 4 2 to 8 8 but the d values of micas from the eclogites fall within a narrow range of 87 to 71 both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals with reversed fractionations between omphacite and garnet in some eclogite samples the 18 o values of 4 to 1 for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water rock interaction before the high to ultrahigh pressure metamorphism heterogeneous 18 o values for the eclogite protoliths implies not only the varying degrees of the water rock interaction before the metamorphism at different localities but also the channelized flow of fluids during progressive metamorphism due to rapid plate subduction retrograde metamorphism caused oxygen and hydrogen isotope disequilibria between some of the minerals but the fluid for retrograde reactions was internally buffered in the stable isotope compositions and could be derived from structural hydroxyls dissolved in nominally anhydrous minerals

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

nile delta extreme case of sediment entrapment on a delta plain and consequent coastal land loss abstract accelerated erosion of egypt s nile delta coast during this century has generally been attributed to construction of two dams at aswan entrapment of sediment in lake nasser behind the high dam and effects of barrages and river control structures on river nile deposition below aswan also considered important are natural factors including delta subsidence rising sea level and strong coastal current processes this study proposes that more influential in controlling coastal land loss is the near complete entrapment of modern and reworked nile sediment on the nile delta plain sediment is primarily retained in an extremely dense network of irrigation and drain channels and also in wetlands in the northern delta the increased number of artificial canals more than 10 000 km of waterway is a response to egypt s drive to augment its much needed agricultural production by perennial irrigation the drastically reduced amount of sediment now reaching the sea discharged primarily from lagoon outlets and several canal mouths is removed by strong easterly directed coastal and innermost shelf currents the nile delta is an extreme example of a depocenter which has been completely altered by man from an active prograding delta to a locally eroding coastal plain

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

petrology of ultrahigh pressure rocks from the southern su lu region eastern china abstract in the su lu ultrahigh p terrane eastern china many coesite bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet quartz jadeite rock and kyanite quartzite in addition to garnet omphacite rutile coesite other peak stage minerals in some eclogites include kyanite phengite epidote zoisite talc nyboite and high al titanite the garnet quartz jadeite rock and kyanite quartzite contain jadeite quartz garnet rutile zoisite apatite and quartz kyanite garnet epidote phengite rutile omphacite assemblages respectively coesite and quartz pseudomorphs after coesite occur as inclusions in garnet omphacite jadeite kyanite and epidote from both eclogites and metasediments study of major elements indicates that the protolith of the garnet quartz jadeite rock and the kyanite quartzite was supracrustal sediments most eclogites have basaltic composition some have experienced variable crustal contamination or metasomatism and others may have had a basaltic tuff or pyroclastic rock protolith the su lu ultrahigh p rocks have been subjected to multi stage recrystallization and exhibit a clockwise p t path inclusion assemblages within garnet record a pre eclogite epidote amphibolite facies metamorphic event ultrahigh p peak metamorphism took place at 700 890 c and p 28 kbar at c 210 230 ma the symplectitic assemblage plagioclase hornblende epidote biotite titanite implies amphibolite facies retrogressive metamorphism during exhumation at c 180 200 ma metasedimentary and metamafic lithologies have similar p t paths several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in situ ultrahigh p metamorphism during the triassic collision between the sino korean and yangtze cratons